From: Robert J. Bradbury (bradbury@aeiveos.com)
Date: Sun Mar 19 2000 - 16:17:37 MST
On Sun, 19 Mar 2000, Stirling Westrup wrote:
> A bunch of fascinating questions, which I've had the temerity to try to
> answer to the best of my abilities.
Cool!
> 1) Re: Microlensing & dark matter
>
> A partial answer can be found at http://www.cfht.hawaii.edu/News/Lensing/
> [snip]
This is large-scale dark matter, while I was more interested in the microlensing
observations from the MACHO, OGLE, PLANET groups et al. The best explanation
for their data is ~400 billion 0.3-0.5 M_sun objects orbiting our galaxy.
But one of the many problems with this work is that they can only look
in very specific directions (nearby galaxies), so extrapolations are *iffy*.
The Hubble north and south deep fields suffer from the same problem.
Now, I do have an explanation for the large scale dark matter... <grin>.
The development of life to the limits of physics may have a large timescale
distribution, i.e. in some galaxies it takes 3 billion years, while in
others it takes 10 billion. Or, some galaxies may get populated by Buddhists
and others get populated by Klingons (which could have very different
expansionist policies). If either of these is accurate, then some galaxies
will "go dark" relatively quickly. If star lifting is possible, then
calculations by Robert Freitas show that you could consume all of the
fuel in the galaxy in relatively short order, probably leaving behind
burned out iron memory banks, some black holes and neutron stars. Then
they might colonize & consume neighboring galaxies that go dark, etc.
The dark regions with mass are where life got lucky and got an early start
or is particularly aggressive in its energy use or colonization principles.
And yes, you are right it is kind of scarey.
> > 2 & 3) Re: Self-replication & evolution speed-limits...
>
> Are these questions about the absolute limits under any circumstance (at
> which point I would say it looks to be around 1E-30 to 1E-40 seconds for
> both questions), or is it a question about what parameters are critical to
> setting a particular speed limit under particular circumstances. This is a
> far more complex, and IMHO a far more interesting question.
They are questions about the minimum rates at which stuff can be
built or evolve. Since Tom McKendree and JoSH have pointed out that the
fastest way to build stuff is to build ~0.6 the mass of your
final product as assemblers, then have the assemblers build
the final product (disassembling themselves as necessary), the
question becomes how fast you can build the mass of assemblers.
There is a very big rate-of-assembly gap between a nanoassembly arm
replicating itself and Eric's 1 Kg replication systems. Biological
micro & macro-scale replication rates seem to fall between Eric's
doubling times. There are a host of sub-questions -- what
determines the final limit? Chemical reaction rates? Tip movement
time? Delivery of material to the tip? Heat removal? What makes
the fastest material? Do TiC "biochemistries" do better because
it can tolerate higher operating temperatures (i.e. less volume
and energy needs to be devoted to heat removal)?
With evolution its a similar can of worms. Xenology by Robert Freitas
lays a foundation for some of the various "natural" biochemistries that
could exist in the universe. Does life develop in any of them? Does
it develop faster or slower? How dependent is the rate of evolution on
the available mass? Operating temperature? Mutation sources? Global-scale
stresses (extinction events)? Are there artificial biochemistries
in which evolution can proceed more quickly?
> > 4) Re: number of useful "biochemistries"
>
> If you are limiting yourself to chemistry then the answer depends on how
> big a difference is necessary to consider two biochemistries 'distinct'.
> [snip discussion re large # of amino-acids].
I wasn't so much interested in Carbon/Water biochemistries (there are
clearly lots of those) as Carbon/Ammonia or Carbon/H2S or systems
based Si or TiC or InGaAs. You have 92 natural elements, how many ways
can they be put together to produce self-replicating systems that can
"host" intelligent consciousness? For extra credit determine which
chemistries are optimal for the architectures in Question 9...
> > 6) Re: Breakout of amoral alife...
>
> About the same probability that a chemist mixing amino acids in a lab will
> accidentally create a plague-form capable of wiping out our species.
>
Not clear. There are a few labs doing life creation and
evolution of enzymes experiments and those experiments presumably
work with moderately large number of molecules. But, there are a lot
of bits flying around and that high rate of growth means that the
quantity of information being played with by computers exceeds the
quantity being played with in chemistry experiments at some point.
Would an AmoralAlife@Home program find the "dark"-ring before the chemists do?
> Note that this is a vastly lower probability than the chance that a
> deliberately constructed, amoral, self-evolving, self-replicating AI/Alife
> will "breakout" by accident.
We have examples of those today with computer viruses. Fortunately
there aren't any nanoassemblers for them to take over and the people
doing the ALife work are pretty responsible and we seem to be getting
better at producing firewalls and speeding up the rate at which
software loophole fixes are applied (for example there are bots now that
crawl the net warning people about security holes).
Thanks Sterling for taking the time to respond.
Robert
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