Time Machines

July 8, 2009 |

Using a time machine would be more difficult than it seems.

100 Responses to Time Machines

  1. MainFragger May 18, 2010 at 6:22 am #

    would need to look at matter and time as two intersecting spots on a map and send someone to a given spot of matter at a given spot of time in order to avoid the whole earth is moving problem. Of course, you don’t want to KNOW how big of a database you’d need to pull THAT off..

  2. Anonymous May 12, 2010 at 9:17 am #

    i already went back and look i am living forever and ever

  3. Anonymous May 14, 2010 at 12:37 pm #

    Yeah great “theories” – reads just like a summary of everything somebody else has already said and that you repeated like a parrot.

  4. Anonymous May 14, 2010 at 12:30 pm #

    There might, at some time, be a way to isolate one region of Spacetime from all other regions of Spacetime from a temporal perspective – you could call that region a kind of time-machine; or you could call it a deep-freeze; or a can of beans.

    I really don’t know how that would help you identify changes in the timeline external to your Spacetime region, ‘though.
    1] You’re either experiencing the same relative Time, or you’re not. You’re either outside your safe region or not.
    2] Whether out or in your region, that region and all regions of Spacetime around it are still in the same Dimension or Reality you started out in, and in which, it’s safe to assume, the same “timeline” will apply – as the same Spacetime and timeline will exists everywhere, Universally and in each tiny part of the Universe the same, now matter where and how it is – it’s just experienced relativistically.
    Changes in what you call the “timeline” would mean changes not just on Earth in respect of Hitler, but Universally down to each tiny element, and for the whole of Spacetime, for that Dimension: so your little safe Spacetime region experiment has only isolated you relativistically, like a freezer – your freezer will still be in the Universe, and the temporal displacement you are trying to avoid by the exercise would still apply to you, Universally – you would just “experience” it Relativistically [although you wouldn’t actually experience anything, as has been pointed out].

    So the answer is, maybe.
    But it doesn’t matter at all because:
    A] You wouldn’t be able to “avoid” the changes in the way you describe, and
    B] everything you have written is nonsense.


  5. Anonymous May 14, 2010 at 11:58 am #

    Whoever thought this up and then sat there typing it in, believing it made any kind of sense, is a total idiot.

  6. Anonymous December 1, 2009 at 7:19 pm #


  7. Anonymous December 1, 2009 at 7:17 pm #


  8. Anonymous December 1, 2009 at 7:16 pm #


  9. Anonymous December 1, 2009 at 7:16 pm #


  10. Anonymous December 1, 2009 at 7:15 pm #


  11. Anonymous August 17, 2009 at 5:09 am #

    A collapsing Universe is just a theory – and we’re only able to account for less than 5% of the mass in the universe that math indicates that there should be for that discussion to even go anywhere. We’re a long way from being able to say anything at all about that for certain.

    But anyway – so it contracts and explodes again? Does it, ‘though? This seems to be supposition: which is based on what?
    Everything happens “mostly the same” each time? Oh really? Why should it? This seems to be presumption: which is based on what?

    We “should” be reborn every time the Universe is reborn? Should we, indeed? Why is that? This looks a lot like supposition; presumption; assumption and wild conjecture.

    The 3rd paragraph is just confused.

    The 4th paragraph [sigh..] is irrelevant. You can’t travel back in time, and if you could, you cant kill your grandfather or you wouldn’t be around to be travelling back in time. Other than that it just states the obvious.

    The probability discussion, blah, blah, blah – well-trodden philosophical ground, but mixed in with the themes of paragraph 4 in an attempt to support this overall position – which is largely unsupportable, as above.

    Overall, this is ridiculous and is the exact problem with this whole “time-travel” discussion – bedroom theories that aren’t validated by the basic science principle of structured auto-criticism, [but instead seek to self-affirm!], that aren’t properly evidenced or supported with reasonable logic and that are laced with just enough half-truth of terms and concepts not fully understood to make those theories seem reasonable.

    Disclaiming such terribly poor science or logic by saying it’s “just for discussion” is insufficient – and insulting! Otherwise I could just post “Green eggs and ham, green eggs and ham – the Universe is a triangle- because I said so. [It’s just for discussion]”.

    Absolute nonsense! And the reason why the Internet is a minefield.

  12. Anonymous August 20, 2009 at 5:58 am #

    The argument is that, although Science Fiction and Science are related, they are very different things – and they have the flavours of “good” and “bad”.
    The “good” tends to be scrupulous in understanding the surrounding existing, science, terms and logic of the condition it is attempting to speculate on – not much of value comes of a poor foundation.

