Fundamental Physical Limits on Computation
Warren D. Smith, NECI
06/19/92
abstract
We consider limitations on the performance of computers
arising from thermodynamics and the laws of physics.
We provide upper bounds on three quantities:
sustained information flux, information storage density, and
sustained computational speed.
All of these upper bounds are ``tight''
in the sense that they could be
approached by plausible-sounding physical systems,
and they all arise from a single unified point of view.
We also make a conjecture about the rate of inevitable decay of
stored information. This conjecture may be thought of as a
quantitative extension
of the second law of thermodynamics. It leads to a
bound on the density of stable information.
We carefully elucidate the assumptions behind these bounds.
We give a list of 4 open problems at the end.
KEYWORDS: thermodynamics, computation, reversible Turing machines,
blackbody radiation, decay of information, physics, entropy,
information transmission and storage, cooling requirements.