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Dyson Spheres: The White Dwarf Factor

I often think of Dyson structures around stars as surprisingly benign places, probably motivated by encountering Larry Niven’s wonderful Ringworld when it was first published by Ballantine in 1970. I was reading it in an old house in Iowa on a windy night and thought to start with a chapter or two, but found myself so enthralled that it wasn’t until several hours later that I re-surfaced, wishing I didn’t have so much to do the next day that I had to put the book aside and sleep.

I hope I’m not stretching the definition of a Dyson construct too far when I assign the name to Niven’s ring. It is, after all, a structure built by technological means that runs completely around its star at an orbit allowing a temperate climate for all concerned, a vast extension of real estate in addition to whatever other purposes its creators may have intended. That a technological artifact around a star should be benign is a function of its temperature, which makes things possible for biological beings.

But a Dyson sphere conceived solely as a collection device to maximize the civilization’s intake of stellar energy would not be built to biological constraints. For one thing, as retired UCLA astrophysicist Ben Zuckerman points out in a new paper, it would probably be as close to its star as possible to minimize its size. That makes for interesting temperatures, probably in the range of 300 K at the low end and reaching perhaps 1000 K, which sets up emissions up to 10 µm in wavelength, and as Zuckerman points out, this would be in addition to any emission from the star itself.

Zuckerman refers to such structures as DSRs, standing for Dyson spheres/rings, so I guess working Niven in here fits as well. Notice that when talking about these things we also make an assumption that seems reasonable. If civilizations are abundant in the galaxy, they are likely long-lived, and that means that stellar evolution has to be something they cope with as yellow dwarf stars, for example, turn into red giants and, ultimately, white dwarfs. The DSR concept can accommodate the latter and offers a civilization the chance to continue to use the energy of its shrunken star. Whether this would be the route such a civilization chooses is another matter entirely.

Image: Artist depiction of a Dyson swarm. Credit: Kevin McGill/Wikimedia Commons.

One useful fact about white dwarfs is that they are small, around the size of the Earth, and thus give us plenty of transit depth should some kind of artificial construct pass between the star and our telescopes. Excess infrared emission might also be a way to find such an object, although here we have to be concerned about dust particles and other potential sources of the infrared excess. Zuckerman’s new paper analyzes the observational limits we can currently derive based on these two methods.

The paper, published in Monthly Notices of the Royal Astronomical Society, uses data from Kepler, Spitzer and WISE (Wide-field Infrared Survey Explorer) as a first cut into the question, revising Zuckerman’s own 1985 work on the number of technological civilizations that could have emerged around main sequence stars that evolved to white dwarfs within the age constraints of the Milky Way. Various papers exist on excess of infrared emissions from white dwarfs; we learn that Spitzer surveyed at least 100 white dwarfs with masses in the main sequence range of 0.95 to 1.25 solar masses. These correspond to spectral types G7 and F6, and none of them turned up evidence for excess infrared emission.

As to WISE, the author finds the instrument sensitive enough to yield significant limits for the existence of DSRs around main sequence stars, but concludes that for the much fainter white dwarfs, the excess infrared is “plagued by confusion…with other sources of IR emission.” He looks toward future studies of the WISE database to untangle some of the ambiguities, while going on to delve into transit possibilities for large objects orbiting white dwarfs. Kepler’s K2 extension mission, he finds, would have been able to detect a large structure (1000 km or more) if transiting, but found none.

It’s worth pointing out that no studies of TESS data on white dwarfs are yet available, but one ongoing project has already observed about 5000, with another 5000 planned for the near future. As with K2, a deep transit would be required to detect a Dyson object, again on the order of 1000 kilometers. If any such objects are detected, we may be able to distinguish natural from artificial objects by their transit shape. Luc Arnold has done interesting work on this; see SETI: The Artificial Transit Scenario for more.

Earlier Kepler data are likewise consulted. From the paper:

From Equation 4 we see that about a billion F6 through G7 stars that were on the main sequence are now white dwarfs. Studies of Kepler and other databases by Zink & Hansen (2019) and by Bryson et al. (2021) suggest that about 30% of G-type stars are orbited by a potentially habitable planet, or about 300 million such planets that orbit the white dwarfs of interest here. If as many as one in 30 of these planets spawns life that eventually evolves to a state where it constructs a DSR with luminosity at least 0.1% that of its host white dwarf, then in a sample of 100 white dwarfs we might have expected to see a DSR. Thus, fewer than 3% of the habitable planets that orbit sun-like stars host life that evolves to technology, survives to the white dwarf stage of stellar evolution, and builds a DSR with fractional IR luminosity of at least 0.1%.

