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Take a look at this picture

enter image description here

Now if a person falls inside a black hole and he stretches his arms outside. At some point the region which is red in colour will exactly match the width of the person who has stretched his arms out. At that time will he be able to touch space out there?

( PS - I am a high school student. So if possible please don’t give complicated answers. )

Qmechanic
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Aaryan Dewan
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    That's not "Width", that's a 2 dimensional representation of a bottomless gravity well. It's an indication of direction, a bit like, if you're standing on the North Pole, every step you take is south. Inside the event horizon of a black hole, every direction is toward the center. There is no moving away from the center. That's what the diagram represents. That and, when are we not touching space? – userLTK Jan 20 '17 at 04:19
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    Possible related: http://physics.stackexchange.com/a/13839/2451 and links therein. – Qmechanic Jan 20 '17 at 12:28
  • It seems to me the question is pretty clear with a straight-forward answer, so I'm not sure where these close votes as unclear are coming from. – Kyle Kanos Jan 22 '17 at 19:35

1 Answers1

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This is an embedding diagram. It illustrates the curvature of a 2D manifold by embedding it in a manifold of higher dimensionality - in this case 3D.

But this is just an illustration. The extra dimension doesn't exist in general relativity. Instead the curvature of the manifold is intrinsic. Because the extra dimension doesn't exist occupants of the universe cannot move into it, so in the diagram you show the observers are confined to the sheet and cannot move out of it into the third dimension. An observer falling into the black hole follows the trajectory within the sheet I've shown in red:

Trajectory

So it isn't possible to move out of the sheet to the middle of the throat and then stretch out your arms to toch the sheet at either side, because the throat doesn't actally exist.

John Rennie
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