by Paul Gilster | Jan 20, 2022 | Astrobiology and SETI |
The Dyson sphere has become such a staple of SETI as well as science fiction that it’s hard to conceive how lightly Freeman Dyson himself took the idea. In a 2008 interview with Slate, he described the Dyson sphere as no more than ‘a little joke,’ and noted “it’s amusing that of course you get to be famous only for the things you don’t think are serious.” Indeed, Dyson’s 1960 paper “Search for Artificial Stellar Sources of Infrared Radiation,” was but a one-page document in Science that grew out of his notion that an intelligent civilization might not have any interest in communicating. How, then, would astronomers on Earth go about finding it?
Waste heat was his answer, a nod to the laws of thermodynamics and the detectability of such heat in the infrared. Coming hard on the heels of Frank Drake’s Project Ozma (a likewise playful name, coined out of affection for L. Frank Baum’s imaginary land of Oz), Dyson saw a search for what would come to be called Dyson spheres as a complement in the infrared to what Drake had begun to do with radio telescopes. And in fact, Dyson didn’t refer to spheres at all, but biospheres. Let me quote him on this from the 2008 interview:
I suggested that people actually start looking in the sky with infrared telescopes as well as regular telescopes. So that was the proposal. But unfortunately I added to the end of that the remark that what we’re what we’re looking for is an artificial biosphere, meaning by biosphere just a habitat, something that could be in orbit around the neighboring star where the aliens might be living. So the word biosphere didn’t imply any particular shape. However, the science-fiction writers got hold of this and imagined a biosphere means a sphere, and it has to be some big round ball, so out of that there came these weird notions which ended up on Star Trek.
Changing Notions of a Dyson Sphere
Dyson told Slate he hadn’t been thinking remotely of a shell around a star, but a ‘a swarm of objects surrounding a star,’ one that from the outside would look more or less like a dust cloud. He was also quick to give credit for the concept to writer Olaf Stapledon, who as we saw in the previous post introduced it in his novel Star Maker all the way back in 1937. And indeed, we find Stapledon writing about a way to tap the energies of entire stars through “a gauze of light traps, which focused the escaping solar energy for intelligent use, so that the whole galaxy was dimmed…”
That Star Trek reference is to an episode of Star Trek: The Next Generation that ran on October 12, 1992 (Season 6 Episode 4). It depicted the Enterprise crew encountering a shell-like Dyson sphere. Dyson didn’t mention Larry Niven’s wonderful Ringworld (1970), which draws on the shell concept to envision a vast ring around its star, a ‘cut-through’ of a full Dyson shell. I suspect he read it somewhere along the line, as he was frequently in conversation with science fiction writers who increasingly found his work a source for good ideas.
Image: Olaf Stapledon, author of Star Maker and Last and First Men.
As far as his light-hearted approach to the things he is best remembered for, I take that as a personal quirk. When I interviewed Dyson back in 2003, I found him quick to shift credit for ideas to other people and charmingly dismissive of his own contributions. I think his was an intellect so formidable that it surprised him with ideas that seemed to well up unbidden, so that in a real sense he didn’t want to lay claim to them.
And on Stapledon’s Star Maker, a further thought. It’s fun to note that Dyson sphere hunter Jason Wright at Penn State maintains a blog he calls Astrowright. It’s a fine play on words, I assume intentionally containing a nod to Stapledon. For if a shipwright is a maker of ships, an astrowright is surely a ‘star maker.’
The paper by Wright and Macy Huston that I looked at yesterday notes the distinction between Dyson shells and Dyson spheres; i.e., between a solid spherical shell and a vast collection of objects in orbit around the star, adding that ‘for simplicity of language, we refer to any configuration of a starlight-manipulating megastructure as a Dyson sphere.’ I think that’s common usage throughout the literature, saving the intriguing work on Shkadov thrusters, which are inherently asymmetrical and don’t fit Dyson sphere modeling. But moving stars is a topic for another day.
How Dyson Sphere Searches Proceed
Playful or not, it didn’t take long for Dyson’s SETI notion to take hold. In 1966, Carl Sagan and Russell Walker delved into “The Infrared Detectability of Dyson Civilizations” in a paper for the Astrophysical Journal. This too is no more than a note, but it makes the case for looking for astronomical sources that would appear as blackbodies with a temperature of several hundred K. Such detections were possible, the authors argued, but “discrimination of Dyson civilizations from naturally occurring low temperature objects is very difficult, unless Dyson civilizations have some further distinguishing feature, such as monochromatic radio-freqency emission.”
