RE: copy method important?

From: Brent Meeker <>
Date: Thu, 23 Jun 2005 23:03:31 -0000

>-----Original Message-----
>From: Bruno Marchal []
>Sent: Monday, June 20, 2005 1:33 PM
>To: Norman Samish
>Subject: Re: copy method important?
>Le 18-juin-05, à 20:36, Norman Samish a écrit :
>> I'm no physicist, but doesn't Heisenberg's Uncertainty Principle forbid
>> making exact quantum-level measurements, hence exact copies? If so,
>> then
>> all this talk of making exact copies is fantasy.
>Many good answers has been given. And my comment will overlap some of
>The most physicalist one is to referindeed to Tegmark's paper where he
>justifies by Everett/decoherence that the evidence is that our brain,
>when seen as an information handling computing machine, acts as a
>classical machine. But comp makes physicalism wrong, and Tegmark's
>answer cannot be "fundamentally" genuine.
> The importance of quantum decoherence in brain processes
>M Tegmark 2000, quant-ph/9907009, Phys. Rev. E 61, 4194-4206
> 161 Why the brain is probably not a quantum computer
>M Tegmark 2000, Information Sciences 128, 155-179
>Then, concerning the comp 1-person indeterminacy, even if my
>computational state is a quantum states, the Universal Dovetailer
>Argument (UDA) is still going through. This is a consequence of the
>fact that quantum computation does not violate Church's thesis. That
>entails that you can simulate a quantum computer with a classical
>computer. Sure, there is a relative exponential slow-down of the
>computation, but this is not relevant because the universal dovetailer
>is naturally slow down by its heavy dovetailing behavior, and then the
>first person cannot be aware of that slow down.
>And then I recall I gave an exercise: show that with comp the
>no-cloning theorem can easily be justified a priori from comp. As I
>said this follows easily from the Universal dovetailer Argument.

But the UDA and the comp-hypothesis are not the same thing.

>argument shows that physical observable reality (relatively to what you
>decide to measure here and now) emerges as an average on all
>computations (generated by the UD) going through your actual state.
>Suppose now that you decide to observe yourself with at a finer and
>finer level of description. At some moment you will begin to observe
>yourself at a level below you substitution level (which I recall is the
>level where you survive through copy).

How do you know you can observe that level?

>Below that level comp predict
>you will be confronted with the 1-comp indeterminacy, that is you will
>"see" the many computation/histories.

If comp predicts that then it seems to involve a self-contradiction. It
implies that there was no substitution level after all.

Brent Meeker
Received on Fri Jun 24 2005 - 02:55:40 PDT

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