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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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1 Answers1

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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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