Re: Freitas on Gray Goo

From: Michael S. Lorrey (retroman@turbont.net)
Date: Sun May 14 2000 - 07:46:24 MDT


hal@finney.org wrote:
>
> Robert Bradbury pointed to http://www.foresight.org/NanoRev/Ecophagy.html,
> a paper by Robert Freitas, author of Nanomedicine, on the gray goo
> problem.
>
> I've looked this paper over and I have a number of concerns. Before I
> get into that I should thank the author for providing hard numbers in a
> debate which has too often been about generalities. Also I appreciate
> Robert Bradbury for making the paper available in html form.
>
> Obviously the goo can't help being detected at some point. The 20 month
> scenario just doesn't make sense.
>
> A more plausible scenario is described where the gray goo grows somewhat
> faster and the temperature is allowed to rise more: "For example, taking
> t = 100 sec, TEarth = 300K, and Ediss ~ 100 MJ/kg, the transition to
> the ETPL regime occurs when total global nanomass reaches ~5 1010 kg,
> or only 0.001% of total global biomass, and the last ~17 population
> doublings remain to be completed over a time span of ~2 tlast = 210^7
> sec (~7 months)." 7 months still sounds like quite a bit of warning,
> although not as generous as 20 months.

There is also another problem, I'm not sure if its been discussed. Like
any microbiological growth, there will be a mass of nanoorganisms. Those
in the center will either have to cannibalize their neighbors or die or
deactivate. Only those on the frontier of the colony will actually be
doing any digesting. If the organisms are programmed to travel x
distance after being born before beginning to digest its surroundings,
that x distance will still need to increase with each successive
generation to avoid congestion at some point. Adding travel time to each
generation will slow down replication times, as will congestion, given
that only those on the frontier of the nanomass will have the resources
to replicate. Programming organisms on the frontier to cooperate with
inner organisms, to deliver resources to them, will also take up time.



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