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Geometry inside a black hole

  1. Apr 17, 2012 #1
    I'm taking general relativity and I understand how things work mathematically, but I'm trying to find ways of describing black holes to a general audience.

    Would it be fair to say that inside a black hole, space is curved in such a way that all possible paths lead to the singularity? Or, put another way, no matter what direction you try to move in the black hole you will always be moving toward the singularity and hence you can not avoid colliding with it.

    I know its difficult to put these sort of things in to words but I'm just looking for something the average joe who doesn't understand physics can appreciate. Does the above sound reasonable?
  2. jcsd
  3. Apr 17, 2012 #2
    Sounds good to me. Is the audience you're talking to aware of space-time? If so you could enhance the idea by describing how the path of an object through the time dimension always leads to the singularity. Same idea, but I find it can help when people don't get why you can't just go the exact other way.
  4. Apr 17, 2012 #3


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    To second this point, note that spacelike paths need not lead to the singularity. Then you note that all matter/energy must follow timelike or lightlike paths (travel locally less than or equal to speed of light). All of these paths reach the singularity.

    It is also useful to note that even a 'moment' before reaching the singularity, it is still possible (for a body) to move in any spatial direction (at least a small amount). But all these directions of spatial motion are still approaching the singularity - in the precise sense that whatever direction you move, your time to reaching the singularity is always decreasing along any path you choose. [Edit: It is actually possible to be on a path where you would reach the singularity in e.g. 1 second, and change to a path such that it takes you, e.g. 1.5 seconds to reach the singularity.]
    Last edited: Apr 17, 2012
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