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PaleMoon
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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?
PaleMoon said:As collapse is not unitary does he say that collapse never occurs?
PaleMoon said: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?
PaleMoon said: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.
PaleMoon said:wigner himself is not a quantum object.
PaleMoon said:What do you think about Susskind's sentence: in quantum mechanics informationd can never be lost?
PaleMoon said:any collapse would break the unitarity
I haveDemystifier said: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.
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.Demystifier said: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.
PaleMoon said:it is in "the black hole war" by Susskind at the end of paragraph 22
PaleMoon said:wigner himself is not a quantum object.l
PeterDonis said: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.
bhobba said:Yes he is - we all are.
Why is that?atyy said:The statistical ensemble interpretation has collapse.
PaleMoon said: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...
nrqed said: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.
nrqed said: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.
Fra said: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).
PeroK said:Suppose we say that "Wigner is a physicist". Can that be translated into quantum mechanics?.
PaleMoon said:Hi Bhobba
i am glad to read you. i am also fond of things like Busch-Gleason theorem. probabilities are traces
and in your two axioms all is about operators and outputs
i wonder if the purification theorem is not the key to this no information loss
observed operators obey Lindblad equations and entropy may increase.
but it is possible to enlarge the hilbert space so that the global state follpws a schrodinger evolution
could it be what is suggested by these physicists?
stevendaryl said:Well, there are two different roles of measurement in QM:
Simple interactions do not do either of these.
- Singling out a preferred basis (namely, the observable being measured)
- The selection of one outcome out of a set of possibilities, according to the Born rule.
Fra said:. 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 no one 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.
/Fredrik
stevendaryl said:Well, there are two different roles of measurement in QM:
Simple interactions do not do either of these.
- Singling out a preferred basis (namely, the observable being measured)
- The selection of one outcome out of a set of possibilities, according to the Born rule.
Fra said:In my post i should have emphasized more that no one that has structured and explained this in a formal way yet. Surely the standard formalism is inadequate to described things in the spirit i envisioned.
PaleMoon said:take an electron, you want to observe its spin along some direction. you send it through a stein gerlach apparatus and it inreracts with it. at this level you have measured nothing. you need a screen in front of the possible paths. you need something to encode the output.
so any interaction is not an observation. it has something to do with reversibility and unitarity.
PeroK said:if citizenship is a defining property of a human being, then a human being is not a quantum object
PeroK said:the question is whether a complex system can assume properties not inherent in the underlying atomic configuration. The reductionist position would be that it cannot.
PeroK said:does that mean that what someone has written or achieved in life is either not a defining part of them or is inherent in their current atomic structure?
Yes, we agree here.stevendaryl said:Well, the standard formalism assumes that when someone performs a measurement, he knows what it is that he is measuring, and furthermore that he can recognize a distinct outcome for the measurement. It doesn't really explain these two things, but just assumes them. The founders of the Copenhagen interpretation, Bohr and Heisenberg and those guys, made the distinction between microscopic systems, which are described by quantum mechanics, and measurements/observations, which are (approximately) described by classical mechanics.
PeterDonis said:No, that's not the reductionist position. The reductionist position is that, no matter what set of properties a complex system has, the system is still made of the same small set of fundamental objects. Or, to put it another way, you don't need any new laws of physics or any new fundamental constituents of matter to make, say, US citizens, as opposed to, say, rocks. You just need to put together the same fundamental constituents, using the same laws of physics, in different ways.
bhobba said:I think 1. has been solved, at least Schlosshauer thinks it has (I do as well but am not as expert as he is).