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Comment by fullstackchris | Hacker News Reader

Always have to comment on the meme Dyson spheres posts with the following: has anyone ever thought, for one second, that a civilization capable of building these massive energy systems would actually be capable of generating energy in other different ways that we can't even imagine? This whole "Type I, II, III" civilization crap is stupid because it is based off one paper, of one guy, who had a creative idea. Props to him for the creativity, but millions of scientists every day have possibly creative ideas about space fairing civilizations. Its like sci-fi novels creeped into real science. Literally ape brain to just "wrap a star and capture its energy!"

I think most people "like" the idea because it's so tangible. But that doesn't make it any more or less likely that it actually exists or makes sense.

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OK, let's talk about energy generation for a minute. If we assume there exists some completely new physics, then... that could be anything. Advanced civilizations could take on any form. We can speculate all day about magic and elves too.

If we don't assume any new physics and / or thermodynamics, then that constrains the discussion a lot. We have two basic ways of generating a lot of power, fission and fusion.

Fission uses fissile materials, which are relatively rare, not just on Earth, but in the Universe at large. There's plenty enough for us at our current energy generation needs, but not nearly enough for a galaxy spanning civilization. That leaves us with fusion.

Fusion reactors, as currently conceived use Helium-3 or something like that. There's enough of that around the solar system to power a civilization for a long time, even though the mass of oddball elements like Helium-3 make up a very tiny fraction of the total mass of the solar system (which is mostly the Sun with a smidgen of Jupiter).

Most of the solar system's mass is plain hydrogen: one proton and one electron.

Is it possible to fuse most / all of this mass in the solar system? Yes. We won't go into the details, but trying to fuse regular hydrogen (regular protons) together is highly impractical outside of the core of a star. Preferably a red dwarf type star which can more completely burn its fuel than our own Sun will, and live a lot longer to boot (a trillion years vs. ~10 billion for the Sun).

So now we're talking about some kind of solar collectors, and if you want to collect _all_ the energy from a star, you want a sphere of some sort. Or a swarm of objects in orbit achieving the same effect.

Hence Dyson sphere / swarm.

> and if you want to collect _all_ the energy from a star,

For what? What are you doing with it? Not to forget the fact that all energy used eventually turns into heat. All of it (with the exception of electrochemical transformations). You're bringing all of that into Earth you're cooking everybody alive.

How are you bringing that energy from the sphere to (wherever place)?

Putting solar panels on Earth itself works much better. Heck, make a Dyson sphere on Earth (facing outside), that makes more sense.

It is typically assumed that by the time you are making a Dyson swarm, that most life exists digitally. And spread out through the solar system.

So in the best case scenario, you are powering computronium, upon which trillions of sophonts live out their digital lives. Hopefully doing some science, or at least playing some interesting games. A vast distributed network.

In the worst case scenario, Blockchain and spam emails.

Either way, people will put that energy to use.

With a Dyson swarm, energy is received on the inside, towards the star, and heat is radiated outward. Lower power systems can run off the heat radiation of the inner swarm similarly. It is all eventually released as very low level heat, but diffused across the entire outer surface of the swarm. No hotspots... because someone would come along and use it.

The Earth would also likely be deconstructed by this time, so don't worry about the biosphere, there won't be any.

> For what? What are you doing with it?

One example: powering lasers for light sail ships to colonize other star systems.

You are not pushing a light sail ship to another star system, sorry.

Light sails are "theoretically" possible but you don't need that much energy to push something that's feasible to push.

Or better, there's a better source of light radiation: the sun itself. No need for a laser, just use a focusing mirror and you can have 100x more pressure than just from the sun itself.

Light sails are practical, and have already been tested in orbit.

https://www.planetary.org/articles/lightsail-2-successful-fl...

Light from the Sun isn't coherent, and you can't focus it with mirrors very far away. Lasers have many orders of magnitude less divergence when talking about distances measured in light-years.

