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
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.
It's still a philosophical question whether 1980 exists "out there" in
the block-time sense or actually doesn't exist "anymore", with
"anymore" being an physically ill defined linguistic concept. The 1980
in the block-time sense is analogous the MWI branches, you can never
have any direct interaction with your copy in 1980.
Saibal
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