# Would a Type 2 Kardashev Civilization really build a Dyson Sphere around their own sun?

We are currently estimated to be about 0.7 on the Kardashev Scale.

I am interested in the second level of the Kardashev Scale:

Type II

"A civilization capable of harnessing the energy radiated by its own star (for example, the stage of successful construction of a Dyson sphere), with energy consumption at $\approx4\times10^{33}$ erg/sec. Lemarchand stated this as "A civilization capable of utilizing and channeling the entire radiation output of its star. The energy utilization would then be comparable to the luminosity of our Sun, about $4\times10^{33}$ erg/sec ($4\times10^{26}$ watts)."

Theoretically, how would a Civilization achieve this level of scientific advancement and what resources would they require to be able to harness the energy of an entire star?

I am imagining something like a Dyson Sphere would require incredible resources to build, so wouldn't such a civilizaton need to have invented some kind of interstellar travel to obtain all the resources required? And if that is the case, would it be better to define a Type 2 Civilization as one that can harness the energy radiated by a star, rather than its own?

I am just assuming that in building a Dyson Sphere any planets orbiting that star would be negatively impacted by the building of a Dyson Sphere (Dyson Spheres extend out to the habitable zone of a solar system, where the Civilizations homeworld would be located). So there would be a transitional period where the Dyson Sphere isnt ready yet, but the planet your civilization lives on is being impacted significantly by the partly constructed Dyson Sphere.

Would a Type 2 Kardashev Civilization really build a Dyson Sphere around their own sun? Surely they would do this to another star? And if they would use another star, why does the very definition of a Type 2 Civilization specifically mention a civilization using its own star?

Am I missing something here? Or am I just over thinking this?

• Logistically the infrastructure already in place in the home system makes it the ideal candidate - plus it's most likely where the energy will be used. As all other planets (and indeed asteroids) would be consumed in the construction of the DS, there would be no impact on the other stellar bodies in the system. – Scott Downey Jan 20 '15 at 14:26
• It is hard to imagine a civilization that would completely consume the resources of a sun before expanding to other solar systems. That type of energy could disintegrate the planets of the solar system with little more than a hiccup on the surface of the sun (or at least our solar system). I can't imagine requiring more energy than that. – Neil Jan 20 '15 at 16:07
• I'm reminded of Gandhi's (perhaps apocryphal) reply when asked what he thought of British civilization: that it would be a good idea. Why would a civilization use, or have any need to use, that much energy? – jamesqf Jan 20 '15 at 18:40
• I think you do not mean 4*1026 watts, but either 4*10$^2$$^6$ or 4+E26 watts. – SJuan76 Jan 21 '15 at 0:40
• Dyson sphere's are cool much a little like ringworld, but it reminds me of one of the quotes of the characters in ringworld. Paraphrasing "why put all your eggs (population) in one basket. One of the reasons it makes sense to colonize space is even if the homeworld is destroyed then the species still survives in other worlds. – tls Jan 21 '15 at 8:55

My intuition is that they will not.

A Type II civilization would be able to get fusion energy, information, and raw-materials from multiple solar systems; it is capable of evolutionary intervention, interstellar travel, interstellar communication, stellar engineering, terraforming, star cluster-scale influence and can be expected to be so within 1000 to 2000 years from today and last for a few tens of thousands of years.

A Dyson Sphere derives its energy from Solar radiation in a similar way to how it is done today by solar panels but expected to be much more efficient.

My opinion is that a civilization that has mastered interstellar travel must have developed propulsion systems and a dominion over matter and space that are unimaginable today. In terms of comparisons could the Romans have imagined the engineering and energy methods of production or even the sources of energy today, their efficiency, most surely not to a large extent. In the same way I would think that in 2000 years new unimaginable methods could be devised. Who knows, perhaps extracted from the vacuum of space, mini black holes created in laboratory, antimatter produced in sufficient quantities in particle accelerators and other more compact and efficient forms of energy extraction than today even if at optimal efficiency conversion rates. I believe radiation extraction like today's solar energy is not a very efficient energy source as compared to fossil fuels, nuclear fission or renewable sources as its is today and my believe (I am no expert on energy) is that it will be the same in the future.

