Explain xkcd: It's 'cause you're dumb.
A perpetual motion machine is a hypothetical device that is supposed to move infinitely with no external forces helping it, thus providing an unlimited source of energy. The existence of such an object would contradict the laws of thermodynamics, so perpetual motion machines are known to be impossible.
A conspiracy theory called free energy suppression asserts that it really is possible to get infinite energy and special interest groups have worked to hide it. In the comic, Randall says that he posted to a forum dedicated to the idea back in 2004, and the thread is still active — it kept on going forever, like the perpetual motion machine they desire (in contrast with real attempts to build such a machine, which all stop quite soon). Of course, the reason the thread continues is that its advocates continue to add energy to it, in the form of comments. "Hot air", if you will.
The second law of thermodynamics states that the entropy of an isolated system never decreases. See this video about entropy. Thus, even if you could build a perpetual motion machine, you wouldn't be able to use it to produce energy that could be consumed by another device.
The three supposed comments show humorous forms of scientific ignorance:
- The first comment is simply wrong; neither pole of a magnet reverses entropy.
- The second comment confuses the first law of thermodynamics (conservation of energy) with Isaac Asimov's First Law of robotics (robots may not injure humans).
- The third comment invalidly conflates the notions of physical law and US law, hoping for legal loopholes to make a flywheel spin forever. Perhaps Congress would repeal the law of gravity on one side.
Furthermore, the avatar being used by the second poster is that of a power strip plugged into itself, which is often jokingly thought of as a perpetual motion machine.
The title text refers to the fact that inventors have been trying to create perpetual motion machines, but have all failed to succeed. But given the fact that they all failed, the total time any perpetual motion machine has been running is 0 seconds, while the search has been going on for a long time.
- [A page from a very long thread on "Free Energy Forum."]
- Thread: You're all crackpots who don't understand thermodynamics.
- Page 547 of 547
- Poster 1: No, idiot, only the north end of a magnet increases entropy. The south end decreases it.
- Poster 2: I wiki'd this "First Law" and I don't see the issue. My device isn't a robot and doesn't harm humans.
- Poster 3: What if we trick the government into only suppressing the left side of the flywheel?
- Ironically, the argument I started on a perpetual motion forum in 2004 shows no signs of slowing down.
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Anyone know if there really is a thread for this? I Googled the title as shown in quotes and it didn't give me any results. Without quotes gave me the xkcd forums as well as some Creationist stuff. 126.96.36.199 07:39, 28 January 2013 (UTC)
-- Haha! I did exactly the same, but in the hour and a half since you searched, some enterprising soul has created what appears to be a tribute thread at . PabloVergos (talk) 08:57, 28 January 2013 (UTC)
Also, 0.999... ≠ 1 and the government covered it up. 188.8.131.52 00:35, 29 January 2013 (UTC)
The explanation for the third post should make note of the situation where you hang a flywheel (e.g. a bicycle wheel) by each end of its axis using cords, spin the wheel then cut one cord, and the bicycle wheel will keep spinning in the same position! There was a YouTube video for this, but I cannot find it, there must be more people who know what I'm talking about. It has something to do with centripetal (No, Mr. Bond, I expect you to die). :) 184.108.40.206 05:32, 29 January 2013 (UTC)
- I think it refers to this, not gyroscopes. Bugefun (talk) 06:27, 29 January 2013 (UTC)
I did some digging and found http://www.physicsforums.com/showthread.php?t=29697&page=4
Not sure if it has any relation, but it's hard to believe its a coincidence that the thread is from 2004 and the final comment is "I think this thread has run its course, and I'm getting tired of deleting crackpot posts from it. Any objections? Good." Ornj (talk) 09:36, 29 January 2013 (UTC)
Can anyone identify the icons at the left of the three postings in the comic? The first looks to be a generic head, but the second is a device of some kind, with (perhaps) a push-button, and a wire leading from and connecting back to the device. The third might be a person standing next to a Tesla coil or Van de Graaff generator. Vere Nekoninda (talk) 14:42, 31 January 2013 (UTC)
The second device is a power strip plugged into itself. Free energy, after all.
This thread lives on youtube: http://www.youtube.com/watch?v=287qd4uI7-E
Perpetual Motion Machines are not free energy. For that to happen, you need it to output more energy than it uses :( SilverMagpie (talk) 16:53, 22 May 2017 (UTC)
Alright I have no problem with giving a link to rational wiki but can someone explain to me why we are redirecting people there when it has significantly less credible citations than wikipedia's pseudoscience page?--Lackadaisical (talk) 20:29, 7 November 2013 (UTC)
What started with a single click on Wikipedia's "self-replicating machine" page has led to an ever-increasing number of tabs in my browser containing articles on self-replication. Please help. --220.127.116.11 23:13, 16 July 2016 (UTC)
the total time any perpetual motion machine has been running is 0 seconds
Pretty sure that, while literally true in the sense that no perpetual motion machine exists and therefore has never run for any length of time, that's not what Randall meant: I'm sure he meant the total time any attempted perpetual motion machine has run may be in the weeks and months but not the many years since he started the argument. I will edit in 24 hours if nobody objects. AmbroseChapel (talk) 00:50, 1 September 2017 (UTC)