    So, none of our technology started as an idea in a “ridiculous” book or play. I might accept that some of it started in a “good” book or play – that obeyed the criteria of “good” above – but even that might be arguable.

    Yes, of course, in the name of creativity, you can position anything you please; but it all depends what you want to achieve – a genuine flight of fancy, or properly constructed, rationally plausible prediction – that has some basis in science?

    Isn’t a decision there one of the reasons we now find a DaVinci sketch of a helicopter so astonishing? I’m sure there were others of the time who drew their wild dreams of things that could fly – but, from a scientific perspective, who now cares?

    My argument is that plausibility, based on a clear understanding of principles, (and, yes; educated speculation), is what separates what may be possible from the clearly impossible, regardless of the probability of the speculation – and it is that which ignites further investigation and brings Fiction into Reality, therefore it is that we should seek to apply.

    I’ve no doubt that the two examples you give may have been declared insane, impossible or improbable at some point, yet they were plausible.
    Fiction predicted space-flight, but it didn’t declare that the rockets would be powered by faeries – the prediction was plausible.
    And let’s not forget; it wasn’t the mere saying of it that made them so, it was the iterative application of scientific principles to the ideas, by scientists, not writers, that brought speculation into reality.

    I really didn’t mean to rain on your parade, stifle your creativity; or appear rude – and if I did, I apologise.

    As I said, creativity is valid – absolutely necessary actually – but I am the one in slightly the wrong place. I was just looking for “what-if’s” where the creativity and speculation are balanced by some kind of regard to what we know of principles.
    Personally, speculation that is not supported that way drives me insane because, otherwise, in my view, that really is pure science fiction – and we could just sit here and say anything at all about this idea or anything else, none of it arguable beyond “OK” – and where that’s the case, I’d have to ask myself where’s the value in it?
    And, bizarrely enough, now I stop to think of it – it’s discussions on *science fiction* sites that are far more concerned with remaining in the bounds of scientific plausibility than appears on this particular discussion – in the Science Blog. Go figure…

  13. MainFragger August 18, 2009 at 11:46 am #

    and I don’t even try to deny or shrug that off. I like scientic discussion..regardless of whether it is science fact, science fiction, or just plain science wackiness.

    The fact is, I’m not bothered by improbabilities or unlikeliness in a discussion, because the way I see it, the fact we are even here on this planet, proves that the extremely improbable and unlikely happen and continues to happen on a daily basis.

    I realize that science is often based off of hypothesis, experimentation, theories and verification.. But somewhere in those is room for open ended jaunts into the rediculous..If not..I suspect Quantum Mechanics and several arms of medicine and other general sciences would have been dropped as a viable form of science long ago.

    How many of our current technology started as an idea in a rediculous book or play written ages ago by people who were just trying to tell an interesting story. Robots for example. Cloning. And lots of other stuff.

    In science, truth is often stranger than fiction. There are plenty of legitimate articles on this blog alone to demonstrate that fact.

  14. Anonymous August 10, 2009 at 6:03 pm #

    I agree, you would break your ankle, miss the bus, or have your gun jam. How about you do kill him (though why would any sane person WANT to kill their grandfather?) only to return to your own time and find out you were adopted and you killed someone else’s grandfather. Don’t try it. He might know you’re coming and kill you first. Paradox solved.

  15. Anonymous July 29, 2009 at 12:18 pm #


  16. Anonymous July 27, 2009 at 2:10 pm #

    There’s at least 2 ways of looking at time travel (assuming it’s possible).

    1) A time traveller goes back in time and changes history. According to string theory (or what’s probably more popular now m-theory), the change causes an alternate reality to be created…one which we live in and the other which is an offshoot from the point of the change caused by the time traveller.

    2) A time traveller goes back in time and changes history. Per the previous respondent, ppl would not know any different since that change ripples across time to our present day. For example, if the “original” timeline was that Hitler was supposed to win WW2 but a time traveller killed him or made it so Hitler lost WW2, we would not know about the “original” historical timeline (since everything in our history reflects the “new” timeline).

    Regardless of which of the above (or some other theory) is true, my question is…is there a way to measure or determine that history has changed? Is there a way to anchor a point in our timeline so that should a time traveller change our past, we can at least notice something strange happened? Being able to do this would confirm time travel is possible and occurring.

  17. Anonymous July 26, 2009 at 3:32 pm #

    I wonder how these peoples would view this discussion?


    Time among the Kalingas: An Account of a People in the North Luzon Highlands, Philippines

    by Dr. Robert Lawless

    Abstract: Kalinga concepts of time are distinct in several ways from concepts of time in Western cultures. Rather than noting how Kalingas define time, this article focuses on how Kalingas experience and measure time, noting that they use both linear and circular concepts. Using both concepts allows Kalingas to integrate historical change while maintaining an adherence to their indigenous customs. Knowledge of these differences may prove helpful in understanding how human beings deal with a known past, a changing present, and an unknown future.

