On 09-12-2017 12:01, Bruce Kellett wrote:
On 9/12/2017 9:44 pm, smitra wrote:
On 09-12-2017 02:48, Bruce Kellett wrote:
On 9/12/2017 11:49 am, smitra wrote:
On 09-12-2017 00:03, Bruce Kellett wrote:
On 9/12/2017 4:21 am, Bruno Marchal wrote:
On 08 Dec 2017, at 00:22, Bruce Kellett wrote:
On 8/12/2017 3:31 am, Bruno Marchal wrote:
On 06 Dec 2017, at 12:19, Bruce Kellett wrote:
But as I pointed out, thermal motion gives momenta of
magnitudes such that the quantum uncertainties are negligible
compared to the thermal randomness. And thermal motions are not
coherent.
You seem to work in Bohr QM, with some dualism between the
quantum reality and the classical reality.
Not at all. The (semi-)classical world emerges from the quantum
substrate; if you cannot give an account of this, then you have
failed to explain our everyday experience. And explaining that
experience is the purpose of physics.
No problem with this, except for your usual skepticism of
Everett's program (say).
Skepticism is the scientific stance.....
You are right that this does not change anything FAPP, but our
discussion is not about practical applications, but metaphysics.
No, we were talking about tossing a coin, we were not talking
about metaphysics. Your metaphysics has served merely to confuse
you to the extent that you do not understand even the simplest
physics.
That is ad hominem remark which I take as absence of argument.
You don't take kindly to criticism, do you Bruno?
All I said is that without collapse, shaking a box with some coin
long enough would lead to the superposition of the two coin state.
You seem to be the one confusing the local decoherence with some
collapse. The Heisenberg uncertainties are great enough to amplify
slight change of the move of the coin when bouncing on the wall.
That is simply assertion on your part, without a shred of argument
or
justification. When one looks at the arguments, such as that put
forward by Albrecht and David (referred to by smitra), one finds
that
the emperor has no clothes!
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. And I gave an argument
with
an actual calculation -- not just an assertion. Uncertainties in
the
constituents of the object are uncorrelated, random, and cancel
out.
So although the superposition originating from the big bang is
intact
from the bird's point of view, it is so completely irrelevant for
everyday purposes that it is an insult to even refer to the
classicality of the world as FAPP -- it is complete. Relying on the
charge of "FAPP" as a justification for your assertions is
nonsense.
It's not irrelevant if you don't have the information that locates
you in a sector where the uncertainties are indeed small enough. You
have to start with the complete state in the bird's view, and then
consider the sector where you have some definite information and
then project onto that subspace. If you do that, then your coins are
not at all in a precisely enough classical state but rather in
superpositions (entangled with the environment) that lead to wildly
different outcomes of coin tosses.
E.g. in the bird's view there exists exact copies of me that live on
planets that are not the same, some will have a radius of a few
millimeter larger than others. Here exact copy means exactly the
same conscious experience, which is then due to exactly the same
computational state of the brain described by some bitstring that's
exactly the same.
So, from totally different decoherent branches of the wavefunction
one can factor out some bitstring describing a conscious experience,
the reduced state of the rest of the universe in that sector is then
a superposition of a many different effectively classical states.
If this were not true then each single conscious experience would
contain in it information about such things as the exact number of
atoms in the Earth, Sun etc. etc.
I prefer to live in the real world, so I would rather not indulge
your
fantasies.
The real world is not what you think it is. It was only when you read
about the fact that dinosaurs had once existed that the sector you
were in diverged from other sectors where dinosaurs had never existed
and some other evolutionary path of mammals led to you and the exact
same information in your brain before becoming aware of the existence
of dinosaurs.
Evidence?????
This is generically the case in a MWI setting. Of course, the MWI may
not be correct, QM may not be the ultimate foundation of the laws of
physics, but if we assume the MWI, then some observer who is aware of
precisely the information specified by some bitstring b (and nothing
more or less than specified by b), the observer should consider
him/herself to be in a superposition of all branches where b appears in.
So, when you project the global quantum state on the subspace spanned by
b you get the superposition of all branches that are relevant to b. Then
when the observer adds one bit to b, e.g. whether not dinosaurs once
roamed the Earth, the state gets reduced further.
Saibal
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