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Black holes and time travelling

  1. Feb 11, 2004 #1
    Hi all in this forum. =)

    Oftentimes when i read books about blackholes or time travelling, i'm bound to come across the notion about how time travelling and black holes(particularly the singularity beneath the event horizon) are linked. If i'm not wrong, it only applies to rotating black holes that have ring singularities, right?
    So i'd like to inquire now; why and how is time travelling possible with the use of black holes? If possible, i'd appreciate very much if anyone could guide me through step by step the whole process from after the formation of a black hole to once an entity has time travelled.
    Thank you. =)
     
  2. jcsd
  3. Feb 13, 2004 #2
    First just let me say, I’m no physicist. I’m sure someone else will give a much more detailed and accurate response. However if I’m not mistaken, the reason why time travel is theoretically possible within a singularity is because anything is theoretically possible inside a singularity. Physics as we know it simply doesn’t exist in that state. The most likely thing that would happen to someone who was attempting to “time travel” using a black hole… compression, on an atomic scale. Every atom in your body would be instantly imploded; the energy that was released would be consumed by the black hole and used to feed its own mass and rate of rotation. This would happen long before the time traveler ever got near the singularity. Of course that’s just a guess :P
    However, if I’m not mistaken it is theoretically possible to travel forward in time. Based on both relativity, and special relativity. It is possible to change the passage of time, or slow it down. GPS wouldn’t work without these temporal calculations.
    If you really want to understand this stuff you should read more about the the man who’s brilliance inspired the majority of this forum. Albert Einstein. I would recommend the book “The everything Einstein book”.
     
  4. Feb 14, 2004 #3
    No, physics states nothing about "anything goes" inside a black hole horizon (not singularity -- which is a point, and has no 'inside'). We don't know what happens inside the event horizon, because anything inside is forever isolated from everything outside. Time travel arises when the spacetime (i.e. solutions to Einstein's equations) is curved in such a way as to allow what are called "closed timelike curves". In the same way a circle drawn on a piece of paper "ends" at the same place it "starts" (in space), a closed timelike curve would represent a trajectory in spacetime which begins and ends at the same place in space *and* time (hence you literally come back to where you started, same place, same time).

    Unfortunately, there are various conjectures which suggest that formation of closed timelike curves is impossible (the most notable being the "Chronological protection conjecture", coined by Hawking et al). Violation of cause-effect relationships (which would be introduced by time travel) are unfavorable from every standpoint.
     
  5. Feb 16, 2004 #4
    I think the part where Shawn Wheeler mentioned "the reason why time travel is theoretically possible within a singularity is because anything is theoretically possible inside a singularity. Physics as we know it simply doesn’t exist in that state..." makes alot of sense. Could be one reason how singularities make time travel allowable. But that doesn't answer my question. So, how does that make time travelling feasible?

    Correct me if i'm wrong, in my opinon, this is how time travelling can take place. A person falls into a black hole beyond it's event horizon. He reaches the ring singularity and with much luck missed bumping onto it. Now, the crucial part. By sucussfully going through the gap of the ring singularity, he managed to travel either into another space or time "location" because that region in the gap acts as the passage to those travels.
     
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