## Value of g near a black hole (re-visited)

 Quote by PAllen I think I will have to let someone else answer your questions after this. Somehow, I think I'm being clear and you get something quite different from what I said out of it. Someone else may express it in a way you get it. Repeating yet again: You don't see them actually cross the horizon if you remain outside. No exception. The turning black is just a matter of infinite red shift and time dilation relative to you if you are hovering further away. If they divert from crossing at the last minute, sometime before infinite redshift, you see them turn on their thrusters and (as in my tandem example) get closer to you (you having already hovered). All this is due to light delay. You never see turning fully black and reappearing[edit: you can see someone have arbitrarily close to infinite redshift, then approach you becoming less redshifted, even pass you]. Ultimately, after infinite time, you can infer they crossed if you never detect that they stopped and hovered. Finally, yes, the moment you cross you see prior infallers as of the moment they crossed.
Then you can see objects crossing the horizon (because you're one plank length away and they're in front of you), so light is escaping from inside the horizon?

 Quote by PAllen I don't understand this at all. The one that is hovering simply sees the one that turns off thrusters fall towards the horizon, get redder, ultimately black, just outside the horizon. Nothing about the history from horizon to singularity can be seen by the one remaining outside.
The bit I'm having trouble with is seeing distance between you (hovering a plank length above the horizon) and another object but niether of you have crossed the horizon. You could therefore move alongside the other observer and niether of you would have crossed the event horizon, so you can't have been next to the horizon in the first place?

Blog Entries: 1
Recognitions:
Gold Member
 Quote by Spin-Analyser Then you can see objects crossing the horizon (because you're one plank length away and they're in front of you), so light is escaping from inside the horizon? The bit I'm having trouble with is seeing distance between you (hovering a plank length above the horizon) and another object but niether of you have crossed the horizon. You could therefore move alongside the other observer and niether of you would have crossed the event horizon, so you can't have been next to the horizon in the first place?
I say "you never see x" . You respond: "Then you can see x". We will never get anywhere this way.

Classically, Planck length is irrelevant. Quantum mechanically, nobody knows. Take your pick depending on approach to a partial theory of quantum gravity: (a) there is nothing resembling a horizon (and surface of smallest visibility is smaller than EH as predicted by GR); (b) there is something that is not a horizon microscopically, but it looks a lot like it macroscopially; (c) there is a horizon, but with some difference in properties from the classical picture; (d) a horizon never forms and matter is always outside what would be the horizon radius.

I don't understand your second paragraph at all.
 Let me be clearer. You're saying you can observe light coming out to your eye from inside the horizon as you hover just above it (because you see distance between you and objects ahead of you), but you're seeing light that hasn't reached the horizon yet?

Blog Entries: 1
Recognitions:
Gold Member
 Quote by Spin-Analyser Let me be clearer. You're saying you can observe light coming out to your eye from inside the horizon as you hover just above it (because you see distance between you and objects ahead of you), but you're seeing light that hasn't reached the horizon yet?
Nope, never said this, said the opposite several times. I said if you are outside, you only see light that was emitted outside as well. It may look like it comes from a distance such that if the object is still that distance from you it would be inside. But the light is old, from outside the horizon.
 It's old light from outside the horizon coming at you from inside the horizon of light that hasn't reached the horizon yet?

Blog Entries: 1
Recognitions:
Gold Member
 Quote by Spin-Analyser It's old light from outside the horizon coming at you from inside the horizon of light that hasn't reached the horizon yet?
I give up. I write English, you twist into word soup.

Recognitions:
Gold Member
 Quote by Spin-Analyser It's old light from outside the horizon coming at you from inside the horizon of light that hasn't reached the horizon yet?
No, it's old light from outside the horizon that has never been inside the horizon.

If you and your partner are both falling into the black hole, then from your point of view, you and your partner are stationary and the event horizon is rushing towards you at the speed of light. You see your partner 10 feet in front of you at all times. The image you see has been delayed 10 nanoseconds; you see where your partner was 10 ns ago.

At exactly the moment you reach the event horizon (i.e. at a distance of zero, not a distance of 1 planck length) you see, 10 feet in front of you, what your partner was doing 10 ns earlier, which was crossing the event horizon. (10 ns ago the event horizon was 10 ft in front of you, as was your partner.)

This illustrated in the left-hand spacetime diagram below.

If you decide at the last minute to brake and hover at a small fixed distance outside the event horizon, you see your partner's image slow down, red-shift and darken and never actually cross the horizon. This illustrated in the right-hand spacetime diagram below.
Attached Thumbnails

 Quote by DrGreg If you and your partner are both falling into the black hole, then from your point of view, you and your partner are stationary and the event horizon is rushing towards you at the speed of light. You see your partner 10 feet in front of you at all times.
Sorry but I cannot agree with this.
I think you are forgetting the tidal forces between them.

Blog Entries: 1
Recognitions:
Gold Member
 Quote by Passionflower Sorry but I cannot agree with this. I think you are forgetting the tidal forces between them.
If you go back to the post I introduced this scenario, I specified a supermassive black hole. Tidal forces can be made as small as desired by making the mass large enough, as you have noted in other discussions.

 Quote by DrGreg No, it's old light from outside the horizon that has never been inside the horizon. If you and your partner are both falling into the black hole, then from your point of view, you and your partner are stationary and the event horizon is rushing towards you at the speed of light. You see your partner 10 feet in front of you at all times. The image you see has been delayed 10 nanoseconds; you see where your partner was 10 ns ago. At exactly the moment you reach the event horizon (i.e. at a distance of zero, not a distance of 1 planck length) you see, 10 feet in front of you, what your partner was doing 10 ns earlier, which was crossing the event horizon. (10 ns ago the event horizon was 10 ft in front of you, as was your partner.) If you decide at the last minute to brake and hover at a small fixed distance outside the event horizon, you see your partner's image slow down, red-shift and darken and never actually cross the horizon. This illustrated in the right-hand spacetime diagram below.
As you approach you see objects in front of you crossing the horizon, and you're seeing light from the other side of the event horizon. When you move away the light from previous observers moves back across the event horizon. So what if you stop one plank length away from the horizon and the one in front of you never reached the horizon either? The event horizon is no longer in one place. If you moved alongside and hovered next to the one in front of you then you would still be outside the horizon. It doesn't work. The event horizon must be moving inwards at c, not outwards.

Blog Entries: 1
Recognitions:
Gold Member