QM, EPR, A/B

[Tyler Durden]

Actually, Tyler Durden (ie, me) wrote what is attributed to the generic 
anonymous name of Norman Nescio. Anyway,...


>Part of the problem is that the detection equipment is many fermions
>looking at single particles.  I think QM is easier to understand when
>looking at an ion trap.  There are lots of photons around for every atom
>but the interactions are with fields and the detection is of single
>photons (again with massive amounts of equipment, but the atoms don't
>interact directly as in EPR or double slit).

With all due respect, Pooey Dr Mike. Take a nice, straightforward EPR using 
two correlated photons produced by KDP-downconversion. How do you exaplain 
the EPR experiements where pairs of photons are created via KDP 
downconversion? The two particles are separated at birth and travel through 
different paths through the apparatus. (And this apparatus can be made 
aribtrarily large.) If the apparatus does not permit us to determine the 
path of any single photon, the two photons will have completely coupled 
measureables (eg, polarization) at the output. The moment will are able to 
determine the path of ONE of the photons, then the measureable of the other 
becomes completely de-correlated from the other. This is true on the single 
photon level, and looked at up close its pretty startling.

Now the odd thing (if this isn't odd already), is that we can (and have) 
perform the change from isolatable to nonisolatable AFTER THE PHOTONS HAVE 
ENTERED THE APPARATUS. (This was suggested by Wheeler and done around '94 as 
I remember). In a sense, then, the photons are 'aware' of events happening 
(relatively speaking) backwards in time. And this is not theoretical. It was 
predicted via quantum theory and seen in the lab many times.

Now obviously we could step back and say that "QM is a useful computational 
tool. Let's not worry about reality", but that's an intellectual dodge. 
Classical physics grew up around the desire to understand natural reality, 
and this "new" fad of ignoring what QM says about reality only arose as a 
way to move QM forward in the early days. Look, it's not like we say "Don't 
think of light as an electromagnetic wave. E-M theory is merely a useful 
computational tool". Likewise just because we are in the odd situation of 
not knowing what QM says about the universe doesn't mean its not saying 
anything, or that what its saying is of no interest.

With EPR (and, arguably, A-b), we are confronted with obvious "proof" that 
these particles communicate in ways that are completely different from the 
models developed prior to 1910 or so. (One of the few intelligent thoughts 
I've had on the subject is that the particles are still a single quantum 
object prior to measurement.)

With respect to Cypherpunks and cryptography, then, we would be 
intellectually hypocritical if we thought there was anything inherently more 
secure about quantum cryptography. But we (I mean, pretty much every working 
physicist in the world) DO believe this, because this is really the way 
reality "works". Wavefunction collapse actually "objectively" (if that's the 
right word in the quantum world) happens and there's no undoing it. It's a 
basic physical property of the universe.


With respect to many worlds, David Deutch, et al have argued that for any 
single path taken by a particle in a quantum there are innumerable "shadow 
photons" in the other universes that communicate with the observed photon. 
We also see just one possible but the complete collection of shadow photons 
take all possible outcomes. Now while I don't really buy this explanation, I 
DO buy Deutch's desire to find a picture of the underlying reality (we once 
spoke on this issue and wildly agreed).

I could go on but I've got work to do. No one's actually read this far 
anyway, have they?

-Tyler Durden






>
>QM is a nice model that works.  It is a good mathematical description of
>observed phenomena.  What else do we need?  The idea that a photon
>"passes thru" one slit or the other is just a model.  What is the slit?
>It's really a whole bunch of fermions in a spacial pattern, and when an
>electron or photon interacts with that distribution we get the observed
>"self interaction" result.  The model is self interaction.  That may have
>nothing to do with reality.
>
>Patience, persistence, truth,
>Dr. mike


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