> Light from the Sun isn't coherent, and you can't focus it with mirrors very far away. Lasers have many orders of magnitude less divergence when talking about distances measured in light-years.

To expand on your point, those characteristics become even more important when using the light received to decelerate at your destination, though it is worth noting that there are alternative means of deceleration that don't have the same requirements (eg. electric and magnetic sails).

Why not? Light sails can reach 10% the speed of light, and sending out thousands of colony ships in multiple directions seems like a feasible way to colonize a galaxy relatively quickly.

As the other poster mentioned, harnessing the sun's energy and turning it into a better form suited for light sails is the way to go. Sailing on the solar wind within a star system is a different tech with a different purpose.

> Heck, make a Dyson sphere on Earth (facing outside), that makes more sense.

I’m missing something here, because even if we decided to build a Dyson swarm of course we are going to start with putting solar on and around Earth because this is where all the stuff we care about is.

That’s just the first step in a journey of a miles miles. (TIL where that quote comes from: https://en.wikipedia.org/wiki/A_journey_of_a_thousand_miles_...).

This seems so obviously it can’t be what you’re taking about though.

It's premature to say what's practical with fusion and what isn't. It's entirely possible that we find a way to build an efficient hydrogen fusion reactor. In which case it might not make sense to travel so far away from our planet just to collect energy from photons when that costs more than just doing the fusion ourselves. Remember it's actually more expensive to travel towards the sun than away from it (because you have to shed velocity relative to the starting velocity on Earth.) It's too arrogant to think we know the answer to that now.

> It's premature to say what's practical with fusion and what isn't. It's entirely possible that we find a way to build an efficient hydrogen fusion reactor.

Would it not surprise you that fusion in general has been studied extensively by physicists for nearly a century? It takes very high temperatures, pressures and quantum tunneling to get two protons to fuse.

Here's some reading to get you started:

https://courses.lumenlearning.com/physics/chapter/32-5-fusio...

Or read about how the Large Hadron Collider works.

It doesn't surprise me. Your arrogance does though, I didn't expect you to double down on an unreasonable position. How can we possibly know what we don't know yet. Not about how fusion works in theory, but about the limits of the economics of fusion reactors at any point in the future.

What I'm saying is it's too soon to say what's possible with fusion and what isn't. We don't even have a break even reactor yet. We can even say for certain that we ever will.

> It doesn't surprise me. Your arrogance does though, I didn't expect you to double down on an unreasonable position.

I'd give your criticism some consideration if I thought you had even the slightest knowledge of what we're talking about.

Let's talk about the core of the Sun, where p-p fusion takes place. Remember, I said at the top: no new physics.

The core of the Sun is hot, like really, really hot. How hot? 15 million Kelvin. So no solid material ... made of atoms ... can be anywhere close by because it would vaporize. You can talk about active cooling or whatever, and that's not going to help. But let's assume we have some magical material that can deal with that temperature, and keep going.

We're going to skip the pressure that really hot plasma is under, and assume we have terrifically awesome magnetic confinement that can handle that. We don't actually, but let's move on.

The other problem with 15 million K is that all that energy wants to radiate away. Yes, you want to absorb some of that radiation (hard gamma, by the way, very nasty) as part of the energy generation process, but if you let the plasma cool off, the reaction rate drops. "Cool" in this context is relative, at 7 million K, the reaction rate is very close to zero.

The last problem we will talk about today is volume. The above conditions get us a fusion power density of... 276 watts / cubic meter. To have a fusion plant that generates 1GW of power, we'd need to contain a cube 153 meters on a side of 15 million Kelvin plasma.

Oh, wait, that assumes the magnetic containment and everything else requires zero power to run. So we'll have to go bigger, much bigger.

Are you starting to understand the scale of the problem... trying to design a proton - proton fusion reactor?

I am not the arrogant one, I'm just listening to the fusion scientists who have been studying how all this works.

> We don't even have a break even reactor yet. We can even say for certain that we ever will.

