A Dyson sphere around a black hole

There is no point to go and harness energy around a star or a black hole, when you can just produce it locally with a lot less resources/waste and materials. The sun itself is actually very inefficient in producing energy.

There is no need to harness the sun million of km away, when you can recreate it in your home planet. The only way to produce a dyson like of sphere, is to tame an over-heated sun, and reflect away un-needed energy. But there is no point to build one to just harness it.

It makes great sci-fi stories, but that's about it. Scientifically, it just doesn't make sense.

Lets say, you want to manufacture new planets/planetary sized spaceships. You would need very big fusion reactors and you probably want to save the special fusion fuel for those, when they are on their voyage to other worlds. Because then they need fusion.

But why build a fusion reactor, when you already have a big one avaiable?

The additional benefit is the amount of power. With the power of a star at your disposal, beaming your energy using lasers and microwaves, even if only 1% efficient, would instantly solve the energy needs of any planet in a solar system. If we did it, we could instantly colonize all planets in our solar system because things like "running an AC on Mercury" or "Hovercraft in Jupiter Atmosphere" becomes trivial when you have limitless power.

Heck, you could start projects like moving planets in orbits or collecting astroids to built a planet if you wanted.

Black holes are the stage after that since you can use a spinning black hole to convert a given mass into energy at >10% efficiency (given E=MC^2). That would allow a civilization to power multiple solar systems at the cost of a few planets per year.

Granted, the sphere is difficult to build, but that is what you have dyson swarms for.

Umm...

The sun is about 2×10^30 kilograms. The rest of the solar system is about 3×10^27 kilograms and we kind of need it to live on and make things with. Put in other words, the entire solar system including the Sun is 1.0014 Solar masses. Why not go with the process we have rather than fusing everything we have to do the same thing?

If you're saying that we don't need that much energy then I think that's pretty meaningless since we have no idea what we could get up to or need in the far future.

Well, hydro energy is just there, requires comparatively little ongoing maintenance, and has less catastrophic failure modes.

I think the same caveats work for Dyson spheres.

Few planets are similarly sized as Earth already btw, although with varying densities.

After that your efficiency declines until... Well you end up with fusion reactors that look like the sun. You also end up fusing all the mass that we need to live our lives on and make stuff out of.

If you don't think a civilisation could ever need the amount of energy that a Dyson sphere could provide, that's fine, we don't need one.

But if you imagine a civilisation that does need the energy a Dyson sphere can provide, then they make a lot of sense.

And I just assume that a civilisation advanced enough to build a dyson sphere, can handle the non trivial orbital mechanics, too. But maybe still cannot travel FTL. So indeed rather choose to build planets, or planet sized space stations.

That would require lots of energy and maybe the need to harvest the sun directly and control the light going out towards the planets.

It's unstable without active stabilisation. The stabilisation has to be perfect because otherwise you get massive distorting spherequakes propagating through it, which will make it a very uncomfortable ride for a short time and will soon tear it apart.

A perfect spherical stabilising solution with components and sensors that are light minutes - or possibly light hours - from each other is impossible because of the signalling delays.

Ringworlds have the same problem. Even if the ring is made of infinitely strong unobtanium, it won't stay in a useful orbit for long enough to be built, never mind inhabited.

Swarms have more potential, because you can build them with sparse shells and move things around to handle instabilities. But you still need massive computational effort to keep swarm units from colliding with each other, possibly at very high speed.

None of this matters, because the limiting factor for civs is collective intelligence, not energy.

We already have access to far more energy than we could possibly use on earth for any technology that's actually buildable. But we're not using it because we don't have the species IQ to make the right choices.

That is a lot of mass to extract and transport to the power stations (accelerate, decelerate). So it just makes sense to only needing to build the facilities to collect the power from existing sources (stars, black holes) without the logistics of transporting the fuel.

Moreover, the space around a star or black hole is real estate that would go unused otherwise, while asteroids, moons, ... are more likely usable by such an advanced civilization.