As a matter of comparison and to illustrate the difficulties of imagining the future Jules Verne the acclaimed writer was one of the best thinkers of technologies of the future and thought of submersibles and flying machines. However in his visions he imagined that personal travelling in late XX century would be done in aerostatic living rooms fully furnished with early XIX acommodations.

So imagining the future seems rather simple but it is extremely complicated as exponential growth in discoveries of different sciences provide paradigm shifts which can not be thought during large temporal scales.

• Your answer may not have the most votes, but its the one I agree with the most. – Jimmery Feb 12 '15 at 21:30
• I also agree, Dyson Sphere seems terribly primitive for very advanced civilisation - for example annie-plants seem much more resonable. – Mithoron Feb 17 '15 at 18:50
• Annie-plants? Greetings fellow Schlock Mercenary reader. Also being able to capture and utilize the energy from direct matter to energy conversion would negate the need to build something like a Dyson Sphere. But I can see a Type II civilization doing such a thing, if for no other reason than 'Because they can.' – Mr. Smythe Jan 27 '16 at 15:42
• The point about a stars energy is it is free energy, it is being produces whether you want it or not. Using it is the same reason we use use solar now even though we have more efficient energy production methods, The energy is free all you need to so is collect it. – John May 19 at 3:46

What is missing is parsing the requirement accurately.

Type II definition includes "capable of utilizing and channeling the entire radiation output of its star", and then continues to discuss the energy utilization.

This does not require actually capturing all solar radiation of their star. For example, we could harness the equivalent energy to all incoming solar radiation on our planet, through the use of fossil and atomic fuels. If our energy utilization is comparable, then we reach Type I. In the estimate of our civilization as being .7 - it should be clear that we do not actually capture 70% of all incoming solar radiation - we harness 70% of the equivalent.

If some civilization has some magic energy factory capable of putting out energy comparable to the output of their star, they meet the criteria. The reference to "its star" is just providing a benchmark to measure against.

Dyson spheres are frequently mentioned because they would be a clear identifier of using that much energy - it would be much harder to identify a fusion power plant burning the atmosphere of a Jovian planet, or part of their ocean, as an example of an alternative.

• Minor correction: Kardashev scale is not linear (I suppose logarithmic?), so .7 does NOT mean we consume energy equivalent to 70% of the Sun's radiaton. It's actually WAY less. – kutschkem Jan 21 '15 at 9:33
• @DarrylC I am a little confused. Type II definition includes "capable of utilizing and channeling the entire radiation output of its star", and then you say "This does not require actually capturing all solar radiation of their star" - surely draining energy from a Jovian planet is not comparable to being capable of capturing the entire radiation output of a star. – Jimmery Jan 21 '15 at 9:52
• @Jimmery: the Sun converts mass to energy at a rate of about 4 * 10^9 kg per second. The mass of Jupiter is about 2 * 10^27 kg. So if only you had the means to convert that mass to usable energy, it would keep you going for a while. Hydrogen-helium fusion only converts about 0.015% of the mass to energy, so sticking to that and using up Jupiter's hydrogen would give you about 40 million years of stellar output, I think. During which time the solar system would have double its current total energy output, assuming the energy your civilisation uses is ultimately radiated away as heat. – Steve Jessop Jan 21 '15 at 12:51
• Oops, missing a term in my back-of-envelope calculation. 1.5 million years. Anyway, the energy is there as a stop-gap if the definition of Kardashev Type 2 is taken in terms of how much energy it uses, rather than specifically being that it must from from a particular source. – Steve Jessop Jan 21 '15 at 12:57

A Dyson sphere is something that would be built over the course of quite a while. It would probably start as a ring around the Sun that just keeps getting bigger as energy needs go up. It would also be using up most if not all of the extra-solar matter in the solar system in order to create this. There would be plenty of habitat area on the pieces in space. the home planet would likely be deconstructed in the process off creating the sphere/swarm so it would have minimal impact on the planets in the system. Even a ring around the sun would have so much more surface area than the sun that 'keeping' the home world around for nostalgia wouldn't be worth the materials Earth represents.

