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Time Travel

  1. Nov 27, 2007 #1


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    Hello everyone,
    I am new to this forum and would greatly appreciate your expertise in answering (or attempting to) a few questions for me. I don't care if you focus on one or all of them, but any answers are appreciated! These are about time travel, with a focus on traveling BACK in time...

    1. Will time travel ever be possible?
    2. If so, how soon? Also, how far back would we be able to travel?
    3. Would our bodies be able to survive time travel?
    4. Would time travellers be able to communicate with other humans, or would they be on a seperate plane of time/dimension?
    5. Is it possible that spaceship sitings are time travel machines from the future?

    Also, if anyone can answer #4 (at least in theory), I'd be grateful.
  2. jcsd
  3. Nov 27, 2007 #2


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    1. Hopefully not (too much power corrupts). Imagine Neo-Nazi travelling back through time & warning Hitler not to attack Russia.
    5. Spaceship Sightings are Fake and no, Humans tend the screw up and make mistakes and we would know about it.
  4. Nov 27, 2007 #3


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    1) It is currently unknown if time travel is theoretically possible within the framework of General Relativity. This is currently an active research topic.

    2) and 3) can't be answered at all given that we don't have the theoretical issues fully resolved. (This is like asking someone who is trying to determine if something is even possible in principle "When is the product based on this idea going to ship to customers?).

    4) cannot be given a definite answer, but it seems highly unlikely.

    If the OP is primarily interested in 5), the best forum would be 'skepticism/debunking', and I'll move the thread there if the OP requests it. However, there will tend to be more information of UFO's and not so much information on time travel there, I think.
  5. Dec 9, 2007 #4


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    I was also wondering how certain most physicists are that wormholes do exist.

    I'm assuming if time travel were ever possible, and someone did visit this century, we of course wouln't know about it. I would think by that time the human race would have evolved at least enough to know that that would have an effect on their own place in time. If they were to announce, "Hey, we're from the future!" it would only serve to endanger their own lives.

    My main concern is the question as to whether time has already been altered (in other words, has any living creature already traveled back in time?). To me, the only way to be sure is to assume that time travel (no matter how far back) will one day (no matter how far in the future) be possible. Also, is it true that the future has already occurred? I assume this would mean that the past, present, and future are occurring simultaneously (correct me if I'm wrong)?
  6. Dec 9, 2007 #5


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    My main concern is whether time travelers would be on a seperate plane or dimension of time if travelling back. Thanks!
  7. Jan 13, 2008 #6
    I'm not a physicist but I will add my two cents worth. Time is nothing but change. In a
    static universe (without change) there would be no such thing as time. We measure time by comparing the rate of change of one process to another.

    As for time travel, to go back in time every change would have to be reversed. Since changes in the positive direction follow the principles of thermodynamics, going from high energy to low energy and from order to disorder, where would the energy come from to reverse all the changes? To go back in time every change in the whole universe would have to be reversed. It would take an all powerful God could accomplish that. Time travel sounds pretty far fetched to me.

    There are some theories of how the universe works that would allow time travel, the one which specifically comes to mind is the proposal that there is no change in the universe, motion is an illusion. The author (whose name I don't remember) states that the universe is controlled by a gigantic wave function that describes the position of every particle in the universe, and the "now" runs through this wave function taking the most probable course. In this view of the universe it is only the "now" that moves.

    There would still be the problem of energy. The most probable course would still follow the laws of thermodynamics, so for the "now" to retreat from one spot in the wave function to an earlier state, it would still take energy to reduce the entropy to the earlier state.
  8. Jan 13, 2008 #7


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    If time is an illusion and is a function of distance, and is relative, why would everything in the universe need to be revsered for one time traveller?
  9. Jan 13, 2008 #8


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    Where do you get the idea that time is an illusion? It most certainly is not.
  10. Jan 15, 2008 #9
    time is not an illusion einstein said that gravity is described as the wraping of space and time near an object with mass the more gravity the more wraping of space and time
    so you could say that that gravity and time are pretty much related
  11. Jan 15, 2008 #10
    Time, space, energy, velocity, mass, force, wave function, etc...

