Quote:
Originally Posted by Dave2042
Agree with all this, but a slight expansion on the last point.
It is certainly true that we don't know what is going on inside S, in the sense that it is not something we have observed, and potentially can't observe even in principle, and so it's entirely possible that our current understanding of this is not entirely correct (ie some aspects of GR will require some modification). Of course this is a subset of the broader truth that we know that both GR and QM can't be completely correct and that one or both will need some adjustment.
That said, I don't think it's fair to say that we don't know in the sense of being entirely clueless. We know that GR is a very good description of most things. In a large enough black hole, well away from the singularity, space locally doesn't look different from space outside a black hole. Therefore it is reasonable to assume that it's pretty unlikely that GR isn't a good description of it.
I do get annoyed when people (not directed at you, Steven, or anyone else in particular) suggest that just because we don't perfectly understand some extreme phenomenon, that means all science is up for grabs and scientists can't be trusted on anything.
Harrumph.
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Hello Dave,
About the only the thing we do know as you have stated is that for a sufficiently massive black holes the local space time on either side of the horizon is essentially equivalent.
The problem is how one measures space and time inside the horizon.
For example if you ask astrophysicists how they would measure the distance between the singularity to a spacecraft orbiting outside the event horizon of a BH, they will give a convoluted answer known as the circumferential distance. In other words they can only calculate the distance through the circumference of the orbiting spacecraft.
Suppose the orbiting astronauts attempted to directly measure the distance using a "gigantic" measuring stick. Outside the event horizon each pointer on the measuring stick is separated by a distance interval but not separated in time as a clock at each pointer is measuring the same time.
What happens when the measuring stick is passed over the horizon.
Assuming the stick isn't destroyed by tidal forces, part of the stick outside the horizon is still measuring distance at the same time.
The part of the stick inside the horizon, something very strange is happening, if the mathematics describing what is occurring inside the horizon is correct, then the pointers are no longer separated by distance but are separated by time.
Hence it is impossible to directly measure the distance as time and space inside the horizon is very different from the astronaut's own frame of reference.
The point is we don't understand what's going on inside a BH because we can't even measure what we trying to define.
I think the point Alex was making is "what is it like on the inside" rather than what is it like from the perspective of someone looking in.
I have absolutely no doubt on the existence of BHs given the overwhelming evidence.
Regards
Steven