On Time Travel (for my 100th entry & 1 year anniversary on wordpress)

Having just gotten a notification from wordpress that I registered my blog a year ago today (though it looks like my first entry was published on the 12th) and seeing as I’m at 99 published entries, now seems a novel time to publish entry number 100, and to share some thoughts on time travel, as we are on the topic of time.

I was discussing the possibility of time travel with a friend the other day, and I brought up a pretty decisive point that a professor once shared with me. The idea is that time travel is logically impossible, because it entails that, if I went back in time to 1968 (a most interesting year, in my opinion, due to the civil rights movement, politics and music), stipulating that the population of New York City was 7,000,000, it would be the case that the population of NYC is 7,000,000 and the case that the population of NYC is not 7,000,000, it is 7,000,001. In other words, history is constituted of facts about what happened, and time travel involves contradicting those facts by making other facts the case.

To those who say that time travel changes the course of history, and that’s an understood consequence of time travel, I’d say you’re missing the point. Time travel movies and TV shows have the famous warning to characters not to interfere in events, lest they alter history. But this misses the point that their presence, whether detected or not, has changed facts about history, regardless of whether the consequences are noticeable upon their return. All that history is, in an important sense, is a collection of facts, so if one’s presence changes the facts of the time then it only makes sense that one has not actually gone to the year 1968. The point of all this is that time travel is inherently contradictory – we cannot travel back in time, to 1968 or elsewhere, but we can be taken into a simulation of what 1968 was like or an alternate reality of 1968, with everything identical save for the details and facts involving the time travelers. Whether actions in this simulation or alternate reality have far reaching consequences for present reality is another question altogether, and one best left to sci-fi films.

During that discussion I articulated another reason why time travel is contradictory, and it is this reason that I am eager to share today. In order to travel back in time it must be the case that time is not one-directional. This is a big assumption in itself and one that I think is useful to bring to the fore because it reveals how paradoxical time travel is. Let us imagine that in four years I create a time machine, and I go back to the year 1968. In order for it to be genuine “time travel” it will have to be said that it becomes a fact that I was alive in the year 1968. If it becomes a fact in four years that I was alive in 1968 then it is a fact right now that I was alive in 1968. But even stipulating that I do create a time machine and travel back in time to 1968 in the future it wouldn’t be a fact right now that I’ve been alive in 1968. I can’t actually go back in time to 1968 without it always being the case that I’ve been alive in 1968, but that seems false, as I would only have come to be alive in 1968 in 2018. So again, what this suggests is that traveling back in time to 1968 is impossible, and at most one can go to an alternate reality with a different course of history, and this is enough to avoid saying that I’ve ever been alive in “the real” 1968 and with it that I’ve always been alive in 1968.


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  1. #1 by SelfAwarePatterns on November 12, 2014 - 6:39 pm

    Congratulation on your anniversary! And on your 100th post! Nicely coordinated 🙂 I didn’t realize that we started around the same time.

    On time travel, in my mind, there are three possibilities:
    1. Time travel is impossible. Given the lack of tourists from the future, this seems the most likely scenario.
    2. Time travel is possible, but with limitations of some kind that prevents tourists from the future. Maybe it costs the mass of a million suns to send someone into the past. Or maybe it requires a time travel receiver at the destination.
    3. Time travel is possible, but humanity will be extinct too soon for there to be many, if any, tourists from the future.

    Some people will posit things like a Prime Directive of time, with all time travellers following a code not to interfere or at least not to reveal themselves. But the probability that this would be consistently adhered to by all members of all future societies seems infinitesimal.

    • #2 by ausomeawestin on November 12, 2014 - 10:39 pm

      Thanks, it worked out quite well, too strange of a coincidence to pass up on. Sorry I missed your one year mark, actually figured you’d been on here longer, given your extensive list of frequent commenters. I guess you just work harder (or better) than me; but that’s not surprising, cheers to you my friend! lol

      I like your three points. The latter part of point two had me cracking up. I’m imagining a flood of persons pouring out of the first time machine as soon as it turned on for the first time.

      Did you ever see the time travel film “Looper”? The most insightful idea of the movie (and don’t get me wrong, I did enjoy it) is the background that given the possibility of misuse, as soon as time travel was created it was outlawed, and so is only used by organized crime groups. This is one way of working with this Prime Direction of time idea, in a way that strikes me believable. As you say, though there is this prime directive, not all persons would adhere to it. (I also haven’t seen every time travel flic ever, thought I’ve seen a lot, so it might be that this point isn’t original; still I like it.)

      Your saying this makes me think that, in a way, the problem of time travel is sort of like the problem of evil for God. If God exists then why was there the holocaust? Likewise, if time travel is ever created in the future then why has the holocaust occurred?

      Thanks, as always, for your fascinating and thought-provoking comments. Until next time.