EDT: Went to get some numbers.

Earth volume = $1.08321 \times 10^{12}\, \text{ km}^3$ (whole earth, including water etc.)
Earth orbit distance = $1.49597870 \times10^8\, \text{ km}$

So this means there is about $7.2048 \times10^4\, \text{ km}^3$ of earth for each $\text{km}$ of orbit, so if the earth was rolled out like play dough in its orbit to make a surface $0.5\, \text{ km}$ thick, it would cover a strip about $1.45\times10^4\, \text{ km}$ wide of the sphere to encompass the sun. This is not dealing with all the other matter that would be needed for plants and animals (including humans) to survive. For comparison, the full surface area of an earth-orbit Dyson sphere is $2.81\times10^{17}\, \text{ km}^2$ and the width of our surface is comparable to Jupiter's diameter at $1.4\times10^4\, \text{ km}$.

• Excellent point. A Type II Kardashev civilization in the strictest sense may not even be possible, since in order to come anywhere close to using all the resources of the sun, you will probably need to be a Type III Kardashev civilization if merely for the resources required. – Neil Jan 20 '15 at 16:03
• It would probably start as a ring around the planet  typo. Ring around the SUN – roryok Jan 20 '15 at 17:00
• @roryok - even prior to a full ring...it'd be more of a station that orbits the sun and builds towards being a ring, which in turn builds towards being a sphere – Twelfth Jan 20 '15 at 17:29
• @bowlturner So, building a Dyson Sphere is possible with the resources found inside a solar system - but would a civilization really do this to their own solar system? The affects of mining the resources required and building the DS would undoubtedly destroy their homeworld, and all the culture and historical significance it would bring. – Jimmery Jan 21 '15 at 9:43
• A civilization isn't necessarily limited to the mass of the planets in the solar system. If you have the technology to mine it, there is a lot of mass in the star itself. – Rubberduck Jan 21 '15 at 10:33

I imagine these kinds of Dyson spheres very close to the star. This means that if you could use one cubic km of matter for each square km of the sphere, about six earths would be enough to cover the sun. You wouldn't have to travel interstellar distances to get 6 earths of mass.

You can also use a geometric progression to help you out. If one square km section of sphere gets you enough energy over say, 20 years, to collect 2 cubic kms of matter from somewhere in the solar system and fashion them into two more sections of sphere, you could have the whole sphere finished in 800 years.

Also, the nice thing about a Dyson sphere is that you can leave bits of it open. For instance, with half a Dyson sphere, you can cover only the far side of the sun and capture vast amounts of energy without changing our own blue skies.

• Won't the "half-sphere" need to be steered in order to prevent it from blocking light from reaching the planet? – March Ho Jan 20 '15 at 17:39
• @MarchHo Not sure... once you set it spinning at the correct rate, you may only need small adjustments. You could also build a full, non-rotating sphere with each section pivoting like a shutter when it's not supposed to block the light. – Peter Jan 20 '15 at 17:51
• @Peter to spin it around at the same speed like the earth it needs his center of mass at the same orbit as the earth. – nbar Jan 21 '15 at 19:15

The one question I haven't seen addressed yet is that of the chaotic effects of moving significant quantities of mass around the solar system. Considering the intractability of the three body problem due to nonlinear effects, determining the long term stability of a Dyson ring or sphere system seems impossible. The best that could be done likely would be constant approximation and correction techniques used to maintain as much stability as possible.

