# Time and Gravity

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 33250.  Mon Nov 21, 2005 1:59 pm Here's an interesting fact about Black Hoels. If you watched a spaceship be sucked into a Black Hole it would take infinite time for you to see the Spaceship disappear.

 33253.  Mon Nov 21, 2005 2:03 pm What if another spaceship was sucked into the same place?

33258.  Mon Nov 21, 2005 2:21 pm

 Kevino7 wrote: Here's an interesting fact about Black Hoels. If you watched a spaceship be sucked into a Black Hole it would take infinite time for you to see the Spaceship disappear.

I suppose that could be the QI equivalent of watching paint dry.

"Hey what's the American version of The Office like?" "It's like watching a space ship disappear over the event horizon of a black hole."

 33259.  Mon Nov 21, 2005 2:23 pm Inform the Oxford Dictionary of Phrases!

 33261.  Mon Nov 21, 2005 2:28 pm I'll see if I can slip that one in to my next Physics lesson.

33483.  Tue Nov 22, 2005 8:34 am

 Kevino7 wrote: Here's an interesting fact about Black Hoels. If you watched a spaceship be sucked into a Black Hole it would take infinite time for you to see the Spaceship disappear.

That's because, as previously mentioned, time slows down in the presence of a gravitational field. As the gravitational field increases towards the centre of the black hole, the time frame of the person falling will appear to a stationary observer to be running slower and slower.

When the person reaches the event horizon, the stationary observer will see their time frame come to a complete halt. Thus, you'll never actually see anyone fall completely into a black hole.

If another person falls in to the same spot, you'll see the same thing, only having started later they'll always be a bit behind the first person.

33488.  Tue Nov 22, 2005 8:40 am

 Rory Gilmore wrote: No, I meant towards each other at the speed of light.

Same rules apply. Nothing can travel faster than the speed of light.

Imagine you have three people, A, B, and C, standing in a line in that order. Person A is travelling towards person B at the speed of light. Person C is also travelling towards person B at the speed of light. A and C are therefore moving towards each other quite quickly.

Person A will see both B and C moving towards him at the speed of light. He will not, therefore, see them moving relative to each other. He will pass person B first and later on pass person C.

Person C will see A and B moving towards him at the speed of light. He will also see them stationary with respect to each other. He will pass person B first and then pass person A.

Person B will see A and C both moving at the speed of light, but in opposite directions. From the point of view of person B, A and C will both reach him at the same time, pass each other at that same point, and then continue to carry on away from him.

Confused yet? :)

 33538.  Tue Nov 22, 2005 12:42 pm Yes. This would be so much easier if we were all blind.

 33605.  Tue Nov 22, 2005 3:18 pm What would a blind man hear if his two friends were flying away from him at close to the speed of light?

 33623.  Tue Nov 22, 2005 5:27 pm A sonic boom if in an atmosphere, nothing at all otherwise.

 33726.  Wed Nov 23, 2005 7:46 am In space, no-one can hear you flying away from a blind man at the speed of light! Hmm, doesn't have the same ring to it somehow.

 33770.  Wed Nov 23, 2005 11:17 am Well it didn't really crop up in the film, so it wouldn't be a very relevant slogan.

 33776.  Wed Nov 23, 2005 11:26 am Nah, that bit was editted out of the final version :)

 33778.  Wed Nov 23, 2005 11:29 am Notice in the first film the creature was damn near invincible and in the last one, they like shot it with a gun?

33818.  Wed Nov 23, 2005 1:03 pm

 dr.bob wrote: Imagine you have three people, A, B, and C, standing in a line in that order. Person A is travelling towards person B at the speed of light. Person C is also travelling towards person B at the speed of light. A and C are therefore moving towards each other quite quickly. Person A will see both B and C moving towards him at the speed of light. He will not, therefore, see them moving relative to each other. He will pass person B first and later on pass person C.

How much later?

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