[1] https://www.quora.com/What-would-the-estimated-weight-of-Mou... (I took the highest estimate in the first answer)

This. The entire “moving planets” and “powering asteroids” theme is just a projection of our historical aggressive reproduction, which is not even a requirement for an advanced civilization. Earth alone could serve us a few billions of happy years, if we didn’t have the happy urge to multiply until critical shortage. That’s far from intelligent, imo.

With that, being happy does not seem to be a universal quality of life; some would even posit that the opposite is true (ask Gautama B.)

I don't see humans completely overcome their biological nature any time soon, if ever.

Humans are exceptional in this regard as that can expand beyond the limits, and at the expense of, all other known species. Humans are also exceptional in that they could extinguish themselves, either by choice on their own folly.

It's the inevitable end-result of Bitcoin.

Not intentionally, but we've managed to create societies where reproduction is extremely costly in every conceivable way and are even working to convince people that reproduction is outright tyrannical, sexist, and environmentally genocidal.

The instinct will certainly remain, but population decline seems inevitable the way things are going. Even a few decades from now, the human breadbaskets of the developing world adopt the anti-natalist systems we have in the developed world.

Why couldn't a Dyson sphere have uncoordinated movement joints distributed all around to absorb those spherequakes? Or even active locally coordinated ones?

I'm sure a Dyson-sphere-building civilization would figure this out.

https://en.wikipedia.org/wiki/Projections_of_population_grow...

Given incidence of dam bursts like the 1975 Banqiao dam failure[1], with an estimate death toll of 26,000 to 240,000 people and flooding of over 12,000 square kilometers, I'm inclined to disagree with this assessment.

[1]https://en.wikipedia.org/wiki/1975_Banqiao_Dam_failure

I don't see any requirement why an intelligent civilisation would need to grow its population forever. It seems far more intelligent to attack the cause of the energy need instead of building crazy structures like Dyson spheres around black holes.

Repeat at 90 degrees, 45 degrees, etc until you have a sphere.

You're right that speed-of-light delays make negative feedback control difficult, but it might be possible to have rockets that sense local photon flux on the inner surface of the ring/sphere and fire autonomously when it increases.

https://en.wikipedia.org/wiki/Star_lifting

Even without considering what to do with the resultant mass star lifting is just good stellar husbandry for a civilization looking to last.

Of course. But they reach a limit. Only one species is able to exploit resources, and the biosphere, to its own ends. Agriculture, mining, and technological advancement are peculiar to humans. All of these permit us to live longer, with fewer setbacks, and in environments no other animals can survive (space, and soon other planets). Are these not exceptional traits?

We can also engineer a virus, or deploy strategic weapons that could wipe out our entire species (and a bunch of others). Is that not exceptional?

So what if it's inefficient? It's happening anyway and it's not like you can siphon the hydrogen off and do anything else with it.

What kind of purism is it to not tap the largest energy sources in existence because you bristle at their inefficiency.

But some animals have agriculture (ants?) and some plants exploit metals in the soil (phytomining)! Still, Sapiens are the champs.

That's just what species are selected for. If you have two competing populations and one multiplies and expands just slightly better than the other, everything else equal, then that one will eventually outcompete the slower one.

But it does not have to be that way. Humans are the top predator, so no competition here. We could make do with limiting expansion if we chose to. It's still life, but without this "quality" that you seem to consider a necessity.

The technology required to build a tier 1 swarm is not advanced. All you need is the ability to build a thin reflector (aluminium foil would work) with radio and a basic onboard computer. You do not even need onboard propellant because a reflector can generate the required thrust for minor corrections with solar pressure alone. These reflectors can then concentrate that light from close in to the star out to collectors further out in the system. This essentially makes your habitable zone as large as you want since you can also light entire planets this way and only utilize less than a percent of a percent of your total energy budget.

