On 8/16/2013 4:57 PM, [email protected] wrote:
Citeren meekerdb <[email protected]>:
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.
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.
But that's where I disagree - not about the conclusion, but about the possibility of the
premise. I don't think it's possible to erase, in the quantum sense, just your memory.
Of course you can given a drug that erases short term memory and so it may be possible to
create a drug that erases long term memory too, i.e. induces amnesia. But what you
require is to erase long term memory in a quantum sense so that all the informational
entanglements with the environment are erased too. So I don't think you can be to the
"erased memory" state you need.
Brent
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