explain xkcd - User contributions [en]

2028: Complex Numbers

2018-09-11T13:46:58Z

Chrisahn: algebreic (sic!)

{{comic
| number = 2028
| date = August 3, 2018
| title = Complex Numbers
| image = complex_numbers.png
| titletext = I'm trying to prove that mathematics forms a meta-abelian group, which would finally confirm my suspicions that algebreic (sic!) geometry and geometric algebra are the same thing.
}}

==Explanation==
The {{w|complex number}}s can be thought of as pairs <math>(a,\ b)\in\mathbb{R}\times\mathbb{R}</math> of real numbers with rules for addition and multiplication.

: <math>(a,\ b) + (c,\ d) = (a+c,\ b+d)</math>

: <math>(a,\ b) \cdot (c,\ d) = (ac - bd,\ ad + bc)</math>

As such, they can be modelled as two-dimensional {{w|Euclidean vector|vectors}}, with an interesting rule for multiplication. The justification for this rule is to consider a complex number as an expression of the form <math>a+bi</math>, where <math>i^2 = -1</math>, i.e. ''i'' is the square root of negative 1. Applying the common rules of algebra and the definition of ''i'' yields rules for addition and multiplication above.

Regular two-dimensional vectors are pairs of values, with the same rule for addition, and no rule for multiplication.

The usual way to introduce complex numbers is by starting with ''i'' and deducing the rules for addition and multiplication, but Cueball is correct to say that some uses of complex numbers could be modelled with vectors alone, without consideration of the square root of a negative number.

The teacher, [[Miss Lenhart]], counters that to ignore the natural construction of the complex numbers would hide the relevance of the {{w|fundamental theorem of algebra}} (Every polynomial of degree ''n'' has exactly ''n'' roots, when counted according to multiplicity) and much of {{w|complex analysis}} (calculus with complex numbers; the study of analytic and meromorphic functions), but she also agrees that mathematicians are too cool for "regular vectors." Just because the complex numbers can be interpreted through vector space, ohwever, doesn't mean that they ''are'' just vectors, any more than being able to construct the natural numbers from set logic mean that natural numbers are ''really'' just sets.

In mathematics, a {{w|group (mathematics)|group}} is the pairing of a binary operation (say, multiplication) with the set of numbers that operation can be used on (say, the real numbers), such that you can describe the properties of the operation by its corresponding group. An {{w|Abelian group}} is one where the operation is commutative, that is, where the terms of the operation can be exchanged: <math> a \cdot b = b \cdot a</math> The title text argues that the "link" between algebra and geometry in "algebreic [sic] geometry" and "geometric algebra" is the operation in an Abelian group, such that both of those fields are equivalent. Algebraic geometry and geometric algebra are mostly unrelated areas of study in mathematics. {{w|Algebraic geometry}} studies the properties of sets of zeros of polynomials. It runs relatively deep. Its tools were used for example in Andrew Wiles' celebrated proof of Fermat's Last Theorem. For its part, a {{w|geometric algebra| geometric algebra}} (a {{w|Clifford algebra| Clifford algebra}} with some specific properties) is a construct allowing one to do algebraic manipulation of geometric objects (e.g., vectors, planes, spheres, etc.) in an arbitrary space that has a resultant geometric interpretation (e.g., rotation, displacement, etc.). The algebra of quaternions, often used to handle rotations in 3D computer graphics, is an example of a geometric algebra, as is the algebra of complex numbers. {{w|Metabelian group|Meta-Abelian groups}} (often contracted to metabelian groups) is a class of groups that are not quite abelian, but close to being so.

Randall's joke in the mouseover text is a wordplay combining the concepts of (meta-)abelian groups and change in the order of word orders with the general idea of "meta".

==Transcript==
:[Cueball (the student) is raising his hand and writing with his other hand. He is sitting down at a desk, which has a piece of paper on it.]
:Cueball: Does any of this really have to do with the square root of -1? Or do mathematicians just think they're too cool for regular vectors?

:[Miss Lenhart (the teacher) is standing in front of a whiteboard.]
:Miss Lenhart: Complex numbers aren't just vectors. They're a profound extension of real numbers, laying the foundation for the fundamental theorem of algebra and the entire field of complex analysis.

:[Miss Lenhart is standing slightly to the right in a blank frame.]
:Miss Lenhart: '''''And''''' we're too cool for regular vectors.
:Cueball (off-screen): I '''''knew''''' it!

==Trivia==
This comic is similar to [[1724: Proofs]].
{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Miss Lenhart]]
[[Category:Math]]
[[Category:Analysis]]

2035: Dark Matter Candidates

2018-09-11T13:20:00Z

Chrisahn: /* Black Holes ruled out by: */ typo

{{comic
| number = 2035
| date = August 20, 2018
| title = Dark Matter Candidates
| image = dark_matter_candidates.png
| titletext = My theory is that dark matter is actually just a thin patina of grime covering the whole universe, and we don't notice it because we haven't thoroughly cleaned the place in eons.
}}

==Explanation==
{{incomplete|Every section needs to be filled and explained. Do NOT delete this tag too soon.}}
{{w|Dark matter}} is a hypothetical, invisible form of matter used by the vast majority of astronomers to explain the far too high apparent mass of objects at large scales in our universe. In galaxies, stars are orbiting faster than the gravitational force of the sum of the masses of visible matter in the galaxy could cause, and entire galaxies are observed moving much faster around each other than their visible masses could explain. In galactic collisions, the mass can appear to separate from the visible matter, as if the mass doesn't collide but the visible matter does. A small handful of galaxies have been observed to not have this property, suggesting that it is a *thing* that a galaxy can have more or less of and is separable from. At scales of our solar system, those effects are too small and can't be measured. The most plausible explanation for all of these phenomena is that there is some "dark matter" that has gravity, but is otherwise undetectable. In cosmology, dark matter is estimated to account for 85% of the total matter in the universe.

This comic gives a set of possibilities for what dark matter could possibly be, charted by mass from smallest (given in {{w|Electronvolt#Mass|electronvolts}}) to largest (given in kilograms). Masses in the range 10-15 kg to 10-3 kg are given in grams together with appropriate prefixes, while the ton takes the place of 103 kg.

Only massive objects ranging from subatomic particles up to super massive ones are covered in this comic. There are also {{w|Dark matter#Alternative hypotheses|alternative hypotheses}} trying to modify general relativity with no need of additional matter. The problem is that these theories can't explain all different observations at once. Nonetheless dark matter is a mystery because no serious candidate has been found yet.

The joke in this comic is that the range of the mass of the possible particles and objects stretch over 81 powers of ten, with explanations suggested by astronomers covering only some portions of that range. [[Randall]] fills the gaps with highly absurd suggestions.

==== Axion ====
An {{w|Axion|axion}} is a hypothetical elementary particle postulated in 1977 to resolve the strong CP problem in {{w|Quantum chromodynamics|quantum chromodynamics}}, a theory of the strong force between {{w|Quark|quarks}} and {{w|Gluon|gluons}} which form {{w|Hadron|hadrons}} like {{w|Proton|protons}} or {{w|Neutron|neutrons}}. If axions exist within a specific range of mass they might be a component of dark matter. The advantage of this particle is that it's based on a theory which could be proved or also disproved by measurements in the future. Other theories, not mentioned in this comic, like the {{w|Weakly interacting massive particles|Weakly interacting massive particles (WIMPs)}} are much more vague.

==== Sterile neutrino ====
{{w|Sterile neutrino|Sterile neutrinos}} are hypothetical particles interacting only via gravity. It's an actual candidate for dark matter. The well known {{w|Neutrino|neutrinos}} are also charged under the {{w|Weak interaction|weak interaction}} and can be detected by experiments.

==== Electrons painted with space camouflage ====
{{w|Electron|Electrons}} are fundamental particles which compose the outer layers of atoms. A large number of electrons in the galaxy would be relatively easy to detect, as they not only interact with light (which dark matter does not appear to), but also have a strong electric charge. Presumably, space camouflage is a positively-charged coating which prevents electrons from interacting with light. (Needless to say, this is not an actual candidate for dark matter.) The mass of an electron is about 0.5 MeV which fits well into the graph.

==== Neutralino ====
A {{w|Neutralino|neutralino}} is a hypothetical particle from {{w|Supersymmetry|supersymmetry}} and is also a current candidate for dark matter. But there is not evidence whether or not supersymmetry is correct and none of the predicted particles have been found yet.

==== Q-ball ====
In theoretical physics, a {{w|Q-ball}} is a stable group of particles. It's an actual candidate for dark matter.

(In billiards, a cue ball is the white (or yellow) ball hit with the cue in normal play. In addition, [[Cueball]] is the name explainxkcd uses for the most common xkcd character.)

==== Pollen ====
{{w|Pollen}} is a joke candidate, though people with seasonal allergies may suspect that the universe is genuinely made up entirely of pollen in the springtime.

==== No-See-Ums ====
{{w|Ceratopogonidae|No-See-Ums}} are a family (Ceratopogonidae) of small flies, 1–4 mm long, that can pass through most window screens. Another joke candidate, because dark matter is invisible and the name "no-see-ums" implies that the flies are invisible.

==== Bees ====
Insects of the clade {{w|Bee|Antophila}} are major pollinators of flowering plants. In recent years {{w|Colony collapse disorder|bees have been disappearing}} at an alarming rate; {{w|The Stolen Earth|Doctor Who explained}} that they are in fact aliens leaving Earth prior to a Dalek invasion.

==== 8-balls ====
In pool, the {{w|Pool (cue sports)|8-ball}} is a black ball numbered 8. It's a pun with Q-ball/cue ball. Unless undetected aliens have discovered billiards and become addicted to it, 8-balls are found only on Earth and are, hence, unlikely dark matter candidates. The 8-ball is also a popular unit of sale for black market pharmaceuticals like cocaine, where it stands for 1/8th of an ounce (3.5g). This doesn't make sense as a dark matter candidate either -- unless dark matter is hard to detect because it's illegal & trying to avoid the cops.

==== Space Cows ====
Cows are {{w|Bovinae|bovines}} extensively farmed on Earth for milk and meat. Although there is folklore concerning cows {{w|Hey diddle diddle|achieving circum-lunar orbits}}, not to mention their appearance on a {{w|Shindig (Firefly)|beloved space western TV show}}, as Muppet cow [http://muppet.wikia.com/wiki/Natalie Natalie] in the Sesame Street News Flash (and [https://tvtropes.org/pmwiki/pmwiki.php/Main/SpaceWestern others less-remembered]), they have yet to be found elsewhere in the Universe. In the television show "Too Close for Comfort", one of the characters is the cartoonist of a comic strip called "Cosmic Cow". {{w|Spherical cow|Spherical cows}} have also been used (humorously) by physicists needing to simplify some source of mass in a given problem.

==== Obelisks, Monoliths, Pyramids ====
While those human constructions are huge on a human scale, they're negligible at universe-scale. It would take a large number of such constructions, distributed through space, to replicate the effects of dark matter; while a scenario could be envisioned where enough such constructs existed, with properties and distribution allowing them to match observations, this is obviously not a likely explanation.
They often show up in fiction and pseudo-scientific literature as alien artifacts generating immense unknown power out of nowhere, with the most famous and influential example being the three monoliths from {{w|2001: A Space Odyssey (film)|2001: A Space Odyssey}} (with the largest having a mass of about 500,000 tonnes).

==== Black Holes ruled out by: ====
{{w|Black hole|Black holes}} are known to occur in sizes of a few solar masses (about 1030-1031 kg) as remnants of the core of former big stars, as well as in quite large sizes at the centers of galaxies (millions or even billions of solar masses). But recent gravitational wave detections indicate that black holes at 50 or 100 solar masses also exist, though their origin is still not understood. Randall doesn't mention this but some astronomers hope that these could fill at least a part of the gap. While black holes are widely reported to be ruled out as a candidate for dark matter for various reasons Randall has listed, such constraints are based on "monochromatic" mass distributions -- meaning that all such black holes are assumed to have the same mass -- which is considered physically implausible for populations of merging bodies which are known to have vastly different masses. See: [https://arxiv.org/pdf/1709.07467.pdf Primordial Black Holes as Dark Matter (2017)] and [https://arxiv.org/pdf/1705.05567.pdf Primordial black hole constraints for extended mass functions (2017)] (That this is a common practice in cosmology may be part of the reference to "buzzkill" astronomers.) He rules out all black holes in the range of approximately 1010 kg to 1033 kg even when below some gaps at the bars appear.

Except the last item, all range below the mass of the sun (2x1030 kg) while the smallest known black hole is about four solar masses.
* Gamma rays: If dark matter were black holes of this size, the black holes could be evaporating by the predicted {{w|Hawking radiation}}, and we'd see a buzz of gamma rays from every direction if many of those objects would exist. Nonetheless this radiation is still hypothetical and not been observed on any known black holes. Furthermore those objects would be very small because the Schwarzschild radius of a 1012 kg black hole is approximately 148 fm (1.48×10−13 m), which is between the size of an atom and an atomic nucleus.
* GRB lensing: {{w|Gamma-ray burst|Gamma-ray bursts}} (GRBs) are the brightest events in the universe and have been observed only in distant galaxies. While gravitational microlensing (see below) is an astronomical phenomenon, it doesn't make much sense here. GRBs are short (milliseconds to several hours) and are often detected only by space-borne sensors for gamma-rays -- rarely at any other wavelengths. Measuring lensing effects would be very difficult. This [https://arxiv.org/abs/1406.3102 paper] discusses the probability of detecting lensing effects caused by {{w|Dark matter halo|galactic halo objects}} among the known GRBs given sufficient objects to represent the missing mass.
* Neutron star data: {{w|Neutron star|Neutron stars}} aren't black holes, but they're also very small highly compact objects at about 1.4-2.16 solar masses. While black holes can't be observed directly, neutron stars are detectable in many wavelengths. The number of them gives a clue about the number of black holes close to the mass of the sun, a number which is far too low to make up dark matter.
* Micro lensing: {{w|Gravitational microlensing}} is a gravitational lens effect, (the path of radiation is changed by passing through space bent by nearby mass). This was predicted by Einstein's {{w|General Relativity|Theory of General Relativity}} and was first confirmed in 1919 during a solar eclipse, when a star which was nearly in line with the sun appeared more distant to the sun than usual. Astronomers have found many so called {{w|Einstein ring|Einstein rings}} or Einstein crosses where a massive object in front of other galaxies bends the light toward us. Those massive objects may be black holes, but the number is far too low to explain dark matter.
* Solar system stability: Our {{w|Solar system|solar system}} is 4.5 billion years old and has been very stable since shortly after its formation. If not, we wouldn't exist. If dark objects at 1024 kg - 1030 kg (mass of Earth up to mass of Sun) accounted for dark matter and were distributed throughout galaxies, there should be many of them in the vicinity of our solar system and the system wouldn't be stable at all.
* Buzzkill Astronomers: Black holes above a certain size are thought by some astronomers to be impossible to miss, due to the effects they have on nearby matter. At the mass of some 1030 kg there must be many supernova remnants we still haven't found. Black holes of about 1035 kg have long been considered dark matter candidates by a minority group of cosmologists, as could be seen here [https://arxiv.org/pdf/1001.2308.pdf Primordial Black Holes as All Dark Matter (2010)] and the Milky Way's first discovered intermediate mass black hole falling in this range shown here [https://www.nao.ac.jp/en/news/science/2016/20160115-nro.html Signs of Second Largest Black Hole in the Milky Way].
Not covered by this comic are {{w|Massive compact halo object|massive astrophysical compact halo objects (MACHOs)}} composed of hard to detect dim objects like black holes, neutron stars, brown dwarfs, and other objects composed of normal {{w|Baryon|baryonic}} matter. Nevertheless observations have shown that the total amount of baryonic matter in our universe on large scales is much smaller than it would be needed to explain all the measured gravitational effects.

==== Maybe those orbit lines on space diagrams are real and very heavy ====
Diagrams of our solar system (or any planetary system) often show lines representing the elliptical paths the planet takes around its sun. These lines don't show real objects, though. Astronomers just draw them on pictures of the solar system to show where the planets move. If you draw a line on a map to give someone directions, that line isn't an object in real life; it's just on the map. If these lines were real, they would be ''huge'' (Earth's would be 940 million km long (2π AU) and Neptune's would be 28 ''billion'' kilometers long). [https://www.youtube.com/watch?v=0fKBhvDjuy0 Powers of Ten (1977)] gives a good sense of just how large these orbit lines need to be in order to be visible in space diagrams. If these orbit lines were also very dense, they would have a huge mass and could possibly account for the missing 85% of the mass in the universe. But they would also constantly be impaling the planets, including the Earth, which would probably be a problem. Their mass would also affect planetary motions in ways which we would detect. A related worry about space travel was expressed in previous centuries; it was thought that the planets were embedded within {{w|Celestial spheres|crystal shells}} (spheres or Platonic solids), and a rocket into space could smash the shells and send planets plummeting to Earth. Another joke candidate.

==== Title text ====
The title text refers to the fact that space is just vast emptiness where a little bit of dirt could be overlooked. Actually the mean density of detectable matter in the universe, according to NASA, is equivalent to roughly [https://map.gsfc.nasa.gov/universe/uni_matter.html 1 proton per 4 cubic meters]. And because this matter is mostly located in galaxies -- and inside there in stars and clouds -- the space between is even more empty. For comparison, one gram hydrogen consists of {{w|Avogadro constant|6.022 x 1023 atoms}}. Like at home wiping with a cleaning cloth in which we can see the dirt that wasn't clearly visible on the surface we have wiped, Randall believes that some few atoms more per cubic meter could stay undetected in the same way. This isn't true because in the space between galaxies astronomers can detect matter as it spreads over thousands or millions cubic light years. Atoms can't hide; there is always radiation.

