[VariableStar]

One aspect that I find problematic with the idea of Dyson spheres is: where will the energy be dissipated? In the civilization's planet's surface? It seems to me that it would create serious energy imbalances and soon climate disruption.

[Karellen]

One solution to this is the Matrioshka brain, which consists of many nested "shells" around the star. Each one absorbs the radiation from the hotter shell inside it (or from the star, if the inner shell), and radiates waste heat to the cooler shell outside it. The temperature differential between the inside and outside of each shell is what allows work to be done. The outer surface of the outermost shell, maybe 5 billion km (~35AU, or a bit further out than Neptune) from the star, will be close to the ambient temperature of the interstellar medium, and will radiate heat at only a few Kelvin into it.

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

[micw]

So instead of seing a hot "small" spot (the star), we'd see a warm (a bit above absolute zero) but very large sphere?

[javcasas]

Well, seeing it may be an exaggeration. It would be barely less black than the space around it. Though it may shadow other stars and distant objects.

[quadragenarian]

Isn't the point (and I could be wrong) with a Dyson sphere that it should have a spectrum that approaches that of a perfect blackbody radiator? Or would any radiation that sneaks past the swarm drown out the blackbody spectrum?

[javcasas]

> Isn't the point (and I could be wrong) with a Dyson sphere that it should have a spectrum that approaches that of a perfect blackbody radiator?

Pretty much. The lower the temperature of that blackbody radiator, the higher energy you can extract via temperature difference. Until you reach the background radiation of the universe, which could be considered the lowest possible temperature of a thing that still extracts energy.

> Or would any radiation that sneaks past the swarm drown out the blackbody spectrum?

If that's the case, you can improve your sphere and capture that extra energy.

[cletus]

See my comment for a more detailed explanation but the short version is: a Dyson Swarm (preferred term) is merely a cloud of orbitals (ie not a rigid shell; there is no known or even theorized material with the strength to build a shell that large). The orbitals dissipate heat into space. That's what the infrared radiation is that they're looking for.

[VariableStar]

I see that. My point is that if the captured energy is used, and thus ultimately dissipated as heat, on the planet's surface, that planet is sooner than later going to have climatic imbalance.

[cletus]

There are several possibilities here.

First, the Earth already receives a ton of energy from the Sun that is "wasted". We estimate that at about 10^16 Watts of power, compared to humanity's energy usage, estimated at 10^10-10^11 watts. So Earth has a ton of energy dissipiation "built in" that we're not "using".

Second, there is some inefficiency and thus heat dissipation in converting solar output into usable energy. Doing that in space means a bunch of heat dissipation happens in space rather than on your planet.

Third, it's relatively straightforwward to counter any increased heat dissipation on your planet by reducing that solar output that hits your planet. How? You build something at the EArth-Sun L1 Lagrange point. Reducing that solar output that hits the EArth by 1% would likely be unnoticeable to us but could cool the Earth significantly. Also, what do you build there? Well, lots of things. More orbitals, solar power collectors, etc.

Fourth, how do you get power down to a planet? There are several candidates. One is to beam it down. This adds a conversion cost. But here's another: you build a n orbital ring [1] 100-150km above the EArth's surface. There are a ton of reasons you'd want to do this: interplanetary travel, cheap travel to and from LEO and easier travel across the planet (ie up to the ring, down to another point on Earth on cable cars, basically). But consider this: it gives you a rigid structure to attach solar power collectors to and you can run power transmission cables down from the ring to the planet's surface.

[1]: https://www.youtube.com/watch?v=LMbI6sk-62E

[ericd]

I wonder how much reaction mass we’d need every year to keep something stationed at a Lagrange point to block 1% of earth’s light, for combatting global warming. 1% of earth’s light would be a heck of a solar sail.

Looks like 1% would be 13.3 watts per meter, cross section of earth yields ~5.4x10^14 watts. Assuming perfect reflective, multiplying by 2/c gives 3.6x10^6 N. So like half of the thrust of one of Saturn V’s engines? So… a lot of reaction mass, or some really powerful ion engines and a ton of power. So maybe not the most practical idea.

[cletus]

It's true that the L1 Lagrange point is unstable so would need some station-keeping. It's an issue but it's a solvable issue. For one thying you have a bunch of energy to spend. For another, the solar wind itself can be used to provide momentum going out if what you have there is sufficiently light.

But there's another option: statites [1]. Statites are solar power collectors that have an incredibly thin sail to the point that they don't need to orbit the Sun at all. This means you have a bunch more options for positioning. Clearly the Earth will continue to revolve around the Sun but a sufficient swarm of statites on the EArth's orbital plane could have the same net effect as, say, driving beneath a bunch of stationary umbrellas.

