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In his book "the black hole war" Susskind writes that in quantum mechanics information cannot be lost because it is unitary. As collapse is not unitary does he say that collapse never occurs?
I believe Susskind favors the MWI, which is a no collapse interpretation, so he would probably say that yes, collapse never occurs.As collapse is not unitary does he say that collapse never occurs?
There is only a bit of bias. The AdS/CFT correspondence is one of the most stunning developments in theoretical physics. It may provide a complete theory of quantum gravity in some universe. The caveats are that although there is much evidence for the correspondence, it remains unproved; also it may not be able to describe qusntum gravity in our universe.susskind does not use the word collapse.
he recalls that black holes evolution can be equvalently described by two
theories GR in 3+1 dimension and an ADS quantum theory in a different space.
he concludes that Hawking lost the war because information is never lost in quantum mechanics
is there a bias in his conclusion?
The statistical ensemble interpretation has collapse. If you wish to preserve unitarity, then you should look at either Bohmian mechanics or the Many-worlds interpretation as apptoaches to the measurement problem.i have of course no answer to the measurement problem but i think that collapse is a wrong concept.
mw interpretation is not the only possibible way to avoid it. collapse only concerns individual measurements.
Statisrical ensemble interpretation does not need collapse and unitarity is safe.
Why not?wigner himself is not a quantum object.
Please give a specific reference. We can't comment on out of context quotes.What do you think about Susskind's sentence: in quantum mechanics informationd can never be lost?
The models you are talking about do not contain any measurements, so the question of whether collapse takes place or not is irrelevant. These models are just the same as, for example, the "internals" of a double slit experiment, where even collapse interpretations agree that the evolution of the wave function is unitary; the only "collapse" is at the end of the experiment when the pattern is observed on the detector screen. The equivalent of that in the models you refer to is the universe in the infinite future, when all of the black holes have evaporated and all that is left is an infinite expanse of radiation at extremely low temperature. What "unitary evolution" means in this context is that, for a hypothetical observer in that infinite future universe, they can't tell from any of their measurements whether the infinite expanse of radiation came from the evaporation of black holes or from some other process (like matter-antimatter annihilation leaving only radiation behind) that didn't involve black holes at all.any collapse would break the unitarity
I haveNot necessarily. In the usual collapse interpretation of QM, the non-unitary evolution happens only at the instant of measurement. So even if one accepts the collapse interpretation associated with measurement, one still expects that evolution should be unitary before measurement. On the other hand, black hole evaporation seems to imply a non-unitary evolution before the measurement.
I have always wondered why the absorption of matter by a black hole could not be considered a type of measurement, which would then take care of the loss o information. I am sure this is stupid for some reason but I have never seen a clear explanation why so.Not necessarily. In the usual collapse interpretation of QM, the non-unitary evolution happens only at the instant of measurement. So even if one accepts the collapse interpretation associated with measurement, one still expects that evolution should be unitary before measurement. On the other hand, black hole evaporation seems to imply a non-unitary evolution before the measurement.
Which is a pop science book, so it's not a valid source for discussion here. You need to look at actual textbooks or peer-reviewed papers.it is in "the black hole war" by Susskind at the end of paragraph 22
Yes he is - we all are. There is a coarse graining argument that shows how our classical world emerges from the scale below us - but that scale is quantum and so is our scale - its just - as I mention below different physics emerges at different scales - but it's all quantum stuff. You cant choose to view and not view him as a quantum object - he is one all the time.wigner himself is not a quantum object.l
I just want to mention Susskind does write some excellent actual textbooks for a 'lay' audience under the Theoretical Minimum series. You just need a bit of calculus and its quite accessible if you think a bit - you are not not spoon fed - its real physics. They of course can be freely discussed here. Popular writings, while often interesting to read, I read them myself, are problematical to the aims of a forum like this.Which is a pop science book, so it's not a valid source for discussion here. You need to look at actual textbooks or peer-reviewed papers.
Suppose we say that "Wigner is a physicist". Can that be translated into quantum mechanics? I guess it's possible that you could define some properties of a bunch of atoms that represented physicist from non-physicist. But, it seems to me, that it may be impossible to disentangle that property from the atomic configuration.Yes he is - we all are.
Why is that?The statistical ensemble interpretation has collapse.
This seems a wise statement that is as close to the truth we can come, and not as but not as silly as it may first seem.this is written by Jean Pierre Luminet
any collapse would break the unitarity. so physicists insist on the fact that unitarity is a law of quantum field theory.
one often read that states evolve unitarily except when they do not....
Well, something that is strange about the loss of information in a black hole, compared with a normal measurement is this: In a normal measurement, you choose an observable to measure, and (presumably) after the measurement, the system is in an eigenstate of that observable. If you choose to measure the spin of an electron along the x-axis, then afterward the electron is either spin-up or spin-down along that axis (and not a superposition of those two possibilities). If you don't know the result of the measurement, but only know what was measured, then you would describe the system afterward as a mixed state of the two possibilities (which is mathematically different from a superposition of the two possibilities).I have always wondered why the absorption of matter by a black hole could not be considered a type of measurement, which would then take care of the loss o information. I am sure this is stupid for some reason but I have never seen a clear explanation why so.
I do not see anything stupid with this. As extension to this, I have always "wondered" why not ANY interaction can not be seen as an "observation" - give the right perspective (ie. choice of observing system). Any my own understanding and journey has come to make me completely convinced that this CAN indeed be so. And that its even the KEY to understanding interactions and their unification. But there is still noone that has structured and explained this in a formal way. So except for the fact that we have still to see a fundamental paper that solves and explains this, i an totally convinced it is the best way to understand this.I have always wondered why the absorption of matter by a black hole could not be considered a type of measurement, which would then take care of the loss o information. I am sure this is stupid for some reason but I have never seen a clear explanation why so.
Well, there are two different roles of measurement in QM:I do not see anything stupid with this. As extension to this, I have always "wondered" why not ANY interaction can not be seen as an "observation" - give the right perspective (ie. choice of observing system).
QM is about matter and energy - not human concepts such as occupation.Suppose we say that "Wigner is a physicist". Can that be translated into quantum mechanics?.