And here you are expressing doubt that we'll achieve even the easiest kind of fusion reactor. We have achieved fusion, just to be clear. We can reach the temperatures and pressures to see some reactions.

Assuming civilization does not collapse (climate change, war, etc) we will be able to engineer a fusion reactor that is some kind of practical.

But it won't be proton-proton.

Edit: Actually, the material issues mentioned above probably won't be an issue, as long as the confinement is good. You still have the issue of keeping the plasma hot enough for long enough.

But the scaling issue doesn't go away unless you go with even higher temperatures and pressures.

> I'd give your criticism some consideration if I thought you had even the slightest knowledge of what we're talking about.

Doesn't sound like an arrogant person to me...

FYI I understand how magnetic confinement fusion works at a high-level, as a non-scientist.

There's a lot of assumptions you're making here. First that we need hydrogen-hydrogen fusion. Many current reactor designs use deuterium and tritium (nasty stuff tritium.) It doesn't have to be plain hydrogen, it just has to be elements common enough that we won't run out (or that we can breed using neutrons - that gamma radiation you talk about - from the fusion reactor.) Some designs are more exotic with fuel using isotopes of helium, lithium, boron. Second many current reactor designs use a plasma temperature well above 15M K. I've heard of 100M K and that's not an upper limit.

But you're also making assumptions about the volume of a reactor - we don't even know if magnetic confinement fusion will end up being the best design, but if we assume it does - then stronger magnetic fields really decrease the volume required. In fact development of stronger magnets based on high-temperature superconductors may be the biggest breakthrough in fusion research in the last decade - see https://news.mit.edu/2021/MIT-CFS-major-advance-toward-fusio...

> And here you are expressing doubt that we'll achieve even the easiest kind of fusion reactor.

We don't have a break-even reactor yet by the way - we have achieved fusion for short periods of time and by putting in far more energy than could be produced. That milestone is probably still at least a decade away.

My point again is that we don't know enough to be able to say what's possible and what isn't. History is littered with people arrogant enough to say what we can never achieve and humans keep surprising. Sometimes even things that seem impossible - like detecting planets around other stars when the physics of optics is very clear that an optical telescope could never directly image a planet in another solar system. That was wrong on two fronts, one it doesn't account for gravitational lensing, and two it didn't account that we might cheat and detect planets indirectly. And so the arrogant people were wrong again. Don't make that mistake.

> We have two basic ways of generating a lot of power, fission and fusion

I think there are more. Like radiation from evaporating black holes.

> I think there are more. Like radiation from evaporating black holes.

Evaporating black holes?

Yes, if you are willing to wait a very, very long time, and have collectors over a large area.

However, if you want to get stuff done before your protons evaporate, you could instead throw matter into a black hole, thus increasing its mass. The radiation given off by the accretion disc is substantial, and can be collected... over a large area.

IIRC, the mass-to-energy efficiency is something like 40%, which is really good.

They are a little difficult to set up however...

I mean, we're talking about timescales and construction projects like Dyson spheres. It's entirely feasible that people with such technology could create microscopic black holes that evaporate quickly for these purposes. Hawking radiation at this scale is substantial.

Ah, yes, I do recall reading about that somewhere.

That is an interesting prospect, with a very high mass-to-energy efficiency. Of course it requires careful management of inflowing matter. And you can shut if down if needed by stopping the inflow, assuming you have enough stored energy to recreate the micro black hole sometime later.

You'll probably enjoy this video:

https://youtu.be/EzZGPCyrpSU

Good channel too.

A Dyson sphere is technically possible without any new physics with a few decades of work. By contrast, while we have the physics to analyze how black holes much smaller than a proton would behave, we have no plausible way to go about making one.

> A Dyson sphere is technically possible without any new physics with a few decades of work

Not a chance. I disagree 100%. The materials science and orbital mechanics for coordination alone are way beyond our capabilities.

Dyson sphere as conceived by Dyson himself is a swarm of orbiting objects, not a literal sphere around a star (that's Star Trek interpretation). We could start sending out solar panels to orbit the Sun today, and start adding space stations later this/next decade.

