# Time travel to the past is not possible **URL:** \ **Category:** Great Debates\ **Created:** [February 29, 2008, 8:09am UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621 "2008-02-29T08:09:59Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![begbert2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/begbert2/32/3357_2.png) [@begbert2](https://boards.straightdope.com/u/begbert2)\ **Post date:** [February 29, 2008, 6:40pm UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621/41 "2008-02-29T18:40:07Z")
[QUOTE=Polerius] What exactly is metatime? [/QUOTE] Time outside the scope of the time we percieve. Like, the universe is a space-time continuum, with its time contained within it; however, how can we know that the universe itself doesn’t exist within a larger arena, with its own time, that we cannot percieve because we are locked into our own time? Presumably, any entities (if any) existing in this outer sphere could observe active alterations to the ‘past’ part of our space-time continuum. An example of metatime would be our time’s relationship to the time in books and movies. A movie has its own time, but we can look at the whole thing independent of the movie’s time, because we have our own separate time framework. If we alter the ‘past’ of the movie, the in-movie universe and characters have no way of being aware of their “prior” state, but we outside of it can be so aware. (Not to say that there one single speck of evidence that there’re spheres of existence or time outside of our universe; I just find it odd that the OP presumes so firmly that there _isn’t_.) ---
**Author:** ![Polerius](https://avatars.discourse-cdn.com/v4/letter/p/d78d45/32.png) [@Polerius](https://boards.straightdope.com/u/Polerius)\ **Post date:** [February 29, 2008, 6:46pm UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621/42 "2008-02-29T18:46:26Z")
[QUOTE=Indistinguishable] Of course, outlawing time travel altogether imposes even _more_ constraints on where you can go and what you can do when you get there. 🙂 [/QUOTE] No, it only imposes restrictions on where you can go. Since you can’t go back, there are no restrictions on “what you can do when you get there”. Also, a blanket restriction seems more reasonable than a very narrow restriction. It would be like building a space-travel machine (e.g. a spaceship) from some new materials, and saying that you can only use it to travel to a particular street in Rome, and nowhere else. It would be strange for the laws of physics to be so precise on where they allow you to travel. It would make sense that your new space travel machine either works (and you can go anywhere), or doesn’t work at all. > [@](#): > > Incidentally, though only **begbert2** can speak for himself, my assumption would be that “metatime” is supposed to be like a second dimension of time; for example, rather than just locating events in spacetime with a single temporal coordinate, we can imagine there to be both a time and a, let’s say, “sime” axis. For example, if one were to “change the past”, the way this would be realized would be saying things like that at time-my-birthday-1995 and sime-16, I wore a red shirt, while at time-my-birthday-1995 and sime-17, I wore a blue shirt. (I.e., changing the shirt I wore on my birthday took one year of sime, but, of course, was entirely localized to just one moment in time). Interesting idea. Any hints that this second temporal coordinate exists? ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [February 29, 2008, 6:46pm UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621/43 "2008-02-29T18:46:38Z")
[QUOTE=Polerius] There are a _lot_ of things you did not do in 1995, so if time travel to 1995 were possible, you could go back to 1995, but could not do any of those things. But how would that be possible? You find yourself back in 1995 but something is somehow preventing you from opening a pie shop or meeting your former self? How would that work? [/QUOTE] I think the idea of most time travel scenarios, is that your older self would exist _as another person_ from your self that exists in his own proper time. There would be two Polerii running around. I’m actually posting this after having read through post #75 on this thread, but I wanted to post a comment as post number 43, so I traveled back in time and am posting it now. Of course, I had to get my younger self away from the keyboard for a few minutes. And y’all are going to be _very_ interested in post #57. Veeeerrrrry interested. I don’t think my life will ever be the same. ---