Note that last comment, because we’ll come back to it. It’s insightful in describing the nature of Dyson sphere searches and the possible results from a detection.
Which brings me to the Russian radio astronomer Vyacheslav Ivanovich Slysh, who in the 1980s examined sources identified by the Infrared Astronomical Satellite (IRAS) in a search for just the kind of waste heat Dyson had discussed. In 2000, Slysh’s work was followed up by M. Y. Timofeev, collaborating with Nikolai Kardashev (most famous, of course, for the ‘Kardashev scale’ ranking technological civilizations).
Richard Carrigan, a scientist emeritus in the Accelerator Division at the Fermi National Accelerator Laboratory, went to work on IRAS data as well and in a 2009 search, used the data on 250,000 infrared sources (covering 96 percent of the sky), looking for both full and partial Dyson spheres in a blackbody temperature region from 100 K to 600 K.
The result: Some 16 candidates with temperatures below 600 K in a field of objects out to 300 parsecs. And as Carrigan noted, most of these have non-technological explanations, and all are in need of further study before any conclusions are drawn. I should also mention the searches for Dyson spheres by Jun Jugaku and Shiro Nishimura when talking about IRAS. Their work in the 1990s found no Dyson spheres around the roughly 550 stars they surveyed within 25 parsecs.
This is a good time to mention some useful background materials. The first is a video presentation Jason Wright made to a seminar at Penn State in 2020, helpfully made available online. It’s an excellent encapsulation of the Dyson sphere concept and the investigations into it, including the subsequent searches using WISE [Wide Field Infrared Survey], with higher resolution than IRAS could provide. One problem with all of these is what Wright dubs ‘infrared cirrus,’ which basically refers to diffuse dust that greatly compromises the consequent data. Carrigan would doubtless have retrieved a much higher number of candidates if he could have worked without this background.
The second reference is Wright’s overview “Dyson Spheres,” which ran in the Serbian Astronomical Journal, Issue 200 (2020), with preprint available here. For those wanting to come up to speed on the origins and development of the idea of Dyson spheres, their purpose, their engineering, and their detectability, this is an excellent resource.
Until reading the Huston & Wright paper, I had been unaware of Massimo Teodorani, whose 2014 paper in Acta Astronautica presented what he called a ‘pragmatic strategy’ for searching for Dyson spheres involving infrared excess and anomalous light curves using Spitzer data to locate such signatures at G-class stars. A common theme in much of this work is the recognition that the goal is to identify interesting targets for further study. A detection of an interesting source would not in itself be proof of an extraterrestrial civilization, but rather identification of an object that could be followed up with more conventional methods such as laser or radio search. There is no single ‘aha!’ moment, but steady and careful analysis.
The search space for Dyson spheres has been expanding dramatically. In the late 1990s, James Annis analyzed the rotational dynamics of 137 different galaxies in the Ursa Major and Virgo galaxy clusters, looking for Kardashev Type III civilizations. He found no evidence for them, but going to this scale inevitably reminds us of the Fermi paradox. As Annis told Lee Billings in 2015:
“Life, once it becomes spacefaring, looks like it could cross a galaxy in as little as 50 million years. And 50 million years is a very short time compared to the billion-year timescales of planets and galaxies. You would expect life to crisscross a galaxy many times in the nearly 14 billion years the universe has been around. Maybe spacefaring civilizations are rare and isolated, but it only takes just one to want and be able to modify its galaxy for you to be able to see it. If you look at enough galaxies, you should eventually see something obviously artificial. That’s why it’s so uncomfortable that the more we look, the more natural everything appears.”
The mid-infrared WISE survey [Wide-field Infrared Survey Explorer] gave us far more data within which to conduct such a search. Wright’s work using WISE data has been extensively covered in these pages, including an article he wrote for Centauri Dreams called Glimpsing Heat from Alien Technologies, the name of the program he started at Penn State. The G-HAT program led to a search through WISE data that culled out some 100,000 galaxies looking for unusually strong signatures in the mid-infrared. Fifty of these galaxies showed interesting infrared properties, though as with Carrigan’s results, without any definitive signs of a technology.
