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...in reality the question of no collapse or collapse is not an
interpretational question at all. It is a question of correct or incorrect
physics.
This fact has become very evident with the rise of the theory of
Decoherence. Decoherence at last provides a real physical process to explain
how
quantum measurement works. And many experiments have been done , even
involving the reverse process of re coherence which as will be made clear
shortly, provide significant support for the validly of this idea.
The debate between collapse and no collapse is really the debate on the
fundamental question of time symmetry. All Collapse models violate time
symmetry invariance. The no collapse models on the other hand generate an arrow
of time statistically, just as we see in classic physics.
A look as a thought experiment can make this point clear. Measure the spin
of electrons in the Z axis. This will give us two possible results.
We then take every electron in the state [ U>_Z and measure it's spin for
the X axis. We would of course get 50% up and down spins. ( This would of
course be true if we used the [d>_Z state also)
Now however we time reverse the entire measurement process. Of course we
can't really do this but this is a thought experiment. ( There have been
experiments where much simpler systems have been reversed, which does lend in
my view support for the no collapse model. )
Based on the collapse models the quantum states are completely destroyed.
Therefore if we measure the spin of the electron in the Z axis after this
reversal we should get a mix of up and down spin results. However, based on
the no collapse model, the quantum state was never lost, merely submerged
in the environmental states. So the no collapse model predicts that we
would get 100% up spins in the Z axis.
This in the same as if we could time reverse all the trajectories of gas
molecules in a container so that they once again become concentrated in a
smaller volume. Of course this experiment is not possible either.