The real challenge is having good enough automation to construct and send these stations out without requiring too much oversight, and getting good enough at construction off earth (since you really don't want to deal with that gravity well). We're definitely close to having the required automation technology and we should be performing the first manufacturing off earth before the end of the next decade.

Artificial fusion can be made far more efficient than the fusion in the core of our sun, yes. However, the sun outputs enough energy to light 2 billion earths worth of surface. Moreover, it essentially contains all of both the hydrogen and rocky material in the solar system with the other bodies being essentially a rounding error in comparison, so even in a controlled fusion based economy, you would still create a Dyson sphere like construct since you would be using that star as your main fuel and mass source.

Black holes though? They make even aneutronic fusion look like a fire cracker in comparison. You're getting less than a percent mass energy conversion with even the best theoretical fusion models there are, whereas with black holes, you can get anywhere from 16% to 40% depending on the technique and mass range of the black hole. Stellar black holes have so much energy inside that they would dwarf even our star (consider that their progenitors were stars with far more mass than our own and with an even bigger disparity in power output). They also last for periods of time that make even red dwarfs look like still births. If you could make artificial ones in the gigaton and megaton ranges, then they can also make for amazing batteries. In this case, you are able to tap the hawking radiation emitted for power and this promises potentially even greater efficiencies than the stellar mass ones (albeit, you would not be gaining a net power gain here, this is strictly for power storage and potentially gravity generation purposes).

And it's such a banal obvious claim I'm making, and yet it's being downvoted to oblivion. I can't imagine cane toads doing anything I mentioned.. or even ants having some sort of hegemonic control over the fate of all other species.

We have no predators but we do have a lot of existential threats. The more we spread out the more chances we have of surviving. If we sit on our hands and stay put we’ll wind up like the dinosaurs one way or another.

> it just makes sense to only needing to build the facilities to collect the power from existing sources (stars, black holes) without the logistics of transporting the fuel.

Yeah OK, but then you have to transport your entire reactor to the fuel. For that matter, you also have to transport the energy where it's needed once you've harnessed it.

[0] https://en.wikipedia.org/wiki/Kardashev_scale

With D + D fusion (easy to believe compared to CNO) an interstellar civilization could be essentially independent of stars.

I'm sure part of the resolution of the Fermi paradox is that dry inside-the-frost-line planets like Mercury, Venus, Earth and Mars are not the generic places you find life.

If things were a bit different I could see a would-be Galileo on an less cooked version of Io or a more cooked version of Europa who looks at the Earth with a spectroscope and sees oxygen and has a huge amount of trouble with his local "church" that thinks it is impossible to have life on a planet with less tidal activity, less radiation, inside-the-frost-line dryness, etc.

Even if creatures like us became interstellar we might have millions of kilometers of condominiums and shopping malls in the oort cloud and could care less about inner solar system planets.

Seems like it would require, at minimum, several planets worth of raw material.

Yet there are actual dust rings and discs in the sky surrounding stars for long periods without falling into the star, being blown out of the gravitational influence of the star, or condensing into planets on life-evolving timescales.

Some of them are pretty occlusive and get hot (~ 1000 degC) and are consequentially observational targets for MATISSE at the European Southern Observatory. It's not at all my field, but I gather https://theskylive.com/sky/stars/kappa-tucanae-star is a principal hot dust belt target.

Retreating towards my islands of comfort, there are plenty of small rocky bodies ( flavour of "dust" in the sense of the previous paragraphs) in the solar system that are in no immediate danger of colliding, plunging inwards, or escaping to infinity in spite of ablation from solar radiation, differential radiation pressure and other effects that lead to the term "active asteroid". Most of them will be there, and have been there, for billions of years despite evil Jupiter trying to mess them up. Speculating a little away from my weak-gravity island, I would be surprised if there were no ongoing organic chemistry reactions in the more icy carbonaceous active asteroids in our solar system. It's not a huge leap from that to an asteroid-based power station that slowly produces some alcohol(s) at much denser concentrations than the wood alcohol molecular clouds like in W3(OH) astrophysical alcohol megamaser region. [1]

Icy-carbonaceous bodies in closer orbit and with sufficient spin angular momentum (perhaps supported by the Yarkovsky effect) for cheap thermal management could in principle host terrestrial photoautotrophs suitable for processing into biodiesel. Impractical at small scale, but maybe useful if one has many billions of such "power plants" around a single star. And of course, one could use the photoautotrophs to feed microbes more suitable for the production of more complicated molecules like, oh I dunno, oxycodone (for fun and profit).

