Are dyson spheres dangerous?

[daniel l.]

When you consider the potential mass of a fully terraformed Dyson sphere you also notice that obviously the center of mass is at the center of the sphere, With the size and mass of such a structure its gravity at that central point would be enormous, and considering that there is always a star at the center of a dyson sphere, wouldn't the added gravity of that central point of mass be likely also at the center of the star (assuming the sphere doesn't have a wobble in its orbit), And as such that added gravity could collapse the star either into a black hole or make it go supernova, either way wouldnt the sphere be destroyed along with any orbiting planets?

[Rakaydos]

The net gravity of any point inside a uniform hollow sphere is zero. IT all cancels out. Only the star itself has a gravity to worry about.

[Bill Phil]

The problem is really that it's not all that stable.

[PB666]

Most of the points on a dyson sphere cannot be in non-inertial reference frames, as a result those n-i points want to collapse inward, points perpendicular to the points on the orbital plane want to collapse into the star. You cannot terreform a dyson sphere, its a glorified space station. 

[softweir]

7 hours ago, Bill Phil said:

The problem is really that it's not all that stable.

Exactly correct!

To elaborate: It has been pointed out that even if one could build a Dyson sphere and make it strong enough to not collapse into the star, there would be no force or effect preventing it wandering, so the star is no longer at the centre. Eventually, the sphere would wander far enough that the star would burn through the wall of the sphere.

[pincushionman]

Remember that the "classical" (pop-culture) Dyson sphere doesn't work. For structural reasons. The "real" Dyson sphere is actually a swarm of satellites and habitats in orbit. Which does mean gravitational effects on the central star, but the distribution of mass should be relatively homogeneous in the large scale, so the net effect should be small.

[Vanamonde]

Unless you're hauling all that mass into the solar system from somewhere else at inconceivable cost, the mass will already have been orbiting the star anyway, just in a different distribution. 

[Kerbart]

5 hours ago, softweir said:

Exactly correct!

To elaborate: It has been pointed out that even if one could build a Dyson sphere and make it strong enough to not collapse into the star, there would be no force or effect preventing it wandering, so the star is no longer at the centre. Eventually, the sphere would wander far enough that the star would burn through the wall of the sphere.

Actually, there is. Larry Niven suggests so in Ringworld; build a giant (superconductor) network into your ring (or sphere) and use the generated magnetic field to keep the star in place.

I have no clue about the amount of energy it takes but hey, if you can imagine a dyson sphere, you can imagine that, right?

[PB666]

3 hours ago, Kerbart said:

Actually, there is. Larry Niven suggests so in Ringworld; build a giant (superconductor) network into your ring (or sphere) and use the generated magnetic field to keep the star in place.

I have no clue about the amount of energy it takes but hey, if you can imagine a dyson sphere, you can imagine that, right?

You could pulse the star with microwaves to keep it in place also, but you could use a much more efficient cannae drive to keep the sphere in position with the star.

 

[ZetaX]

You could also use solar winds. For example, add some huge surfaces that can open to outside space to let particles (and hence impulse that would otherwise push against the sphere) out on the side farthest from the star.

[Rune]

Ok, now that I have finally got rid of that quote (any mod is welcome to remove the useless post above, and while you are at it you can tell Kasper that the forum is a bit broken to reply using an Android device running Firefox).

Anyhow, that control system for a Dyson sphere is neat, and I can suggest an improvement: playing with the reflectivity inside the sphere. If you switch it from reflecting to absorbing light at will (like the Ikaros lightsail, for example), and you control where and how you dump the waste heat on the outside, you can not only keep the star in check, you can use it for freaking propulsion.

 

Rune. Now THAT would be travelling in style.

 

Edited December 20, 2015 by Rune

[Wjolcz]

Just remember not to suck your parent star all at once or it might end badly.

Edited December 20, 2015 by Veeltch

[YNM]

A dyson sphere left by itself (no corrections) is never really that stable. Wait for a few generations... wait, since when sector (insert any number here) becomes mercury-like ?

A ring, or a swarm, may sliightly be more reliable. Although, how do you make strong surface gravity in small chunks ?

[Kerbol Macrosystems]

Applying gravity at the center of mass is just a simplification that makes physics problems easier to solve. All of the mass-energy still sits out at the physical elements of the Dyson sphere. The only case where you would end up in trouble is of you managed to rapidly collapse your sphere into its star. 

[AngelLestat]

I don't believe in dyson spheres, I will bet a lot that there is none in the universe.   But in case you want to build one for no apparent reason..  I dont find any trouble with its construction and stability.

The main point is to harvester almost all the energy from the star at the lower cost dont you?

Well, you must use the least amount of material possible, then is easier..  You just need a lighter PV film in sphere around the star.
Solar sails moves using the light pressure, so your sphere does not need to be so close or light enough to counter gravity due the same high radiation pressure. If the sphere moves just a little out of its gravity center, it means it has a side where it receives more light pressure because is closer to the sun.. so the system is always in equilibrium.

Your sphere just need to be strong enough to resist solar flares, which they can increase the force over the limits on one side.

But you can also solve that if you can turn the angle of some PV panels (in a netsphere) to let pass the extra pressure.
  

[Chakat Firepaw]

23 hours ago, Kerbart said:

Actually, there is. Larry Niven suggests so in Ringworld; build a giant (superconductor) network into your ring (or sphere) and use the generated magnetic field to keep the star in place.

