On 5/2/2018 2:44 PM, [email protected] wrote:
On Wednesday, May 2, 2018 at 6:01:28 PM UTC, Brent wrote:
On 5/2/2018 4:48 AM, [email protected] <javascript:> wrote:
On Monday, April 30, 2018 at 3:33:23 AM UTC, [email protected]
wrote:
Implied by standard QM insofar as the theory is inherently
irreversible, that is, irreversible in principle at the
quantum level since the wf cannot be recovered by time
reversal. AG
I argued this conclusion on the Entanglement thread. Here I will
add some additional considerations. When you think of time
reversibility, say for an electron being measured by SG device,
you naturally think of passing the measured electron backward
along the same path, trying to recover the original wf by running
time backward. Of course you can't run time backward during or
even after a measurement because QM doesn't provide any time
dependent equations for the measurement process. But even if you
could do the thought experiment, according to QM, if the
measurement was, say, spin UP, it remains spin UP by virtue of
the measurement postulates of QM. Further, This MUST be the
backward in time measurement result if you simply accept time
symmetry, and not appeal to the measurement postulates of QM.
Thus, it seems highly plausible that the original wf, a
superposition, cannot be recovered after the measurement, and
that QM is a time IRREVERSIBLE theory. AG
In MWI the is both a spin UP and a spin DOWN, as projections on
orthogonal subspaces. The theory is mathematically reversible in
the sense that if you reversed the evolution of the state vector
it would reverse the projection in both subspaces.
Brent
In MWI and CI we have projection operators, aka in CI as collapse.
Aren't they all non unitary regardless of the interpretation, implying
IIUC, that they can't be time-reversed. AG
Yes, a projection operator is non-unitary. Maybe I didn't phrase it
well, but that's why I avoided invoking projection operators. The
subspaces become orthogonal in the approximation that we can average out
the cross terms, but that approximation is only a good one when
decoherence has taken place.
Brent
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