(A sufficiently dense dust belt in the goldilocks zone could even make use of ideas from the panspermia hypothesis, so that one only has to populate an initial fraction of the bodies with economically useful microbes, and the little bugs will reproduce and spread throughout.)

One can easily imagine greater efficiencies from engineering non-organism power collectors and storage systems instead of adapting blue-green algae to output biological compounds, and one would probably want to do this for a dust that is in bulk much hotter than the vast majority of our solar system's asteroids tend to get, or if practically the entirety of the dust is manufactured rather than already in place ready for populating with mats or colonies of economically useful microbes.

Returning to the paper at the top, I think the only advantage a black hole gives is that a sufficiently large one might have a much larger localised "goldilocks" volume which one might seed with small icy-carbonaceous body light-powered power plants, compared to having many such belts around many many stars. However density of production could be an important advantage, even if one has to move a swarm of objects to it rather than adapt a swarm of substrate objects already in place.

Super-concisely: Earth has a lot of oil, inefficiently, seemingly by accident, after a long delay from initial "activation" of the biosphere, and with a fairly high collection cost because it below so much atmosphere (and water and rock) through which it would have to be lifted for off-world use. Sufficiently advanced aliens (and perhaps future humans), if they wanted oil, undoubtedly could do better than Earth.

- --

[1] http://www.star.bris.ac.uk/mark/w3oh.html but don't inhale it, the W is for Wood alcohol (hydroxymethane).

If you really want to extract mass from a star, just wait long enough, or find one ready to release a suitable amount. There are plenty of options from CMAs to flares to UV Ceti style flare stars, to deflagrating white dwarfs, novas, and supernovas. Let the star's nuclear energy do the "heavy lifting", eliminating all the problems catalogued before the "... plasma jets hundreds or thousands of astronomical units long ... [t]he details of extracting useful materials from [that has] not been extensively explored".

(The linked article at the top discusses relativistic jets driven by million-solar-mass and larger black holes. The jets are likely to be more constant and/or more predictable than natural mass outflows from stars, but extracting and storing energy from that is even less "extensively explored". An option in between is to use the natural mass flow from a companion star onto a compact star (white dwarf, neutron star, black hole) by sticking the moral equivalent of a water wheel into the stream. It's just a (compared to water hot & sparse) fluid flowing downhill, and there are plenty of examples in our galaxy.)

Why do people keep insisting on the Dyson concept as though it was real, even though it's just the fanciest thing we can imagine with our current understanding of physics?

The same way in the 19th century nuclear power couldn't be envisioned, there's definitiely a bunch of technology we don't know about now that an alien civilization could be using; we could even be observing this right now and we would be none the wiser. Talking about Dyson shperes, or swarms, or rings, and then concluding that there's now alien civilzations because we can't see them is just anthropocentrism, failing to consider other possiblities

One solution is for the expansion joints to have infinite range— a disconnected swarm of platforms which is exactly what a Dyson swarm is.

If the argument is that somehow the former is more environmentally friendly, then I don’t understand why we should accept dystopia for an uncaring god.

A.) Keep it in place and not hit the star/black hole.