==Transcript==
:Dark matter candidates:
:[A line graph is shown and labeled at left quarter in eV and further to the right in g together with some prefixes.]
:[The labels read:]
:µeV, meV, eV, keV, MeV, GeV, TeV, 10-18kg, ng, µg, mg, g, kg, TON, 106kg, 1012kg, 1018kg, 1024kg, 1030kg

:[All items are shown in bars ranging between two approximately values:]
:< 1 µeV - 10 meV: Axion

:1 eV - 10 keV: Sterile neutrino

:0.5 MeV (exactly): Electrons painted with space camouflage

:10 GeV - 10 TeV: Neutralino

:100 TeV - 10-17 kg: Q-ball

:1 ng - 100 ng: Pollen

:0.1 mg - 1 mg: No-See-Ums

:10-1 g (exactly): Bees

:10 g - 100 g: 8-balls

:100 kg - TON: Space cows

:TON - 109 kg: Obelisks, monoliths, pyramids

:109 kg - 1033 kg: Black holes ruled out by:
::109 kg - 1013 kg: Gamma rays
::1013 kg - 1017 kg: GRB lensing
::1015 kg - 1022 kg: Neutron star data
::1021 kg - 1030 kg: Micro lensing
::1024 kg - 1030 kg: Solar system stability
::1030 kg - 1033 kg: Buzzkill astronomers

:1033 kg - >1036 kg: Maybe those orbit lines on space diagrams are real and very heavy

{{comic discussion}}

[[Category:Science]]
[[Category:Physics]]
[[Category:Astronomy]]
[[Category:Line graphs]]

Talk:2027: Lightning Distance

2018-08-02T19:44:33Z

Chrisahn:

Calculations I used:

<math>t_1=\frac{s}{v_1}</math>

<math>t_2=\frac{s}{v_2}</math>

Substract:

<math>t_1-t_2=\Delta t=\frac{s}{v_1}-\frac{s}{v_2}=\frac{sv_2-sv_1}{v_1v_2}=s\frac{v_2-v_1}{v_1v_2}=s\frac{\Delta v}{v_1v_2}</math>

Therefore

<math>s=\Delta t\frac{v_1v_2}{\Delta v}</math>

I evaluated <math>\frac{v_1v_2}{\Delta v}</math> and it came to be 13.6 billion. Can someone verify it's correct? [[Special:Contributions/172.68.51.112|172.68.51.112]] 13:08, 1 August 2018 (UTC)

:The comic begins with the question "how many miles away", so converting to kilometers isn't the right calculation.[[Special:Contributions/172.69.71.24|172.69.71.24]] 17:06, 1 August 2018 (UTC)

I used refractive index for visible light of 1.000277 (air at STP as opposed to 0C 1atm) and arrived at around 7.9 billion instead. Refractive index of 1.000337 is then required for the radio waves for the comic to be correct. [[Special:Contributions/172.68.11.221|172.68.11.221]] 13:46, 1 August 2018 (UTC)

:Do you mean 7.9 billion to convert to miles or to kilometers? Because my 13.6 bilion is to kilometers.

::I'm sure the actual comic is referring to miles and 5 billion was picked to match with the "divide by five" rule for miles. [[Special:Contributions/172.69.70.131|172.69.70.131]] 13:59, 1 August 2018 (UTC)

:::I did mean kilometers. If we use miles, 1.000314 fits almost precisely! (5.04 billion) [[Special:Contributions/172.68.11.17|172.68.11.17]] 14:42, 1 August 2018 (UTC)

If you can count several seconds, as is suggested in the comic, the flash is still billions of miles away, the widest possible distance between Earth and Neptune is about 5 billion km. Sebastian --[[Special:Contributions/172.68.110.40|172.68.110.40]] 14:51, 1 August 2018 (UTC)

:Not to mention that there's not a lot of air within a few billion miles of earth, so the dispersion will be much lower for all but the last 100-ish miles, AFAIK.[[Special:Contributions/172.68.54.142|172.68.54.142]] 20:12, 1 August 2018 (UTC)

::Also, while Jupiter has {{w|Great Red Spot|VERY gigantic storms}}, they are still too small to see the lightning from them from Earth. -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 23:17, 1 August 2018 (UTC)

Do you really need to know the spectrum of the flash? If we assume that a flash contains UV and X-ray radiation and that the visible light is generated at the same time as the UV or X-ray radiation then you only need to know the refractive index of light/UV/X-ray in air under the same temperature conditions and not the exact spectrum. [[User:Condor70|Condor70]] ([[User talk:Condor70|talk]])

:I initially made the mistake of thinking this referred to time difference between visible and UV/X-ray, but it specifically says "brightness." If you want to compare the brightness at a distance to the brightness at the source you'll need to know the brightness at the source, i.e. the spectrum of the flash itself. With this technique you don't need to know the dispersion "only" the relative attenuation, but I suspect that would be a more error-prone measurement.[[Special:Contributions/172.68.54.142|172.68.54.142]] 18:54, 1 August 2018 (UTC)

I understand the joke Randall was going for, but have a problem with the wording. "Count the number of seconds" won't work for fractions of anything. "Measure" would work, but spoils the gag a bit. Counting numbers are integers; counting the seconds between the visible and radio frequency flashes will give you zero. [[Special:Contributions/172.69.71.24|172.69.71.24]] 17:00, 1 August 2018 (UTC)

:You're certainly correct, but the joke works (for me at least) by its comparison to the standard rule of counting seconds, and humans are not generally precise enough to resolve better than one second. By keeping Megan's wording as close to the customary rule as possible I think it optimizes the humor. That "Billion" at the end is the whole joke for me, the replacement of "sound" with "radio wave" can be glossed-over on first reading, until you get to the unexpected extra 9 orders of magnitude in the conversion.[[Special:Contributions/172.68.54.142|172.68.54.142]] 18:54, 1 August 2018 (UTC)

::Just realized I also glossed-over the replacement of "divide" with "multiply." The brain is a funny thing.[[Special:Contributions/172.68.54.142|172.68.54.142]] 20:07, 1 August 2018 (UTC)

Do these account for the air pressure variability common in most thunderstorms?

I think explanation and transcript are pretty complete now. [[Special:Contributions/172.68.51.112|172.68.51.112]] 20:58, 1 August 2018 (UTC)

:There is the additional problem that a flash is no instantaneous, but progresses at a fraction of the speed of light. Who says that radio waves and light at different wavelenghts or xrays have their maximum at the same moment? ;-) --[[Special:Contributions/162.158.91.59|162.158.91.59]] 08:05, 2 August 2018 (UTC)

:: I added a few words about the problem that a flash is not instantaneous and removed the 'incomplete' tag. Hope that's OK. [[User:Chrisahn|Chrisahn]] ([[User talk:Chrisahn|talk]]) 19:41, 2 August 2018 (UTC)

Here's a variation of the calculation above that simplifies numeric evaluation:

The {{w|refractive index}} is defined as <math>n=\frac{c}{v}</math>, so <math>v=\frac{c}{n}</math> and thus <math>t=\frac{s}{v}=\frac{s\,n}{c}</math>.

<math>t_1=\frac{s\,n_1}{c}</math>

<math>t_2=\frac{s\,n_2}{c}</math>

Subtract:

<math>t_1-t_2=\Delta t=\frac{s\,n_1}{c}-\frac{s\,n_2}{c}=s\frac{n_1-n_2}{c}=s\frac{\Delta n}{c}</math>

Therefore

<math>s=\Delta t\frac{c}{\Delta n}</math>

and the factor we want to calculate is

<math>\frac{c}{\Delta n}</math>

With the numbers given in the sources in the main text:

<math>n_1=1.000315</math>

<math>n_2=1.000277</math>

<math>\Delta n=n_1-n_2=0.000038</math>

For kilometers: <math>\frac{c}{\Delta n}\approx\frac{300,000\,km/s}{0.000038}\approx7.9\cdot10^9\,km/s</math>

For miles: <math>\frac{c}{\Delta n}\approx\frac{186,000\,mi/s}{0.000038}\approx4.9\cdot10^9\,mi/s</math>

[[User:Chrisahn|Chrisahn]] ([[User talk:Chrisahn|talk]]) 18:28, 2 August 2018 (UTC)

== Assumptions on the medium properties sound? ==

Refractive index of *dry* air might be pretty close to 1 for both light and RF EM waves, but:

Let's assume that the air is humid, if not even full of water drops. After all, lightning.

Let's further assume that an air/water mixture or solution has electromagnetic properties between these two materials.

In water, refractive index for light is about <math>n_{\text{water, optical}}=1.33 n_{\text{air, optical}}</math>, (as easily demonstrated by the optical refractive effects); for RF, we typically use values of <math>\frac{n_{\text{water, RF}}^2}{\mu_r}=\epsilon\approx 80</math>. So, <math>n_{\text{water, RF}}\approx \sqrt{80}n_{\text{air, RF}}</math>.

Let's assume a 10⁻³ "EM-effective" water content in the comic air.

That would lead to <math>\frac{v_{\text{opt.}}}{v_{\text{RF}}} = \frac{\frac34}{\sqrt{80}^{-1}}= \frac34\sqrt{80}=6.7</math>.

:While the humidity (amount of water vapor) is certainly higher during the rain, I don't think that would count as a proper "water-air mixture". Wikipedia says that "Violent rain" is above 5 cm/h. If you divide it by 3600 (to get cm/s), and then imagine stretching that all the way to the cloud, you'll find out there's not that much water at given moment in the air. [[Special:Contributions/172.68.51.112|172.68.51.112]] 19:12, 1 August 2018 (UTC)

::Great point. To finish the calculation let's use a typical terminal velocity for a large raindrop (it's a big storm, I'm sure) of 9m/s. 0.05 m/hr / 3600 s/hr / 9 m/s = 0.00015% water by volume. Sure seems like more than that when I have to drive through it! Then it seems more like [http://what-if.xkcd.com/12/].[[Special:Contributions/172.68.54.142|172.68.54.142]] 20:32, 1 August 2018 (UTC)

Talk:2027: Lightning Distance

2018-08-02T19:42:06Z

Chrisahn:

Calculations I used:

<math>t_1=\frac{s}{v_1}</math>

<math>t_2=\frac{s}{v_2}</math>

Substract:

<math>t_1-t_2=\Delta t=\frac{s}{v_1}-\frac{s}{v_2}=\frac{sv_2-sv_1}{v_1v_2}=s\frac{v_2-v_1}{v_1v_2}=s\frac{\Delta v}{v_1v_2}</math>

Therefore

<math>s=\Delta t\frac{v_1v_2}{\Delta v}</math>

I evaluated <math>\frac{v_1v_2}{\Delta v}</math> and it came to be 13.6 billion. Can someone verify it's correct? [[Special:Contributions/172.68.51.112|172.68.51.112]] 13:08, 1 August 2018 (UTC)

:The comic begins with the question "how many miles away", so converting to kilometers isn't the right calculation.[[Special:Contributions/172.69.71.24|172.69.71.24]] 17:06, 1 August 2018 (UTC)

I used refractive index for visible light of 1.000277 (air at STP as opposed to 0C 1atm) and arrived at around 7.9 billion instead. Refractive index of 1.000337 is then required for the radio waves for the comic to be correct. [[Special:Contributions/172.68.11.221|172.68.11.221]] 13:46, 1 August 2018 (UTC)

:Do you mean 7.9 billion to convert to miles or to kilometers? Because my 13.6 bilion is to kilometers.

::I'm sure the actual comic is referring to miles and 5 billion was picked to match with the "divide by five" rule for miles. [[Special:Contributions/172.69.70.131|172.69.70.131]] 13:59, 1 August 2018 (UTC)

:::I did mean kilometers. If we use miles, 1.000314 fits almost precisely! (5.04 billion) [[Special:Contributions/172.68.11.17|172.68.11.17]] 14:42, 1 August 2018 (UTC)

If you can count several seconds, as is suggested in the comic, the flash is still billions of miles away, the widest possible distance between Earth and Neptune is about 5 billion km. Sebastian --[[Special:Contributions/172.68.110.40|172.68.110.40]] 14:51, 1 August 2018 (UTC)

:Not to mention that there's not a lot of air within a few billion miles of earth, so the dispersion will be much lower for all but the last 100-ish miles, AFAIK.[[Special:Contributions/172.68.54.142|172.68.54.142]] 20:12, 1 August 2018 (UTC)

::Also, while Jupiter has {{w|Great Red Spot|VERY gigantic storms}}, they are still too small to see the lightning from them from Earth. -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 23:17, 1 August 2018 (UTC)

Do you really need to know the spectrum of the flash? If we assume that a flash contains UV and X-ray radiation and that the visible light is generated at the same time as the UV or X-ray radiation then you only need to know the refractive index of light/UV/X-ray in air under the same temperature conditions and not the exact spectrum. [[User:Condor70|Condor70]] ([[User talk:Condor70|talk]])

:I initially made the mistake of thinking this referred to time difference between visible and UV/X-ray, but it specifically says "brightness." If you want to compare the brightness at a distance to the brightness at the source you'll need to know the brightness at the source, i.e. the spectrum of the flash itself. With this technique you don't need to know the dispersion "only" the relative attenuation, but I suspect that would be a more error-prone measurement.[[Special:Contributions/172.68.54.142|172.68.54.142]] 18:54, 1 August 2018 (UTC)

I understand the joke Randall was going for, but have a problem with the wording. "Count the number of seconds" won't work for fractions of anything. "Measure" would work, but spoils the gag a bit. Counting numbers are integers; counting the seconds between the visible and radio frequency flashes will give you zero. [[Special:Contributions/172.69.71.24|172.69.71.24]] 17:00, 1 August 2018 (UTC)

:You're certainly correct, but the joke works (for me at least) by its comparison to the standard rule of counting seconds, and humans are not generally precise enough to resolve better than one second. By keeping Megan's wording as close to the customary rule as possible I think it optimizes the humor. That "Billion" at the end is the whole joke for me, the replacement of "sound" with "radio wave" can be glossed-over on first reading, until you get to the unexpected extra 9 orders of magnitude in the conversion.[[Special:Contributions/172.68.54.142|172.68.54.142]] 18:54, 1 August 2018 (UTC)

::Just realized I also glossed-over the replacement of "divide" with "multiply." The brain is a funny thing.[[Special:Contributions/172.68.54.142|172.68.54.142]] 20:07, 1 August 2018 (UTC)

Do these account for the air pressure variability common in most thunderstorms?

I think explanation and transcript are pretty complete now. [[Special:Contributions/172.68.51.112|172.68.51.112]] 20:58, 1 August 2018 (UTC)

:There is the additional problem that a flash is no instantaneous, but progresses at a fraction of the speed of light. Who says that radio waves and light at different wavelenghts or xrays have their maximum at the same moment? ;-) --[[Special:Contributions/162.158.91.59|162.158.91.59]] 08:05, 2 August 2018 (UTC)

:: I added a few words about the problem that a flash is not instantaneous and removed the 'incomplete' tag. Hope that's OK. [[User:Chrisahn|Chrisahn]] ([[User talk:Chrisahn|talk]]) 19:41, 2 August 2018 (UTC)

Here's a variation of the calculation above that simplifies numeric evaluation:

The {{w|refractive index}} is defined as <math>n=\frac{c}{v}</math>, so <math>v=\frac{c}{n}</math> and thus <math>t=\frac{s}{v}=\frac{s\,n}{c}</math>.

<math>t_1=\frac{s\,n_1}{c}</math>

<math>t_2=\frac{s\,n_2}{c}</math>

Substract:

<math>t_1-t_2=\Delta t=\frac{s\,n_1}{c}-\frac{s\,n_2}{c}=s\frac{n_1-n_2}{c}=s\frac{\Delta n}{c}</math>

Therefore

<math>s=\Delta t\frac{c}{\Delta n}</math>

and the factor we want to calculate is

<math>\frac{c}{\Delta n}</math>

With the numbers given in the sources in the main text:

<math>n_1=1.000315</math>

<math>n_2=1.000277</math>

<math>\Delta n=n_1-n_2=0.000038</math>

For kilometers: <math>\frac{c}{\Delta n}\approx\frac{300,000\,km/s}{0.000038}\approx7.9\cdot10^9\,km/s</math>

For miles: <math>\frac{c}{\Delta n}\approx\frac{186,000\,mi/s}{0.000038}\approx4.9\cdot10^9\,mi/s</math>

[[User:Chrisahn|Chrisahn]] ([[User talk:Chrisahn|talk]]) 18:28, 2 August 2018 (UTC)

== Assumptions on the medium properties sound? ==

Refractive index of *dry* air might be pretty close to 1 for both light and RF EM waves, but:

Let's assume that the air is humid, if not even full of water drops. After all, lightning.

Let's further assume that an air/water mixture or solution has electromagnetic properties between these two materials.

In water, refractive index for light is about <math>n_{\text{water, optical}}=1.33 n_{\text{air, optical}}</math>, (as easily demonstrated by the optical refractive effects); for RF, we typically use values of <math>\frac{n_{\text{water, RF}}^2}{\mu_r}=\epsilon\approx 80</math>. So, <math>n_{\text{water, RF}}\approx \sqrt{80}n_{\text{air, RF}}</math>.

Let's assume a 10⁻³ "EM-effective" water content in the comic air.

That would lead to <math>\frac{v_{\text{opt.}}}{v_{\text{RF}}} = \frac{\frac34}{\sqrt{80}^{-1}}= \frac34\sqrt{80}=6.7</math>.