Science fiction writers will want to go through Zuckerman’s section on the motivations of civilizations to build a Dyson sphere or ring, which travels deep into speculative territory about cultures that may or may not exist. It’s an imaginative foray, though, discussing the cooling of the white dwarf over time, the need of a civilization to migrate to space-based colonies and the kind of structures they would likely build there.

There are novels in the making here, but our science fiction writer should also be asking why a culture of this sophistication – able to put massive objects built from entire belts of asteroids and other debris into coherent structures for energy and living space purposes – would not simply migrate to another star. The author only says that if the only reason to travel between the stars is to avoid the inevitable stellar evolution of the home star, then no civilization would undertake such journeys, preferring to control that evolution through technology in the home system. This gives me pause, and Centauri Dreams readers may wish to supply their own reasons for interstellar travel that go beyond escaping stellar evolution.

Also speculative and sprouting fictional possibilities is the notion that main sequence stars may not be good places to look for a DSR. Thus Zuckerman:

…main sequence stars suffer at least two disadvantages as target stars when compared to white dwarfs; one disadvantage would be less motivation to build a substantial DSR because one’s home planet remains a good abode for life. In our own solar system, if a sunshield is constructed and employed at the inner Earth-Sun Lagrange point – to counter the increasing solar luminosity – then Earth could remain quite habitable for a few Gyr more into the future. Perhaps a more important consideration would be the greater luminosity, say about a factor of 1000, of the Sun compared to a typical white dwarf.

Moreover, detecting a DSR around a main sequence star becomes more problematic. In the passage below, the term τ stands for the luminosity of a DSR measured as a fraction of the luminosity of the central star:

For a DSR with the same τ and temperature around the Sun as one around a white dwarf, a DSR at the former would have to have 1000 times the area of one at the latter. While there is sufficient material in the asteroid belt to build such an extensive DSR, would the motivation to do so exist? For transits of main sequence stars by structures with temperatures in the range 300 to 1000 K, the orbital period would be much longer than around white dwarfs, thus relatively few transits per year. For a given structure, the probability of proper alignment of orbital plane and line of sight to Earth would be small and its required cross section would be larger than that of Ceres.

So we are left with that 3 percent figure, which sets an upper limit based on our current data for the fraction of potentially habitable planets that orbit stars like the Sun, produce living organisms that produce technology, and then construct a DSR as their system undergoes stellar evolution. No more than 3 percent of such planets do so.

There is a place for ‘drilling down’ strategies like this, for they take into account the limitations of our data by way of helping us see what is not there. We do the same in exoplanet research when we start with a star, say Proxima Centauri, and progressively whittle away at the data to demonstrate that no gas giant in a tight orbit can be there, then no Neptune-class world within certain orbital constraints, and finally we do find something that is there, that most interesting place we now call Proxima b.

As far as white dwarfs and Dyson spheres or rings go, new instrumentation will help us improve the limits discussed in this paper. Zuckerman points out that there are 5000 white dwarfs within 200 parsecs of Earth brighter than magnitude 17. A space telescope like WISE with the diameter of Spitzer could improve the limits on DSR frequency derived here, its data vetted by upcoming 30-m class ground-based telescopes (Zuckerman notes that JWST is not suited, for various reasons, for DSR hunting). The European Space Agency’s PLATO spacecraft should be several times more sensitive than TESS at detecting white dwarf transits, taking us well below the 1000 km limit.

The paper is Zuckerman, “Infrared and Optical Detectability of Dyson Spheres at White Dwarf Stars,” Monthly Notices of the Royal Astronomical Society stac1113 (28 April 2022). Abstract / Preprint.

{ 45 comments… add one }
  • Alex Tolley May 13, 2022, 9:59

    If there is any advantage to living in a Dyson swarm close to a white dwarf, then I don’t see the value in living through the red giant phase of the star to reach that status. Far better to send a [robotic] constructor fleet to a nearby WD to build the swarm, and then migrate civilization to that swarm well before the homeworld becomes unliveable.

    If the civilization is already largely living in space colonies, then migrate them directly to the WD over time, and well before the red giant stage. There is a lot of time to do this for a long-lived, stable civilization.

    IDK how advantageous a ringworld is in practice. It needs to be constantly stabilized. Any severe damage like a puncture would result in a slow loss of volatiles. Untreatable plagues or diseases would have no boundaries unless sections were permanently sealed off from each other. Unless there were deployable sunshades, it would be a very inflexible design to adapt to changes in the star, whether increasing luminosity as the main sequence stage aged or declining luminosity over the lifetime of the WD.

    If any civilization has interstellar migration capability, then as has been argued by many, the likelihood of colonizing such stars and building swarms if far greater than the likelihood of such structures if they were forever only built around the home world’s star.

