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According to FutureTimeline.net, A Dyson sphere could be built around the solar system around the year 3100 when the world reach the Kardashev type 2 scale. This is what is written there about the issue:

3100 AD

Humanity is becoming a Type 2 civilisation on the Kardashev scale

The exponential growth of AI has allowed the manipulation of matter on scales barely dreamed of before. The largest structure now being built in space is a "Dyson Sphere".* This hollow shell is of such gargantuan proportions that its radius stretches from the Sun to beyond the orbit of Jupiter.

Under the direction of a Godlike superintelligence, vast swarms of automated, self-replicating ships are building it, using material from the asteroid field, Kuiper Belt and Oort Cloud.

The sphere's primary purpose is to harvest literally all of the energy output from the Sun: some 386 yottajoules (YJ) per second.* However, it also serves the function of shielding our inner solar system from gamma rays and other incoming hazards. Even the potential possibility of alien invasion has been taken into consideration during the sphere's design.

The interior walls have a gravitational field of 1G and are made from wholly new states of matter that were unknown to science in previous centuries. These can withstand the colossal tensile forces required to maintain structural integrity. This curved, impossibly large surface – equivalent to billions of planet Earths – is becoming a habitat for many sentient lifeforms, with portions being terraformed and given stable atmospheres, oceans and landmass. A sizeable percentage of citizens are now migrating to these strange artificial worlds. This includes a diverse mix of biological humans, as well as transhumans, synthetics, clones, androids, sentient animals and other communities. A series of additional Dyson Spheres are being constructed around neighbouring star systems – some even larger.

Having begun its journey to the stars in the 22nd century, humanity is reaching a landmark in its exploration of space. A region nearly 1,000 light years in radius has now been settled (or about 2 percent of the total length of our galaxy).

Well, I understand that the sphere would be made by kinds of matter that is unimaginable today (this is obvious) and the Dyson sphere could have several walls and some of the portion of such walls could be terraformed. But I didn`t get when it says that such artificial worlds would be strange - strange in which sense? Could the terraformed portions look alien and artificial compared to life on Earth? And what about the other portions of the sphere - Could material science be so advanced that these artificial worlds would be really dazzling, bizarre and surreal even for science fiction addicts? I believe that these worlds would be so bizarre and large that even virtual reality would not replace the will to visit them.

If a person was in one of these worlds inside the Dyson sphere and looked at the sky, what the sky could look like, since they would be inside a set of hollow closed shells? Would this person still be able to see stars or the sky could look like something else?

It is also written as if the world population will increase in trillions of people as humanity have the technology to create artificial beings - even sentient humanoid animals.

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    $\begingroup$ Please format the citation as such. Else it is hard to tell which is your words and which is the citation. $\endgroup$ – L.Dutch Jun 19 at 2:43
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    $\begingroup$ Hold on. If we've settled a radius of 1000 lightyears by 3100 that means that we have to get space traveling quickly. Even if we started at the year 2000 we would have to average out 45% of the speed of light in both directions, not counting the time needed to accelerate and decellerate (or the time necessary to actually colonize anything!). And the longer we wait the faster we have to go to reach that sphere. $\endgroup$ – Demigan Jun 19 at 8:55
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    $\begingroup$ @Demigan: worse: 1000 ly radius! that means expansion at the speed of light from 22nd to 32nd century. $\endgroup$ – ths Jun 19 at 10:32
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    $\begingroup$ this whole quote is nonsense. "The interior walls have a gravitational field of 1G" where does this come from? a hollow shell doesn't have any interior gravity. $\endgroup$ – ths Jun 19 at 10:38
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    $\begingroup$ That's one of the most ridiculously unrealistic depictions of the future that I've ever heard - and it is competing with some real doosies. $\endgroup$ – conman Jun 19 at 12:15
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This is not a reasonable depiction of a Dyson Sphere.

