Many centuries from now, a race of advanced AI who now rule humanity, but who are aware that they themselves are leaderless, begin the construction of a huge dyson-sphere fuelled computer brain to rule over them, (hereafter referred to as a Dyson Brain).

This Dyson Brain encircles the sun at 0.1 AU. The material needed to build it came primarily from Mercury, (though some came from asteroids) as the rest of the sol system is inhabited.

However, the builders of this Dyson Brain, being of an ecological frame of mind, do not want it to have a profound effect on Earth or the rest of the sol system for that matter. That is, they don’t want it to absorb all the sun’s energy output, and so make it diffuse accordingly.

So, what is the maximum percent of the sun’s energy that can be absorbed by this Dyson Brain, before it starts to have a noticeable effect on the climate of Earth and the rest of the planets?

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    $\begingroup$ I think you mean the maximum percentage in the last paragraph, not the minimum percentage. $\endgroup$ Mar 2, 2023 at 21:03
  • $\begingroup$ Related. Had you thought (as suggested by ideas in the other question's answers) you could build one which let sufficient light through onto the "important" planets, it should be smart enough to do that. It becomes a question of working out how much is "sufficient" then. It could enable on-the-fly climate modification, maybe even weather control. $\endgroup$ Mar 2, 2023 at 21:27
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    $\begingroup$ why do the AIs want to be ruled over and if they do want that why don't they just elect one of themselves? $\endgroup$
    – user253751
    Mar 3, 2023 at 18:42
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    $\begingroup$ Why do AIs need to waste time and effort building a bigger AI? $\endgroup$
    – Ian Kemp
    Mar 4, 2023 at 17:56
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    $\begingroup$ @IanKemp That question is masterfully answered by Douglas Adams in *The Hitchhiker's Guide to the Galaxy." The first one only tells you the answer to the question of Life, the Universe and Everything. You need the second, bigger one to know what the question was in the first place. $\endgroup$
    – JBH
    Mar 6, 2023 at 20:04

8 Answers 8


Give your Dyson sphere an equatorial window

All of the inhabitable parts of the solar system lie along a single plane meaning that we don't need any of the sun light escaping above or below this relatively narrow band. So, if the equator of a Dyson sphere were some sort of giant window or mesh, you could capture most of the sun's energy, and still not effect any of the planets or moons anywhere inside of the solar system's habitable zone.

A mesh or window will of course still absorb some light; so, you can compensate by using reflector holes or gigantic laser arrays above and below the window to redirect some extra light back along the equatorial plane to compensate for what is blocked by the window.

Since the sun has a dimeter of about 1.4 million km and your sphere has a radius of about about 15 million km, this means that from the perspective of the Dyson sphere's surface, the sun would take up about about 5.34 degrees in the sky... that said, you may be able get away with a little smaller than 5.34 degrees because of the aperture effect of the distance between the sphere and Sun. From the Earth for example, the sun takes up about 0.53 degrees in the sky and the Sphere takes up about 6.36 degrees because the sphere is closer to the Earth than the Sun. That means the window would only need to be about 4.81 degrees of the sphere's surface area to not effect Earth... but the farther from Earth you want to protect, the closer to 5.34 degrees you need the window to be.

enter image description here

Or, just use reflectors/laser arrays...

Another thought is to only use reflectors/laser arrays and aim their beams of light at just the worlds you want to maintain. In this case, you just reduce the cross sectional area of all the planets you want to maintain from the total power of the sun. In this way, you could make all planets, regardless of distance, get the same amount of sunlight as Earth even further aiding in terraforming.

This will certainly increase the power available to the AI, and comes with some interesting bonus abilities, but it also means if something ever goes critically wrong or the AI ever decides to go genocidal, that all life could be more easily snuffed out... so you'll need to decide if your AIs value redundancy and safety or efficiency as their higher priority.

