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214 points SkyMarshal | 5 comments | | HN request time: 0.878s | source
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ardit33 ◴[] No.28231727[source]
The whole concept of a Dyson sphere is kinda idiotic. Any civilization that is capable to build one, it is probably able to work out fusion energy very efficiently.

There is no point to go and harness energy around a star or a black hole, when you can just produce it locally with a lot less resources/waste and materials. The sun itself is actually very inefficient in producing energy.

There is no need to harness the sun million of km away, when you can recreate it in your home planet. The only way to produce a dyson like of sphere, is to tame an over-heated sun, and reflect away un-needed energy. But there is no point to build one to just harness it.

It makes great sci-fi stories, but that's about it. Scientifically, it just doesn't make sense.

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zaarn ◴[] No.28231799[source]
There is a point still, because a star is massively more efficient at fusion by way of "production at scale" effects.

The additional benefit is the amount of power. With the power of a star at your disposal, beaming your energy using lasers and microwaves, even if only 1% efficient, would instantly solve the energy needs of any planet in a solar system. If we did it, we could instantly colonize all planets in our solar system because things like "running an AC on Mercury" or "Hovercraft in Jupiter Atmosphere" becomes trivial when you have limitless power.

Heck, you could start projects like moving planets in orbits or collecting astroids to built a planet if you wanted.

Black holes are the stage after that since you can use a spinning black hole to convert a given mass into energy at >10% efficiency (given E=MC^2). That would allow a civilization to power multiple solar systems at the cost of a few planets per year.

Granted, the sphere is difficult to build, but that is what you have dyson swarms for.

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TheOtherHobbes ◴[] No.28232083[source]
The sphere isn't difficult to build. It's impossible to build.

It's unstable without active stabilisation. The stabilisation has to be perfect because otherwise you get massive distorting spherequakes propagating through it, which will make it a very uncomfortable ride for a short time and will soon tear it apart.

A perfect spherical stabilising solution with components and sensors that are light minutes - or possibly light hours - from each other is impossible because of the signalling delays.

Ringworlds have the same problem. Even if the ring is made of infinitely strong unobtanium, it won't stay in a useful orbit for long enough to be built, never mind inhabited.

Swarms have more potential, because you can build them with sparse shells and move things around to handle instabilities. But you still need massive computational effort to keep swarm units from colliding with each other, possibly at very high speed.

None of this matters, because the limiting factor for civs is collective intelligence, not energy.

We already have access to far more energy than we could possibly use on earth for any technology that's actually buildable. But we're not using it because we don't have the species IQ to make the right choices.

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1. TuringTest ◴[] No.28232509[source]
Bridges have expansion joints to absorb temperature-induced expansion and contraction, passively stabilizing the structure.

Why couldn't a Dyson sphere have uncoordinated movement joints distributed all around to absorb those spherequakes? Or even active locally coordinated ones?

I'm sure a Dyson-sphere-building civilization would figure this out.

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2. politician ◴[] No.28233510[source]
The expansion joints will throw off the center of mass of the entire shell, leading to a positive feedback loop of orbit decay and expansion compensation. Without coordination, this is catastrophic. However, coordinating nodes are light minutes apart, making timely coordination impossible.
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3. dognotdog ◴[] No.28233815[source]
Why do you think it's impossible? To me, it seems like all effects (eg. mechanical waves) would propagate at much slower speeds than the speed of light. This kind of control system experiencing significant delays and dead-times is not uncommon.
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4. politician ◴[] No.28234658{3}[source]
You need a force to balance the change in orbital velocity due to expansion or contraction of an expansion joint of a fully connected shell; otherwise, the shell will begin to wobble. The forces would be enormous and tear the shell apart from multiple places.

One solution is for the expansion joints to have infinite range— a disconnected swarm of platforms which is exactly what a Dyson swarm is.

5. vimacs2 ◴[] No.28235742[source]
But the effort required to build such a structure, even if physically possible is far more than building the equivalent in a swarm and the utility of such a swarm is greater especially when you consider that the typical sci-fi trope of living on the surface inside of that sphere is ruined by the complete absence of any gravity exerted by the actual sphere on that surface. This means that all of those hapless residents would instead get pulled from the surface into the star in the centre.

This is precisely the appeal of Larry Niven's Ringworld concept. You instead take a slice of that sphere and spin it around the star and generate gravity through centrifugal force. They can take a number of configurations but the default one would give you the equivalent of 2 million earth's worth of living space inside one continual surface. This is obviously hugely mass intensive and having a ring of that kind of radius spinning at the tangential velocities required for the equivalent of one g of simulated gravity (around 1200 km/s) requires materials so magically strong that they make graphene look like soggy tissues. The only material that could do this even in the theoretical realm is magmatter, which would be materials constructed out of magnetic monopoles, something that has been predicted to exist by some but has yet to be observed.

However, you could construct one using known materials by creating a superstructure around the ring that is much more massive and orbits the other direction at normal orbital speeds for a body about an AU out from the sun with the ringworld electromagnetically suspended from the superstructure, normalising their collective momentum to zero. That obviously greatly increase the mass requirements but this could mostly take the form of hydrogen and helium which is far more abundant than heavier elements and would be usable as fuel for fusion reactors. That superstructure can contain many smaller rotating habitats and the whole thing could be used as a vast habitat for microgravity living as well - something I envision as many humans doing as living on worlds with gravity by the time we would have constructed one of these.

You also want to have a superstructure because at such a high tangential velocity, if a human being of 80 kg struck the ring from the outside, it would blow with the kinetic energy of a thermonuclear bomb. Point defence is absolutely necessary and the superstucture offers both an excellent shield covering the non sun lit side of the ring and a great platform for hosting those point defence systems. Ringworlds are also not in stable orbital configurations over astronomical timescales so you need to maintain their orbit through corrective thrust. This could be done through light sails which would also be appealing for it's mechanical simplicity.

Ringworlds are very mass intensive especially if your civilisation still has no access to unobtanium building materials and I don't think this would be something we would ever build a lot of in our particular solar system but even with that mass cost, you could easily gather enough rocky material from the sun to build a few and still have the vast majority of people living in other far smaller structures (but only relative to a star encompassing ring) in the swarm.