assume the brain dissipates 1/10 of this; 200 kilocals per day. The human brain is pretty hungry. http://www.pnas.org/content/99/16/10237.full http://www.pnas.

assume the brain dissipates 1/10 of this; 200 kilocals per day. The human brain is pretty hungry. http://www.pnas.org/content/99/16/10237.full http://www.pnas.org/content/99/16/10237.full says around 1/5th of resting human metabolism is to power the brain. So double all numbers in that post. This puts an upper limit on how much the brain can calculate, assuming it is an irreversible computer: 5 10^19 64 bit ops per second.* It's one thing to put a theoretical upper limit on the human brain's computational abilities. It's another thing to claim the human brain actually performs anywhere near that level. Using the same math, a lawnmower engine puts out 1,000 joules per second, so the upper bound on its computational ability is 10^22 ops/sec. I think more than one equation is needed to get a good idea of the brain's performance. Evolved brains are highly suboptimal. There's no evolution fairy waving a wand and selecting solely for brainpower. Much of the selection pressure is for basic things like famine resistance. Even when selecting for intelligence, evolution can only make incremental improvements. It's going to have trouble stumbling on something like the wheel or the impeller. And it shows. Brains have no API, no debugger, and they certainly aren't end-user modifiable. I can't, by thinking, dedicate a small group of neurons to mental arithmetic. I have to expend significant effort to do the math in my head, and even then I'm not always correct. Neurons fire at a rate of only 20 hertz or so, meaning any mental computation has to finish in 100-200 steps for a person to respond in real-time. The signals sent by neurons only travel at around 100 meters per second. That's 0.0000004c. Less than one one-millionth the speed of light! And that's not going to change soon, because evolution can't change substrates. It's forced to use neurons instead of silicon or carbon. >Even if brains are computationally only 1/1000 of their theoretical efficiency Based on what I've said above, I think brains are far far less efficient than that.