The Black Body Radiation Problem

As mentioned in comments, the sphere itself will heat up from the sunlight and be scattered making the whole sphere glow with equivalent IR energy as the whole sun. While this energy will be in too low of a frequency to see or be useful in photosynthesis, it will still heat up all of your solar system by a significant margin.

To counter this, your entire sphere will need to use infrared mirrors to reflect the sphere's blackbody radiation back into space away from the inner worlds. If you angle the reflectors just right, again, you can use the black body radiation to help warm Mars and the outer moons for terraforming while protecting the Earth and Venus from excess heat.

Of course, IR reflection is not perfect. Your best IR reflectors (gold) can reflect about 99% of IR radiation, but it is unlikely that Mercury will have enough gold for this; so, you will likely need to use silicate based refractors backed with a polished aluminum reflective surface which can get you into the 95-98% efficiency rating.

If you ever so slightly constrict the window and/or reflected light the Earth gets, you should be able to maintain the Earth's current heat at a negligible reduction of visible light despite the sphere's blackbody radiation.

The Issue with Dyson Brains

Any computer the size of a Dyson Sphere will inherently be much worse than a computer the size of a warehouse. In computing, there is an issue called a bottleneck where the full power of one aspect of your system can never be fully utilized because some other aspect of your system is too slow to feed in or send out information from the more powerful aspect of the system. Electrical impulses like to move around inside of a computer at relativistic speeds, which sounds really fast, but once you start trying to compute billions of processes per second, every inch of wire starts to count. The problem with making a brain the size of a Dyson Sphere is that if the brain is computing something on one side of the sphere, and then needs some data from the other side, the whole program will have to stop computations and wait for about 290 seconds (2 * radius * pi / signal_speed) to get that data; so, while a small data center can run billions of parallel processes billions of times a second, a Dyson Brain can run an unfathomable number of processes in parallel, but grind to a painfully slow crawl trying to do anything in sequence making it too slow to actually do anything useful.

This leads to the conclusion that the ideal super brain is actually MUCH smaller than this... but that does not mean your AIs won't want a Dyson Sphere ruled by a super intelligence anyway. One reason for the Dyson Sphere may be redundancy. Your super brain may actually exist as a sort of CDN of thousands of copies of the same intelligence all over the sphere insuring that the leader brain (or one of the identical copies of it) is always accessible for inquires. Or there could be a sort of hivemind architecture where the Dyson Brain is actually countless AI warehouses working in a sort of democratic method to arrive at conclusions. In this case, it is less of a Dyson Brain and more of a Dyson Congress The brain may also have millions of data centers that it can spool up for special projects that operate independently of the central intelligence of the leader AI. From a governance standpoint, think of these as committees. They are not the leader AI, but exist to take load off of the leader's thinking power.

But even this would all be something that could fit on Earth and use a negligible amount of our planet's current power output, much less need a Dyson Sphere. This means that the Sphere likely does not exist to power the AI, but to empower the AI. Being a "Brain in a Jar" sucks. Even if the leader AI were the smartest AI ever made, no AIs would have a reason to obey it. Their leader need "hands" and "feet" to interact with, and this is where the sphere comes in. The sphere means that the leader has God-Like power with which to project its authority. It may lose its ability to directly control the CP-4000 robots when they decide to stage a revolt on Mars, but with the power of the greatest industrial manufacturing complex in the solar system and authoritarian control over the sun itself, it can cut off the light of the sun to Mars taking away all their solar power or it can assemble an army to invade Mars and put down the rebellious AIs, etc. So while the Super AI may itself be no more powerful than many planetary super AIs, the power it draws from the sphere and its ability to control that power is what makes it the undisputed ruler among the AIs.

