On 12/11/2017 3:48 AM, smitra wrote:
On 10-12-2017 23:09, Brent Meeker wrote:
On 12/10/2017 4:42 AM, smitra wrote:
On 09-12-2017 21:18, Brent Meeker wrote:
On 12/9/2017 4:00 AM, smitra wrote:
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.
But what does "aware of" refer to? A brief thought that "b is true"?
When the thought passes is he no longer in that superposition? Is he
flitting from one superposition to another as he has thoughts b, c,
d... Or is it enough that he could recall these these? But what
causes the recall? What if he forgets them?
Let's step back and consider the usual formalism of quantum mechanics
involving a complete set of commuting observables. So, one assumes
that for any physical system there exists observables and you can add
more and more that commute with each other until you have some maximum
number. You can measure these observables simultaneously, the set of
eigenvalues that you find completely specifies the physical state of
the system.
Now, one can argue that an observer only ever measures his/her own
state directly. So, if I claim to have measured the spin of an
electron, what I really have observed directly is some brain processes
that in turn were triggered by signals coming into my brain that in
turn were caused by the experimental set-up for measuring the spin.
So, why not apply the formalism involving a complete set of commuting
observables directly to the brain of the observer him/herself? If we
imagine the observer to be a robot controlled by a computer that has
well defined computational states that can be specified by bitstrings,
then we can consider the complete set of commuting bitstring
operators O_k that measure the kth component of the bitstring.
My point is then that the observer is always finds him/herself in a
simultaneous eigenstate of all the O_k,
But now you have slipped in a homunculus who measures the brain and
puts it into an eigenstate of the observable.
Doesn't really matter. If an external agent where to measure the
computational state then it's clear that this is a well defined
process within conventional QM, and the results will be compatible
with what the subject subjectively feels. I.e. there exists a
correspondence between what a neurologists measures and what the
subject subjective feels, even if the translation between the two
things is extremely complex. So, the set of commuting observables that
describe the measurements the neurologist performs defines via some
unknown mapping a set of commuting observables for the subject
itself.
?? Measuring an observable puts the system into an eigenstate of that
observable. It changes the system. So how can you assert that the
measurement is compatible with what the subject feels absent the
measurement? I agree that it's almost certainly possible to measure
a brain to a level that would tell you what the person was thinking -
BUT that can be done precisely because a brain is not a quantum
system, it's too big and too hot, so it is a classical computer, which
is just what you would expect evolution to produce. I notice you did
not even address my point that an observer measuring itself is not a
well defined quantum process. You have not answered any of my
questions about the so-called observer moment:
_But what does "aware of" refer to? A brief thought that "b is
true"?_
_When the thought passes is he no longer in that superposition? Is
he_
_flitting from one superposition to another as he has thoughts b, c,_
_d... Or is it enough that he could recall these these? But what_
_causes the recall? What if he forgets them? _
I think you have confused the commonplace that awareness of b is in
the brain and not "out there" with the idea that there is an observer
in the brain who "sees" b.
Bent