:While the humidity (amount of water vapor) is certainly higher during the rain, I don't think that would count as a proper "water-air mixture". Wikipedia says that "Violent rain" is above 5 cm/h. If you divide it by 3600 (to get cm/s), and then imagine stretching that all the way to the cloud, you'll find out there's not that much water at given moment in the air. [[Special:Contributions/172.68.51.112|172.68.51.112]] 19:12, 1 August 2018 (UTC)

::Great point. To finish the calculation let's use a typical terminal velocity for a large raindrop (it's a big storm, I'm sure) of 9m/s. 0.05 m/hr / 3600 s/hr / 9 m/s = 0.00015% water by volume. Sure seems like more than that when I have to drive through it! Then it seems more like [http://what-if.xkcd.com/12/].[[Special:Contributions/172.68.54.142|172.68.54.142]] 20:32, 1 August 2018 (UTC)

Talk:2027: Lightning Distance

2018-08-02T19:41:04Z

Chrisahn: why I removed the 'incomplete' tag

Calculations I used:

<math>t_1=\frac{s}{v_1}</math>

<math>t_2=\frac{s}{v_2}</math>

Substract:

<math>t_1-t_2=\Delta t=\frac{s}{v_1}-\frac{s}{v_2}=\frac{sv_2-sv_1}{v_1v_2}=s\frac{v_2-v_1}{v_1v_2}=s\frac{\Delta v}{v_1v_2}</math>

Therefore

<math>s=\Delta t\frac{v_1v_2}{\Delta v}</math>

I evaluated <math>\frac{v_1v_2}{\Delta v}</math> and it came to be 13.6 billion. Can someone verify it's correct? [[Special:Contributions/172.68.51.112|172.68.51.112]] 13:08, 1 August 2018 (UTC)

:The comic begins with the question "how many miles away", so converting to kilometers isn't the right calculation.[[Special:Contributions/172.69.71.24|172.69.71.24]] 17:06, 1 August 2018 (UTC)

I used refractive index for visible light of 1.000277 (air at STP as opposed to 0C 1atm) and arrived at around 7.9 billion instead. Refractive index of 1.000337 is then required for the radio waves for the comic to be correct. [[Special:Contributions/172.68.11.221|172.68.11.221]] 13:46, 1 August 2018 (UTC)

:Do you mean 7.9 billion to convert to miles or to kilometers? Because my 13.6 bilion is to kilometers.

::I'm sure the actual comic is referring to miles and 5 billion was picked to match with the "divide by five" rule for miles. [[Special:Contributions/172.69.70.131|172.69.70.131]] 13:59, 1 August 2018 (UTC)

:::I did mean kilometers. If we use miles, 1.000314 fits almost precisely! (5.04 billion) [[Special:Contributions/172.68.11.17|172.68.11.17]] 14:42, 1 August 2018 (UTC)

If you can count several seconds, as is suggested in the comic, the flash is still billions of miles away, the widest possible distance between Earth and Neptune is about 5 billion km. Sebastian --[[Special:Contributions/172.68.110.40|172.68.110.40]] 14:51, 1 August 2018 (UTC)

:Not to mention that there's not a lot of air within a few billion miles of earth, so the dispersion will be much lower for all but the last 100-ish miles, AFAIK.[[Special:Contributions/172.68.54.142|172.68.54.142]] 20:12, 1 August 2018 (UTC)

::Also, while Jupiter has {{w|Great Red Spot|VERY gigantic storms}}, they are still too small to see the lightning from them from Earth. -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 23:17, 1 August 2018 (UTC)

Do you really need to know the spectrum of the flash? If we assume that a flash contains UV and X-ray radiation and that the visible light is generated at the same time as the UV or X-ray radiation then you only need to know the refractive index of light/UV/X-ray in air under the same temperature conditions and not the exact spectrum. [[User:Condor70|Condor70]] ([[User talk:Condor70|talk]])

:I initially made the mistake of thinking this referred to time difference between visible and UV/X-ray, but it specifically says "brightness." If you want to compare the brightness at a distance to the brightness at the source you'll need to know the brightness at the source, i.e. the spectrum of the flash itself. With this technique you don't need to know the dispersion "only" the relative attenuation, but I suspect that would be a more error-prone measurement.[[Special:Contributions/172.68.54.142|172.68.54.142]] 18:54, 1 August 2018 (UTC)

I understand the joke Randall was going for, but have a problem with the wording. "Count the number of seconds" won't work for fractions of anything. "Measure" would work, but spoils the gag a bit. Counting numbers are integers; counting the seconds between the visible and radio frequency flashes will give you zero. [[Special:Contributions/172.69.71.24|172.69.71.24]] 17:00, 1 August 2018 (UTC)

:You're certainly correct, but the joke works (for me at least) by its comparison to the standard rule of counting seconds, and humans are not generally precise enough to resolve better than one second. By keeping Megan's wording as close to the customary rule as possible I think it optimizes the humor. That "Billion" at the end is the whole joke for me, the replacement of "sound" with "radio wave" can be glossed-over on first reading, until you get to the unexpected extra 9 orders of magnitude in the conversion.[[Special:Contributions/172.68.54.142|172.68.54.142]] 18:54, 1 August 2018 (UTC)

::Just realized I also glossed-over the replacement of "divide" with "multiply." The brain is a funny thing.[[Special:Contributions/172.68.54.142|172.68.54.142]] 20:07, 1 August 2018 (UTC)

Do these account for the air pressure variability common in most thunderstorms?

I think explanation and transcript are pretty complete now. [[Special:Contributions/172.68.51.112|172.68.51.112]] 20:58, 1 August 2018 (UTC)

:There is the additional problem that a flash is no instantaneous, but progresses at a fraction of the speed of light. Who says that radio waves and light at different wavelenghts or xrays have their maximum at the same moment? ;-) --[[Special:Contributions/162.158.91.59|162.158.91.59]] 08:05, 2 August 2018 (UTC)

:: I added a few words about the problem that a flash is not instantaneous and removed the 'incomplete' tag. Hope that's OK. [[User:Chrisahn|Chrisahn]] ([[User talk:Chrisahn|talk]]) 19:41, 2 August 2018 (UTC)

Variation of the calculation above that simplifies numeric evaluation:

The {{w|refractive index}} is defined as <math>n=\frac{c}{v}</math>, so <math>v=\frac{c}{n}</math> and thus <math>t=\frac{s}{v}=\frac{s\,n}{c}</math>.

<math>t_1=\frac{s\,n_1}{c}</math>

<math>t_2=\frac{s\,n_2}{c}</math>

Substract:

<math>t_1-t_2=\Delta t=\frac{s\,n_1}{c}-\frac{s\,n_2}{c}=s\frac{n_1-n_2}{c}=s\frac{\Delta n}{c}</math>

Therefore

<math>s=\Delta t\frac{c}{\Delta n}</math>

and the factor we want to calculate is

<math>\frac{c}{\Delta n}</math>

With the numbers given in the sources in the main text:

<math>n_1=1.000315</math>

<math>n_2=1.000277</math>

<math>\Delta n=n_1-n_2=0.000038</math>

For kilometers: <math>\frac{c}{\Delta n}\approx\frac{300,000\,km/s}{0.000038}\approx7.9\cdot10^9\,km/s</math>

For miles: <math>\frac{c}{\Delta n}\approx\frac{186,000\,mi/s}{0.000038}\approx4.9\cdot10^9\,mi/s</math>

[[User:Chrisahn|Chrisahn]] ([[User talk:Chrisahn|talk]]) 18:28, 2 August 2018 (UTC)

== Assumptions on the medium properties sound? ==

Refractive index of *dry* air might be pretty close to 1 for both light and RF EM waves, but:

Let's assume that the air is humid, if not even full of water drops. After all, lightning.

Let's further assume that an air/water mixture or solution has electromagnetic properties between these two materials.

In water, refractive index for light is about <math>n_{\text{water, optical}}=1.33 n_{\text{air, optical}}</math>, (as easily demonstrated by the optical refractive effects); for RF, we typically use values of <math>\frac{n_{\text{water, RF}}^2}{\mu_r}=\epsilon\approx 80</math>. So, <math>n_{\text{water, RF}}\approx \sqrt{80}n_{\text{air, RF}}</math>.

Let's assume a 10⁻³ "EM-effective" water content in the comic air.

That would lead to <math>\frac{v_{\text{opt.}}}{v_{\text{RF}}} = \frac{\frac34}{\sqrt{80}^{-1}}= \frac34\sqrt{80}=6.7</math>.

:While the humidity (amount of water vapor) is certainly higher during the rain, I don't think that would count as a proper "water-air mixture". Wikipedia says that "Violent rain" is above 5 cm/h. If you divide it by 3600 (to get cm/s), and then imagine stretching that all the way to the cloud, you'll find out there's not that much water at given moment in the air. [[Special:Contributions/172.68.51.112|172.68.51.112]] 19:12, 1 August 2018 (UTC)

::Great point. To finish the calculation let's use a typical terminal velocity for a large raindrop (it's a big storm, I'm sure) of 9m/s. 0.05 m/hr / 3600 s/hr / 9 m/s = 0.00015% water by volume. Sure seems like more than that when I have to drive through it! Then it seems more like [http://what-if.xkcd.com/12/].[[Special:Contributions/172.68.54.142|172.68.54.142]] 20:32, 1 August 2018 (UTC)

2027: Lightning Distance

2018-08-02T19:37:07Z

Chrisahn: /* Explanation */ split paragraph

{{comic
| number = 2027
| date = August 1, 2018
| title = Lightning Distance
| image = lightning_distance.png
| titletext = The index of radio refraction does have a lot of variation, which might throw off your calculations, so you can also look at the difference in brightness between the visible flash and more-attenuated UV and x-rays.
}}

=Explanation=
The usual trick for determining the distance to a {{w|lightning}} flash is to count the seconds from when you see the flash until when you hear {{w|thunder}}, and divide by five to get miles (or three to get kilometers). This works because the {{w|speed of light|transmission of light}} is essentially instantaneous over the relevant distances, while the {{w|speed of sound}} is 331.2 m/s (1,087 ft/s, 1,192 km/h, or 741 mph, varying a bit based on temperature), or about 1/5 mile per second (1/3 kilometer per second).

This comic subverts the usual trick by having Megan describe a highly impractical alternative method. Megan's method is based on the fact that the speed of electromagnetic radiation, which includes light and radio waves, is not truly infinite. The radiation produced by lightning on Earth also has to travel through air, which changes its speed in a fashion which depends on its frequency.

According to {{w|List_of_refractive_indices|Wikipedia}} and [https://hypertextbook.com/facts/2005/MayaBarsky.shtml other sources], refractive index of air at 0°C is about 1.000277, which equates to a speed of light around 299709.4 km/s (186230.8 miles/s). According to [https://www.fig.net/resources/proceedings/fig_proceedings/fig_2002/Js28/JS28_rueger.pdf this paper] (table on page 8), refractive index for radio waves in similar conditions is 1.000315, which equates to a speed around 299698.1 km/s (186223.7 miles/s). This means that to get the distance, the time difference in seconds between visible flash and radio burst should be multiplied by about 4.9 billion for miles, or about 7.9 billion for kilometers. More details for the calculations are in the comments below.

With sufficiently precise instruments, it would theoretically be possible to use this effect to determine the distance to a source of extremely short bursts of visible light and radio waves. The joke is that it is impractical for humans, both because we can't measure such small time intervals (one nanosecond for every 4.9 miles or 7.9 kilometers of atmosphere) and because we can't detect radiation outside the visible spectrum without very specialized instruments.

Yet even with specialized instruments, we probably couldn't measure the light and radio wave emissions of lightning with sufficient precision because a flash is not instantaneous, but {{w|Lightning|lasts about 60 to 70 microseconds}} - the signals we receive would rise and fall somewhat erratically over a time about five {{w|orders of magnitude}} longer than the time difference we want to measure.

For the purpose of the joke, the "5 billion" value used in the comic is a fair estimate which also references the original rule of 5 seconds per mile nicely, though the result can have a huge margin of error depending on actual conditions (temperature, humidity, etc.), as the title text suggests ("the index of radio refraction does have a lot of variation").

Even if lightning was farther away, for example, if we were observing another planet, the time difference still would not be substantial, because the visible and radio waves travel at essential the same speed as each other in the vacuum of space (the difference in speed discussed above applies only to travel through air).

The title text suggests another method of calculating distance to lightning. Since the absorption of light is also different in different wavelengths, it would be possible to calculate the difference by comparing the brightness instead of delays. This would, however, require the knowledge about prior relative brightness of lightning, i.e. the spectrum, in the compared wavelengths.

==Transcript==
:[Cueball and Megan stand on either side of a window, observing a bolt of lightning in a dark sky.]
:Cueball: What's that trick for telling how many miles away lightning is?
:Megan: Just count the seconds between the visible flash and the radio wave burst, then multiply by 5 billion.
{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]

2027: Lightning Distance

2018-08-02T19:36:12Z

Chrisahn: /* Transcript */ delete {{incomplete transcript}} tag

{{comic
| number = 2027
| date = August 1, 2018
| title = Lightning Distance
| image = lightning_distance.png
| titletext = The index of radio refraction does have a lot of variation, which might throw off your calculations, so you can also look at the difference in brightness between the visible flash and more-attenuated UV and x-rays.
}}

=Explanation=
The usual trick for determining the distance to a {{w|lightning}} flash is to count the seconds from when you see the flash until when you hear {{w|thunder}}, and divide by five to get miles (or three to get kilometers). This works because the {{w|speed of light|transmission of light}} is essentially instantaneous over the relevant distances, while the {{w|speed of sound}} is 331.2 m/s (1,087 ft/s, 1,192 km/h, or 741 mph, varying a bit based on temperature), or about 1/5 mile per second (1/3 kilometer per second).

This comic subverts the usual trick by having Megan describe a highly impractical alternative method. Megan's method is based on the fact that the speed of electromagnetic radiation, which includes light and radio waves, is not truly infinite. The radiation produced by lightning on Earth also has to travel through air, which changes its speed in a fashion which depends on its frequency.

According to {{w|List_of_refractive_indices|Wikipedia}} and [https://hypertextbook.com/facts/2005/MayaBarsky.shtml other sources], refractive index of air at 0°C is about 1.000277, which equates to a speed of light around 299709.4 km/s (186230.8 miles/s). According to [https://www.fig.net/resources/proceedings/fig_proceedings/fig_2002/Js28/JS28_rueger.pdf this paper] (table on page 8), refractive index for radio waves in similar conditions is 1.000315, which equates to a speed around 299698.1 km/s (186223.7 miles/s). This means that to get the distance, the time difference in seconds between visible flash and radio burst should be multiplied by about 4.9 billion for miles, or about 7.9 billion for kilometers. More details for the calculations are in the comments below.

With sufficiently precise instruments, it would theoretically be possible to use this effect to determine the distance to a source of extremely short bursts of visible light and radio waves. The joke is that it is impractical for humans, both because we can't measure such small time intervals (one nanosecond for every 4.9 miles or 7.9 kilometers of atmosphere) and because we can't detect radiation outside the visible spectrum without very specialized instruments. Yet even with specialized instruments, we probably couldn't measure the light and radio wave emissions of lightning with sufficient precision because a flash is not instantaneous, but {{w|Lightning|lasts about 60 to 70 microseconds}} - the signals we receive would rise and fall somewhat erratically over a time about five {{w|orders of magnitude}} longer than the time difference we want to measure.

For the purpose of the joke, the "5 billion" value used in the comic is a fair estimate which also references the original rule of 5 seconds per mile nicely, though the result can have a huge margin of error depending on actual conditions (temperature, humidity, etc.), as the title text suggests ("the index of radio refraction does have a lot of variation").

Even if lightning was farther away, for example, if we were observing another planet, the time difference still would not be substantial, because the visible and radio waves travel at essential the same speed as each other in the vacuum of space (the difference in speed discussed above applies only to travel through air).

The title text suggests another method of calculating distance to lightning. Since the absorption of light is also different in different wavelengths, it would be possible to calculate the difference by comparing the brightness instead of delays. This would, however, require the knowledge about prior relative brightness of lightning, i.e. the spectrum, in the compared wavelengths.

==Transcript==
:[Cueball and Megan stand on either side of a window, observing a bolt of lightning in a dark sky.]
:Cueball: What's that trick for telling how many miles away lightning is?
:Megan: Just count the seconds between the visible flash and the radio wave burst, then multiply by 5 billion.
{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]

2027: Lightning Distance

2018-08-02T19:35:03Z

Chrisahn: /* Explanation */ delete {{incomplete}} tag

{{comic
| number = 2027
| date = August 1, 2018
| title = Lightning Distance
| image = lightning_distance.png
| titletext = The index of radio refraction does have a lot of variation, which might throw off your calculations, so you can also look at the difference in brightness between the visible flash and more-attenuated UV and x-rays.
}}

=Explanation=
The usual trick for determining the distance to a {{w|lightning}} flash is to count the seconds from when you see the flash until when you hear {{w|thunder}}, and divide by five to get miles (or three to get kilometers). This works because the {{w|speed of light|transmission of light}} is essentially instantaneous over the relevant distances, while the {{w|speed of sound}} is 331.2 m/s (1,087 ft/s, 1,192 km/h, or 741 mph, varying a bit based on temperature), or about 1/5 mile per second (1/3 kilometer per second).

This comic subverts the usual trick by having Megan describe a highly impractical alternative method. Megan's method is based on the fact that the speed of electromagnetic radiation, which includes light and radio waves, is not truly infinite. The radiation produced by lightning on Earth also has to travel through air, which changes its speed in a fashion which depends on its frequency.

According to {{w|List_of_refractive_indices|Wikipedia}} and [https://hypertextbook.com/facts/2005/MayaBarsky.shtml other sources], refractive index of air at 0°C is about 1.000277, which equates to a speed of light around 299709.4 km/s (186230.8 miles/s). According to [https://www.fig.net/resources/proceedings/fig_proceedings/fig_2002/Js28/JS28_rueger.pdf this paper] (table on page 8), refractive index for radio waves in similar conditions is 1.000315, which equates to a speed around 299698.1 km/s (186223.7 miles/s). This means that to get the distance, the time difference in seconds between visible flash and radio burst should be multiplied by about 4.9 billion for miles, or about 7.9 billion for kilometers. More details for the calculations are in the comments below.

