On 8/15/2013 6:18 AM, [email protected] wrote:
Citeren meekerdb <[email protected]>:
On 8/14/2013 6:41 PM, [email protected] wrote:
I guess I don't understand that. You seem to be considering a simple case of
amnesia - all purely classical - so I don't see how MWI enters at all. The
probabilities are just ignorance uncertainty. You're still in the same branch of the
MWI, you just don't remember why your memory was erased (although you may read about
it in your diary).
No, you can't say that you are in the same branch. Just because you are in the
clasical regime doesn't mean that the MWI is irrelevant and we can just pretend that
the world is described by classical physics. It is only that classical physics will
give the same answer as QM when computing probabilities.
Including the probability that I'm in the same world as before?
With classical I mean a single world theory where you just compute the probabilities
based "ignorance". This yields the same answer as assuming the MWI and then comouting
the probabilities of the various outcomes.
If what you are aware of is only described by your memory state which can be encoded
by a finite number of bits, then after a memory resetting, the state of your memory
and the environment (which contains also the rest of your brain and body), is of the
form:
"The rest of my brain"?? Why do you suppose that some part of my brain is involved in
my memories and not other parts? What about a scar or a tattoo. I don't see that
"memory" is separable from the environment. In fact isn't that exactly what makes
memory classical and makes the superposition you write below impossible to achieve?
Your brain is a classical computer because it's not isolated from the environment.
What matter is that the state is of the form:
|memory_1>|environment_1> + |memory_2>|environment_2>+..
with the |memory_j> orthonormal and the |environment_j> orthogonal. Such a completely
correlated state will arise due to decoherence, the probabilities which are the squared
norms of the |environment_j>'s are the probabilities. They behave in a purely classical
way due this decomposition.
The brain is never isolated from the environment; if project onto an |environment_j> you
always get a definite classical memory state, never a supperposition of different
bitstrings. But it's not the case that projecting onto a ddefinite memory state will
always yield a definite classical environment state (this is at the heart of the
Wigner's friend thought experiment).
I think Wigner's friend has been overtaken by decoherence. While I agree with what you
say above, I disagree that the |environment_i> are macroscopically different. I think you
are making inconsistent assumptions: that "memory" is something that can be "reset"
without "resetting" its physical environment and yet still holding that memory is classical.
So, I am assuming that the brain is 100% classical (decoherence has run its complete
course), whatever the memory state of the brain is can also be found in the environment.
Then the assumption that I'm making is that whenever there is information in the
environment that the observer is not aware of,
What does "aware of" mean?...physically encoded somewhere? present in consciousness as a
thought?...a sentence? You seem to be implicitly invoking a dualism whereby awareness and
memory can be changed in ways physical things can't.
Brent
the observer will be identical as far as the description of the observer in terms of its
memory state is concerned accross the branches where that information is different. So,
if the initial state is:
|memory>|environment>
and in the environment something happens which has two possible outcomes, and you have
yet to learn about that, then the state will evolve to a state of the form:
|memory>(|environment_1> + |environment_2>)
and not:
|memory_1>|environment_1> + |memory_2>|environment_2>
because the latter would imply that you could (in principle) tell what happned without
performing a measurement, and I don't believe on psychic phenomena.
So, the "no-psychic phenomena postulate" would compel you to assume that:
|memory>(|environment_1> + |environment_2>)
is the correct description of the state and that only after you learn about the fact you
become localized in either branch. This applied to the memory resetting implies what I
was arguing for.
Saibal
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