On Feb 23, 7:13 pm, Jesse Mazer <laserma...@hotmail.com> wrote:

> Having read the book a while ago, my memory is that Price offered this idea 
> as a conceptual argument for how one *might* explain things using the EPR 
> experiment, but I don't think he ever would have said that this idea makes 
> delayed-choice and EPR "trivial" to explain--to really explain them, you'd 
> have to provide a quantitative theory showing the precise connection between 
> these ideas about causality and the results of those experiments, and Price 
> didn't have one.

it's true that Price is not a physicist, so he has to rely on others
to provide a theoretical underpinning, or not as the case may be. if
understand him correctly, and I'm quite willing to admit that I may
have failed to do so, his suggestion is that the physical theory
already exists, and is the standard formulation of quantum mechanics.
My use of "trivial" was only intended to indicate that using his
approach allows these phenomena to be explained using standard quantum
theory, while most other explanations require some sort of extra input
- faster than light signalling, and so on. (I believe the MWI doesn't
require any extras to explain EPR?)

When you mention "hidden variables," I assume you mean that particles
are in a definite state at a given time, rather than "undecided until
measured" ? If so, then I believe that is (supposedly) an outcome of
Price's approach, assuming I've understood him correctly. I don't
think there is a problem explaining why you can't send information
back in time. Surely to obtain a useful back-in-time signal from the
system would require some form of amplification that would also have
to operate backwards in time? But Price is only suggesting that time-
symmetry is significant within a given quantum interaction; it can't
be ampified.

> Another thing to keep in mind is that Newtonian laws dealing with things like 
> gravity and elastic collisions are time-symmetric too, as are Maxwell's laws 
> of classical electromagnetism, but you don't see anything analogous to the 
> EPR experiment or the delayed choice experiment in classical physics 
> (including relativity without quantum theory). So merely pointing to the 
> time-symmetry of QM doesn't in itself explain much about these phenomena.

I wouldn't say that Price is "merely" pointing to the time-symmetry.
He is suggesting that, given the time symmetry that most physicists
agree exists, then there are certain outcomes we should expect in
systems where the information content is very limited, i.e. to quantum
states, and that these seem to match those we observe (e.g. Bell's
inequality, etc). Having read any number of very complex attempts to
explain why there is an "arrow of time" given the apparent
indifference of most physical laws, this seems to me to be a line of
enquiry that is at least worth pursuing.


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