**Author:** ![the\_PC\_apeman](https://avatars.discourse-cdn.com/v4/letter/t/ac8455/32.png) [@the\_PC\_apeman](https://boards.straightdope.com/u/the_PC_apeman)\ **Post date:** [February 29, 2008, 6:57pm UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621/44 "2008-02-29T18:57:20Z")
[QUOTE=CurtC] I think the idea of most time travel scenarios, is that your older self would exist _as another person_ from your self that exists in his own proper time. There would be two Polerii running around. I’m actually posting this after having read through post #75 on this thread, but I wanted to post a comment as post number 43, so I traveled back in time and am posting it now. Of course, I had to get my younger self away from the keyboard for a few minutes. And y’all are going to be _very_ interested in post #57. Veeeerrrrry interested. I don’t think my life will ever be the same. [/QUOTE] Sock alarm! Sock alarm! ---
**Author:** ![begbert2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/begbert2/32/3357_2.png) [@begbert2](https://boards.straightdope.com/u/begbert2)\ **Post date:** [February 29, 2008, 7:02pm UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621/45 "2008-02-29T19:02:17Z")
[QUOTE=the PC apeman] Sock alarm! Sock alarm! [/QUOTE] No, see, a sock is when one person is using two logins. In this case, two(?) people are using _one_ login, so it’s not anything like a sock. It’s the _opposite_ of a sock. (I propose the term “mitten”.) (afterthought on edit: we don’t consider it mittenning when an older version of a person posts to the same account if they do it the right amount _later_, so I don’t see why it should be mittenning if they do it a little off-schedule. So, his time-travel self is neither a sock _or_ a mitten, by my thinking.) ---
**Author:** ![the\_PC\_apeman](https://avatars.discourse-cdn.com/v4/letter/t/ac8455/32.png) [@the\_PC\_apeman](https://boards.straightdope.com/u/the_PC_apeman)\ **Post date:** [February 29, 2008, 7:04pm UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621/46 "2008-02-29T19:04:01Z")
Good point. Mitten alarm! Mitten alarm! 😉 ---
**Author:** ![the\_PC\_apeman](https://avatars.discourse-cdn.com/v4/letter/t/ac8455/32.png) [@the\_PC\_apeman](https://boards.straightdope.com/u/the_PC_apeman)\ **Post date:** [February 29, 2008, 7:14pm UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621/47 "2008-02-29T19:14:13Z")
Ah but we have two entities that are free to act independently [del]here[/del] now… in effect two personas using one account. There’s no guarantee that the one will eventually become the other. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [February 29, 2008, 7:21pm UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621/48 "2008-02-29T19:21:15Z")
> [@](#): > > No, see, a sock is when one person is using two logins. In this case, two(?) people are using one login, so it’s not anything like a sock. It’s the opposite of a sock. > > (I propose the term “mitten”.) > > (afterthought on edit: we don’t consider it mittenning when an older version of a person posts to the same account if they do it the right amount later, so I don’t see why it should be mittenning if they do it a little off-schedule. So, his time-travel self is neither a sock or a mitten, by my thinking.) Can’t you get in trouble doing that? ---
**Author:** ![begbert2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/begbert2/32/3357_2.png) [@begbert2](https://boards.straightdope.com/u/begbert2)\ **Post date:** [February 29, 2008, 7:28pm UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621/49 "2008-02-29T19:28:19Z")
[QUOTE=the PC apeman] Ah but we have two entities that are free to act independently [del]here[/del] now… in effect two personas using one account. There’s no guarantee that the one will eventually become the other. [/QUOTE] But regardless of whether the younger **CurtC** ever becomes the older one, the older **CurtC** definitely _was_ the younger one. So, at worst he’s only half a mitten; (say, two fingers and half a thumb), and that’s _only_ if the younger version doesn’t in fact become the older version at some point. (Ain’t time-travel great?) ---
**Author:** ![XT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/xt/32/456_2.png) [@XT](https://boards.straightdope.com/u/XT)\ **Post date:** [February 29, 2008, 7:35pm UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621/50 "2008-02-29T19:35:24Z")
Put me in the many worlds crowd as well. I think time travel is not impossible by our currently understood physics (though it makes a lot of my physics major friends a bit nervous sometimes). Myself, I think that if one does travel back in time it essentially creates a new universe or branching that diverges from our own universe/time stream. -XT ---
**Author:** ![gonzomax](https://avatars.discourse-cdn.com/v4/letter/g/e8c25b/32.png) [@gonzomax](https://boards.straightdope.com/u/gonzomax)\ **Post date:** [February 29, 2008, 8:37pm UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621/51 "2008-02-29T20:37:22Z")
Is someone 100 light years away and observing us looking at us from 1908. Is that is the same events 100 years apart occurring simultaneously. Is it the action or the observer. ---