      • #3 by SelfAwarePatterns on November 13, 2014 - 9:56 am

        On commenters, it seems to fluctuate wildly over time. I’ve gone through long stretches where it seemed like hardly anyone was interested in commenting, and others where there’s lots of activity. I’ve given up trying to figure out what causes those swings and just try to plow through them and enjoy the conversations when they come.

        I did see Looper and enjoyed it. Although if I scrutinize it, some issues come out. What stops people from coming back to stop the assassinations? Or law enforcement from simply going back and stopping the whole enterprise? How are people conscious of the changes taking place in their timeline? I know, I know. Sometimes it’s just best to shut up and enjoy the movie 🙂

        I never thought about the problem of evil pertaining to time travel. Interesting. For me, it’s the Fermi paradox of time travel: where is everyone?

  2. #4 by bloggingisaresponsibility on November 13, 2014 - 8:59 am

    What if we assume time is an illusion, or rather, an abstraction? That is, there is only change. A “minute” is simply a word I use to “measure” the occurrence of a particular event (say the motion of a hand on a clock).

    If this is so, then time travel involves undoing all the changes that have accumulated until the “date” desired. That is, every particle must be restored to its previous state.

    What would it mean then for “me” to time travel? How do I undo all reality only for myself? How possible would it be to even do this, and how localized must this undoing be (planetary, galactic, universal?) Then there’s the question of whether I can even do this. Can I always predict the previous state given a current state? There are many systems where this is impossible (systems in which multiple states can give rise to the same next state, thus making reversion impossible).

    Just some thoughts.

    • #5 by ausomeawestin on November 13, 2014 - 8:52 pm

      Truly excellent points. Of course, the jury is still out on the nature of time, but I think you’re right that part of the essence of time is change, in that its passage is known through change. Looking at time this way is quite useful for seeing that genuine time travel would seem to involve the undoing of changes, not just being picked up and dropped into another time. The former seems far more implausible than the latter, and time travel begins to look altogether implausible.

      Thanks for sharing the interesting thoughts!

      • #6 by bloggingisaresponsibility on November 14, 2014 - 8:50 am

        Thank you. Another perspective is that time isn’t the change itself, but the “space” in which changes unfold, much like physical space is the “space” in which objects are located. Just as I can move forward or back to note other objects in physical space, then I can (theoretically) move forward or back in “time space'” to different events.

        This view seems to imply that everything that has or will happened, has already done so, and its only an an accident of our biology that prevents us from seeing it all. In this case, thinking of time as the 4th dimension really is informative.

        If that is the case, then it raises questions about our ability to actually affect time. But maybe the issue is deeper; in assuming I can move through time, I’m assuming I’m outside of time. But is this the case?

        When I observe a picture, the picture is out there, and I’m outside of the system looking in. Yet, what does it mean for an element of the picture to observe the picture itself?

        Ok, now my head hurts.

        I love your posts; really thought provoking stuff!

  3. #7 by ignacioggm on November 13, 2014 - 1:00 pm

    In the 80’s Kip Thorne a solution to Einstein’s relativistic equations that would allow one to “build” a kind of wormhole that, to differentiate it from your typical all-destructive wormhole, he denominated as “traversable wormhole”.

    In principle, such a space-time geometry would be stable, this is, it would not collapse due to runaway quantum effects, and could allow a time traveler to go through it without being completely obliterated. So far so good, however there is a catch, to make this kind of wormhole possible one needs to create (or find) some kind of “exotic matter” which, in contrast to normal matter, would possess negative mass-energy. Again, in principle, no one has proven that this kind of matter is prohibited by the laws of physics, but on the other hand, no one has a clear idea about how to create it, perhaps it is impossible in practice? Although phenomenons such as the Cassimir effect have been observed (where one can indeed produce regions of negative energy). In any case, it seems to be a rather big leap to go from a negative energy gap sandwiched between two metal plates to produce a spaceship made of exotic matter.

    Regarding some of the most common paradoxes and contradictions that time travel seems to arise, Kurt Gödel found that if one’s world line (the trajectory that an object defines in Minowskian space-time) could be regarded as “closed-loops” then one might completely avoid some of the most typical paradoxes.

    Sorry for the vagueness of this comment, but a more thorough review of the topic would indeed need one or several blog entries where a fairer discussion can be exposed.

    Anyway, I am always fascinated to discuss these issues. This entry seems like a very appropriate anniversary celebration. Congrats!

    • #8 by ausomeawestin on November 13, 2014 - 9:07 pm

      Thanks for the kind words and the stimulating comments. I follow you in regards to the idea of making a ship of negative mass-energy, but I’d be interesting in hearing more about how closed-loops resolve some paradoxes. I was sort of gesturing at the idea before that time travel requires that time can flow in more than one direction, and so looping around and coming up on the past event via a point further in the past might seem to do the trick. Still, I wonder how even this approach can resolve many time travel paradoxes if it still seems to require, at some point in the looping process, going backwards in time. I understand that this is a big topic, but perhaps I can hope for your writing a blog entry on the topic?


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