  18. Anonymous July 24, 2009 at 6:33 pm #

    think of everyone as a merry go round.with infinite versions of yourself or all the possible personalities of yourself, riding your merry go round. and everyone around you touching in the same dimension on their own merry go rounds. the personalities in this dimension is the person you are now. the people you know and their personality is only one of an infinite number of possibilities, therefore there are an infinite number of possibilities of existence and dimensions. so it makes sense that you could exist in a dimension where your grandfather didnt exist, assuming time travel was possible and he was killed.

  19. Anonymous July 24, 2009 at 5:29 am #

    Perhaps you could go back in time and re-learn proper spelling.

    Or maybe learn it for the first time? Just a thought.

  20. Anonymous July 23, 2009 at 8:30 pm #

    Time is presence of motion and forces. Time is due to expansion of the universe (space.) Time is slow where expansion of space is slow as around large masses. Gravitons radiated by large masses interact with space to slow the expansion which then causes time to slow down.

    There is no time travel. Only present is real. Past is only a memory of events. Future does not exist.
    For more on this line of thought visit http://www.timephysics.com

  21. Anonymous July 23, 2009 at 6:29 pm #

    if you go to the past you creat a difrent parallel univers because your whole persence changes it, you can kill your dad but you wont diddapear because you killed an alternate you and you cant go back into the future because that parral universis future hasnt happend yet and you cant come back from where you started your trapped in that time and universe idefently

  22. Anonymous July 22, 2009 at 9:38 pm #

    yep. 10.

  23. Anonymous July 22, 2009 at 9:37 pm #

    haha i know right! my favourite one is the one 9 up from this one though. beats all the other mindf**ks of comments here.

  24. Anonymous July 22, 2009 at 9:27 pm #

    more like just the next season.

  25. Anonymous July 22, 2009 at 5:49 am #

    do you honestly think that if human beings were to think like this, we’d have achieved anything at all? we’d have sat under trees waiting to get eaten until there weren’t any humans left. and, right now, some other species would be acting guardians of earth, not us. in a way, youre insane.

  26. Anonymous July 22, 2009 at 5:20 am #

    unbelievably absurd.

  27. Anonymous July 22, 2009 at 2:56 am #

    this makes no sense.

  28. Anonymous July 21, 2009 at 9:33 pm #

    I think this strip is on stumble less for content and more for the comments… haven’t laughed so hard in months!

  29. Anonymous July 20, 2009 at 3:10 am #


  30. Anonymous July 20, 2009 at 2:58 am #

    I’m with you. I think the question defeats itself.

    You were born. What has occurred in the past cannot be changed because I’d imagine principles in the Universe would be self protecting against such anarchy as going back and preventing that what HAS happened, from happening. It’s a nonsense, because either it did, or it did not. And it did.

    Meaning: there is a huge arrogance in an assumption about going back and killing your grandfather – you can only know so much about the past, and nothing about your future.
    In your future, you anticipate going back and making the kill.
    You go back to the past and find you’ll find that your gun jams, or you miss the train, or you trip and break your ankle and any number of number of literally limitless possibilities that will conspire to maintain the continuity in the Universe or dimension in which you presently reside – the one in which you exist. Your grandfather will survive no matter what you do – he MUST, or you would not exist.
    Even while you are programming the co-ordinates into your machine, you should be thinking – “I am going back – therefore I failed. If I could succeed I wouldn’t be here to be doing this in the first place”.

    That’s if going “back” is an option anyway, which I don’t think it is. Another story, perhaps, but I’d imagine part of the Universe protection against anarchy is that it’s not possible and if it were, the only way the scenario can work is in the answer above yours, where you interaction with the past of ANOTHER dimension or reality, not your “own”.
    As above, the fact of your existence means it’s impossible to change what has already been for yourself – you will have killed an “ALTERNATE” grandpa. You get home and yours will still be in your house.

    Better to get some counselling and learn to live with each other.


  31. Anonymous July 13, 2009 at 5:54 pm #

    how retardedly irrelevant

  32. Anonymous July 13, 2009 at 5:04 pm #

    I think that’s how LOST is going to end.

  33. Anonymous July 13, 2009 at 4:19 pm #

    Time is not a straight line. It is more like ripples in the ocean of space-time. No one can change or even visit the past. Once you theoretically are in the past your very presence regardless of what you do or not you start traveling in an alternate “ripple” of time. Think alternate realities instead of changing time you are now visiting an alternate timeline and have therefore changed nothing.

