On Mon, Nov 12, 2018 at 9:35 PM Bruno Marchal <marc...@ulb.ac.be> wrote:

>> You've got it backwards, physics can simulate a Turing Machine but a
>> Turing Machine can't simulate anything or do anything at all without the
>> help of matter that obeys the laws of physics.
>
>
> *> That is plainly false. If u is a universal machine/number, phi_u(x, y)
> emulate the number/machine x on the input y. *
>

So you say, but I see precisely ZERO evidence that "phi_u(x, y)" can
emulate a machine or emulate anything a or in fact do anything at all
because "phi_u(x, y)" never changes, not in time and not in space. You
wrote "phi_u(x, y)"  in the above about 11 hours ago thousands of miles
from me, but here I am looking at "phi_u(x, y)"  and "phi_u(x, y)" is still
just "phi_u(x, y)" .


> >>A mathematical model is a description of something written in the
>> language of mathematics, like most descriptions it is not complete,
>
>
> *> You are using “model” in the sense of the physicist, and logicians call
> that a theory, which can be seen indeed as a (incomplete) theory. But a
> model, in the logician sense is complete * [...]


Then logicians are talking about something that is self contradictory
because nothing mathematical or logical can be both complete and
consistent.

 > [...]* by definition*.


You have a tendency to use those 2 words as if they were the final mark of
authority, but the words "by definition" does not cause things to suddenly
spring into existence, that utterance is no more magical than
"abracadabra".  Hogwarts Castle is a school for wizards BY DEFINITION,
there is absolutely no doubt about it, but do you think it would be worth
your time to go looking for it?


> > *It is usually infinite,*
>

Yet another reason to suspect it does not exist.

> *A model is a model of a theory.*
>

So I guess a model of a theory is a model of a model of a theory, and a
model of a model of a theory is a model of a model of a model of a theory,
and a model of....

 John K Clark



>

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