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Time travel

  1. Apr 30, 2004 #1
    Yes, i have 2 questions about time travel.

    - If an object exceeds the speed of light (which i think is impossible becuase e=mc^2, right?) will it travel forward or backward in time, or nothing happen.

    - Also, Disregarding passing the speed of light, is there any strong theories that time travel is/isn't possible?
  2. jcsd
  3. Apr 30, 2004 #2
    Going by e=mc^2, an object can't exceed the speed of light. The truth still depends on whether Einsteins theories are correct. I could be incorrect, but I believe that we have yet to truly turn matter into energy or vice versa. A nuclear bomb (either fission or fusion) still doesn't destroy matter, it only changes it into other matter with less inherent energy.

    Time is a measurement of motion, more or less used only to determine velocity. Time could change at any moment without us knowing it because our perception (which is based on motion) would alter with time.

    Time is just a way of measuring the velocity of the motion of an object through the 3 real dimensions. In order to go into the future you would have to stop your particles for the desired amount of time (basically cryogenics). Your particles weren't present to have their effect on the future so the outcome would be slightly different than what it would have been. In order to go into the past you would have to reverse the past motion of all other particles in the universe (an exact reverse of physical law that affects everything but you). Going by that logic, I am lead to 'believe' that going into the past is literally impossible, but going into the future isn't very difficult at all. Now, if you are one that believes (I'm not saying I are or aren't) that the mind is immaterial then that still leaves the possibility for mental time travel.
  4. Apr 30, 2004 #3
    I agree, travelling to the future is possible. Just wait awhile and you'll be there! :tongue:
  5. Apr 30, 2004 #4


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    First things first youhave to understand that talking about objects (locally at least) exceeding the speed of light is nonsensical (excepting hypothetical tachyons which already have velocities greater than c) and is really a non-question.

    There's nothing in modern physics that rules out time travel, infact using a few extremely hypotheical geometries, solutions have been found in general relativity which involve closed time-like loops (i.e.'time travel').
  6. Apr 30, 2004 #5


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    The "m" in the equation is not stand for "matter", but "mass". And yes, matter has been converted to energy and (more recently) energy to matter. A nuclear bomb does indeed change matter into a different matter with less inherent energy but, more importantly, less mass. The mass that is lost constitutes the energy of the explosion.

    However, matter/antimatter reactions, which have been observed in colliders, do convert matter entirely (or almost entirely) into energy. And in the last decade or so, certain collider experiments have succeeded in converting energy into matter.

    Regarding light speed and time travel, it does seem that we will never know for certain. The inability to exceed light speed renders experimental verification impossible. So we are left with theory and speculation. However, the speculation behind the theory does seem rational enough;

    We know that time slows down as one approaches light speed, and stops entirely at light speed. It seems therefore logical to deduce that time reverses beyond light speed.
  7. Apr 30, 2004 #6
    If time stops entirely at light speed then wouldn't light not be affect by time since it is moving light speed. That would mean light would have an infinite velocity.
  8. Apr 30, 2004 #7


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    There is no valid refernce point at c, so it's incorrect to say 'time stops at lightspeed'. Extrapolating is fine, but first you must make sure tht the extrapoltion is valid, in this case it isn't.
  9. Apr 30, 2004 #8
    What people dont realize is that we are already "time traveling into the future." We are time traveling into the future because we are going slower than the speed of light(Relativity). If the earth would to suddenly speed up then we would move even faster into the future.
  10. May 1, 2004 #9
    Heh, nicely put astermind...im gonna use that sometime "We are already time traveling".
  11. May 1, 2004 #10


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    Yes, from its own perspective light can be thought of as having infinite velocity (if there's any truth to relativity). That is to say, for a photon to travel from one point to another, no matter how distant, the amount of time the trip will take as measured by the photon will be zero.
  12. May 1, 2004 #11


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    Not only does time stop for a photon but all length is contracted to zero. So its velocity is not infinite, it takes no time to travel no distance... no trouble. :)
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