    I know, I’m from the future.

  34. Anonymous July 13, 2009 at 2:21 pm #

    were always changing the future…every minute of every day

    if i time machine will be made it would come back and change time no matter what it did…all the possible existences with time machines have already played out…time machines may have existed but in this timeline they never will…otherwise we would be a different timeline

  35. Anonymous July 13, 2009 at 1:22 pm #

    But that’s after you kill him. Once you kill him, you kill yourself too. You were in existence until you killed your grandfather.

  36. Anonymous July 13, 2009 at 1:15 pm #

    My question is about the grandfather paradox thing…
    So, if you killed your grandfather after traveling back in time, he wouldn’t exist anymore, which would cause you to not exist. But because you don’t exist anymore, you couldn’t have killed him, so your grandfather re-exists, causing you to re-exist, causing you to kill him.
    The universe gets confused, so it implodes the Earth. I’m correct in my thinking, no?

  37. Anonymous July 13, 2009 at 12:54 pm #

    The only problem I see with the theory that you would void the need to go back in time in the first place, is the parallel universe theory. The way I see it is that there is only one time line that just keeps going on. Just one, not several different time lines that form because of time travel. So when you go back in time you automatically change the whole future everything restarts. So killing Hitler would completely alter the future. You might not even exist. and there wouldn’t be any need to travel back in time. think of time travel as a straight blue line, and think of time travel as loop back into the past, and wherever you end up in the past the blue line turns red and all the line since your entry into it will eventually turn red as time goes on. Then lets say that someone in the future creates another time travel machine and travels back to another point in time, and their time travel line is green, then the time line since his or her entry into the past turns green and so on.

    I also believe that realistically once time travel is created the whole world should be informed of this machines existence, then the machine should not be used for a week after it’s creation. Then from that point on time travel should be limited to only one week into the past to reverse things that have happened. (9/11 type things) the reason for the delay is so everyone knows that time travel exists and would be freaked out if I told them i’m here from a week in the future. But never more than a week so that one week in the future is not too heavily affected by this change. I don’t know about you guys but I can imagine a world in which something like 9/11 didn’t happen plus no one is born withing a week. so you wouldn’t be preventing anyone from being born. You might prevent them from being “created” but not any 8 month baby’s from being born. get it? It’s a safer bet than time travel into the distant past.

  38. Anonymous July 12, 2009 at 10:40 pm #

    good observation

  39. Anonymous July 12, 2009 at 8:47 pm #

    You’re so smart!

  40. Anonymous July 12, 2009 at 3:10 pm #

    It would not, it would only make the past and present slightly (meaning imperceptibly on the universal scale) more or less dense

  41. Anonymous July 12, 2009 at 2:59 pm #

    Most conceivable ways of building a time machine by their very nature would not be able to send energy or matter further back in time than when the first time machine was turned on. There are many ideas for how to bend space-time that are possible under Eisenstein Relativity, which you might enjoy looking up.

    As for the matter of consciously changing the future, I personally changed the future by responding to this post. “The Future” is not any particular path, it is a series of paths that could occur based on what choices are made. To use the example of inventing a time machine, there are essentially infinite variations of two basic paths, one where time machines have been invented, one where time machines have not been invented. Both are (theoretically) equally possible, and various events will collapse those infinityx2 paths into the one that will actually happen. Most of the events (and therefore the path) are not theoretically predetermined at all, as you say, but will be mostly caused by human decisions.

  42. Anonymous July 12, 2009 at 2:53 pm #

    So, like, check it out.

    First, there is a universe before time travel is invented. Then some sci-fi adventurer goes back in time, and, say , kills Adolf “the furious Fuhrer” Hitler at birth. Well that might create 2 realities: the one we live in, where Hitler lived; and the new one minus Hitler. In both realities a future will come about in which time travel is “once again” invented. In the first world, “our world,” Hitler is killed by the first time assassin, and then another time assassin is sent back to kill Joseph Stalin. In the world without Hitler the first time assassin can skip straight to killing Stalin. Now you have 3 dimensions: one without Hitler or Stalin, one without Hitler but with Stalin, and our world which includes both Hitler and Stalin in out history.

    Alternate realities would just keep being created unless the death of Hitler actually changed the reality from which the time traveler came, which would mean that all the people who died in WWII would have lived and bred, and every sperm that beat the mind-boggingly great odds in order to fertilize an egg probably would not win that race again. Basically, by killing Hitler the sci-fi adventurer would delete the future in which he was conceived and born and replace it with another with a whole new set of people.

  43. Anonymous July 12, 2009 at 2:28 pm #

    Really? that makes so much sense… we either will or we wont i was in a total other direction here thinking the other possible outcome would of been the solution but you’ve truly narrowed it down to two. Thank you sir.

