HISTORY: Dyson Shells

Robert J. Bradbury (bradbury@www.aeiveos.com)
Mon, 23 Aug 1999 19:40:04 -0700 (PDT)

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.


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".