# Why you cannot cross an event horizon

Discussion in 'Physics & Math' started by zanket, Dec 27, 2002.

1. ### zanketHumanValued Senior Member

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Suppose you hover near a black hole’s event horizon and prod it with a stick. Consider the stick’s point of view. As you prod, the stick moves closer to the hole. The stick experiences you age faster and faster due to gravitational time dilation. You die before the stick reaches the horizon. Therefore you cannot prod the hole. Nor can you cross the horizon, because if your stick can’t cross it, neither can you.

What do you think?

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3. ### James RJust this guy, you know?Staff Member

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I think that if you're close enough to prod the event horizon with a stick, you won't have any trouble at all in doing so. The only problem you'll have is in pulling the stick back after it crosses the horizon. Any bits which cross must hit the singularity of the black hole. The stick will either break or be totally pulled into the hole.

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5. ### ClockwoodYou Forgot PolandRegistered Senior Member

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If you cross the event horizon the only direction anything can go is towards the singularity. If you could exert enough force you could hold still but only if you were largely massless. Life processes would stop as blood could not circulate.

Question: You have an indestructible rod of immense length. You feed one end into a black hole and another into another black hole. What then?

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7. ### James RJust this guy, you know?Staff Member

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There are no indestructible rods.

8. ### zanketHumanValued Senior Member

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James R – How is your thought compatible with the math that shows that part of the stick experienced your death (your death is in part of the stick’s past light cone)?

9. ### James RJust this guy, you know?Staff Member

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zanket,

I don't believe that the event of my death is at any time contained within the stick's past light cone.

We're back to the same discussion as before.

10. ### zanketHumanValued Senior Member

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Fair enough. I learned something since we last discussed. You are right that an observer falling into the hole does not see an infinite blueshift. Only a hovering (accelerating) observer sees a blueshift. Allant pointed that out.

11. ### orbieRegistered Senior Member

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so you're somehow still alive, hovering above the even horizon while poking it with a stick. I like the imagination

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12. ### zanketHumanValued Senior Member

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Welcome to sciforums orbie.

13. ### orbieRegistered Senior Member

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hehe. Thanks. It's my first night here. Cool place.