You cannae break the laws of physics, Jim

When some reality-challenged transhumanist tells us that within two decades the human/computer interface will consist of injecting our brains with a swarm of subcellular-sized nanobots to stimulate neurons at the molecular level, Jerry Fabin is the person who comes to mind:

Giant Cell invades Earth

It is hard to decide where the gap between the transhumanist vision and the physical constraints of microscopic scale is greatest.* Transhumanists really seem to imagine cellular biochem as if scaled up to the size of a room you can walk into (I blame Will Burtin), with molecules made up of colour-coded balls-&-sticks like they are in high-school chemistry, so the nanobots can use visible-light wavelengths to identify the molecules that surround them.

Evan forbid that the nanobots should have to blunder around blindly, with no way of sensing their neighbourhood other than making and breaking chemical bonds, and no helpful "You Are Here" maps printed on each cell membrane to label it as a cell and help them tell their dendrite from their axon. Without such information, perhaps they would not perform any better than the chaotic, unplanned, thermal-noise-driven processes of normal cell biology; and that would clash with the central assumption that engineers can do better than four billion years of evolution at designing a rational biology.**

Not making this up:

“By the late 2020s, nanobots in our brain, that will get there noninvasively, through the capillaries, will create full-immersion virtual-reality environments from within the nervous system. So if you want to go into virtual reality the nanobots shut down the signals coming from your real senses and replace them with the signals that your brain would be receiving if you were actually in the virtual environment. So this will provide full-immersion virtual reality incorporating all of the senses.”

Going into all the conflicts with reality here would involve the Explaining Voice. Fortunately, a neurobiologist has already done the work, pointing out that the brain is not in fact full of empty space through which nanobots might float serenely like so many flying cars converging on the roof-top helipad; but rather is as tightly-packed as a holiday suitcase, with even the gaps between cells filled up with working parts. His like-minded commenters wonder how these myriad nanobots will be powered, and whether a working brain can handle their waste heat (given that the human brain is already pushing the cooling capacity of cerebral circulation, and has no margin for double-clocking).

Other commenters, more optimistic, argue that these concerns are nugatory if the brain in question is already dead, and the nanobots are only destroying it in the process of recording its condition (in order to revive its erstwhile owner's consciousness as a computer emulation). Readers may or may not find consolation in this.

It sounds as if the transhumanist (one Ray Kurzweil) is having belated doubts about the adequacy of existing human/computer interfaces like Dragon Systems.

Ray Kurzweil was disappointed by the absence of catsuited Raquel Welches within the brain's microanatomy.

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* On-line poll possibility!

** Do you think it could be a control fantasy? Let's ask Old Uncle Bill!