From Paul Bieleski
You report on new calculations of a fundamental limit to computing power (8 May, p 12). Back in 1962, Hans Bremmermann derived a more absolute limit, based on the fundamental coarseness of space-time. He calculated a limit of no more than 1.6 × 1047 bits per gram per second.
As Ross Ashby pointed out in the 1966 paper “Modeling the brain”, which alerted me to Bremmermann’s work, whether the gram of matter is in the most advanced type of computer or inside someone’s skull is irrelevant.
Nelson, New Zealand
