In 1960, Freeman Dyson proposed an audacious form that future technology might take: the Dyson Sphere. It’s a simple idea, once you stop thinking in terms of “I wonder how that could be done?” and start thinking along the lines of “I wonder what is physically possible?” Dyson reasoned that an efficient civilization wouldn’t want all of the valuable energy from its home star to fly uselessly into outer space, so they would try to capture it. The solution is then obvious: a sphere of matter that encircles the entire star. It’s worth quoting a bit from Dyson’s original paper:

The material factors which ultimately limit the expansion of a technically advanced species are the supply of matter and the supply of energy. At present the material resources being exploited by the human species are roughly limited to the biosphere of the earth, a mass of the order of 5 x 10¹⁹ grams. Our present energy supply may be generously estimated at 10²⁰ ergs per second. The quantities of matter and energy which might conceivably become accessible to us within the solar system are 2 x 10³⁰ grams (the mass of Jupiter) and 4 x 10³³ ergs per second (the total energy output of the sun).

The reader may well ask in what sense can anyone speak of the mass of Jupiter or the total radiation from the sun as being accessible to exploitation. The following argument is intended to show that an exploitation of this magnitude is not absurd. First of all, the time required for an expansion of population and industry by a factor of 10¹² is quite short, say 3000 years if an average growth rate of 1 percent per year is maintained. Second, the energy required to disassemble and rearrange a planet the size of Jupiter is about 10⁴⁴ ergs, equal to the energy radiated by the sun in 800 years. Third, the mass of Jupiter, if distributed in a spherical shell revolving around the sun at twice the Earth’s distance from it, would have a thickness such that the mass is 200 grams per square centimeter of surface area (2 to 3 meters, depending on the density). A shell of this thickness could be made comfortably habitable, and could contain all the machinery required for exploiting the solar radiation falling onto it from the inside.

Old news, right. What I hadn’t realized is that there is something called the Fermilab Dyson Sphere search program, led by Richard Carrigan, which recently updated its results (summarized in the title of this post). A star like the Sun radiates something pretty close to a blackbody spectrum; but if you capture all of the energy in the Sun’s radiation, and then re-radiate it from a much larger sphere (e.g. one astronomical unit in radius), it comes out at a much lower temperature — a few hundred Kelvin. Dyson therefore proposed a search strategy, looking for blackbody objects radiating in the far infrared, around 10 microns in wavelength.

And the search is now going on! Indeed, Carrigan’s most recent results were just released on astro-ph a few weeks ago:

IRAS-based whole-sky upper limit on Dyson Spheres
Authors: Richard A. Carrigan Jr

Abstract: A Dyson Sphere is a hypothetical construct of a star purposely cloaked by a thick swarm of broken-up planetary material to better utilize all of the stellar energy. A clean Dyson Sphere identification would give a significant signature for intelligence at work. A search for Dyson Spheres has been carried out using the 250,000 source database of the IRAS infrared satellite which covered 96% of the sky. The search has used the Calgary data collection of the IRAS Low Resolution Spectrometer (LRS) to look for fits to blackbody spectra. Searches have been conducted for both pure (fully cloaked) and partial Dyson Spheres in the blackbody temperature region 100 < T < 600 deg K. Other stellar signatures that resemble a Dyson Sphere are reviewed. When these signatures are used to eliminate sources that mimic Dyson Spheres very few candidates remain and even these are ambiguous. Upper limits are presented for both pure and partial Dyson Spheres. The sensitivity of the LRS was enough to find solar-sized Dyson Spheres out to 300 pc, a reach that encompasses a million solar- type stars.

It’s too bad the search has thus far not turned up too many promising candidates. The Fermi Paradox continues to be paradoxical.

One famous account of the first contact between an extraterrestrial civilization and the human race was told in the classic 1951 Robert Wise film, The Day the Earth Stood Still. It’s now been remade by director Scott Derrickson, starring Keanu Reeves as the alien Klaatu, and will open next Friday. In the emerging spirit of science and entertainment exchanges, there will be a panel discussion at Caltech’s Beckman Auditorium this Friday (the 5th) with Derrickson and Reeves holding up the Hollywood side of things, and roboticist Joel Burdick and I holding up the science end. Don’t quote me on this, but I think it’s at 6:00, and the movie will be screened before the panel. Should be fun.