First of all, it must be stated that this kind of Dyson Sphere - a solid "Dyson Shell" - while a popular description, is universally regarded as unrealistic by serious writers, even in the context of a civilization capable of building solar system sized megastructures. Even if the absurd amounts of material could be found (far, far more than all the planets in the solar system combined), the force of the shell's own gravity and pressure (multiple planets worth, from every direction at once) would rip it apart. Even if a magic, unbreakable material was made that could resist this unimaginable stress, its position would be "metastable" which is, in real world terms, unstable - any slight minuscule perturbation would cause it to lose "balance" and crash into the sun. It could be adjusted through constant active correction, but if you're capable of producing the amount of constant force necessary to accomplish this you don't even need a Dyson Sphere.

Realistic projections of Dyson Spheres include swarms of orbiting satellites (a Dyson Swarm) or separate "statites" that "hover" above the Sun using wide solar sails/collectors (a Dyson Bubble) - some of these satellites may contain habitats. Given enough material, statites may be connected with thin, flexible wires or sheets, potentially forming a hollow "bag", but most of the bag would not be habitable by humans, consisting of a thin solar sail. (It may be habitable by computerized minds that live in a thin network of wires.)

But supposing it was...

But supposing a magic civilization did create a set of nested, solid shells size of planetary orbits, what would it look like between two shells? On Earth, the horizon exists because of Earth's curvature, but this is not the only thing that causes objects in the distance to be less visible - the atmosphere causes far-off objects to "fade". On a clear day on Earth, it is possible to see to the horizon, but inside this world the horizon would be unimaginably further away and this would never happen. Looking into the distance, both the sky and the ground would converge in the distance and eventually fade away into a "band" of what would appear to be a fog of sorts.

As for how bizarre these worlds could be - well, there's no real limit, since any civilization capable of constructing such an impossible structure is effectively using Sufficiently Advanced Technology that is indistinguishable from magic.

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    $\begingroup$ Um not so much "Given massive transmutation of elements, we can convert Jupiter into a spherical shell 93 million miles in radius and maybe ten to twenty feet thick. If we don't have transmutation, we can still do it, with a thinner shell." - Larry Niven Bigger than Worlds. We could in fact build a Dyson Shell without leaving the solar system if we had the technology to actually build one, and that's without Starlifting which would make it truly easy to do. $\endgroup$ – Ash Jun 19 at 12:18
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    $\begingroup$ @Ash If the goal was to build a thin shell (such as the aforementioned Dyson Bubble) we would indeed have enough mass in the solar system to do so. However if the surface of this shell were to have planet-like environments with planet-like gravity, it would have to be a lot thicker than ten to twenty feet at each point. $\endgroup$ – IndigoFenix Jun 19 at 12:30
  • $\begingroup$ Not if you have artificial gravity generation, which is the only "realistic" way to have gravity on the surface of such a bubble. You don't need a very thick shell to have Earth-like biomes under those circumstances, the Ringworld is quite right in that regard. $\endgroup$ – Ash Jun 19 at 12:40
  • $\begingroup$ @Ash There is no known method of artificial gravity generation apart from centrifugal force, and the only way to get sufficient centrifugal force on a sphere that big would be to spin it at an appreciable fraction of the speed of light. If you have enough spare energy to spin a solar-system sized ball at relativistic velocities, you probably don't need a Dyson Sphere in the first place. This is, of course, still ignoring the other problems with a Dyson Shell, like the strength of the materials used to make it and maintaining its stability. $\endgroup$ – IndigoFenix Jun 19 at 12:56
  • $\begingroup$ Spin gravity won't give you gravity across the whole surface, only a narrow band near the equator; you need gravity field generators or a Dyson Shell is largely, if not completely, uninhabitable and if you have those the rest of the make up of the shell is pretty unimportant you only need enough matter to hold the generators and do some landscaping. $\endgroup$ – Ash Jun 19 at 13:15
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There's a few things which would make it strange.

The first is that these biomes are bespoke. Someone created them with a purpose. Environments as we are used to occurred through the evolution of chaotic processes. Accordingly, each one would decidedly show the fingerprint of its creator (or purchaser). If you're going to spend $1,000,000,000,000,000 to create your own biome, or some similarly lavish figure, you're the kind of person that gets exactly what they want.

