The discussion revolves around the Black Hole Information Paradox, exploring various theories and interpretations regarding the nature of information in black holes. Participants examine different perspectives on whether information is lost or preserved, as well as the implications of these theories in the context of quantum gravity and unitarity.
Participants express multiple competing views regarding the Black Hole Information Paradox and the nature of unitarity in quantum gravity. There is no consensus on the resolution of these issues, and the discussion remains unresolved.
Participants highlight limitations in the current understanding of quantum gravity and the potential for inconsistencies in semiclassical theories. The discussion reflects ongoing debates and uncertainties in the field.
Pallavi said:the black hole paradox?
Thank u for your response.Scott said:It's called the Black Hole Information Paradox.
Physics isn't like a religion. So "beliefs" are simply working theories. Today you can work with the theory that the information disappears ("Black Holes have no hair.). Tomorrow you can work with the theory that it is preserved.
That said, it seems that most Physicists are more comfortable with the preservation of information than with its loss.
There is also a Black Hole Firewall Paradox. My personal view on that one is that there is no paradox. You would pass through the event horizon without issue and without a firewall. The fact that you would describe the event differently that people other reference frames is not an issue since you will never get to compare notes with those other people.
I was referring to the black hole information paradoxPeterDonis said:What paradox? @.Scott referred to two of them in his post, but he's just guessing that one of those is the one you meant.
A specific reference to what you are asking about would help.
The first resolution basically says that it is not a paradox. It is a paradox only if one insists on unitarity. I personally don't understand why all this is considered a problem. If the conclusion is that unitarity is violated, then so be it. Why call it a problem and try to resolve it (unsuccessfully so far)?Demystifier said:A list of proposed solutions, each with its advantages and disadvantages, is given here: https://en.wikipedia.org/wiki/Black_hole_information_paradox#Postulated_solutions
First, all other quantum theories are unitary, so it is not clear why exactly quantum gravity should be different.martinbn said:If the conclusion is that unitarity is violated, then so be it.
Ok, but gravity is very different from other things, so no need to expect that quantum gravity will be the same as other quantum theories. Also semiclassical gravity suggests that unitarity is not preserved.Demystifier said:First, all other quantum theories are unitary, so it is not clear why exactly quantum gravity should be different.
Ok, but as far as I am aware all these approaches are not finished yet even as a formulation.Demystifier said:Second, various specific approaches to quantum gravity (e.g. AdS/CFT) seem to be saying explicitly that quantum gravity is unitary, so from that perspective one only needs to understand how exactly unitarity is realized in the case of black holes.
How exactly is it different in a way relevant for unitarity?martinbn said:Ok, but gravity is very different from other things,
True, but semiclassical theory is a mixture of classical and quantum theory, so it is not unexpected that it may lead to inconsistencies.martinbn said:Also semiclassical gravity suggests that unitarity is not preserved.
You are right about that. But I am not offering a proof that gravity is unitary. Perhaps it isn't. What I am offering is arguments why the idea that gravity might not be unitary should not be taken easily.martinbn said:Ok, but as far as I am aware all these approaches are not finished yet even as a formulation.
I don't know if it is relevant for unitarity. But it is quite different from the rest, so the argument "everything else is, thus gravity should be" seems weak.Demystifier said:How exactly is it different in a way relevant for unitarity?
True, that is a possibility. But I've never seen people expressing any doubt that black hole may not radiate.Demystifier said:True, but semiclassical theory is a mixture of classical and quantum theory, so it is not unexpected that it may lead to inconsistencies.
I agree with all this. May be I have the wrong impression, but it seems to me that most people think that it has got to be this way.Demystifier said:You are right about that. But I am not offering a proof that gravity is unitary. Perhaps it isn't. What I am offering is arguments why the idea that gravity might not be unitary should not be taken easily.
In string theory, which is the most popular approach to quantum gravity, gravity is certainly not much different from the rest. The same can be said about effective field theory approaches.martinbn said:I don't know if it is relevant for unitarity. But it is quite different from the rest, so the argument "everything else is, thus gravity should be" seems weak.
Yes, physicists are prone to prejudices too.martinbn said:but it seems to me that most people think that it has got to be this way.