On 8/8/2019 2:41 PM, smitra wrote:
On 08-08-2019 21:30, 'Brent Meeker' via Everything List wrote:
On 8/7/2019 10:13 PM, smitra wrote:
No disagreement with that, but my point all along is that "many
somethings" associated with the qubits in the quantum computer,
can
lead to many minds which can have many experiences, when the
quantum
computer executes computational traces which create conscious
states.
Do you disagree with this?
No. As far as I know minds are classical like processes in
brains.
That's why you are never really "of two minds". Superpositions
corresponding to neurons firing and not-firing decohere far too
quickly. See Tegmark's paper.
Classical objects do not exist in this universe that works
according to quantum mechanics. What happens is that due to
decoherence macroscopic properties of objects behave as if they are
described by classical mechanics, and Tegmark has shown that this is
also true for brain processes. This only debunks the idea that a
normal computer could never be conscious as e.g. Penrose has
claimed. But because everything is still quantum mechanical, a brain
observing the z-component of a spin that is polarized in the
x-direction will still end up in an entangled superposition with the
spin and the local environment. The brain consist of atoms and the
many particle wavefunction of all the atoms in the brain and the
environment will evolve according to the Schroedinger equation.
Saibal
True. But there are two entanglements with the environment
(including Wigner) which are orthogonal and cannot interact. I
realize this is statistical mechanics type phenomenon, i.e. it depends
on there being many degrees of freedom. But I think there must be a
lower bound on non-zero probabilities, possibly imposed by
cosmological considerations. So the density matrix must become
strictly diagonal in some basis. This is the same as "some things
happen and some don't".
It should be noted that this would require new physics that violates QM.
Right. But "modifies" rather than "violates".
According to QM the density matrix of the entire system (we keep track
of all the degrees of freedom that end up interacting with the spin)
can only be diagonal in the basis where one basis vector is the
superposition of the two outcomes. Note that whatever physics is
needed to explain observation, it will happen within a finite time. A
measurement may e.g. take a minute, and in that minute only a finite
number of physical degrees of freedom can get entangled with the spin.
So, no physical explanation of observation can be fundamentally based
on having to take the limit of complete decoherence which would
involve taking the limit of entanglement with an infinite number of
degrees of freedom.
But it could be based on having /enough /degrees of freedom so that it
is irreversible (which could be the case by simply sending out some
infrared photons ad in the C60 double slit experiment).
If a density matrix describes a true statistical mixture of more than
one outcomes, then there exists a basis where it is diagonal with more
than one nonzero entry on the diagonal. The entries being
probabilities sum to 1, and the squares sum to strictly less than one
because you have more than one nonzero probabilities on the diagonal
and they are numbers between zero and 1. So, tr(rho^2) < 1.
But the density matrix of a pure state |psi> is |psi><psi| and rho^2 =
rho, so tr(rho^2) = 1, and this is of course invariant under change of
basis.
Of course if you include enough local environment in the system, then
the reduced density matrix can be diagonal, while the overall system
still has tr(rho^2)=1. The problem, as Bruce points out, is that the
degrees of freedom almost inevitably include radiation that escapes to
infinity at the speed of light and cannot operationally be captured as
part of the environment.
Brent
Saibal
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