explain xkcd - User contributions [en]

Talk:2040: Sibling-in-Law

2018-08-31T20:09:24Z

162.158.234.46:

Unless you want to go completely nuts on this topic, avoid reading Jane Austen, where the the term "X-in-law" is used to mean, roughly, "someone to whom you are related for legal reasons". It can be used to refer to, for example, what we today might refer to as step/half-siblings, adopted siblings, etc. [[User:Arcanechili|Arcanechili]] ([[User talk:Arcanechili|talk]]) 15:51, 31 August 2018 (UTC)

> The title text refers to incestual relationships, which are generally frowned upon in Western culture.
How on earth this refers to incest if persons are only legally, not genetically related??? It's just that Randall doesn't know how to call new relatives but cannot stop their arrival. {{unsigned ip|162.158.91.251}}

Yes, I also don't think it refers to incest. {{unsigned ip|172.68.94.40}}

:I'm not sure if that is right or not, but that was my interpretation of that text, based on the "a reason why these two should not be wed." Unless there is a different issue with this, also involving marriage? [[Special:Contributions/162.158.59.190|162.158.59.190]] 16:44, 31 August 2018 (UTC)

::I read the title text as... the reason he is objecting has nothing to do with the couple getting married, it's simply the selfish reason that Randall doesn't want the confusion of having to figure out what to call the new extended-family members. [[User:N0lqu|-boB]] ([[User talk:N0lqu|talk]]) 17:37, 31 August 2018 (UTC)

Somehow I don't have this problem whatsoever...as I'm a single child who married a single child. I have zero siblings-in-law. In fact, my future kids won't even have (regular) cousins... {{unsigned ip|162.158.74.231}}

Am I the only one that thinks there's an error in this comic? Shouldn't spouse's sibling be the sibling-in-law of Cueball's *sibling*? But then, maybe I'm also making Randall's point... [[User:Sspenser|Sspenser]] ([[User talk:Sspenser|talk]]) 18:28, 31 August 2018 (UTC)

The Russian language actually has different words for both "types" of brothers in-law (spouse's brother vs. sister's husband), also for parents and children in-law on either side: https://ru.wikipedia.org/wiki/Свойство_(родство) .
But all these in-law distinctions are based on the respective spouse's sex, so it won't work for same-sex marriages. {{unsigned ip|162.158.234.58}}

The way this is defined, you and your spouse both have the same set of siblings and siblings-in-law. In other words, if someone is your spouse's sibling or sibling in law then that person is your sibling in law if that person is not your sibling. The relationship chains across a maximum of one sibling relationship. [[User:Probably not Douglas Hofstadter|Probably not Douglas Hofstadter]] ([[User talk:Probably not Douglas Hofstadter|talk]]) 18:56, 31 August 2018 (UTC)

Off topic but I can't resist:
:DARK HELMET: I am your father's brother's nephew's cousin's former room-mate.
:LONE STARR: What's that make us?
:DARK HELMET: Absolutely nothing....
Spaceballs (1987) parody Star Wars --[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 19:51, 31 August 2018 (UTC)

Talk:2040: Sibling-in-Law

2018-08-31T18:39:31Z

162.158.234.46: unencode Russian wikipedia URL

Unless you want to go completely nuts on this topic, avoid reading Jane Austen, where the the term "X-in-law" is used to mean, roughly, "someone to whom you are related for legal reasons". It can be used to refer to, for example, what we today might refer to as step/half-siblings, adopted siblings, etc. [[User:Arcanechili|Arcanechili]] ([[User talk:Arcanechili|talk]]) 15:51, 31 August 2018 (UTC)

> The title text refers to incestual relationships, which are generally frowned upon in Western culture.
How on earth this refers to incest if persons are only legally, not genetically related??? It's just that Randall doesn't know how to call new relatives but cannot stop their arrival. {{unsigned ip|162.158.91.251}}

Yes, I also don't think it refers to incest. {{unsigned ip|172.68.94.40}}

:I'm not sure if that is right or not, but that was my interpretation of that text, based on the "a reason why these two should not be wed." Unless there is a different issue with this, also involving marriage? [[Special:Contributions/162.158.59.190|162.158.59.190]] 16:44, 31 August 2018 (UTC)