**Author:** ![XT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/xt/32/456_2.png) [@XT](https://boards.straightdope.com/u/XT)\ **Post date:** [February 29, 2008, 8:41pm UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621/52 "2008-02-29T20:41:55Z")
If someone is 100 light years away and has powerful enough observation equipment they could indeed be observing the Earth as it was in 1908. Same as our own observation of stellar objects allows us to view them as they were in the past…not as they are today. That isn’t exactly the same things as time travel though as they are essentially just observing events with no way to effect them. If they have the technology to bore a hole through space to the Earth they will find…us, here in 2008. Not the Earth as it was in 1908. -XT ---
**Author:** ![the\_PC\_apeman](https://avatars.discourse-cdn.com/v4/letter/t/ac8455/32.png) [@the\_PC\_apeman](https://boards.straightdope.com/u/the_PC_apeman)\ **Post date:** [February 29, 2008, 8:44pm UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621/53 "2008-02-29T20:44:29Z")
Someone observing us from 100 light years away is merely collecting and processing 100-year old photons. It’s not much different than us viewing 100 year old photographs of ourselves. ---
**Author:** ![XT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/xt/32/456_2.png) [@XT](https://boards.straightdope.com/u/XT)\ **Post date:** [February 29, 2008, 8:52pm UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621/54 "2008-02-29T20:52:08Z")
Or early motion pictures. -XT ---
**Author:** ![AHunter3](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ahunter3/32/368_2.png) [@AHunter3](https://boards.straightdope.com/u/AHunter3)\ **Post date:** [February 29, 2008, 9:29pm UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621/55 "2008-02-29T21:29:06Z")
My problem with time travel is as follows: a) Time is a coordinate just as the spatial coordinates are coordinates. b) At a certain longitude and latitude and elevation and time, some certain thing exists. You can “travel” on any of the four coordinates and thereby “go” somewhere else but any combo of all four coordinates brings up a specific reality. What’s there is there. c) Inverting that understanding, we can think of “you” as an object extending through four-dimensional spacetime. Just like a block of wood exists from here to there and over to here and stops there, you, too, have “edges”. You are (or were) here in this space at this time, and here in this other space at this other time. You are where you are. You aren’t where you aren’t. d) For you to “go” back in time and (also) “be” in a place where you “were” not means that we have redefined “you”. A different set of coordinates have been added to the definition where previously you were not. If “previously” has any meaning here. Which it does not. What you’re describing is a state of paradox. “You” can’t “were not in Tulsa Oklahoma on July 3 1848” and also “were, too, in Tulsa Oklahome on July 3 1848” as equally valid components of that which defines “you”. e) And if you “were there”, then part of your “coordinates” can be expressed as “these were the thoughts that were passing through your mind, your emotional state, sensory impressions, and other relevant mental processes”. So to “go back” to a coordinate that is indeed part of “you” simply means to reference a coordinate in four dimensional spacetime, at which point you had thoughts and experiences etc that go with that part of “you”. Whereas if you “were not there” you also “are not there”, see above about paradox. In short, it’s a nonsensical formulation akin to “What would it be like for a 2 kilogram object to be 500 kilograms?” or “The next time you’re totally unconscious, please make a note of it and where you are and what time of day it happened”. ---
**Author:** ![msmith537](https://avatars.discourse-cdn.com/v4/letter/m/d9b06d/32.png) [@msmith537](https://boards.straightdope.com/u/msmith537)\ **Post date:** [February 29, 2008, 9:32pm UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621/56 "2008-02-29T21:32:46Z")
> [@Polerius](#): > > e.g. with special relativity theory, which has been experimentally verified, you can essentially time travel to the future if you go close to the speed of light. I don’t think it’s so much that you are traveling to the future like it’s another place. It’s just that the rest of the universe is moving through time much faster than you are. And I’m not sure if I believe it’s possible to travel in the opposite direction. First of all, it would mean that 1995 has to exist somewhere. If so, where? String theory seems to predict additional dimensions beyond the ones we perceive. So maybe 1995 (as well as every other possible point in time) exists along those dimensions. Quite frankly, it’s a little hard to fathom as anything other than interesting artifacts left over from some physics equations. ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [February 29, 2008, 9:32pm UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621/57 "2008-02-29T21:32:51Z")