I’ve quoted Wright on this result before, but that was years ago, so let me pull this out again:
“Our results mean that, out of the 100,000 galaxies that WISE could see in sufficient detail, none of them is widely populated by an alien civilization using most of the starlight in its galaxy for its own purposes. That’s interesting because these galaxies are billions of years old, which should have been plenty of time for them to have been filled with alien civilizations, if they exist. Either they don’t exist, or they don’t yet use enough energy for us to recognize them.”
Note the phrasing: This is explicitly a search for Kardashev Type III, one manifestation of which would be civilizations that fill their galaxy with Dyson spheres. The G-HAT results do not close the book on Dyson sphere searches, but they do tell us that such Type III civilizations are not detected within the energy levels we might expect.
Image: A false-color image of the mid-infrared emission from the Great Galaxy in Andromeda, as seen by Nasa’s WISE space telescope. The orange color represents emission from the heat of stars forming in the galaxy’s spiral arms. The G-HAT team used images such as these to search 100,000 nearby galaxies for unusually large amounts of this mid-infrared emission that might arise from alien civilizations. Credit: NASA/JPL-Caltech/WISE Team.
G-HAT is all about putting upper limits on energies emitted as waste heat in nearby galaxies, and while Dysonian SETI methods seem to diverge from earlier radio and laser SETI, the two approaches actually work quite well together. As the search continues, anomalous objects form a catalog which can be consulted by the entire SETI community, using its resources at various wavelengths to probe the result more deeply.
Search References
Although I’m out of time today, I want to make the point that Dyson spheres shouldn’t be thought of purely as means of energy collection, because the manipulation of a star at this level could involve changing the character of the star itself. In a future article I’ll look at why a civilization might want to do this, and who has been investigating the matter. Until then, here are references to the searches we’ve talked about today.
The Sagan and Walker paper is “The Infrared Delectability of Dyson Civilizations,” Astrophysical Journal 144 (3), (1966), p. 1216 (abstract).
The Slysh paper is “A Search in the Infrared to Microwave for Astroengineering Activity,” in The Search for Extraterrestrial Life: Recent Developments, M. D. Papagiannis (Editor), Reidel Pub. Co., Boston, Massachusetts, 1985, p. 315.
Timofeev and Kardashev wrote “A Search of the IRAS Database for Evidence of Dyson Spheres,” Acta Astronautica 46 (2000), p. 655.
Richard Carrigan’s 2009 study is “The IRAS-based Whole-Sky Upper Limit on Dyson Spheres,” Astrophysical Journal 698 (2009), pp. 2075-2086. Abstract / preprint.
The Teodorani paper is “A strategic “viewfinder” for SETI research,” Acta Astronautica Vol. 105, Issue 2 (December 2014). Abstract.
On G-HAT, see Griffith et al., “The ? Infrared Search for Extraterrestrial Civilizations with Large Energy Supplies. III. The Reddest Extended Sources in WISE,” Astrophysical Journal Supplement Series Vol. 217, No. 2, published 15 April 2015 (abstract / preprint).
by Paul Gilster | Jan 18, 2022 | Astrobiology and SETI |
Although so-called Dysonian SETI has been much in the air in recent times, its origins date back to the birth of SETI itself. It was in 1960 – the same year that Frank Drake used the National Radio Astronomy Observatory in Green Bank, West Virginia to study Epsilon Eridani and Tau Ceti – that Freeman Dyson proposed the Dyson sphere. In fiction, Olaf Stapledon had considered such structures in his novel Star Maker in 1937. As Macy Huston and Jason Wright (both at Penn State) remind us in a recent paper, Dyson’s idea of energy-gathering structures around an entire star evolved toward numerous satellites around the star rather than a (likely unstable) single spherical shell.
We can’t put the brakes on what a highly advanced technological civilization might do, so both solid sphere and ‘swarm’ models can be searched for, and indeed have been, for in SETI terms we’re looking for infrared waste heat. And if we stick with Dyson (often a good idea!), we would be looking for structures orbiting in a zone where temperatures would range in the 200-300 K range, which translates into searching at about 10 microns, the wavelength of choice. But Huston and Wright introduce a new factor, the irradiation from the interior of the sphere onto the surface of the star.
This is intriguing because it extends our notions of Dyson spheres well beyond the habitable zone as we consider just what an advanced civilization might do with them. It also offers up the possibility of new observables. So just how does such a Dyson sphere return light back to a star, affecting its structure and evolution? If we can determine that, we will have a better way to predict these potential observables. As we adjust the variables in the model, we can also ponder the purposes of such engineering.
