I Can you indeed rescue a person from a Black Hole?

[DuckAmuck]

TL;DR Summary

Can you indeed rescue a person from a blackhole?

Let's say Bob falls into a blackhole, and Alice is sufficiently far away that she is not falling in. She sees Bob's clock stop and his image fade away and all that. However, from Alice's perspective Bob never actually crosses the horizon. From her perspective, Bob is sitting frozen and invisible near the horizon. So does she get an arbitrary amount of time to build a rescue ship that can travel fast enough to avoid the event horizon and scoop Bob up from certain death?

 

[Vanadium 50]

No.

 

[Ibix]

No. There is a definite time when Bob entering the hole is no longer in Alice's causal future, at which point she is too late.

Bob's horizon crossing never enters Alice's causal past, which means she is always free to construct time coordinates where he isn't dead yet. But she cannot reach him before he crosses the horizon.

 

[Vanadium 50]

Besides, what do you pick Bob up with? The "hook" will suffer Bob's fate.

 

[berkeman]

Let's say Bob falls into a blackhole

Poor Bob. Is/was he wearing a red uniform shirt?

 

[PeterDonis]

From her perspective, Bob is sitting frozen and invisible near the horizon.

That is what Alice sees sitting far away, but what she sees is out of date information; it takes time for the light Bob emitted as he was falling to climb back out to Alice, and that time gets larger and larger the closer Bob gets to the horizon (and when Bob reaches the horizon, the light he emits can no longer climb back out at all, so Alice never sees it). If Alice tries to fly down towards the horizon in a ship to pick Bob up, she will find that he is not there; the light she sees coming from Bob doesn't show him getting any closer and she can fly as close to the horizon as she wants (assuming she has a rocket with sufficient thrust and fuel) and she will not find Bob.

 

[haushofer]

Besides, what do you pick Bob up with? The "hook" will suffer Bob's fate.

I read "The hooker will suffer Bob's fate" and wondered whether I entered a new subforum.

 

[PhysicsEnjoyer31415]

If bob fell into the black hole....well bob is dead, and so is the revolution of bringing him back from a black hole

Remember the rhyme - if you see bob going red , he is already dead