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Does Spaghettification contradict space/time swap in a black hole

  1. Mar 25, 2014 #1
    Hi, I've heard and read that if someone was to fall towards a black hole, say feet first, they would undergo spaghettification at a certain distance, as the gravity at their feet would be much greater than the gravity at their head, and their body wouldn't be able to reisist the pulling effect. I also heard that if the black hole is big enough, it could happen inside the black hole's event horizon.

    However, I've also heard and read that inside a black hole, the radial dimension becomes the time dimension and the time dimension becomes a spatial dimension, so that the quantum singularity is no longer a distance away in space, but in the future, and you can't escape the future.

    If that's the case, then this would be at odds with spaghettification, as at any point in that person's proper time, all parts of that person would be the same distance away from the singularity, and that distance would be a purely time distance.

    Does this contradict spaghettification?

    Also, if the singularity is in the future, then it would not be in any spatial direction.
    Last edited: Mar 25, 2014
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  3. Mar 25, 2014 #2

    Simon Bridge

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    Welcome to PF;
    If the hole were really big, you simply would not get the effect.

    What happens inside the event horizon is open for speculation.
    Thinking about what happens there is tricky - it would help if you told us where you are reading these things.
    It sounds like you have been reading pop-science accounts that are not meant to be linked.

    Have a look at:
  4. Mar 25, 2014 #3


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    The singularity _is_ in the future, but that doesn't prevent tidal forces from happening.
  5. Mar 25, 2014 #4
    Where did you read that? I want to know more about this.

  6. Mar 26, 2014 #5


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    MTW https://www.amazon.com/Gravitation-Physics-Series-Charles-Misner/dp/0716703440 has a rather poetic discussion of this:

    http://arxiv.org/abs/0705.1029 "No Way Back" has a more detailed, technical discussion of some related issues.
    Last edited by a moderator: May 6, 2017
  7. Mar 26, 2014 #6
    I'd double check that second paragraph. It doesn't sound right. I think you've misinterpreted something.

    Inside an event horizon all forward-time paths lead closer to the centre but that isn't to say that all points on them are equidistant from it. You could still expend energy to slow your acceleration towards the centre, or to move laterally, but there is no amount of energy that is going to stop you from accelerating towards it.
    Last edited: Mar 26, 2014
  8. Mar 26, 2014 #7


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    Spaghettification is a description of curvature, which is local. The statement that all timelike world-lines end at the singularity is a description of the global, not local, properties of the spacetime.

    Curvature is not a vector that points in a certain direction. For example, the ocean tides on earth have tidal bulges that rise on both sides of the planet. By observing the tides, you can't tell in which direction the moon lies.

    This is a nice way of showing that GR can't be properly understood in terms of Newton's law of gravity and instantaneous action at a distance. The fact that you're running into so many problems applying the Newtonian description is fundamentally because that description doesn't make sense in this example.

    As a side note, it's not true that all points on the observer's body would be the same temporal "distance" from the singularity at a fixed proper time.
  9. Apr 1, 2014 #8
    Thanks to all the replies.

    In answer to Simon Bridge's question, I read about spaghettification inside a black hole in a Wikipedia article on Spaghettification. I read and heard about space and time being reversed in an online course on general relativity from Stanford University and elsewhere on the web, perhaps in Wikipedia as well but I can't remember exactly where. Thanks also for that paper.

    Thanks pervect for the other paper. I've already read that one several years ago.
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