On 8/6/2019 8:53 PM, smitra wrote:
On 07-08-2019 02:19, Bruce Kellett wrote:
On Wed, Aug 7, 2019 at 10:04 AM smitra <[email protected]> wrote:
On 07-08-2019 00:45, Bruce Kellett wrote:
The trouble with that argument is that in any simulation, you get
to
set the rules of physics that obtain. There is then no guarantee
that
the results of your simulation have any relation to physics in
the
real (unassimilated) world. For decoherence to work, all that is
required is a sufficient number of environmental degrees of
freedom
for multiple copies of the result to be recorded by the
"environment
as witness", in Zurek's words. Quantum Darwinism then ensures
that the
result is permanent and irreversible.
If you measure the z-component of a spin polarized in the
x-direction,
then however astronomically large the number of environmental
degrees of
freedom there are that get entangled with the spin, it's still a
finite
number. One minute after the measurement all the degrees of freedom
that
can be entangled are within one light-minute of the experimental
set-up.
So, the recording of the result in the environment are going to be
a
superposition of the two possible recordings.
It is called the "relative state" interpretation for a reason. The
entanglement with the environmental degrees of freedom that leads to
the recording of the result in the environment is relative to each
possible experimental outcome. Within the decoherence time (typically
of the order of a few nanoseconds or less) these "relative states"
become effectively orthogonal, and the measurement becomes
irreversible. Because there is no longer any possibility of
interference between the results, there is no longer any
superposition. You guys seems so desperate to hold on to a
superposition that no longer has any practical consequences. Get used
to it -- measurements have definite outcomes. That is the fact that
has to be incorporated into your theory.
Yes, but this is relative to each component. The inability to
demonstrate interference does not demonstrate that there is no
superposition. To prove that these superpositions really can vanish
you need to do an experiment that demonstrates a violation of unitary
time evolution of a completely isolated system. Saying that there is
no superposition just because in a particular experiment you cannot
see a particular signature of that anymore, is like saying that
momentum isn't conserved if we bounce a ball against the ground. The
inability to detect the change in the momentum of the Earth doesn't
mean that there is no such change. Unitary time evolution is
established just as rigorously as momentum conservation.
Superposition just means you are using a basis for the Hilbert space
which happens not to have a basis vector that coincides with the state.
There's still just one state vector and the computation is still just
rotating the state vector around. To say a superposition vanishes just
means the state vector rotated so it was orthogonal to one (or both)
components.
Brent
Saibal
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