::I read the title text as... the reason he is objecting has nothing to do with the couple getting married, it's simply the selfish reason that Randall doesn't want the confusion of having to figure out what to call the new extended-family members. [[User:N0lqu|-boB]] ([[User talk:N0lqu|talk]]) 17:37, 31 August 2018 (UTC)

Somehow I don't have this problem whatsoever...as I'm a single child who married a single child. I have zero siblings-in-law. In fact, my future kids won't even have (regular) cousins... {{unsigned ip|162.158.74.231}}

Am I the only one that thinks there's an error in this comic? Shouldn't spouse's sibling be the sibling-in-law of Cueball's *sibling*? But then, maybe I'm also making Randall's point... [[User:Sspenser|Sspenser]] ([[User talk:Sspenser|talk]]) 18:28, 31 August 2018 (UTC)

Russians actually have different words for both "types" of brothers in-law (spouses brother vs. sisters husband), also for parents or children in-law on either side: https://ru.wikipedia.org/wiki/Свойство_(родство)

2034: Equations

2018-08-17T09:20:03Z

162.158.234.46:

{{comic
| number = 2034
| date = August 17, 2018
| title = Equations
| image = equations.png
| titletext = All electromagnetic equations: The same as all fluid dynamics equations, but with the 8 and 23 replaced with the permittivity and permeability of free , respectively.
}}

==Explanation==
{{incomplete|Created by an EQUATION - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
This comic gives a set of equations supposedly from different areas of mathematics and physics. To anyone not familiar with the field in question they look pretty similar to what you might find in research papers or on the relevent Wikipedia pages. To someone who knows even a little about the topic, they are clearly very wrong and only seem even worse the more you look at them.
{| class="wikitable"
!style="width:20%"|Equation
!style="width:20%"|Field
!style="width:60%"|Explanation
|-
|<math>E = K_0t + \frac{1}{2}\rho vt^2</math>
|All kinematics equations
|This equation literally states: "Energy equals a constant <math>K_0</math> multiplied by time plus half of density multiplied by speed multiplied by time squared". The first term here is hard to interpret - it could be correct if <math>K_0</math> is a constant power applied to the system, this symbol would more normally be used to denote an initial energy and so multiplying by <math>t</math> would be wrong. The second term looks similar to the traditional kinetic energy formula <math>\frac{1}{2}mv^2</math> but with a density instead of the mass. This is then wrong without some accompanying volume term (on either side of the equation).
|-
|<math>K_n = \sum_{i=0}^{\infty}\sum_{\pi=0}^{\infty}(n-\pi)(i-e^{\pi-\infty})</math>
|All number theory equations
|Taken literally the equation says: "The nth K-number is equal to for all i in 0 to infinity, for all pi in 0 to infinity; subtract pi from n and multiply it with i minus e (to the power of pi minus infinity)". A twofold misconception can be seen here. The first is the reassignment of pi as a variable instead of the constant (3.14). This might be a jab at how in number theory letters and numbers are used interchangeably, but where some letters are all of a sudden fixed constants. The second misconception is the use of infinity in the latter part of the formula. Naively this would signify that (with the reassigned pi values) the part in the power would range from minus infinity to zero. However infinity is not a number and cannot be used as one without using a limit construct.
|-
|<math>\frac{\partial}{\partial t}\nabla\cdot p = \frac{8}{23}