    • Michael May 13, 2022, 16:53

      In the Red giant phase it emits more energy and there is huge amount of collectable matter, 100’s of thousands of earth masses of material.

      • Alex Tolley May 13, 2022, 22:43

        So for a billion years, the civilization has to live through the red giant phase, while the inner system is burnt to a crisp, and the expelled matter is thinly dispersed. Would it really not be more pragmatic to go to another system and start afresh?

        • Michael May 14, 2022, 12:44

          There is plenty of material in the outer solar system, plenty of water and building materials, potentially an earth’s worth. If a techalien race took hold in a globular cluster they would pretty much be made as there are plenty of white dwarfs there. Using the inner solar system to power lasers would work well, imagine a planet wide phased array on Mercury and how far and fast it could propel heavy craft to interstellar destinations.

        • Adam Crowl May 18, 2022, 5:35

          Hi Alex
          Pragmatism is star-lifting to avoid the Red Giant demise ;-)

  • Michael Fidler May 13, 2022, 10:18

    Something struck me reading about DSR. The ultra short orbital period of some of the exoplanets transits may be multiple planets, flat earth disks or other round forms in the same orbital plane but orbiting further out from the star. They just look like the same planet! This should make it much easier to stabilize and control them plus having maybe 20 or more worlds with very short transit time between them. How could we tell the difference since the reflected light from them would just merge with the stellar signal. Flat earth disks could be put in different orbital planes without causing any major interference between different planes.
    1000 habitable area disks would show a much lower temperature individually but in combination could cause a grazing reflections of a much higher temperature???

    A very simple way of cloaking ET’s existence?

    With a population thresholds of quadrillions…

    • Alex Tolley May 13, 2022, 14:57

      Very clever idea. The same arrangement would change the radial velocity measurements, most likely zero out with a symmetric arrangement of planets.

      So this incompatible data would indicate an artificial construct.

      • Michael Fidler May 14, 2022, 0:08

        Not necessarily, We dream of a second earth, so why not build one? Flat disk or half spheres would work but be light weight. Long cigar shaped with light coming down a central main shaft could be much closer to their sun but have the same light and heat levels as our earth.
        The big advantage in sharing the same orbit is how easy it would be to reach each enclosed world from the main planet. What would make sense is the build a layer closer to the sun of many such worlds since trade would require less energy to transport materials. They would have the long tube end facing the sun so transits look like planets. An extremely lightweight planet would seem to indicate an artificial structure.
        Now we come to places like Trappist 1, where such structures could be very long cigars and since recent research indicates these resonate chain systems should not exist, they may be designed by higher intelligence. Could there be a whole other planes of planets or artificial structures orbiting Trappist one? We would not see such transits but might find out soon with JWST, hopefully.

        • Alex Tolley May 14, 2022, 12:59

          A long tube would not result in a flat-bottomed transit curve, but more of a U-shaped one due to the tube presenting at an angle on either side of the mid-transit. Maybe we would miss this in the noise, but IDK.

          However, I like the idea of a tube, essentially an O’Neill Island 3 that maintains an orbit perpendicular to the sun. To prevent any gyroscopic effects from the rotation to create artificial gravity on the inner surface, 2 tubes would be coupled together to contra-rotate (as O’Neill suggested). This wouldn’t affect the transit observation, although if we could eventually get high-resolution images we might detect this configuration.

          Now if the civilization was a robotic one, they might abandon the need for gravity and even illumination, making the cylinder more like an open structure to space, with sufficient structural affordances to navigate the tube, like spiders in a vast web.

          Be that as it may, this concept of tube structures orbiting close to a star is novel to me and rather interesting. It seems to offer advantages of the classic Dyson swarm, but with extra advantages of transport between structures and energy harvesting with less mass.

          [Is this your own novel idea or did you read it or see it in a SciFi book or movie?]

          • Michael Fidler May 14, 2022, 21:13

            Actually most of my concepts come to me as I write but in this case just an extension of O’Neill’s idea. One other report that has always intrigued me is from Switzerland in 1762.

            “Monstrator: The Odd, Ephemeral Mystery Object That “Dropped Anchor” in 1762”


            It does have many advantages, being able to put colonies closer to the sun, increased interior population, and easy transport if a series of objects orbit in the same orbit. This could hold large populations without the dynamics problems of sun encircling rings or spheres. Cables used in space elevators would work for interior structural strength and 2000 miles interior width would have very small effects from rotation to produce 1G artificial gravity.
            It would seem taking an asteroid and adding a solar furnace could produce a continuous sheet with the correct curvature in space. Like a giant 3D printer!

