On 10/23/2012 5:50 AM, Roger Clough wrote:
Hi meekerdb

There are a number of theories to explain the collapse of the quantum wave 
(see below).
1) In subjective theories, the collapse is attributed
to consciousness (presumably of the intent or decision to make
a measurement).

There are also 'subjective' epistemological interpretations in which the 'collapse' is just taking account of the change in information provided by a measurement (c.f. Asher Peres or Chris Fuchs arXiv:1207.2141 <http://arxiv.org/abs/1207.2141> ).

2) In objective or decoherence theories, some physical
event (such as using a probe to make a measurement)
in itself causes decoherence of the wave function. To me,
this is the simplest and most sensible answer (Occam's Razor).

Decoherence has gone part way in explaining the apparent collapse of the wave function, but it still depends on the existence of a preferred (einselected) basis in which the density matrix is diagonalized by environmental interactions. Tracing over the environmental degrees of freedom is our mathematical operation - it's not part of system physics.

3) There is also the many-worlds interpretation, in which collapse
of the wave is avoided by creating an entire universe.
This sounds like overkill to me.
So I vote for decoherence of the wave by a probe.

It's not true that disturbance by the measurement device causes the (apparent) collapse; it's the interaction with an environment, and ultimately it may require assumption of retarded wave propagation. I highly recommend the review article on decoherence by Schlosshauer arXiv:quant-ph/0312059 <http://arxiv.org/abs/quant-ph/0312059>.


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