\int\!\!\!\!\!\!\!\!\!\;\;\bigcirc\!\!\!\!\!\!\!\!\!\;\;\int
\rho\,ds\,dt\cdot \rho\frac{\partial}{\partial\nabla}
</math>
|All fluid dynamic equations
|-
|<math>|\psi_{x,y}\rangle = A(\psi) A(|x\rangle \otimes |y\rangle)</math>
|All quantum mechanic equations
|
|-
|<math>\mathrm{CH}_4 + \mathrm{OH} + \mathrm{HEAT} \rightarrow \mathrm{H}_2\mathrm{O} + \mathrm{CH}_2 + \mathrm{H}_2 \mathrm{EAT}</math>
|All chemistry equations
| A modification of the combustion of methane. The correct form is often taught and a good example problem but obviously there are more chemistry problems.<math>\mathrm{HEAT}</math> is normally shorthand for {{w|activation energy}}, but in Randall's version it's jokingly used as a chemical ingredient and becomes <math>\mathrm{H}_2\mathrm{EAT}</math>, taking the hydrogen atom freed by the combustion equation shown. To deliver the punchline while maintaining proper stoichiometry, <math>\mathrm{OH}</math> (which should be <math>\mathrm{OH}^-</math>, since the oxygen keeps a free electron when it combines with a single hydrogen) is shown instead of <math>\mathrm{O}_2</math>. The proper methane combustion equation would be: <math>\mathrm{CH}_4 + 2 \mathrm{O}_2 \rightarrow 2 \mathrm{H}_2\mathrm{O} + \mathrm{CO}_2</math>
|-
|<math>SU(2)U(1) \times SU\left(U(2)\right)</math>
|All quantum gravity equations
|This is more similar to equations which appear in {{w|Grand_Unified_Theory|Grand Unified Theory}} (GUT) than general quantum gravity. Unlike some of the other equations, this one has no interpretation which could make it mathematically correct. This type of equation is used to describe the symmetry group of a particular phenomena in terms of mathematical {{w|Lie_Group|Lie Groups}}. A real example would be the Standard Model of particle physics which has symmetry according to <math>\rm{SU(3)\times SU(2) \times U(1)}</math>. Here, <math>\rm{SU}</math> and <math>\rm{U}</math> denote the special unitary and unitary groups respectively with the numbers indicating the dimension of the group. Loosely, the three terms correspond to the symmetries of the strong force, weak force and electromagnetism although the exact correspondence is muddied by symmetry breaking and the Higgs mechanism.

Of course, an expression missing an "=" sign, is difficult to interpret as an "equation", because equations normally express an "equality" of some kind. Nobody knows whether Randal refers to a horse here (equidae)

Randall's version clearly involves some similar groups although without the <math>\times</math> symbol it is hard to work out what might be happening. A term like <math>\rm{SU(U(2))}</math> has no current interpretation in mathematics, if anyone thinks otherwise and possibly has a solution to the quantum gravity problem they should probably get in touch with someone about that.
|-
|<math>S_g = \frac{-1}{2\bar{\varepsilon}}i\eth \hat{\big(} \zeta_0 \dotplus p_\epsilon \rho_v^{abc}\cdot \eta_0 \hat{\big)} f_a^0 a\lambda(\xi) \psi(0_a)</math> 
|All gauge theory equations
||This equation looks broadly similar to the sorts of things which appear in gauge theory such as the equations which define {{w|Yang–Mills_theory#Quantization|Yang-Mills Theory}}. By the time physics has got this far in, people have normally run out of regular symbols making a lot of the equations look very daunting. The actual equations in this field rarely go far beyond the greek alphabet though and no-one has yet to try putting hats on brackets. The appearence of many sub- and superscripts is normal (this links to the group theory origins of these equations) and for the layperson it can be impossible to determine which additions are labels on the symbols and which are indices for an {{w|Einstein_notation|Einstein Sum}}.

The left-hand side <math>S_g</math> is the symbol for some {{w|Action_(physics)|action}}, in Yang-Mills theory this is actually used for a so-called "ghost action". On the right-hand side we have a large number of terms, most of which are hard to interpret without knowing Randall's thought processes (this is why real research papers should all label their equations thoroughly). The <math>\frac{1}{2\bar{\varepsilon}}</math> looks like a constant of proportionality which often appears in gauge theories. The factor of <math>i = \sqrt{-1}</math> is not unusual as many of these equations use complex numbers. The <math>\eth</math> symbol looks similar to a <math>\partial</math> partial derivative symbol especially as the {{w|Dirac_equation#Covariant_form_and_relativistic_invariance|Dirac Equation}} uses a slashed version as a convenient shorthand.