            • Michael Fidler May 15, 2022, 10:49

              Another concept that would make these a much more practical object is wrapping them with helical coils. Using a superconducting coil around the tube would make a powerful magnetohydrodynamic (MHD) thruster in the solar wind. This may be used for station keeping or moving it around in the solar system and even generate electricity for the colony. And wait, there’s more! No nasty hard particle radiation since this would act just like earth’s magnetosphere… ;-}

            • Alex Tolley May 15, 2022, 12:08

              Actually most of my concepts come to me as I write but in this case just an extension of O’Neill’s idea.

              I appreciate your modesty. The O’Neill cylinders were designed for 1 AU, with mirrors deflecting sunlight directly through the longitudinal “windows”. He did envisage making the mirror a concentrator to allow the cylinders to have Earth-like insolation in very deep space. But I have never seen any modification that placed the structure close to the star and directed the much more intense sunlight along the length of the cylinder and dispersed at a lower intensity along the length of the cylinder. The only analogous approach I have read about was illuminating building interiors using light-trapping fibers to direct light throughout the building from a roof collector. Today we would use solar PV and use the power to power LED lights instead.
              Using a location like Mercury to collect energy and beam/transport it through the solar system is perhaps a variant often seen in SciFi.

              The second novelty is that the cylinder colonies would be much closer together, reducing communication latency, both electronic and physical transport of people and materiel. While this is similar to swarms of economies in Earth orbit, I had not read of anyone suggesting placing them in tight orbits around a star, well inside the HZ.

              [OT. The UK tech program “Click” has a section this week on space structures. Aparent 1 atom thick graphite layers can act as efficient protection from solar heating of space stations and spacecraft. Manchester University is currently experimenting with using graphite-covered carbon fiber to build hulls, obviating the need for thick insulating layers.]

      • Michael Fidler May 14, 2022, 1:54

        I just wonder how many candidate planets from Kepler and and TESS have had radial velocity measurements? How many artificial planets/disks/cigars would it take to give a negative RV? Would 3 or 4 or more evenly spaced objects give unusual RV readings and has anyone looked for anomalies in the data? These are our two main sources of exoplanets information, transits and RVs, so taking a closer look at the data may help.
        According to the exoplanet.eu none of these overlap between RV and transits!
        NASA’s Exoplanet exploration is showing some 8887 candidates which means only 8 percent have been found via RV with none being transits???

        We could be sitting on one hell of a big pile of artificial structures if we light a fire under the astronomy community to do RV measurements of transiting systems and the same for the transiting scopes looking at RV exoplanet systems. Have I missed something here or is there hard data for RV/Transit exoplanet systems out there???

      • Michael Fidler May 14, 2022, 2:34

        Looking through the “The Extrasolar Planets Encyclopaedia” RV listing I found 30 Kepler, K2, TOI and CoRot transits with RV measurements.
        Twenty-nine were from February 2021 to now except one at the end of 2019 out of a thousand RV measurements. The rest all had standard names so no way of knowing if both RV and transits info without going through the whole list individually.

    • Michael Fidler May 14, 2022, 3:33

      Aliens could say hello by arranging planets in prime number pattern.

      Aliens could say hello by arranging planets in prime number pattern
      A sufficiently advanced alien civilisation would be able to arrange the orbits of the planets in its star system in a pattern that could never form naturally, signaling its existence to others.


      Mathematical encoding within multi-resonant planetary systems as SETI beacons.


      • Scott Guerin May 14, 2022, 21:10

        Michael, is is a nice turn of thought, rapid transits as Dyson Swarms.

        I wrote about what I called a Dyson Shutter Beacon some years ago toward the end of this Centauri Dreams post.


        • Michael Fidler May 15, 2022, 10:27

          Thanks for the link, made me think of a Trappist 1 system with only one orbit but different size planets with increasing number of planets as you go from h to be in the same orbit. Like the old shutter systems for animations!

  • Henry Cordova May 13, 2022, 11:24

    I would like to repeat a post from the previous thread, just in case you folks missed it. If any one of you can suggest a link that discusses these
    issues and can bring me up to date, I would appreciate it.

    (begin quote)

    I used to think that any planet in the habitable zone (where water is a liquid) around an old and stable star could be a candidate for life.

    Now I understand there are many other contraindications, such as tidal locking, a lack of a large moon to stabilize rotation and produce tides, not having a nickel iron core to generate a magnetosphere, failing to have plate tectonics, lack of vulcanism, too much vulcanism, a history of collisions with other planets, and so on. No doubt there are others.

    I don’t know how many of these are fully agreed upon as non-starters by the astrobiology community, and which ones may or may not be controversial. Is there a list somewhere I can consult?

    Personally, I think life will arise anywhere except in the most hostile and extreme of environments, although I’ll be the first to admit that’s just my unsupported opinion.

