> Date: Mon, 22 Feb 2010 21:42:54 -0800
> Subject: Re: Many-worlds vs. Many-Minds
> From: charlesrobertgood...@gmail.com
> To: everything-list@googlegroups.com
> On Feb 23, 6:08 pm, "rmiller" <rmil...@legis.com> wrote:
> > If we accept what the laws of physics appear to say,
> > that nature is for the most part indifferent to the direction of time,
> > this implies that quite a few things are a lot less strange than we
> > think. Delayed-choice and ERP experiments become trivial to explain,
> > for example, once we stop thinking of the particles involved as
> > similar to macroscopic objects with a clear arrow of time, and assume
> > their state is equally constrained by past and future boundary
> > conditions (e.g. the emitter and detector). This view is similar to
> > Cramer's Transactional Interpretation and Wheeler-Feynman Absorber
> > Theory, but makes them both look unnecessarily complicated, since it
> > doesn't require any new physics, it merely suggests we take the
> > existing physics at face value (as Hugh Everett III once did, with
> > similarly interesting results).
> >
> > Agree in part. It seems as though the same processes that result in the
> > "laws" of thermodynamics/entropy may operate similarly across MW.
> Time-symmetry does appear to make a lot of "quantum weirdness" as less
> weird. To take the ERP experiment, there is no need to assume any
> action at a distance or FTL effects if we allow the state of the
> measuring apparatus to contribute to the state of the emitter. (Also,
> if we aren't going to accept time symmetry, there is an explanatory
> burden as to why the apparent time-symmetry isn't real.)

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. He suggested that it might be fruitful to look for a hidden-variables 
theory where things that happen to particles at later times can affect the 
values of hidden variables at earlier times (in contrast to Cramer's 
transactional interpretation which is *not* a hidden-variables theory as I 
understand it), but he didn't have a detailed theory of this kind to offer. 
Such a theory would also have to explain why we are not able to use things like 
the delayed choice quantum eraser to actually send information backwards in 
time--for example, we can't look at the screen behind a double-slit and 
determine whether the which-path information for the particles that hit the 
screen will in the future be erased or preserved (see the last two paragraphs 
of the section 'The experiment' at 
http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser#The_experiment for a 
summary of why this doesn't work).
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.                        

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