From: Anders Sandberg (asa@nada.kth.se)
Date: Thu Dec 19 2002 - 14:19:46 MST
On Thu, Dec 19, 2002 at 02:51:14AM -0800, Robert J. Bradbury wrote:
>
> > If panspermia is true it might affect the Great Filter in interesting
> > ways. The emergence of life can be extremely rare, but interplanetary
> > and interstellar spread makes this low probability be multiplied by a
> > macro multiplier.
>
> This is a very interesting area that really should be explored more fully.
> I think Eugene's subsequent messages "dis" the whole interstellar spread
> possibility -- *BUT* one doesn't need "LIFE" to survive interstellar
> transport -- one only needs some of the components for "LIFE" to survive.
I don't buy this, with possibly the exception of the transfer of a
self-replicating ribozyme. But I leave this to you and Rafael.
> > On the other hand the spread might be patchy - the
> > seeding will be random, and the drift rate can be so slow that large
> > regions have had no time yet to be reached by any spores.
>
> As always, Anders has cut to the chase. I'm not so sure I understand
> the "Great Filter" perspective since it seems to me the G.F. is based
> on an evolved "intelligent" life form. That is somewhat different
> from the distribution of genomic "sub-units" based on astronomical
> impacts, random phenomena, etc. (I.e. one is "intentional" while the other
> is "random"). But Anders does seem to sum up the essential differences.
Imagine that life is spread around by spores, encysted bacteria or
ribozymes in rocks thrown away by meteor impacts. There is a tiny
transfer between the planets of the solar system (with some biases) and
an even tinier leakage of lifebearing pieces into interstellar space.
Occasionally pieces fall down in suitable environments, and then
life breaks loose quickly.
I did a quick and dirty Matlab model of this (included below), assuming
that spores are drifting slowly through interstellar space while stars
buzz around at ~200 km/s. If the probability of release and infection
are high enough you get a cool-looking chain reaction - at first one
little star has life, leaving a trail of very dilute spores. Eventually
another star system with a suitable planet passes by and is infected,
and so on. Looks very nice, and one gets a typical Gompertz growth
curve. The next thing would be to run this in 3D and with calculated
release probabilities, death rates in space and impact probabilities. I
think we will end up in the boring "almost never happens"-range, but it
is a doable calculation (and maybe a nice paper?).
Spread from low gravity worlds to high gravity worlds is preferred, and
I would guess interstellar spread is easier from outer worlds than from
inner worlds. If there are brown dwarf gardens they might be a powerful
reservoir of life and a source of spores.
> It would appear that the question revolves around whether or not
> "our" universe just happens to be in the state of the "emergence"
> of intelligence. So we have a mix of genomic code being distributed
> by panspermia (and slowly evolving) with current or emerging capabilities
> destined to soon overwhelm it with our own self-directed evolution. All of
> this combined with a lack of knowledge of what really exists (now)
> outside of our light-cone. (So we could really be in a multi-state
> phase space.)
This could be possible to partially estimate from this kind of model; we
could at least estimate the time constant of the Gompertz curve,
especially by adding other features to the life model of the stars.
Assume the growth of life is a kind of Markov process, with low
probability filters for going to the next "higher" stage. Once you get
expansive rationality the game is over. We might not have much on the
later probabilities, but extending this simple model to single-celled
life, multicellular and intelligent life based on estimates from Earth
fossil records could give us some hints.
> What a *very* strange web it is that we weave.
But is it a small world, random or ordered web? :-)
--
f=figure;
set(f,'DoubleBuffer','on');
suitable=0.1;
N=50; % 30 ly
nstar = N*N*0.6*suitable; % 0.6 stars/ly3
%nstar=10;
ly=3e5*3600*24*365; % 1 ly in km
v0star = 200; % (km/s)
density=zeros(N);
Dlife=1e-3;
star=rand(nstar,2)*N;
vstar=zeros(nstar,2);
for k=1:nstar
theta=rand*2*pi;
vstar(k,:)=v0star*randn*[cos(theta), sin(theta)];
end
alive=zeros(nstar,1);
alive(1)=1;
glife=1;
death=1-0.01;
h=1e9; % Timestep
pbecomealive=1e-5*10;
pop=zeros(50000,1);
for t=1:50000
star=star+h*vstar/ly;
for k=1:nstar
if (star(k,1)<0) star(k,1)=star(k,1)+N; end
if (star(k,2)<0) star(k,2)=star(k,2)+N; end
if (star(k,1)>N) star(k,1)=star(k,1)-N; end
if (star(k,2)>N) star(k,2)=star(k,2)-N; end
xx=ceil(star(k,2));
yy=ceil(star(k,1));
density(xx,yy)=density(xx,yy)+glife*alive(k);
if (rand < density(xx,yy)*pbecomealive) alive(k)=1; end
pop(t)=pop(t)+alive(k);
end
density=density*death;
dd1=[density(:,2:N) density(:,1)];
dd2=[density(:,N) density(:,1:(N-1))];
dd3=[density(2:N,:); density(1,:)];
dd4=[density(N,:); density(1:(N-1),:)];
density=density+Dlife*(dd1+dd2+dd3+dd4-density);
if (rem(t,10)==0)
clf
hold on
imagesc(0:N,0:N,density);
for k=1:nstar
if (alive(k)<1)
plot(star(k,1),star(k,2),'w*');
else
plot(star(k,1),star(k,2),'g*');
end
end
drawnow
end
end
--
-----------------------------------------------------------------------
Anders Sandberg Towards Ascension!
asa@nada.kth.se http://www.nada.kth.se/~asa/
GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y
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