The rest of the equation cannot be mathematically correct as the choice of indices used does not match that on the left-hand side (which has none). In particle physics subscripts (or superscripts) of greek letters (usually <math>\mu</math> or <math>\nu</math>) indicate terms which transform nicely under Lorentz transformations (special relativity). Roman indices from the beginning of the alphabet relate to various gauge transformation propetries, the triple index seen on <math>p^{abc}_v</math> would likely come from some <math>\rm{SU(3)}</math> transformation (related to the strong nuclear force). Since <math>S_g</math> has none of these (and is thus a scalar which remains constant under these operations), we would need the right-hand side to behave in the same way. Most of the indices which appear are unpaired and so will not result in a scalar making the equation very wrong. For those not familiar with this type of equation, it is a similar mistake messing up units and setting a distance equal to a mass.
|-
|<math>H(t) + \Omega + G \cdot \Lambda \, \dots \begin{cases} \dots > 0 & \text{(HUBBLE MODEL)} \\ \dots = 0 & \text{(FLAT SPHERE MODEL)} \\ \dots < 0 & \text{(BRIGHT DARK MATTER MODEL)} \end{cases}
</math>
|All cosmology equations
|
|-
|<math>\hat H - u_{0} = 0</math>
|All truly deep physics equations
|<math>\hat H</math> is the hamiltonian operator, which when applied to a system returns the total energy. In this context U would usually be the potential energy. However there is also a subscript 0 and a diacritic making indicating some other variable. Much of physics is based on Lagrangian and Hamiltonian mechanics. The Lagrangian is defined as <math>\hat L = \hat K - \hat U </math> with K being the kinetic energy and U the potential. Hamiltonian mechanics uses the equation <math>\hat H = \hat K + \hat U </math>. The Hamiltonian must be conserved so taking the time derivative and setting it equal to zero is a powerful tool. The principle of least action says allows most modern physics to be derived by setting the time derivative of the Lagrangian to zero.
|-

|<math>\frac{\partial}{\partial t}\nabla\cdot p = \frac{\epsilon_0}{\mu_0}
\int\!\!\!\!\!\!\!\!\!\;\;\bigcirc\!\!\!\!\!\!\!\!\!\;\;\int
\rho\,ds\,dt\cdot \rho\frac{\partial}{\partial\nabla}
</math>
|All electromagnetic equations
|This equation has superficial resemblance to portions of [//en.wikipedia.org/wiki/Maxwell%27s_equations Maxwell's Equations], but just miscellaneous bits, some from the integral forms and some from the differential forms.
|}

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
[TODO: Avoid using math markup here because the images of these equations isn't helpful in a transcript. Sigh.]
[Nine equations are listed and labeled as followed:]
 
E = K0t + 1/2 pvt2 
ALL KINEMATICS EQUATIONS 
 
<math>K_n = \sum_{i=0}^{\infty}\sum_{\pi=0}^{\infty}(n-\pi)(i-e^{\pi-\infty})</math> 
ALL NUMBER THEORY EQUATIONS 
 
∂/∂t ∇ ⋅ p = 8/23 (∯ ρ ds dt ⋅ ρ ∂/∂∇) 
ALL FLUID DYNAMIC EQUATIONS 
 
<math>|\psi_{x,y}\rangle = A(\psi) A(|x\rangle \otimes |y\rangle)</math> 
ALL QUANTUM MECHANIC EQUATIONS 
 
CH4 + OH + HEAT → H2O + CH2 + H2EAT 
ALL CHEMISTRY EQUATIONS 
 
SU(2)U(1) × SU(U(2)) 
ALL QUANTUM GRAVITY EQUATIONS 
 
<math>S_g = \frac{-1}{2\epsilon}i\eth \hat{\big(} \zeta_0 \dotplus p_\epsilon \rho_v^{abc}\cdot \eta_0 \hat{\big)} f_a^0 a\lambda(\zeta) \psi(0_a)</math> 
ALL GAUGE THEORY EQUATIONS 
 
<math>H(t) + \Omega + G \cdot \land \, ... \begin{cases} ... > 0 & \text{(HUBBLE MODEL)} \\ ... = 0 & \text{(FLAT SPHERE MODEL)} \\ ... < 0 & \text{(BRIGHT DARK MATTER MODEL)} \end{cases}
</math> 
ALL COSMOLOGY EQUATIONS 
 
