nature.com Physicists bid farewell to reality? Seite 1 von 4 ... - CoQuS

news @ nature.com - Physicists bid farewell to reality? - Quantum mechanics just g...
http://www.nature.com/news/2007/070416/full/070416-9.html
Seite 2 von 4
19.04.2007
Assistant / Associate
Professor
Education
NVCI
Las Vegas, NV
More science jobs
Feedback
About this site
About us
For librarians
TOP STORIES
Physicists bid farewell to
reality?
18 April 2007
Full fossil found for the
earliest trees
18 April 2007
Orangutans have it easy
18 April 2007
Changes to pesticide
spraying could reduce
GM harm
18 April 2007
Should kids take
antidepressants?
17 April 2007
Decades needed to tell
whether ocean currents
are slowing
17 April 2007
Tales of the expected
17 April 2007
Dark matter looks to be
particularly wimpy
17 April 2007
mechanics in the early twentieth century. The theory seemed to
show that, in the quantum world, objects are defined only
fuzzily, so that all we can do is work out the probability that
they have particular characteristics — such as being located in a
specific place or having a specific energy.
Allied to this assault on reality was the apparent prediction of
what Albert Einstein, one of the chief architects of quantum
theory, called 'spooky action at a distance'. Quantum theory
suggests that disturbing one particle can instantaneously
determine the properties of a particle with which it is
'entangled', no matter how far away it is. This would violate the
usual rule of locality: that local behaviour is governed by local
events.
We have a little more
evidence that the world
is really strange.
Anton Zeilinger
University of Vienna
Failed test
Einstein could not believe that the
world was really so indeterminate.
He supposed that a deeper level of
reality had yet to be uncovered —
so-called 'hidden variables' that
specified an object's properties
precisely and in strictly local terms.
In the 1960s the Irish physicist John Bell showed how to put
locality and realism to the test. He deduced that if both ideas
applied to the quantum world, then two particular quantities
calculated from measurements made on a pair of entangled
photons would be equal to one another. If so, there would be
nothing 'spooky' about entanglement after all.
Experiments were done to test his prediction in the ensuing two
decades, and results showed that Bell's equality was violated.
Thus, either realism or locality, or possibly both of these ideas,
do not apply in the quantum world.
But which is it? That's what Zeilinger, based at the University of
Vienna in Austria, and his colleagues tried to find out.
They came up with a similar test to Bell's, to see whether
quantum mechanics obeys realism but not locality. Again the
experiment involves comparing two quantities calculated from
measurements on entangled photons, to see if they are equal.
But whereas in Bell's test these quantities are derived from the
so-called 'linear' polarization of the photons — crudely, whether
their electromagnetic fields oscillate in one direction or the
other — Zeilinger's experiment looks at a different sort of
polarization, called elliptical polarization.
Like Bell's, Zeilinger's equality proved false. This doesn't rule
out all possible non-local realistic models, but it does exclude an
important subset of them. Specifically, it shows that if you have
a group of photons that all have independent polarizations, then
you can't ascribe specific polarizations to each. It's rather like
saying that you know there are particular numbers of blue,
white and silver cars in a car park — but it is meaningless even
to imagine saying which ones are which.
Soil May
Buckybal
100-Year
Climate Z
Never Se
Beyond IQ
Can Focu
Hand Do
Battling B
Protein
more sc