--- In [EMAIL PROTECTED], "Marvin Long, Jr." <[EMAIL PROTECTED]> wrote:
> On Mon, 19 Feb 2001, Dan Minette wrote:
>
>
>>1) The spin in direction 2 is either up or down. That is to say the
>> hidden variables are so arranged that up will be measured or
>> down will be measured.
>>2) The distributive law is true:[snip]
>>3) Statistical analysis of finite numbers of random events is
>> valid.[snip]
>>4) The empirically confirmed laws of physics are valid
>>5) There are no backwards in time signals.
>
> [I assume 4 and 5 are lumped together below. -msl]
>
>What I don't understand is how getting rid of the first assumption >doesn't
undermine science, i.e. QM. My (quite possibly erroneous) >belief is that
QM stipulates that for each of the three "axes of >rotation" (directions 1,
2, 3) a photon must "spin" either up or >down.
No, it doesn't. And that's absolutely critical. In QM, the state is given
as (|u>+|d>)/sqrt(2). It is in a superposition of up and down in every
direction.
>In other words, it seems to me on the face of it that to
>abandon #1 above implies that QM, as a description of reality, is >either
wrong or incomplete.
But it was never meant to be a desription of reality apart from us. It is a
desription of what we observed. Science is not about reality; its about
observations.
>
> *****
> Actually, maybe we should make sure my (dumbed down) grasp of the gist of
> the mystery is sufficiently valid for us to talk coherently to each other.
>As I understand it, when you measure--in sufficiently high quantity >to get
statistically irrefutable results--the states of entangled >photons that are
sufficiently far apart that no light-speed signal >could pass between the
two sites of detection in the interval between
>measurements, you get results that deviate significantly from the >results
predicted by established QM.
No. We get results that are consistant with established QM. They are
inconsistant with local hidden variable theories: theories that attempt to
preserve realism.
>The size of correlation between the various directional spins of >entangled
photons isn't as high as expected.
Its exactly what is expected by QM. Its inconsistant with local realism.
>
>The discrepancy in this case suggests that somehow information is >passing
between entangled photons at FTL speed, a violation of >special relativity,
Not unless you assume realism. There are spacelike correlations. But, the
operators commute: that is to say it doesn't matter which measurement you do
first, the answers are the same. That's not true with signals. If send a
signal from A to B, it matters whether I look at B for the signal, and then
send one from A or if I send a signal from A and then look at B for the
signal. That's why this is not a signal. There is no way to know what is
being done at A by measuring at B.
>because it implies that the photons' entangled properties are not >fixed at
the time that they're still connected.
That is true, but it doesn't violiate SR.
>
> a. Why is questioning #1 above (which to me appears to mean >questioning
an empirically established fact...isn't it?...of QM)
>better than questioning #4 or #5?
No. QM and the emperically established facts and SR are all consistant.
Indeed, in quantum field theory, relativistic QM, one defines locality as
"spacelike operators must commute (see above).
>
>b. At what point do we pass from saying, "Here's a natural
>occurance we don't understand; our theories don't account for it, so
>we need to refine our theories," to, "The disagreement of this
>natural occurance with established theory undermines the assumption
>of realism that the world can be known through science."
Well, after 70 years of verification of a wide range of predictions, after
the introduction of wide ranging techonology based on QM, after >15 orders
of magnitude have been investigated without showing any significant
difficulties with QM, I think it is fair to start challanging metaphysics.
The theory fits the data perfectly well...its the realistic interpretation
that has problems.
>
>c. Precisely which assumption of realism is undermined by QM?
Electrons, photons, quarks are things that exist apart from our
observations. This lack of microrealism quickly undermines macrorealism.
> d. Why should we say, "Realism has a hard time accounting for
>quantum mechanics," instead of, "Quantum mechanics has a hard time >dealing
with the behavior of entangled photons measured in this
>particular way?"
Because QM deals perfectly well with these entangled photons, through the
use of superpositions.
Dan'm Traeki Ring of Crystallized Knowledge.
Known for calculating, but not known for shutting up
