[FOM] The unreasonable soundness of mathematics
Timothy Y. Chow
tchow at alum.mit.edu
Mon May 2 21:08:52 EDT 2016
On Mon, 2 May 2016, Mario Carneiro wrote:
> It sounds like what you are objecting to is the very concept of a
> "specification".
Not quite. As an ultrafinitist, I'll grant you the ability to specify a
concrete computer with a specific, feasible number of components and a
specific, feasible amount of memory. The sticking point arises when
generalizing/idealizing to an unbounded amount of memory.
The classical mathematician is, on the basis of a *single* formal proof,
making a prediction about the behavior of an unbounded number of concrete
machines. The ultrafinitist, on the other hand, has to separately build a
megabyte-sized machine, a gigabyte-sized machine, a terabyte-sized
machine, etc., and only when each of these machines runs to completion can
the ultrafinitist assert that there are no positive integers A and B *in a
certain range* such that A^2 = 2*B^2. For each concrete machine, the
ultrafinitist can understand what a spec is for that machine, but the
classical mathematician's "spec" is, in effect, quantifying over specs of
*arbitrary size* and it is this step that the ultrafinitist cannot
understand. Like the memoryless goldfish's little plastic castle in Ani
DiFranco's poem, the computational result is a surprise every time to the
ultrafinitist.
Tim
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