What is the definition of "computer" in this case? Can it be a circuit that only performs one floating point 32bit operation and then evaporates after a nanosecond?

all the energy you expend between knowing the inputs and knowing the outputs counts as energy spent on compute. No cute loophole creating something that only works for one specific flop with known inputs. A computer has to work with arbitrary 32-bit numbers that were not provided until runtime.

The ultimate limit of the current paradigm would be one electron per transistor switching event, times the band gap of the semiconductor. The 4090 has 76E9 transistors switching at 2.2E9hz to do 88E12 flops. So that’s about 1.9E6 switching events per flop. Half the time the transistor state doesn’t change, and Knock off another order of magnitude if some of the transistors are for other purposes or could be eliminated from a more efficient design. SC band gaps are at least circa 0.5V. That gives us a lower bound of 50KeV per flop.

@JonathanRay If compute can only ever get ~1000x more energy efficient than it is now, that has huge implications for AI - ems may never be viable