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Often this is asked if it was pointed towards a black hole. so I thought, if a scientist decided to sacrifice himself and jumped in a black hole, released some dry-ice mist and pointed a laser pointer away from him, what would he see.

(The scientist is just to help you understand. Maybe this experiment is impossible because he'd get spaghettified first)

And the laser pointed is pointed directly away from a black hole, not slightly to the left or right, where I'd assume it would curve and fall back.

Qmechanic
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yolo
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    Why, if you think that the light would "fall back" in the case where it is not directly pointed away from the hole, do you think it wouldn't in this case? Do you expect balls thrown directly upward to not fall back to earth? – ACuriousMind Feb 25 '18 at 12:37
  • It seems like a weird idea of photons just pooling up inside the laser pointer, that's all. – yolo Feb 25 '18 at 12:39
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    And, even I'm stupid enough to realise this, the whole point of this site is to make people more intelligent, rather than trying to put down those who aren't. Down-voting this for this reason therefore defeats the purpose. – yolo Feb 25 '18 at 12:40

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The scientist would not see anything amiss in their locality. The laser light would travel away from him (female scientists can also jump into black holes...), at the speed of light.

From the point of view an observer well outside the event horizon, light emitted from inside the event horizon always moves towards the central singularity. From the point of view of the falling scientist though, the light continues to appear to travel outwards. One way of thinking about this is in terms of the waterfall analogy. The light is like a fish that has a certain speed with respect to the water, but if the water is flowing fast enough (inside the event horizon) the fish will be swept downstream according to an observer on the river bank. However for an observer in a free-floating boat, the fish will still be swimming away upstream from them.

Some more details about the return trip: laser - scattering medium - back to observer - can be found in the second part of my answer to Taking selfies while falling, would you be able to notice a horizon before hitting a singularity? but basically you would continue to see the path of the laser until you hit the singularity.

ProfRob
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  • So you are saying the light would escape the black hole? – yolo Feb 25 '18 at 12:43
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    @yolo What do you mean by that? How would you define that the light has escaped? From the "external observer at infinity" point of view the emitted light moves inwards if it was emitted inside the Schwarzschild radius. But you asked about it from the point of view of the falling scientist. – ProfRob Feb 25 '18 at 12:45
  • Escaped the gravitational pull. If the light is going away from the scientist, who is entering the black hole, it would go away from the singularity. – yolo Feb 25 '18 at 12:46
  • @yolo No, all the light emitted after the laser crosses the EH hits the centre of the BH, but the scientist gets there first. – PM 2Ring Feb 25 '18 at 14:12
  • Ok, in what way. Will it be like an umbrella? or would it fall back on itself towards the bh – yolo Feb 25 '18 at 14:28
  • Good answer except for this: In the frame of reference of an external observer GR doesn't have global frames of reference. –  Feb 25 '18 at 16:06
  • @BenCrowell I understand your point and have modified. – ProfRob Feb 25 '18 at 16:37
  • Thanks. So you are saying the laser beam will be shaped straight. Not like a fountain towards the singularity – yolo Feb 26 '18 at 19:25