From: Robert J. Bradbury (bradbury@www.aeiveos.com)
Date: Fri Sep 17 1999 - 16:15:23 MDT
On Fri, 17 Sep 1999, Robin Hanson wrote:
> At 01:18 PM 9/17/1999 -0700, you wrote:
>
> Jugaku & Nishimura may have used Papagianis 84 to *motiviate* their
> choice of a cutoff to search for, but the data they get does not
> *assume* this cutoff. The ask directly whether more than 1% of the
> starlight from each star is coming out at IR temps, and they find no.
Agreed. However J&N, and almost all other SETI searches point
their telescopes at stars. So they all *assume* an advanced ETC
cannot or does not "hide" the star. I would argue strongly
(because of the exponential growth discussed elsewhere) that
*all* long-lived advanced ETC do "hide" the star. The place
you have to start is with "bright" infrared sources, not
"visible" stars. I tried pointing this out to Stuart Bowyer
(Acting President of IAU Cmsn 51) at the Bioastronomy conference
but he was pretty closed minded about it. In contrast if you
look at the Russian approach for the last ~20 years, they
have consistently moved in this direction.
>
> >a) It is possible that at the time we are at they are already harvesting
> > 90% of the photons.
>
> This doesn't answer the question about the 10% we see.
Because they are at the point of "diminishing" returns.
You and I don't eat all of the food on our plate if we
are sufficiently "full".
>
> >b) H & He are not particularly good materials for building things
> > (Solid H has the hardness of butter). It is possible that "stars"
> > are the most efficient ways to convert H & He into C, O & Al, W, etc.
>
> This is irrelevant regarding the lost photons. Even if you don't want
> to build with star material, and even if you want stars to make metals,
> why let all those photons go?
Because you don't have the metal to harvest them! You have to allocate your
materials to (a) Energy harvesting, (b) Computronium; (c) Communications.
In our solar system, we do not have enough material (even after all the
planets, comets, asteroids, etc.) to construct radiators that can
radiate near the background temperature of the universe. We (in our
solar system) would probably end up 10-40K above the background temp.
That is, thermodynamically & computationally, not the most efficient
place to be. The only solutions are to harvest material remotely
and ship it back and that is very expensive or breed it locally
(from energy) and that takes a long time.
We still see stars because there isn't enough metal in the Galaxy
to "optimally" hide them all yet.
>
> You seem to be saying that you *know* that *all* advanced aliens
> want *only* "computational throughput", *and* that colonization
> cannot typically offer such throughput well. I'm skeptical about
> both claims. Almost all creatures today do not value only
> computational throughput; why should we expect such creatures to
> dominate the future?
I am talking about technological civilizations advanced to the
limits allowed by physics. Maybe some civilizations stop short
of those limits, but I would argue that is a risky position to
be in, since galactic accidents in the long run will eliminate
those civilizations that do not prevent or avoid those accidents.
Natural selection favors those civilizations/entities that can
predict & avoid or stop those things which can destroy them.
Computational thoughput provides these abilities.
Humans dominate the planet because their computational ability
exceeds that of almost all the other species. Say we choose
to remain as "humans" and go "colonize". What happens when
we encounter a Dyson Shell Supercivilization? We lose!
It can see us coming and be prepared to give us a planet
of little interest to it, or wipe us out of the sky.
Men and ants don't compete with each other. One
lives off the crumbs left behind by the other and
tries to avoid getting squashed.
> And I'm sure we could define computational problems that are so
> hard that one could compute them more quickly by sending out probes
> to turn the universe into computers, rather than just using one system
> to compute with. How can you know that advanced creatures aren't
> interested in such problems?
Yes, but there is probably only a small set of computational
problems where the data can be separated into logical subdivisions
that do not require significant communication of inputs and outputs.
Within a Dyson shell you will have a huge bandwidth and memory.
Between Dyson shells you are going to be sharply constrained.
It is going to be much worse than the communications difference
over a fiber cable and a telegraph wire.
You win much more by figuring out the optimal computer architecture
and building it locally, than you do by colonizing the nearest stars.
Paraphrasing Feynman -- "There is *more* room at the bottom!".
Getting smaller gains you much more than getting bigger.
Ultimately, I think Alien Dyson Shell Civilizations have to
deal with the problem of dismantling their star and putting
it effectively on the "outside" of their computronium.
Anders has (or is) submitting a paper on some various architectures
to the J. of Transhumanism. I'll be interested in seeing
whether he addresses this problem.
>
> Even slow colonization is a problem, given how old the universe is.
> And are we to conclude that all the stars we see are zoos containing
> life? And all aliens everywhere have the same taste in zoos?
>
Quite possibly. Aliens could feel nostalgic for primitive life forms.
Or they could also be experimenting with us. Advanced civilizations
have the ability to *see* literally everything in the Galaxy and
model the future paths of development extensively. They may have
decided on a focus of interest and constructed an optimal computing
architecture for that focus. They may have no way of knowing however
whether they have computed or discovered everything and because
random mutation and natural selection increases diversity and
may invent something new. It may be to their advantage to maintain
zoos. They may not have the same taste, but they may all have them.
In that respect, Papagiannis may have gotten something right.
[See "Regional Jurisdiction in Our Galaxy", Bioastronomy -
The Next Steps, p. 281].
Just a side note, I don't disagree that there may be a "colonization"
phase during the evolution of a galaxy. But I do think that most
of ours is developed already, like our planet Earth. We do not
colonize now, in fact in many cases we "uncolonized". For the most
part we develop what we've got. Now, this perspective is good because
it generates a testable hypothesis. As we look back in time (at
increasingly distant/older galaxies), they should exhibit characteristics
of less and less colonization, in theory they should become more
"star-filled" and visibly brighter. Unfortunately I don't believe we
have the telescope resolution to determine this yet.
Robert
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