Think of irradiation as Dyson shell ‘feedback.’ We immediately run into the interesting fact that adding energy to a star causes it to expand and cool. The authors explain this by noting that total stellar energy is a sum of thermal and gravitational energies. Let’s go straight to the paper on this. In the clip below, E* refers to the star’s total energy, with Etherm being thermal energy:
When energy is added to a star (E? increases), gravitational energy increases and thermal energy decreases, so we see the star expand and cool both overall (because Etherm is lower) and on its surface (because, being larger at the same or a lower luminosity its effective temperature must drop). A larger star should also result in less pressure on a cooler core, so we also expect its luminosity to decrease.
Image: Artist’s impression of a Dyson sphere under construction. Credit: Steve Bowers.
Digging into this effect, Huston and Wright calculate the difference in radius and temperature between the normal and irradiated stellar models. Work on irradiated stars goes back to the late 1980s, and includes the interesting result that a star of half a solar mass, if subjected to a bath of irradiation at a tempearature of 104 K, has its main sequence lifetime shortened by approximately half. The star expands and cools overall, but the distribution of the thermal energy causes its central temperature to increase.
A bit more on this background work: The 1989 paper in question, by C. A. Tout and colleagues, has nothing to do with Dyson spheres, but provides data on stellar irradiation of the sort that would be produced by proximity to a quasar or active galactic nucleus. Tout et al. worked on isotropic radiation baths at constant temperatures up to 104 K, finding that while the effects on stars whose energy is radiative are minor, convective stars increase in size. Keep in mind that cooler stars of low-mass are fully convective; hotter and more massive stars transport their energies from the interior through a radiative zone that forms and expands from the core.
Applying this to Dyson spheres, a star surrounded by technology would have light reflected back onto the star, while at the same time the sphere would become warm and emit thermal energy. I was intrigued to see that the paper gives a nod to Shkadov thrusters, which we’ve discussed in these pages before – these are stellar ‘engines’ using a portion of a star’s light to produce a propulsive effect. See Cosmic Engineering and the Movement of Stars, as well as Greg Benford’s look at the physics of the phenomenon, as developed by himself and Larry Niven, in Building the Bowl of Heaven.
Huston and Wright model how a Dyson sphere would affect the structure and evolution of a star, incorporating Dyson sphere luminosity as returned to the surface of the star. Each star is modeled from the start of its enclosure within the Dyson Sphere to the end of its main sequence lifetime. Beyond luminosity, the authors use Wright’s previous work on Dyson sphere parameters and his formulation for radiative feedback, while deploying a tool called Modules for Experiments in Stellar Astrophysics to assist calculations.
The authors consider stars in a mass range from 0.2 to 2 solar masses while varying luminosity fractions from 0.01 to 0.50. The effects of energy feedback on stars and the calculations on Dyson sphere properties produce absolute magnitudes for combined systems incorporating a central star and the Dyson sphere around it. From the paper:
Irradiated stars expand and cool. A Dyson sphere may send a fraction of a star’s light back toward it, either by direct reflection or thermal re-emission. This returning energy can be effectively transported through convective zones but not radiative zones. So, it can have strong impacts on low mass main sequence stars with deep convective zones which extend to the surface. It causes them to expand and cool, slowing fusion and increasing main sequence lifetimes. For higher mass stars with little to no convective exterior, the returned energy cannot penetrate far into the star and therefore has little effect on the star’s structure and evolution, besides some surface heating.
The effects are observationally significant only for spheres with high reflectivity or high temperatures – remember that Dyson assumed a sphere in the ~300 K area to correspond to a planet in the habitable zone. The authors combine the spectrum of the host star and the Dyson sphere into a ‘system spectrum,’ which allows them to calculate absolute magnitudes. The calculations involve the star itself, the interior of the sphere (both would be hidden) and the exterior of the sphere, which would be unobscured.
Wright has previously developed a set of five defining characteristics of a Dyson sphere, involving the intercepted starlight, the power of the sphere’s thermal waste heat, its characteristic temperature and other factors in a formalism called AGENT. The authors run their calculations on hot Dyson spheres and their opposite – cold, mirrored Dyson spheres that return starlight to the star without significant heating. Thus we go through a range of Dyson spheres intercepting starlight, including the familiar notion:
As the classical idea of a Dyson sphere, we can examine a solar mass star with low transmission of starlight through the sphere and a Dyson sphere radius of roughly 1 AU. We see that the feedback levels are very low and that the systems will appear, relative to a bare solar mass star, to be dimmed in the optical range and reddened in both optical and infrared colors.
