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.
so, it can always be specified by a bitstring, simply because the
observer is always measuring itself.
Observer measuring itself is not a well defined quantum process. I
don't even know what it would mean.
The bitstring thus specifies everything the observer is aware of.
If someone named John in New York has pain in his left toe then the
bistring
What bitstring?
specifies not just this pain there but also that's it's John
experiencing this pain including everything that John knows about his
own life, and all other knowledge he has right at that moment.
So, b is then what we've in this list called an "observer moment".
Another ill defined concept.
The bitstring will contain in it information about memories of the past.
All memories? What will be the difference between memories one has in
consciousness and ones which are only in memory?
These then refer to other observer moments that are not completely
specified. So, we have only an illusion about having evolved in time,
in reality we only ever exist in single observer movements.
How long is an "observer moment"? How are they ordered? These concepts
of "observer moment" and "memory bitstring" are tossed around like
just-so stories. But they seem to have no operational meaning that can
be tested.
When we recall having been at some place in the past, then that memory
does refer to a real event,
Even if we've never been there? Memories can be false, even though they
are real as memories.
except that it's just as much of a parallel world event as in other
MWI branches.
Just like the MWI-skeptics can argue that you can never prove the
reality of other branches, you can apply exactly the same arguments to
show that you can never prove the reality of the 1980s.
Not at all. The 1980s are an hypothesis that gives rise to lots of
predictions about what can be observed and tested now. MWI predicts
branches which can never have observable effects.
The local nature of the laws of the laws of physics means that any
experiment or observation you do can only ever involve interactions
with the here and now.
So, just like we can reasonably conclude that there exists a past and
a future based on what exists here and now, we can also reasonably
conclude that there exists other MWI branches.
I'm afraid MWI branches are far more uncertain that 1980.
Brent
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