With sufficiently precise instruments, it would theoretically be possible to use this effect to determine the distance to a source of extremely short bursts of visible light and radio waves. The joke is that it is impractical for humans, both because we can't measure such small time intervals (one nanosecond for every 4.9 miles or 7.9 kilometers of atmosphere) and because we can't detect radiation outside the visible spectrum without very specialized instruments. Yet even with specialized instruments, we probably couldn't measure the light and radio wave emissions of lightning with sufficient precision because a flash is not instantaneous, but {{w|Lightning|lasts about 60 to 70 microseconds}} - the signals we receive would rise and fall somewhat erratically over a time about five {{w|orders of magnitude}} longer than the time difference we want to measure.

For the purpose of the joke, the "5 billion" value used in the comic is a fair estimate which also references the original rule of 5 seconds per mile nicely, though the result can have a huge margin of error depending on actual conditions (temperature, humidity, etc.), as the title text suggests ("the index of radio refraction does have a lot of variation").

Even if lightning was farther away, for example, if we were observing another planet, the time difference still would not be substantial, because the visible and radio waves travel at essential the same speed as each other in the vacuum of space (the difference in speed discussed above applies only to travel through air).

The title text suggests another method of calculating distance to lightning. Since the absorption of light is also different in different wavelengths, it would be possible to calculate the difference by comparing the brightness instead of delays. This would, however, require the knowledge about prior relative brightness of lightning, i.e. the spectrum, in the compared wavelengths.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Cueball and Megan stand on either side of a window, observing a bolt of lightning in a dark sky.]
:Cueball: What's that trick for telling how many miles away lightning is?
:Megan: Just count the seconds between the visible flash and the radio wave burst, then multiply by 5 billion.
{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]

2027: Lightning Distance

2018-08-02T19:34:05Z

Chrisahn: /* Explanation */

{{comic
| number = 2027
| date = August 1, 2018
| title = Lightning Distance
| image = lightning_distance.png
| titletext = The index of radio refraction does have a lot of variation, which might throw off your calculations, so you can also look at the difference in brightness between the visible flash and more-attenuated UV and x-rays.
}}

=Explanation=
{{incomplete|Created by a RADIO BURST - Update calculations and added values in km and miles. Do NOT delete this tag too soon.}}
The usual trick for determining the distance to a {{w|lightning}} flash is to count the seconds from when you see the flash until when you hear {{w|thunder}}, and divide by five to get miles (or three to get kilometers). This works because the {{w|speed of light|transmission of light}} is essentially instantaneous over the relevant distances, while the {{w|speed of sound}} is 331.2 m/s (1,087 ft/s, 1,192 km/h, or 741 mph, varying a bit based on temperature), or about 1/5 mile per second (1/3 kilometer per second).

This comic subverts the usual trick by having Megan describe a highly impractical alternative method. Megan's method is based on the fact that the speed of electromagnetic radiation, which includes light and radio waves, is not truly infinite. The radiation produced by lightning on Earth also has to travel through air, which changes its speed in a fashion which depends on its frequency.

According to {{w|List_of_refractive_indices|Wikipedia}} and [https://hypertextbook.com/facts/2005/MayaBarsky.shtml other sources], refractive index of air at 0°C is about 1.000277, which equates to a speed of light around 299709.4 km/s (186230.8 miles/s). According to [https://www.fig.net/resources/proceedings/fig_proceedings/fig_2002/Js28/JS28_rueger.pdf this paper] (table on page 8), refractive index for radio waves in similar conditions is 1.000315, which equates to a speed around 299698.1 km/s (186223.7 miles/s). This means that to get the distance, the time difference in seconds between visible flash and radio burst should be multiplied by about 4.9 billion for miles, or about 7.9 billion for kilometers. More details for the calculations are in the comments below.

With sufficiently precise instruments, it would theoretically be possible to use this effect to determine the distance to a source of extremely short bursts of visible light and radio waves. The joke is that it is impractical for humans, both because we can't measure such small time intervals (one nanosecond for every 4.9 miles or 7.9 kilometers of atmosphere) and because we can't detect radiation outside the visible spectrum without very specialized instruments. Yet even with specialized instruments, we probably couldn't measure the light and radio wave emissions of lightning with sufficient precision because a flash is not instantaneous, but {{w|Lightning|lasts about 60 to 70 microseconds}} - the signals we receive would rise and fall somewhat erratically over a time about five {{w|orders of magnitude}} longer than the time difference we want to measure.

For the purpose of the joke, the "5 billion" value used in the comic is a fair estimate which also references the original rule of 5 seconds per mile nicely, though the result can have a huge margin of error depending on actual conditions (temperature, humidity, etc.), as the title text suggests ("the index of radio refraction does have a lot of variation").

Even if lightning was farther away, for example, if we were observing another planet, the time difference still would not be substantial, because the visible and radio waves travel at essential the same speed as each other in the vacuum of space (the difference in speed discussed above applies only to travel through air).

The title text suggests another method of calculating distance to lightning. Since the absorption of light is also different in different wavelengths, it would be possible to calculate the difference by comparing the brightness instead of delays. This would, however, require the knowledge about prior relative brightness of lightning, i.e. the spectrum, in the compared wavelengths.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Cueball and Megan stand on either side of a window, observing a bolt of lightning in a dark sky.]
:Cueball: What's that trick for telling how many miles away lightning is?
:Megan: Just count the seconds between the visible flash and the radio wave burst, then multiply by 5 billion.
{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]

2027: Lightning Distance

2018-08-02T19:32:47Z

Chrisahn: /* Explanation */ wording

{{comic
| number = 2027
| date = August 1, 2018
| title = Lightning Distance
| image = lightning_distance.png
| titletext = The index of radio refraction does have a lot of variation, which might throw off your calculations, so you can also look at the difference in brightness between the visible flash and more-attenuated UV and x-rays.
}}

=Explanation=
{{incomplete|Created by a RADIO BURST - Update calculations and added values in km and miles. Do NOT delete this tag too soon.}}
The usual trick for determining the distance to a {{w|lightning}} flash is to count the seconds from when you see the flash until when you hear {{w|thunder}}, and divide by five to get miles (or three to get kilometers). This works because the {{w|speed of light|transmission of light}} is essentially instantaneous over the relevant distances, while the {{w|speed of sound}} is 331.2 m/s (1,087 ft/s, 1,192 km/h, or 741 mph, varying a bit based on temperature), or about 1/5 mile per second (1/3 kilometer per second).

This comic subverts the usual trick by having Megan describe a highly impractical alternative method. Megan's method is based on the fact that the speed of electromagnetic radiation, which includes light and radio waves, is not truly infinite. The radiation produced by lightning on Earth also has to travel through air, which changes its speed in a fashion which depends on its frequency.

According to {{w|List_of_refractive_indices|Wikipedia}} and [https://hypertextbook.com/facts/2005/MayaBarsky.shtml other sources], refractive index of air at 0°C is about 1.000277, which equates to a speed of light around 299709.4 km/s (186230.8 miles/s). According to [https://www.fig.net/resources/proceedings/fig_proceedings/fig_2002/Js28/JS28_rueger.pdf this paper] (table on page 8), refractive index for radio waves in similar conditions is 1.000315, which equates to a speed around 299698.1 km/s (186223.7 miles/s). This means that to get the distance, the time difference in seconds between visible flash and radio burst should be multiplied by about 4.9 billion for miles, or about 7.9 billion for kilometers. More details for the calculations are in the comments below.

With sufficiently precise instruments, it would theoretically be possible to use this effect to determine the distance to a source of extremely short bursts of visible light and radio waves. The joke is that it is impractical for humans, both because we can't measure such small time intervals (one nanosecond for every 4.9 miles or 7.9 kilometers of atmosphere) and because we can't detect radiation outside the visible spectrum without very specialized instruments. Yet even with specialized instruments, we probably couldn't measure the light and radio wave emissions of lightning with sufficient precision because a flash is not instantaneous, but {{w|Lightning|lasts about 60 to 70 microseconds}} - the signals we receive would rise and fall over a time about five {{w|orders of magnitude}} longer than the time difference we want to measure.

For the purpose of the joke, the "5 billion" value used in the comic is a fair estimate which also references the original rule of 5 seconds per mile nicely, though the result can have a huge margin of error depending on actual conditions (temperature, humidity, etc.), as the title text suggests ("the index of radio refraction does have a lot of variation").

Even if lightning was farther away, for example, if we were observing another planet, the time difference still would not be substantial, because the visible and radio waves travel at essential the same speed as each other in the vacuum of space (the difference in speed discussed above applies only to travel through air).

The title text suggests another method of calculating distance to lightning. Since the absorption of light is also different in different wavelengths, it would be possible to calculate the difference by comparing the brightness instead of delays. This would, however, require the knowledge about prior relative brightness of lightning, i.e. the spectrum, in the compared wavelengths.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Cueball and Megan stand on either side of a window, observing a bolt of lightning in a dark sky.]
:Cueball: What's that trick for telling how many miles away lightning is?
:Megan: Just count the seconds between the visible flash and the radio wave burst, then multiply by 5 billion.
{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]

2027: Lightning Distance

2018-08-02T19:29:48Z

Chrisahn: /* Explanation */ wording

{{comic
| number = 2027
| date = August 1, 2018
| title = Lightning Distance
| image = lightning_distance.png
| titletext = The index of radio refraction does have a lot of variation, which might throw off your calculations, so you can also look at the difference in brightness between the visible flash and more-attenuated UV and x-rays.
}}

=Explanation=
{{incomplete|Created by a RADIO BURST - Update calculations and added values in km and miles. Do NOT delete this tag too soon.}}
The usual trick for determining the distance to a {{w|lightning}} flash is to count the seconds from when you see the flash until when you hear {{w|thunder}}, and divide by five to get miles (or three to get kilometers). This works because the {{w|speed of light|transmission of light}} is essentially instantaneous over the relevant distances, while the {{w|speed of sound}} is 331.2 m/s (1,087 ft/s, 1,192 km/h, or 741 mph, varying a bit based on temperature), or about 1/5 mile per second (1/3 kilometer per second).

This comic subverts the usual trick by having Megan describe a highly impractical alternative method. Megan's method is based on the fact that the speed of electromagnetic radiation, which includes light and radio waves, is not truly infinite. The radiation produced by lightning on Earth also has to travel through air, which changes its speed in a fashion which depends on its frequency.

According to {{w|List_of_refractive_indices|Wikipedia}} and [https://hypertextbook.com/facts/2005/MayaBarsky.shtml other sources], refractive index of air at 0°C is about 1.000277, which equates to a speed of light around 299709.4 km/s (186230.8 miles/s). According to [https://www.fig.net/resources/proceedings/fig_proceedings/fig_2002/Js28/JS28_rueger.pdf this paper] (table on page 8), refractive index for radio waves in similar conditions is 1.000315, which equates to a speed around 299698.1 km/s (186223.7 miles/s). This means that to get the distance, the time difference in seconds between visible flash and radio burst should be multiplied by about 4.9 billion for miles, or about 7.9 billion for kilometers. More details for the calculations are in the comments below.

With sufficiently precise instruments, it would theoretically be possible to use this effect to determine the distance to a source of extremely short bursts of visible light and radio waves. The joke is that it is impractical for humans, both because we can't measure such small time intervals (one nanosecond for every 4.9 miles or 7.9 kilometers of atmosphere) and because we can't detect radiation outside the visible spectrum without very specialized instruments. Yet even with specialized instruments, we probably couldn't measure the light and radio wave emissions of lightning with sufficient precision because a flash is not instantaneous, but {{w|Lightning|lasts about 60 to 70 microseconds}} - the signals we receive would be spread out over a time about five {{w|orders of magnitude}} longer than the time difference we want to measure.

For the purpose of the joke, the "5 billion" value used in the comic is a fair estimate which also references the original rule of 5 seconds per mile nicely, though the result can have a huge margin of error depending on actual conditions (temperature, humidity, etc.), as the title text suggests ("the index of radio refraction does have a lot of variation").

Even if lightning was farther away, for example, if we were observing another planet, the time difference still would not be substantial, because the visible and radio waves travel at essential the same speed as each other in the vacuum of space (the difference in speed discussed above applies only to travel through air).

The title text suggests another method of calculating distance to lightning. Since the absorption of light is also different in different wavelengths, it would be possible to calculate the difference by comparing the brightness instead of delays. This would, however, require the knowledge about prior relative brightness of lightning, i.e. the spectrum, in the compared wavelengths.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Cueball and Megan stand on either side of a window, observing a bolt of lightning in a dark sky.]
:Cueball: What's that trick for telling how many miles away lightning is?
:Megan: Just count the seconds between the visible flash and the radio wave burst, then multiply by 5 billion.
{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]

2027: Lightning Distance

2018-08-02T19:28:30Z

Chrisahn: /* Explanation */ wording

{{comic
| number = 2027
| date = August 1, 2018
| title = Lightning Distance
| image = lightning_distance.png
| titletext = The index of radio refraction does have a lot of variation, which might throw off your calculations, so you can also look at the difference in brightness between the visible flash and more-attenuated UV and x-rays.
}}

=Explanation=
{{incomplete|Created by a RADIO BURST - Update calculations and added values in km and miles. Do NOT delete this tag too soon.}}
The usual trick for determining the distance to a {{w|lightning}} flash is to count the seconds from when you see the flash until when you hear {{w|thunder}}, and divide by five to get miles (or three to get kilometers). This works because the {{w|speed of light|transmission of light}} is essentially instantaneous over the relevant distances, while the {{w|speed of sound}} is 331.2 m/s (1,087 ft/s, 1,192 km/h, or 741 mph, varying a bit based on temperature), or about 1/5 mile per second (1/3 kilometer per second).

This comic subverts the usual trick by having Megan describe a highly impractical alternative method. Megan's method is based on the fact that the speed of electromagnetic radiation, which includes light and radio waves, is not truly infinite. The radiation produced by lightning on Earth also has to travel through air, which changes its speed in a fashion which depends on its frequency.

According to {{w|List_of_refractive_indices|Wikipedia}} and [https://hypertextbook.com/facts/2005/MayaBarsky.shtml other sources], refractive index of air at 0°C is about 1.000277, which equates to a speed of light around 299709.4 km/s (186230.8 miles/s). According to [https://www.fig.net/resources/proceedings/fig_proceedings/fig_2002/Js28/JS28_rueger.pdf this paper] (table on page 8), refractive index for radio waves in similar conditions is 1.000315, which equates to a speed around 299698.1 km/s (186223.7 miles/s). This means that to get the distance, the time difference in seconds between visible flash and radio burst should be multiplied by about 4.9 billion for miles, or about 7.9 billion for kilometers. More details for the calculations are in the comments below.

With sufficiently precise instruments, it would theoretically be possible to use this effect to determine the distance to a source of extremely short bursts of visible light and radio waves. The joke is that it is impractical for humans, both because we can't measure such small time intervals (one nanosecond for every 4.9 miles or 7.9 kilometers of atmosphere) and because we can't detect radiation outside the visible spectrum without very specialized instruments. Even with specialized instruments, we probably couldn't measure the light and radio wave emissions of lightning with sufficient precision because a flash is not instantaneous, but {{w|Lightning|lasts about 60 to 70 microseconds}} - the signals we receive would be spread out over a time about five {{w|orders of magnitude}} longer than the time difference we want to measure.

For the purpose of the joke, the "5 billion" value used in the comic is a fair estimate which also references the original rule of 5 seconds per mile nicely, though the result can have a huge margin of error depending on actual conditions (temperature, humidity, etc.), as the title text suggests ("the index of radio refraction does have a lot of variation").

Even if lightning was farther away, for example, if we were observing another planet, the time difference still would not be substantial, because the visible and radio waves travel at essential the same speed as each other in the vacuum of space (the difference in speed discussed above applies only to travel through air).

The title text suggests another method of calculating distance to lightning. Since the absorption of light is also different in different wavelengths, it would be possible to calculate the difference by comparing the brightness instead of delays. This would, however, require the knowledge about prior relative brightness of lightning, i.e. the spectrum, in the compared wavelengths.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Cueball and Megan stand on either side of a window, observing a bolt of lightning in a dark sky.]
:Cueball: What's that trick for telling how many miles away lightning is?
:Megan: Just count the seconds between the visible flash and the radio wave burst, then multiply by 5 billion.
{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]

2027: Lightning Distance

2018-08-02T19:26:50Z

Chrisahn: /* Explanation */

{{comic
| number = 2027
| date = August 1, 2018
| title = Lightning Distance
| image = lightning_distance.png
| titletext = The index of radio refraction does have a lot of variation, which might throw off your calculations, so you can also look at the difference in brightness between the visible flash and more-attenuated UV and x-rays.
}}

=Explanation=
{{incomplete|Created by a RADIO BURST - Update calculations and added values in km and miles. Do NOT delete this tag too soon.}}
The usual trick for determining the distance to a {{w|lightning}} flash is to count the seconds from when you see the flash until when you hear {{w|thunder}}, and divide by five to get miles (or three to get kilometers). This works because the {{w|speed of light|transmission of light}} is essentially instantaneous over the relevant distances, while the {{w|speed of sound}} is 331.2 m/s (1,087 ft/s, 1,192 km/h, or 741 mph, varying a bit based on temperature), or about 1/5 mile per second (1/3 kilometer per second).

This comic subverts the usual trick by having Megan describe a highly impractical alternative method. Megan's method is based on the fact that the speed of electromagnetic radiation, which includes light and radio waves, is not truly infinite. The radiation produced by lightning on Earth also has to travel through air, which changes its speed in a fashion which depends on its frequency.

According to {{w|List_of_refractive_indices|Wikipedia}} and [https://hypertextbook.com/facts/2005/MayaBarsky.shtml other sources], refractive index of air at 0°C is about 1.000277, which equates to a speed of light around 299709.4 km/s (186230.8 miles/s). According to [https://www.fig.net/resources/proceedings/fig_proceedings/fig_2002/Js28/JS28_rueger.pdf this paper] (table on page 8), refractive index for radio waves in similar conditions is 1.000315, which equates to a speed around 299698.1 km/s (186223.7 miles/s). This means that to get the distance, the time difference in seconds between visible flash and radio burst should be multiplied by about 4.9 billion for miles, or about 7.9 billion for kilometers. More details for the calculations are in the comments below.

