Charles H. Bennett

Charles H. Bennett (1943– ) is the IBM polymath who keeps quietly overturning things everybody "knew". Everybody knew computing must burn energy — he proved it needn't. Everybody knew Maxwell's demon was safely dead — he showed it had been killed for the wrong reason, for 115 years. And when he once had to describe himself online, he went with "a founder of quantum information theory" — which is a bit like Neil Armstrong saying he's "been on some trips".

The chemist who saw computation everywhere

Bennett's PhD was in chemistry — simulating how molecules jiggle and move. That odd start turned out to be a superpower: he later realised that RNA polymerase, the molecular machine copying your DNA right now, is a computer — one that can run forward and backward, nudged along by thermal noise. In 1973 he turned that insight into a theorem: any computation can be done reversibly, saving a history of its steps and then uncomputing the mess to clean up without ever erasing a bit. Result: computation has no minimum energy cost — at a time when nearly everyone was sure it did. His beloved Brownian computers drift to their answers on random jostling alone.

Since 1867, Maxwell's demon — a tiny imp who sorts molecules to cheat the second law of thermodynamics — had been "explained away" by claiming that measuring a molecule must cost energy. In 1982 Bennett showed that's wrong: measurement can be free. The demon's real problem is its memory — eventually it must forget what it saw, and by Landauer's principle that erasure costs exactly the energy the demon seemed to gain. The books balance; the second law survives; the cost was in forgetting, not finding out.

Secrets, beaches and teleporters

In 1984, with Gilles Brassard, Bennett invented quantum cryptography — the BB84 protocol, partly worked out on a beach (napkins were involved). The idea: encode a secret key in single quantum particles, so any eavesdropper unavoidably disturbs them and gives herself away. The first working prototype sent a quantum key across a mighty 32 centimetres of air on a lab bench — audibly, since the power supply hummed differently for 0s and 1s. From that desktop toy grew today's satellite-based quantum key distribution. Then in 1993 he and five colleagues invented quantum teleportation — a way to transmit an unknown quantum state using entanglement plus an ordinary phone call. Playful to the core, Bennett treats physics the way Shannon treated maths: as the best game in town.