It doesn't count as a Dyson swarm until it captures a large percentage of the sun's output. As I said, that science and the computational power needed to coordinate those kinds of orbital mechanics are beyond us.

You'll see.

It doesn't all have to be at a single distance from the Sun. Some objects can be as far as Earth is and other objects can be at Mars level, at Merkur level or wherever else. There's plenty of space for this to be too hard.

That doesn't matter if we're talking about scenarios where a significant fraction of the sun's surface area is covered. That requires enough mass for each fragment to make such a loose "shell" that they would influence each other gravitationally and perturb each other's orbits.

Not to mention that that much surface area would catch a lot of solar wind, causing all sorts of rotational moments that will need constant correction. The control theory needed for this sort of thing is complicated and N body problems are undecidable in general.

It would catch approximately all the solar wind. "All sorts of rotational moments that will need constant correction" means that, if your orbiters are thin enough, they don't need reaction wheels or thrusters to change course to avoid an imminent collision — just solar-sail louvers. An occasional collision is unimportant to the viability of the system, like dust settling on solar panels, or dermis cells dying in a follicle to grow hair.

N-body problem instances are never undecidable in the automata-theory sense; you can answer any question about the future trajectory from given initial conditions straightforwardly, if slowly, with interval arithmetic. The question of whether initial conditions exist that evolve to a given result is undecidable, but as with undecidability results in general, we do not need to decide it in order to build a working system, only to prove the optimality of a given program.

You seem to be making up reasons to justify a preselected conclusion without bothering to think about whether they are true or relevant or not, and I wish you would not do that.

Not significantly. Do the math: a thickness of 100 microns with existing silicon solar panels, or perhaps as little as 0.1 microns, out of, say, 1 AU (1.5e11 m). We're talking about filling 2e-15 of a 1-AU sphere with solid orbiters, totaling roughly the mass of Earth's moon, if we're using current silicon solar cells, and potentially a few orders of magnitude less than that.

You could use a smaller or larger radius, resulting in higher or lower irradiance and higher or lower orbiter density, but we have a lot of experience with different kinds of solar panels at 1 AU, so we know it will work.

No, there's no problem with orbital dynamics, control, computation, communication, or any of that nonsense. 50 years ago those were potentially challenging problems, but not now. Today the only remaining obstacles for a Dyson sphere are manufacturing and politics.

It's just a bunch of automated drones flying in formation. Trying to calculate their orbits ahead of time in any kind of detail would be a fool's errand, instead we'd just use solar light pressure to steer them as needed (they would be very thin, there's no point to making them thick).

With really thin sails (0.78 g/m^2) they don't even need to orbit, as they can use light pressure to compensate for gravity (what Robert Forward termed a 'statite'). The light they reflect hits other sails on the other side, but this isn't a problem if they are distributed uniformly.

I wonder how practical it is to sustain right-sized artificial black holes. Small ones should irradiate much more.

Existing proposals use a plumb bob mechanism or directed light traversing the ergosphere in analogy with sound amplification via linear or in this case rotational energy transfer rather than relying on the feasibility of a complete sphere to absorb any randomly directed radiation from the interior or accretion disk: https://news.ycombinator.com/item?id=30402679

Eh, it's typical retrofuturism type stuff, extending current technologies quantitatively rather than trying to predict categorical changes in available tech.

Also the issues of dyson spheres aren't that bad. they could for instance channel the heat loss energy in a narrow beam out of the galactic plane so at least they'd be hard to spot by other galactic observers.

Frequently; that comes up in basically every Issac Arthur video on the topic.

Unless such a civilisation can dump the waste heat as something other than infrared light or send that waste to somewhere other than the visible universe, it’s still extremely visible.