    (end quote)

    • Adam Crowl May 13, 2022, 19:21

      Hi Henry
      There’s no list that I’m aware of, merely separate papers looking at the various risk factors. I think astrobiologists are wary of anything spelling like a “Rare Earth” factor since it stinks of Evangelical attempts at arguing for the Divine Hand of God in selecting our blue-green Earth.

      • henry cordova May 13, 2022, 21:49

        A perceptive observation. Astrobiologists cannot afford too much self-censorship.

        I don’t doubt these “Rare Earth” objections are valid some of the time, perhaps even most of the time; but certainly not all the time. Life is tenacious. It, like the Earth, abides. Whether we can say the same for sentience, intelligence, or a physics-based technology capable of communication across light-years, is something else again.

      • NS May 14, 2022, 2:40

        IIRC there were similar objections to the Big Bang theory (proposed by the Vatican astronomer) because it could be taken to imply a sort of Biblical creation. I think scientists have to go where the evidence leads them. They can’t (any more than can literary writers or artists) stop someone else from taking what they say and running with it for their own purpose. If we’re afraid of saying something we think is true because it might be misinterpreted or misused, we’ll soon be saying nothing at all.

        • henry cordova May 14, 2022, 9:19

          Still, the difference between the scientific and religious methods is that scientists, when eventually confronted with incontrovertible evidence, are still capable of changing their minds.

          I do believe the great appeal SETI has for scientifically-oriented thinkers is that the discovery of ET will play a role very similar to the discovery of the 3 degree microwave background radiation.

          When I was a young man, there were still astronomers who championed the Steady State Model, and Darwinian Evolution was dismissed as “just a theory” in my high school.

          • tesh May 16, 2022, 9:29

            “…Darwinian Evolution was dismissed as “just a theory” in my high school”

            still is – sadly…

    • Geoffrey Hillend May 14, 2022, 16:56

      I thought the same thing that all we need is an Earth sized exoplanet in the life belt. I now think there are a lot of contingencies in order for a exoplanet to have intelligent life. The question is if microscopic life evolves on an Earth sized exoplanet without a Moon, will there be enough of it to be detectible from Earth? I expect to see a lack of oxygen and I assume any abiotic oxygen will be to faint to detect. We did detect oxygen on Mars through a telescope with a spectrometer, but we knew there was not a lot of it before we sent a remote sensing probe there to confirm it so there is the possibility we could see some oxygen in the spectra of exoplanets. Hopefully the JWST will answer some of these questions shortly. If the oxygen is easily detectible, it will be hard for me to not think there is some kind of life with photosynthesis there. Being conservative, I don’t think I will see it and we will have to look at a lot more exoplanets and star systems before we find it. I will be surprised to see it with all the contingencies scientists have now thought in the past ten years.

  • Mike Serfas May 13, 2022, 14:30

    I think that these megastructures are an example of where fiction will lead us very badly astray. From a novelistic point of view, they are highly enticing – simple, easy to explain, with a few miraculous components (gravity generators or scrith) that help make the story interesting. They don’t come to exist in an organic way, but this again favors the novelist. It is easier to write about a game of thrones than a game of millions of people making comments and choices in the course of their daily lives. Even a wicker Dyson sphere demands some emperor to place the rings and determine how they are made, and a villain on comparable scale to unravel it.

    Nonetheless, the benefit of these structures (collecting sunlight) seems tremendously flexible and no less mundane, with little need for high level organization. Sunlight can be reflected by statites, absorbed by satellites to be beamed far abroad as microwave or laser light, or used to warm the croplands of floating colonies; it might even be absorbed by thin rafts of some astoundingly resilient substance designed to float on the surface of WD 0346+246. These and many more notions will occur at the same time, and an alien civilization will pursue them all.

    Like trees seizing real estate in a forest canopy, their society’s major powers may duel (or collaborate) for control of the light. But they’ll do so in a process that we should recognize, because we’ve already started it: SOHO, discarded rocket boosters, the ISS when it passes the limb of Earth, even the Voyager spacecraft count as part of our Dyson swarm. (But not JWST for a while, fingers crossed) We just need a lot more of these objects before our “swarm” can be taken seriously.

    What I’m curious to hear is what the most efficient way is to use as much orbital space and sunlight as possible, without blocking the light or risking mishap. So far as I know, existing efforts in this direction around Earth (Bogota Declaration) have been aimed more at creating artificial scarcity and saleable “real estate” than at finding the most efficient solution for weaving strands of mobile “wicker” together into something like a Dyson sphere. Yet somehow, many spacecraft are being put into orbit without collisions! What is the state of the art now? Is there a way to come up with a single logical design accommodating a diverse cloud of spacecraft around Earth and eventually the Sun, or does this decision depend too heavily on the values and priorities of those making it?

