B Is Decoherence Possible Without Collapse?

[jlcd]

Beta decay, quantum fluctuations, even random vacuum polarizations are all manifestation of collapse, isn't it?

The arguments being that in pure unitary wave function, there will be no phase randomization of any kind.

Do you consider beta decay as example of decoherence?

For decoherence to exist, there should be collapse first. Right.

 

[DuckAmuck]

If one state decays into another, it's usually represented by a probability amplitude of the overlap between the initial and final states. I'm not sure what you mean by "collapse". It's not the same thing as "collapsing a wave function", if that's what you're asking.

 

[Demystifier]

Beta decay, quantum fluctuations, even random vacuum polarizations are all manifestation of collapse, isn't it?

In a sense yes, but not necessarily in a way you might think.

Do you consider beta decay as example of decoherence?

Yes.

For decoherence to exist, there should be collapse first. Right.

Definitely no. Decoherence comes first.

 

[jlcd]

In a sense yes, but not necessarily in a way you might think.Yes.Definitely no. Decoherence comes first.

Please go to this thread where I inquired exactly this. I gave links and the arguments that without collapse, there is no decoherence. Don't you agree with it and why? The argument goes like this:

Mathematically, decoherence is the decay of the off-diagonal elements of the system density matrix in a specific basis. Now the paper
http://philsci-archive.pitt.edu/10757/1/Einselection_and_HThm_Final.pdf (see also http://transactionalinterpretation....ally-split-in-the-many-worlds-interpretation/) is saying that "The crucial point that does not yet seem to have been fully appreciated is this: in the
Everettian picture, everything is always coherently entangled, so pure states must be viewed as a
fiction -- but that means that it is also fiction that the putative 'environmental systems' are all
randomly phased. In helping themselves to this phase randomness, Everettian decoherentists
have effectively assumed what they are trying to prove: macroscopic classicality only ‘emerges’
in this picture because a classical, non-quantum-correlated environment was illegitimately put in
by hand from the beginning. Without that unjustified presupposition, there would be no
vanishing of the off-diagonal terms and therefore no apparent diagonalization of the system’s
reduced density matrix that could support even an approximate, ‘FAPP’ mixed state
interpretation."

Therefore, without collapse to randomize the phases where initially "everything is always coherently entangled", there is no decay of the off-diagonal elements of the system density matrix hence no decoherence. Do you agree or not and how come?

 

[StevieTNZ]

Please go to this thread where I inquired exactly this. I gave links and the arguments that without collapse, there is no decoherence. Don't you agree with it and why? The argument goes like this:
...
Therefore, without collapse to randomize the phases where initially "everything is always coherently entangled", there is no decay of the off-diagonal elements of the system density matrix hence no decoherence. Do you agree or not and how come?

See my post https://www.physicsforums.com/threads/decoherence-clarification.828712/#post-5314332

 

[Nugatory]

Please go to this thread where I inquired exactly this. I gave links and the arguments that without collapse, there is no decoherence. Don't you agree with it and why? The argument goes like this:
..."The crucial point that does not yet seem to have been fully appreciated is this: in the Everettian picture...

Note the text that I have marked in boldface. The paper you are quoting from is talking about the Everettian picture has with decoherence; it doesn't have anything to do with the way that decoherence appears as a consequence of unitary evolution and it most certainly is not saying what you're claiming it does.

As this thread is based on a misunderstanding that has already been corrected repeatedly, it is closed. Your other thread on decoherence and collapse remains open.