On 30 May 2017, at 11:28, Telmo Menezes wrote:
On Tue, May 30, 2017 at 3:47 AM, Pierz <pier...@gmail.com> wrote:
On Tuesday, May 30, 2017 at 9:14:07 AM UTC+10, Bruce wrote:
On 29/05/2017 11:21 pm, Telmo Menezes wrote:
On Mon, May 29, 2017 at 3:06 PM, Bruce Kellett
<bhke...@optusnet.com.au> wrote:
On 29/05/2017 10:42 pm, Telmo Menezes wrote:
On Mon, May 29, 2017 at 2:26 PM, Bruce Kellett
<bhke...@optusnet.com.au> wrote:
On 29/05/2017 6:26 pm, Telmo Menezes wrote:
On Mon, May 29, 2017 at 3:26 AM, Bruce Kellett
<bhke...@optusnet.com.au> wrote:
I would say that there is only one history leading to our
present
state.
Whether you take an MWI view or a collapse view, the wave
function
branches
deterministically at every point, so if you follow your
current
twig
back
down to the main trunk etc, there will be a unique path.
I don't think we can say we are in a specific twig. Many things
about
out present state are unknown/undefined. I can imagine that
there
are
many well-defined present states that are compatible with my
current
subjective state.
Sure, but we are talking about wave functions, not subjective
states.
Replace "subjective" with "incomplete knowledge".
Doesn't help. Of course our knowledge is incomplete, the wave
function
isn't
completely known either -- but the result of specific
measurements are
what
is at stake here, and they are known quantum states.
In my view, what's at stake here is the possibility of latent
variables having some degree of freedom leading to the same macro
states (provided that there is incomplete information about these
macro states, as is the case for humans).
I am still not clear about what you are trying to say. It is
certainly
true that many internal details of your microscopic organization
could
be changed and you wouldn't know the difference. For that matter, an
almost infinite number of details about the rest of the universe
could
be different and you would still be the same. But that is not what
we
were talking about. I understood the issue to be whether there was a
unique past, or whether several (or many) different paths lead to
our
current state. The determinism of the Schrödinger equation would
suggest
that your unique state has a unique history. Variations in
microscopic
details of with your body, or the universe, would correspond to
different decohered worlds with no overlap with our world. So
while such
variations are possible, they do not amount to multiple histories
leading to our current state. We don't need to know that state in
detail
to be able to argue the consequences of determinism.
In fact you can perform a quantum erasure experiment, and be
sure
that
your current state goes through at least two different shortest
paths
to the root, and it becomes nonsensical to say that one is the
"correct" one. I don't think anyone knows how far this can go
into
the
macroscopic world, but I don't see any reason to believe that
it
doesn't.
I don't understand what you think you are getting in a quantum
erasure
experiment. If the "which way" information that was gathered is
erased,
normal interference patterns are seen in the double slit
situation.
The
two
paths (through the separate slits) are in unresolved
superposition
until
they hit the detector, when decoherence takes over. There are
not two
separate worlds, and your state is the result of the superposed
paths,
not
of either path separately. There is no ambiguity about which
the the
"correct" path -- neither is, both contribute equally.
I would say that the delayed choice version of the experiment
makes it
clear that there are two possible pasts that lead to the same
present
state -- they differ by one bit of information.
That is not what is implied by delayed choice quantum erasure.
Whether
an
interference pattern is seen or not is determined by whether the
"which
way"
information is erased or not. But whether it is or not, the
interference is
only seen when coincidence measurements tell one which photons to
count. And
the timing information necessary for coincidence determination is
available
only *after* all decisions about erasure or not have been made,
whether
that
decision is made before or after the other photon of the
entangled pair
has
reached its detector.
"Delayed choice" is perhaps a misleading phrase in this context,
and it
does
not lead to an ambiguity of path -- it merely tells whether
there was
an
intact superposition or not.