  44. Anonymous July 12, 2009 at 1:21 pm #

    Ok Mr Wizard, thanks.

  45. Anonymous July 12, 2009 at 11:45 am #

    The Flux Capacitor!

    It’s what makes time travel possible

  46. Anonymous July 12, 2009 at 11:45 am #


  47. Anonymous July 12, 2009 at 10:23 am #

    If there is no light or matter being sent back, then obviously there was no time machine invented in the future (or should I say there will be no time machine invented). Anyways, the way I see it, is that our only hope for a time machine would be to change a theoretically predetermined sequence of events, and invent a time machine. Basically we either will or we won’t invent a time machine, but most likely we won’t. In addition, there is no way to consciously change the future because we don’t know what the future is. So cheers to the lucky fellow who blindly invents a time machine.

  48. Anonymous July 12, 2009 at 9:48 am #

    We are all constantly traveling through time.

    Currently the trip is only possible in one direction and only at a rate of 1 second per second, though relativity does allow for you to travel faster than others while still yourself only experiencing a rate of 1 second per second.

  49. Anonymous July 12, 2009 at 1:05 am #

    Okey dokey. if there is time travel, then any alterations to history would become history. thus they would be imperceptible to everyone else in their own personal timeframe. so it follows that any change to history has already happened, and will continue to always happen. ultimately, everyone’s, especially the time traveler’s, past present and future becomes their immutable past, regardless alterations. in fact, in accomodation of those alterations. so that means that history is not a story which is delicately balanced on events. it is a jigsaw puzzle, with each perception of time fitting together to form a picture, which is balanced not on events but on points of view. read some douglas adams. he explains it better than i

  50. Anonymous July 12, 2009 at 1:05 am #

    Okey dokey. if there is time travel, then any alterations to history would become history. thus they would be imperceptible to everyone else in their own personal timeframe. so it follows that any change to history has already happened, and will continue to always happen. ultimately, everyone’s, especially the time traveler’s, past present and future becomes their immutable past, regardless alterations. in fact, in accomodation of those alterations. so that means that history is not a story which is delicately balanced on events. it is a jigsaw puzzle, with each perception of time fitting together to form a picture, which is balanced not on events but on points of view. read some douglas adams. he explains it better than i

  51. Anonymous July 11, 2009 at 11:40 pm #

    Man i agree with you.
    And also we could see back in time already with the Telescopes looking at the stars.
    we are looking at stars that might not even exist anymore

  52. Anonymous July 12, 2009 at 9:20 am #

    The earth is not an inertial frame. It is accelerating around the sun. same goes with the sun, or for that matter, pratically ANY object in our universe. However, the relative accelerations are pretty small so it is usually acceptable to estimate the earth as an inertial frame. but yea, you are right in that you’d probably end up only a few hundred feet above (or below) your original location if you only go back a few hours….

  53. Anonymous July 12, 2009 at 4:19 am #

    The current idea is to turn on a machine that somehow connects through the time dimension in a loop between itself in the future and itself in the past. Things enter this loop in our time and leave it in another time when the machine was/will be active.
    It would only work for light at first, restricting its use to the transfer of information, but if we found a way to transport matter it would likely use a similar effect. Spatially, travelers would appear in the same position that the machine is located in that time frame.

  54. Anonymous July 12, 2009 at 4:12 am #

    Another theory suggests a seires of coincidences would stop you from killing your own grandfather or whatever.

  55. Anonymous July 12, 2009 at 1:43 am #

    if we are really going to get sth like time machine, then their must be some people from future coming to our time and trying to change some sequence of event which might be intended to avoid some big calamity in future but can we really any way come to know of what is getting changed. i think never, can we avoid a calamity like 9/11 by the help of such tech…i dont think our future counter parts are still able to do so.. or if they able to then also they must have came to know that disturbing the equilibrium of sequence of naturally occurring event can be hazardous to whole universe equilibrium.

  56. Anonymous July 12, 2009 at 1:20 am #

    If the scientist had travelled through time, but not through space, he probably would have travelled roughly along the same path as the earth, since he would have been in an inertial frame of reference.

    If anything, he would have ended up high in the air over the earth.

    But if we’re ignoring that little bit of relativistic mechanics, you forgot the fact that the sun is travelling at enormous speeds around the edge of the galaxy, which is, itself, travelling at huge speeds relative to other galaxies around it. But taking relativity into account, the earth should be pretty much stationary as far as the scientist is concerned, unless he moved into the sun’s inertial frame to travel through time, in which case, the acceleration alone probably would have killed him… Bending space, though, isn’t much different from bending time, so if he invented a time machine, I’m sure he could have easily had it manipulate his position in space as well, although it would be pretty unnecessary.

