On 12 Dec 2017, at 13:13, Bruce Kellett wrote:
On 12/12/2017 10:55 pm, Bruno Marchal wrote:
On 12 Dec 2017, at 11:14, Bruce Kellett wrote:
On 12/12/2017 8:26 pm, Bruno Marchal wrote:
On 12 Dec 2017, at 02:02, Bruce Kellett wrote:
On 12/12/2017 11:44 am, smitra wrote:
On 11-12-2017 23:15, Bruce Kellett wrote:
On 12/12/2017 1:12 am, Bruno Marchal wrote:
On 10 Dec 2017, at 23:38, Bruce Kellett wrote:
On 11/12/2017 2:19 am, Bruno Marchal wrote:
On 09 Dec 2017, at 00:03, Bruce Kellett wrote:
On 9/12/2017 4:21 am, Bruno Marchal wrote:
Similarly, a shroedinger car, once alive + dead, will never
become a pure alive, or dead cat. It will only seems so for
anyone looking at the cat, in the {alive, dead} base/
apparatus.
Superposition never disappear, and a coin moree or less
with a
precise position, is always a superposition of a coin
with more
or less precise momenta. The relation is given by the
Fourier
transforms, which gives the relative accessible states/
worlds.
I pointed out that for a macroscopic object such as a
coin, the
uncertainty relations give uncertainties in positions and/or
momentum far below any level of possible detection.
Of possible practical detection. That is good FAPP, but
irrelevant
for theoretical consideration.
This is a purely rhetorical objection, Bruno. And when you
trot
this out, as you do regularly, I know that your purpose is to
obfuscate, and hide the fact that you have no rational
argument to
offer.
You confuse physics and metaphysics. The difference is not
rhetorical, but fundamental in this thread.
Rubbish. The central point of contention on this thread is
whether a
coin toss can be regarded as a classical event, with
probabilities
given by ignorance of the initial conditions, or as a quantum
event
with probabilities given by purely quantum uncertainties.
This is a straightforward question of physics, and has nothing
to do
with metaphysics. As usual, you introduce the term 'metaphysics'
merely to obfuscate, because you have no intelligent response
to the
clear physics of the situation.
That the probabilities are given by classical physics does not
imply
that there is no branching due to the coin toss.
It does, because there is no superposition of head/tails -- no
possibility of interference between heads and tails.
You are begging the question. The point was that without
collapse, the shaking of the dice or coin can make the
superposition of the positions (inherent in the Heisenberg
uncertainty) can add up to make the coin behaving sufficiently
differently to obtain a superposition of the head+tail or 1+2+...
+6 superposition.
No, shaking the coin cannot make non-coherent uncertainties add up
to anything. The physics is against you here, Bruno. There is no
superposition, and no splitting of worlds on the toss. If you
think different, prove it.
Just to be sure, do you agree that without collapse, the
schroedinger cat remains in the state alive+dead, even after
observation, and we see it alive OR dead, just by the first-person
mechanist indeterminacy (or something akin to it) ?
The superposition exists in the original quantum state --
essentially the radioactive nucleus which is a quantum system in a
superposition of decayed/not-decayed. Because of the experimental
set up, this superposition is amplified so that it becomes entangled
with the environment, including the cat and us. So:
|nucleus>|box>|cat>|observer>|rest of the world> --> (by unitary
evolution)
{|decayed>|poison spilt>|cat dead>|see dead cat>|rest of world
confirms dead cat> +
|not decayed>|poison bottle intact>|cat alive>|see live cat>|rest
of world confirms live cat>}
And the decoherence of the quantum phases into the |rest of the
world> environmental states diagonalizes the density matrix FAPP.
Yes. FAPP.
If you insist, the superposition is intact in the bird view, but
such a superposition can never recohere, and there are NO
consequences of the existence of other branches, practical or
otherwise. Maintaining their existence might satisfy your
existential angst, but it has nothing to do with physics or
experience.
The existence of those branches is more frightening than angst
appeasing. But we cannot make them disappear in the frame of the
quantum mechanics without collapse. It is just a question of being
consistent with what we are assuming.
Also, how could the quantum uncertainties becoming non-coherent?
Decoherence, without collapse is something relative to the
environment when its get itself entangled with the superposition of
the object observed. The splitting of worlds is not due to the
toss, but to the fact that the position of the coin diffuse, which
means get different in the multiverse. Instead of shaking the box,
waiting long enough would work as well.
The coin case is different in an essential way -- it does not start
from a single quantum state that can be expanded into {|heads> + |
tails>} by any single quantum event. The system starts off decohered
and non-coherent. So just as you can never bring the two branches of
the cat back together, you can never take an initially decohered
state and reconstruct some imagined coherent superposition, unitary
evolution and the laws of thermodynamics forbid it. There is no part
of the multiverse in which such a superposed {|heads> + |tails>}
state exists, it never did and it never will.
The coin does not start in a state of the kind {|heads> + |tails>},
but it starts with a state of having mulitiple positions and multiple
momenta, spreaded in the multiverse according to the Heisenberg
Uncertainty. The tiny difference in the position can lead to different
bouncing in the box, and so, by shaking it a long time enough, I don’t
see why we could avoid a superposition of head and tails eventually.
Yes, for the same reason we can't “re-cohere” the cat state, we can’t
recover the coin state, so we agree … as long as we are interested in
local prediction, but apparently not on the “bird” view.
Bruno
Bruce
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