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My world is a 1AU radius, 12000km thick Dyson Sphere with 6 equally spaced holes, 4 filled with water. The two main problems I have are gravity and heat. This question concerns heat and how to stop everything on the inside from being incinerated.

The majority of the inhabitants live on the inside of the sphere, so it is perpetually day. This means they are constantly heating up. I designed a heatsink to deal with it but I don't think it's enough.

Would making the sphere bigger (like, TNO bigger, there are no planets in this case) mean less heat is generated per square meter? There would be more surface area for heat to dissipate.

Our solar systems habitable zone is where it is because of the surface area of the planet so would making a DS move it out further?

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    $\begingroup$ Keep in mind that if you make it too big, some other civilization may try to make a smaller one inside it. Life hack! $\endgroup$
    – DqwertyC
    Jul 26, 2018 at 22:58
  • $\begingroup$ Strongly recommend reading Dyson sphere FAQ for anyone interested in Dyson sphere and related concepts. $\endgroup$
    – StephenG - Help Ukraine
    Jul 27, 2018 at 1:36
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    $\begingroup$ How do people walk on the inside, where there is no gravity? Also, if the star is sun-like, if you make it bigger than 1 AU the light will not be Earth-like; for reference, Jupiter is about 5 AU from the sun, but the lighting it receives is 1/25th of Earth's $\endgroup$
    – SilverCookies
    Jul 27, 2018 at 7:58
  • $\begingroup$ @SilverCookies exactly my point. We actually receive more light than we 'need', so if everything was moved further away it would heat up slower because energy would be less concentrated. $\endgroup$
    – ZoneWolf
    Jul 27, 2018 at 8:21
  • $\begingroup$ In Ringworld, there are shades between the sun and the ringworld to simulate day/night cycle and seasons. The Heat/Radiation thing: The Dyson Sphere is meant to collect all energy from the sun. So you just have to use your superconductors and bring the energy where you need id (gravity genration, normal civilization needs and of course the spacecraft drydocks outside of the sphere.) $\endgroup$
    – Julian Egner
    Jul 27, 2018 at 13:12

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You can design an air and water circulation systems to convey heat to your radiators, making your surface cooler. To me, it seems a better option than to make a bigger, costlier, sphere. I recommend watching Isaac Arthur take on Dyson spheres. It may help you understand it better. There are a lot of better alternatives if you plan on making a full Dyson sphere.

There is one very important fact you should keep in mind. You would not be able to stand on the sphere on the inside because you would just fall into the sun. There is no gravity on the inside. If you still want inhabitants living on the sphere, you could put them on the outside. I recommend calculating the surface gravity for that.

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  • $\begingroup$ The gravity on the outside is going to be very, very small (about 0.0006g for our sun). At that rate, it will take you 16 minutes to hit the ground again if you jump. You'll pretty much need to use spin-gravity or some magic gravity generator if you want to have some gravity. $\endgroup$
    – Jarred Allen
    Jul 27, 2018 at 1:52
  • $\begingroup$ @JBH I am not following; where does the 1000g comes from? The Sun surface gravity is about 22g if I recall correctly, the inner surface of the sphere would have no apparent gravity, and the outer surface would have many times less than that (0,06 g according to my calculation) $\endgroup$
    – SilverCookies
    Jul 27, 2018 at 8:05
  • $\begingroup$ @SilverCookies, Dang. It was late and I misread Jarred's comment. Regrettably, he's still in error. While the gravity on the inner surface will be low, it will be in the direction of the sun. You'll never settle again on the sphere. The gravity outside the sphere depends on the mass of the shell. $\endgroup$
    – JBH
    Jul 27, 2018 at 15:14
  • $\begingroup$ @JBH of course, what I meant is that the shell would have no gravity on the inside $\endgroup$
    – SilverCookies
    Jul 28, 2018 at 12:42
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Let's answer your question on its own terms

No, you can't solve the problem by making the sphere larger. All that does is reduce the amount of heat absorbed per-square-meter (density of heat absorbtion on the inner surface). It slows the process down, but doesn't solve the problem because you need to absorb 100% of the star's energy over its lifetime anyway.1

Others have mentioned using heatsinks to get the heat from the inner surface to the outer surface. That seems so 2018. I believe that 100% of the sun's emissions are photonic,2 let's put that to use.

  • Layered solar panels such that each layer captures a different wavelength spectrum, substantially increasing the efficiency of energy capture. This would reduce a ton of the heat because you don't need, what, 99.99999% of the surface of the sphere? But you do need to put the energy to use or, well, boom... you know... boom.3 Think "stick a capacitor in a light socket" boom, but bigger.

  • Massive pinwheels in space that are driven by the solar wind. This converts mass amounts of solar energy to kinetic energy. It has the benefit of creating night/day zones on the inner surface. You could build giant poles to hold them in place, or just use rockets to do so (If you have the energy to spend building a Dyson sphere, you have plenty to spend doing this).

  • You could let the heat build up and then use massive thermoelectric generators to convert excess heat to electricity. Your world will be a bit more like the Dagobah system, but hey... Swamp Thing needs a place to hang, too. Like the first idea, you need to do something with the energy afterward.