With sufficiently precise instruments, it would theoretically be possible to use this effect to determine the distance to a source of extremely short bursts of visible light and radio waves. The joke is that it is impractical for humans, both because we can't measure such small time intervals (one nanosecond for every 4.9 miles or 7.9 kilometers of atmosphere) and because we can't detect radiation outside the visible spectrum without very specialized instruments. Even with specialized instruments, we probably couldn't measure the light and radio wave emissions of lightning with sufficient precision because a flash is not instantaneous, but {{w|Lightning|lasts about 60 to 70 microseconds}} - about five {{w|orders of magnitude}} longer than the time difference we would need to measure.

For the purpose of the joke, the "5 billion" value used in the comic is a fair estimate which also references the original rule of 5 seconds per mile nicely, though the result can have a huge margin of error depending on actual conditions (temperature, humidity, etc.), as the title text suggests ("the index of radio refraction does have a lot of variation").

Even if lightning was farther away, for example, if we were observing another planet, the time difference still would not be substantial, because the visible and radio waves travel at essential the same speed as each other in the vacuum of space (the difference in speed discussed above applies only to travel through air).

The title text suggests another method of calculating distance to lightning. Since the absorption of light is also different in different wavelengths, it would be possible to calculate the difference by comparing the brightness instead of delays. This would, however, require the knowledge about prior relative brightness of lightning, i.e. the spectrum, in the compared wavelengths.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Cueball and Megan stand on either side of a window, observing a bolt of lightning in a dark sky.]
:Cueball: What's that trick for telling how many miles away lightning is?
:Megan: Just count the seconds between the visible flash and the radio wave burst, then multiply by 5 billion.
{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]

2027: Lightning Distance

2018-08-02T19:11:29Z

Chrisahn: /* Explanation */ link to {{w|Lightning}}

{{comic
| number = 2027
| date = August 1, 2018
| title = Lightning Distance
| image = lightning_distance.png
| titletext = The index of radio refraction does have a lot of variation, which might throw off your calculations, so you can also look at the difference in brightness between the visible flash and more-attenuated UV and x-rays.
}}

=Explanation=
{{incomplete|Created by a RADIO BURST - Update calculations and added values in km and miles. Do NOT delete this tag too soon.}}
The usual trick for determining the distance to a {{w|lightning}} flash is to count the seconds from when you see the flash until when you hear {{w|thunder}}, and divide by five to get miles (or three to get kilometers). This works because the {{w|speed of light|transmission of light}} is essentially instantaneous over the relevant distances, while the {{w|speed of sound}} is 331.2 m/s (1,087 ft/s, 1,192 km/h, or 741 mph, varying a bit based on temperature), or about 1/5 mile per second (1/3 kilometer per second).

This comic subverts the usual trick by having Megan describe a highly impractical alternative method. Megan's method is based on the fact that the speed of electromagnetic radiation, which includes light and radio waves, is not truly infinite. The radiation produced by lightning on Earth also has to travel through air, which changes its speed in a fashion which depends on its frequency.

According to {{w|List_of_refractive_indices|Wikipedia}} and [https://hypertextbook.com/facts/2005/MayaBarsky.shtml other sources], refractive index of air at 0°C is about 1.000277, which equates to a speed of light around 299709.4 km/s (186230.8 miles/s). According to [https://www.fig.net/resources/proceedings/fig_proceedings/fig_2002/Js28/JS28_rueger.pdf this paper], refractive index for radio waves in similar conditions is 1.000315, which equates to a speed around 299698.1 km/s (186223.7 miles/s). This means that to get the distance, the time difference in seconds between visible flash and radio burst should be multiplied by about 4.9 billion for miles, or about 7.9 billion for kilometers. More details for the calculations are in the comments below.

With sufficiently precise instruments, it would theoretically be possible to use this effect to determine the distance to a source of extremely short bursts of visible light and radio waves. The joke is that it is impractical for humans, both because we can't measure such small time intervals (one nanosecond for every 4.9 miles or 7.9 kilometers of atmosphere) and because we can't detect radiation outside the visible spectrum without very specialized instruments. Even with specialized instruments, we probably couldn't measure the light and radio wave emissions of lightning with sufficient precision because a flash is not instantaneous, but {{w|Lightning|lasts about 60 to 70 microseconds}} - about five {{w|orders of magnitude}} longer than the time difference we would need to measure.

For the purpose of the joke, the "5 billion" value used in the comic is a fair estimate which also references the original rule of 5 seconds per mile nicely, though the result can have a huge margin of error depending on actual conditions (temperature, humidity, etc.), as the title text suggests ("the index of radio refraction does have a lot of variation").

Even if lightning was farther away, for example, if we were observing another planet, the time difference still would not be substantial, because the visible and radio waves travel at essential the same speed as each other in the vacuum of space (the difference in speed discussed above applies only to travel through air).

The title text suggests another method of calculating distance to lightning. Since the absorption of light is also different in different wavelengths, it would be possible to calculate the difference by comparing the brightness instead of delays. This would, however, require the knowledge about prior relative brightness of lightning, i.e. the spectrum, in the compared wavelengths.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Cueball and Megan stand on either side of a window, observing a bolt of lightning in a dark sky.]
:Cueball: What's that trick for telling how many miles away lightning is?
:Megan: Just count the seconds between the visible flash and the radio wave burst, then multiply by 5 billion.
{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]

2027: Lightning Distance

2018-08-02T19:09:31Z

Chrisahn: /* Explanation */ additional problem: flashes last much longer than measurable time difference between light and radio waves

{{comic
| number = 2027
| date = August 1, 2018
| title = Lightning Distance
| image = lightning_distance.png
| titletext = The index of radio refraction does have a lot of variation, which might throw off your calculations, so you can also look at the difference in brightness between the visible flash and more-attenuated UV and x-rays.
}}

=Explanation=
{{incomplete|Created by a RADIO BURST - Update calculations and added values in km and miles. Do NOT delete this tag too soon.}}
The usual trick for determining the distance to a {{w|lightning}} flash is to count the seconds from when you see the flash until when you hear {{w|thunder}}, and divide by five to get miles (or three to get kilometers). This works because the {{w|speed of light|transmission of light}} is essentially instantaneous over the relevant distances, while the {{w|speed of sound}} is 331.2 m/s (1,087 ft/s, 1,192 km/h, or 741 mph, varying a bit based on temperature), or about 1/5 mile per second (1/3 kilometer per second).

This comic subverts the usual trick by having Megan describe a highly impractical alternative method. Megan's method is based on the fact that the speed of electromagnetic radiation, which includes light and radio waves, is not truly infinite. The radiation produced by lightning on Earth also has to travel through air, which changes its speed in a fashion which depends on its frequency.

According to {{w|List_of_refractive_indices|Wikipedia}} and [https://hypertextbook.com/facts/2005/MayaBarsky.shtml other sources], refractive index of air at 0°C is about 1.000277, which equates to a speed of light around 299709.4 km/s (186230.8 miles/s). According to [https://www.fig.net/resources/proceedings/fig_proceedings/fig_2002/Js28/JS28_rueger.pdf this paper], refractive index for radio waves in similar conditions is 1.000315, which equates to a speed around 299698.1 km/s (186223.7 miles/s). This means that to get the distance, the time difference in seconds between visible flash and radio burst should be multiplied by about 4.9 billion for miles, or about 7.9 billion for kilometers. More details for the calculations are in the comments below.

With sufficiently precise instruments, it would theoretically be possible to use this effect to determine the distance to a source of extremely short bursts of visible light and radio waves. The joke is that it is impractical for humans, both because we can't measure such small time intervals (one nanosecond for every 4.9 miles or 7.9 kilometers of atmosphere) and because we can't detect radiation outside the visible spectrum without very specialized instruments. Even with specialized instruments, we probably couldn't measure the light and radio wave emissions of lightning with sufficient precision because a flash is not instantaneous, but lasts about 60 to 70 microseconds - about five {{w|orders of magnitude}} longer than the time difference we would need to measure.

For the purpose of the joke, the "5 billion" value used in the comic is a fair estimate which also references the original rule of 5 seconds per mile nicely, though the result can have a huge margin of error depending on actual conditions (temperature, humidity, etc.), as the title text suggests ("the index of radio refraction does have a lot of variation").

Even if lightning was farther away, for example, if we were observing another planet, the time difference still would not be substantial, because the visible and radio waves travel at essential the same speed as each other in the vacuum of space (the difference in speed discussed above applies only to travel through air).

The title text suggests another method of calculating distance to lightning. Since the absorption of light is also different in different wavelengths, it would be possible to calculate the difference by comparing the brightness instead of delays. This would, however, require the knowledge about prior relative brightness of lightning, i.e. the spectrum, in the compared wavelengths.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Cueball and Megan stand on either side of a window, observing a bolt of lightning in a dark sky.]
:Cueball: What's that trick for telling how many miles away lightning is?
:Megan: Just count the seconds between the visible flash and the radio wave burst, then multiply by 5 billion.
{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]

2027: Lightning Distance

2018-08-02T18:32:44Z

Chrisahn: /* Explanation */ 7.0 kilometers -> 7.9 kilometers

{{comic
| number = 2027
| date = August 1, 2018
| title = Lightning Distance
| image = lightning_distance.png
| titletext = The index of radio refraction does have a lot of variation, which might throw off your calculations, so you can also look at the difference in brightness between the visible flash and more-attenuated UV and x-rays.
}}

=Explanation=
{{incomplete|Created by a RADIO BURST - Update calculations and added values in km and miles. Do NOT delete this tag too soon.}}
The usual trick for determining the distance to a {{w|lightning}} flash is to count the seconds from when you see the flash until when you hear {{w|thunder}}, and divide by five to get miles (or three to get kilometers). This works because the {{w|speed of light|transmission of light}} is essentially instantaneous over the relevant distances, while the {{w|speed of sound}} is 331.2 m/s (1,087 ft/s, 1,192 km/h, or 741 mph, varying a bit based on temperature), or about 1/5 mile per second (1/3 kilometer per second).

This comic subverts the usual trick by having Megan describe a highly impractical alternative method. Megan's method is based on the fact that the speed of electromagnetic radiation, which includes light and radio waves, is not truly infinite. The radiation produced by lightning on Earth also has to travel through air, which changes its speed in a fashion which depends on its frequency.

According to {{w|List_of_refractive_indices|Wikipedia}} and [https://hypertextbook.com/facts/2005/MayaBarsky.shtml other sources], refractive index of air at 0°C is about 1.000277, which equates to a speed of light around 299709.4 km/s (186230.8 miles/s). According to [https://www.fig.net/resources/proceedings/fig_proceedings/fig_2002/Js28/JS28_rueger.pdf this paper], refractive index for radio waves in similar conditions is 1.000315, which equates to a speed around 299698.1 km/s (186223.7 miles/s). This means that to get the distance, the time difference in seconds between visible flash and radio burst should be multiplied by about 4.9 billion for miles, or about 7.9 billion for kilometers. More details for the calculations are in the comments below.

With sufficiently precise instruments, it would theoretically be possible to use this effect to determine the distance to a lightning flash, as proposed by Randall. The joke is that it is impractical for humans, both because we can't measure such small time intervals (one nanosecond for every 4.9 miles or 7.9 kilometers of atmosphere) and because we can't detect radiation outside the visible spectrum without very specialized instruments. For the purpose of the joke, the "5 billion" value used in the comic is a fair estimate which also references the original rule of 5 seconds per mile nicely, though the result can have a huge margin of error depending on actual conditions (temperature, humidity, etc.). Even if lightning was farther away, for example, if we were observing another planet, the time difference still would not be substantial, because the visible and radio waves travel at essential the same speed as each other in the vacuum of space (the difference in speed discussed above applies only to travel through air).

The title text suggests another method of calculating distance to lightning. Since the absorption of light is also different in different wavelengths, it would be possible to calculate the difference by comparing the brightness instead of delays. This would, however, require the knowledge about prior relative brightness of lightning, i.e. the spectrum, in the compared wavelengths.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Cueball and Megan stand on either side of a window, observing a bolt of lightning in a dark sky.]
:Cueball: What's that trick for telling how many miles away lightning is?
:Megan: Just count the seconds between the visible flash and the radio wave burst, then multiply by 5 billion.
{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]

Talk:2027: Lightning Distance

2018-08-02T18:28:55Z

Chrisahn: Variation of the calculation above that simplifies numeric evaluation

Calculations I used:

<math>t_1=\frac{s}{v_1}</math>

<math>t_2=\frac{s}{v_2}</math>

Substract:

<math>t_1-t_2=\Delta t=\frac{s}{v_1}-\frac{s}{v_2}=\frac{sv_2-sv_1}{v_1v_2}=s\frac{v_2-v_1}{v_1v_2}=s\frac{\Delta v}{v_1v_2}</math>

Therefore

<math>s=\Delta t\frac{v_1v_2}{\Delta v}</math>

I evaluated <math>\frac{v_1v_2}{\Delta v}</math> and it came to be 13.6 billion. Can someone verify it's correct? [[Special:Contributions/172.68.51.112|172.68.51.112]] 13:08, 1 August 2018 (UTC)

:The comic begins with the question "how many miles away", so converting to kilometers isn't the right calculation.[[Special:Contributions/172.69.71.24|172.69.71.24]] 17:06, 1 August 2018 (UTC)

I used refractive index for visible light of 1.000277 (air at STP as opposed to 0C 1atm) and arrived at around 7.9 billion instead. Refractive index of 1.000337 is then required for the radio waves for the comic to be correct. [[Special:Contributions/172.68.11.221|172.68.11.221]] 13:46, 1 August 2018 (UTC)

:Do you mean 7.9 billion to convert to miles or to kilometers? Because my 13.6 bilion is to kilometers.

::I'm sure the actual comic is referring to miles and 5 billion was picked to match with the "divide by five" rule for miles. [[Special:Contributions/172.69.70.131|172.69.70.131]] 13:59, 1 August 2018 (UTC)

:::I did mean kilometers. If we use miles, 1.000314 fits almost precisely! (5.04 billion) [[Special:Contributions/172.68.11.17|172.68.11.17]] 14:42, 1 August 2018 (UTC)

If you can count several seconds, as is suggested in the comic, the flash is still billions of miles away, the widest possible distance between Earth and Neptune is about 5 billion km. Sebastian --[[Special:Contributions/172.68.110.40|172.68.110.40]] 14:51, 1 August 2018 (UTC)

:Not to mention that there's not a lot of air within a few billion miles of earth, so the dispersion will be much lower for all but the last 100-ish miles, AFAIK.[[Special:Contributions/172.68.54.142|172.68.54.142]] 20:12, 1 August 2018 (UTC)

::Also, while Jupiter has {{w|Great Red Spot|VERY gigantic storms}}, they are still too small to see the lightning from them from Earth. -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 23:17, 1 August 2018 (UTC)

Do you really need to know the spectrum of the flash? If we assume that a flash contains UV and X-ray radiation and that the visible light is generated at the same time as the UV or X-ray radiation then you only need to know the refractive index of light/UV/X-ray in air under the same temperature conditions and not the exact spectrum. [[User:Condor70|Condor70]] ([[User talk:Condor70|talk]])

:I initially made the mistake of thinking this referred to time difference between visible and UV/X-ray, but it specifically says "brightness." If you want to compare the brightness at a distance to the brightness at the source you'll need to know the brightness at the source, i.e. the spectrum of the flash itself. With this technique you don't need to know the dispersion "only" the relative attenuation, but I suspect that would be a more error-prone measurement.[[Special:Contributions/172.68.54.142|172.68.54.142]] 18:54, 1 August 2018 (UTC)

I understand the joke Randall was going for, but have a problem with the wording. "Count the number of seconds" won't work for fractions of anything. "Measure" would work, but spoils the gag a bit. Counting numbers are integers; counting the seconds between the visible and radio frequency flashes will give you zero. [[Special:Contributions/172.69.71.24|172.69.71.24]] 17:00, 1 August 2018 (UTC)

:You're certainly correct, but the joke works (for me at least) by its comparison to the standard rule of counting seconds, and humans are not generally precise enough to resolve better than one second. By keeping Megan's wording as close to the customary rule as possible I think it optimizes the humor. That "Billion" at the end is the whole joke for me, the replacement of "sound" with "radio wave" can be glossed-over on first reading, until you get to the unexpected extra 9 orders of magnitude in the conversion.[[Special:Contributions/172.68.54.142|172.68.54.142]] 18:54, 1 August 2018 (UTC)

::Just realized I also glossed-over the replacement of "divide" with "multiply." The brain is a funny thing.[[Special:Contributions/172.68.54.142|172.68.54.142]] 20:07, 1 August 2018 (UTC)

Do these account for the air pressure variability common in most thunderstorms?

I think explanation and transcript are pretty complete now. [[Special:Contributions/172.68.51.112|172.68.51.112]] 20:58, 1 August 2018 (UTC)

:There is the additional problem that a flash is no instantaneous, but progresses at a fraction of the speed of light. Who says that radio waves and light at different wavelenghts or xrays have their maximum at the same moment? ;-) --[[Special:Contributions/162.158.91.59|162.158.91.59]] 08:05, 2 August 2018 (UTC)

Variation of the calculation above that simplifies numeric evaluation:

The {{w|refractive index}} is defined as <math>n=\frac{c}{v}</math>, so <math>v=\frac{c}{n}</math> and thus <math>t=\frac{s}{v}=\frac{s\,n}{c}</math>.

