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Time Travel Yeah I know! maybe some parallel universe talk too!

  1. Jun 10, 2006 #1
    Ok...I know there have been tons of threads on this, but I would like to hear some opinions on this. So, after reading and reading about this I have learned that there are tons of theories and reasoning as to why it is possible, but what I really want to know is what all of your opinions are about this. All so I would like to know your thoughts on the lacing of this in with parallel universe theory, and your opinions about the validity of parallel universes.
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  3. Jun 10, 2006 #2

    Andrew Mason

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    Are you asking whether Special Relativity and its prediction of time dilation is true? Or are you asking whether it will be technologically possible for a person to experience significant time dilation by travelling at relativistic speeds?

  4. Jun 10, 2006 #3
    My favorite among all the time travel devices we could construct is the Tipler Cylinder:

    Mostly because, even though it would be incredibly difficult to build, it provides a way to travel backwards in time without violating ANY laws of physics (At least to my understanding).
  5. Jun 11, 2006 #4


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    Tipler's paper was groundbreaking at the time, but it inspired further research to show that it won't work, at least with a finite cylinder. (Note that the math in Tipler's paper was for an infinite cylinder, as that case was easier to analyze).

    Specifically, as Steve Carlip says:

    So you need either an infinite cylinder, or some sort of exotic matter (which violates the weak energy condition).

    It appears that it may be possible to violate the weak energy condition, however.
  6. Jun 11, 2006 #5


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    I think that any answer to this would have to be highly speculative.
  7. Jun 11, 2006 #6
    I am asking, if you think that it is theoretically possible to travel through time, and if so, how you think this goes along with parallel universe theory?
  8. Jun 11, 2006 #7


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    Certain classical solutions to Einstein's equations suggested that closed timelike curves (commonly called time-travel) could exist, i.e. would not be inconsistent with Einstein's equations.

    At this point, quantum mechanics hasn't entered the picture at all.

    Sometime after this, I think, partially due to the science fiction movie contact, wormholes were hypothesized.

    It was soon realized that wormholes, if they existed, could be turned into time-machines. This is a bit more user friendly than the CTC's - with a wormhole turned time-machine, a person could just step through the wormhole and travel into his past, or future.

    Here, interestingly enough, quantum mechanics seems to act to make time travel more difficult, perhaps even impossible. "Quantum vacuum fluctuations" would tend to act to close any wormholes that were on the verge of becoming time machines.

    The situation is unclear enough that is hard to make any definitive statements. I don't think time travel can be totally ruled out at this point, nor can it be said with a certanity that it's possible.

    As far as "parallel universes" and quantum mechanics go, I would try the QM forums. Quantum mechanics doesn't necessarily imply "parallel universes", at least in the usual sense. There is quite a bit of debate about that topic, too.
  9. Jun 12, 2006 #8
    If we view the spacetime continuum as a static object through which we pass then theoretically past, present and future all exist at the same time. If the past and future exist in concert with the present then there is no reason that we should not expect to be able to move from one part of time to another.
  10. Jun 13, 2006 #9


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    On the other hand, if we vew time from the point of cause / effect, time travel gets to be very confusing.

    Some primitive versions of the grandfather paradox involving billiard balls havea been discusssed in the literature and shown to not create logical paradoxes.

    see for instance http://www.pbs.org/wgbh/nova/transcripts/2612time.html

    So this leads to one possilbe resolution of the issues with time travel and causality. Interestingly enough, there can be more than one possible solution for classical billiard balls when a time machine is introduced - the intial conditions do not necessarily pre-determine the outcome anymore.

    A good semi-popular source for this information is Kip Thorne's excellent book "Black Holes and Time Warps: Einstein's outrageous legacy".

    I believe some work has been done with replacing the classical billiard balls with quantum particles.

    Google finds a aource of somewhat unknown provenance, though it is an .edu site and it appears to make sense:

    http://www.isr.umd.edu/Labs/CSSL/simonlab/pubs/physics_world_ctcs.pdf [Broken]

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  11. Jun 13, 2006 #10

    George Jones

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    From looking at the Publications link at


    it seems that this paper was published in Physics World, which is roughly the British equivalent of Physics Today, and that this guy was a very serious researcher in relativity before experiencing a major change in research direction somewhere along his timelike worldline.
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  12. Jun 13, 2006 #11
    Time travel is easy. I do it all the time. But not backwards time travel. Can't be done. Nope. And anyhow, there isn't really any time. All this stuff like time and past and future is just a bunch of concepts to do with measuring motion. And you can't move a negative distance...

    Oh, Lordy me! Negative velocity:

    Last edited: Jun 13, 2006
  13. Jun 14, 2006 #12
    Here's something about Time that I found on the internet. I share the sentiment that time is not something real, it's like heat in that it's a "derived effect".

    http://www.beotel.yu/~mmalovic/newtime.htm [Broken]

    "So we build an instrument to do the simple task of demonstrating a standard uniform motion, and we cause this instrument to record its accruing motion in some manner, which we calibrate to mimic the Earth's rotation. Since this instrument accomplishes no other task, but to move uniformly, we call it a clock and say it is measuring time. We then declare this TIME, that we claim to be measuring, to be a universal property of nature and a separate dimension. We are violating Occam's razor, because we are inventing a TIME concept that is unnecessary and confusing. Our motion-clock is not measuring Time; rather it is measuring Motion, its own Motion."
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  14. Jun 14, 2006 #13
    Here is a time machine i built earlier...