  57. Fred Bortz July 8, 2009 at 11:27 am #

    Very cute!

    If the cartoon hero paid attention to Einstein, he would have built a spacetime machine.

    Read my interpretation of what Hawking wrote about time travel in a limerick and review of his book The Universe in a Nutshell.

    Limericiously yours,
    “Dr. Fred” Bortz
    Science Books for Young Readers
    Science Book Reviews

  58. Anonymous July 17, 2009 at 1:43 am #

    I am not able to know that how it works. In fact I think that is it possible to make that type of imaginary machine. Please get in touch with me.
    William Brown

  59. Anonymous July 16, 2009 at 1:04 pm #

    To kill our grandparents ofcourse.

  60. Anonymous July 13, 2009 at 11:34 am #

    Maybe you should go back in time and live in a cave…. back away from the keyboard dude.

  61. Anonymous July 13, 2009 at 11:31 am #

    “because time moves at a constant pace”
    Ah, no it doesn’t. Time travels at pace relative to your speed. So it IS possible to go into the future. Many people have done it, but it’s such a small amount of time that it doesn’t matter. Now, if your traveling say 1/2 the speed of light for 1 year (6 months out and 6 months back) then you may go a few days into the future.

  62. Anonymous July 13, 2009 at 10:45 am #

    We only know one version of history so far. The victors side of history. Being able to go to the past would allow us to rewrite what we think is history, and actually get it right. It could also disprove or maybe just question many religions and beliefs many people hold as fact.

  63. Anonymous July 13, 2009 at 10:37 am #

    Who the F!!! cares! if its gonna happen its gonna happen, noone knows how where why when or anything about it, so why talk about it.

  64. Anonymous July 13, 2009 at 10:15 am #



    make another version which takes into account string theory :)

  65. Anonymous July 13, 2009 at 9:33 am #

    If we built a time machine, why would we go into the past anyway? I mean, we already know how the story goes so far.

  66. Anonymous July 11, 2009 at 11:13 pm #

    perhaps time travelers are walking around right now and history has, in fact, been altered and we just don’t know because its kept secret from everyone that doesn’t need to know. Or maybe we don’t know about it because its not significant enough of a change. Or maybe its because time travelers are traveling to change history. A lot of people assume that time travelers will “right” the “wrongs” and perhaps that’s not the case at all. Perhaps Hitler needed to exist for reasons beyond our comprehension and the same goes for other world leaders that we assume time travelers would kill…. Alexander the Great, Hannibal, Genghis Khan…why not get them all when they are babies? If we really want to consider eliminating evil from our history then it might make sense to go back in time and eliminate Jesus. This way the endless wars and deaths that people caused in his name might never have happened……the

    If time travelers are in our present I doubt they are concerned about killing humans that might alter their very existence….why risk it? the earth is still in tact in their present day and well, their technology progressed far enough to create time traveling.

  67. Anonymous July 11, 2009 at 11:00 pm #

    The idea of space-time travel is thought provoking.
    Could the ‘ufo’s’ actually be human scienists from a later time?

    Or maybe not.

  68. Anonymous July 11, 2009 at 10:55 pm #

    Looks like someone’s been reading Spider Robinson!

    He mentions this fact in Callahan’s Con when Zooey uses the Meddlers belt to go forward in time. She ends up just like the guy in the comic. Luckily, she has a daughter who can time travel, so she was saved.

    (It’s quite difficult to explain how she was saved, so read the book if you’re curious. It’s a hilarious read, anyway.)

  69. Anonymous July 11, 2009 at 10:43 pm #

    none of you have ever traveled through time. so all of your theories are wrong.

  70. Anonymous July 11, 2009 at 10:33 pm #

    As Steven Hawking said: “If time travel is possible, where are the time travelers.”

    I have an answer now. In space. They are meteorites.

  71. Anonymous July 11, 2009 at 9:52 pm #

    Those people would have never existed in the first place. Anyone that would go back in time and kill themselves can never exist. So therefore, the only people that exist today, are people who would not go back in time and eliminate them self.

  72. Anonymous July 11, 2009 at 9:45 pm #

    traveling back in time would leave an instantaneous vacuum where you were while at the same ‘time’ instantly pushing every atom apart at your reappearing in the past. immediate destruction of both present and past would result, totally destroying the universe instantly.

  73. Anonymous July 11, 2009 at 9:39 pm #

    The reason Hitler exists is because our timeline hasn’t reached the point where time travel is possible. The future is impossible to travel to, because time moves at a constant pace, but when our current time reaches the time-travel age, it is possible everything will change. Maybe now Hitler existed, but years from now, who knows?