<math>t_1=\frac{s\,n_1}{c}</math>

<math>t_2=\frac{s\,n_2}{c}</math>

Substract:

<math>t_1-t_2=\Delta t=\frac{s\,n_1}{c}-\frac{s\,n_2}{c}=s\frac{n_1-n_2}{c}=s\frac{\Delta n}{c}</math>

Therefore

<math>s=\Delta t\frac{c}{\Delta n}</math>

and the factor we want to calculate is

<math>\frac{c}{\Delta n}</math>

With the numbers given in the sources in the main text:

<math>n_1=1.000315</math>

<math>n_2=1.000277</math>

<math>\Delta n=n_1-n_2=0.000038</math>

For kilometers: <math>\frac{c}{\Delta n}\approx\frac{300,000\,km/s}{0.000038}\approx7.9\cdot10^9\,km/s</math>

For miles: <math>\frac{c}{\Delta n}\approx\frac{186,000\,mi/s}{0.000038}\approx4.9\cdot10^9\,mi/s</math>

[[User:Chrisahn|Chrisahn]] ([[User talk:Chrisahn|talk]]) 18:28, 2 August 2018 (UTC)

== Assumptions on the medium properties sound? ==

Refractive index of *dry* air might be pretty close to 1 for both light and RF EM waves, but:

Let's assume that the air is humid, if not even full of water drops. After all, lightning.

Let's further assume that an air/water mixture or solution has electromagnetic properties between these two materials.

In water, refractive index for light is about <math>n_{\text{water, optical}}=1.33 n_{\text{air, optical}}</math>, (as easily demonstrated by the optical refractive effects); for RF, we typically use values of <math>\frac{n_{\text{water, RF}}^2}{\mu_r}=\epsilon\approx 80</math>. So, <math>n_{\text{water, RF}}\approx \sqrt{80}n_{\text{air, RF}}</math>.

Let's assume a 10⁻³ "EM-effective" water content in the comic air.

That would lead to <math>\frac{v_{\text{opt.}}}{v_{\text{RF}}} = \frac{\frac34}{\sqrt{80}^{-1}}= \frac34\sqrt{80}=6.7</math>.

:While the humidity (amount of water vapor) is certainly higher during the rain, I don't think that would count as a proper "water-air mixture". Wikipedia says that "Violent rain" is above 5 cm/h. If you divide it by 3600 (to get cm/s), and then imagine stretching that all the way to the cloud, you'll find out there's not that much water at given moment in the air. [[Special:Contributions/172.68.51.112|172.68.51.112]] 19:12, 1 August 2018 (UTC)

::Great point. To finish the calculation let's use a typical terminal velocity for a large raindrop (it's a big storm, I'm sure) of 9m/s. 0.05 m/hr / 3600 s/hr / 9 m/s = 0.00015% water by volume. Sure seems like more than that when I have to drive through it! Then it seems more like [http://what-if.xkcd.com/12/].[[Special:Contributions/172.68.54.142|172.68.54.142]] 20:32, 1 August 2018 (UTC)

Talk:1773: Negativity

2017-01-06T01:01:28Z

Chrisahn: fixed SMBC link

Any chance that 'the pain and negativity of the internet' is a reference to [http://www.smbc-comics.com/comic/the-talk-3 this recent SMBC comic] where SMBC's artist Zach challenges Randall to 'out-nerd him now' (seen when you click the red button just below the comic).
I've been wondering whether the first XKCD after that (that is: today's XKCD comic) would refer to it.
[[Special:Contributions/141.101.104.173|141.101.104.173]] 14:55, 16 December 2016 (UTC)
: I kinda doubt it. SMBC wasn't being "negative" or objectionable - if anything it was a challenge - and even a kind of complement. An adequate response to that kind of a challenge might take longer than a few days to prepare. If we're going to see anything in response, I suspect it'll be more obvious. [[User:SteveBaker|SteveBaker]] ([[User talk:SteveBaker|talk]]) 14:02, 17 December 2016 (UTC)
:: We better be seeing a string theory joke sometime in the next week... [[Special:Contributions/108.162.216.226|108.162.216.226]] 02:38, 19 December 2016 (UTC)
::: [http://www.explainxkcd.com/wiki/index.php?title=171 Here you go.] [[Special:Contributions/162.158.122.126|162.158.122.126]] 12:55, 19 December 2016 (UTC)
:: @SteveBaker That was my doubt too. Looking forward to an adequate response from Randall though :) [[Special:Contributions/141.101.104.173|141.101.104.173]] 07:44, 19 December 2016 (UTC)
:: The negative interpretation might as well be humorously exaggerated. Alluding to political correctness gives the defense some weight. A point in favor of our observation, that I came just here to validate, would be the lawn. "Get of my lawn" is a common meme, but even the lawn is impressed with Zach. Anyway I chuckled. [[Special:Contributions/162.158.114.10|162.158.114.10]] 17:46, 21 December 2016 (UTC)
:: The link at the top does not work. [http://www.smbc-comics.com/comic/the-talk-3 This one should] . [[Special:Contributions/108.162.246.35|108.162.246.35]] 16:00, 27 December 2016 (UTC)

This article mentions XKCD number 1749 as involving "talking to inanimate organisms", but nobody talks to the mushroom in that strip. Neither does the mushroom talk to them, it merely growls. [[User:Ajfaraday|Ajfaraday]] ([[User talk:Ajfaraday|talk]]) 09:41, 21 December 2016 (UTC)
: I would object to "inanimate". Things are inanimate, and well, maybe dead organisms; but a growling and talking organism is obviously alive.[[Special:Contributions/162.158.91.171|162.158.91.171]] 16:14, 21 December 2016 (UTC)

1621: Fixion

2015-12-27T10:39:14Z

Chrisahn: /* Table of Phenomena */

{{comic
| number = 1621
| date = December 25, 2015
| title = Fixion
| image = fixion.png
| titletext = My theory predicts that, at high enough energies, FRBs and perytons become indistinguishable because the detector burns out.
}}

==Explanation==
The second [[:Category:Christmas|Christmas comic]] in a row, the first being [[1620: Christmas Settings]].

This comic was released on {{w|Christmas}} day as a present from [[Randall]] to all {{w|physicists}}. It introduces a new particle, the ''Fixion'', which explains everything. The word "Fixion" can be read as a pun: Either it can mean something like "fix-i-on," with "[https://en.wiktionary.org/wiki/-on#Suffix -on]" being a suffix for many particles, and this particle being able to "fix" things; or it means "fiction" (in English, the pronunciations of "-xion" and "-ction" are indistinguishable). Alternately, "Fixion" could be a portmanteau of "fix" and "ion", implying that the particle is not subatomic but is a different type of ion.

In physics, there are still many {{w|List of unsolved problems in physics|big questions and mysteries}}. There are many phenomena which don't seem to fit, and we don't know how to explain yet. The "Fixion" is satirically presented as a particle which acts as a {{w|Deus ex machina}}, (see also [http://tvtropes.org/pmwiki/pmwiki.php/Main/DeusExMachina tvtropes]), which solves all of these mysteries without any serious fundamental reasons.

The style of the chart suggests a {{w|Feynman diagram}} - an easy way of drawing particle interactions. Every time there is an interaction, the main central Fixion-line changes direction. Typically, {{w|fermions}} (the "solid" particles like {{w|electrons}} and {{w|quarks}}) are shown with solid lines, {{w|photons}} (and generally the weak-force-carrying {{w|bosons}}) are shown with wavy lines, {{w|gluons}} with spiraling lines and other mediating particles (such as {{w|pions}} in the {{w|nuclear force}}, or the {{w|Higgs boson}}) with a dotted line. Randall obeys these rules only very loosely, which makes sense - many of the things involved in this Feynman diagram are either so theoretical that they have no widely used standard representation, or would never appear in a sensible diagram (spacecrafts, for instance). All mentioned types of lines - and even more types - are presented in the diagram. All that the Fixion does is described in the [[#Table of Phenomena|table below]].

The title text is a continuation of one of the jokes already mentioned in the main comic (fourth phrase from the top to the left) about {{w|Fast radio burst}}s (FRBs) and {{w|Peryton (astronomy)|perytons}}. See explanation in the last entry in the [[#Table of Phenomena|table below]].

===Table of Phenomena===
*Below, all the phenomena mentioned in the comic (and in the title text) have been listed and described.
*The order is the top left phenomenon first, and then alternating between right and left down to the bottom and then the title text at the end.
{| border =1 width=100% cellpadding=5 class="wikitable"
|'''Phenomenon''' || '''In the comic''' || '''Description''' || '''Solved?'''
|-
| Main component of dark matter
|| An arrow points to the very first part of the main line.
|| Our best measurements of the universe predict that visible matter is only about one-sixth of the matter in the universe; the remaining matter is "{{w|dark matter}}" that cannot be seen. The leading candidates for dark matter are {{w|weakly interacting massive particles}} (WIMPs). These would be new, undiscovered forms of matter which barely interact except through gravity and thus give off little or no light. Some of the dark matter is likely made up of {{w|Massive compact halo objects}} (MACHOs); effectively dead stars too dim to see. MACHOs are probably only a minority of the dark matter, however. Studies of two colliding galaxy clusters suggest that dark matter can pass through other matter without slowing down, unlike ordinary matter. Moreover, calculations of the elements produced during the {{w|big bang}} - which match the observed distribution of elements in the universe very precisely - don't leave room for enough additional {{w|protons}} and {{w|neutrons}} to form the dark matter.
|| No. Proving the nature of dark matter will most likely win someone a {{w|Nobel Prize}}.
|-
| Confines quarks and gluons
|| An arrow points to the very first part of the main line.
|| {{w|Quark confinement}} means that we never see particles with {{w|colour charge|color charge}} (i.e. {{w|quark}}s and {{w|gluon}}s) on their own. They only exist in groups that cancel out the color charge. Try to separate the groups, and the energy you add will instead cause new particles to pop into existence.
|| The basic facts of confinement are well understood, but some of the details are too complicated to tease out.
|-
| Neutralizes monopoles
|| An arrow points to the first solid line going away from the main line, left and upwards. This is thus a solid particle going out from the Fixion.
|| {{w|Magnetic monopoles}} (e.g., a north charge without a south charge) should exist, according to many {{w|Grand Unified Theory|grand unified theories}} (GUTs) and {{w|String theory|string theories}}, but none have ever been seen.
|| No! Despite claims that pop up in the news every year, creating a monopole-like state in the magnetic spins of a crystal is not the same as creating a real monopole.
|-
| Suppresses antimatter in early universe
|| No arrow.
|| The universe today is made almost entirely of matter. {{w|Antimatter}} and matter are identical, except that the charges are opposite. Antimatter and matter "{{w|Annihilation|annihilate}}" when they come into contact? So why is the universe made of matter? Why didn't the universe have equal amounts of both, and if it did, why didn't it annihilate itself immediately? This is a big question in physics today. Of course, the Fixion explains this by its ability to suppress the formation of antimatter in the early universe.
|| Lots of theories, no conclusive evidence for any yet. The most notable theories revolve around the {{w|weak interaction}}, which has been shown to treat matter and antimatter asymmetrically. Now that the {{w|Higgs boson}} has been found, the biggest project for the {{w|Large Hadron Collider}} experiments is to try to crack this.
|-
| Spontaneously emits dark energy
|| Two arrows points to two dotted lines going out left and downwards below the first solid line. It is thus two mediating particles that go out from the Fixon.
|| Prior to the 1990s, most {{w|cosmologists}} expected that the universe's expansion after the Big Bang would either slow down or stay constant. In 1998, cosmologists discovered that the expansion of the Universe is accelerating. Under {{w|Einstein|Einstein's}} theory of {{w|general relativity}}, the observed acceleration predicts that ordinary matter and dark matter make up about 30% of the universe's total energy, with the rest coming in the form of "{{w|dark energy}}." The nature of dark energy is not certain. However, the leading candidate is that space itself has intrinsic energy (either constant or variable), and so as space expands, the energy of the universe increases.
|| Again, Nobel Prize territory.
|-
| Mediates proton decay, but then hides it.
|| An arrow point to several lines going to and from the main line. The outer line does not connect with the main line. Maybe this represents the hiding part of this proton decay mediator.
|| Many GUTs predict that {{w|proton decay|protons will decay}}, but experiments have shown the proton to have a half-life of at least 1033 years very much longer than the {{w|age of the universe}} (1.38x1010 years).
|| It's not ''necessarily'' a problem. All theories predict that proton decay is a very slow process (1032+ seconds), which is consistent with the current data.
|-
| Introduces dispersion in perytons from kitchen microwaves, explaining fast radio bursts
|| Two arrows point to four wavy lines. The waves of the lines have different wave length. The one line coming out left is of the same at wavelength as the top of the three coming out right. The two below each decrease in wavelength compared to the one before them. Maybe this is not meant to represent photon-like particles, but are just different frequencies of microwaves from the microwave oven – thus relating to the subject.
|| {{w|Fast radio burst}}s (FRBs) are unexplained bursts of radio-frequency energy from space, they could even be extragalactic signals, with speculations that they might be signs of {{w|extraterrestrial intelligence}}. {{w|Peryton (astronomy)|Perytons}} are things that ''look like'' FRBs, but come from Earth (specifically, from the {{w|microwave oven}} at {{w|Parkes Observatory}}). Randall's Fixion makes some perytons change frequency distribution so they appear to come from space; thus in fact all FRBs come from microwave ovens.
|| No, but it's probably something very big - a star collapsing to a {{w|black hole}} or (as now looks likely) a {{w|magnetar}} (magnetic neutron star)
|-
| Broken symmetry causes ϴ=0, explaining unobserved neutron dipole moment
|| An arrow points to the part of the main line just before the first wavy line.
|| The {{w|neutron electric dipole moment}} is a measure of how balanced electric charge is inside the neutron. ϴ (theta) is a number in {{w|quantum chromodynamics}} (QCD) which quantifies the breaking of a type of symmetry called {{w|CP violation|CP symmetry}}. If ϴ is not 0, one result of this should be a neutron dipole moment. {{w|Symmetry breaking}} is a common explanation of effects in some areas of theoretical physics (for instance, it's an important part of {{w|Peter Higgs|Higgs'}} theory about why particles have mass), but normally it explains why a value is ''not'' zero. Presumably the Fixion breaks CP symmetry independently of QCD, which means that ϴ can be 0 while preserving observed CP-breaking effects.
|| Again, it's not (yet) a problem - the predicted dipole moment is tiny, and we're only just reaching the point when we can measure it that accurately.
|-
| Causes alpha effect
|| No arrow.
|| Ther {{w|alpha effect}} is a weird effect from chemistry, where putting an "alpha" atom with a {{w|lone pair}} of electrons close to a molecule makes the molecule more likely to give up its electrons. The Fixion is the reason for this effect.
|| Lots of competing explanations.
|-
| Covers naked singularities
|| No arrow – but the text is situated next to the middle of the three wavy lines going right.
|| A {{w|naked singularity}} is like a black hole without an {{w|event horizon}}. So far no naked singularity has been observed (except, arguably, the big bang) and the {{w|cosmic censorship hypothesis}} suggests they can't exist, although some people have suggested ways of making them. Of course if any did exist then the Fixion will cover it, so it won’t become embarrassed by its nudity. Randall has mentioned these in his latest [[what if?]]: [http://what-if.xkcd.com/140/ Proton Earth, Electron Moon].
|| Not necessarily something that needs explaining - none have been seen, and most theories say they don't exist. If support grows for {{w|loop quantum gravity}}, then we might have to start really searching.
|-
| Intercepts certain gravitational waves before they're observed.
|| An arrow points to a spiraling line going upwards to the left, so this is drawn like a gluon.
|| If {{w|gravity}} behaves like {{w|Fundamental interaction|the other forces}}, it must be conveyed by waves. Our best detector, {{w|LIGO}} has yet to detect any {{w|gravitational waves}}, though this is probably just due to the low probability of events that would be detectable. Only extreme events like {{w|binary black hole}} mergers are detectable with the current setup. The proposed {{w|LISA Pathfinder}} spacecraft will be able to see things like orbiting black holes and {{w|neutron stars}}. Since the Fixion intercepts gravity waves before they are observed we should not get our hopes up too high about observing any even with LISA.
|| Let's wait for the LISA data before jumping to conclusions.
|-
| Causes coronal heating
|| No arrow – but the text is situated next to the middle of the three wavy lines going right.
|| For some reason the outer layer of the {{w|sun}} (the {{w|corona}}) is hotter than most reasonable theories predict. This is for instance mentioned in Randall’s new book ''[[Thing Explainer]]'' in the entry about the sun. This can also be seen on the [[Thing_Explainer#Preview Pages |back cover of the book]]. The phenomenon is explained by the Fixion…
|| It's a mystery, but it possibly has something to do with waves in the corona (for example, the {{w|High Resolution Coronal Imager}} has seen "braids" in the corona that whip around and unravel themselves).
|-
| Higgs-ish
|| As this is just a property of the Fixion there is no arrow.
|| The {{w|Higgs boson}} is a manifestation of the Higgs field... but many supersymmetry and string theories predict multiple Higgs-like particles. It's almost a prerequisite of any new theory that it has a Higgs-ish element. So the Fixion blends in with this.
|| N/A
|-
| Superluminally smooths anisotropies in early universe (but adds faint polarization for BICEP3 to find)
|| An arrow points to the point of the main line just below the bottom space probe.
|| The {{w|Cosmic Microwave Background}} (CMB) is incredibly uniform. In fact it is so uniform that the conclusion is that these areas must have been in contact at some time in the early universe. But with the universe being infinite, and the speed of light being finite, most parts of the universe will never be able to interact (any more at least). The explanation usually given for the uniformity is that the universe expanded really fast in the beginning during what is called the {{w|Inflationary epoch}}. {{w|BICEP_and_Keck_Array#BICEP2|BICEP2}} is a {{w|radio telescope}} at the South Pole whose operators claim to have seen polarization in the CMB indicative of inflation. (See [[1365: Inflation]] that references BICEP2's results). The Fixion fixes the problem since it allowed {{w|Faster-than-light|superluminally}} smoothing of the early anisotropies to explain the smoothness observed today. The Fixion adds just enough signal that the new {{w|BICEP_and_Keck_Array#BICEP3|BICEP3}} telescope will be able to find them.
|| As stated, {{w|Inflation (cosmology)|inflation}} is the standard explanation and it holds up fairly well. Other studies haven't seen the polarization that BICEP2 has - the {{w|Planck (spacecraft)|Planck space telescope}} also suggests that the BICEP2 team were looking at an unusually dusty bit of space, which could cause polarization. Hopefully this will improve with the BICEP3 data that should be published in 2016.
|-
| Accelerates certain spacecraft during flybys
|| Two arrows point to two solid lines going away from the main line (left and right). At the end of each line there is a space craft with satellite dish and solar panels, representing the items that the Fixion interacts with.
|| This refers to the {{w|flyby anomaly}} which is sometimes (but not always) seen when spacecraft fly close to planets and pick up more speed than expected. It's not always seen – for instance the {{w|Rosetta (spacecraft)|Rosetta space probe}} had no flyby anomaly when it swooped extremely close to Mars. Another anomaly for spacecraft’s (a deceleration this time) has been mentioned in the title text of [[502: Dark Flow]].
|| It could be an unpredicted quirk of gravity and relativity... or it could be experimental error.
|-
| Triggers Siberian sinkholes
|| No arrow, but it is right next to the solid line with an arrow going into the main line just before the first hole where the main line disappears and becomes dotted. Thus it could be a reference also to these holes.
|| Recently, (2014), several {{w|sinkholes}} opened up in {{w|Yamal_Peninsula#Yamal_craters |remote parts}} of Siberia. The explanation is currently unknown, except of course we now know that it was the Fixion that caused it.
|| While there are lots of weird theories, there's a good chance they were caused by {{w|Arctic methane release}} due to melting {{w|permafrost}} which is probably caused by {{w|global warming}}. See ([http://www.independent.co.uk/news/science/mystery-of-the-siberian-holes-at-the-end-of-the-world-solved-scientists-offer-explanation-9642988.html Mystery of the Siberian holes… solved]).
|-
| Melts ice in "Snowball Earth" scenario
|| No arrow.
|| {{w|Snowball Earth}} is the theory that the whole planet was covered in ice at some point. To melt all that ice by the {{w|greenhouse effect}} would require far more carbon dioxide in the atmosphere than seems plausible. However, if volcanoes were to deposit black soot on the surface of the ice, it would start absorbing heat more efficiently (in scientific terms, the Earth's {{w|albedo}} would decrease) and that would also make the planet heat up. Of course it was the Fixion was the cause of the melting ice.
|| There are {{w|Snowball_Earth#Scientific_dispute|scientific dispute}} regarding the theory for a Snowball Earth. There is no conclusive evidence that it ever occurred, but those in favor has presented lots of {{w|Snowball_Earth#Evidence|evidence}}…
|-
| Transports neutrinos faster than light, but only on certain days through one area of France
|| An arrow points to the part of the main line that becomes dotted between the two “{{w|wormholes}}”. This is where the neutrinos move faster than light…
|| Refers to the {{w|faster-than-light neutrino anomaly}}, where it seemed that a neutrino beam from {{w|CERN}} on the France/Switzerland border to the {{w|OPERA experiment}} in Italy traveled faster than light. Scientists were not able to reproduce the result. Of course it was because of the Fixion. This Neutrino experiment was also mentioned in [[955: Neutrinos]], where there are more explanation on the subject.
|| In the end, there was no mystery, just a [http://www.redorbit.com/news/science/1112551696/cern-confirms-neutrinos-not-faster-than-light/ defective cable causing a measurement error].
|-
| Suppresses sigma in experiments
|| No arrow but the last solid line, with an arrow pointing left, that is going away from the main line, point almost directly at it.
|| Sigma (σ) refers to the {{w|standard deviation}} - a mathematical measure of how much an observed value differs from the expected value. For a formal scientific discovery in particle physics, the standard is 5 sigma which means that there is about a 1 in 3.5 million chance that the results were caused by random errors (of course, they could be caused by ''systematic'' errors, such as measurement problems). Some tantalizing experiments have found interesting results at 3 or 4 sigma but either can't reach 5 sigma or {{w|Oops-Leon|are subsequently dis-proven}}. The question is, if the way the Fixion works here in this comic pushes the sigma value one way or the other? Does it suppress the value so it goes below or above the level of significance? Is it artificially pushed in the direction so a result seems like it is significant when it is not (see for instance [[882: Significant]]), or if it is the other way so some experiments, which could have found what the experimenters wanted to find, did not because the sigma has been artificially lowered below the proof threshold. Either way it is a very annoying fact of the Fixion, but it would explain a lot, and probably also make it very hard to find the Fixion because of this intrinsic behavior.|| N/A
|-
| My theory predicts that, at high enough energies, FRBs and perytons become indistinguishable because the detector burns out.
|| From the title text.
|| This is a continuation of the joke already mentioned above regarding Fast radio bursts (FRBs) and perytons. GUTs normally predict that all the forces we see are the different low-energy versions of a single force which can only be seen at extremely high energies (much higher than any Earth-based collider could produce). A high-energy FRB would be a {{w|gamma ray burst}} and if it came from a close enough object, would obliterate all life on Earth... It would also wreck the sensitive electronics at Parkes Observatory. This "high energy unification" is stated in a way reminiscent of the unification of electromagnetic and weak forces at high energies; but unlike the latter, it involves two things only "appearing" (or, in this case, not appearing) to be the same, not actually becoming the same.
|| N/A
|}

