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Questions about time travel

  1. Jan 30, 2010 #1

    1. If a person drive a car in 100 kph, while another person walks in 5 kph, will then time go slower for the driver?
    I saw a video on youtube about Einsteins theory of relativity. They said that the faster we travel, the slower time goes. So will then the person who walks be longer into the future then the person who drive?

    2. If one day a person would be able to travel as fast as the speed of light, would then time stop for that person? And if he were able to go faster than the speed of light, would he then be able to go to the past?

    3. If we one day could travel to the past, would we then be able to change the future, or will everything be the same?

    Thanks for answers :)
  2. jcsd
  3. Jan 30, 2010 #2
    1. The increase of life due to the increase in speed would be negligible, because it is the difference in speed relative to the speed of light. If someone travelled at almost C for most of their life, then they would be younger than their identical twin on earth.

    2. For a human to travel at the speed of light would be impossible without science fiction because the force required to move something at the speed of light is massive, and a photon is only able to accomplish this because it has negligible mass. And as for travelling into the past, cosmologically, everything exists at the same time, because if we look at the big bang, the fact that we are getting light from a fraction of a time after the big bang means that if we were to trace the light back, we would be at that time, so to travel faster than the speed of light, well i dont know 'where' or 'when' you would be but past and present in terms of the universe are highly relative concepts, because the 'past' is i guess the position of light in a certain space at that 'time.' I dont know if im completely right about the conjectural part, but i think thats the general idea of how the past works, in terms of light.

    3. If we could travel in the past, we would change the future, because we would change the events that lead to a change in the events in the future. I'm not really sure how to explain this, but its true:)

    Hope this helped :)
  4. Jan 30, 2010 #3


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    To give you an idea of the magnitude here, time is passing 1.000000000000004 times faster for the man walking. So, you'll have to keep this experiment up for several million years to measure even a one second difference in what their clocks will measure.
    Last edited: Jan 30, 2010
  5. Jan 30, 2010 #4
    It sure helped, thanks for good answers! :D I just have some few questions about your answers :P

    1. with "C", do you mean the speed of light, or something else? :P

    2. So the past and the present exists today? So does Albert Einstein live today, but in a different position of light? (correct me if i'm wrong, i'm pretty new to this time travelling stuff :P )

    3. I have also heard about this parallell universes. That if you could travel to the past, you would go to a parallell universe so that you would not harm the time in your own universe. (maybe im wrong, but that's how I understood it)
    So this is not how it works? We can only travel back in time, in our own universe?
  6. Jan 30, 2010 #5
    That was a very small differens :P So then it means that the faster we go, the slower time goes. But we have to travel very fast to be able to notice it.
    Does time go faster for the man in the car? doesn't it go slower for him?
    Last edited: Jan 30, 2010
  7. Feb 1, 2010 #6


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    Acceleration is key to determining who[m] is moving. The person walking percieves the one in the car streaking away. The person in the car perceives the pedestrian as streaking away. Only when the accelerated observer returns, is it apparent there is a discrepancy.
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