    It’s possible his existence will be erased, but not yet.

  74. Anonymous July 11, 2009 at 9:06 pm #

    If someone was to go back in time and kill their past self, which would be entirely possible if time travel were. The present time from which they came would cease to exist and if/ when they went back to said time. The person themselves would no longer exist instantly because if they killed themselves in the past, they would never be able to go back in time in the future in the first place. Well anyways time travel is too complicated to ever exist.

  75. Anonymous July 11, 2009 at 8:49 pm #

    theory one: since what has happened in the past has already happened you would not change anything if you went back in time because if you do go back in time then you already did go back in time and everything is still the way it is/was. My point being that when and if time travel is possible no one will change anything because everything is the way it is. So if you understand my first theory then you realise that no one who will be able to kill hitler by going back in time will because we all know that Hitler existed thus no one killed him.
    theory two: if going back in time could alter our reality we wouldn’t notice because we would have lived our lives with the memories of how things were changed.
    theory three: there is an infinite amount of time lines containing every single possibility ever and if you go back in time and mess something up you will end up in a different time line.

    Great comic by the way it represents a funny loophole in the idea of time travel

  76. Anonymous July 11, 2009 at 8:45 pm #

    I’ve heard you can travel forward in time. Travel away from earth for 5 years in a ship that approaches the speed of light. Turn around and come back at the same speed. You will have aged 10 years, but the earth will have aged about 1000.

  77. Anonymous July 11, 2009 at 8:30 pm #

    We can´t go back in time, because if we did our body would crash into our previous body that was already there. Take object A1, going back to where object A2 already stands, exists. Object A1 would certainly hit A2. This is another paradox of traveling back in time.

  78. Anonymous July 11, 2009 at 8:18 pm #

    Quite simple solution when wormholes are used though. If you think of it in a sense of a tunnel you travel through that crosses space/time, then the ends of the worm hole would be created in a time/space suitable for human life.

  79. Anonymous July 11, 2009 at 8:11 pm #

    Ya… why wouldn’t one? Well, the simple answer is because time travel (as much as I wish it would) will never happen and never happens.

  80. Anonymous July 11, 2009 at 8:07 pm #

    I kinda get it.

    So, why did we have to end up with this version of events dang it! (I don’t expect an answer, of course :)

  81. Anonymous July 11, 2009 at 7:40 pm #

    there would be motive until you went back in time and killed baby hitler.

    then the paradox happens.

  82. Anonymous July 11, 2009 at 7:39 pm #

    If we did build a time machine we could only go back to the day it was built. Because where would you pop up?

  83. Anonymous July 11, 2009 at 7:38 pm #

    the problem with ‘computers’ solving the issues… well that is not totally correct.

    the big problem is, there is no Universal Constant. expand the idea, the solar system is moving.. the galaxy is moving… the universe is expanding..

    where is the single point in space, that you could pinpoint WHERE the earth would be in the future or past.

    IF time travel is possible, you would also have to travel through space. and think on how far the galaxy travels in 1 hour, let alone how fast the universe is expanding….

    that is the true problem of time travel. “where are we”

  84. Anonymous July 11, 2009 at 7:31 pm #

    But if Hitler was aborted, there would be no motive to abort the fascist dictator, as he never existed. He would never take Europe hostage, never start the holocaust, and most importantly, never do anything that anyone would want him dead for, as he was never born.

    As for traveling back in time and striking oneself; you would have the memory of being struck by your future self, again, removing the motive for time travel, which in turn, removes the memory of being struck.

    Backwards time travel is impossible. Fun to think about though.

  85. Anonymous July 11, 2009 at 7:20 pm #

    i thought about this a while back. My physics-geek best friend said it all depends on your frame of reference.

  86. Anonymous July 11, 2009 at 7:15 pm #

    If we could travel through time, Hitler would have been aborted.

    Plus, I would have come back in time to slap me in the head for being stupid…

    It’ll never happen.

  87. Anonymous July 11, 2009 at 6:55 pm #

    I’ve been saying this for years! I always told myself that it was corrected for by the time travel process itself, like some sort of magnetic thing, or a linking of the machine’s locations, or whatever the hell flimsy excuse.

    It’s like saying “A phaser doesn’t work like that!”

    How the hell do we know? Ultimately.

  88. Anonymous July 11, 2009 at 5:54 pm #

    i think computers can work these things out these days haha

  89. Anonymous July 11, 2009 at 5:53 pm #

    beautiful strip

  90. Anonymous July 11, 2009 at 5:37 pm #

    Me too!

    See, time travel is harder than it looks.