• I tend to agree. Building a Dyson Sphere would be so destructive, that even if a civilization could do it, I doubt they would do it to their home system. – Jimmery Jan 21 '15 at 9:55
• I would guess that a Kardashev 2 civilization has solved the $n$-body problem. – Paŭlo Ebermann Feb 11 '17 at 16:26

Mankind's yearly energy consumption early 21st century was around $5\times10^{20}J$ Each year, while the sun outputs about $1.2×10^{34}J$ per year, which means we use about 10 femto-suns of power. To Nikolai Kardashev reaching out to the sun seemed like an obvious thing to do. Think about it: you have this immense amount of free energy streaming out into space, and essentially every Joule of it is wasted. You don't have to build a nuclear reactor, you don't have to worry about fuel. All you have to do is reach out and harness it. Since the intensity of the irradiance descreases with the square of the distance, you can maximize your capture and minimize the surface area needed for a particular amount of power generation by placing your generators closer to the source.

Solar Irradiance at the Planets

Mean       Perihelion        Aphelion

Mercury      9116.4      14447.5            6271.1
Venus        2611.0       2646.4            2575.7
Earth        1366.1       1412.5            1321.7


There is a vast, vast amount of matter in the Solar system, some of it conveniently outside of the massive gravity wells of the rocky and giant planets, so it's not an insane guess to expect that we'd use Asteroid Belt matter first, then the even larger Oort cloud resources. Obviously we wouldn't just make a Great Leap Forward and become a Type II overnight. We'd first have to reach Type I, defined roughly as making use of the resources of a home planet. If we take the Yearly solar irradiance of Earth, at $5.5×10^{24}J$, we still have a ten-thousand fold growth curve to ascend to even reach Type I. To do a Fermi simplification, let's assume 100% capture efficiency, so if you built solar panels at the Mercury perihelion, to reach Type I via solar you'd need 12 million sq. km. of panels, which is in the same order of magnitude as the area of Europe. Might seem like a lot, and it would doubtlessly require far more resources than we can currently even dream about harnessing, but the area of a sphere at the orbit of Mercury's perihelion is about 6.6e15 sq. km, so you've only built about 2 billionths of a Dyson sphere. Yeah, space is BIG. You can see from that that you can go a long way towards a Dyson sphere before anything at all would be noticeable on Earth, and with some level of planning, you can ensure that even a near-complete Dyson sphere does not shade Earth (or the other planets) at all.

We got a long way to go.

Ok, let's talk mass requirements, at a conservative 840 tons / sq. km, the structure required to bring us up to Kardashev I would weigh about 1E13 kg, less than the mass of Mars' Phobos, easily achievable using Asteroid belt materials (ignoring ancillary structures for energy storage, transmission, repair, etc, -- you can quadruple my estimate if you want, and then triple it again if you want to assume 30% efficiency, which still leaves you within an order of magnitude of the first estimate anyway). For a full Dyson sphere you'd need at least 5.5E21 kg of mass, which puts you around the combined mass of the asteroid belt. Throw in a few hundred massive Oort objects if you need to. So doable without dismantling planets. We might need to to some transmutation of materials, but with so much free power, shouldn't be a major issue.

Now, to the question of whether a genuine Type II civ would actually build a Dyson sphere, we can't really know. Perhaps a civilization so advanced has found far less crude methods to extract energy than from the wiggle of electrons on a slab facing a natural fusion reactor, from burning complex carbon molecules in a tin can, or from using atomic decay to boil water and using the vapor to make some brushes spin.

I recall reading once that there is enough zero-point energy is the volume contained by a regular mug to boil all of Earth's oceans away. And that's the stuff we know about. Who knows what wondrous tricks the descendants of Humankinds will come up with in the future?