The title is a bit misleading; what is being referred to is not a realistic cosmological model at all. But it’s interesting to see that not every professional astronomer believes in the Big Bang model; there are still some out there who are sticking with the Steady State theory. Seriously.

A Realistic Cosmological Model Based on Observations and Some Theory Developed Over the Last 90 Years
Authors: Geoffrey Burbidge

Abstract: This meeting is entitled “A Century of Cosmology.” But most of the papers being given here are based on work done very recently and there is really no attempt being made to critically review what has taken place in the last 90 or 100 years. Instead, in general the participants accept without question that cosmology equates to “hot big bang cosmology” with all of its bells and whistles. All of the theory and the results obtained from observations are interpreted on the assumption that this extremely popular model is the correct one, and observers feel that they have to interpret its results in terms of what this theory allows. No one is attempting to seriously test the model with a view to accepting it or ruling it out. They are aware, as are the theorists, that there are enough free parameters available to fix up almost any model of the type.

The current scheme given in detail for example by Spergel et al (206, 2007) demonstrates this. How we got to this stage is never discussed, and little or no attention is paid to the observations obtained since the 1960s on activity in the centers of galaxies and what they imply. We shall show that they are an integral part of a realistic cosmological model. In this paper I shall take a different approach, showing first how cosmological ideas have developed over the last 90 years and where mistakes have been made. I shall conclude with a realistic model in which all of the observational material is included, and compare it with the popular model. Not surprisingly I shall show that there remain many unsolved problems, and previously unexpected observations, most of which are ignored or neglected by current observers and theorists, who believe that the hot big bang model must be correct.

For those with any lingering doubts, the Big Bang model — the idea that the universe has evolved from a hot, dense, smooth initial state — is correct, and the Steady State model should have been put to bed a long time ago. Evidence for the Big Bang is overwhelming. It’s a model that keeps making predictions, which keep turning out to be correct, while the Steady State theory made many predictions that turned out to be wrong.

But it’s an interesting case study in how science works. Reading Burbidge’s paper, the parallels with anti-evolutionists are striking. In both cases, one is repeatedly told that the establishment’s supporter’s can’t prove that their theory is correct. Which is undeniably true, as science never proves anything; it just accumulates evidence, and in the case of the Big Bang and natural selection, the evidence puts the case beyond reasonable doubt. Which doesn’t imply that there are no interesting questions remaining to be addressed. For both the Big Bang and natural selection, many of the details concerning the way in which the broad framework is specifically implemented in the real world remain to be answered. And in both cases, the skeptics like to pretend that open questions about the details are the same as open questions about the framework. But they’re not.

Nevertheless, one of the virtues of the tenure system is that a Big Bang skeptic can keep their position as a professor of physics, writing heterodox articles and submitting them to the arxiv. And this really is a virtue, not a flaw. Geoffrey Burbidge has done lots of respectable work in observational astronomy. Long ago, he and his wife Margaret collaborated with Fred Hoyle and Willy Fowler on an important paper that helped established the theory of nucleosynthesis in stars. Part of the motivation for the paper was the realization that conditions in the Big Bang were not right for synthesizing elements much heavier than lithium — you could explain the universe’s helium abundance, but not the existence of carbon and iron and so forth. Hoyle, of course, was one of the originators of the Steady State theory, and that was certainly part of his motivation at the time. As it turns out, in the real world, some elements are synthesized in the early universe, and some in stars, and some in supernovae; the real world can be a messy place.

Would a young cosmologist who didn’t believe in the Big Bang be offered a faculty job, or receive tenure, today? Probably not. Faculty jobs are scarce commodities, and a university is going to want to hire people who will do interesting and productive work that is of some use to the wider community. Believers in the Steady State model aren’t going to produce such work, any more than creationists or astrologers or experts in the plum-pudding model of the atom. And eventually support for the model will fade away entirely, opening the door for the next generation of heterodoxies.