Notice the range of temperatures we are talking about, for this is where we can expand our thinking on what a Dyson sphere might involve:
For our 0.2 and 0.4 M stars, feedback levels above roughly 1% cause at least a 1% change in nuclear luminosity; their effective temperatures do not significantly change. For our 1 and 2 M stars, feedback levels above roughly 6% cause at least a 1% change in the star’s effective temperature; their nuclear luminosities do not significantly change. Physically, these limits may correspond with a cold, mirrored surface covering the specified fraction of the star’s solid angle. For light-absorbing, non-reflective Dyson spheres, these feedback levels correspond to very hot spheres, with temperatures of thousands of Kelvin.
Dyson spheres in the latter temperature ranges are utterly unlike the more conventional concept of a civilization maintaining habitable conditions within the shell to gain not just energy but vastly amplified living space. But a hot Dyson sphere could make sense from the standpoint of stellar engineering, for feedback mechanisms can be adjusted to extend a star’s lifetime or reduce its luminosity. Indeed, looking at Dyson spheres in the context of a wide range of feedback variables is useful in helping jog our thinking about what might be found as the signature of an advanced technological civilization.
The paper is Huston & Wright, “Evolutionary and Observational Consequences of Dyson Sphere Feedback,” accepted at the Astrophysical Journal (abstract / preprint). The paper by Tout et al. is “The evolution of irradiated stars ,” Monthly Notices of the Royal Astronomical Society Volume 238, Issue 2 (May 1989), pp. 427–438 (abstract). For an overview of Dyson spheres and their background in the literature, see Wright’s “Dyson Spheres,” Serbian Astronomical Journal Issue 200, Pages: 1-18 (2020). Abstract / preprint. Thanks to my friend Antonio Tavani for the early pointer to this work.
by Paul Gilster | Mar 4, 2019 | Advanced Rocketry |
Let’s start the week by talking about gravitational assists, where a spacecraft uses a massive body to gain velocity. Voyager at Jupiter is the classic example, because it so richly illustrates the ability to alter course and accelerate without propellant. Michael Minovitch was working on this kind of maneuver at UCLA as far back as the early 1960s, but it was considered even before this, as in a 1925 paper from Friedrich Zander. It took Voyager to put gravity assists into the public consciousness because the idea enabled the exploration of the outer planets.
Can we use this kind of maneuver to help us gain the velocity we need to make an interstellar crossing? Let’s consider how it works: We’re borrowing energy from a massive object when we do a gravity assist. From the perspective of the Voyager team, their spacecraft got something for ‘free’ at Jupiter, in the sense that no additional propellant was needed. What’s really happening is that the spacecraft gained energy at the expense of the planet. Jupiter being what it is, the change in its own status was invisible, but it lent enough energy to Voyager to prove enabling.
According to David Kipping (Columbia University), the maximum speed increase equals twice the velocity of the planet we’re using for the maneuver, and when you look at Jupiter’s orbital speed around the Sun (around 13.1 kilometers per second), you can see that we’re only talking about a fraction of what it would take to get us to interstellar speeds. But the principle is enticing, because traveling with little or no propellant is a longstanding goal, one that drives research into solar sails and their fast cousins, beamed lightsails. And it has been much on Kipping’s mind.
For gravitational assists from planets are only one aspect of the question, there being other kinds of astrophysical objects that can help us out. Depending on their orbital configuration, some of these are moving fast indeed. In the early 1960s, Freeman Dyson went to work on the physics of gravitational assists around binary white dwarf stars — he would ultimately go on to consider the case of neutron star binaries (back when neutron stars were still purely theoretical). Such concepts obviously imply an interstellar civilization capable of reaching the objects in the first place. But once there, the energies to be exploited would be spectacular.
While I want to begin with Dyson’s ideas, I’ll move tomorrow to Kipping’s latest paper, which addresses the question in a novel way. Kipping, well known for his work in the Hunt for Exomoons with Kepler project, has been pondering Dyson’s notions but also applying them to what would seem, on the surface of things, to be an entirely different proposition: Beamed propulsion. How he combines the two may surprise you as much as it did me, as we’ll see in coming days.
