And then the point goes out. All at once, as if God turned off the switch. You have crossed the event horizon of the black hole.
and:
But Alice cannot see Bob either, because in order to do so, she has to turn her head toward her own past. The distortion of spacetime is so great that the spatial direction in which Bob lies relative to her is actually in her past. In technical terms, any light that comes to her from Bob will fall perpendicular to her eyeballs, regardless of which direction she turns her head.
When I read this, I believed that it was wrong (but well-written, making it more dangerous!). (However, he described Gravity Probe B’s verification of the geodetic effect correctly.)
An observer crossing a black hole event horizon can calculate the moment they’ve crossed it, but will not actually see or feel anything special happen at that moment. In terms of visual appearance, observers who fall into the hole perceive the black region constituting the horizon as lying at some apparent distance below them, and never experience crossing this visual horizon.[7] Other objects that had entered the horizon along the same radial path but at an earlier time would appear below the observer but still above the visual position of the horizon, and if they had fallen in recently enough the observer could exchange messages with them before either one was destroyed by the gravitational singularity.[8] Increasing tidal forces (and eventual impact with the hole’s singularity) are the only locally noticeable effects.
Engulfed in blackness? NO!
It is a common misconception that if you fall inside the horizon of a black hole you will be engulfed in blackness. More specifically, the story is that as you fall towards the horizon, the image of the sky above concentrates into a smaller and smaller circular patch, which disappears altogether as you pass through the horizon. The misconception arises because if you lower yourself very slowly towards the horizon, firing your rockets like crazy just to stay put, then indeed your view of the outside universe will be concentrated into a small, bright circle above you. Click on the button to see what it looks like if you lower yourself slowly to the horizon. Physically, this happens because you are swimming like crazy through the inrushing flow of space (see Waterfall), and relativistic beaming concentrates and brightens the scene ahead of (above) you. See 4D Perspective for a tutorial on relativistic beaming. But this is a thoroughly unrealistic situation. You’d be daft to waste your rockets hovering just above the horizon of a black hole. If you had all that rocket power, why not do something useful with it, like take a trip across the Universe? If you nevertheless insist on hovering just above the horizon, and if by mistake you drop just slightly inside the horizon, then you can no longer stay at rest, however hard you fire your rockets: the faster-than-light flow of space into the black hole will pull you in. Whatever you choose to do, the view of the outside Universe will not disappear as you pass through the horizon.
This explanation agrees with everything I know (when hovering outside the event horizon, you are accelerating instead of being in free fall).
Can you confirm that the Reddit post was incorrect, and Wikipedia and its cited link are correct?
The last two quotes are indeed correct, and the reddit one is a mix of true and false statements.
To begin with, the conclusion subtly replaces the original premise of arbitrarily high velocity with arbitrarily high acceleration. (Confusing velocity and acceleration is a Grade 10 science error.) Given that one cannot accelerate to or past the speed of light, near-infinite acceleration engine is indeed of no use inside a black hole. However, arbitrarily high velocity is a different matter. It lets you escape from inside a black hole horizon. Of course, going faster than light brings a host of other problems (and no, time travel is not one of them).
As you continue to fall, the event horizon opens up beneath you, so you feel as if you’re descending into a featureless black bowl. Meanwhile, the stars become more and more crowded into a circular region of sky centered on the point immediately aft.
This is true if you hover above the horizon, but false if you fall freely. In the latter case you will see some distortion, but nothing as dramatic.
And then the point goes out. All at once, as if God turned off the switch.
This is false if you travel slower than light. You still see basically the same picture as outside, at least for a while longer.
If you have a magical FTL spaceship, what you see is not at all easy to describe. For example, in your own frame of reference, you don’t have mass or energy, only velocity/momentum, the exact opposite of what we describe as being stationary. Moreover, any photon that hits you is perceived as having negative energy. Yet it does not give or take any of your own energy (you don’t have any in your own frame), it “simply” changes your velocity.
I cannot comment on the Alice and Bob quote, as I did not find it in the link.
Actually, I can talk about black holes forever, feel free to ask.
This Reddit post says things like:
and:
When I read this, I believed that it was wrong (but well-written, making it more dangerous!). (However, he described Gravity Probe B’s verification of the geodetic effect correctly.)
Wikipedia says:
And it cites http://jila.colorado.edu/~ajsh/insidebh/schw.html which says:
This explanation agrees with everything I know (when hovering outside the event horizon, you are accelerating instead of being in free fall).
Can you confirm that the Reddit post was incorrect, and Wikipedia and its cited link are correct?
The last two quotes are indeed correct, and the reddit one is a mix of true and false statements.
To begin with, the conclusion subtly replaces the original premise of arbitrarily high velocity with arbitrarily high acceleration. (Confusing velocity and acceleration is a Grade 10 science error.) Given that one cannot accelerate to or past the speed of light, near-infinite acceleration engine is indeed of no use inside a black hole. However, arbitrarily high velocity is a different matter. It lets you escape from inside a black hole horizon. Of course, going faster than light brings a host of other problems (and no, time travel is not one of them).
This is true if you hover above the horizon, but false if you fall freely. In the latter case you will see some distortion, but nothing as dramatic.
This is false if you travel slower than light. You still see basically the same picture as outside, at least for a while longer.
If you have a magical FTL spaceship, what you see is not at all easy to describe. For example, in your own frame of reference, you don’t have mass or energy, only velocity/momentum, the exact opposite of what we describe as being stationary. Moreover, any photon that hits you is perceived as having negative energy. Yet it does not give or take any of your own energy (you don’t have any in your own frame), it “simply” changes your velocity.
I cannot comment on the Alice and Bob quote, as I did not find it in the link.
Actually, I can talk about black holes forever, feel free to ask.
Awesome, thanks.
I swear it was there, but now I can’t find it either.
I’d be interested to hear your opinion of Gravity Probe B.