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 JrAbstract: 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.
How would we distinguish a ringworld type structure from something natural, like a particularly dense asteroid belt?
While we have been “intelligent” here on earth for more than a million years, I doubt that we could credibly argue that we have been intelligent enough for space travel for that entire period of time. I don’t think H. erectus and H. habilis would have been capable of a space program, no matter how much time we allow for cultural evolution, though both would certainly qualify as intelligent species.
Kenneth above provided the following link
http://arxiv.org/abs/astro-ph/0503580
which does address the question of how to distingish between an asteroid ring and an ET artifact.
Lawrence B. Crowell
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How about somebody taking a look for some of these Dyson-predicted objects?
Maybe they exist, or for that matter we humans might release self-replicating nano-bot/AI systems into the solar system. However, if some other solar system is inhabited by such things they would need to make some sort of measurable impact on the stellar system. We appear to be on the cusp of being able to observe fine details of extrasolar systems. I think we can expect lots of scientifically interesting developments, but I suspect we will probably not find anything like ring worlds, Dyson spheres or any massive ET engineering of these systems.
Lawrence B. Crowell
The total power available is much larger. In theory, you could compress an object, say an asteroid, into a black hole. Such a black hole would emit Hawking radiation at huge powers. You can then feed it using the matter from the star. This then converts matter into energy much more efficienctly than fusion processes in the star.
Actually, thinking about this a bit more, I think that you wouldn’t expect that advanced civilizations would bother to make Dyson spheres because the energy that is leaking away is insignificant to the energy they can generate themselves. They can do that using black holes as I explained above. It is then practical to use a big mass of cold matter instread of a hot star. So, they may use brown dwarfs for this purpose.
So, perhaps the signature of an advanced civilization would be high energy neutrino emissions from cold dark objects like brown dwarf stars. If the civilization captures all the gamma rays emitted from their micro black holes, then the high energy neutrinos will still escape.
A dyson-like sphere or ring around a large Kerr type black hole would be set up to extract the rotational eneryg of the black hole according to the second laws of BH thermodynamics. It would have to be a big thing, and it could extract a significant portion of the BH’s mass-energy.
If atom sized black holes exist or can be manufactured in some ways a confinement system could keep feeding matter in at the same rate energy in the form of radiation comes out. Of course black holes that size probably quantum produce a lot of neutrinos. Of course this thing would require some tricky balancing to make work. An interruption in the matter feed could cause it to explode.
Lawrence B. Crowell
I’d like to point out that the “Dyson Sphere” is a conjecture about what an advanced spacefaring civilization might come to look look like overall, and not necessarily some sort of colossal “public works project” that such a society would build on a whim. I.e. they would begin with only a modest array of orbiting collectors, and after a few aeons of slow geometric growth (assuming availability of building materials), the collectors might attain such an enormous multitude as to noticeably occlude the star itself.
I can’t see aliens hanging around in one solar system long enough to bother with Dyson spheres.
Once they’ve discovered all the laws of physics they can verify, and catalogued everything in nature on their planet, and written every tune and told every joke in a hundred ways (all preserved in some super-duper Wikipedia-like repository, perhaps plugged straight into their minds) the only thing left to save a remorseless decline is to head off for pastures new and see more of nature’s variety.
We’ve all heard about lone astronauts zooming off at close to the speed of light, and returning in a few of their years to find centuries or eons have passed back home, and this gloomy scenario is seen as proof that star travel is impractical.
But suppose *everyone* heads off at the same time, and coordinates their arrival elsewhere to compare notes. This isn’t so far-fetched when you consider that populations will probably decline once robots become ubiquitous, and when you take into account the likelihood of civilizations going stale or even turning ugly in some sense if they hang around together in the same place for too long.
I pursued this idea further in the final comment on Jennifer Ouellette’s recent blog article on Little Green Men.
In summary, I believe the reason we’re unlikely to see Dyson spheres, or intercept alien signals, is that from our standpoint all the aliens spend decades or centuries travelling at 0.99c and have no reason to be even awake during their journey let alone chattering via radio.
Of course, that’s not to say they’d be so quiet when they meet at their rendezvous, and recharge their batteries (perhaps literally).
I wrote a book which discusses the physics of interstellar exploration. I consider the prospect of sending robotic probes more than any actual star travel. The little book is more as a way of discussing classical mechanics and relativity than any serious proposal. However, I do think it is possible to explore nearby extrasolar systems. The big limitation is energy. A low gamma probe gamma < 2 or so has velocity < .86c, or half or less of the the mass-energy on the craft be in its relativistic kinetic energy. It is not impossible of course, but it is difficult. There are various approaches which might work, where some form of solar concentrated light or radiation on a large sail might be feasible. I also discuss elecromagnetically propelled nano-probes as well.
If we were to find a rocky planet around a star within 25 to 50 light years of Earth that has biological signatures a considerable scientific premium would be placed on plopping a probe down there to look at things close up.
