Bruno says:

"...the notion of computability is absolute." 

David Deutsch says:

"We see around us a computable universe; that is to say, of all
possible mathematical objects and relationships, only an infinitesimal
proportion
are ever instantiated in the relationships of physical objects and physical
processes. (These are essentially the computable functions.) Now it might
seem that one approach to explaining that amazing fact, is to say "the
reason
why physical processes conform to this very small part of mathematics,
'computable mathematics,' is that physical processes really are computations
running on a computer external to what we think of as physical reality." But
that relies on the assumption that the set of computable functions -- the
Turing computable functions, or the set of quantum computable operations
-- is somehow inherently privileged within mathematics. So that even a
computer
implemented in unknown physics (the supposed computer that we're
all simulations on) would be expected to conform to those same notions of
computability, to use those same functions that mathematics designates as
computable. But in fact, the only thing that privileges the set of all
computational
operations that we see in nature, is that they are instantiated by
the laws of physics. It is only through our knowledge of the physical world
that we know of the difference between computable and not computable. So
it's only through our laws of physics that the nature of computation can be
understood. It can never be vice versa."

http://www.qubit.org/people/david/Articles/PPQT.pdf


If it is only through our knowledge of the physical world
that we know of the difference between computable and not computable, and I
don´t see any flaw in David´s argument that leads up to that statement, then
the notion of computability definitely is not absolute.

LN



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