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Does it need light speed or not

  1. Jul 22, 2012 #1
    Hi,
    If there is really one way to go back the past, must the way be through light speed or not? If the answer is yes, I really do not believe that the human beings or any animals are able to endure light speed technically!

    Best Regards
     
    Last edited: Jul 22, 2012
  2. jcsd
  3. Jul 22, 2012 #2

    tiny-tim

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    Welcome to PF!

    Hi HuaMin! Welcome to PF! :smile:
    No, that's only in science fiction …

    (unless there are "wormholes") there is no way of going back into the past :smile:
     
  4. Jul 22, 2012 #3
    Thanks. I know Wormhole is one of the research area in Physics. What speed is needed if one day we will go through the wormhole?

    Many thanks
     
  5. Jul 22, 2012 #4

    tiny-tim

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    wormhole research is on an entirely mathematical basis

    you could pass through a wormhole (if any exist, and are large enough not to crush you) at any speed you like, same as you can go to alpha centauri at any speed you like (both slower than light, of course) :wink:
     
  6. Jul 22, 2012 #5
    Many thanks. Can I have more details for the wormhole that leads to the past across the time dimension?
     
  7. Jul 22, 2012 #6

    Drakkith

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    You could try here: http://en.wikipedia.org/wiki/Wormhole

    Just be warned that time travel is generally frowned upon here at PF, so I would be careful in discussing it. (Meaning I probably wouldn't discuss it here)
     
  8. Jul 23, 2012 #7
    Thanks. I know wormhole does exist only in the multi-dimensional Mathematical models. Do you think it will be technically possible to locate that in reality?

    Best regards
     
  9. Jul 23, 2012 #8

    Nabeshin

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    This actually isn't true. A wormhole requires only the 4 spacetime dimensions we're used to. We usually depict such a structure by embedding it in a higher dimensional space, but this embedding is not required for its existence; it's merely a byproduct of the visualization.
     
  10. Jul 24, 2012 #9
    Seriously, HuaMin, Google is your friend.

    There are also quite a few books on wormholes intended for lay audiences:

    Cosmic Wormholes by Paul Halpern

    Black Holes & Time Warps -- Einsteins Outrageous Legacy by Kip Thorne

    Black Holes, Wormholes and Time Machines by Jim Al-Khalili

    The Physics of Stargates -- Parallel Universes, Time Travel and the Enigma of Wormhole Physics by Enrico Rodrigo

    Unveiling the Edge of Time -- Black Holes, White Holes, Wormholes by John Gribbin

    The bottom line is that, despite a lot of theoretical effort, the the existence of wormholes cannot be ruled out. This especially true in the context of quantum theory or when one considers reasonable generalizations of Einstein's theory of gravity.
     
  11. Jul 24, 2012 #10

    Ryan_m_b

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    It is possible that even with wormholes time travel will still not be possible (or even if it is changing history will not be possible).
    http://homepages.mcs.vuw.ac.nz/~visser/general.shtml
     
  12. Jul 24, 2012 #11
    This seems the most misguided part of your post to me. Speed does not have any effect on what a traveller feels, only acceleration does. And even acceleration would not, if it were uniform, as in from a gravity field, as opposed to spread around along the body through stress and elastic forces.
     
  13. Jul 24, 2012 #12

    Ryan_m_b

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    Perhaps I'm misunderstanding something but this doesn't seem correct. The human body can only widthstand certain accelerations for certain amounts of time without health complications.
     
  14. Jul 24, 2012 #13

    jbriggs444

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    That is because the acceleration is non-uniform. Take, for instance a high G decelleration in a rocket sled. It is the lack of uniform acceleration that kills you -- for instance your blood, your retinas or your aorta failing to decellerate along with the rest of your body.

    If, hypothetically, you could decellerate your entire body uniformly (e.g. in a high strength, uniform gravitational field) then you would feel nothing out of the ordinary.
     
  15. Jul 24, 2012 #14

    Ryan_m_b

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    :redface:
    *smacks forehead. That's pretty obvious now
     
  16. Jul 24, 2012 #15
    Many thanks to you all.
    Jbriggs,
    Is there any evidence/lab completed to prove such things?
     
  17. Jul 24, 2012 #16
    Not true. A high strength, uniform gravitational feild will likely kill you over a long time period. High gs in a rocket sled don't count because they are over a short peroid of time. E.g a slap is 100g or something, and that doesn't kill you because its over really quickly.
     
  18. Jul 24, 2012 #17

    jbriggs444

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    Do you have evidence for your claim here that the equivalance principle is false?

    We're talking about free fall in a high strength gravitational field where tidal forces are assumed away.
     
    Last edited: Jul 24, 2012
  19. Jul 24, 2012 #18

    Drakkith

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    If the field is uniform, and you are in free fall, then you experience no G forces and it will have no detrimental effects. If you are in a high strength field and NOT in free fall, such as standing on the surface of something, then you will promptly be squished into a pile of mush, just like standing on the surface of a neutron star would do.
     
  20. Jul 25, 2012 #19
    Thanks a lot to you all. Is it possible to technically make the wormhole a "free fall" state or not?
     
  21. Jul 25, 2012 #20

    rbj

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    Hua, can you get out of this Star Trek science fiction mode and ask questions about physics?


    oh, and to the other guys, jerk (the time-derivative of acceleration) isn't the only thing that will kill you, but sufficient g's of acceleration will too. even if you slowly accelerated to, say, 20 g's (so the jerk is small), and slowly decellerate back to your original velocity (so that living people can examine you), you'll be deader than a doornail.
     
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