At 02:09 AM 12/27/2012, David Roberson wrote:
Abd, it is all in the perception of the various observers. Each one does not detect anything special about their own situation. We, as the far off guys, see the fellow on the ship being affected by the gravitational field he is within. That field is so intense that we see it slow his time measurements down to zero eventually.
Maybe. You say so. Why? At the event horizon, the field is not infinitely strong.
He does not see this happening from his point of view. He sees that big black zero ahead of him and kisses his butt goodbye. It takes very little time as far as he is concerned until he becomes bacon. For us, an eternity passes before he dies.
I don't know what he sees.
Now, I find it interesting what we should observe during this process. I agree with you that initially the ship leaving our vicinity must appear to accelerate toward the black hole. I am confident that we could bounce radar pulses off of the ship and measure its velocity and distance from us and that these measurements would show what is expected for a while.
Okay. What would they show?
The acceleration of the ship would increase as the ship got further away from us until time dilation caught up with the device.
Time dilation is inferred, it is not observed by us unless we can observe a clock. But I don't know, here, how to distinguish doppler shift in the signal coming to us from the gravitational shift, from time dilation.
There must exist a distance from us at which the ship begins to slow down from our perspective.
That is not a consequence of time dilation. And the speed of light remains the same. If we send radar pulses to the ship, the time of flight would correctly show the distance. However, there would be a point where the radar pulses don't return.
The concept that the ship slows down would imply that this point is never reached. However, it appears, matter *is* falling into the black hole. It is disappearing. A writer here imagined that incoming matter was "smeared all over the face of the black hole," which is a different perspective, i.e, that it never falls in, to an outside observer.
I think this whole thing is a mess.... I'm fully aware that the mess is in my thinking, but I rather doubt it's just me.
I have not read any definitive discussion of black holes from anyone who actually understands the concept, in all its detail. I haven't read Hawking. Maybe I should, but not now.
This must be where the time dilation due to the gravity field exceeds the apparent acceleration due to the pull of the field. As the time dilation wins the battle, the ship appears to decelerate until it eventually comes to a stop.
We don't see time dilation, so this is incorrect, I think. That is, we can see that time *on* the ship is slowed, if we can observe a ship clock, but we want to measure the ship's velocity in *our* frame, not the ship frame.
I suspect that you can obtain an idea of how a signal behaves when transmitted from us to the spaceman by thinking of behavior that is reversed from the other direction. All of the frequencies we transmit will be blue shifted by the same proportion. Have you practiced your Donald Duck speak lately? Perhaps a bottle of helium might help!
Yes, I've looked at this from the other direction, that is a useful analytical approach. If we are using radar, our radar pulses will hit the ship having been blue-shifted by gravity. But the ship is gaining velocity as it approaches the black hole, so that's an effect in the other direction. When the come back to us they are again red-shifted. Were the ship stationary in our frame (as is being proposed, roughly), and outside the horizon, the blue shift and red shift would cancel out. What would time-of-flight show?
I think we really need to understand what the gravity is at the event horizon. If it's true that no path of light can escape, *from what perspective is this true.* Is there some absolute locaion for the event horizon in our frame (center of mass frame for the black hole, but with external anchors or reference points). The black hole is stationary in our frame.