  • Jer May 13, 2022, 20:01

    Though I don’t personally believe that it is the inevitable and prevailing destiny for the majority of intelligent constituents of ‘seriously’ advanced civilizations to want to glom together at any particular place for an extended multi-generational-equivalent period, even the human-equivalent habitable zone of a star, I have envisioned the ‘coming together’ of several independent traveling arks/ refitted asteroids/ hybrid-tech/celestial vessels, on occasion, to exchange not easily transmittal rare substances (advanced materials, organic samples, exotic plasmas, etc.,) in close physical proximity. Such ‘conventions’ would assume that the constituents would be functionally immortal, reasoning algorithms/ memory-cases, with or without ‘sensory container’ (i.e. biological body, non-natural-material intelligent repository, smart gas, etc). These gatherings could take place, I assume, in any group shape or configuration that allowed minimal effort to maintain relative parking locations to each other and host stellar entity(ies). To enter such a solar system (of whatever configuration) and easily align with the others, I would assume would be relatively trivial. One could imagine massive gatherings of various loose orbits, bunch sizes, varying spacefarer craft types/ rogue planetoid or 2, emitting fluctuating levels of energy. Such vast patterns of high-traffic inner solar system activities, at sufficient scale, could possibly betray noticeable, anomalous readings detectable to others as compared to ‘before the party started’. Let us not assume fixed super-objects as the only accumulation of intelligently-coordinated components worth detecting.

    • Terrance J May 15, 2022, 11:33

      Fascinating that the solar-orbitting Swarm could indeed be a temporary, spherical, bumpy spread and accumulation of fabricated or re-positioned and re-purposed occupiable objects. Perhaps the early stages of the Great Move – a shifting of the asteroid belt and N(E)Os into a useful shell formation at some orbit relative to the star which would be convenient for planet-dwellers to inhabit, before moving on or returning. Unclear on how stable this could be if far out of the solar ecliptic.

  • Geoffrey Hillend May 14, 2022, 16:36

    The amount of steel or any material to make a ring world is just as impossible as a Dyson sphere since the circumference of Earth’s orbit around the Sun 940 million kilometers. The Dyson sphere was based on the energy levels of obsolete power technology or incorrect extrapolation of such technology and energy needs into the future which are way too high or inefficient. Hawking came up with the same idea. I don’t agree with it. Solar cells were invented in 1954 and were still new in 1960, the year of the Dyson sphere idea. Solar power alone can easily satisfy our energy needs. Also we have nuclear reactors and nuclear fusion on the horizon. How many starships could we make with the metal needs for a Dyson sphere and even a world ring. A lot. I see these ideas as obsolete today, so I don’t expect to ever see any elsewhere in our galaxy. I can’t hurt to look though. It’s the sheer size and impracticality of these ideas that make them obsolete. It seems to me that an orbital, revolving, wheel space station for artificial gravity, world ships or ever a spherical “death star” might take precedence over these for all intelligent life. The idea of space travel especially interstellar travel is to have a power source independent from the Sun. We should not be completely dependent on the Sun. There is only starlight in interstellar space. If all of our resources were wasted on a Dyson sphere, then there would be no interstellar travel. There is only so much metal ore on the surface of our Earth. We can’t get any from the core due to the pressures there.

    • Adam Crowl May 17, 2022, 7:31

      Hi Geoffrey
      The Dyson Sphere is named for Freeman Dyson. And, despite the attribution, he never meant it to be thought of as a solid structure. Instead it’s more of a cloud of habitats, maximised for solar collection. Dyson also stated the concept was inspired by Olaf Stapledon’s “Star Maker” (1937) which featured lone stars surrounded by energy collecting surfaces.

      Kardashev Level II Civilizations utilizing all the energy supplied by their star represents the thermodynamic maximum for the longest period possible, short of making black holes and drip feeding them mass to power their accretion discs. Any other energy source ultimately derives from the stars or their by-products, or closely emulate them (controlled fusion is the usual go to.)

      The real issue for any megastructure like these is material strength. No known material is strong enough to wrap around a star. The only solution is gossamer thin surfaces that can levitate on starlight. In that case the total material required is surprisingly small – about the mass of Ceres.

      • Geoffrey Hillend May 17, 2022, 19:23

        I like to look at the purpose for the idea. I’ve just read recently the idea that the Dyson sphere was habitats before I posted the idea of solar cells and power utilizing the Sun power being a new idea in 1960 when Dyson thought of his sphere to allow us to utilize all of the solar energy. I agree with you on the material strength considering how stars form. The gravity, angular momentum and centrifugal force would make it impossible to build a Dyson sphere around a star no matter how much metal one had and it’s composition. I didn’t think about that due to the obvious impracticality the building of a Dyson sphere, so I did not do all the thought experiments in physics to invalidate it which I like to try and do when thinking about an idea. Thankyou for pointing that out to me Adam Crowl.

