We know that nanobots are possible because, in a very real way, they already exist.
It’s a point that’s been made before, most famously in the Drexler-Smalley debates, but it bears repeating. Single celled life is “the ultimate existence proof of the feasibility of a molecular assembler.” This is not a metaphor. Life is nanotech, literally. Our future nanobots may bear a striking resemblance to yeasts and other single celled life.
Here’s a great example:
Salmonella Bacteria Turned Into Cancer Fighting ‘Robots’
KurzweilAI.net, Mar. 31, 2008
[Notice this is dated March 31 and not the day after.]
University of Massachusetts Amherst researchers are turning Salmonella bacteria into tumor killing “robots” that use their flagella to go deep into tumors where conventional chemotherapy can’t reach, and once in place, manufacture drugs that trigger cancer cells to kill themselves.
Normally, mice with tumors all die within 30 days. After receiving this bacterial system and getting a dose of radiation, all the mice in their lab tests survived beyond the 30 days, which could translate into months or years in people.