Citeren meekerdb <>:

On 8/15/2013 6:18 AM, wrote:
Citeren meekerdb <>:

On 8/14/2013 6:41 PM, 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.


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