On 02 Jun 2015, at 19:47, John Clark wrote:
On Mon, Jun 1, 2015 at 5:46 PM, LizR <[email protected]> wrote:
> A Turing Machine is actually an algorithm
Yes, a algorithm that is a set of instructions that explains how to
organize matter that obeys the laws of physics in such a way that it
can make any finite calculation.
> It doesn't explain how to organise matter - which is obvious from
the fact that all sorts of systems can be Turing-universal,
There are many ways to make a computer and Turing's 1936 paper said
nothing about the practicalities and engineering details, but he did
prove that the logical schematic of any computer
Any human computer. Computer did not exist at the time of Turing.
Indeed, he is the discoverer of the mathematical abstract computer
(modulo Babbage).
can be reduced to something that we now call a Turing Machine; but
you can't make a calculation with just a schematic, you need matter
that obeys the laws of physics too.
You cannot, but that has nothing to do with the fact that computations
are mathematical objects, and that the space of all computation
(constructively defined by the DU) is entirely executed, in the math
sense, in a tiny part of arithmetic. With computationalism, this is
exploited to extract the appearance of the physical laws, without
committing an ontological commitment in a physical universe.
> The fact that to build one we have to use matter is a contingent
fact;
Yes, if you don't mind that your Turing Machine isn't actually
making a calculation, or doing anything of any sort, then matter
that obeys the laws of physics is unnecessary.
In arithmetic, you have both the Turing machines, and their execution.
They are immaterial, and not usable to get money, but they do exist
(in the math sense), and the physical apparent (phenomenological)
existence is explained through them.
> Similarly (to take a simpler example) there are many ways one can
add two numbers together, but that doesn't mean that addition is a
material process.
Nobody has ever added two numbers together without using a physical
process to do so, and nobody has the slightest idea of how non-
material addition would even be possible.
No Aristotelian physicists. (Not "nobody").
> if performed correctly the calculation always gives the same
result regardless of the physical medium used
The calculations are all done in a different way, but without
exception they all have one thing in common, they all need matter
that obeys the laws of physics, otherwise nothing happens.
This is refuted, unless you mean happens relatively to your body, but
we don't assume such bodies, and on the contrary show that such notion
does not make sense, once we postulate computationalism.
You said once that you can conceive that the physical reality is not
primary, but here you assume the existence of a primary physical
universe all the time.
>which suggests that an abstract process is being instantiated
physically,
Which suggests a physical process that can be thought about
abstractly.
Turing did not get the computer from abstracting it from a physical
computer or processes but by analysis of the human mind and how they
compute with paper and pencil, or mentally. The notion of computation
does simply not rely on anything physical. It is an arithmetical
notion, definable in RA or PA.
> not that it is a physical process (if so, which one?).
How about F=MA ? A force accelerates the Turing tape until it is
under the read head then another force stops it, then yet another
force accelerates ink to form either a 1 or a 0 on the tape.
That plays a role in the physical implementation of a computer, but
not in their arithmetical implementations, which is what concern us in
the derivation of physics from arithmetics with the goal to test comp
(and up to now, comp not only get right the non trivial quantum
tautology, but it makes the weirdness into the expected).
Bruno
John K Clark
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