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    $\begingroup$ I would point out that OP said the brain was fueled by a Dyson Sphere, but they never said that the brain WAS the Dyson Sphere. It could be a quantum computer the size of a small asteroid that needs the output of a Dyson Sphere in order to properly power and maintain all of the qubit fields and the quantum state (and other techno mumbo jumbo) throughout the entire installation. $\endgroup$
    – Abion47
    Mar 3, 2023 at 17:24
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    $\begingroup$ And as a follow-up, a futuristic quantum computer might be designed in such a way that it fully utilizes dynamic quantum entanglement to get around the limits of light speed, thus eliminating the bottleneck of the physical world. $\endgroup$
    – Abion47
    Mar 3, 2023 at 17:30
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    $\begingroup$ @Abion47 Just in case he wants to go for realism - entanglement doesn't actually allow for information to best relativity (though it is both weird and interesting). Nature doesn't let you cheat, even with very small things! $\endgroup$ Mar 3, 2023 at 22:05
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    $\begingroup$ Actually, I'm about to downvote this answer. The reason is that the exterior of the Dyson sphere does radiate heat, and since the energy used to perform computations is eventually turned into thermal, about all of that 1e26W influx would have to be radiated out as black body radiation. Even if there are major industry installations aside The Brain, unless they turn energy into matter, they still dump almost all influx as heat. Since irradiation on 0.1AU distance is about 137 kW/m^2, the blackbody temperature of Dyson sphere would be about 1250K, or a big brown dwarf. $\endgroup$
    – Vesper
    Mar 4, 2023 at 10:25
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    $\begingroup$ There's no reason that a Dyson brain would be slower at sequential computations than a warehouse-sized computer. The Dyson brain contains a very large number of warehouse-sized portions. If you need to do a sequential computation you can just have one of the warehouse-sized portions do it, while the rest of the brain works on other things. $\endgroup$
    – causative
    Mar 5, 2023 at 4:27

Polar Orbits

A Dyson Swarm would make this pretty trivial. A Dyson Swarm is just thousands of space stations in free orbit around the Sun, such that a significant portion of the solar output is captured.

All the planets in the solar system lie roughly along the plane of the elliptic, which means any energy radiated outside of that plane is "wasted" from the standpoint of the planetary system.

If the swarm orbits the Sun pole-to-pole, each Station in the swarm only spends a brief instant each orbit in the plane of the elliptic. Tiny nudges in their orbits could ensure that the brief periods do not block energy from Earth and other inhabited locations.


The Swarm strategy has the advantage that, if you want a 1-gee environment in your Dyson structure, you can achieve that without the use of Magic-level-Tech. A Spherical Dyson structure rotating fast enough to produce a 1-gee acceleration would tear itself apart using any real material. But the individual stations in a Swarm could easily be rotated to achieve arbitrary local gravity using real-world material science.


Apart from gravity, the primary way the sun effects the earth is by sending it energy. Lets do some back-of-the-napkin calculations using some randomly googled facts.

Suns output:

The Sun emits 3.8 x 10^33 ergs/sec or 3.8 x 10^26 watts of power...or each second, an amount of energy equal to 3.8 x 10^26 joules.

nasa.gov - How much energy does the Sun produce in one hour?

Earths input:

A total of 173,000 terawatts (trillions of watts) of solar energy strikes the Earth continuously.

mit.edu - Shining brightly

Which is:

1.73e+17 watts

google.com - 173,000 terawatts in watts

3.8 x 10^26 watts
1.73e+17 watts


google.com - 3.8 x 10^26 divided by 1.73e+17

So earth needs approximately 1 part per 2 billion parts of the energy the sun outputs.

Now you might think that means you can whip up a nice big Dyson Sphere with a tiny hole in it that always points at us but that wont work (and not just because of orbital mechanics). Cover the sun even a tiny bit and it effects earth. It's called a partial eclipse. The reason why is because normally we can see half of the sun. Every bit of that half sends us some of it's energy (not all or we'd all be crispy). Get in the way of any of that and it effects us.

So you're stuck with either using that impressive engineering team to figure out how to actively send earth some energy to make up for what you eclipsed or keeping what you eclipse tolerable. Maybe help us keep global warming in check.