• 8.4 tons per sq. km; if your source and my math (and google provided calculator) is correct. – user3082 Jan 21 '15 at 0:45
• 84 mg/cm2 -> tons per km2; $10^{10}$cm2/km2; $10^9$ mg in 1 metric ton. 8.4*$10^{11}$ /$10^9$= 8.4*$10^2$=840 tons/km$^2$. – Serban Tanasa Jan 21 '15 at 0:53
• Or perhaps an advanced civilization has figured out how to achieve things using less energy. For instance, not so long ago it took 60 watts to produce the 800 lumens of light that now takes about 12 watts; computer performance measured in Gflops/watt keeps increasing; figuring out how to build a space elevator gives you essentially zero-energy access to space... – jamesqf Jan 21 '15 at 4:10
• @jamesqf Indeed. Nontheless, humanity's energy expenditure has been rising continuously and exponentially since the early industrial age. – Serban Tanasa Jan 21 '15 at 12:50
• @Serban Tanasa: But humanity is not an advanced civilization :-) – jamesqf Jan 21 '15 at 18:40

That definition of a type 2 civilization is actually incorrect. It is not being able to harness 100% of the energy of a star, but energy equal to the output of a star from any source.

This could be dyson swarms getting 10% of the output of 10 stars, or it could just be billions of fusion reactors spread over 1000 planets. The source of the energy is irrelevant, it's only the amount that matters

Depending on how high you want to go with your tech, there are a couple of possibilities for creating a Dyson sphere that don't involve interplanetary travel for resources.

The first is energy-to-matter conversion. Theoretically at least, we should be able to turn energy into matter. So what you'd do is start with something like a ringworld and use the energy that collects to slowly grow into a sphere. This might follow organic patterns more than mechanical - think of a genetically created Startree that collects light with giant leaves (and I mean giant on a planetary scale), and uses that energy to slowly grow itself out until it envelopes it's entire star. You could even make it so perhaps these evolved, and are spreading through the galaxy with seeds.

The other possibility is harnessing the solar wind. This is composed primarily of charged protons and electrons, and with a bit of hand-waving you should be able to start harvesting it and converting that into other materials.

Both of these will likely be quite slow - I'll try and dig up some resources and see what the conversion rates would likely be later - but they would have exponential growth, the more you grow the more you can collect, so the faster you grow. You could even combine the two and do both to grow faster. But there are a couple of other advantages. First, you don't have to go anywhere else, and second, you don't have to mess around with destroying your current solar system to build it.

I don't think a Type II civilization would build a Dyson Sphere because I don't think Dyson Spheres are very practical. Larry Niven explained some of the physics/engineering advantages of a ring over a sphere in Ringworld, so it seems more likely that a Type II would build one of those instead (and Niven had to invoke implausible materials science just to hold the ring together). Of course, if you don't want to actually live on the Dyson sphere, you can have much looser constraints, but you still have the stability problem (active management of the sphere's distance from the star).

The main trick with a ring is that you want to spin it for stability (which helps maintain the shape, but doesn't do anything for the orbit/position relative to the star). A ring perpendicular to the ecliptic would occlude the sun 2x a year, unless you also spun it with the earth (but that would introduce a bunch of forces that you probably don't want to deal with). However, if you can engineer a ring that large, you can probably come up with a way to maintain a moving hole that lets the earth-bound light through.

The real question is whether a Type II civ needs to build a Dyson Sphere/Ring. If you build one small and close to the star, for energy only, you need to beam it around to where you want to use it. While the sun is giving you a lot of "free" energy, it seems more plausible that such a civ would prefer to generate the energy more local to the point of use, and would likely be able to harness fusion energy at much smaller than stellar scales. Even a "micro-star" near home planet orbit would probably be more convenient than aiming a giant stellar-energy maser at/near Home.

However, a Dyson Sphere may be constructed not for civilian use, but for military defense. The civ may deem it necessary to focus their entire star's energy to power a "stellar X/gamma-ray cannon" to deter/repel enemy invasions of their solar system. Whether this involves focusing the stellar energy with arrays of mirrors/lenses, or capturing it and converting it directly via a massive laser, the point is that Type II civs must believe that other spacefaring races may one day visit them, with less than peaceful intentions. Being able to blast them out of your solar system with the full power of your star may be considered an essential first step to becoming a credible interstellar civilization.

