The Singularity is Near: When Humans Transcend Biology

by Ray Kurzweil

Estimating a global population of around ten billion (1010) humans, Freitas estimates around 1016 (ten thousand trillion) nanobots for each human would be acceptable within this limit.132 We would need only 1011 nanobots (ten millionths of this limit) per person to place one in every neuron. By the time we have technology of this scale, we will also be able to apply nanotechnology to recycle energy by capturing at least a significant portion of the heat generated by nanobots and other nanomachinery and converting that heat back into energy. The most effective way to do this would probably be to build the energy recycling into the nanobot itself.133 This is similar to the idea of reversible logic gates in computation, in which each logic gate essentially immediately recycles the energy it used for its last computation.