  91. Anonymous July 11, 2009 at 5:17 pm #

    because then we’d be friends

  92. Anonymous July 11, 2009 at 5:10 pm #

    That’s a really good point that I don’t think I would have thought of in a million years. Great post.

  93. Anonymous July 11, 2009 at 4:59 pm #

    The Doctor has solved this problem.

  94. Anonymous July 14, 2009 at 7:25 am #

    Think of “Back to the Future,” where Doc Brown talks of causing perceivable “time” to “skew off into an alternate tangent,” by traveling back in time. At the very moment you kill your grandfather, you’ve created (in a sense) a parallel universe in which you, consequently, don’t exist. This is a hypothetical version of you that may or may not exist in an infinite number of parallel universes that all exist simultaneously.
    So, the original “you” still exists, because you originated in a universe where your grandfather was NOT killed.

  95. MainFragger August 13, 2009 at 7:16 pm #

    What I am about to talk abouut is extremely unlikely to a rediculous degree. So keep in mind, this is strictly for explaining a potential how for the purpose of (hopefully) interesting discussion.

    I have heard talk about how the universe expands and contracts. And supposedly, once it contracts it explodes out again and restarts the universe. Now… If we suppose that everything happens mostly the same each time. Then we should be reborn every time the universe is reborn.

    Now, a further discussion on this expanding and contracting universe is that the force of the contraction and the follow up explosion is so powerful, that it actually stretches back in time and further into the future each time the process starts over. So theoretically, however the universe was originally created, is now replaced with an earlier creation of the universe. (which so far is just another big bang). Assuming this is the case, we have NO idea how many times this has already happened.

    Now..If you kill your grandfather in the past, you WILL cease to exist. BUT when the universe recreates itself, there is a chance you will not decide to go back and kill him, so you will continue to exist. You just won’t know that that is the route you took to get there.

    So that is idea one.

    Of course we know about Schroedinger’s box…
    My other idea is that if the universe has defenses against such things from happening, then that defence might be as simple as switching your probability track. In other words, assuming there is a good, neutral, and evil path to every decision when you choose an evil path that was not your original path, you are not creating a new path, you are choosing a different one that exists at the same time. But in order to keep you alive, the universe might choose to route you back to the good path of probability. That way, even though you killied your grandparent, you swtiched to a reality in which they didn’t die or you never tried to kill them and somehow they made it long enough to have your parents. The thing is, we tend to think of that time line as coincidental, but it doesn’t have to be completely coincidental. For example.. In time line “A” your parents were born in 1955, you kill your grandparent in 1950…you should cease to exist..but instead, reality finds a timeline in which your grandparents gave birth to your parents even earlier than 1950, so now you can continue to exist. You are no long part of timeline “A” you are now on a totally different timeline. You might even be a figment of our imagination if you had originally started in our probabilty and now got switched over. But you will be as real to you as we are to ourselves, and its anyone’s guess how many of the people you have met in your life will now be met in your new reality.


  96. Anonymous July 13, 2009 at 4:09 am #

    if u had a time machine u wouldnt tell anyone would u

  97. Anonymous July 13, 2009 at 4:05 am #

    what and u have

  98. Anonymous July 16, 2009 at 3:03 am #

    Why do explanations of time travel paradox use killing of grandparents as an example.? If you went back to when your mother of father were small kids and killed them you wouldn’t be born. Even if only one parent died the surviving one’s offspring wouldn’t be you. DNA would be different and their life would be different enough to prevent your time travelling exploits. I think i’m correct !

  99. Anonymous July 15, 2009 at 5:46 am #

    Wouldn’t it be you already attempted to kill your grandafther… But then failed because you’re still alive? I’d think it would be impossible to change the past, because even before you built the time machine you would have already tried to kill your grandpappy.


    Star Trek.

  100. Anonymous person January 25, 2010 at 8:58 pm #

    Just because something has not been done it does not mean it is impossible. What you have just said is contradicted by many statements made with a similarity. (Ex: many people believed that the earth was flat – foolish – until someone with the guts actually sailed around the earth.) When someone long time ago introduced an idea that has never been heard of – like when Newton said there are forces like gravity constantly acting in the earth’s atmosphere – he/she will most likely be mocked unless proven true. Even now we are the “long time” past of our future and will prove what is right later. Even Newton was probably mocked by some people until he actually proved gravity with solid evidence. The truth is that people do not know if a subject like this is true at all. They usually make assumptions based on their fantasy and wishes for something like this to be true. One or NONE of the theories may be right. Most likely humans will not be able to control time traveling. We’ve yet barely made 2/3 successful patriot missiles. If time traveling was real and possible to create, the future would already have done so.

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