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Why can't we time travel in backward?

  1. Aug 21, 2011 #1
    Why can't we time travel in backward??

    Consider a person traveling in space (Straight road)
    O
    <|>
    /\
    _______________________________________________
    0 Km 12 Km
    He travels at 100 m/s and completes 12km in 2 minutes.

    Now plotting the time line
    O
    <|>
    /\
    _______________________________________________
    0 Seconds 120 seconds

    Here are my observations

    1) He loses 2 minute of his life
    2) Space "CHANGES" (moves forward or backward - the person can move 12 km in any direction) BUT time "ADVANCES" (can move only in forward direction)

    NOW....time and space travel are like lateral inversions yet symmetrical...its trivial as it is

    Thus, if we were to perform time travel, then
    Time "CHANGES" (moves forward or backward) BUT space "ADVANCES" (can move only in forward direction - which means we can go to the space in future, not in the past)
    Thus we cannot time travel backwards...


    This is my observation and I am just a degree student searching for research areas and I made this observation just now..I would like to take opinions from great brains and professionals
     
  2. jcsd
  3. Aug 21, 2011 #2

    Pengwuino

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    Re: Why can't we time travel in backward??

    Explain this statement, I don't understand what you're trying to say.

    Again, I don't understand what you're saying in the slightest.
     
  4. Aug 21, 2011 #3
    Re: Why can't we time travel in backward??

    NOW....time and space travel are like lateral inversions yet symmetrical...its trivial as it is

    What I meant by this is that time and space are the coordinates

    Thus, if we were to perform time travel, then
    Time "CHANGES" (moves forward or backward) BUT space "ADVANCES" (can move only in forward direction - which means we can go to the space in future, not in the past)
    Thus we cannot time travel backwards..

    Now this means that in normal travel time moves only in forward and space changes in any direction
    In time travel the reverse happens which means that space can move only in forward direction which is the future
     
  5. Aug 21, 2011 #4

    phinds

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    Re: Why can't we time travel in backward??

    Uh dude ... what direction is forward?

    I think the whole thing sounds like nonsense
     
  6. Aug 21, 2011 #5
    Re: Why can't we time travel in backward??

    Interesting idea.
     
  7. Aug 21, 2011 #6
    Re: Why can't we time travel in backward??

    Any direction..if we are traveling in space we can travel in any direction say east or west or south.
    And Yes it could be complete nonsense but please tell me which part sounds nonsense to you.
     
  8. Aug 21, 2011 #7

    BruceW

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    Re: Why can't we time travel in backward??

    To say time only moves in one direction is not specific. Why should it move in one direction? For example, if we're talking about billiard balls, then we can calculate the position of billiard balls at specific times, but there is nothing to say that time flows in one direction.

    There are 3 examples where time does flow in one direction, (According to a book I read by Paul Davies). These are:
    Thermodynamic - i.e. entropy always increases or stays the same with time
    Cosmological - because near the big bang, the universe had high density and since then, density has been decreasing.
    Psychological - we only remember the past, not the future.

    I'm not sure if Davies is right, but is your question about one of these? I think your question about the direction of time doesn't have a simple answer.
     
  9. Aug 21, 2011 #8
    Re: Why can't we time travel in backward??

    Nooo...that's not in my question but I like your point.

    Its like this
    In normal travel (like on car, walking) time increases(moves forward) and space changes.
    Which means that in time travel space can move in forward only i.e time travel into the future
     
  10. Aug 21, 2011 #9

    BruceW

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    Re: Why can't we time travel in backward??

    But the reason you say time travels forward when you are walking is because you remember your watch being at an earlier time, and you remember being at some other position at an earlier time.

    Your question looks like it is about the psychological arrow of time.

    If you imagine the person's path through spacetime, you could justify that either direction is forward through time (except for the arrows of time I mentioned before).
    Of course, if you define the direction of time, then all the people on earth would agree on the direction of time, since we share the same frame of reference.

    Special relativity does prohibit a circular path through spacetime (i.e. meeting up with your former self). Is this what you meant about time travel?
     
  11. Aug 21, 2011 #10

    Andrew Mason

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    Re: Why can't we time travel in backward??

    Start the analysis by asking the question: what does it mean to go back in time? I think it has to mean that the entire universe returns to a previous state and thereby erase all evidence of its present state. If some part of the universe does not return to a previous state, it could be used as a clock to show that time reversal had not occurred.