    All these concepts are variables in equations. You can take one of several subsets of these and call them "independent" or "real" and the rest will be "dependent" on that subset, or "illusions." So which ones are "real" and which ones are "illusions?" Who's to say? Maybe none are real...
  12. Jan 15, 2008 #11


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    Staff: Mentor

    No. You are misusing those words. Just because something is variable or relative does not mean it is not real.
  13. Jan 15, 2008 #12
    I don't understand what you mean... The concept of travelling back in time is to travel to a time that has already been in the timetravelers life (or before that). So why should it be another dimension of time (Whatever that is..) or a seperate plane? Or are you asking whether one will be in the past "at the same time" as the dear beloved ones left i the "now" - like there being two sets of time or something?

    If that's the case: The discriptions of time machines which I've read about are dealing with the same spacetime as the one we are in now - just different places at a different time.

    These time travel machines were based on theories on black holes or tunnels between different parts of space/time. They needed so enormeous amounts of energy in order to create the right circumstances that it is unlikely it'll ever work and also unlikely anybody will be able to experiment with such a construction in our lifetime.
  14. Jan 15, 2008 #13
    Ok,so what's your definition, Morpheus? :)
  15. Jan 15, 2008 #14
    Ok if you could go back in time I don’t think you could change anything think about it if you wanted to change something so bad that you went back in time to do then in the future it would be fixed and you wouldn’t have to go back in fix it there for ether not altering the future of undoing existence as we know it
  16. Jan 15, 2008 #15

    Ok if you could go back in time I don’t think you could change anything think about it if you wanted to change something so bad that you went back in time to do then in the future it would be fixed and you wouldn’t have to go back in fix it there for ether not altering the future of undoing existence as we know it

    and time is a Time is a diminution but also just a word

    I have more info that is more scientific but may I ask why you want to know this
  17. Jan 22, 2008 #16
    I agree. If you come back to now from the future, anything you do now "was" part of the history in the future you left.

    I find it very strange what the nature of time is. I never much believed the idea of time being a result of change. I think time must have to do with interaction between energies. Otherwise why would it pass differently depending on the field of gravity and the velocity.
  18. Jan 22, 2008 #17
    E = m * c^2.

    Did any of you read The future of time(2006). A good place to start. Many questions were approached realistically, by a number of the world's leading physicists!

    Hawking gave a decent description of what would have been entailed to make time travel a realism. I think some Mathmatics was used, but I cannot remember exactly. Sorry if I am off topic, just thought that book containing relevant material might help. :approve:
  19. Jan 23, 2008 #18
    you say that to be able to go back in time all changes must be reversed....if this could be done or if this actually happens naturally then, or rather, therefor they are also changes ...these new ''reversed'' changes are also processes with a rate of change one respect to another...so i'm sure this would not conclude in travelling backwards in time.
    your idea of all movement , which is a change from one state to another and the time this change takes to become something else is i understand being studied here in spain...i saw this on a science programm a few months after i was working on this issue myself....
    the idea being that ''time is unity or of value one'' always for the whole cosmos.
    this means that all processes will always sum the same one for the whole cosmos.
    its a bit dificult to explain...maybe somewhere i can get some more info....

  20. Jan 27, 2008 #19
    hypothesis that one where to somehow travel between two different planes of time/space. If all planes are relative to each other but not necessarily traveling at the same speed, then after making this transition and say waiting a week and then travelling back to the original plane you would enter at a time relative to the plane you just left. Unless both planes in this equation were traveling at the same precise speed then you would have gone back in time relative to both planes.
  21. Feb 3, 2008 #20
    Would every change need to be reversed?

    I haven't been on the forum until now, but your question of why reversal of time requires every change to be reversed requires an answer.

    If you assume that only certain changes would have to be reversed, who would decide which ones to be reversed? To truely go back in time, you would have to find everything as it was at the earlier date. If it were not, then how could one really say that they had gone back in time?

    To go back in time the past must still exist. We cannot experience anything that doesn't exist except in our minds (memories?). Time travel necessarily assumes a theory of the universe (or infinite universes) that allows the past to exist. If it still exists, all changes would of necessity be reversed.

    To travel to the future would require a deterministic view of all change. By that I mean any future state could be determined if the present state were known. While classical mechanics would allow this, quantum mechanics has eliminated the deterministic view of change.
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