I’m going to nitpick (mainly because of how much reading I’ve been doing about thermodynamics and information theory since your engines of cognition post):
Human neurons … dissipate around a million times the heat per synaptic operation as the thermodynamic minimum for a one-bit operation at room temperature. … it ought to be possible to run a brain at a million times the speed without … invoking reversible computing or quantum computing.
I think you mean neurons dissipate a million times the thermodynamic minimum for an irreversible one-bit operation at room temperature, though perhaps it was clear you were talking about irreversible operations from the next sentence. A reversible operation can be made arbitrarily close to dissipating zero heat.
Even then, a million might be a low estimate. By Landauer’s Principle a one-bit irreversible operation requires only kTln2 = 2.9e-21 J at 25 degrees C. Does the brain use more than 2.9e-15 J per synaptic operation?
Also, how can a truly one-bit digital operation be irreversible? The only such operations that both input and output one bit are the identity and inversion gates, both of which are reversible.
I’m going to nitpick (mainly because of how much reading I’ve been doing about thermodynamics and information theory since your engines of cognition post):
I think you mean neurons dissipate a million times the thermodynamic minimum for an irreversible one-bit operation at room temperature, though perhaps it was clear you were talking about irreversible operations from the next sentence. A reversible operation can be made arbitrarily close to dissipating zero heat.
Even then, a million might be a low estimate. By Landauer’s Principle a one-bit irreversible operation requires only kTln2 = 2.9e-21 J at 25 degrees C. Does the brain use more than 2.9e-15 J per synaptic operation?
Also, how can a truly one-bit digital operation be irreversible? The only such operations that both input and output one bit are the identity and inversion gates, both of which are reversible.
I know, I know, tangential to your point...