Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!mips!dimacs.rutgers.edu!aramis.rutgers.edu!athos.rutgers.edu!nanotech From: bsmart@bsmart.tti.com (Bsmart) Newsgroups: sci.nanotech Subject: Re: Is this stuff for real? Keywords: reality nanotech questions Message-ID: Date: 16 Mar 91 04:16:01 GMT Sender: nanotech@athos.rutgers.edu Organization: Citicorp+TTI Lines: 65 Approved: nanotech@aramis.rutgers.edu In article , cphoenix@csli.stanford.edu (Chris Phoenix) writes: > replicating the machine. However, computer memory has one feature > that the DNA doesn't: it has a computer. I think part of the problem is that the point of nanomachines is that they operate at the molecular (or even submolecular) level, and are presumably implemented on a similar scale. Nanocomputers probably won't work like the digital electronic computers we're familiar with today; they'll be mechanical devices that represent logic states by chemical composition, physical arrangement of their components, or some such trick. Now, there's no reason why a mechanical computer can't be digital in its operation (every now and then Marvin Gardner presents some delightful macro-scale mechanical computers in Scientific American; one of my favorites was an enormous hypothetical contraption composed of ropes and pulleys and operated by grunting, sweating teams of slaves) but the fact remains that computers (or any other kind of gadgetry) implemented on a molecular scale will be subject to chemical and radiation interference at the same scale. Just as old-fashioned core memory (does anybody still remember?) represented information by imposing different magnetic charges on iron doughnuts, nanocomputers will most likely represent bits by moving an oxygen atom (or something) from HERE to THERE in their structure, and "execute" their "programs" by folding and unfolding and cleaving and binding -- kinda the way natural proteins do. If a mutagenic chemical or other influence came along and moved the atom elsewhere, the result would be pretty similar to what happens in an electronic computer in response to a voltage surge or a stray cosmic-ray hit. Perhaps the error could be corrected by some kind of detection scheme (we do it with memory errors all the time on the macro scale) but if the error were severe enough, or if it happened to hit the error-correcting part of the nanocomputer, then on come the red lights and it no longer behaves like a computer. Even a computer has to be made out of something, and when you're working with a device composed of only a few hundreds or even a few thousands of atoms, you have to live with some constraints and failure modes that just don't apply on larger scales. My concept of a nanocomputer is that it's basically some exotic and complicated chemical compound -- or maybe a soup containing several such carefully constructed compounds. Perhaps structures on a somewhat larger scale (bigger than molecular, but not bigger than cellular) would fall into the "nanotechnology" realm as well, but even these would be dependent upon very small effects for their operations. Discussion, gentlebeings? [The current tentative designs for assemblers and nano-robots with nanocomputer "brains" are on the order of billions, even up to a trillion, of atoms. Even proteins, which are very special-purpose machines, run into the thousands of amino acids, at a handful of atoms each. If an alpha particle came whiffling through a nanocomputer of the design Eric Drexler has talked about with the rod logic, I would imagine it sould seize up and not work at all, so many random bonds would form between closely-spaced moving parts. This is one more reason expect solid-state, i.e. no moving parts, designs to be used wherever possible--alphas will still give you transient errors (a la DRAM) but wouldn't trash the whole machine. Your nanocomputer would have to reboot, though. Hopefully we can make necessarily moving parts (arms) with tolerances and geometries such that the bonds we put there, reform after ionization. --JoSH]