On 27 Oct 2015, at 23:28, Brent Meeker wrote:
On 10/27/2015 3:04 PM, Stathis Papaioannou wrote:
On 28 Oct 2015, at 1:30 AM, John Clark <[email protected]> wrote:
On Mon, Oct 26, 2015 at 5:16 PM, Stathis Papaioannou <[email protected]
> wrote:
>> From examples in the physical world. You can give as
many botanical definitions of the word "tree" as you want but it
will just be a word defined by other words that are themselves
defined by yet more words that are.... If you tried to dig for
meaning all you'd find is a endless loop, it would just be a game
where words are manipulated
according to the rules of botany until somebody forgot about
definitions and pointed to the ASCII string "t-r-e-e" and then
pointed to a large photosynthesizing organism made largely of
cellulose that exists in the physical world. Then even a martian
would notice a correspondence between this game of manipulating
symbols called "botany" that humans had invented and the way these
large photosynthesizing organism made largely of cellulose live.
> What about a virtual world with trees and observers, and
no I/O devices connecting it to outside trees?
There would still be I/O devices connected to the virtual
trees made by a computer that operated according to the laws of
physics, if not the trees wouldn't even be virtual. And the books
on both virtual botany and real botany would still be more than a
just a symbol manipulation game, they would have semantic
content because there would be a correspondence between
the way the symbols are manipulated and the way the virtual
(or real) large photosynthesizing organism live. Regardless
of if they are virtual or real if you want to know how trees
live studying those botany symbols in virtual (or real) books will
help, so they must have semantic content .
The requirement that a computation be able to interact with the
real world puts a restriction on what qualifies as a computation.
You've challenged Bruno many times to perform a difficult
computation using his Platonic computer. Well, that computation is
occurring in front of you now in the thermal motion of the atoms in
your desk, which under an appropriate interpretation are
implementing a Turing machine. But you and Bruno don't have that
appropriate interpretation, and if you did, you would have the
result of the calculation already. In other words, the thermal
motion computation is not understandable as such in, and cannot
interact with, the world at the level of the substrate of its
implementation; so it would usually be said that either there is no
computation being implemented, or it is being implemented only in a
trivial and useless sense. But remove the requirement for
interaction in the real world, and this objection falls down. The
computation is being implemented, your difficult calculation has
been completed, and it is being appreciated by the virtual
observers who are clapping and cheering - even though you can't
hear them.
That's essentially Bruno's MGA, except it stops one step short.
Bruno takes the last step and says even if the atoms of your desk
were doing absolutely nothing there is an interpretation in which
that is a computation; hence the atoms are superfluous. But
clearly then it is the interpretation which is providing the
computation.
I do not agree with this. We might have something like that with
analogical computation, if that could ever mean something, but with a
computation in the sense of Church, you must be able to name the
universal number doing the computation, and there are virtually no
chance that a sequence of digital states constitute a computation
(which does have the right counterfactuals). In the MGA we arrive at
the idea that nothing do any specific computation by assuming
materialism and mechanism, but that is what is judged absurd in the
reductio ad absurdum to show the incompatibility between materialism
and mechanism.
If someone pretend that a rock or something do a computation, I will
ask here which one, and what is the universal number doing it, and
what is the program (or how to justify that there is a program, even
in principle).
Some physicist estimates that there is no computation at all in
nature: only continuous analogical partial imitation of computation.
For them, computations exists *only* in arithmetic, which is not
implemented in nature, which use real numbers, and which approximates
the natural numbers by infinite trigonometrical functions. I am open
to that idea, but I think we just don't know. Computationalism might
entaill something like that.
Bruno
Brent
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