- #1

DennisN

2020 Award

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## Summary:

- Are my 3 posted scenarios regarding an observer passing a black hole event horizon reasonable or incorrect?

Hi all, I've just read this entire thread and watched the videos about black holes posted by @PeroK, which I liked very much (thanks @PeroK! ).

I am not particularly well aquainted with GR and my questions are concerning the often mentioned statement that an observer that passes the event horizon won't notice it.

But is this really correct?

I have recently thought about different scenarios and I have three particular ones below that I would like others to consider. First of all, let's assume the black hole is massive enough that significant tidal forces (spaghettification) will not be of concern before or at the event horizon, and furthermore that there is no firewall at the event horizon.

Very simple: An observer is falling quite slowly towards the event horizon with his arm and hand stretched out before him towards the horizon. When his hand suddenly passes the event horizon, does it disappear completely from his view, since the light can't reach his eyes? And as his arm continues to pass the event horizon, does the arm in the same way gradually disappear from his view?

An observer is sitting at the right end of a long container that is passing through the event horizon at the left. Along the length of the container are 10 candle lights at different positions. Does the observer see one light after another from 1 to 10 get gradually dimmer (and maybe briefly distorted?) and then completely disappear from his view?

(in the picture below candle light 1 and 2 has passed the event horizon and cannot thus be seen by the observer).

Beyond the event horizon it is my understanding that all paths lead to the singularity, which is a point in time and not in space. Is it therefore correct to assume that an observer will become invisible to himself, i.e. he won't be able to see his own body and limbs, since there is no way for the light from these to reach his eyes?

Thanks for you consideration, and I look forward to hearing if my scenarios are reasonable or incorrect. Cheers!

I am not particularly well aquainted with GR and my questions are concerning the often mentioned statement that an observer that passes the event horizon won't notice it.

But is this really correct?

I have recently thought about different scenarios and I have three particular ones below that I would like others to consider. First of all, let's assume the black hole is massive enough that significant tidal forces (spaghettification) will not be of concern before or at the event horizon, and furthermore that there is no firewall at the event horizon.

**Scenario 1: An observer and his hand**Very simple: An observer is falling quite slowly towards the event horizon with his arm and hand stretched out before him towards the horizon. When his hand suddenly passes the event horizon, does it disappear completely from his view, since the light can't reach his eyes? And as his arm continues to pass the event horizon, does the arm in the same way gradually disappear from his view?

**Scenario 2: An observer in a long container**(it's an extension of scenario 1, see attached picture below).An observer is sitting at the right end of a long container that is passing through the event horizon at the left. Along the length of the container are 10 candle lights at different positions. Does the observer see one light after another from 1 to 10 get gradually dimmer (and maybe briefly distorted?) and then completely disappear from his view?

(in the picture below candle light 1 and 2 has passed the event horizon and cannot thus be seen by the observer).

**Scenario 3: Invisibility beyond the event horizon**Beyond the event horizon it is my understanding that all paths lead to the singularity, which is a point in time and not in space. Is it therefore correct to assume that an observer will become invisible to himself, i.e. he won't be able to see his own body and limbs, since there is no way for the light from these to reach his eyes?

Thanks for you consideration, and I look forward to hearing if my scenarios are reasonable or incorrect. Cheers!

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