Explain xkcd: It's 'cause you're dumb.
Cueball activates a time machine to go back into the past. The time machine rewinds time, but in the process rewinds the event where the time machine itself was turned on, turning the time machine off in the process. He is now a few seconds in the past, prior to having activated the time machine, but he is baffled that he does not seem to have accomplished anything and turned off the time machine unintentionally. It would seem that the time machine is the world's most technologically-advanced "useless machine" (a device whose only purpose is to switch itself off when it is switched on).
The title text mimics a countdown to an event. "T minus 10," for example, means 10 seconds until the event. When the event is the activation of a time machine traveling back in time, after 10 seconds it will once again be "T minus 10," and a second later it will be "T minus 11," counting up rather than down. This casts doubt on the value of the countdown because, from the perspective of the time traveler, the event has already taken place.
Cueball is only able to travel back in time a few seconds because in this comic time is seen as continuous and linear, so he can only travel back in time to the moment he activated the machine (the first series of "E"s is the machine warming up and the second series of "E"s is that in reverse) the logic behind this is because time is continuous, Cueball's input was required for the machine to work.
- The problem with time machines:
- [Cueball has his hands on the lever of a time machine.]
- [Cueball flips the switch from OFF to ON.]
- [Cueball flips the switch from ON to OFF.]
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- [Cueball is puzzled.]
This one kinda went over my head; the explanation is the best I could come up with. Alpha (talk) 05:00, 24 April 2013 (UTC)
- Examine the transcript and Cueball's movement in the second and third panel. The time machine in this comic is a time-reversing one, not a time jumping one. Davidy²²[talk] 05:13, 24 April 2013 (UTC)
Cueball turns on the time machine, which starts up and they start going back in time, returning to the time the machine it turned on. Time is going in perfect reverse, so the machine switches off and then he is back where he started. 220.127.116.11 05:10, 24 April 2013 (UTC)
I didn't get it when I first read it, and this explanation seems to make the most sense; if it is the intended joke, I wish Randall would have reversed the sound effect "click" in the third panel ("!kcilC"), which would indicate that time is moving backwards (from the reference frame we're watching it from), which would have made this explanation more obvious for me.18.104.22.168 18:22, 24 April 2013 (UTC)larK
The Machine even turns back Cueballs actions, so maybe even his memory of turning it on, what might make him so puzzled - eventually - if he decides rational to try the machine (and if desicdes always rational) - he will get in a loop of turning it on - travelling back and forgetting that event - and turning it on again. - That might get Interesting 22.214.171.124 05:32, 24 April 2013 (UTC) Lupo
I don't think he looks puzzled because nothing happened, I think he's curious b/c he just came across a Time Machine. That is, the last frame of the strip takes place seconds before the first. So the "trouble" with time machines (of this variety) is that if you go back in time you can't take the present with you, and nothing changes.
126.96.36.199 06:00, 24 April 2013 (UTC)
Alternative view: Feedback. Stephen Hawking has discussed the general problem with a whole class of time machines (namely, wormwhole based time machines), where the energy from the future is added exponentially to the system due to system feedback. More or less as a microphone cannot get too close to its speaker without having that horrible sound. This would explain who the guy in the comic turns the machine off... there is a large buildup of energy feedback and this can be observed in the EEEEE...
"In the end, I think a wormhole like this one can't exist. And the reason for that is feedback. If you've ever been to a rock gig, you'll probably recognise this screeching noise. It's feedback. What causes it is simple. Sound enters the microphone. It's transmitted along the wires, made louder by the amplifier, and comes out at the speakers. But if too much of the sound from the speakers goes back into the mic it goes around and around in a loop getting louder each time. If no one stops it, feedback can destroy the sound system.
The same thing will happen with a wormhole, only with radiation instead of sound. As soon as the wormhole expands, natural radiation will enter it, and end up in a loop. The feedback will become so strong it destroys the wormhole. So although tiny wormholes do exist, and it may be possible to inflate one some day, it won't last long enough to be of use as a time machine. That's the real reason no one could come back in time to my party.
