Heidegger

THE AFSHAR EXPERIMENT - IS THIS THE END FOR THE COPENHAGEN THEORY?
IS THIS THE FINAL *GOODNIGHT VIENNA* FOR BOHR’S COMPLEMENTARY
INTERPRETATION OF QUANTUM MECHANICS
AND ONE OF METAPHYSICS FAVOURITE CRUTCHES?

The principle of complementarity states that two complementary physical
observables cannot both be measured for any given quantum particle without one
measurement disturbing the other. An example of two complementary physical
observables in quantum mechanics is the observation of the wave and particle
nature of light simultaneously. The application of complementarity in this case
states that we can not observe and measure the purely wave and particle like
behavior of a single photon (the particle of light) at the same time. The
most basic way of showing the wave like nature of light is to create
interference patterns between two sources of coherent light (coherence meaning that the
two sources of light have a fixed phase relationship).

When this is done, an interference pattern is created as the peaks and
troughs of the two waves re-enforce each other or cancel each other out. However
when this is performed on with a stream of photons (each photon thus seemingly
a particle), the surprising result is that the interference pattern remains.
This raises the question of which way the photon went (i. e. which hole it
passed through). This is highly problematic but a solution for how to think
about light was formulated in the Copenhagen interpretation of quantum
mechanics. In essence this interpretation states that if it is known which way the
photon goes, it is impossible to demonstrate interference. The demonstration of
this is to block one of the holes, at which point the interference pattern is
replaced by an apparently clear path that the photon must have taken. Some
interpretations of the Afshar experiment claim that it disproves the
Copenhagen interpretation, while others claim that the results are perfectly
consistent with it. Waves and particles are mutually exclusive. Something can be
either a wave or a particle but not both. In the quantum world, if we try to
observe light as a particle it appears to be a particle and if we try to observe
light as a wave it appears to be a wave. The Afshar experiment has introduced
a new twist to this view. Afshar placed a wire grid in light path of the
classical Thomas-Young double slit apparatus. He placed the grid at a null point
where the lightwaves cancel so that light could pass through the apparatus
uninterrupted if it is traveling as a wave. The grid serves essentially as a
particle detector because light particles `photons’ should be partially blocked
by the wire grid since particles travel in straight lines but light as a
wave can go around the wires as though they were not even there. Afshar then ran
the experiment in a way that would look for light as a particle with the
light being observed as a particle all the way from the laser source to the
detectors. He found that light as a particle was not diminished by the presence
of the grid and concluded that light is not a particle even when we observe it
to be a particle. Critics of the Afshar experiment say that his experiment
only demonstrates that light can be either a particle or a wave but I think
Afshar is correct in saying that light is not a particle.
 http://www.theory.physics.ubc.ca/rebel.h…
 http://en.wikipedia.org/wiki/Afshar_expe…
 http://www.analogsf.com/0410/altview2.sh…

Afshar’s experiment uses a variant of the classic Thomas Young double-slit
experiment. Such interferometer experiments typically have two “arms” or paths
a photon may take. One of Afshar’s assertions is that, in his experiment, it
is possible to check for interference fringes of a photon stream (a
measurement of the wave nature of the photons) while at the same time observing each
photon’s path (a measurement of the particle nature of the photons).

Regards,

Jud Evans.

Personal Website. http://evans-experientialism.freewebspac…

Posted on Tuesday, April 24th, 2007 at 8:25 am
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