On 10/27/2015 3:04 PM, Stathis Papaioannou wrote:
On 28 Oct 2015, at 1:30 AM, John Clark <[email protected]
<mailto:[email protected]>> wrote:
On Mon, Oct 26, 2015 at 5:16 PM, Stathis Papaioannou
<[email protected] <mailto:[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.
Brent
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