From: Robert J. Bradbury (bradbury@www.aeiveos.com)
Date: Fri Sep 17 1999 - 14:18:41 MDT
On Fri, 17 Sep 1999, Robin Hanson wrote:
>
> I referred in my paper to:
> Jun Jugaku and Shiro Nishimura. A search for dyson spheres around
> late-type stars in the solar neighborhood ii. pp. 707-710 in Cristiano B.
> Cosmovici, Stuart Bowyer, and Dan Werthimer, editors. Astronomical
> and Biochemical Origins and the Search for Life in the Universe,
> number 161. Editrice Compositori, 1997.
>
> The 1% isn't an assumption, but rather a measured bound on starlight
> reradiated at IR temps at these stars.
Yes, Jugaku & Nishimura have been searching for Dyson spheres
for a long time. If you go back to their first paper, you will
discover that they cite "Papagianis (1984, p. 268)" [The Search
for Extraterrestrial Life: Recent Development] as the source
for the 1% number. And if you look there, you will dicover that
Papagiannis provides no calculations and *assumes* that you are
using the mass in the solar system to construct "habitats" for
humans. Most probably these habitats are modeled after those
he discussed in "The Number N of Galactic Civilizations Must Be
Either Very Large or Very Small", p 45 from Strategies for the Search
for Life in the Universe [1980].
So Jugaku & Nishimura are using the Papagiannis assumptions.
And you are using their assumptions. In light of nanocomputers,
singularities, nanotechnology enabling dismantling planets, etc.
those assumptions are silly.
>
> Are you suggesting that aliens may in fact be intercepting more than 1%
> of the starlight from these 100 nearby stars that Jugaku observed,
> but are reradiating it at near 3K?
I am suggesting that unless an alien civilization is severely mass
constrained (much less matter at their disposal than say the planet
Mercury), it will *likely* use all of that mass to intercept ~100% of the
starlight *and* will reradiate as a black body in the infrared.
The people who have gotten this right are Dyson, Kardashev, Slysh
and a few other Russians. See for example any of the papers by
Kardashev and in particular:
V. I.. Slysh, "A Search in the Infrared to Microwave for Astroengineering
Activity", in The Search for Extraterrestrial Life: Recent Developments,
M. D. Papagiannis (ed.), D. Reidel, Dordrecht (1985).
The Slysh paper explains in detail the frequencies, how far away we
could detect them with the IRAS data, etc.
> Or are you suggesting that there are at least hundreds of other stars
> that have been completely enclosed and are reradiating at near 3K?
I'll only offer the observation that 90% of the mass in the galaxy
is "missing", meaning *only* we can't see it using current instruments,
*and* current instruments are virtually incapable of seeing objects
emitting in the mid-far infrared region unless they are within a few
light years.
> Under either of these scenarios you have to ask: why these aliens
> are leaving all these stars to throw their valuable hot photons off
> to infinity?
a) It is possible that at the time we are at they are already harvesting
90% of the photons.
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.
c) The rapid "colonization" perspective requires the economic assumption
that you justify the risks of colonization with a big payoff.
If all civilizations eventually hit the singularity and eventually
turn all of the matter in their solar system into a big hunk
of computronium (using all of the star's energy), then the
payoff of rapid colonization decreases *significantly*. There
may be colonization, but it is likely to take place at a slow
pace and for reasons like Ball's Zoo hypothesis, it may choose
to ignore places where other intelligent life might develop.
>
> It would be very far from efficient to carefully manage the less than 1%
> of light you did intercept while completely ignoring the 99% you let go by.
Yep, thats why I think they harvest it all!
> And it would be far from efficient to so patiently manage one star while
> completely ignoring others nearby.
>
You have to ask yourself what the "currency" of advanced civilizations
is. Is is matter, energy or "computational throughput"? You get
more matter and more energy by exploring, but you derive little
additional "computational throughput". You colonize a 2nd star
and double the number of instructions you have, but the propagation
delays synchronizing your two "processors" kill you. Even with
very large collectors (telescopes the diameter of the moon), you
will have to start putting a lot of your power into the lasers
to send your "thoughts" across a light year. The more power you
put into computation the less you have for local thought. The
tradeoffs get *very* complex.
Robert
This archive was generated by hypermail 2.1.5 : Fri Nov 01 2002 - 15:05:11 MST