On Sunday 12 August 2007 12:48, Pat Hayes wrote:
> > ...
> >
> >Anyway, there are some so-called "interpretations" of quantum theory
> >that suggest a limited form of backward-in-time influence. I'm
> > thinking of John Cramer's "Transactional Interpretation of Quantum
> > Mechanics"
>
> +1 ! My absolute favorite explanation of QM. Way
> more convincing (and intuitive) than the
> Copenhagen interpretation, with all its
> mysterious overlapping states and half-dead cats
> and collapsing wave functions and so on. See
> http://www.npl.washington.edu/npl/int_rep/tiqm/TI_toc.html
> for a pretty readable account. (01)
If only they were half-dead. But completely dead and fully alive at the
same time? (02)
> ...
> >
> >Personally, I find it delightfully mind-boggling. ...
>
> But the delicious thing is the observation that
> (following special relativity), these are in fact
> contemporary over long enough distances. Put
> another way: from the photon's point of view, it
> takes no time at all to go any distance. So going
> backwards or forwards in time at the speed of
> light isn't really much of a big deal. At the
> speed of light, there is no time in the ordinary
> sense. (03)
I like to think of it, metaphorically, of course, as the
photon "kissing" both the emitter and absorber simultaneously. Cute,
eh? (04)
One simple, everyday way to think about this is that photons are
not "cast off" by emitters, they are _exchanged_ by mutual "agreement"
of the emitter and absorber. (05)
It suggests an interesting gedanken experiments. For example, what would
happen if a single hydrogen atom in a non-ground state were situated at
the center of a perfectly reflecting sphere? Would it ever emit a
photon? The only destination for that photon would be the same atom. If
photon were cast off, then a photon would be emitted, reflected by the
inside of the spherical surface and impinge again on the atom that
emitted it. It would either be absorbed or continue to be reflected
inside the sphere until it eventually were absorbed, leaving the
hydrogen atom again in an excited state. (06)
On the other hand, the transactional interpretation would suggest that
the excited hydrogen atom would remain in its excited state, since it
cannot participate in the transaction that allows it to absorb the
photon it would emit. (07)
Unfortunately, for a number of reasons, I cannot think of a way to carry
out such an experiment. (08)
The next thing to do is dispense with all this "many worlds" nonsense
that some justify based on the single-photon, multiple-slit
experiments. It boggles my mind (in an entirely unpleasing way) that
the proponents of this notion completely overlook the fact that photons
are bosons and don't interfere with each other, let alone themselves,
in this manner. When you apply the transactional interpretation to the
observation that in a two-slit experiment where only a single photon
ever traverses the apparatus at a time and yet an interference pattern
emerges in the distribution of the photon absorption locations, you
immediately see that it's the wave function of the emitter that
produces the interference pattern (since it is defined throughout the
light cone of the emission event), not the photons traversing the
path(s) between the emitter and the absorber (detector). (09)
Another way to think about this is that photons cannot "cancel" each
other out, since their energy must be absorbed (or they keep
propagating). How could two (or two ... what? copies? ... of the same
photon) interfere with each other and have their energy disappear? Of
all the "laws" of physics that have had to be reconsidered, the
conservation laws stand strong. (010)
> Which is one reason I love the Cramer picture. (011)
I love it because I still think it offers a way to signal backward in
time. I've even devised an experiment, which I think could be carried
out in any decent laser optics lab, that would illustrate (or not) the
phenomenon I have in mind. (012)
> Pat (013)
Randall Schulz (014)
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