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When a particle crosses the event horizon of a black hole, at one short moment in time would it appear for that particle as if it was surrounded by a black hole?

Regardless of which direction you look, from that particle, you would look towards the center of that black hole?

It would be impossible to determine, for that particle - from which direction the gravity was pulling.

This leads to the following question, which some seem to think is absurd:

Could the expansion of the observable universe, in fact be spaghettification of the observable universe?

Spaghettification sounds like a very one-dimensional effect, which fits poorly with uniform expansion in every direction - but I have a feeling that also this could be explained - either by introducing more dimensions or - even more absurdly, placing the particle closer to the center of the black hole.

Qmechanic
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frodeborli
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1 Answers1

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No, an infalling observer would not see what you describe.

It turns out that an observer falling towards the black hole sees an apparent horizon that retreats before them, and in fact they never cross the horizon. The distance to the apparent horizon measured by the falling observer decreases as the observer falls towards the singularity, but only becomes zero at the singularity.

This is explored in the question Taking selfies while falling, would you be able to notice a horizon before hitting a singularity? and you might find that interesting reading. Also relevant are Would the inside of a black hole be like a giant mirror? and Does someone falling into a black hole see the end of the universe?.

Googling will find you various web sites with calculations of what an infalling observer would see. The JILA site is one of my favourites. There is visual distortion, but nothing like you describe.

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John Rennie
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  • Nice link, very informative! Thanks for sharing :) – CoilKid Oct 09 '15 at 14:15
  • If looking straight away from the BH, you would see that the entire universe was "framed" in a small dot straight above you - extremely blue shifted. In all other directions, you would be looking at the black hole. The closer to the event horizon, that small dot will become smaller and smaller until what you see in every direction is the black hole. If the black hole is extremely big, you would not even be torn apart due to tides when this happens. Just roasted by gamma rays from the rest of the universe in the dot above you. http://casa.colorado.edu/~ajsh/singularity.html#historyofuniverse – frodeborli Oct 11 '15 at 20:47
  • @frodeborli: this is true only for an observer hovering at a fixed distance from the black hole. This is not what is seen by a freely falling observer. – John Rennie Oct 12 '15 at 05:43
  • @JohnRennie Thank you for making that distinction. Apparently you'd see the entire universe as a narrow bright band around you, while above and below you'd see the black hole. https://youtu.be/5feVWB1SY-Y?t=5m47s – frodeborli Oct 12 '15 at 07:41