You are entitled to think he is wrong.:shrug: The thing is to show he is wrong, and I don't believe that has been done. The nature of Hawking Radiation is still rather less than certain as per the near certainty of GR say, but again as I have said, appears as a rather logical extension imh of quantum theory.

I disagree. The trans-Planckian problem shows that the original derivation by Hawking is not a derivation but an absurdity. Because it depends on absurd assumptions.

Now, Unruh argues that one can, nonetheless, show that Hawking radiation exists. Fine, but in this case, he has to show this. It is not me who has to show that he is wrong. For me, it is sufficient to show that the argument is not decisive.

The next point is to clarify that in some part of this I agree that it exists - namely, during the collapse and a very, exponentially, short time after the collapse. As well, I do not doubt at all that this exponentially decreasing radiation will be like Hawking radiation, namely, it will be the radiation of a black body with the temperature computed by Hawking. The disagreement is about the effective size of this black body. I think this size will exponentially decrease after the collapse. So, I do not claim that everything is wrong in Unruh's papers, not at all. All the computations which show that the radiation will be radiation similar to a black body of Hawking temperature are fine. I have no problem at all "acknowledging" that 1 sec. after the collapse the black hole will radiate like a black body of Hawking temperature of size $$e^{-10^5}m$$. As well, I have no problem "acknowledging" that during the collapse itself there will be Hawking radiation. Because above statements simply are what I think.

Then, there is a third point. The point is that in the hydrodynamic analogy there is no general covariance. Or, better, there is general covariance in the large distance approximation. But there is none in the fundamental, microscopic domain. But the microscopic domain is the relevant one. It is the domain where, following Unruh, the absurd assumptions are transformed into a more reasonable one.

In other words, the Hawking radiation following Unruh is Hawking radiation in an ether theory. General covariance no longer holds, thus, one can no longer apply the equivalence principle, except in the large distance approximation. What is indistinguishable in the large distance approximation - if the ether moves or is at rest - is distinguishable in Unruh's analog gravity. The velocity of the "ether" is, in this analog theory, simply the velocity of the liquid. And I have found in Unruh's earlier papers places where this point is accepted, that one has to make assumptions about the "preferred frame". And, in particular, he assumes the preferred frame to be that of an infalling observer.

This is, indeed, the preferred frame of the black hole analog. The liquid is flowing in such a way that it is initially in a normal range and, then, inside a nozzle, reaches supersonic velocity. And this is also the natural preferred frame during the gravitational collapse itself - all the matter is infalling, so, it would be natural to have an infalling ether too.

Unfortunately, this is not the natural frame for an ether after the collapse. There is no opening of the nozzle at the center of the black hole for a constant inflowing ether to go away. So, what one has to expect for the gravitational collapse is, after some time, a stable configuration of the ether. But if the ether is stable, there will be no Hawking radiation. This is well established and acknowledged - stable stars do not Hawking-radiate.