Sending a crew to other stars does what we see with more parochial space exploration now, it magmifies the costs and energy requirements enormously. Any form of intelligent life is probably faced with the same resource/energy/cost limitations. I suspect that ET is a very rare occurrence in the universe (one per so many galaxies), and far rarer will be cases where they manage to control the external world in space on magnitudes seen in science fiction stories of star travel or with thinks such as ring worlds or Dyson spheres.
Lawrence B. Crowell
Lawrence, your book sounds fascinating and I must buy a copy. However, in the long run the inexorable social progression (or decline) of advanced civilizations are probably the best determinants of how interstellar travel will pan out, or the overriding motive to start it, and maybe psychologists or even historians are better placed to provide insights on that.
You mention cost as a limiting factor. But in the twinkling of an eye, as we can anticipate even today, there will be armies of robots waiting on us hand and foot. Few now dispute that, except for the timing (which admittedly has always seemed to be “in about 20 years” ever since I can remember!).
As well as removing any advantages of having hordes of humans, as now (the point in my preceding post about populations declining), robots with their replication and self-repair abilities also obviously allow engineering projects of a qualitatively higher scale but at a similar “start up” cost, just as today’s PCs calculate PI to billions of d.p.s at the push of a button, in contrast to 19th century human calculators who struggled for years to find a mere 100 d.p.s or so.
Global warming? No problem – program an army of robots to excavate rock from under the antarctic ice sheets and build a vast 10,000 mile long perimeter wall round that continent to contain a repository of ice there twice as thick as it is today. (Actually the weight of all that extra ice would probably depress the crust, which might cause problems. But that’s an example of the kind of project which couldn’t be contemplated in practice today.)
The same applies in space. I imagine the first thing an alien (or future human) team will do on arriving in a new unoccupied solar system is to instruct robots to start mining asteriods and building tremendously long rail guns, or a relay of dozens of these, all to be aligned ready for their departure. In due course they would have the means to literally shoot out of that solar system at a large percent of light speed, after which the robots would dismantle it all including finally themselves, and leave everything as it was found.
You may be right about ET being a very rare occurrence, but the sheer number stars even in one galaxy (the number of grains in a large barrel full of sand) must increase the odds. Also, of course once one star-hopping ET civilization emerges perhaps one of their goals will be to nudge life in a direction favourable to the emergence of intelligent life, or even resculpt whole solar systems for that purpose if the fancy takes them. So it may not be solely a matter of blind chance.
In parting I’ll return to my first theme, the decline of population. With the knowledge of past multitudes that occupied the Earth, the few people living in that time will feel that in a sense the party’s over at least in its current form. As the Good Book says (Lamentations v1 ch1) “How doth the city sit solitary, that was full of people!”. I’m certain there will be a feeling that it’s time to move on to pastures new, reinforced by a growing belief (perhaps of a cult) that our solar sytem is only a stepping stone or “cradle” and our destiny lies in further travel. After all travel, or a change of scenery, is a human instinct, from our nomadic ancestors.
I think that these robots will simply take over from us. We will make faster and larger computers until we become obsolete outdated technology ourselves.
If you are a robot then you can travel at the speed of light from one civilization to another by uploading your brain to a machine located at the other civilization via radio communications or perhaps using lasers.
A civilization can spread itself to other uninhabited solar systems by sending nanotech machines that build up some infrastructure there. Then they can upload themselves to the new location.
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The Ramsden/Iblis ideas here are a bit “far out.” I will say right off that the best way to reduce global warming problems is to stop doing what we are doing! If we have to engage in heroic technological programs or space activities to hedge global warmings I imagine we could build large panels woven with carbon nanotubes which Mie scatter sun light to reduce the illumination of Earth. These could be placed at the L1 Lagrange libration point, and if we are ambitious enough we might reduce the illumination or irradiance of the Earth’s surface by .5 watts/m^2 and counter the effects of CO_2 warming.
I do disucss the prospect of nanoprobes sent to other stars. I discuss using railgun type of technology to send the little buggers out to other stars. The fly in the ointment is how to stop them once they get there? But a small number of these might find their way to an asteroid on another solar system and once there they replicate to build a network which acts as an exploration-teleresponding system that sends data back to us.
We might end up unleashing self-relicating AI systems or nano-bots into the solar system or other solar systems. This might prove to be another uncontrolled experiment we humans are so good at setting up, where a case of this is global warming.
Lawrence B. Crowell
Even if they find nothing, negative findings are data too… Though personally I dislike the Dyson sphere as a concept on aesthetics alone. You’d get all the energy sure, but your solar system would end up looking like shit…
Nestor: That is an excellent point. What we have seen and probed of the solar system has a beauty to it. Stark maybe, but there is a beauty to it. The rover-robots moving around Mars have shown a landscape that is devoid of life, but it is artfully sculped by nature. This is also why I am generally opposed to grand schemes on Earth to dam up rivers or change the landscape. The current mountain topping coal mining in the Appalachian mountains I think is an abomination.
Lawrence B. Crowell
I have one major concern about the issue of building a dyson sphere, or even a Niven type ring….. Where would we get planning prmission from?