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tommac
2008-Dec-04, 02:56 PM
From the reference point of a distant external observer time stops and distances compress ( in the direction of gravity ) at the EH of a black hole ...correct?

From the perspective of the someone just outside of the EH looking back at the distant observer would they see external time speeding by and distances as expansive?



Here is another way to ask the question:

Observer A and Observer B

A-----------------------B

B is in a deep gravitational well close to one that would create an EH so that time-space is very curved from the perspective of A.

How does B observe A?

grant hutchison
2008-Dec-04, 04:01 PM
The answer depends on what B is doing: falling or hovering?

Grant Hutchison

Tzarkoth
2008-Dec-04, 04:10 PM
I think that A wouldn't see anything other than B fade away as B becomes infinitely red shifted. The closer to the event horizon B gets the more the light is delayed, the more red shifted he becomes.

Not sure what would happen if he is hovering ...

Hornblower
2008-Dec-04, 04:28 PM
If B is hovering near the event horizon, deep in the well, I think he would see A as blueshifted and having a faster clock.

Once again, don't take my remarks as gospel. I have been away from serious physics for nearly 40 years. I am here to learn as well as to offer answers.

WaxRubiks
2008-Dec-04, 05:10 PM
I think that B will see the Universe as if through a convex lens, ie it will look smaller, and he will even see stars that are behind the black hole.....also as time is faster in the rest of the universe, the light would be blue shifted and very bright(ie more photons/sec)...I'm thinking, although I'm not sure about the hovering/non-hovering bit....

mugaliens
2008-Dec-04, 05:37 PM
The answer depends on what B is doing: falling or hovering?

Grant Hutchison

If B is falling, things would move progressively faster until they all rushed together and *poof"

The end.

If B is hovering, I think someone already mentioned that A would appear blueshifted.

tommac
2008-Dec-04, 05:48 PM
The answer depends on what B is doing: falling or hovering?

Grant Hutchison

Well it is hovering ... that is keeping its distance to A constant.

grant hutchison
2008-Dec-04, 08:06 PM
Well it is hovering ... that is keeping its distance to A constant.Well, remember that it's falling objects that are shortened along their vertical axis in the vicinity of the event horizon, as measured by a distant observer. They're moving through a steep gradient in gravitational time dilation. A stationary object hovering above the event horizon isn't going to be affected in the same way.
I honestly don't know if there is a standard by which we could reasonably compare the heights of stationary objects near the event horizon with those far away.
But we do know that the stationary object near the event horizon sees more distant objects blue-shifted. (Whereas a falling observer gets a complex mix of gravitational blueshift and relativistic doppler redshift.)

Grant Hutchison

tommac
2008-Dec-04, 10:08 PM
Well, remember that it's falling objects that are shortened along their vertical axis in the vicinity of the event horizon, as measured by a distant observer. They're moving through a steep gradient in gravitational time dilation.

Yes they get shorter as they fall ... which it would have had happen as it fell to the point where it started hovering.

No it wont compress further but it is already compressed / dialated compared to what it was before it got that close to the BH.

grant hutchison
2008-Dec-04, 10:36 PM
Yes they get shorter as they fall ... which it would have had happen as it fell to the point where it started hovering.

No it wont compress further but it is already compressed / dialated compared to what it was before it got that close to the BH.You're assuming both ends come to rest at the same time as measured by a distant observer.
And you're assuming that the only way to get to a stationary hover is to free-fall and then stop. You can creep downwards as slowly as you like, even pausing now and then.

Grant Hutchison

tommac
2008-Dec-08, 11:42 PM
You're assuming both ends come to rest at the same time as measured by a distant observer.
And you're assuming that the only way to get to a stationary hover is to free-fall and then stop. You can creep downwards as slowly as you like, even pausing now and then.

Grant Hutchison
Not sure if I assume either.

QUestion ... does the compression happen during decent? Or does it occur from the Gravitational well. My point is that the compressions / timedilation is a state function based on the current depth of the gravitational well you are in. Hovering just keeps the depth of the well constant.

The way I am seeing it ... if this is correct or not I dont know ...
Is that the compression is happening because you are moving relative to space-time.

Space time is being consumed by the black hole and moving like a treadmill. To hover I need to run on that treadmill. From a distant observer I am just standing still ( hovering ). But I ( being near the BH ) have my jets on ... and I see other things moving back into the hole so I feel for the most part that I am speeding through space time.

I AM travelling at near the speed of light just to keep my distance from the BH when I am near the EH.

For a distant observer it appears that I am stuck in time and barely moving.