explain xkcd - User contributions [en]

Talk:1537: Types

2015-06-12T12:46:27Z

141.101.97.214:

Relevant: WAT talk https://www.destroyallsoftware.com/talks/wat

Are (6) and (7) about completing sequences?

If the sequence was [1, 2, 3, ?] we would expect the ? to be a placeholder for 4. So [1, 2, 3]+2 is wrong := FALSE. But [1, 2, 3]+4 is correct := TRUE.

"+2 appears to be applying a unary + to the number 2" : or it adds the number of the line, 10, to 2 => 12. Also, the eleventh line, "2+2" may add 2 to all the following 2, explaining line 12. (that theory is from a friend of mine) [[User:Seipas|Seipas]] ([[User talk:Seipas|talk]]) 12:17, 12 June 2015 (UTC)
: Also, for the lines 6 and 7, the operation "[1,2,3]+x" may add x to the set [1,2,3] and return true if the operation succeeded or false if not. Adding 2 to the set [1,2,3] returns false because 2 is already in [1,2,3]. [[User:Seipas|Seipas]] ([[User talk:Seipas|talk]]) 12:23, 12 June 2015 (UTC)

Yellowish Blue: http://www.livescience.com/17948-red-green-blue-yellow-stunning-colors.html is NaN!

''"The ironic thing is that fractions with 2 in the nominator are not the kind of numbers that typically suffer from floating point impreciseness."''
- This is not technically correct. Should read "fractions with 'power of 2' in the '''de'''nominator. However, the 3/2 would cause precision errors.

== "normally" ==

<blockquote>This would make sense if it was <code>[] + 2</code></blockquote>

It really wouldn't. Javascript returns <code>"2"</code> (god knows why) and Python gives an error. Don't really feel like testing many other languages, but I also think it's not really a logical assumption to make at all. Can't think of a reason for <code>[] + 2</code> to return <code>[2]</code>... ever. It ''might'' make a little bit of sense in Randall's oddly typed language, but not in any sane one. --[[User:TotempaaltJ|TotempaaltJ]] ([[User talk:TotempaaltJ|talk]]) 12:35, 12 June 2015 (UTC)

: Javascript first converts <code>[]</code> (the empty array) to the empty string (using the rule "stringify each element and join with a comma"), then treats the operation as <code>"" + 2</code>, which results in conversion of the other operand to string and then concatenation. [[Special:Contributions/141.101.97.214|141.101.97.214]] 12:46, 12 June 2015 (UTC)

1520: Degree-Off

2015-05-13T08:35:11Z

141.101.97.214: grammar fix

{{comic
| number = 1520
| date = May 4, 2015
| title = Degree-Off
| image = degree off.png
| titletext = I'M SORRY, FROM YOUR YEARS OF CONDESCENDING TOWARD THE 'SQUISHY SCIENCES', I ASSUMED YOU'D BE A LITTLE HARDER.
}}
==Explanation==
[[Cueball]] (physics), [[Hair Bun Girl]] (biology), and [[Megan]] (chemistry) appear to be on a talk show called Degree-Off, hosted by [[Hairy]], where representatives of different fields, try to explain why their field is the best and why to get a degree in their field. The title "Degree-Off" is a portmanteau of "{{w|Academic degree|degree}}", as in the recognized completion of studies at a school or university, and "{{w|face-off}}", a direct confrontation between two people or groups. Since there are three participants, this is not a true face-off, unless Megan, who does not speak, is not counted.

The host asks the physicist Cueball to go first. He light-heartedly begins to tell what appears to be long story, beginning with a {{w|Richard Feynman}} anecdote. During the {{w|Manhattan Project}} in Los Alamos, Richard Feynman got bored because of the isolation and started learning {{w|lock picking}} on the secret documents safes. Using these new skills, he played lots of pranks on his colleagues, like leaving notes and spooking them into believing there was a spy among them (which, of course, {{w|Klaus_Fuchs|there was}}). He finishes his case with [http://en.wikiquote.org/wiki/Ernest_Rutherford a quote] from {{w|Ernest Rutherford}}, implying that his speech was quite long and winding. The quote communicates the idea that physics is the only fundamental framework, so that the job of chemists, biologists and other scientist simply is to catalog and systematize observations ("collect stamps") on phenomena too complicated to presently be fully described in terms of physics. This idea was earlier lampooned by [[Randall]] in [[435: Purity]] (and is also stated in the title text of [[1158: Rubber Sheet]]).

The biologist, Hair Bun Girl, goes next, showing with a graph (see below) that the field of biology has helped reduce disease. She then goes on to claim that the heroes in biology (the part known as Medicine) has even "slain" one of the {{w|Four Horsemen of the Apocalypse}}. Originally these were Conquest, War, Famine and Death, but in popular culture Conquest is usually re-interpreted as {{w|Four_Horsemen_of_the_Apocalypse#As_infectious_disease|Pestilence}} - Hair Bun Girl implies that the field of biology has almost eliminated Pestilence. (The imagery of Pestilence being thwarted by modern medicine was also used in the book {{w|Good Omens}}, by {{w|Terry Pratchett}} (of whom Randall is a fan, see [[1498: Terry Pratchett]]) and {{w|Neil Gaiman}}, where Pestilence has retired after the discovery of {{w|Penicillin}}, and been replaced by {{w|Pollution}}.)