As others have noted, such a system can very likely be built out of a medium-sized planet or less--surely with the materials we see in most extra-solar planetary systems. And if you care about Home, it should be apparent why you build this device around Home Star and not Elsewhere.

• Dyson spheres are actually more stable than ringworlds - spinning doesn't really help. Dyson spheres are stable with gravity, rings are not - knock them off and they will start falling into the star. A sphere gets knocked out of position and will just sit there. A better design is a bunch of smaller ringworlds in planetary orbits, slightly offset so they get a 50/50 sunlight/dark cycle. – Dan Smolinske Jan 22 '15 at 3:57
• Not sure why you think a sphere is more gravitationally stable than a ring. When the sphere gets off-center, the side closest to the star will feel an increased force. Unless the sphere is extremely rigid, this will at least deform the sphere, and if the star is close enough, will likely cause the sphere to break/collapse. A spinning ring does not need to bear the weight of itself w.r.t. the star (depending on its angular velocity, of course). – Lawnmower Man Feb 21 '15 at 1:47

Peter's answer (and now Serban's as well) is mostly what I was going for (ie: get closer to the star for energy collection):

You only want a full DS (ie: cover the Sun at Earth orbit distance) if you need habitable space (and for some reason don't want to rely on artificials). If you just want the star's energy - get closer to it, which means less space / surface area need to cover the Sun. You don't need more than a couple millimeters of thickness of matter of coverage (if you're not so close that you've got heat dissipation problems) to collect energy - I mean, how thick is the solar cell in your handheld disposable calculator? Of course, you'd want something more robust/better/more efficient; but we'd probably be at least as good as that. You'd need some infrastructure to hold it in place, but not a lot, just enough to push against the solar wind. If you balanced it right, solar wind would counteract the Sun's gravitational pull.

Routing and storing all that power (90 billion H-bombs/second), of course, is a whole mess of other problems. Cabling, beaming power, whatever else - could eat up some matter.

But 'far side of the Sun' is a misnomer, and you don't want to give up the other ~1/2 of the Sun's output.

Also, you don't freeze the Earth, even if you cover a large percentage of the Sun. You leave a small belt of un-harnessed energy in the invariable plane (which is only a 6 degree belt of the Sun's surface), which will give all the planets just as much as they had been getting in the past.

That's for an unshuttered (read: less complex) system. For next to ideal, you could have something tracking each comet, and planet, and opening up a hole in your collector so everything gets the solar output it would've gotten before.

Of course, natural sunlight is vastly inefficient (but 100% natural; including all the bad things: CME, solar flares, variable output, etc). If you have that much collected/spare power, why not route it nearer each planet, and pour it out artificially, in a conditioned and nice, safe manner? Kinda the difference between a sunlamp and going outside for sun. Except you'd place your huge sunlamp far enough away that it illuminates the whole planet, and rotates around it mimicking the normal day/night cycle. Outputting everything but the neutrinos.

• The solar wind wouldn't counteract gravity, mostly because in a Dyson sphere the solar wind on one side cancels out the wind on the other side. – Thane Brimhall Jan 20 '15 at 18:11
• @Thane Umm, what? Gravity works on both sides, pulling you into the sun. Solar wind comes out of the Sun, pushing things away from the Sun. Now, bigger (and closer) your item is, the more gravity effects it. So lighter, further away == less gravity pull. Which means the sweet spot might not be as close as you could get with other limitations (heat dissipation, etc). Further away, means you'd need more mass to construct it. – user3082 Jan 20 '15 at 18:35
• @user3082 "You'd need some infrastructure to hold it in place, but not a lot, just enough to push against the solar wind." - surely you would need enough infrastructure to make sure the Dyson Sphere doesnt collapse into the Star, or get ripped apart due to gravitational forces? – Jimmery Jan 21 '15 at 12:04

The mass of a single habitable planet is small relative to the mass of a solar system. Slightly less so if you eliminate the star.

