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Taking the plunge

  1. Nov 16, 2005 #1
    this was a kind of interesting HW problem i was working on. handed in the solution already, but dont know if it was right. ill run it by the forum and see what the members think.

    what would a person see if they where falling feet first radially into a Swarzschild black hole. The person is looking at their feet the whole time. Are they always able to see their feet? (especially when their feet are inside the event horizon and their head is not). Once they cross the horizon are they still able to see their feet? Assume of course that they are not stretched apart by the tidal forces.
  2. jcsd
  3. Nov 16, 2005 #2


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    This page says that you could see your feet (which is what I'd have guessed, since otherwise it seems like the equivalence principle would be violated):
    If you want more of an explanation though, you'll have ask one of the GR experts on this board...
  4. Nov 16, 2005 #3
    yeah that was my conclusion eventually, thanks for the link. i answered it by referencing the space time diagram with the light cones tilting in as you approach the event horizon. my reasoning was that even thought the light emitted from the feet in the radially "outward" direction is still approaching the singularity they dont do so as fast as the persons head.

  5. Nov 16, 2005 #4


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    Yeah, I think the tilted light cones would be the key to understanding this, that web page also emphasized them in its explanation. But what's the "they" that you're saying doesn't approach the singularity as fast as the head--the feet, or the photons? I figure once your feet cross the horizon but your eyes haven't, you can still see your feet, but you're seeing light that was emitted from your feet before they crossed the horizon. And is it also true that when you see your feet after you've crossed the horizon, you're always seeing light that was emitted from your feet when they were at a greater distance from the singularity than your eyes are currently? From the tilted light-cone diagrams, I think it must be, since the radial dimension basically becomes your time dimension once you've crossed the horizon.
  6. Nov 16, 2005 #5
    I must point out that there are very many interesting GR articles on that site as may be seen by the TOC.
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