B.) Avoid it being demolished by intercepting every piece of space trash, comet, asteroid in a solar system?

https://www.cold-takes.com/this-cant-go-on/

Hypothetical scenarios can be constructed for both methods of power generation (What if Braidwood plant melts down, somehow killing the 5 million people living within a 50 mile radius? What if the Three Gorges Dam busts, inundating an area inhabited by 600 million people?[1]) Either way, it is far from obvious to me that hydro has the superior safety profile, especially when their fatality rates are on the same order of magnitude even when the Banqiao incident is removed[2]*.

[1] https://web.archive.org/web/20210620174812/https://www.japan... p/opinion/2020/09/01/commentary/world-commentary/big-china-disaster/

[2] https://ourworldindata.org/safest-sources-of-energy

* Sovacool et al. (2016), the source of the data in [2] includes a hydro fatality rate per tWh 2.4x larger than nuclear when Banqiao is included.

When in the past, unanswered, mystery questions like these were finally answered (for example "how come light seems to appear in discrete packets?"), the answer ended up being a door to a completely new understanding of reality, and not a little footnote question at the End of Physics

So yeah, when there are no more unanswered physics questions, I will consider that the laws of physics have been exhausted. Right now that's not the case.

That's an interesting take. It does seem that we're more limited by our poor choices than by underlying physical limits. We invest ridiculous amounts of money into weapons by comparison to things like nuclear and fusion power.

EDIT: Inb4 the downvotes.

This is precisely the appeal of Larry Niven's Ringworld concept. You instead take a slice of that sphere and spin it around the star and generate gravity through centrifugal force. They can take a number of configurations but the default one would give you the equivalent of 2 million earth's worth of living space inside one continual surface. This is obviously hugely mass intensive and having a ring of that kind of radius spinning at the tangential velocities required for the equivalent of one g of simulated gravity (around 1200 km/s) requires materials so magically strong that they make graphene look like soggy tissues. The only material that could do this even in the theoretical realm is magmatter, which would be materials constructed out of magnetic monopoles, something that has been predicted to exist by some but has yet to be observed.

However, you could construct one using known materials by creating a superstructure around the ring that is much more massive and orbits the other direction at normal orbital speeds for a body about an AU out from the sun with the ringworld electromagnetically suspended from the superstructure, normalising their collective momentum to zero. That obviously greatly increase the mass requirements but this could mostly take the form of hydrogen and helium which is far more abundant than heavier elements and would be usable as fuel for fusion reactors. That superstructure can contain many smaller rotating habitats and the whole thing could be used as a vast habitat for microgravity living as well - something I envision as many humans doing as living on worlds with gravity by the time we would have constructed one of these.

You also want to have a superstructure because at such a high tangential velocity, if a human being of 80 kg struck the ring from the outside, it would blow with the kinetic energy of a thermonuclear bomb. Point defence is absolutely necessary and the superstucture offers both an excellent shield covering the non sun lit side of the ring and a great platform for hosting those point defence systems. Ringworlds are also not in stable orbital configurations over astronomical timescales so you need to maintain their orbit through corrective thrust. This could be done through light sails which would also be appealing for it's mechanical simplicity.

Ringworlds are very mass intensive especially if your civilisation still has no access to unobtanium building materials and I don't think this would be something we would ever build a lot of in our particular solar system but even with that mass cost, you could easily gather enough rocky material from the sun to build a few and still have the vast majority of people living in other far smaller structures (but only relative to a star encompassing ring) in the swarm.

You could mine it from asteroids, which have plenty of base metals. There's already a speculative market for investors wishing to mine them. The only thing is; the technology for transporting it around doesn't exist yet. (We can land probes on them however for recon, but that's about it so far!).

I've heard Dyson spheres referred to as a K2 Civ's wonder or vanity project.

  Science advisor:
    Eternal leader, those pesky Alpha Centaurans just completed work on a galactic wonder, the Dyson Sphere! [+1000 energy, +100 habitat]
    Shall we redirect our own Dyson Sphere efforts to a new project?

  Eternal leader:
    Damnit! Yeah fine whatever, let's switch to building a Kemplerer Rosette.