==Transcript==
:[Caption above the panel:]
:A Christmas gift for physicists:
:The '''Fixion'''
:A new particle that explains everything

:[A chart resembling a Feynman diagram is shown. It begins with a solid line coming down at the top, going a little to the left. The line continues downwards all the time, but changes direction 16 times before exiting at the bottom almost straight under the starting point. At every point where it changes direction, there is some kind of “interaction” with something outside this line. There are 19 phrases, 10 on the left and 9 on the right. 11 of these are distinct labels for points on the line as 14 gray curved arrows points between these 11 phrases to specific points on the line. Three of the phrases on the left has two arrows pointing to two different, but close, parts of the line. The main central line is solid all the way, except at the very bottom, where it “disappears” inside a hole only to “reappear” later from a similar hole. Between these two holes the line is dotted. The lines going away (or to) the main line can be straight and solid, straight and dotted, wavy lines (with different waviness), even looking like a spiral. Two straight solid lines ends up at two space probes, and finally the last two straight solid lines coming in (and out) on either side of the “hole” in the line has arrow pointing in and out. Below the phrases will be listed in reading order, taking one on each side alternatingly. Above each is described if there are any arrow and, if there are, what they points at.]

:[Left: Arrow pointing to the very first part of the main line:]
::Main component of dark matter

:[Right: Arrow pointing to the very first part of the main line, but below the previous arrow:]
::Confines quarks and gluons

:[Left: Arrow points to the first solid line going left and upwards:]
::Neutralizes monopoles

:[Right: No arrow:]
::Suppresses antimatter in early universe

:[Left: Two arrows points to two dotted lines going out left and downwards below the first solid line:]
::Spontaneously emits dark energy

:[Right: Arrow pointing to several lines going almost parallel with the main line. The first line closest to the arrow is not connected with the main line. It bends closer to the other lines in the middle. The next line is connected to the main line, and is thus actually two lines going in to the main line. The same goes for the inner line, where there is some distance between the entry and exit, as the middle of these three lines connect to the main line in between. In principle there are four lines going in/out and one not connected, but it looks like three lines:]
::Mediates proton decay but then hides it

:[Left: One arrow points to the first wavy line (7 peaks) coming out and up towards the dotted lines above. A second arrow points further down the main line where there are three more wavy lines coming out, but to the right, they are all of the same length and go almost straight right, only a little down. The first has as short a wave length as the line above to the left, but as it is shorter it only has 6 peaks. Then the wavelength decreases to a very long one for the last, 5 peaks and then 3 peaks. The arrow points almost where the middle wavy line exits the main line:]
::Introduces dispersion in perytons from kitchen microwaves, explaining fast radio bursts

:[Right: An arrow point to the part of the main line between the three parallel lines and the first wavy line:]
::Broken symmetry causes ϴ=0, explaining unobserved neutron dipole moment

:[Left: No arrow:]
::Causes alpha effect

:[Right: No arrow, but right next to the middle of the three wavy line:]
::Covers naked singularities

:[Left: An arrow points to a spiraling line going upwards to the left:]
::Intercepts certain gravitational waves before they're observed.

:[Right: No arrow, but right next to the bottom of the three wavy line:]
::Causes coronal heating

:[Left: No arrow:]
::Higgs-ish

:[Right: A long arrow point to the point of the main line just below the line pointing to the bottom (and left) of the space probes:]
::Superluminally smooths anisotropies in early universe (but adds faint polarization for BICEP3 to find)

:[Left: One arrows point towards the point on the main lines where a solid line goes to the right and up and another arrow points on another solid line going away from the main line towards left and down. At the end of both lines are drawn spacecrafts with satelite dish and solar panels:]
::Accelerates certain spacecraft during flybys

:[Right: No arrow, but right next to the solid line with an arrow going into the main line just before the first hole where the main line disappears and becomes dotted:]
::Triggers Siberian sinkholes

:[Left: No arrow:]
::Melts ice in "Snowball Earth" scenario

:[Right: Arrow points to the dotted part of the main line between the two holes:]
::Transports neutrinos faster than light, but only on certain days through one area of France

:[Left: No arrow but the last solid line, with an arrow pointing left, that is going away from the main line, point almost directly at it:]
::Suppresses sigma in experiments

{{comic discussion}}

[[Category:Christmas]]
[[Category:Charts]]
[[Category:Science]]
[[Category:Astronomy]]
[[Category:Physics]]
[[Category:Space]]
[[Category:Puns]]
[[Category:Language]]
[[Category:Portmanteau]]

1602: Linguistics Club

2015-11-18T09:00:14Z

Chrisahn: /* Explanation */ 3 times in 2 years is once every 8 months, not every 18 months

{{comic
| number = 1602
| date = November 11, 2015
| title = Linguistics Club
| image = linguistics_club.png
| titletext = If that's too easy, you could try joining Tautology Club, which meets on the date of the Tautology Club meeting.
}}

==Explanation==
A "[[wiktionary:sesquiannual|sesquiannual]]" meeting is one that occurs one and a half times every year; equivalently, 3 times every 2 years, or once every 8 months. It comes from the Latin prefix "[[wiktionary:sesqui|sesqui-]]", which directly means "a half and…", and "[[wiktionary:annual|annual]]", which equates to "…one (per) year".

The joke suggests that only a competent linguist could understand the word “sesquiannual”. One reason for this is that the prefix “sesqui-” is rare, so those who know its meaning are likely to be linguists. Another is that a competent linguist should be able to distinguish between “sesquiannual” and “sesquiennial”.

If you understands this then you can join the '''Linguistics Club'''. Once the applicant correctly understands the frequency of meetings, presumably they are told at least one meeting date in the cycle so that an attendance can be made.

Another possibility is that there are literally one and a half meetings per year, because every third meeting spans midnight on December 31/January 1.

“Sesquiannual” is not to be confused with “[[wiktionary:sesquiennial|sesquiennial]]”, meaning "a half and one years (per…)" or every one and a half years (18 months). Note that the Wiktionary entry on sesquiannual has both meanings listed – both 8 month and 18 months intervals. This is an extension of the common confusion between "biannual," meaning "twice a year", and "biennial", meaning "once every two years". Compare with the {{w|Sesquicentennial Exposition}} celebrating the first 1½ centuries of the United States, and "sesqui''bi''centennial", being 'half and two' hundred years, i.e. 250.

This confusion is related to the distinction between 'biweekly' and 'semiweekly'. In the absence of an equivalent "-ennial"/"-annual" distinction, 'biweekly' ''might'' mean either twice per week or once every two weeks, whilst semiweekly is strictly maintained as once every half-week, i.e., the former. There's a similar problem with bimonthly (possibly twice a month, but nominally every two months) and semimonthly (always twice per month).

However, even the very slight difference in spelling and pronunciation of 'biannual' and 'biennial' doesn't help. 'Biannual' is not the same as 'biennial'/'semiannual', but is all too easily used in this way. It is normally advised that an alternate term such as 'fortnightly' (once every two weeks) or a direct statement such as 'twice a year' should be used, to remove ambiguity in normal communication.

A common method of having meetings "on the first and third Monday of every month" is strictly twice-monthly but also mostly, and ironically, once every two weeks; though three-week gaps occur when 'five Monday' month rolls over to the next, four or five times a year. But everyone should at least be able to understand the schedule, just from a cursory glance at a calendar.

The society in the comic, however, deliberately instills an ambiguity for those outside their target demographic. Their membership will thus swell with the desired cognoscenti who remain unconfused, and maybe also a few lucky guessers.

Regarding the title text, a {{w|tautology (rhetoric)|tautology}} is a statement that is true (or self-evident) because of its logical form, such as "all birds are birds" or "A = A." As such, the statement "the Tautology Club meets on the date of the Tautology Club's meeting" is itself tautological.

While the membership requirement for the Linguistics Club is merely to know the intended frequency, the Tautology Club's stipulation appears to require an eligible member to derive a valid meeting date from thin air without any clue at all (and no indication that there is even a regular cycle of any kind). This would definitely be more of a challenge.

The title text has a connection to [[703: Honor Societies]] in which Cueball announces that “the first rule of Tautology Club is the first rule of Tautology Club.”

==Transcript==
:[Megan talks to Ponytail.]
:Megan: You should come to our Linguistics Club's sesquiannual meeting.
:Megan: Membership is open to anyone who can figure out how often we meet.

{{comic discussion}}
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Ponytail]]
[[Category:Language]]

Talk:1494: Insurance

2015-03-08T14:20:06Z

Chrisahn: Most airports don't check the luggage tags, but I've been to some that do.

Well...suck for you.
[[Special:Contributions/108.162.215.57|108.162.215.57]] 05:17, 4 March 2015 (UTC) RobotGoggles

'''Incomplete tag?'''
I know it's pretty early, and the explanation is bound to be rewritten, but the current explanation is a little confusing, and makes a couple jumps that I wouldn't necessarily make. Maybe the incomplete tag shouldn't be removed yet? I'd do it, but I don't really know enough about actually editing the explanations to feel comfortable doing it yet.
[[User:ARoseByAnyOtherName|ARoseByAnyOtherName]] ([[User talk:ARoseByAnyOtherName|talk]]) 08:52, 4 March 2015 (UTC)

: I mean, I had written an explanation I'd say was a bit clearer (if a bit more complicated), but some unregistered user removed most of it... Makes me a bit grumpy. The newly added ''Lifehacks vs. IT hacks'' section brings up most of the things that person removed, though, so this should be complete enough. [[User:Obskyr|Obskyr]] ([[User talk:Obskyr|talk]]) 09:44, 4 March 2015 (UTC)

:: Well, for what it's worth, I liked your version better. --[[User:RenniePet|RenniePet]] ([[User talk:RenniePet|talk]]) 10:47, 4 March 2015 (UTC)
:::Not only that. The new version was so bad I decided to revert to Obskyr's. [http://www.explainxkcd.com/wiki/index.php?title=1494%3A_Insurance&diff=85633&oldid=85624] [[Special:Contributions/108.162.221.201|108.162.221.201]] 13:54, 4 March 2015 (UTC)

;Any meaning to conveyer?

The spelling error in the alt text seems like a simple typo.

Lawyer? I assumed it was a salesman or HR guy. --[[User:RenniePet|RenniePet]] ([[User talk:RenniePet|talk]]) 08:50, 4 March 2015 (UTC)
:: Insurance agent. Not exactly a salesman; agents have multiple hats. You don't get fire insurance from HR.[[User:Taibhse|Taibhse]] ([[User talk:Taibhse|talk]]) 09:34, 4 March 2015 (UTC)
:::So you're saying the agents are TF2 players. [[Special:Contributions/108.162.237.161|108.162.237.161]] 04:45, 6 March 2015 (UTC)

This is probably a reference to those youtube videos of ''life hacks'' of questionable legality. Eg signing up for one flight to take another[[Special:Contributions/108.162.219.100|108.162.219.100]] 16:44, 4 March 2015 (UTC)

I guess this might also relate to that (from my experience) programmers tend to like to break things (anything claimed to be "secure" seems to attract lots of people wanting to test out how secure) or find workarounds for things? [[User:Pinkishu|Pinkishu]] ([[User talk:Pinkishu|talk]]) 10:11, 4 March 2015 (UTC)

;Hacking

Please read [https://stallman.org/articles/on-hacking.html On Hacking]. I think the term you're looking for is cracking, or at least black hat hacking. Hacking a system would mean getting a system to do something unique and/or interesting. Or interacting with the system in a way that wasn't predicted. [[Special:Contributions/108.162.238.191|108.162.238.191]] 10:19, 4 March 2015 (UTC)
:You're right. But there is at least a second common usage for the word hack that is described by wikipedia as "an inelegant but effective solution to a computing problem". When the insurance guy speaks about "cool hacks", he's probably not refering to Stallman's definition. [[User:Nytux|Nytux]] ([[User talk:Nytux|talk]]) 09:41, 5 March 2015 (UTC)

;Hard hacks
Things like lock-picking is often also seen as physical equivalents of hacking, not necessarily illegal but still something most people would look on with suspicion.[[Special:Contributions/108.162.254.98|108.162.254.98]] 10:21, 4 March 2015 (UTC)

:Agree, this is excellent example on "hacking the computer": there is nothing illegal on lock-picking itself. Even if you use it on someone's else door without permission, it would not be crime unless you actually ENTER the door (or damage the lock). Locksmiths MUST know how to do it. But ... first thing you think about when hearing lock-picking is that thiefs do it. -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 11:37, 4 March 2015 (UTC)
::Before coming down into the comments, and seeing the last set of comments, I felt it necessary to make an edit to highlight just such an issue regarding the confusion about 'hacking'. As a historical sideline, note also the term "cracksman" as used for those who illegally open safes (and others skilled with locks and barred entranceways, in a criminal manner), which predates all the above computer-era terminology. But I didn't want to add ''too'' much more to the explanation. [[Special:Contributions/141.101.98.181|141.101.98.181]] 17:25, 4 March 2015 (UTC)

