From: Robert J. Bradbury (bradbury@www.aeiveos.com)
Date: Mon Aug 23 1999 - 20:40:04 MDT
I thought some of you might be interested in a brief "history"
piece I wrote for Joe Placa over at NPR. It points out some
of the problems that can occur with bad reporting and bad
science.
Robert
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In the event that you do ask around to the SETI people and/or any
astronomers regarding Dyson spheres/shells, it would be good if you
understood the complete history, so when some of the "canned"
responses come back you are prepared for them.
Dyson published the paper discussing the evolution of technological
civilizations in Science in 1960. Within a few weeks this was picked up
and broadcast in a simplified form in Science News. Problem number 1
arose when the Science News reporter mistook Dyson's concept and
called it a "ball". [That imbedded in the popular consciousness
the "sphere" concept that shows up in many subsequent works, including
one or two episodes from Star Trek: Next Generation.] Problem
number 2 arose when some physicists thought about the sphere concept and
argued that such a structure was impossible or could not be stable.
One of them quickly wrote about this to Science, and over several years,
multiple papers were published about these problems in Russia.
In his response to the Science letters Dyson indicated that he did not intend
the construction of a "sphere", but orbiting sun-enveloping objects, such
as planetoids. I doubt the Russian authors who much later wrote about the
problems were aware of Dyson's response. Dyson was very careful to
never use the word "sphere" in his original paper.
Problem Number 3 arose in the mid-1980's. Michael Papagiannis, who
later became chairman of the Astronomy Dept. at Boston University,
became quite active in SETI/Bioastronomy work. I believe he played
an active role in the formation of the International Astronomical Union's
(IAU) Commission 51: Bioastronomy: Search for Extraterrestrial Life,
so he was a fairly prominant individual within the Bioastronomy/SETI
community. At the Bioastronomy conference in 1985, he "proved"
Dyson "spheres" could not exist (perhaps in ignorance of Dyson's
comments that he never intended "spheres"), and claimed that
"independent space structures" would only intercept 1% of the
starlight. It is unclear how he derived this number. If he assumed that
the "structures" were "planetoids", with a "reasonable" gravity, then
his numbers may be correct. Keep in mind that in 1960,
Dyson would not have known that humans in space require gravity
because this was long before extended spaceflights, while Papagiannis
may have made his computations based on the assumptions that
supercivilizations would *only* organize their material as planetoids.
The other possibility one can imagine is that he considered organizing
the material as O'Neill-type colonies since some of this information had been
published as early as 1974. But O'Neill had at least 4 models for such
structures in his 1974 paper and it isn't clear which of them Papagiannis
might have selected to reach his conclusions.
At any rate, the major consequence of these "results", has been that
only one astronomer (Dr. J. Jugaku in Japan) has seriously looked for
Dyson Shells and he has unfortunately (in my opinion) focused these
searches only on "visible" stars (exactly the same as the work being
done by the both SETI camps [those who believe a radio carrier
is the best communication method and those who believe that an optical
carrier, e.g. lasers, is the best communication method]).
Now the plot thickens.
Two science fiction writers, Fred Pohl & Jack Williamson figured out
how to build a solid Dyson Sphere that could resist gravitational collapse
using an advanced technology called "momentum transfer". The
parameters for this type of construction are difficult but not "impossible".
"Momentum transfer" is the basis behind solar sails and the laser launched
satellites currently being investigated by NASA, so it is not a "fantasy".
My calculations show that Dr. Papagiannis made a number of questionable
assumptions or outright mistakes. There is more mass available than he
estimated. One does not need planetoids with gravity because (a) we can
engineer humans so they don't need gravity [some of the first biology
experiments NASA will do on the new space station will focus on trying
to understand this problem]; or (b) we can do away with the humans
entirely (by using much more efficient nanotechnology based computational
engines). These perspectives allow one to construct complete
star-envoloping Dyson shells.
So, if by chance, you encounter someone who says "Dyson spheres
are impossible", you should consider saying, "Really! Using what
assumptions?", or simply, "au contraire, I believe you to be misinformed".
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