<div class="toccolours mw-collapsible mw-collapsed">
This graph shows the death rate from infectious disease in USA, similar to that shown in the comic presented by Hair Bun Girl, as both have the range of 1900-2000. The spike is attributable to the {{w|1918 flu pandemic}}. The graph has been published in this paper [http://jama.jamanetwork.com/article.aspx?articleid=768249 Trends in Infectious Disease Mortality in the United States During the 20th Century].
<div class="mw-collapsible-content">[[File:Crude_Infectious_Disease_Mortality_Rate_in_the_United_States_from_1900_Through_1996.gif]]</div>
</div>

Hair Bun Girl then goes on to directly accuse Cueball (i.e. physicists) of creating a new Horseman to replace the one slain by the biologists. She claims that they gathered in the desert to do so. Given Cueball's opening remark, she must be referring to the development of the {{w|atomic bomb}}, which was built and tested in the {{w|New Mexico desert}}. The new horseman is therefore the atomic bomb, or the various perils associated with it.

Hair Bun Girl's implied condemnation of the physics community has been echoed by some of the scientists involved in the project itself. After the test detonation of the first nuclear weapon on July 16, 1945, {{w|J. Robert Oppenheimer}}, the director of the {{w|Los Alamos National Laboratory}}, found himself quoting the {{w|Bhagavad Gita}}: "Now I am become Death, the destroyer of worlds."

This harsh moral judgement shocks Cueball, who exclaims "I thought this was supposed to be fun and lighthearted!" While the set-up is of a frivolous friendly competition, Hair Bun Girl's presentation is surprisingly dark. Her retort in the final panel reveals that she was angered by the off-hand dismissal of 'soft' sciences as "stamp-collecting", and turned the game from a light-hearted fun into something more disturbing.

In the title text the biologist goes on to declare in {{w|All caps}} that she is surprised a physicist isn't "harder", after all their condescending towards the "squishy" sciences. The use of 'hard' and 'squishy' is a play on the colloquial division between the so-called 'hard' sciences (such as physics and chemistry) and 'soft' sciences (such as biology and geology). 'Hard' sciences usually refer to the perception that in fields like physics, precisely repeatable experiments and measurements are possible, as opposed to 'soft' sciences seen as placing less emphasis on precisely quantifiable predictability - however Hair Bun Girl is extending 'hard' to its meaning of 'stoic', mocking Cueball for not being able to weather a personal moral attack. Again she is indicating that she's upset by directly referencing a mocking portrayal of other fields allegedly made by Cueball.

In [[520: Cuttlefish]] Randall shows that he personally respects biologists - or at least fears them.

==Transcript==
:[Hairy is acting as the host of a TV talk show, ''Degree-Off''. Cueball, Hair Bun Girl, and Megan are acting as representatives of Phys (Physics), Bio (Biology), and Chem (Chemistry) respectively. They each stand behind their own Lectern with the respective subject label.]

:Hairy: Welcome to the ''Degree-Off'', where we determine which field is the best! Physics, wanna go first?
:Cueball: Sure! I'd like to tell the story of Richard Feynman's Manhattan project lockpicking pranks...

:Cueball: ...and as he said, "all science is either physics or stamp collecting."
:Cueball: Thank you.
:Hairy: ''Great!'' Bio, you wanna go next?
:Hair Bun Girl: Okay.

:[A graph labeled "Per 100,000 is shown above Hair Bun Girl]
:Hair Bun Girl: This is a graph of the death rate from infectious disease in this country.

:[Hair Bun Girl raising her left hand]
:Hair Bun Girl: The heroes of my field have ''slain'' one of the four horsemen of the apocalypse.

:[Hair Bun Girl pointing at Cueball]
:Hair Bun Girl: While the heroes of ''your'' field gathered in the desert to create a new one.

:Cueball: ...Jeez, what the hell? I thought this was supposed to be fun and lighthearted!
:Hair Bun Girl: ''You must have been thinking of stamp collecting.''

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Hairy]]
[[Category:Comics featuring Hair Bun Girl]]
[[Category:Science]]
[[Category:Charts]]
[[Category:Physics]]
[[Category:Biology]]
[[Category:Portmanteau]]

1366: Train

2014-05-13T09:38:59Z

141.101.97.214: /* Explanation */

{{comic
| number = 1366
| date = May 9, 2014
| title = Train
| image = train.png
| titletext = Trains rotate the Earth around various axes while elevators shift its position in space.
}}

==Explanation==
This comic, which appeared the day before {{w|National Train Day}}, plays on the fact that a choice of a {{w|Inertial frame of reference|reference frame}} is arbitrary, a {{w|Principle of relativity|basic principle}} in Newtonian mechanisc.