Source: http://www.dailymail.co.uk/home/moslive/article-1269288/STEPHEN-HAWKING-How-build-time-machine.html#ixzz2RMMowXrs" 188.8.131.52 (talk) (please sign your comments with ~~~~)
But with that above analogy, in a sound system, you have external power to amplify the signal - the energy the microphone takes out is not what gets put back out. In a wormhole, unless there is something to amplify the radiation that comes out the other end then it's a closed system (and if you do amplify it then where did THAT energy come from). (Nigel 08:39, 24th April (UTC))
- The wormhole itself does not need to amplify the energy, because it isn't a closed system; more enrgy is being added to it. Interestingly though, this leads to another problem: creating a time machine portal would quite lossibly lead to the instantaneous heat death of the universe. Here is the problem: the instant the portal is opened, radiation moves through. When it comes out in the past, it fractionally increases the total energy in the universe. Logically, after the time until the wormhole is created, the energy will spread out enough that there is at least a chance that the radiation passing through the wormhole will be slightly increased. This causes ian infinite loop, or at least a loop that so dramatically changes the earth that the time machine is no longer created. Athang (talk) 22:54, 6 May 2014 (UTC)
A more generalized flow chart explaining the problem with time machines, assuming you get to keep moving forward: http://i4.minus.com/jqqrkqg1QKp84.png --Willowy burrito (talk) 13:17, 24 April 2013 (UTC)
Another problem with this design of a time machine is that it draws power from the wall. What would happen if he crosses the time when there was no outlet at that location? Or no power grid at all? But that may not pose a problem here because it seems he doesn't get too far back into the past anyway. So, for our future time machine inventors: make those machines self-contained! --184.108.40.206 15:24, 24 April 2013 (UTC)
- I think that pretty much somes up why some people think you can't use a time machine to go back in time before the time machine itself existed. If it was an ancient time machine, you could go back quite far, but if one was made on February 5, 2013 you couldn't travel before that point because the time machine wouldn't exist before that time, so no time machine anymore, no travel. Hence what you said about crossing the time when there was no outlet. Cueball couldn't go back that far. --Dangerkeith3000 (talk) 15:36, 24 April 2013 (UTC)
- Paging <a href="http://en.wikipedia.org/wiki/Sam_Beckett#Dr._Beckett.27s_string_theory">Dr Sam Beckett</a>... 220.127.116.11 16:30, 24 April 2013 (UTC)
- The movie "Primer" deals with a similar time travel conundrum - the protagonists can never travel back in time earlier than when the time machine is turned on, thus the earliest possible date for travel into the past is the date the first machine is turned on. 18.104.22.168 23:44, 1 May 2013 (UTC)
- You can always use lightning ;-) Sebastian, --22.214.171.124 16:58, 24 April 2013 (UTC)
- 1.21 GIGAWATTS! --Dangerkeith3000 (talk) 21:17, 24 April 2013 (UTC)
PRIMER!!!!!!! Robot123 (talk) (please sign your comments with ~~~~)
Ugh! The original explanation (going back in time by one second) is drastically over thought. It's a "time machine" that does nothing other than make a noise -- just a box with a switch. Cueball turns it on, and a second later turns it off, thus having traveled through time into the future by one second. The T numbers are incrementing, just as they always do, even prior to a rocket launch. We're all traveling through time -- "all systems ARE normal." Please reconsider. Jeff. 126.96.36.199 (talk) (please sign your comments with ~~~~)
- Except that he is travelling into the *past* by one second. He goes from T-10 to T-11 - that's back in time. I think the original explanation is on the button. As soon as he starts to go back in time, he undoes the action of activating the machine, so he doesn't get anywhere. MGK (talk) 23:46, 24 April 2013 (UTC)
um... no. it's called "countdown" for a reason.188.8.131.52 17:47, 24 April 2013 (UTC)
- I agree with 184.108.40.206, I also think Cueball moved 1 second into the future, much like 630: Time Travel Saibot84 (talk) 19:12, 24 April 2013 (UTC)
- How about putting this as an alternative explanation? The current explanation makes sense to me but the forward version is just as funny. Alpha (talk) 19:37, 24 April 2013 (UTC)
- But then it wouldn't go "EEEEEeeeee *click*". It would be "*click* EEEEEeeeee"... 220.127.116.11 21:03, 24 April 2013 (UTC)
- Touché. I thought all the events in panel 3 happened at the same time. Alpha (talk) 21:46, 24 April 2013 (UTC)
