On Sun, 21 Oct 2007 21:02:09 -0400, "Neil Bates"
<neil_delver@[EMAIL PROTECTED]
> wrote:
>
>From http://physicsworld.com/cws/article/news/27640
>
>
>RELATED STORIES
> a.. Mesons violate Bell's inequality
> b.. Feature: Quantum theory: weird and wonderful
> c.. Photons denied a glimpse of their observer
>Related Links
> a.. Markus Aspelmeyer
>Restricted Links
> a.. Nature 446 871
> News
>Apr 20, 2007
>
>Quantum physics says goodbye to reality
>Some physicists are uncomfortable with the idea that all individual
quantum
>events are innately random.
Suggestion: take out the word 'innately' and insert 'inherently.' The
quantum events were not literally "born" that way in any theory, no
matter how controversial.
>This is why many have proposed more complete
>theories, which suggest that events are at least partially governed by
extra
>"hidden variables". Now physicists from Austria claim to have performed
an
>experiment that rules out a broad class of hidden-variables theories that
>focus on realism -- giving the uneasy consequence that reality does not
>exist when we are not observing it (Nature 446 871).
>
>Some 40 years ago the physicist John Bell predicted that many
>hidden-variables theories would be ruled out if a certain experimental
>inequality were violated - known as "Bell's inequality". In his thought
>experiment, a source fires entangled pairs of linearly-polarized photons
in
>opposite directions towards two polarizers, which can be changed in
>orientation. Quantum mechanics says that there should be a high
correlation
>between results at the polarizers because the photons instantaneously
>"decide" together which polarization to assume at the moment of
measurement,
>even though they are separated in space. Hidden variables, however, says
>that such instantaneous decisions are not necessary, because the same
strong
>correlation could be achieved if the photons were somehow informed of the
>orientation of the polarizers beforehand.
>
>Bell's trick, therefore, was to decide how to orient the polarizers only
>after the photons have left the source. If hidden variables did exist,
they
>would be unable to know the orientation, and so the results would only be
>correlated half of the time. On the other hand, if quantum mechanics was
>right, the results would be much more correlated - in other words, Bell's
>inequality would be violated.
>
>Many realizations of the thought experiment have indeed verified the
>violation of Bell's inequality. These have ruled out all hidden-variables
>theories based on joint assumptions of realism, meaning that reality
exists
>when we are not observing it; and locality, meaning that separated events
>cannot influence one another instantaneously. But a violation of Bell's
>inequality does not tell specifically which assumption - realism,
locality
>or both - is discordant with quantum mechanics.
>
>Markus Aspelmeyer, Anton Zeilinger and colleagues from the University of
>Vienna, however, have now shown that realism is more of a problem than
>locality in the quantum world. They devised an experiment that violates a
>different inequality proposed by physicist Anthony Leggett in 2003 that
>relies only on realism, and relaxes the reliance on locality. To do this,
>rather than taking measurements along just one plane of polarization, the
>Austrian team took measurements in additional, perpendicular planes to
check
>for elliptical polarization.
>
>They found that, just as in the realizations of Bell's thought
experiment,
>Leggett's inequality is violated - thus stressing the quantum-mechanical
>assertion that reality does not exist when we're not observing it. "Our
>study shows that 'just' giving up the concept of locality would not be
>enough to obtain a more complete description of quantum mechanics,"
>Aspelmeyer told Physics Web. "You would also have to give up certain
>intuitive features of realism."
>
>However, Alain Aspect, a physicist who performed the first Bell-type
>experiment in the 1980s, thinks the team's philosophical conclusions are
>subjective. "There are other types of non-local models that are not
>addressed by either Leggett's inequalities or the experiment," he said.
"But
>I rather share the view that such debates, and accompanying experiments
such
>as those by [the Austrian team], allow us to look deeper into the
mysteries
>of quantum mechanics."
>
>About the author
>Jon Cartwright is a re****ter for Physics Web
>
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