      • Geoffrey Hillend May 17, 2022, 19:29

        I like to look at the purpose for a piece of technology. the idea behind it. I’ve just read recently the idea that the Dyson sphere was habitats before I posted the idea of solar cells and power utilizing the Sun power being a new idea in 1960 when Dyson thought of his sphere to allow us to utilize all of the solar energy. I agree with you on the material strength considering how stars form. The gravity, angular momentum and centrifugal force would make it impossible to build a Dyson sphere around a star no matter how much metal one had and what ever it’s composition. I didn’t think about that due to the obvious impracticality the building of a Dyson sphere, so I did not do all the thought experiments in physics to invalidate it which I like to try and do when thinking about an idea. Thankyou for pointing that out to me Adam Crowl.

        We could build a whole lot of solar panels so surround most of the space around a star, but once again that would not be material efficient, the use of a lot of glass, plastic and aluminum and completely superfluous. I don’t agree with those energy classifications for civilizations; I don’t think we need more energy than the Sun’s output.

      • Mike Serfas May 17, 2022, 19:46

        They can do better than the nominal output of their star. To begin with, they want to collect all the energy the star emits more cheaply, at its surface, by covering it with floating rafts of some resilient material. The rafts are kept chilly by pumping a “refrigerant” (in what may be a very loose sense) between them and the many distant space colonies.

        However, if there is refrigerant being pumped into the rafts, these rafts might as well include projections that extend deeper into the star and increase their surface area. They can suck extra heat out of the upper layers of the star to increase the energy output. As the star’s outer layers cool, it contracts, so the gravitational pressure on its core increases and the rate of fusion goes up. Short of using up all the star’s hydrogen in something akin to a harnessed supernova, the aliens should be able to progress far beyond the “level II” threshold without conceptual barriers (even if I can’t imagine what engineering could tap the new heat at the core).

  • wdk May 15, 2022, 1:06

    The dimensions

    A good point about ring worlds or Dyson spheres: a white dwarf might be a good place to construct a starter set due to relative scale of the habitable zone. The black body properties do vary from case to case and age. I would think it worth reviewing their flare behavior too.
    In the case of nearby WDs, they occur nearby in binary system such as Procyon and Sirius A and B. For Sirius the relative position is problematic for stable planetary motion in A’s habitable zone; to a lesser extent in the Procyon system, but dicey. OTOH, the A stars would not represent as much of a problem to the stability of White Dwarf rings. As for building materials? TBD.

    • Geoffrey Hillend May 15, 2022, 16:15

      There certainly is iron ore on Mars. Impracticality also includes superfluousness and the amount of money, and time needed to build a world ring and a Dysons sphere. We could build huge space stations around Earth and Mars etc. with artificial gravity, space telescopes, etc. for a small fraction of the cost including putting bases on other planets in the solar system. Then there is interstellar travel. We could meet our energy needs with much less expense and time. We have not utilized much of the surface of our Earth with solar panels, but we will in the future. The blocking out of all Sunlight at one AU would put the rest of the solar system into a deep freeze. The world ring would not have that problem. We might be able to detect that ring’s reflection of sunlight, but a Dyson sphere system would be invisible.

      • Geoffrey Hillend May 16, 2022, 15:29

        A Dyson sphere might have an infra red spectrum depending on how hot they the ET’s wanted the backside to get.

  • Brett Bellmore May 15, 2022, 11:45

    Any successful civilization isn’t going to do just this, or just that. They’ll do this AND that. They’ll stay around their star of origin, AND they’ll go colonize nearby stars, AND they’ll colonize Kuiper belt objects and rogue planets. They’ll remain biological AND become disembodied intelligences. They’ll terraform planets to be suitable to their existing form, AND modify their form to be suitable to existing planets.

    They’ll branch out, IOW. Diversify. Successful species become clades.

    • Adam Crowl May 18, 2022, 5:28

      Hi Brett
      Exactly. My hope for our species is to spawn many, many minded beings of all sorts of forms, some post-biological but with fond memories of their meat-bag progenitors.

  • David Claughton May 16, 2022, 20:06

    As has been mentioned (probably numerous times) on this site, no-one could live on the inside of a Dyson sphere or ring since there would be no net gravity (even Niven was forced to address this in his later Ringworld books, adding artificial gravity generators IIRC).

    What interests me, is what about the exterior of a sphere or ring? I’m by no means any kind of expert so I’ll happily be corrected, but I am I right in thinking it is possible for someone standing there to experience some component of the star’s gravity?

