Explain xkcd: It's 'cause you're dumb.
Title text: It's commonly believed that Lorentz contraction makes objects appear flatter along the direction of travel. However, this ignores light travel times. In fact, a fast-moving butt would appear rotated toward the observer but not substantially distorted. Shakira was right.
Gedankedank is a humorous portmanteau of Gedankenexperiment (German for "thought experiment") and badonkadonk (slang term for an attractive, round butt).
Albert Einstein often used thought experiments to explore scientific hypotheses too impractical or impossible to actually perform, in order to examine their consequences. Moving close to the speed of light, c, is nigh-impossible with existing technology; and according to Einstein's theory of special relativity accelerating a mass exactly to c is impossible. Einstein is well known not to have cared about his appearance (e.g. (WARNING: TVTropes link) his uncombed hair, the tongue photo, etc.) so it is unlikely that he pondered how relativistic velocity would affect the appearance of his butt.
Lorentz contraction is a consequence of special relativity, whereby objects contract in the direction of travel. An object traveling exactly at c (rather than near light speed) would be squished completely flat. It would also have infinite mass, infinite energy, and experience no passage of time until slowed by an outside force.
The appearance of rotation while moving close to the speed of light is known as Terrell rotation. The title text then connects this rotation to the Shakira song "Hips Don't Lie".
- [We see a head and shoulders view of Einstein. He looks pensive.]
- [Einstein's "line" is in a thought bubble.]
- Einstein: If I were traveling at the speed of light, my butt would look awesome.
- Einstein was famed for his Gedankedank.
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Should be "Gedankengang" (Plural, it's "Gedanke" + "n"). Means: chain/train/line of thought(s)
22.214.171.124 05:52, 3 July 2013 (UTC)
- Interesting idea, because it matches the text more closely, but he really wasn't that famous for his "chain of thought" - more famous for his Gedankenexperimente, for example, chasing a light beam (leading to Special Relativity) or the thought experiments that lead to the EPR paradox. --126.96.36.199 09:52, 3 July 2013 (UTC)
- Anyway, "Gedankedank" does not really make sense, it's not a word. 188.8.131.52
- Might be refering to "Badonkadonk", even though "Gedankedank" isnt a german word. 184.108.40.206
- That's what I think: He's taken "Gedankenexperiment", which sounds funny in English, and taken the "Gedanken" part and reduplicated it to match the sound of "badonkadonk", without worrying about whether it makes sense in German. --220.127.116.11 12:22, 3 July 2013 (UTC)
- "chain of thought" might be a too literal translation. I think "Gedankengang" is a bit broader than just meaning "chain of thought". Its literal translation would be "go of the thoughts" or "way the thoughts are going". If Randall has done some research before creating the word, then this is also a possiblity. In German one could really say, that Albert Einstein is famous for his "Gedankenexperimente", "Gedanken" or "Gedankengänge". Maybe we should offer both explanations? --18.104.22.168 13:35, 6 July 2013 (UTC)
Also, from reading http://forums.xkcd.com/viewtopic.php?f=7&t=103423, in last week's "what if" there was:
- 20 meters per second is about how fast an average person with a good arm could throw a bouncy ball. Therefore, to determine the result of an impact, we can make use of what Einstein called a gedankenexperiment, or "thought experiment"
22.214.171.124 10:02, 3 July 2013 (UTC)
I'm not sure what the "Lorentz contraction" in the title text is referring to, should this be added to the description? 126.96.36.199 14:06, 3 July 2013 (UTC)
Side note: Logical conclusion -- Shakira's hips must like big butts. JamesCurran (talk) 15:30, 3 July 2013 (UTC)
" it is unlikely that he pondered how relativistic velocity would affect the appearance of his butt. " This, ladies and gentlemen, is why i read this! Funnier than xkcd sometimes... Way too many times, sometimes... 188.8.131.52 03:43, 4 July 2013 (UTC)
I just realized the number of this comic. Friday will be comic 1234. I doubt there will be a joke about it since I think only 404 and 1000 had any self-reference. 184.108.40.206 14:37, 4 July 2013 (UTC)
- Also, as part of a discussion for THIS comic, there was a bit of magnificent basterdry on Randall's part in seeding within his What If all the information needed to get the joke. Almost anyone that read it would get an immediate chuckle out of it. For me, I had even forgotten the source of where I had learned what "gedankenexperiment" meant. 220.127.116.11 05:20, 5 July 2013 (UTC)
AIUI, Einstein shouldn't notice any change himself - well unless he's suddenly also Mr. Fantastic... the MARVEL Mr. Fantastic of the Fantastic Four, and only his lower body is travelling that fast, and his head is in a different frame, where the relative velocities between the two frames is ~c. (But that's stupid. If he was Mr. Fantastic, he'd just fix his butt. Or.. is this superfast motion how Mr. Fantastic gets his powers (and Mystique)? Does that mean Quicksilver and Flash can also exhibit these shape-shifting powers?). Anyway, coming back to the point - I didn't get what the title text states... so I employed some Google-fu and found this: http://faraday.physics.utoronto.ca/PVB/Harrison/SpecRel/Flash/ContractInvisible.html
I think you'd only see the edge of the disk though, and not a ring... given the camera is a 2 dimensional thing in the plane of the disk. Reason I mention that is, I'm still unsure how this works for a 3D object where the object is moving across your FOV. Anyone have any ideas?
18.104.22.168 10:45, 5 July 2013 (UTC)