Taking that planet apart to provide more orbiting solar collection is relatively unimportant -- in our solar system, the mass of the Earth would be a rounding error.

If we did have a incomplete Dyson sphere (from disassembling the other planets), the amount of time we'd be blocked from the sun, and the power needed to generate a "flashlight" that would replace the sun during that time, is pretty low. Assuming that the incomplete Dyson sphere blocks the sunlight no more than it would if it was randomly constructed, only 0.000000001% of the energy it collects would be required to be emitted by a "solar flashlight" to replace the sunlight that it blocks from reaching the Earth. There may be inefficiencies here, but we have lots of zeros to eat up said inefficiencies.

Note that using more energy on Earth than we receive from the Sun is relatively infeasible without building geological scale radiators: keeping a high-energy civilization cool on a plant is tricky. You could deliver it more efficiently than the above "solar flashlight" plan, and the blocking of the sun's rays by the partial Dyson sphere might be well worth it.

I speak about blocking the sun's light as being a problem, as that is about the only one I can think of from having a Dyson Sphere between the Earth and the Sun. Mass wise, the entire rest of the solar system being used to construct a Dyson Sphere within Earth's orbit wouldn't cause any orbital issues: Jupiter is 0.1% of the Sun's mass, and the rest of the solar system is dross. A 0.1% increase in the sun's effective mass might be detectable, but I doubt it would be significant.

• The mass of the earth is only a rounding error when you include the mass of the sun. The sun is 99.8% of the mass of the solar system. Jupiter takes up more than 2/3 of the rest of the mass. So unless you are harvesting material from the sun, the earth is going to be very important for raw materials. – bowlturner Jan 20 '15 at 19:21
• @bowlturner no, Earth is 0.3% of the mass of Jupiter. Now, Earth does have some nice rocks in it: the other inner rocky planets add up to about Earth's mass. So there is that. – Yakk Jan 20 '15 at 19:25
• @Yakk, Seems to me, however, that any civilization beginning construction of a Dyson sphere wouldn't really care what elements are already present. They'd just take the atoms apart and recombine the protons, neutrons, and electrons as they pleased. – Brian S Jan 20 '15 at 22:38

Couldn't find what I believe to be true, so answering despite being late to the party:

A Dyson sphere is instable, requires a lot of material which could be used elsewhere, and is easy to destroy (for a civilisation advanced enough to build one).

On the other hand, a swarm of satellites with solar panels, covering the whole sun, is stable, requires comparably few resources, cannot easily be taken out, and does everything a Dyson sphere does, except look great.

Ergo, it is very unlikely that any Dyson spheres will ever be built, as there are more practical ways to harness the energy of a star, get comparable real estate, and so on.

As to mega structures without a sun in the middle, they would probably look more like a ring world or a very large blood cell than a Dyson sphere, as, once they get big enough to consider gravitational collapse, rotation is the only way to keep such a structure from turning into a hot star or supernova.

I am imagining something like a Dyson Sphere would require incredible resources to build, so wouldn't such a civilizaton need to have invented some kind of interstellar travel to obtain all the resources required?

If said civilisation were to have the technology to turn energy directly into matter then there would be no problem finding enough raw materials. this technology actually has been demonstrated in a lab already! Scaled up it could provide enough matter to build a Dyson sphere

The issue with conceptualizing what a Type II Civilization would or would not do is that they would have the benefit of thousands of years of experience. If I were to tell you what a Type II Civilization were to do it would be like explaining to someone alive during the days of the Roman Empire how to alter image brightness in photoshop or something of that sort - it just wouldn't make sense.

• why not, they had a conception of art, including paintings. More than that they accepted as plausible that statue can be made in the way it will be alive(or something like that, not sure it was Romans, and not Greece). But yes, make direct connection between scientific advances and energy capabilities is bad idea. – MolbOrg Apr 16 '17 at 8:51

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