Citeren meekerdb <meeke...@verizon.net>:
On 8/15/2013 6:18 AM, smi...@zonnet.nl wrote:
Citeren meekerdb <meeke...@verizon.net>:
On 8/14/2013 6:41 PM, smi...@zonnet.nl 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.
The |environment_i> have to be different as they are entangled with
different memory states, precisely due to rapid decoherence. The
environment always "knows" exactly what happened. So, the assumption is
not that the environment "doesn't know" what has been done (decoherence
implies that the environment does know), rather that the the person
whose memory is reset doesn't know why the memory was reset.
So, if you have made a copy of the memory, the system files etc., there
is no problem to reboot the system later based on these copies. Suppose
that the computer is running an artificially intelligent system in a
virtual environment, but such that this virtual environment is modeled
based on real world data. This is actually quite similar to how the
brain works, what you experience is a virtual world that the brain
creates, input from your senses is used to update this model, but in
the end it's the model of reality that you experience (which leaves
quite a lot of room for magicians to fool you).
Then immediately after rebooting, you won't yet have any information
that is in the environment about why you decided to reboot. You then
have macroscopically different environments where the reason for
rebooting is different but where you are identical. If not, and you
assume that in each environment your mental state is different, then
that contradicts the assumption about the abilty to reboot based on the
old system files.
So, you need to learn from the environment what happened before this
information can affect you. This does not mean that the memory is not
classical, rather that it's immune to noise from the environment, this
allows it to perform reliable computations. So, while the environment,
of course, does affect the physical state of the computer, the
computational states of the computer are represented by macroscopic
bits which can be kept isolated.
Saibal
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