Image: An artist’s conception of two orbiting white dwarf stars. Credit: Tod Strohmayer (GSFC), CXC, NASA, Illustration: Dana Berry (CXC).
Nature of the Question
If we talk about manipulating astrophysical objects, a natural objection arises: Why should we study things that are impossible for our species today? After all, we can get to Jupiter, but getting to the nearest white dwarf, much less a white dwarf binary, is beyond us.
But big ideas can be productive. Consider Daedalus, conceived in the 1970s as the first serious design for a starship. The idea was to demonstrate that a spacecraft could be designed using known physics that could make a journey to another star. The massive two-stage Daedalus (54,000 tonnes) seems impossible today and doubtless will never be built. Was it worth studying?
The answer is yes, because once you’ve established that something is not impossible, you can go to work on ways to engineer a result that may differ hugely from the original. Breakthrough Starshot is built around the idea of using lasers to propel a different kind of spacecraft, not of 54,000 tonnes but of 1 gram, carried by a small lightsail, and designed to be sent not as a one-off mission but as a series of probes driven by the same laser installation.
Once again we’re stretching our thinking, but here the technologies to do such a thing may (or may not, depending on what Breakthrough Starshot’s analyses come up with) be no more than a few decades away. The current Breakthrough effort is all about finding out what is feasible.
Again we’re designing something before we’re sure we can do it. The challenges are obviously immense. Consider: To go interstellar with cruise times of several decades, we need to ramp up velocity, and that takes enormous amounts of energy. Kipping calculates that 2 trillion joules — the output of a nuclear power plant running continuously for 20 days — would be needed to send the Breakthrough Starshot ‘chip’ payload to Proxima Centauri. And that’s just for one ‘shot’, not for the multiple chips envisioned in what might be considered a ‘swarm’ of probes.
Working with Massive Objects
Are there other ways to generate such energies? Freeman Dyson’s extraordinary white dwarf binary gravitational assist appears in “Gravitational Machines,” a short paper that ran in a book A.G.W. Cameron edited called Interstellar Communication (New York, 1963). Conventional gravity assists aren’t sufficient because to be effective, a gravitational ‘machine’ would have to be built on an astronomical scale. Fortunately, the universe has done that for us. So we should be thinking about the principles involved, and what they imply:
…if our species continues to expand its population and its technology at an exponential rate, there may come a time in the remote future when engineering on an astronomical scale will be both feasible and necessary. Second, if we are searching for signs of technologically advanced life already existing elsewhere in the universe, it is useful to consider what kinds of observable phenomena a really advanced technology might be capable of producing.
Dyson’s considers the question in terms of binary stars, specifically white dwarfs, but goes on to address even denser concentrations of matter in neutron stars. Now we’re talking about a kind of gravitational assist that has serious interstellar potential. A spacecraft could be sent into a neutron star binary system for a close pass around one of the stars, to be ejected from the system at high velocity. If 3,000 kilometers per second appears possible with a white dwarf binary, fully 81,000 kilometers per second could occur — 0.27 c — with a neutron star binary.
Hence the ‘Dyson slingshot.’ (As an aside, I’ve always wondered what it must be like to have a name so famous in your field that everything from ‘Dyson spheres’ to ‘Dyson dots’ are named after you. The range of Dyson’s thinking on these matters certainly justifies the practice!).
The slingshot isn’t particularly effective with stars of solar class, where what you gain from a gravitational assist is still outweighed by the possibility of using stellar photons for propulsion. But as Dyson shows, once you get into white dwarf range and then extend the idea down to neutron stars, you’re ramping up the gravitational energy available to the spacecraft while at the same time reducing stellar luminosity. An advanced civilization, in ways Dyson explores, might tighten the orbital distance until the binary’s orbital period reached a scant 100 seconds.
Now a gravity assist has serious punch. In other words, there is the potential here for a civilization to manipulate astrophysical objects to achieve a kind of galactic network, where binary neutron stars offer transportation hubs for propelling spacecraft to relativistic speeds. As you would imagine, this plays to Dyson’s longstanding interest in searching for technological artifacts, and we’ll be talking about that possibility as we get into David Kipping’s new paper.