    Its a little slow, but it is a comfotable ride.
  15. Jun 14, 2006 #14


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    This appears to me to be a crank website. The quote isn't the crankiest thing I've seen on time, it's not even the crankiest thing on the website....

    Given the direction that this thread is moving, I was thinking that it could perhaps find a better home in the PF lounge. While relativity does have a few things to say about time travel that are in the peer-reviewed literature, the responses and the OP's question do not seem to be focused around the technical papers.
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  16. Jun 14, 2006 #15


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    Thanks to pervect for bringing it up. I will caution everyone involved to please remember our guidelines. Please do not make any references to some dubious website to support whatever it is you are trying to present. This is not acceptable as a valid citation. If you cannot cite something that is based on accepted physics, or peer-reviewed publications, then don't!

    If anyone wishes to deal with some untested or unproven ideas, you are welcome to submit it to the IR forum. I will leave this thread here for the moment. However, if it starts going south again, it will be the end of it. So all of you decide the fate of this thread.

  17. Jun 14, 2006 #16
    Pervect: I would be grateful if you could point out what's cranky about the website I linked to. Apologies in advance.
  18. Jun 20, 2006 #17
    You may want to have a peek at my thought experiment thread https://www.physicsforums.com/showthread.php?t=124037"

    I believe its one of the first theoretically plausible means of 'universe travel'. Though I'm still ironing out issues (which is why I joined here).

    The idea is basically, if you surround a traveller with event horizon, without the traveller ever passing through it, the only option left, is that the traveller emerges in a different universe. Your more than welcome over on the hollow spherical blackhole thread. :smile:
    Last edited by a moderator: Apr 22, 2017
  19. Jun 21, 2006 #18
    Perhaps slightly aligned towards philosophy, but relevant nevertheless...

    Well, I didn't quite read the whole text, but the parts I did read, it didn't seem to cross the line IMHO. Although the article was somewhat badly written, he didn't seem to be talking about any alternative model to relativity at all (QUOTE: "my notions about time may have little or no impact on today's science").

    Rather he seemed to be merely talking about the very important philosophical notion that there is no metaphysical sense in time, which I think is a relevant notion to OP. This is not some testable claim, it is a simple fact that we only observe motion, and we derive time by comparing the motion of one physical thing to the motion of another physical thing.

    That we use the concept of time in our mathematical and semantical models of reality has no metaphysical meaning to reality itself. For reality to exist, it doesn't require any metaphysical "fabric/dimension" of time to exist.

    Perhaps people were put off by the claim "time dilation is as much a fantasy as time itself." I didn't interpret this as a claim to invalidate relativity or to claim time dilation has not been observed, but rather as an assertion that the observation of time dilation is not an observation of the time dimension, but an observation of physical motion.

    Some may say this is not science but a philosophy, but the matter of the fact is that this is very, very important notion to the philosophy of science and objective thinking overall. It is important to understand that reality is not "like" the spacetime graph we use to understand it.

    In fact, the popular claim that time dimension exists in reality as it does in 4D block of spacetime (where nothing moves), is immediately problematic in a philosophical sense, because metaphysically, the only thing we know to exist for certain, is our conscious experience, and we know that in our experience there exists motion, and such experience has to have a physical cause one way or another. Such physical cause is not offered in the block time interpretation of relativity at all. In short, it must be the objective physical reality that causes our subjective experience of reality, and if our subjective experience is really caused by the motion in our brain, there must in fact exist motion in a metaphysical sense.

    Or to suppose that time dimension metaphysically exists, and there is a metaphysical flow/motion to this dimension, is also philosophically problematic because this motion would be self-referential. Motion requires time, and for time dimension to flow, there would need to be another time dimension to allow the motion to the flow. Any such infinite regress is always caused by a naive model of reality where semantical ideas are thought to really exist as fundamentals (spirit/soul, language, math, thoughts...).

    This should in fact prove that time is not a dimension in a metaphysical sense, and that makes no claim whatsoever about the validity of the mathematical framework of relativity.
  20. Jun 21, 2006 #19
    I also had a related question of my own;

    I understand that there has been teleportation experiments with quantum particles. How/why is it that no information can be passed through this way faster than C? (I suppose this to be so, because otherwise it would be immediately quite trivial to send messages to the past or to the future, if relativity is true and the past and the future do in fact exist in some metaphysical sense)

  21. Jul 22, 2006 #20
    I read all of this article and I must say the guy who wrote this definitley has a realistic view of things. Especially time. Time doesn't exist. We humans made it based on the rotation of the earth. What time really is, is just MOTION and the measurement of it.

    There is simply no physically possible way to travel "back in time." Science fiction my friends!!!

    Although ONE thing I don't understand is, for example. I am in a space ship traveling 99 percent c, and come back to earth, why has my twin aged 7 years faster than I have?? Again, years is a measurement of motion according to the article, but I am comparing the biological processes of the human body. Why is it that motion changes biological clocks so to speak? This is all very hard to visualize.
    Last edited by a moderator: May 2, 2017
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