X-Message-Number: 9269
Date:  Thu, 12 Mar 98 17:15:49 
From: Mike Perry <>
Subject: Re: CryoNet #9267

Thomas Donaldson writes,

> Sorry, but the implied idea that if I don't believe we are finite Turing 
> machines I must therefore believe that we run by supernatural means just 
> doesn't ring any bells with me. If finite nonTuring machines can exist, then
> that is sufficient.
> 
Well, I haven't said that lack of belief that we are finite Turing 
machines *necessarily* means that "we are run by supernatural means."

> Just what would be wrong, metaphysically, if the Church-Turing thesis failed?

I don't see it as a necessary catastrophe. Actually, the CT thesis 
does not even seem necessary for my most general version of a digital 
argument anyway. I don't devote a lot of space in the book to 
defending it per se, though I do make note of it, and it too has its
utility. The digital 
argument, more generally, which doesn't require the CT thesis but is 
implied by it, is useful to be able to argue a case for 
"unboundedness"--that all finite histories, in some sense, are real, 
which is an important underpinning of my book. Another important 
underpinning it supports is "interchangeability"--that the same 
person with the same experiences can occur more than once in the 
multiverse, which renders more credible the idea of resurrecting 
people by creating replicas. It is useful too for such
ideas as a universal language, which I develop, and
for making plausible the idea of uploading. It has a bearing on the 
issue of consciousness. However, I could 
probably soften, or retreat a bit from it
if I had to (I don't see the necessity as yet).
I think our *memories* are digital and don't involve anything but a finite 
information content, which is more important than whether our 
*experiences* more generally are also digital in 
some sense. But the digital nature of memories 
can be used as one more argument that *significant* experiences
must be digital too! 

> 
> If by digital, you simply mean that our own experiences are discrete and
> finite, I will freely admit some kind of finitude, but discreteness is
> going to (at least) require more argument.

I'm sure that my background, to say nothing of the space I can 
reasonably take up with this topic in the book, are both inadequate 
to really dispose of the question. But physics-trained people like 
Tipler and Deutsch seem to agree on what amounts to a digital 
paradigm as the basis of all things that happen in our reality. I 
have studied their arguments as carefully as I could and they seem 
solid enough to merit acceptance, at least on a provisional basis, 
which is about the best we can do with scientific arguments anyway. 

I am aware that many things in our experience 
such as vision *seem* to involve a continuum, not just discrete state 
changes, but I think that is a convincing illusion caused by the vast 
numbers of particles involved. This is certainly true of lumps of 
inert matter, which are made of atoms, and I think so too
for events as well. As for the idea that space and time 
are (possibly) continuous not discrete, I answer that events don't 
happen at every point in spacetime but only at isolated points, when 

"world-lines" intersect and particles interact. On the other hand, if events are
discrete but "incommensurable" it does not necessarily destroy the 
digital paradigm. A case in point would be a hypothetical machine that 
bases its behavior on the successive digits of a dimensionless, 
fundamental constant, assumed to be non-computable,
but can only access finitely many of these 
digits in finite time. Again, I think the digital paradigm is well 
supported by modern physics, though I have to base this opinion 
somewhat on "hearsay" at this point. I hope in the future I can study 
more physics and other things and investigate this interesting question 
further.

> as yet, general relativity and quantum mechanics remain unreconciled.

As I understand it, a major source of "incompatibility" is the 
supposed non-locality of phenomena under quantum mechanics, which 
amounts to faster-than-light signaling, which is forbidden by 
relativity. Locality, 
however, is restored by the many-worlds hypothesis, which does not 
disturb quantum mechanics.

> So think a bit: there must be some wider theory that includes the 
> phenomena explained by each of them, though it may disagree experimentally
> with both. If we base our ideas of human survival upon either or both,
> we may awaken from our suspension to find both theories, and all the 
> philosophies built upon them, to be history only, and dismissed by the
> people of that time as we now dismiss phlogiston.

This is possible, but on the other hand, there is no guarantee of it, 
and I think there's a good chance it won't happen, or if there is 
some problem, it will be remediable without throwing out the whole. 
Quantum mechanics looks pretty solid--as Nick Herbert says in 
*Quantum Reality*, it is "batting 1000"--and it is the major source I 
have for a "digital" argument. If it and relativity still don't jibe, 
even with many-worlds, I suspect relativity (with all due respect to 
Einstein) is what will have to give ground. So I persist.

Endless best,

Mike Perry

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