1. ---
**Author:** ![begbert2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/begbert2/32/3357_2.png) [@begbert2](https://boards.straightdope.com/u/begbert2)\ **Post date:** [February 29, 2008, 9:36pm UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621/58 "2008-02-29T21:36:46Z")
[QUOTE=AHunter3] My problem with time travel is as follows: a) Time is a coordinate just as the spatial coordinates are coordinates. b) At a certain longitude and latitude and elevation and time, some certain thing exists. You can “travel” on any of the four coordinates and thereby “go” somewhere else but any combo of all four coordinates brings up a specific reality. What’s there is there. c) Inverting that understanding, we can think of “you” as an object extending through four-dimensional spacetime. Just like a block of wood exists from here to there and over to here and stops there, you, too, have “edges”. You are (or were) here in this space at this time, and here in this other space at this other time. You are where you are. You aren’t where you aren’t. d) For you to “go” back in time and (also) “be” in a place where you “were” not means that we have redefined “you”. A different set of coordinates have been added to the definition where previously you were not. If “previously” has any meaning here. Which it does not. What you’re describing is a state of paradox. “You” can’t “were not in Tulsa Oklahoma on July 3 1848” and also “were, too, in Tulsa Oklahome on July 3 1848” as equally valid components of that which defines “you”. e) And if you “were there”, then part of your “coordinates” can be expressed as “these were the thoughts that were passing through your mind, your emotional state, sensory impressions, and other relevant mental processes”. So to “go back” to a coordinate that is indeed part of “you” simply means to reference a coordinate in four dimensional spacetime, at which point you had thoughts and experiences etc that go with that part of “you”. Whereas if you “were not there” you also “are not there”, see above about paradox. In short, it’s a nonsensical formulation akin to “What would it be like for a 2 kilogram object to be 500 kilograms?” or “The next time you’re totally unconscious, please make a note of it and where you are and what time of day it happened”. [/QUOTE] Your problem is with your definition of “you”; it’s too rigid to work with time travel. To solve all your problems, either relax your definition, or simply recognize that the “you” that travels into the past is not the same “you” that existed there previously; for practical purposes such as the ones you’re tripping over, you should think of them as being different people. Poof! All your conflicts vanish. ---
**Author:** ![ralph124c](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@ralph124c](https://boards.straightdope.com/u/ralph124c)\ **Post date:** [February 29, 2008, 10:19pm UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621/59 "2008-02-29T22:19:09Z")
…into the future! We ourselves contain atoms which were part of the bodies of people ages ago-i probably contain several million atoms, which once were part of julius caeser. If I were able to return to ca 30 BC-what would happen to me? Would I be part of Julius caeser? ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [February 29, 2008, 10:28pm UTC](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621/60 "2008-02-29T22:28:29Z")
It has been over 20 years ago that I read it in an anthology of Hugo award wining sci-fi short stories, so I can’t recall the author. Basically the author got around a lot of time travel paradoxes by postulating that time was “shaped” like a helix (a spring). The inventor in the story had a time machine that could hop between coils of the time helix, but not travel along them. The turns of the helix amounted to several million years…long enough that what you did in the past had pretty much zero chance of influencing the present. Certainly this is all speculative, but what about the notion of time travel isn’t? I only mention it to illustrate that what time IS is so poorly understood that it is difficult to even determine what false assumptions about it may be influancing our thinking. [Previous page](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621.md?page=2) [Next page](https://boards.straightdope.com/t/time-travel-to-the-past-is-not-possible/439621.md?page=4)