Rather than viewing this situation as a train causing itself to move relative to an immobile Earth, [[Randall]] provides the unconventional perspective of a train remaining fixed in space while causing the Earth itself and all the stars in the sky to rotate instead. In principle either perspective is equally valid (though in practice different trains often move in mutually-exclusive directions, thus each train would have to define its own frame of reference). There is a quotation, attributed to Einstein, that he once asked a ticket collector, "What time does Oxford stop at this train?"

From the Newtonian perspective this choice of frame is valid, but results in unnecessarily complicated maths; the equation of motion would include terms for centrifugal, Coriolis and other so-called "fictional forces" see [[123: Centrifugal Force]]. Newton supposes the existence of "inertial frames", in which these forces are zero, and the surface of the Earth approximates an inertial frame well. In General Relativity, the presence of mass in a system curves the {{w|spacetime}} around of it. The train-earth system could be modeled in general relativity, taking the train as fixed. However the resulting equations would be complex, and not amenable to an exact solution

The title text takes this further by saying that elevators do the same thing by pulling the Earth up and down, rather than moving up and down in a fixed space via cables and weights affixed to pulleys that are themselves moored to fixed points.

These examples use the train and the elevator as fixed points to define relative travel. The more common method to define movement is to use the Earth's surface as fixed point, but other reference points could be the {{w|Earth's_rotation|Earth's center}}, the {{w|Earth's_orbit|Sun}}, predefined {{w|Fixed_star|"fixed" stars}} or the {{w|Galactic_year|center of our galaxy}}. Each of these would result in a completely different movement speed:
* The speed of the train (stationary on the equator) relative to the earth's center: 465 m/s (1,674 km/h or 1,040 mph)
* The speed of the train (on earth) relative to the sun: 30 km/s (108,000 km/h or 67,000 mph)
* The speed of the train (on earth) relative the center of our galaxy: 220 km/s (828,000 km/h or 514,000 mph)

The train, as seen from the earth's surface, doesn't seem to rotate the earth, but it does in fact have a minute, immeasurable effect on the Earth's rotation (see [http://what-if.xkcd.com/41/ what-if? 41: Go West] and [[162: Angular Momentum|comic 162: Angular Momentum]]).

==Transcript==
:'''TRAIN:'''
:[On the upper edge of a circle representing the Earth in a wrong scale, Cueball is in a train car, looking to his left.]
:Cueball:...almost...
:[The train tracks run between another person standing at the 2:00 position, and Hairy standing at the 9:30 position. There's yet another person standing at the 6:00 position, between some snow-capped mountains and some low hills.]
:[There's a counterclockwise arrow in the middle of the circle, and motion lines indicate that everyone and everything on the planet is moving counterclockwise, except for the train, which is motionless.]

:A machine that grabs the Earth by metal rails and rotates it until the part you want is near you

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Physics]]

1366: Train

2014-05-09T13:24:42Z

141.101.97.214: /* Explanation */

{{comic
| number = 1366
| date = May 9, 2014
| title = Train
| image = train.png
| titletext = Trains rotate the Earth around various axes while elevators shift its position in space.
}}

==Explanation==
{{incomplete|First explain - please check or correct anything I may have done wrong.}}

This comic plays on the way everything in the universe can be viewed from a relativistic perspective. Rather than viewing it as the train moving itself relative to Earth, Randall explains it as trains moving the Earth relative to itself.

The title text takes this further by saying that elevators do the same thing by pulling the Earth up and down, rather than moving up and down by themselves.

These examples use the train and the elevator as fixed points to define relative travel. The more common method to define movement is to use the Earth's surface as fixed point, but other reference points could be the {{w|Earth's_rotation|Earth's center}}, the {{w|Sun}}, predefined {{w|Fixed_star|"fixed" stars}} or the {{w|Galactic_Center|center of our galaxy}}. Each of these would result in a completely different movement speed.

It should also be noted that the comic's logic only holds true for single, isolated trains; if all the trains on the planet were actually causing rotation, then their mutually exclusive directions would cause jams. The trains would, however, have a minute, immeasurable effect on the Earth's rotation (see [http://what-if.xkcd.com/41/ 41: Go West] and [[162: Angular Momentum]]).

The logic of the comic also fails when taking acceleration into account. Whether the train or earth is moving can be determined by which one experiences a force due to acceleration or deacceleration when the train starts.

==Transcript==

TRAIN:

''A picture of a tiny planet (presumably meant to be Earth) with [[Cueball]] on the south, [[Hairy]] on the right, and [[Megan]] on the left. At the top is a train on tracks with another cueball in it.''

A machine that grabs the
Earth by metal rails and
rotates it until the part
you want is near you

{{comic discussion}}