  • Finally, just because I'm feeling whimsical, you could make your sphere out of coupled cylinders that gently spin the sun-facing-side to the outside. This might be hard to visualize, but think thread spools laced together into a sphere, each spool spinning. It would play merry havoc with your gravity, but then... zero-G during the day and 1G at night? That might be pretty cool. But it solves the heat problem by allowing the excess to irradiate into space like any planet does. (Now that I think about it, this would allow for a common atmosphere inside and out with the ability to wave to your friends on Cylinder XZ21N-7 as they rotate past. You'd have storms build up between cylinders.... dang, that could be fun...)

BTW: The fact that you have no gravity inside a Dyson sphere is becoming well enough known that you should explain to your audience how you're solving that problem. It's an off-topic comment as the presence of your population is irrelevant to the question, but since you mentioned it, please keep that in mind. Besides, you need to do something with all that excess energy. You might as well use it to drive your artificial gravity generators.

1 If you make the radius so large that the issue of heat absorbtion becomes irrelevant, the value of building the sphere is lost both in terms of its construction cost and the inability to use the star's energy effectively.

2 If I'm wrong about that, please let me know. Thanks!

3 That link is an esoteric joke.... But I like the tune.

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  • $\begingroup$ There is no proof that the internal surface of a Dyson sphere would have no gravity. Following most DS examples they are very thin, unlike mine which is as thick as the earth. Increasing its surface area would solve the problem of heat because it is reducing the heat absorbed/sqm and the radiating surface. On the topic of gravity, if it is far enough away that the sun's gravitational pull on inhabitants is negligible the strongest pull would be coming from directly beneath them, hopefully ~1g $\endgroup$
    – ZoneWolf
    Jul 27, 2018 at 6:25
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    $\begingroup$ Zone, the proof is mathematical. It's called the shell theorem. Basically, whatever gravity is caused by the area beneath your feet is cancelled by the gravity of all the rest of the mass above your head. But that's moot, isn't it? The idea is becoming so prevalent that whether or not it's empirically proven is irrelevant. Your audience will think you the fool. $\endgroup$
    – JBH
    Jul 27, 2018 at 6:47
  • $\begingroup$ so there would be no gravitational pull from 100000km of iridium beneath your feet because theres a sun 800000000km above you? That makes no sense. $\endgroup$
    – ZoneWolf
    Jul 27, 2018 at 6:54
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    $\begingroup$ @ZoneWolf - No, the sun has absolutely nothing to do with it. The gravity exerted by the 100000km of iridium under your feet would be balanced out by the rest of the 100000km thick iridium shell to the sides and above you. The thicker you make the shell under your feet, the thicker the rest also becomes. As long as the shell is uniform, the gravity at any interior point will always cancel out, leaving zero net gravitational influence from the shell. $\endgroup$
    – Dave Sherohman
    Jul 27, 2018 at 7:24
  • $\begingroup$ I spent way too long trying to wrap my head around this. Now I'm trying to think of a different method of keeping people on the inner surface, since the gravity is effectively nothing. Maybe atmospheric buoyancy or graviton something or other $\endgroup$
    – ZoneWolf
    Jul 27, 2018 at 8:17
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Your Dyson sphere has two sides: the inner side, facing the central star and harnessing energy, and the outer side facing the emptiness of space.

Use the outer one has radiative surface to discharge the waste heat: being far from any other star you will be dumping to something just few K above 0 K.

Since the surface radiating to the outside is in a first approximation equal to that harnessing energy, you cannot have problems dissipating heat.

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If it doesn't have to be a sphere, I would recommend changing the structure to be a Dyson Swarm instead since this is a much more practical and easier-built approach to stellar+ size megastructures. If the sphere structure is integral to your work, first, you're going to have to find a way to generate gravity on the inside either through supertechnology or by spinning the sphere. Spinning would create enormous stresses and only provide a gradient of gravity centered perpendicular to the axis of rotation. Alternatively, placing the inhabitants on the outside would work if the sphere was at the correct distance from the Sun to generate 1G of gravity, but their eternal day would have to be manufactured via something like orbiting parabolic mirrors that reflect light coming through holes back onto the outside surface. This would give their world the interesting appearance of having varying numbers of 'suns' in the sky at any given time and position. Or a very bright field of stars that lights their surface. Heat could be provided from below and only just enough light for it to be noon-bright from above. As another user said, Isaac Arthur's perspective on Dyson Spheres is well researched and covers a lot of ground. Also, there's Zepherus's video on that same subject with a bit more coverage.

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  • $\begingroup$ The reason it's always day on the inside is because no matter where you are on the inside, the sun is always directly above you. Meaning it is also eternal night on the outside of the sphere. $\endgroup$
    – ZoneWolf
    Jul 27, 2018 at 6:59
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Use this: https://youtu.be/7a5NyUITbyk

You use materials that radiate heat back straight at the Sun. I have no idea if it'll help the Sun stay active for longer though. So as an alternative you do the following:

You hang multiple sattelites above the surface of the planet. These contain molten salt and water like this Sahara idea: http://www.climateactionprogramme.org/news/plans-for-sahara-to-export-solar-power-to-europe-revive

These sattelites will be the focus of the radiated heat and also heat up because of the Sun. This causes the molten salt and water inside to boil and from that you create electricity. This both cools down the sphere and provides electricity from as much surface area as possible.

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