I think part of the point of today's comic is to point that contracts are somewhat similar to a computer program (both have definitions and rules by which the system must abide), but lack the strict rigor of the latter. So, when programmers read a legal contract they immediately start searching for bugs or vulnerabilities or even syntax optimizations. {{unsigned ip|188.114.98.29}}

;Why is it illegal to do things allowed by the contract?
Why is it illegal if the insurance company agreed that the "fraudulent" maneuver was accepted, by signing the contract allowing it?
[[Special:Contributions/199.27.128.172|199.27.128.172]] 23:22, 4 March 2015 (UTC)
The contract doesn't have a section that says "and fraud is prohibited" because fraud is already prohibited by criminal law; thus, no need to spell it out. It turns out that contracts will have many terms added by implication, particularly commercial contracts.
If you buy a shiny new gun, the instruction manual probably doesn't say "Oh, and by the way, if you point this thing at someone and pull the trigger while it's loaded, you may be charged with a crime." You're supposed to know that this is true BEFORE you buy a gun. That's part of the joke... normal people know that looking for ways to get the insurance to pay out more than it should is insurance fraud. People who think like programmers think they've found a loophole they can exploit. {{unsigned ip|108.162.237.170}}

Uh, why doesn't it mention life hacks at all in the "lifehacks vs IT hacks" section? Especially since I remember some lifehacks actually advocate for plain fucking stealing, like e.g. one which suggested that if you need a free umbrella, go to a restaurant and say you lost a black umbrella. [[Special:Contributions/141.101.89.224|141.101.89.224]] 01:56, 5 March 2015 (UTC)
:I absolutely agree with this point. The comic appears to suggest that programmers apply the conditioning that comes from their jobs (that code exploits are cool, and that the system must be designed to prevent exploits) to life (where exploiting a system's vulnerabilities may look cool but is very probably illegal). The airport luggage registration and screening system allows anyone to walk out the door with any item of luggage, but it is quite simply theft to do so. Likewise, exploiting a loophole in a contract is generally acceptable in order to avoid work or liability, but when you do it to obtain material gain then it is quite simply fraud. It would appear that much of the explanation currently misses the point... [[Special:Contributions/108.162.229.50|108.162.229.50]] 13:35, 5 March 2015 (UTC)

;Checking the luggage

Seems like someone already tried this.
I flew to Saigon last week and they check your luggage against your lost&found tag, before you may leave.
--[[Special:Contributions/108.162.222.156|108.162.222.156]] 15:54, 5 March 2015 (UTC)
: Correct. Most airports don't check the luggage tags, but I've been to some that do. Don't remember which. May have been South Asia too. [[User:Chrisahn|Chrisahn]] ([[User talk:Chrisahn|talk]]) 14:20, 8 March 2015 (UTC)

I disagree that this is a sequel to ''UV'', it may relate, but as mentioned in that comment it's not even close to legal to burn a house then get fire insurance. [[User:Djbrasier|Djbrasier]] ([[User talk:Djbrasier|talk]]) 19:24, 5 March 2015 (UTC)

Also, isn't [[Hairy]] the insurance agent? Should the transcript be updated to name him? [[User:Djbrasier|Djbrasier]] ([[User talk:Djbrasier|talk]]) 19:29, 5 March 2015 (UTC)

Talk:1482: NowPlaying

2015-02-15T18:28:41Z

Chrisahn: Good catch!

So what song is it? [[Special:Contributions/108.162.242.10|108.162.242.10]] 06:11, 4 February 2015 (UTC)
:I believe it is the Main Theme from Jurassic Park. --[[User:Duhsn|Duhsn]] ([[User talk:Duhsn|talk]]) 06:13, 4 February 2015 (UTC)
:If you have good ears you can check for yourself: [https://www.youtube.com/watch?v=-w-58hQ9dLk Link] --[[Special:Contributions/108.162.254.134|108.162.254.134]] 09:05, 4 February 2015 (UTC)
:Nope, not even close. Wrong notes, wrong key (although that doesn't matter as much, could be transposed). Though I thought it was the little bit at the end of "This Old Man", but the last 3 notes don't make sense, and when I try to play it, the first A doesn't quite work (also found sheet music, and that first A should be a B, confirmed). Oh well. - Mikowmer --[[Special:Contributions/108.162.249.218|108.162.249.218]] 11:26, 4 February 2015 (UTC)
:Might it be the folk melody "Country Gardens"? See the Wikipedia entry or look it up one of the many performances on Youtube (there's a charming performance with the Muppets Rowlf and Fozzie Bear) [[Special:Contributions/188.114.103.238|188.114.103.238]] 14:14, 4 February 2015 (UTC)
:I'm your lady by Celine Dion matches the note progression and Brian's friends reactions. [[Special:Contributions/108.162.219.149|108.162.219.149]] 09:01, 6 February 2015 (UTC)

E major, is a chord, not a note...[[Special:Contributions/108.162.249.169|108.162.249.169]] 06:36, 4 February 2015 (UTC)
You can listen to the sequence of notes here: http://onlinesequencer.net/65475
(All notes the same length, and just guessing which octave each should be in...) [[Special:Contributions/108.162.249.169|108.162.249.169]] 06:36, 4 February 2015 (UTC)
:Just because I want to get it stuck in your head :D, Added a bit to the beginning and end and changed octaves. http://onlinesequencer.net/65487 --[[User:Duhsn|Duhsn]] ([[User talk:Duhsn|talk]]) 07:40, 4 February 2015 (UTC)

The image on this page is NOT the same one as on the actual xkcd page. The original comic does not contain the reference to E Major. [[User:Andries|Andries]] ([[User talk:Andries|talk]]) 07:42, 4 February 2015 (UTC)Andries

Is he rick rolling us? [[Special:Contributions/199.27.128.182|199.27.128.182]] 07:48, 4 February 2015 (UTC)
:He must have agreed with your comment about E major not being a note and changed it. --[[User:Duhsn|Duhsn]] ([[User talk:Duhsn|talk]]) 07:54, 4 February 2015 (UTC)

"and his friends Mike and Caitlin appear to be becoming concerned about his choice of music"... really? I thought they were upset that they were getting spammed by a post every second or so?
"and the notion that someone could become concerned about you based on a list of notes is even more ridiculous."... similarly, not so ridiculous if they're concerned about you spamming them with too many postings!
Finally, "The comic's title alludes to the fact that you can "play a song" but can also "play a note." It may also allude to the visual similarities between the hash/pound/number sign (#) and the sharp sign (♯)."... I don't get either of these references. The hash/sharp comparison is cute, except that the sharp sign doesn't appear in the comic. I took it as a simple extension of the usual someone is listening to some song messages linking to searches for that song "on various online music stores" if you click on them... that is, if you click on a particular note, it'll link to a search for songs that include that note - equally as useless as posting the individual notes of a song in the first place.
Extra-finally, I'd love to see Mike & Caitlin's reactions if Brian listened to anything with a glissando...
Haven't made any of these as changes as I'm not sure they're more than just my own opinion. [[Special:Contributions/108.162.249.220|108.162.249.220]] 07:55, 4 February 2015 (UTC)
:Okay, so I've redone the second paragraph for facts, but haven't touched any of the other opinion bits. [[Special:Contributions/108.162.249.220|108.162.249.220]] 08:40, 4 February 2015 (UTC)

Text may also be a reference to an old joke about a composer who writes, and copyrights, a composition consisting of a single note: middle C. All other composers who later included middle C would thus be quoting his composition, entitling him to royalties; all composers who used any OTHER note would be simply transposing the original composition into another key, and would still owe the royalty..." {{unsigned ip|108.162.215.112}}

I've changed the thing about Mike & Caitlin being concerned about music choice, as this is (as noted by other commentators) *much* less likely than their being concerned about having their news feeds spammed.[[Special:Contributions/141.101.98.135|141.101.98.135]] 09:25, 4 February 2015 (UTC)

Would the Axis of Awesome 4 Chords song be a proper citation to prove many (pop) songs are made up of the same chords? Link of their youtube: http://youtu.be/oOlDewpCfZQ I think it would be funny, at least. [[Special:Contributions/173.245.53.192|173.245.53.192]] 14:03, 4 February 2015 (UTC)

Why are the times out of order? [[Special:Contributions/108.162.213.41|108.162.213.41]] 14:59, 4 February 2015 (UTC)

Brian's system or the one hat runs the social network might run on an older Version of Xen, so it gets "time went backwards" isses (e.g., http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=195) and therefore wrong timestamps. Do we require to re-order the notes accordingly? [[User:Renormalist|Renormalist]] ([[User talk:Renormalist|talk]]) 16:09, 4 February 2015 (UTC)

Btw, I interpreted Mike's comment not as annoyance about the entry flooding but that he can "hear" the melody in his head (like Beethoven) and hears a wrong tune. And maybe it's a small special community (like in xkcd/1305, which would also fit to the timestamp issues they have) so he starts discussing that wrong tune. [[User:Renormalist|Renormalist]] ([[User talk:Renormalist|talk]]) 16:45, 4 February 2015 (UTC)

I tried to correct the image, twice, and it still stays the same with the original error. I did this after adding the trivia section with the original image. Hope someone can correct this --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 17:48, 4 February 2015 (UTC)
:Try clearing your browser cache. The image looks correct on my screen. [[User:KieferSkunk|KieferSkunk]] ([[User talk:KieferSkunk|talk]]) 18:53, 4 February 2015 (UTC)

Totally nerd sniped.. [http://www.musipedia.org/result.html?sourceid=melody-url&tx_mpsearch_pi1%5bsubmit_button%5d=Search&tx_mpsearch_pi1%5bpc%5d=lily+e%278+a%278+b%278+d%278+cis%278+b%278+a%278+a%278+e%278+a%278+&coll=m&categories=&L=&filtertext=&rvp=0 Musipedia] seems to think the closest melodic match is "Cream" by Eric Clapton... Hard to get without seconds (so you can get some idea of the rhythm) [[User:BadPirate|BadPirate]] ([[User talk:BadPirate|talk]]) 20:32, 4 February 2015 (UTC)

Surprising no one has mentioned the contrast with John Cage's "As Slow As Possible" now playing in the St Burchardi Church of Halberstadt, Germany. http://en.wikipedia.org/wiki/As_Slow_as_Possible [[User:Taibhse|Taibhse]] ([[User talk:Taibhse|talk]]) 21:47, 4 February 2015 (UTC)
:I suspect the hypothetical service might have trouble with some John Cage works (http://youtu.be/zY7UK-6aaNA), as well as anything relying on nature or ambient sounds, or not conforming to the chromatic scale - untuned percussion instruments, or perhaps a didgeridoo or kazoo. [[Special:Contributions/108.162.249.220|108.162.249.220]] 00:23, 5 February 2015 (UTC)
: Except that "As Slow As Possible" is all tonal, chromatic scale, instrument not even specified though usually organ. The point being it is heard a single note (or chord) at a time, by design. The current performance is planned to last hundreds of years, though it has often been performed in a matter of hours or days. [[User:Taibhse|Taibhse]] ([[User talk:Taibhse|talk]]) 08:18, 5 February 2015 (UTC)

I removed speculations about chords from the explantion - the reference to ''E major'' was a mistake that has been fixed. Also, not all notes appear in all songs, so the search for a note won't return all songs. Each {{w|Key signature|key signature}} only uses seven of the twelve notes, and each note appears only in seven of the twelve key signatures. Excursion: The question in which fraction of all songs a certain note appears might be interesting for musicologists, but also quite hard to even give an educated guess: Many songs contain a few notes that {{w|Accidental (music)|don't belong to their key}}, there are {{w|Modulation (music)|modulations}}, and last but not least, some key signatures are much more common than others - I would guess that in pop music, the upper right half of the {{w|Circle of fifths|circle of fifths}} (from F major to E major) accounts for at least 95% of all songs, which would mean that notes like C flat are much less common than C. [[User:Chrisahn|Chrisahn]] ([[User talk:Chrisahn|talk]]) 13:52, 7 February 2015 (UTC)

"twelve key signatures" ... "notes like C flat are much less common than C". Since you say there are only 12 (major) key signatures and not 15 you must be counting B/Cb, F#/Gb, and C#/Db major as the same keys. But then you talk about the note Cb (diatonic in 2 keys) like it's a different note from B (diatonic in 7 keys). You can't have it both ways. [[Special:Contributions/173.245.52.109|173.245.52.109]] 18:55, 14 February 2015 (UTC)
: Oops. You're right. Good catch. What do we do? Randall's bot probably distinguishes between C sharp / D flat. If we do that too, we'll have to distinguish between enharmonic keys. So how many keys (key signatures) are there? 15 is not enough either - it would exclude {{w|G-sharp major}} and {{w|F-flat major}}. It would be logically correct to say that there are infinitely many key signatures. ;-) I think useful answers could only be found empirically. Alas, I don't think any musicologist will bother to solve this riddle. Humanity will remain ignorant. [[User:Chrisahn|Chrisahn]] ([[User talk:Chrisahn|talk]]) 18:28, 15 February 2015 (UTC)

Talk:1482: NowPlaying

2015-02-07T13:52:41Z

Chrisahn: rationale for my changes

1482: NowPlaying

2015-02-07T13:25:14Z

Chrisahn: /* Explanation */ 1. The chord was a mistake, so I removed references to chords. 2. Not all notes appear in all songs. See discussion.

<noinclude>:''The correct title of this page is '''1482: #NowPlaying'''. It appears incorrectly here because of {{w|mw:Manual:Page title|technical restrictions}}.''</noinclude>
{{comic
| number = 1482
| date = February 4, 2015
| title = #NowPlaying
| image = nowplaying.png
| titletext = If you click on the post, it takes you to search results for the note on various online music stores.
}}

==Explanation==
There are a variety of applications that post a user's music-listening habits on their preferred social network. In this comic, [[Randall]] takes that notion to its extreme, envisioning a program that does this note-by-note, rather than just song-by-song. As notes are much shorter than songs, this would lead to the flooding of friends' notification streams. In the example, the software is sharing the notes that Brian is listening to; and his friends Mike and Caitlin are getting annoyed with the amount of posts they are receiving.

There are typically many hundreds of notes in any song. Any song with more than a single line of music contains multiple different {{w|Note|notes}} whose names according to the English convention are communicated here. All but the slowest songs will require reporting dozens to hundreds of notes every minute (a single {{w|glissando}} may cover a dozen or more notes in less than a second), meaning that anyone who can see your stream of posts will be [[Literally|literally]] inundated by posts from the service. Even if you could keep up with the speed of the posted notes that someone is listening to, the similarity in {{w|Phrase_(music)|phrases}} in many songs (especially pop songs eg: [http://youtu.be/JdxkVQy7QLM Pachelbel's Rant]) means that many different songs may include the same sequence of notes, though possibly in different {{w|Octave|octaves}} or at different speeds.

The comic's title alludes to the fact that you can "play a song" but can also "play a note." It may also allude to the visual similarities between the hash/pound/{{w|number sign}} (#) and the {{w|Sharp (music)|sharp sign}} (♯). ''C sharp'', above Mike's comment, is the only note not given by a single letter (after the correction - see [[#Trivia|Trivia]]).

The title text continues the joke of this new musical service: ''If you click on the post, it takes you to search results for the note on various online music store.'' Since many songs in similar {{w|Key (music)|keys}} contain at least some of the notes posted, you would be given a list of a large part of the music you can buy in any on-line music stores. Of course this is at least as useless as being told which note someone is listening to.

Here are some synthesized versions of the notes in the order they appear in the comic:
*[https://dl.dropboxusercontent.com/u/1079661/65467.ogg OGG]
*[https://dl.dropboxusercontent.com/u/1079661/65467.mid MIDI]

They appear to be the beginning of ''{{w|I'll Be There for You (The Rembrandts song)|I'll Be There For You}}'' by {{w|The Rembrandts}}, the [https://www.youtube.com/watch?v=q-9kPks0IfE title music] of the TV series "{{w|Friends}}". This could be an internal reference to the idea that it "notifies" (converts into musical notes) your "friends" of the notes (a {{w|Pun|play on words}}). Alternatively it could simply be an instance of effective [[356: Nerd Sniping|nerd sniping]].

==Transcript==
:[A social network news feed with user images for each of the three different contributors. The top of the first post is partly obscured, and for the last post only half of the first line is visible.]

:'''Brian''' is now listening to: E
:Today ● 3:28 PM

:'''Brian''' is now listening to: A
:Today ● 3:28 PM

:'''Brian''' is now listening to: B
:Today ● 3:28 PM

:'''Brian''' is now listening to: D
:Today ● 3:28 PM

:'''Brian''' is now listening to: C sharp
:Today ● 3:28 PM

:'''Mike''' What the hell
:Today ● 3:28 PM

:'''Brian''' is now listening to: B
:Today ● 3:28 PM

:'''Brian''' is now listening to: A
:Today ● 3:28 PM

:'''Caitlin''' Can someone call him?
:Today ● 3:28 PM

:'''Brian''' is now listening to: A
:Today ● 3:28 PM

:'''Brian''' is now listening to: E
:Today ● 3:29 PM

:'''Brian''' is now listening to: A

:My new social music service notifies your friends about what notes you're listening to.

==Trivia==
*In the [[Media:OriginalNowPlaying.png|original]] comic there were a few errors/mistakes that were corrected later the same day:
**One of the messages was out of order. The instance where "Brian is now listening to A" above Caitlin's post was {{w|timestamp}}ed at 3:29, but the next two posts were timestamped at 3:28. Now this timestamp has been corrected to 3:28 so only the last timestamp reads 3:29, the rest 3:28.
**The first partially visible "note" post was "{{w|E major}}". This is not a single note but rather a chord or {{w|major scale|scale}}. The "major" was removed from the comic so it now reads simply "E".

{{comic discussion}}
[[Category:Social Networking]]
[[Category:Music]]