Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ptsfa!well!pokey
From: pokey@well.UUCP (Jef Poskanzer)
Newsgroups: sci.misc
Subject: Re: Engines of Creation: Nanotechnology
Message-ID: <4879@well.UUCP>
Date: 1 Jan 88 22:42:43 GMT
References: <1315@sugar.UUCP>
Organization: Paratheo-Anametamystikhood Of Eris Esoteric, Ada Lovelace Cabal
Lines: 48

In the referenced message, peter@sugar.UUCP (Peter da Silva) wrote:
} In article <636@elxsi.UUCP>, merkle@beatnix.UUCP (Ralph Merkle) writes:
}> peter@sugar.UUCP (Peter da Silva) writes:
}> >Even Drexler is uneasy about the "Grey Goo".
}> 
}> Just destroy anything that is not identifiable as 'friend'.  That's
}> the principal the immune system uses, and it seems to work okay most of
}> the time.
} 
}Great job. Your grey goo detector sounds just like the sort of thing to run
}wild and turn you into grey goo. These tiny little machines are going to be
}real susceptible to radiation... so what happens when a carbon-14 in your
}little sliding rod state machine decays and your nanomachine "immune system"
}suddenly forgets that your red blood cells are "friends".

Quoting from "Engines", page 178:

    ...systems can work even when their parts fail; the key is redundancy.
    Imagine a bridge suspended from cables that fail randomly, each
    breaking about once a year at an unpredictable time.  If the bridge
    falls when a cable breaks, it will be too dangerous to use.  Imagine,
    though, that a broken cable takes a day to fix (because skilled
    repair crews with spare cables are on call), and that, though it
    takes five cables to support the bridge, there are actually *six*.
    Now if one cable breaks, the bridge will still stand.  By clearing
    traffic and then replacing the failed cable, the bridge operators
    can restore safety.  To destroy this bridge, a second cable must
    break in the same day as the first.  Supported by six cables, each
    having a one-in-365 daily chance of breaking, the bridge will likely
    last about ten years.

    While an improvement, this remains terrible.  Yet a bridge with ten
    cables (five needed, five extra) will fail only if *six* cables break
    on the same day: the suspension system is likely to last over ten
    million years.  With fifteen cables, the expected lifetime is over
    ten thousand times the age of the Earth.  Redundancy can bring an
    exponential explosion of safety.

So, what happens when a carbon-14 in the little sliding rod state machine
decays is: the other 99 similar state machines performing the same
calculation outvote it, notice the fault, and call in a repair machine.

Peter: read the book.
---
Jef

              Jef Poskanzer   jef@lbl-rtsg.arpa   ...well!pokey
"The only way that Listerine kills germs on contact is if you take the bottle
                           and smash them with it."