To build a brain

For all their progress, computers are still pretty unimpressive. Sure, they can pilot aircraft and simulate nuclear reactors. But even our best machines struggle with tasks that we humans find easy, like controlling limbs and parsing the meaning of this paragraph. It's a little sobering, actually. The average human brain packs a hundred billion or so neurons-connected by a quadrillion (1015) constantly changing synapses-into a space the size of a cantaloupe. It consumes a paltry 20 watts, much less than a typical incandescent lightbulb. But simulating this mess of wetware with traditional digital circuits would require a supercomputer that's a good 1000 times as powerful as the best ones we have available today. And we'd need the output of an entire nuclear power plant to run it.