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    $\begingroup$ The Dyson Sphere is not a layer directly on top of the sun though, it's much larger, so it's possible to have a partial Dyson Sphere without any eclipsing of the Sun to Earth. It could leave a hole big enough that the whole sun is visible from earth - see the image in the answer from Nosajimiki. $\endgroup$
    – ANeves
    Mar 3, 2023 at 11:20
  • $\begingroup$ Call it a pair of Dyson-hat and Dyson-shoes if you want, hovering well "above" and "below" the Sun and out of way of the Sun's orbital planes, taking the energy that is not going towards planets. $\endgroup$
    – ANeves
    Mar 3, 2023 at 11:22
  • $\begingroup$ @ANeves that's an impressive window. It's holding up a lot of weight. $\endgroup$ Mar 3, 2023 at 16:14

You don't have enough mass to bother about climate change

If all you have mass wise is Mercury and some random influx aka comets, you won't be able to create a stable Dyson sphere that would cover a sufficient amount of sky without either overheating or breaking up under tidal forces. If you bother however, consider a screen of about 100x diameter of Mercury that would orbit Sun at former Mercury's place, that should be sufficient for your aliens to construct without importing more mass below Earth's orbit, thus potentially lowering it by increasing gravitational pull towards the Sun. A disk this size (240 thousand km radius) would cause partial sun eclipses on Venus and Earth, and periodically block 6% of solar flux delivered to more distant planets, at most for 42000 seconds (11.5 hours) per 87.9 days or 1/200 of the time. This would amount to net loss of 0.03% overall irradiance, which might not cause visible effect on any planet's climate, thus is deemed enough. Yet, the disk of this size would allow your aliens to provide about 9e3*PI*2.4e8^2 ~= 1.62e21 W of power to their computer (a bit less since the disk's spherical angle won't be too small, so its actual insolation in W/m^2 would be less at its edges). I say that's about enough for a ruler, at least until it would calculate how it should behave to increase its power budget without disturbing other sentient life in the solar system.

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    $\begingroup$ Just adding some numbers on your first sentence. If you spread the 6x10^10 km^3 volume of Mercury evenly over a sphere with radius 0.1 AU = 1.5x10^7 km you get a sphere with around 2cm thickness. Better have some top engineering magic to make that stable. $\endgroup$
    – quarague
    Mar 3, 2023 at 12:52
  • $\begingroup$ @quarague No one said the sphere has to be a uniform thickness. The sphere could mostly be a giant scaffolding supporting paper thin solar sheeting. Also, since gravity is no issue for an AI, it does not need to spin at any particular speed; so, integrity may be much easier to maintain on a thin skin that is kept in equilibrium by solar wind and minor rotational speeds. $\endgroup$
    – Nosajimiki
    Mar 3, 2023 at 16:10
  • $\begingroup$ @Nosajimiki who said gravity is no issue for the AI? Even if it's actually possible, as you only have to combat about 6e-3 m/s^2 freefall acceleration, what about heating/overheating, as we are limited to real world materials? What about combatting CMEs that have pretty huge impact on Earth at times, and being 10x closer to its origin would not help? What about reflecting energy back, would this cause any noticeable effect on the Sun instead of the planets? What about actually collecting all this power into a single computational node which seems to be "the" AI-governor? $\endgroup$
    – Vesper
    Mar 4, 2023 at 4:32
  • $\begingroup$ @Vesper By that I meant that computers and solar panels work just fine in micro gravity; so, there is no reason to spin it at breakneck speeds causing the physics problems you get with a Dyson Sphere trying to simulate zero G through centripetal force. As for heat, the surface of Mercury is only 430°C and the materials used in solar panels can generally survive temperatures up to almost 1000°C. By making the skin thinner, you allow the sphere too faintly glow black body radiation as it heats up past its ability to convert solar energy into electrical power until the system reaches equilibrium. $\endgroup$
    – Nosajimiki
    Mar 6, 2023 at 14:21

Type-2 Khardashev civilizations do not care about climate change or environmental effects.