The next strange thing is the density of things. There's about 15 pound of air above every square inch of your body. Swapping units, that's about 10,000kg of air above every square meter. A sphere extending to Jupiter's orbit would have roughly 10^19 square meters, so 10^23kg of air would be needed to cover the whole thing. That's a whopping 10 millionth of the mass of the entire solar system... just for air. While your sphere may be made of exotic materials, if you want a blue sky and a yellow sun, you're going to have to pay for air. You're going to have to truck it in (or fall back on Mega-Maid if need be)

Finally, there's the raw power of it all. The amount of power that is collected and processed by a Dyson sphere is beyond our comprehension. Imagine finding a bushman in the desert, and handing him the power of a modern jet fighter. His access to power is suddenly increased from what food he can turn into calories and motion to being able to guzzle jet fuel on the order of 10kg per second! And that isn't even remotely close to the power differential between what we see on Earth and what could be done by capturing all of the energy of the sun.

So you have a funny dynamic. Matter is at a premium, but energy is easy to attain (by our modern standards). That will truly create a strange world.

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    $\begingroup$ The bit about "bespoke environments" reminds me rather strongly of Magrathea, the planet-building planet from The Hitchhiker's Guide to the Galaxy. Which, I suppose, is pretty normal by the standards of this megastructure. $\endgroup$ – Cadence Jun 19 at 4:58
  • $\begingroup$ @Cadence Magrathea even has a giant metal shell like this that they use to contain their custom planets during development. $\endgroup$ – DarthFennec Jun 19 at 20:45
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Well, this viewpoint is certainly optimistic. It's also kind of vague, because you're asking us to interpret someone else's projection of a Dyson sphere. Anyway, I'll see what I can do.

Could the terraformed portions look alien and artifitial compared to life on Earth? And what about the other portions of the sphere - Could material science be so advanced that these artifitial worlds would be really dazzling, bizarre and surreal even for sience fiction addicters?

Yes and yes. I think the classic example is trying to explain the concept of a personal computer to some Middle Age European peasant. The fact is that science takes a course that's unpredictable to people who study it for a living, and you're talking about futuristic technology made by (presumably) AI that have passed the Singularity. It'd be bizarre in the 'uncanny valley' sense - if someone like us would see it, it'd just seem wrong somehow, but we'd never be able to put our finger on it, no matter how we were explained how practical the situation was. Imagine a planet which didn't have the typical fauna/flora divide - this seems so wrong that most sci-fi world just instinctually have one.

If a person was in one of these worlds inside the dyson sphere and looked at the sky, what the sky could look like, since they would be inside a set of hollow closed shells? Would this person still be able to see stars or the sky could look like something else?

Presumably these worlds are on the surface, so they'd see the stars. If they were inside the shell, I have no idea. Dyson spheres are just a concept, the technology for which doesn't exist. Like I said, this is an optimistic viewpoint which assumes that the things can be created by technology that we'll definitely invent in the future. (Sounds like cryonics when put that way, doesn't it?) This isn't really a helpful answer, but I'm not sure there can be a helpful answer because of how speculative all this is.

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  • $\begingroup$ I have a curiosity: Do you think that if a dyson sphere existed nowadays could its walls be noticeable enough to look obvious in the sky and even change the night sky appearance, like for exemple the dyson sphere make the sky far more " lifelike" than the usual black sky? $\endgroup$ – Sabrine Crystal Santos Jun 19 at 3:27
  • $\begingroup$ A dyson sphere takes all the energy of the sun, to the point where it wouldn't be noticeable from the Earth, even during broad daylight, because broad daylight wouldn't exist. The only part of the night sky it would effect is the moon, which would no longer reflect light. $\endgroup$ – Halfthawed Jun 19 at 4:50
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    $\begingroup$ @Halfthawed Unless I'm misreading the citation, the Dyson sphere here extends out past Earth's orbit, and Earth is actually inside it. So they would see the sun and moon and, presumably, whatever the inside of the sphere surface looks like. (Mostly black, I should think, since you want as much solar collection as possible and as little reflection as possible.) $\endgroup$ – Cadence Jun 19 at 4:55

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