- I was thinking that too after close inspection. Good point. I think the alternative explanation had some good merits tho, because tho maybe it seems like the *click* comes at different order than the EEEEeeee's just because the sound is relatively closer to us. If it is closer to us, wouldn't we hear the click AFTER the EEEeee's if going backward??? My head hurts. Great comic, this one. --Dangerkeith3000 (talk) 00:00, 25 April 2013 (UTC)
- I believe you have to consider the usual reading sequence, where (Panel two) Cueball is first perceived in action of switching the switch, then he finished and we hear the "Click" noise and then the machines starting sequence is detected as eeE's. The reading sequence of Panel 3 is contextually "hardwritten" by Panel 2, just reversed; after the machine reaches its point where its traveling back in time (between Panel 2 and 3), all events are happening timereversed: Eee's, Click, Cueball (I dont think u would have a perception of that anyway, if u are an observer in the same universe) Anyway, making Cueball unintentionally switching the machine off, will imo result in an endless time loop.* (As i wrote down on this Page at the star *, wich had become a dot for some reason... Go look for that dot.)18.104.22.168 10:03, 26 April 2013 (UTC)
Huh. When I first read the comic, my thought was that the universe had caused Cueball to shut the machine off involuntarily to avoid any paradoxes -- if it had stayed on any longer, something would have happened to cause a paradox, and the only way to win is not to play. I have to say that I like your explanation much better. 22.214.171.124 01:49, 25 April 2013 (UTC)
- But if the time machine "rewinds" time, wouldnt the action of turning it on result in an endless time loop where Cueball switches the switch on and off for all eternity? By "rewinding" time itself, the initial Thought of turning the machine on would also reappear in Cueballs mind. I Believe the Comic itself makes no sense considering the fact that Cueball switched the switch off unintentionally - therefore there is no way of ever reaching panel 4. 126.96.36.199 17:32, 25 April 2013 (UTC)
- He and for that matter the rest of the universe would indeed get stuck in an infinite loop (short of some randomness in the universe which means there is a probability he will turn it on and a probability he won't, but I'm getting off track).. he doesn't intentionally turn the machine off, time rewinds which causes the machine to return to the 'off' state.
188.8.131.52 01:23, 1 May 2013 (UTC)
Maybe this is not a time machine, but a Time machine? DiEvAl (talk) 11:10, 26 April 2013 (UTC)
Maybe Cueball as triggered an universe wide End of Time. If the machine reverse time exactly as it was ten second before, then Cueball will activate the switch again thus creating an infinite loop forbidding the natural flow of time forever!
"Granted, that's a worse case scenario. The destruction might in fact be very localized, limited to merely our own galaxy." Twisell (talk) 14:13, 26 April 2013 (UTC)
- Given panel 4, where he looks dowb at his hands in confusion, it seems to me that he remains concious of his actions, but that his body was moving backwards in time, so he would be aware of what was taking place. As such, he couldn't start an infinite loop. Athang (talk) 22:54, 6 May 2014 (UTC)
Not sure if this has been covered... But is there a significance to the use of the word 'nominal' in the alt text. "all time machine systems nominal" Nominal could be used here to mean existing in name only, giving credence to the interpretation that this 'time machine' is much like the time kayak. Thoughts?Darkfield (talk) 04:49, 27 April 2013 (UTC)
- "All systems nominal." is a sentence of science person jargon that appears as part of a countdown. That's what 'nominal' is doing in the alt text. The absence of a copular verb, which is kind of a thing for news reports and this kind of status report type announcement, is what made your interpretation possible, but I don't think that was intended. 184.108.40.206 (talk) (please sign your comments with ~~~~)
Reminds me of the "Useless Machine": http://www.youtube.com/watch?feature=player_embedded&v=Z86V_ICUCD4 --Mr. I (talk) 03:13, 29 April 2013 (UTC)
- This was my first thought. Thanks for linking to it. --DanB (talk) 21:11, 29 April 2013 (UTC)
The outlet has 1 hole in the first two frames and 2 holes in the last two frames. --220.127.116.11 18:05, 30 April 2013 (UTC)
- Mind. Blown. 18.104.22.168 (talk) (please sign your comments with ~~~~)
I thought perhaps that the idea was that when he flips on the time machine, time does proceed, but at normal speed. Therefore, the "time machine" is just a box with a lever on it that does nothing. 22.214.171.124 (talk) (please sign your comments with ~~~~)