Does GR even describe space as "moving"?
As I understand it yes. It is counter-intuative in the extreme but space and time are said to fall into a black hole. Likewise a spinning black hole drags time and space around with it. All of this would be nonsense unless space itself could move.,,,,Indeed if this were not part of GR then a black hole could never be black or indeed have an event horizon. ...But the photon cannot escape because although it is moving outward at c, that is only relative to space. At the EH space is moving inwards at c and so the photon stays at the EH. Further in space is moving inwards at greater than c and this drags the photon back to the singularity.
Most of that reply is not correct.
While in a novice sense, some consider space itself as 'expanding' I don't think any scientist nor anyone in these forums would agree it 'moves'. That a spinning black hole' drags space and time' is a reference to frame dragging, not any motion. It's an effect our our artifical [theoretical] overlay frame. Read about it in Wikipedia and note the reference to
linear frame dragging: do you also think a moving particle 'drags space and time with it?'...or is it curvature that changes??
http://en.wikipedia.org/wiki/Frame_draggingBlack hole characteristics do NOT involve 'space moving'. That is not part of SR, GR nor cosmological understanding. Any observed photon motion is relative to the observer! Space is NOT moving inwards at C at the event horizon. The only thing that moves at c at the horizon are PHOTONS. Inside the horizon, space is NOT moving towards the singularity at c! What prevents a photon from escaping is gravitational spacetime curvature.
Check this:
In Fabric of the Cosmos, Brian Greene says in a footnote (Chapter 12, #7,Page 527)
"...It's somewhat of misnomer to speak of the "center" of a black hole as if it were a place in space...Just as you can't resist going from one second to the next in time, you can't resist being pulled to the black holes "center" once you've crossed the event horizon...Thus rather than thinking of the black holes center as a location in space it is better to think of it as a location in time...it may be true that its ...where spacetime comes to an end...if we had equations that don't break down deep inside a black hole we might gain important insights into the nature of time..."An observer freely falling from a distance outside a black hole [or a particle], never exceeds c and is in fact unaware when she passes the event horizon: nothing happens there except that in passing, the observer loses causal connection with the outside universe. And from a distant observer's perspective, 'time stops' at the horizon so the infalling local observer APPEARS to hang there forever...to future infinity. But that, too, is a coordinate effect, NOT a physical one.
JesseM explained elsewhere:
Keep in mind that there's no coordinate-independent way to define the amount of time dilation for a clock at various distances from the horizon--what we're talking about is the rate a clock is ticking relative to coordinate time, so even if that rate approaches zero in Schwarzschild coordinates which are the most common ones to use for a nonrotating black hole, in a different coordinate system like Kruskal-Szekeres coordinates it wouldn't approach zero at the horizon at all.
Once again, different COORDINATES change everything!So the basic rule to remember is that in GR, curved spacetime, distance, velocity,acceleration and even energy are ill defined. Different [coordinate] observers 'see' [predict] different things...even at different times [non simultaneity] and these effects are magnified in cosmology because of the vast expanses we try to describe.
Hope all this helps...it sure took me several years to digest what little I know.