For Kipping will take Dyson several steps further, by looking not at neutron stars but black hole binaries and coming up with an entirely novel way of exploiting their energies, one in which a beam of light, rather than the spacecraft itself, gets the gravitational assist and passes those energies back to the vehicle. Kipping calls his idea the ‘Halo Drive,’ and we’ll begin our discussion of it, and a novel insight that inspired it, tomorrow.
The Dyson paper is “Gravitational Machines,” in A.G.W. Cameron, ed., Interstellar Communication, New York: Benjamin Press, 1963, Chapter 12. The Kipping paper is “The Halo Drive: Fuel-free Relativistic Propulsion of Large Masses via Recycled Boomerang Photons,” accepted at the Journal of the British Interplanetary Society (preprint). For those who want to get a head start, Dr. Kipping has also prepared a video on the Halo Drive that is available here.
by Paul Gilster | Oct 11, 2012 | Astrobiology and SETI |
The idea of the multiverse — an infinite number of universes co-existing with our own — has a philosophical and mathematical appeal, at least if you’re a follower of string theory. Indeed, there are those who would argue there could be as many as 10500 universes, each with its own particular characteristics, most probably inimical to the development of life. But I have to say that I’m far more interested in the universe that is demonstrably here, our own, and thus the news that Geoff Marcy has received a grant to look for Dyson spheres catches my eye more than news of a similar grant to physicist Raphael Bousso to probe multiverse theory.
Not that I have anything against Dr. Bousso (UC-Berkeley) and his work, and if he eventually does find a way to make predictions of multiverse theory that can be tested, I’m all for it. But I think the new grants, given to the researchers in a series called New Frontiers in Astronomy & Cosmology International Grants (funded through the UK’s Templeton Foundation), were wisely balanced between the practical (observational astronomy) and the highly theoretical. Marcy will use his to probe the continually swelling Kepler datastream looking for distinctive signatures.
Instead of planets, though, Marcy has more unusual targets, the vast structures Freeman Dyson hypothesized over fifty years ago that could ring or completely enclose their parent star. Such structures, the work of a Kardashev Type II civilization — one capable of drawing on the entire energy output of its star — would power the most power-hungry society and offer up reserves of energy that would support its continuing expansion into the cosmos, if it so chose. Marcy’s plan is to look at a thousand Kepler systems for telltale evidence of such structures by examining changes in light levels around the parent star.
Image: A Dyson sphere under construction. Credit: Steve Bowers.
Interestingly, the grant of $200,000 goes beyond the Dyson sphere search to look into possible laser traffic among extraterrestrial civilizations. Says Marcy:
“Technological civilizations may communicate with their space probes located throughout the galaxy by using laser beams, either in visible light or infrared light. Laser light is detectable from other civilizations because the power is concentrated into a narrow beam and the light is all at one specific color or frequency. The lasers outshine the host star at the color of the laser.”
The topic of Dyson spheres calls Richard Carrigan to mind. The retired Fermilab physicist has studied data from the Infrared Astronomical Satellite (IRAS) to identify objects that radiate waste heat in ways that imply a star completely enclosed by a Dyson sphere. This is unconventional SETI in that it presumes no beacons deliberately announcing themselves to the cosmos, but instead looks for signs of civilization that are the natural consequences of physics.
Carrigan has estimated that a star like the Sun, if enclosed with a shell at the radius of the Earth, would re-radiate its energies at approximately 300 Kelvin. Marcy will turn some of the thinking behind what Carrigan calls ‘cosmic archaeology’ toward stellar systems we now know to have planets, thanks to the work of Kepler. Ultimately, Carrigan’s ‘archaeology’ could extend to planetary atmospheres possibly marked by industrial activity, or perhaps forms of large-scale engineering other than Dyson spheres that may be acquired through astronomical surveys and remain waiting in our data to be discovered. All this reminds us once again how the model for SETI is changing.
For more, see two Richard Carrigan papers, the first being “IRAS-based Whole-Sky Upper Limit on Dyson Spheres,” Journal of Astrophysics 698 (2009), pp. 2075-2086 (preprint), and “Starry Messages: Searching for Signatures of Interstellar Archaeology,” JBIS 63 (2010), p. 90 (preprint). Also see James Annis, “Placing a limit on star-fed Kardashev type III civilisations,” JBIS 52, pp.33-36 (1999). A recent Centauri Dreams story on all this is Interstellar Archaeology on the Galactic Scale but see also Searching for Dyson Spheres and Toward an Interstellar Archaeology.
by Paul Gilster | Dec 26, 2008 | Culture and Society |
Will life spread out from Earth to flourish in the cosmos? Freeman Dyson has always supported the idea, and with great persuasiveness. BBC Four has created an archive of interviews on its Web site, among which is a clip of Dyson discussing life’s variety and the imperative of broadening its range. The theoretical physicist, who played an important role in the development of the ‘atomic spaceship’ concept called Project Orion, doesn’t believe man’s role is simply to send the occasional astronaut out in what he calls ‘a metal can’ to look out a window.