Is this really the limiting factor? I've always assumed the limiting factor was distance. I can envision a species that is more intelligent or more altruistic. But what I can't envision is how collective action is coordinated over interstellar distances. It would seem to me that the extreme communication delay would cause any interstellar civilization to inevitably break apart into a bunch of separate "local" civilizations.

If tomorrow all ants disappear then most land-oriented ecosystems would just collapse.

We humans are having so egoistically anthropocentrical world views that it's not even funny anymore.

Solving world hunger does not need expansion. Stopping climate change does not need expansion. Preventing the upcoming antibiotics crisis does not need expansion. To the contrary, expansion makes all those things worse or has even started them in the first place.

Actually this is another megastructure process known as Star Lifting. And it's not just hydrogen you can siphon off - the sun, by virtue of its immense size, contains the overwhelming majority of every element in the solar system.

Unfortunately because they burn up so quickly, the hydrogen isotopes we would use in fusion reactors are actually incredibly rare in the sun. The sun is estimated to have about the same amount of deuterium as Earth's oceans. On the other hand, Helium-3, another potential fusion fuel, is very abundant - about 10-20 Earth Masses are present. Still though, burning all this helium 3 at the same energy production rate of the Sun would only last us 870,000 years - a drop in the bucket compared to the lifetime of the sun.

This problem is twofold. First is that much food is produced far from many poorly nourished people. This problem is totally solvable by modern transport. There are enough charity donations to prevent hunger everywhere.

Second, and most importantly, it's the social structure what prevents ending the hunger where the hunger still is. People prevent production and distribution of food in order to keep the social structures where they are on top, or are fighting to be on top. They themselves are not hungry, and don't care about the rest much.

> Humans are also exceptional in that they could extinguish themselves, either by choice on their own folly.

Could you imagine ants finding a method to annihilate themselves? I don't claim that animals are unintelligent, but we are unique in our ability to create technology to achieve almost any goal, no matter goal's 'sapience'.

> If tomorrow all ants disappear then most land-oriented ecosystems would just collapse.

I don't dispute this, but it's completely orthogonal to my claim. Humans have disrupted the biosphere in a manner that is unprecedented since when meteor strikes and seismic events were still shaping earth

A Dyson sphere is foolish because one can simply build a small local fusion reactor instead of using the giant free one nearby?

Imagine a sphere of reflective particles around a star. Planets within would never experience nightfall. Free energy would be everywhere. Sounds useful.

Moreover, such a solar system would be difficult to detect. If it is mobile, and uses a low-signature form of propulsion such as UFOs exhibit, then it would be extremely elusive.

This solves the problem of someone launching stealth asteroids at one's base at relativistic speeds.

Moving a solar system presumably requires tremendous power. Using a star as the fusion reactor presumably helps.

On Earth, none of those are available in the quantities needed to provide sufficient energy for us (close to a planetary civilisation in energy needs) on the scale of millions of years.

If you want your civilisation to not deplete available energy in the next million or so years and to allow for growth of energy demands in that time, you're going to have to make use of star power.

A planet only gets so much starlight that it becomes a limiting factor in energy budget. The easiest next step is to make more use of the abundant energy source next door: your star.

There are other options, e.g. using black holes. But those are orders of magnitude more challenging: black holes are extreme stars (extremely far from any developing civilisation).

On Earth, we've seen that every leap-frog in civilisation (fire, agriculture, industrialisation, ...) increased the available energy budget by orders of magnitude. There's not that many orders of magnitude left on this planet to grow further; if we want more, we'll need to get it from elsewhere.

Alien civilisations that remain bounds to their planet's energy budget similarly must remain stuck at a certain level of energy use. They can make advances in efficiency, but their total energy budget is capped.

It's not very hard for ants to collectively commit suicide.

The age of star formation is mostly over yes, but not completely yet - and I believe it's figured that no red dwarf can have reached even a tiny fraction of its lifespan so far?