    Not, certainly, in the case of a ring spinning at orbital speed, but then AIUI it’s not clear that this would be necessary for a ring or would help stabilize it. But a ring operating as a statite, either not spinning or spinning relatively slowly, might work. Such a structure would be held in place by light pressure, perhaps using large mirrors whose angle or reflectivity can be adjusted to correct for perturbations. And the lack of daylight could perhaps be addressed by having large windows that refract starlight into the atmosphere. A race living on the exterior surface would of course also benefit from the ultimate in underfloor heating!

    A sphere would be even more interesting, such a structure could spin at orbital speed at its equator (although any atmosphere would bleed off into space there – not ideal!) and experience an increasing component of the star’s gravity at all latitudes north and south of the equator. Though one imagines it would a bit windy to say the least!

    • Michael May 17, 2022, 7:58

      There is also a tube design in which the a tube rotates on itself simulating gravity in orbit around the Sun.

      • Alex Tolley May 17, 2022, 13:59

        The Stanford Torus design was felt to be better than teh tube for creating artificial gravity through rotation as it could rotate more slowly given the strength of the materials at the time and therefore reduce Coriolis effects.

        One can easily be seen that stacking these tori to form a circumsolar ring could be an alternative to the tube torus design that rotates like a vortex, although I think separate tori would remain a better solution for incremental build out and flexibility.

        All these ideas are starting to seem a bit quaint, as many mega-engineering designs seem to be. Almost follies that serve obsolete purposes, such as vast populations of human flesh for no rational purpose other than a drive for “more or bigger is better”.

        • Michael Fidler May 18, 2022, 6:28

          Yes, Alex but the world population is exploding and as technology improves it will be easy to build such structures. The tube or cigar would seem to be the ideal design for it is similar to ships and has structural integrity without using mirrors or other attachments. The main point being artificial gravity being easy to produce through rotating around the long axis. These would need to be large structures but could be built from a small asteroid to see how well it will work.

          • Alex Tolley May 18, 2022, 13:02

            I wouldn’t characterize the global population as exploding, with a forecast maximum global population of around 10 billion. At the same time, populations are concentrating in cities, now at over 50% in the cities, and suggestions that we should move towards allowing the planet to “rewild” over 30% of the land surface area.

            The problem with the cylinder structure is that the rotation rate for 1 g causes more serious Coriolis forces due to the limits of the structure to withstand the forces with increasing diameter. The torus design was a way to increase the diameter and reduce the disorientating Coriolis forces. [You may recall that the small carousel in the crew module of the Discovery spaceship in 2001: A Space Odyssey was criticized for this very reason.]

            But let’s say we do build such a ring around the Earth to house a much larger population. [Such a structure was described in Lem’s novel “Fiasco” and what happened when it was disrupted.] Even before issues of cosmic or deliberate damage, the structure is prone to spreading diseases, and the same sort of social problems we see on the planet. Imagine a ring-sized war. I would think that separate structures would prove to be more flexible, at the same time as allowing some colonies to head for deep space and the stars should they desire. This is not to say that civilization couldn’t do both. But now with both a ring structure around Earth and separate colonies, what would stop the destruction of the ring by colonies and the murder of many billions of people, the damage to Earth itself, not to mention the vast cost and resources lost to that destruction? It seems to me that given who we are as a species, the bigger we build, the more vulnerable people are too determined actors in pursuit of goals through destruction. We have seen the result of the successful attack on 9/11. I fear for the deliberate destruction of underwater tunnels and very long bridge spans. And the megastructure of our cities that concentrates populations makes them vulnerable to weapons of mass destruction. All of which makes our social structures more authoritarian, which does not seem desirable to me.

            • Mike Serfas May 22, 2022, 19:12

              Great points! It occurs to me that the desire for normal gravity you describe would also tend to spread the colonies out. If you build two flat colonies linked by standard space elevator cables, they should be able to revolve around one another once a day for a nice verisimilitude of Earth, and require much less fuel for launches within the plane; but they’ll need to be roughly a geosynchronous orbit’s worth of distance apart to do that. Countable as members of “the Dyson Swarm”, these habitats could be anywhere in solar orbit (with somewhat more mirror required if nearer or further than Earth), but they would make uncomfortable neighbors in a planetary ring!

  • stephen May 27, 2022, 21:33

    Here’s Larry Niven’s essay, “Bigger than Worlds”, in case anybody here hasn’t read it…you have to be a scribd member to read all of it…


    I like the idea of an Alderson Disc, an actual disk with a star in a hole in the center, though it could just be orbiting a star, without a star in the center. I keep thinking the Disc should be atop a record player…

    • Shaun June 11, 2022, 11:54

      Surely the disk should be atop four elephants riding the back of a turtle?

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