I know, this is not what I am trying to say. I'll choose
something much
simpler:
Suppose there is a computer running in an empty room. This
computer is
connected to a random number generator. At some point it uses the
random value to decide if it's going to show a screen that is all
green or all red. Nobody witnesses it.
If the random number generator is based on quantum randomness,
then in
principle you will get a superposition of red and green screens, but
this is like the question as to whether we see a superposition of
live
and dead cats in Schrödinger's thought experiment. Even if there
is an
underlying quantum event that would give a superposition,
decoherence
steps in and resolves the outcome into separate worlds long before
we
reach the macro level of live/dead cats or red/green screens.
Decoherence does not require anyone to witness it....
I believe Telmo is subscribing to a view of QM, suggested by
Bruno's "comp"
theory, that the observer's subjective state - down to some unknown
level of
resolution (the "substitution level") - is what determines the
possible
future states of that observer (probabilistically, by the measure on
subjective continuations in the UD trace).
I would say that I am assuming the computational theory of mind + MWI,
none of which are really Bruno's idea.
?
"my theory of mind" is (a weaker than usual) CTM. It implies all CTMs
in the literature, which somehow assumes implicitly some substitution
level. It is weaker in the sense that it makes the substitution level
non constructive evidence explicit, and does not bound it.
The UDA is only a "human" way to get quickly the main consequences:
physics is reduced, by the usual Occam, to arithmetic. And so is
testable, and so "theology" is (again) a science.
The AUDA is just the "machine" theory.
I am not sure it is possible to
discuss this issues while shielding ourselves from theories of mind.
With MWI all branches exist anyway. Perhaps what we are discussing is
necessarily about subjective (first person) states.
So you are talking different
languages.
Not sure I agree. We are perhaps implicitly assuming different
theories of mind.
I don't know if Telmo is aware or not of the conventional view of
decoherence - that it is a matter of the spread of information into
the
environment by means of physical interactions between particles.
Telmo's
musings about the effect of destroying memory (could it change the
measure
of different futures?) clearly expresses this subjectivist view.
I get your point with decoherence.
Again, I would say that it all depends on theories of mind. What does
mind supervene on? Perhaps it is true that every single coupling with
the environment prevents the current observer state to become
compatible with other branches. But can we be sure? I feel that such
certainties come from a strong belief in emergentism (which I cannot
disprove, but find problematic).
It is impossible to recohere the past, FAPP.
But only FAPP. To make the blue T-rex interfereing with the red-T-rex,
we must erase the trace of particle interaction between the T-rex in
its whole light-cone, and this without forgetting the particles
"swallowed" by the black-holes, etc. It is just completely impossible,
but to derive from that the unicity of the past, is, it seems to me
(and you if I understood well) is invalid.
FWIW, you
are expressing my own understanding of the situation: there can be no
superposition of red and green screens or dinosaurs, or dead and
live cats,
because there can be no quantum superposition of macroscopic objects.
Superpositions of wave functions are only possible for systems
isolated from
interaction with their environment, which is why quantum computers
are so
fricking hard to make: keeping aggregates of particles isolated from
interactions with the surrounding environment is exponentially more
difficult as the system grows in size.
The main question for me is this: can two branches hold different
observer states, if they differ only by things that are not
observable?
I would say no, intuitively. I would even say "no" just for the things
not observed, even when observable. But this has to be tempered by the
fact that any interaction will count as an observation, making super-
exponentially hard to indeed recover a macroscopic superposition in
the past, even the very close past. Of course, that might change the
day we succeed in building a fault tolerant (topological perhaps)
quantum computer. Unfortunately, the T-rex missed them. yet, if a T-
rex made a solid topological quantum qubit, in the state 0+1, we would
have a past with 0, and a past with 1, as long as we don't look at it.
I read, already a long time ago, some experimental evidence of
temporal Bell's inequality going in this direction, and I think we
don't even need to test them, as we get them with the usual Bell's
inequality violation, if we accept special relativity (and some amount
of physical realism (not the full materialism, to be sure).
Bruno
Telmo.
Bruce
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