I think it's not only about energy generation but what would massive civilization without dyson spheres imply:

1. sidestepping thermodynamic laws - to allow massive energy use without detectable waste heat

and/or

2. sidestepping time lags - so that the system does not need to be bunched as closely together as possible to allow for efficient communication and flows of material

Dyson Spheres are fundamentally unphysical. The stability constraint on a complete sphere turns out to be less of a problem than it might seem, but there are still huge issues with stresses - Sphere Quakes.

And before you can build a full Sphere you have to build a partial Sphere. Which is where stability will really kill you.

Dyson Swarms might be more practical, but you still have a computability problem because you have an insanely huge number of objects in orbit and you somehow have to keep them from colliding with each other.

Not so much a three body problem as an n body problem. With a built-in light lag delay of (at least) minutes.

I'm not sure if anyone has modelled that, but it would be hilarious if the computing and station-keeping power requirements turned out to be a significant proportion of the available energy,

But you did not exhaust all the options. What about spherical constellation of energy gathering sails that stay mostly in place? Can autonomously maintain their position with help of solar wind.

Or even pure radiation pressure. They balance out somewhere around 10^-3 kg/m^2; thinner than that and you have a solar sail.

> spherical constellation of energy gathering sails that stay mostly in place?

Wait, what? You can't have a spherical constellation of unconnected stuff that mostly stays in place, that's not how orbits work. You can have a single orbital ring, but a sphere consisting of many circular orbits would have these orbits intersect with very large relative movement. If you're thinking about non-rotating constellation where the gravitational pull is balanced by solar wind, the problem is that they have gravitational interaction with each other and the planets so it's inherently unstable, they would "want to clump up" and as soon as they do, the balance is disrupted as the same mass has less solar pressure and it starts to fall into the sun.

To me it sounds like "flight heavier than air is impossible!!!!".

Why would a device that has 1kW/m2 at its disposal at all times, be fundamentally unable to counteract gravitational interactions? We are not talking about planetary gravity wells here but much weaker ones.

It’s probably just that colonizing the entire galaxy is really hard and no society ever has an economic need to. Populations don’t expand exponentially forever, the recent explosion is an effect of the industrial revolution, and any species that gets a certain size breaks up into subspecies and starts competing with each other.

There could very well be individual dyson swarms out there and we haven’t seen them or haven’t realized that’s what they are. But building them around every star in the galaxy is something I’ll never understand why it’s taken as a given.

I fully agree with the sentiment.

Speculation what form future tech takes should have be broad and uncommitted.

* Given our current knowledge, Dyson Spheres are essentially impossible (just lesser-known point is that unlike planet, full Dyson Sphere or Ring World would not be attracted to the star that it would be built around, so it would have to be guided to move with it - see Larry Niven's Ring World Engineers). * What a civilization would do with all the energy, whether it would want it, etc are other unknowns.

As you say, turning one person's clever idea into a whole research program at the very least neglects other great scifi novels.

I agree. A hyper-advanced race would probably want to disassemble the star and use its hydrogen for something more efficient than the main-sequence nuclear process, which is pretty wasteful.

The odds that anybody smart enough to be able to build such a thing would not be smart enough to recognize what a bad idea it is, is closer to zero than any mere human can conceive of.

People smarter than you, like Freeman Dyson, have thought otherwise. More generally, a human putting long odds on what anybody much smarter than mere humans would do is self-evidently a way to lose bets. Can you imagine a dolphin or a crow successfully predicting the outcome of the US's withdrawal from Afghanistan?

Any crow, dolphin, or half-wit would have predicted US failure in Afghanistan. Donald Rumsfeld was Secretary of the US DoD at the time of the invasion. There is no public evidence that he predicted failure.

Freeman Dyson never proposed building anything even vaguely like what is called a Dyson Sphere, and was famously irritated at having it attributed to him.

> Dyson had also proposed that the search for extraterrestrial intelligence (SETI) programs should “search for sources of infrared radiation” to “accompany the recently initiated search for interstellar radio communications.”

https://www.inverse.com/science/how-many-dyson-spheres-are-i...