That was part of his retcon after a bunch of physics students paraded around a con chanting "The Ringworld is unstable!"

 

Now, as for Dyson spheres being dangerous:  If you are living anywhere near one, (swarm or shell), you have reason to worry because of a little invention called the Nicoll-Dyson laser.  Imagine a phased-array laser with an emitter 2AU across and access to a significant fraction of a star's energy output.  Now imagine being 10 parsecs away from that system, where the beam would be only a couple metres wide.

[problemecium]

^ Now that's a veritable Death Star you've got there xD

See what I did there?

[Kerbart]

4 hours ago, Chakat Firepaw said:

Now, as for Dyson spheres being dangerous:  If you are living anywhere near one, (swarm or shell), you have reason to worry because of a little invention called the Nicoll-Dyson laser. 

If you’re living anywhere near a Dyson sphere, my primary fear would be the fact that you’re living next to a civilization that can build one in the first place. I'm sure that laser is only one of many things they’ve invented over the years...

[KAL 9000]

What if Starkiller Base is a Dyson Sphere? Da Da Da!

[Chakat Firepaw]

On 20/12/2015 at 5:36 PM, Kerbart said:

If you’re living anywhere near a Dyson sphere, my primary fear would be the fact that you’re living next to a civilization that can build one in the first place. I'm sure that laser is only one of many things they’ve invented over the years...

Dyson swarms just require the ability to make large solar-orbit stations, (they don't even actually need to be habs), once you can do that it's just a matter of scaling up production.

Once thing that makes the Nicoll-Dyson laser the thing to worry about is that it doesn't require a solution to the interstellar travel problem.  Another is the problem that you probably only find out that they even have one because a multi-terawatt laser is slamming into your planet.

Edited December 22, 2015 by Chakat Firepaw
typo

[ZetaX]

1 hour ago, Chakat Firepaw said:

because a multi-terawatt laser is slamming into your planet.

Terawatts is a very small power output when compared to such a thing.

[Kerbart]

4 hours ago, Chakat Firepaw said:

Dyson swarms just require the ability to make large solar-orbit stations, (they don't even actually need to be habs), once you can do that it's just a matter of scaling up production.

“Just”

• They have to be connected to form a sphere. Letting them orbit in loose elements will create fascinating traffic problems around the poles
• But ok, let's assume we can fix those traffic problems. Loose particles is it. To be a "sphere" and not a "ring", "swarm" or a "constellation" you will need a lot. Around. A. Freaking. Star
• Even if that's a tiny mini Jupiter-sized dwarf. That's a lot. As in enough to be a challenge lot

I'm sorry, but saying that it's just a matter of scaling up is claiming that running the marathon under two hours is "just" a matter of walking fast enough.

 

4 hours ago, Chakat Firepaw said:

Once thing that makes the Nicoll-Dyson laser the thing to worry about is that it doesn't require a solution to the interstellar travel problem.  Another is the problem that you probably only find out that they even have one because a multi-terawatt laser is slamming into your planet.

Unless this civilization is just a trigger-happy bunch that, after building said laser, decides just to zap every known planet in the hood just for the hell of it, they still have to figure out where to aim it too, e.g. know where the neighbors live.
Unless, indeed, they decide to pre-emptively clear the neighborhood of any potential competitors.

[Bill Phil]

If the stations are far enough away from the star, then they can "float" with minimal effort. But you're gonna need so many that you'll be intetstellar civilization.

[SomeGuy123]

Nobody would build a physical dyson sphere.  Why would they?  Why not just convert all the solid matter in a solar system to either free flying solar arrays or robots and computers and whatever else a civilization at this level wants to play with.

[Chakat Firepaw]

13 hours ago, Kerbart said:

“Just”

• They have to be connected to form a sphere. Letting them orbit in loose elements will create fascinating traffic problems around the poles

Not really, when building a Dyson swarm, (which is what Dyson _actually proposed_, the Dyson shell is a misunderstanding), you don't have to match orbital altitudes exactly.  It's also perfectly fine to have few/no stations on particular inclinations.

As pointed out above, Dyson shells don't actually work due to the little problem of not being gravitationally linked to the star.

13 hours ago, Kerbart said:

• But ok, let's assume we can fix those traffic problems. Loose particles is it. To be a "sphere" and not a "ring", "swarm" or a "constellation" you will need a lot. Around. A. Freaking. Star
• Even if that's a tiny mini Jupiter-sized dwarf. That's a lot. As in enough to be a challenge lot

I'm sorry, but saying that it's just a matter of scaling up is claiming that running the marathon under two hours is "just" a matter of walking fast enough.

It's still just an engineering and logistics problem.  You don't need to actually figure out any new science or technology to do it.

It's certainly a 'just' when compared to sending any significant physical object to another star system.

13 hours ago, Kerbart said:

Unless this civilization is just a trigger-happy bunch that, after building said laser, decides just to zap every known planet in the hood just for the hell of it, they still have to figure out where to aim it too, e.g. know where the neighbors live.
Unless, indeed, they decide to pre-emptively clear the neighborhood of any potential competitors.

All it takes is some paranoia or religious fanaticism.

Remember that there really are people in the real world who _want_ to trigger a global nuclear war in order to bring about a divine return.  Before you dismiss them as nothing more than fringe wackos may I point out that Vice Presidential candidate, (and half-term Governor), Sarah Palin was closely linked to one such group.