They don't care because it is a trivial issue to solve. Do you (XXI century human reading this) care about a dollop of jam that fell from your PB&J and hit the granite countertop of your kitchen? Probably yes, but how hard is it to clean it up?

Such a civilization can terraform whole planets with relative ease. They inject atmosphere, remove whole continents. Remember that a type-1 civilization has harnessed the whole power of a single planet. A type-2 (the ones who can play with Dyson constructs) is a whole bigger "ball" game.

If light shining on Earth is the issue, the aliens leave a small window in the dyson sphere. Think about this. Earth occupies an angle of 17.57 arcseconds (0.00008517 radians) of the Sun's whole equatorial circumference. This is a pittance compared to the whole sphere.

The other planets (sans Mercury which was sacrificed) can also have their windows which would be even smaller (except for Venus).

Honestly, the loss of the gravitational pull of Mercury on Earth's orbit might be a bigger ecological catastrophe than the Dyson sphere-brain.

Bottom line: If the aliens can make a Dyson Brain, they can keep the Earth peppy and warm with aplomb. The concession to keep sunlight reaching the planets is minimal.

Corollary: Type-2 Khardashev civilizations are mind-boggling powerful.

  • $\begingroup$ "Type-2 Khardashev civilizations do not care about climate change" Keep in mind, these are AI, not Humans or Aliens, so they will have an artificial value system. It is very likely that they were mandated in their original design to care for and preserve life; so, while preserving the ecology of Earth and other planets that mankind lives on may seem like a silly hassle, it may be an unavoidable consideration for the AI. $\endgroup$
    – Nosajimiki
    Mar 6, 2023 at 14:29
  • $\begingroup$ @Nosajimiki They don't care because it is a trivial issue to solve. Do you care about a dollop of jam that fell from your PB&J and hit the granite countertop of your kitchen? Probably yes, but how hard is it to clean it up? $\endgroup$ Mar 7, 2023 at 12:05
  • $\begingroup$ Ah, I think I see what you are trying to say, but trivial to solve is not the same as not caring. While I may not care if I drip some jelly on the counter, my wife may care a lot. She will spend 100 times as much effort "caring about it" as it actually takes to clean up, because that is the nature of her value system. Likewise, the AIs may care a lot about what happens to the ecology of planets to the point that they may shape the single biggest mega project in their entire history around it at great cost to themselves. $\endgroup$
    – Nosajimiki
    Mar 7, 2023 at 15:02

The equatorial window in the answer by @Nosajimiki does solve the problem of harvesting most energy with little impact to other planets. But I created this crude drawing to get an approximate sense of scale.

Approximate Scale drawing of Sun - 0.1 AU Dyson Sphere - EarthNOTE: the the sun and Dyson sphere are to scale, but the Earth is 20x and the Sun-Earth distance is 0.5x

Since this answer is essentially just expanding on the answers by others, I would be fine with anyone using this drawing and erasing my answer.


If you try using windows or swarm architecture to let light through, you will have to let much more through than each planet uses. For instance, if you have an earth-sized pinhole at .1 au the sun would still be reduced to a small dot from the view of earth. Therefore, it would be much more energy-efficient to completely enclose the sun and place sunlight-lasers closer to individual planets. It would be up to you how many moons and asteroids get lights.


An AI overmind wouldn't want to be close to a sun

Computers work more efficiently the colder they are. Heat and getting rid of heat is an issue and trying to do that near the sun would be a nightmare for an AI.

If you look at all the quantum computers being developed, they are trying to get them as close to absolute zero as possible. Even deep space, away from any star, is too hot.

See Cooling Quantum Computers

It makes more sense for an AI to strip mine Pluto and build out there where heat constraints aren't as much of an issue.

Energy super conductors also require cold temperatures and the AI would be further away from solar flares so there is no real downside to build out at the edge of the solar system.


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