Or statites can themselves do station-keeping at L1. They can angle themselves to provide momentum in a bunch of directions. Or they can orbit the L1 point similar to how JWST orbits L2. Their ability to use the solar wind for directional momentum could satisfy station keeping needs.

[1]: https://en.wikipedia.org/wiki/Statite

[ericd]

Oh very cool.

Besides the unstable nature of L1, my main concern was actually mitigating the light pressure of the light being blocked, in order to not be blown earthward, but I guess that’s not really considering that these things could manipulate their solar sails/shades like the statites you’re mentioning.

[pests]

Are you capitalizing it like EArth for a reason or just a typo? Just wondering as you use it a few times but are flip flopping.

[yreg]

You don't redirect all the energy to the home world. You dissipate the heat into space.

Which is why you can't hide, anyone who aims their instruments on your system will detect the heat and see that the star is obstructed.

[kobalsky]

if a civilization needs so much power they build a dyson sphere they probably have terraforming nailed.

that kind of technology probably takes hundred of thousands of years of technological development and we have had electricity for how long?

[pests]

I think you are overestimating by many orders of magnitude.

[vitiral]

Planet? Dyson swarms orbit a SUN, not a planet

[fikama]

Its not where energy is sourced but wher its used. And assuming it will be civilisation's planet like Earth. The whole energy of the swarm will be used there. - It just has to increase temperature (due to additional energy on the planet)

[alchemist1e9]

If they can build a sphere or swarm megastructure then obviously they would have build orbiting habitats either from scratch or terraforming planets or astroids.

[exe34]

> The whole energy of the swarm will be used there

that sounds like a made up problem. the Dyson swarm isn't to collect energy to send to the home planet. it's to collect energy. where that is used is going to be wherever it's needed. mining the asteroids, local computing (the cloud is no longer just a computer on earth, it's the cloud of the swarm elements), powering interstellar trips remotely, etc. the only thing that needs to get to earth is the imports of goods and services.

[aurareturn]

Terraforming a planet is another use case.

[vitiral]

Why would you use the energy on a planet? Clearly you would use the energy in space, probably in some of the same satellites that are gathering energy

[mcmoor]

There's Mathrioshka Brain https://en.m.wikipedia.org/wiki/Matrioshka_brain which uses the energy then and there for computation.

[TheLoafOfBread]

That actually makes no sense. You can't use (destroy) energy, you can only run it through processor, which will change it into heat while transistors inside are switching on/off. It is like a water wheel doing work by water flowing through it, but ultimately amount of water before and behind water wheel is same.

Thus the question still stands, what happens to heat in such thing? Does it get recycled by some unknown device? Then it is closed system, you don't need input from outside. It won't get recycled? Then such device needs to get hot from dissipating that heat.

[kiba]

Earth already do this. We only use some energy for our purpose.

[sdwr]

We are using the sun's energy that hits the earth. Some as light (which turns into heat), some as electricity (which turns into heat), and some as plant food > animal food > oil (which turns into heat)

A Dyson sphere would capture the sun's energy that leaves the sun, not just the fraction that hits earth. Using that energy on earth would release far more heat than our current activities.

[kiba]

It would indeed be inadvisable to use all of sun energy captured on Earth, but they're not going to be used entirely on Earth.

[maxerickson]

The Earth radiates away solar energy, it's only here for a (figurative) moment.

Human activities that convert other energy into heat don't particularly impact this process, the amount of energy from the sun is much larger.

[kjkjadksj]

My assumption is if you demand the energy needs of a dyson swarm you’ve probably figured out how to convert this energy to work with none of it lost to heat.

[TheLoafOfBread]

Then why would you need a Dyson swarm at a first place, when you can just recycle heat energy through your systems with almost 100% efficiency?

[kjkjadksj]

Presumably to fuel things we could not conceive of given our relatively pedestrian in comparison energy needs. But, there is no free lunch. Work takes energy away from the system even with no heat loss by virtue of doing something with that work using energy, as we know from our most basic physics courses that assume a frictionless spherical cow with no heat loss.

[TheLoafOfBread]

Energy can't be destroyed. That's basic physics. Work of any kind is just turning usable energy into unusable heat. If you would have such device which can take heat and turn it into usable energy, then you would just need to take a system, charge it and it would be working forever. Unfortunately this is some Clark-tech level of magic technology.

[kjkjadksj]

How is this hard to imagine for you that heat loss can be minimized to the point of being effectively zero? Even with present tech we have a variety of heat loss efficiencies. No energy needs to be destroyed this is just what you convert in this case all converted to work.