Image: Physicist Freeman Dyson, whose thoughts on life’s spread into the cosmos can be found in the BBC archives. Credit: Dartmouth College.
On the contrary, says Dyson in his interview, humans may have a shepherding role in building a permanent presence in space. Instead of ships full of scientists or colony vessels establishing a new human foothold, Dyson would argue that we humans are representative of a far larger pattern, the spread of living things in all their variety. Our major role is to assist. We’re talking here about migrating whole ecologies, but not as forced transplants on other worlds so much as adaptations that, over the eons, will assume their own unique identities:
If you look at the natural world, you see that everywhere life has gone, it brings tremendous variety. The natural world is beautiful just because there is such a tremendous variety of living creatures — trees, plants, butterflies, birds. And I think the same thing will happen in the universe at large. The universe will just be a far more beautiful and interesting place when life has taken it over.
Note the implication that life has not yet taken the universe over, perhaps a comment on the likelihood of success for our SETI efforts, if not an answer to the Fermi question. Dyson goes on:
Life will spread and diversify everywhere the same way it has on Earth. Life just has this ability to adapt itself to all sorts of different environments, and I don’t think it will stop at one planet, when you see the whole universe waiting there. That’s the reason I believe we shall go out there and take our plants and animals with us.
It’s a bold view and not one that fits readily within the constraints of governmental space programs. But where does it start? Although space settlements near Earth might seem to be the answer, Dyson told his BBC Four interviewer that he had no use for the kind of habitats envisioned by Gerard O’Neill, finding them far too bureaucratic. Instead, he opts for ‘little bands of adventurers’ going out, working at their own risk and with agendas set by themselves. The Mayflower’s voyage across the Atlantic is an analog to what he sees happening in space:
There’s a tremendous amount of stuff already floating around in orbit just waiting to be salvaged by anyone who’s brave enough to go and do it. There’s a lot of stuff on the Moon which is lying there. That’s the way the Mayflower people worked. They didn’t build the Mayflower; they rented it. I imagine we’ll do the same thing. We will certainly make us of whatever the government provides, and that kind of stuff can usually be had very cheap.
As always, Dyson is energizing, and you’ll want to check the BBC Four archive to hear these bits (thanks to Teleread for the tip on this), at the same time wondering, as I do, why interviews like these aren’t offered in their entirety there. But do poke around. Arthur C. Clarke also has some audio clips, including his recollections of Stanley Kubrick’s first contacts with him re 2001: A Space Odyssey. Clarke says he received a letter from Kubrick ‘out of the blue,’ saying he wanted to do the ‘proverbial good science fiction movie, and did I have any ideas.’ At the time, interestingly enough, Clarke not only didn’t know Kubrick, but had never heard of him.
Image: Arthur C. Clarke at work. Credit: Billye Cutchen.
We brainstormed, developing all sorts of ideas, and when we had a fairly clear concept of what we wanted to do, Stanley said ‘write the novel and I’ll derive the screenplay from it.’…There was feedback in both directions, because I would write part of the novel and he would write the screenplay, and I would read the screenplay and feed it back into the novel. Later on, when he was actually filming, I was still feeding things from the film back into the novel. Because the novel didn’t come out until well after the film.
The later novel 2010: Odyssey Two would be developed through an entirely different method. Clarke acknowledges that he had to write 2001: A Space Odyssey with film in mind, creating scenes that he could visualize on screen, but 2010 was written as simply the best novel he could create, and ‘if anyone wants to film it, good luck to them.’ I loved both films, but in many ways still find 2010 the more interesting, a view few of my friends share. In any case, give Clarke a listen, and be aware that in this BBC interview archive, you’ll also find Werner Heisenberg, not to mention literary figures of distinction from Graham Greene to Iris Murdoch, and a host of actors, musicians and philosophers.
