Rolf Landauer (1927–1999) was the physicist who put a price tag on forgetting. Born in Stuttgart, he fled Nazi Germany as a boy, served in the US Navy, and then settled in for a lifetime at IBM — where he spent decades telling anyone who would listen (and plenty who wouldn't) that "Information is physical." He put that slogan on his slides for years while colleagues rolled their eyes. Today it's the founding creed of a whole field: information isn't a ghostly abstraction — it lives in atoms, electrons and magnets, and it obeys the laws of physics like everything else.
In 1961 Landauer asked a question nobody had thought to ask: does computation have to cost
energy? His answer was surgical. Most operations are free in principle — but erasing
a bit is not. Destroying information squeezes many possible states into one, and thermodynamics
sends you the bill: at least
Landauer was famously the field's in-house skeptic — its most feared and most valuable referee. His rule, sometimes called Landauer's razor: if you propose a wonderful new computing scheme, you must state its error rates and energy dissipation, or you haven't proposed anything at all. When quantum computing arrived in a blaze of hype, he was its sternest critic — not to kill it, but to make it honest. Researchers grumbled, tightened their claims, added the error analysis… and the field came out far stronger. Every "but what about noise?" section in a quantum-computing paper carries a little of Landauer's ghost.
Forgetting bits was only half his legacy. For the physics-minded: Landauer also invented one of the key tools of mesoscopic physics — the Landauer formula, which treats electrical conductance in a tiny wire as transmission: electrons don't flow like water, they scatter like waves through an obstacle course, and the conductance simply counts how much gets through. It's the standard language for nanoscale electronics to this day. Two fields, one stubborn conviction: take the physics of small things seriously, and demand the numbers.