    In order to reverse time for even one millisecond, every particle in the universe would have to reverse its direction by exactly 180 degrees without losing any speed. The planets would all have to reverse direction to go back to where they were a millisecond before. Then the would have to reverse direction again so they would be moving in the direction they were moving one millisecond before. And, of course, no one could observe this time reversal because if they could, it would be evidence that time had not reversed.

    Let's look at it macroscopically using a thermodynamics approach. In order for the entire universe to return to a previous state, it would need to go through some form of thermodynamic process. Since moving from that previous state to the present it did not go through a reversible process, it will require that more useful work be done to return to that state than was generated in the forward thermodynamic process. So the universe's supply of low entropy sources have to be consumed (ie. the entropy of the universe has to increase). So, time really has not reversed.

    In short, time cannot be reversed because the universe is too complicated.

    AM
     
  12. Aug 21, 2011 #11

    phinds

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    Re: Why can't we time travel in backward??

    Let's just focus for a minute on my question about direction. The term "forward" has no meaning in physics. You have to specify spacial coordinates. How can you possibly specify "forward" as a general concept? I contend that you cannot. The word really only has meaning in human terms. If I'm walking South, that's forward for me, but that has no meaning in physics and to use it as the basic of a far-fetched theory seems particularly nonsensical.

    As something like playing with words, your concept is very clever but I don't see it having any possible bearing on reality.

    LATER ADDITION: by the way, I don't pretend to be an expert and I'm willing to be wrong in my point of view but I think I have it right.
     
    Last edited: Aug 21, 2011
  13. Aug 21, 2011 #12
    Re: Why can't we time travel in backward??

    So can we time travel to the future?? will that be more complicated???
     
  14. Aug 22, 2011 #13

    SteamKing

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    Re: Why can't we time travel in backward??

    We time travel to the future a day at a time, every day.
     
  15. Aug 22, 2011 #14
    Re: Why can't we time travel in backward??

    I meant to travel into the future at a higher rate..like travel to 2111 AD..
    will that be possible or more possible than time traveling into the past?
     
  16. Aug 22, 2011 #15

    BruceW

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    Re: Why can't we time travel in backward??

    definitely. Just become an astronaut. They travel into our future slightly. I.e. they will age slightly less than us on earth because they are in a high-speed orbit.
     
  17. Aug 22, 2011 #16

    BruceW

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    Re: Why can't we time travel in backward??

    I've tried to think a bit more about why it seems time is different to space - how Arjun was saying that we go left and right in x - and can return to the same spatial coordinate, but we can't return to the same time.

    I've thought about it like this: we humans all travel almost entirely in the same direction of spacetime - that is the component we have labelled time. Which is why we have to make a huge change in our 4-velocity to get back to the same time (only possible by a wormhole or similar). But we only need to make a very small change in our 4-velocity to get back to the same point in space.
     
  18. Aug 22, 2011 #17
    Re: Why can't we time travel in backward??

    Just last week I felt what feeled like an electromagnetic field on my arm but I couldn't feel it on my hand when I positioned my hand where my arm was. About an hour later I experienced what seemed like myself having travelled back in time and reliving an hour.
     
  19. Aug 22, 2011 #18
    Re: Why can't we time travel in backward??

    Hello Aujun.

    There is another way of viewing what Andrew Mason said

    look at posts 8 and 11 of this thread

    https://www.physicsforums.com/showthread.php?t=441627&page=13

    and ask your self what you mean by time travel, either forward or backward and why your idea of time travelling is fundamentally different from moving in space.
     
  20. Aug 22, 2011 #19
    Re: Why can't we time travel in backward??

    Hey guys,

    I have a confession to make..
    It seems that I could see the future in dreams..It sounds stupid but since Newtype has mentioned his experience I think it is worthy to share mine too..
    I was (and still am) able to see the future(not far future just 6 or 7 hours)...Its no big deal but I see this through dreams..
    I could see which episode will come on "courage:the cowardly dog show" that day or what food will my mom cook for breakfast..
    I have also tried to control these dreams and become a lucid dreamer http://en.wikipedia.org/wiki/Lucid_dream" [Broken]

    I was not so unsuccessful and at times I could control these..

    Do you guys think that if we cannot physically travel into the future, we could travel spiritually through dreams?Or are all these just tricks played by our mind?
     
    Last edited by a moderator: May 5, 2017
  21. Aug 23, 2011 #20
    Re: Why can't we time travel in backward??

    .......................................................:uhh:
     
    Last edited by a moderator: May 5, 2017
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