Ĥ - u̧0 = 0 
ALL TRULY DEEP PHYSICS EQUATIONS
 

{{comic discussion}}
[[Category:Math]]

Talk:1878: Earth Orbital Diagram

2017-08-21T22:30:22Z

162.158.234.46:

I guess first off, we should note the "solstice" is *not* the Bristish equivalent of "equinox" -- they are actually opposites. The equinoxes occur in April and September, when the day & night are equal length, and the solstices occur in June and December, when the length of daylight and nightime, respectively, are at their longest. [[User:JamesCurran|JamesCurran]] ([[User talk:JamesCurran|talk]]) 15:30, 18 August 2017 (UTC)

:Technically, the opposite of solstice is the other solstice. Solstice and equinoxes are orthogonal. -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 00:01, 20 August 2017 (UTC)

"Determinant of the date of Easter" refers to the fact that in the Catholic Church (and possibly other Christian denomiations) the date of Easter is the first Sunday after the first full moon of Spring, which means it is an astronomical calculation, but completely unrelated to the indicated angle. [[User:JamesCurran|JamesCurran]] ([[User talk:JamesCurran|talk]]) 16:28, 18 August 2017 (UTC)
:Well, everyone celebrates Easter on the same day, right? So it's the first Sunday after the first full moon for everybody. [[User:Berets|Berets]] ([[User talk:Berets|talk]]) 23:20, 18 August 2017 (UTC)
::No, not all denominations agree on the date of Easter; a particular example being the Orthodox church, which usually has Easter a week after the Catholic church, but sometimes as much as five weeks later. The difference is caused by the two denominations using different idealized calendars, both lunar and solar, as well as a slight difference in the definition. [[Special:Contributions/162.158.69.57|162.158.69.57]] 18:41, 19 August 2017 (UTC)
"Astral planes" might as well be a Unicode reference, taking into account Randall's occasional mention of emoji, since emoji reside on one of the astral planes: https://en.wikipedia.org/wiki/Plane_%28Unicode%29 {{unsigned ip|141.101.105.168}}
:That supplementary planes humorously refer also to {{w|Astral plane|Astral planes}} as mentioned in this explanation.--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 19:54, 18 August 2017 (UTC)

Solstice comes from the Latin ... Sol = Sun .. Sistere = Stand still. It literally means the day the sun stands still and refers to the longest day of the year (summer) and the shortest day of the year (winter). So how does the Sun "stand still". On those days the Earth reaches either end of orbital ellipse and returns around the other side. If you stick a pole in the ground and observe its shadow every day at Noon you will see the shadow grow longer every day from winter to summer and grow shorter every day from summer to winter. The shadow is shortest when the Sun is highest in the sky at mid-summer and the shadow is longest when the sun is lowest in the sky at mid-winter. The sun is either getting higher in the sky or lower in the sky every day. When the Earth is at the end of the ellipse and the transition takes place the shadow will not make any noticeable change from one day to the next and one could say that the "Sun has stood still". [[User:Rtanenbaum|Rtanenbaum]] ([[User talk:Rtanenbaum|talk]]) 19:36, 18 August 2017 (UTC)

I think that Solstice/Equinox thing is a reference to Randall having a hobby of spreading linguistic misinformation, as seen in 1677:Contrails.
[[Special:Contributions/172.68.26.251|172.68.26.251]] 00:32, 19 August 2017 (UTC)

I'm not sure what the labels of the planes are, but they certainly aren't Greek letters. They look like alchemical symbols to me.
[[Special:Contributions/162.158.74.243|162.158.74.243]] 00:56, 20 August 2017 (UTC)

Part of the humor of Declension is that it's a portmanteau of right ascension and declination. Right now only declination is mentioned. [[Special:Contributions/162.158.75.40|162.158.75.40]] 02:43, 20 August 2017 (UTC)

Arctangent is also a music festival in the UK, happening when this comic came out. --[[Special:Contributions/162.158.234.46|162.158.234.46]] 22:30, 21 August 2017 (UTC)