December 17, 2006

Post #2121 – 20061217

Hearing Daniel and Scott read the science project story on NPR Sat a.m. made me think the author believes in “Grey Goo” — scary thought.

“Grey goo

Grey goo refers, usually in a science fictional context, to a hypothetical human extinction event involving nanotechnology, in which out-of-control self-replicating robots (Von Neumann machines) consume the Earth while building more of themselves. The scientific (technical) term for this risk, coined by Robert Freitas, is global ecophagy. In a worst-case scenario, all of the matter in the Galaxy could be turned into goo (with “goo” meaning a large mass of replicating nanomachines lacking large-scale structure, which may or may not actually appear goo-like), killing the Galaxy’s residents. The disaster would most likely be due to an accidental mutation in an assembler.

Assuming a nanotechnological replicator is capable of causing a grey goo disaster, safety precautions might include programming them to stop reproducing after a certain number of generations, or designing them to require a rare material that would be sprayed on the construction site before their release. However, it should be noted that it is unlikely that nanotechnology will be capable of creating grey goo at all.

The primary limitation on even arbitrarily sophisticated nanotechnology which prevents a runaway grey goo reaction is the lack of a sufficient source of energy. A nanomachine wouldn’t be able to get much energy out of eating inorganic matter such as rocks because, aside from a few exceptions (coal, for example) it’s mostly well-oxidized and sitting in a free-energy minimum. This means that the nanobots would be competing with natural life forms for organic matter or sunlight, life forms which have been evolving for over four billion years to optimize their ability to compete for these resources. If the nanomachine is itself composed of organic molecules, then it might even find itself being preyed upon by preexisting bacteria and other natural life forms. If they are built of inorganic compounds or make much use of elements that are not generally found in living matter, then they will need to use much of their metabolic output to fighting entropy as they purify (reduce sand to silicon, for instance) and synthesize the necessary building blocks. Grey goo may only be possible in an environment which lacks indigenous life. ”

Daniel replies:

Funny you should mention it. I had grey goo for lunch.