I remember some discussion of this point in his autobiography. He wasn't talking about the Star Trek version, but certainly the intercept-all-the-sunlight constructions we're talking about.

Anyway, intercept-much-of-the-sunlight. It would be seriously impractical to arrange to intercept radiation leaving a star at high latitudes. And, being made of trillions of independently-orbiting tree-like things, there would be as many small gaps where native starlight would squeak out.

Yeah, I considered getting into that, but it was late and it didn't feel that important.

Not mere trillions, on the order of 10²¹ if we're talking about trees similar in size to existing trees. The latitude is irrelevant, because the rotation of the star has an insignificant effect on the orbits of objects at distances hundreds of times its radius. Yes, there would be many small gaps. That doesn't significantly affect the utility of the artifact.

All of this is obvious to anyone who does the math.

There is no reason to assume that trees in a weightless environment would be limited to sizes seen under 1G acceleration. Metabolism would need to be very different, too, because evaporation is not available to drive transport.

Obviously the rotation of the star has no effect. But the need to move between habitats precludes substantial differences in orbital plane (look up orbital plane maneuver, these take exceptionally large delta-V), keeping things close to the ecliptic.

Doing the math produces a picture very different from what you imagine.

If Alice is going from Arcadia Habitat to Zenith Observatory, and Bob is going the other way, and they're of equal mass, it's a momentum exchange. In a developed solar system the transport network could make a lot of hay out of this principle.

Even if the cities do cluster in one plane, that doesn't imply the power stations will.

I think you're wasting your time; cf. https://news.ycombinator.com/item?id=30408971

Probably. And I probably just wasted more time on another thread from a week ago. Going to take tomorrow off from HN.

Wasting my time, anyway.

Unavoidable until you make the effort to level up a bit, but at least we can avoid wasting the time of more advanced people.

Power stations? You mean trees?

Probably if you believe that dolphins and crows understand human politics and battlefield tactics, and you believe trivially falsifiable things about Freeman Dyson (https://en.wikipedia.org/wiki/Freeman_Dyson#Dyson_sphere), there is not yet any point in talking to you about subjects like this. Maybe in five years.

I'm glad you liked Energia though.

Probably not. Energy is (at least to a high approximation) a conserved resource and stars are the most massive objects around besides black holes.

Based on our understanding of science. But 200 years ago the idea of having a conversation with someone 1000 miles away seemed quite impossible. Is it so hard to imagine that out of the possibly hundreds of millions of civilizations in the Milky Way, someone has found a way to extract energy from the universe in a way which seems physically impossible to us?

I’m always very open to the idea that there could be a lot of physics we don’t understand yet. We could be at 0.1% of an understanding of the basic laws of the universe. I’m not saying I think that is likely or unlikely, but I do think it is possible.

> But 200 years ago the idea of having a conversation with someone 1000 miles away seemed quite impossible

In 1822 the Chappe optical telegraph had been in use since the Revolution, and the electric telegraph was ~20 years away. You'd have had to be singularly unimaginative not to envision an eventual extension to instantaneous voice.

Ah, I guess I was referring specifically to radio transmission. You could say 400 years ago if that matters. A distant civilization could be 1 million years ahead of us.

I definitely agree with you. I’m not a physicist but I did watch a ton of pop sci growing up and saw so much stuff about Dyson sphere, Fermi paradox, etc. I got so bored of it and hate how it drags down most discussions about potential alien life etc. The Fermi Paradox itself was supposed to proof we’ve got something wrong, not that we’re alone in the universe and something scary lurks.

I think the answer may be that most civilizations never need or want to colonize everything in sight. It could also be political: no species gets to the level of being able to build structures like this without breaking up into competing polities. We think about colonizing everything because we’re still in the mode of a creature who evolved on a planet and spread out everywhere.

It’s probably the case that with fusion dyson swarms aren’t used due to the opportunity cost of building them. In 1-200 years we’ll find the idea of surrounding the sun with metal as laughable as there being canals on Mars.

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