# Dyson Sphere Solar system, And Planets?

• May 12th, 2012, 10:23 PM
Japith
Dyson Sphere Solar system, And Planets?
Sure if they could mine every rock in that star cluster just to build this thing, why not build a normal sized planed inside the Dyson there, or why not leave the home planets as they are and have them inside/outside.
How would the planets co exist with the super massive dyson sphere, and this dyson sphere is life habitable and has massive deserts, tropical areas, grasslands, wild life, civilizations.

What if the planets collided with the sphere?

What does gravity do in this situation, planets orbiting the star inside the sphere, and the sphere being so massive having its own gravity?

Super massive spaceships and a life sustaining Dyson sphere? I'm talking moon sized super city space ships.
• May 13th, 2012, 11:58 AM
dmwyant
So your question is if it is possible to create a dyson sphere large enough to encompass an entire solar system? First off, how many planetary bodies are in the system? What is the systems star class? Even if they utilized the material from the systems ort cloud and any non planetary bodies I doubt you could get enough material to enclose an entire stellar system. For example Pluto is 5,906,376,272 km from the sun 5.9 billion kilometers that means your surface area is going to be 438,159,125,170,544,400,000,000,000,000,000,000 Approximately. I am not even sure what that number would be but that is Kilometers you would have to strip hundreds of systems to create something that massive. And forget about moving it. Now I know my math is not exact but it is close. I do not have a scientific calculator handy to work it out so I had to use my computers calculator.
• May 13th, 2012, 06:09 PM
Ken Fabos
It was an interesting thought experiment by Dyson but never anything more. If an extra high tech space based civilisation can be achieved, aiming for Dyson Spheres would not make any real sense. But nor would artificial planets. Why not build a multitude of space habitats? If it's the energy of the sun that is the motivation there are much easier (relatively speaking) ways to tap it. The partway variant - Larry Niven's Ringworld - is no better the way Niven envisaged it. Well, Niven tended to add sciency sounding explanations as afterthoughts for things like Ringworld that are best not examined too closely if you want your sense of wonder to remain unpunctured. What holds the atmosphere to the surface? Centrifugal force won't do it even Niven style. Habitats on the inner surface of a Dyson Sphere or Ringworld would need to be fully enclosed and pressurised.
• May 13th, 2012, 06:38 PM
Japith
I'm sorry, how was anyone suppose to grasp the idea if no information was present about the environment parameters. I got the idea when I was watching a ad of the new game "Halo 4", Halo 4 takes place in a Dyson sphere world populated by a sentient robotic civilization. This image is the exact size and representation of this sphere world and is the environment that my questions formed.
Again as you can see there are planets inside! Now remember this is Sci-Fi so many of the unknowns you may have to imagine, like for example lets say that the sphere has Artificial gravity and thats how it holds its atmosphere ect...
• May 13th, 2012, 07:28 PM
MeteorWayne
Since this is Sci-Fi, perhaps it belongs in that forum?
• May 14th, 2012, 04:52 AM
John Galt
Quote:

Originally Posted by Ken Fabos
Well, Niven tended to add sciency sounding explanations as afterthoughts for things like Ringworld that are best not examined too closely if you want your sense of wonder to remain unpunctured. What holds the atmosphere to the surface? Centrifugal force won't do it even Niven style. Habitats on the inner surface of a Dyson Sphere or Ringworld would need to be fully enclosed and pressurised.

This was dealt with in the original book: the Ringwall (there are, of course, two) circles the edge of the ring rising many tens of kilometres, so entraining the atmosphere. In sequels he dealt with several of the other oversights in a plausible fashion.
• May 14th, 2012, 09:55 AM
Ascended
They had an episode of star trek TNG with a dyson sphere in it. What I didn't get then and still don't is how the gravity translates from the outside to inside, I would imagine like with most spherical planets you would start off from the outside being pulled towards the centre, but at what point would gravity reverse and start to pull you back to the surface?

Also since most of the dyson sphere would be hollow, it would be interesting to see if the sheer size of the thing had any impact on gravity over or above the actual effects of it's mass alone.
• May 14th, 2012, 11:12 AM
Janus
Quote:

Originally Posted by Chrisgorlitz
They had an episode of star trek TNG with a dyson sphere in it. What I didn't get then and still don't is how the gravity translates from the outside to inside, I would imagine like with most spherical planets you would start off from the outside being pulled towards the centre, but at what point would gravity reverse and start to pull you back to the surface?

It doesn't. Inside the Dyson Sphere, gravity due to the sphere's mass would be zero everywhere due to Newton's Shell theorem. The Star's gravity would still be there, pulling everything inward. If you tried to stand on the interior surface, you would fall into the star. One of the disadvantages of the Dyson sphere in which you live on the interior surface is that it would require artificial gravity technology to work, or you would live in sealed, microgravity environments.
Quote:

Also since most of the dyson sphere would be hollow, it would be interesting to see if the sheer size of the thing had any impact on gravity over or above the actual effects of it's mass alone.
• May 14th, 2012, 11:23 AM
Ascended
Picture of a Dyson Sphere
• May 14th, 2012, 06:15 PM
Ken Fabos
John Galt @6 - it sounds plausible to hold atmosphere in centrifugally with high walls but my understanding is that it wouldn't work. I admit I'm not sure of the physical reasons but recall it got a mention by someone with some expertise in atmospheric physics at RealClimate - a diversion during discussing Dr Dyson's views on climate change if I recall correctly. Every molecule moving anti-spinward would tend to lose that outward push? Molecular velocity relative to the strength of that centrifugal push? As far as seemingly scientifically plausible goes, it did work well enough when I first read Ringworld. Far more successfully than the extremely inconsistent explanation of the workings of the Smoke Ring of "The Integral Trees".

Japith, as far as elements of grand scale space opera goes, ideas like Dyson Spheres are great. It's even fun trying to figure out how such things might work in the real universe but this is one that's going to require technologies like artificial gravity that overcome the physical constraints the universe imposes.
• May 14th, 2012, 06:20 PM
skeptic
I see no reason why an intelligent species could not be genetically modified as a zero gravity life form. If there were two spheres (one transparent) to hold the atmosphere, this species could fly around in the in-between zone.

Mind you, I more agree with Ken with the suggestion of many space habitats. That makes far more sense.
• May 14th, 2012, 07:21 PM
Ken Fabos
Skeptic, I'm not sure if I could suspend my disbelief for shelled Dyson Spheres - But in SF that's as much about a writer's abilities as what is physically possible, so maybe. I did get sucked in by Niven's Ringworld, but I suspect I'd find it harder now than back when I first read it. Niven's freefall environment of his Smoke Ring (an inhabitable torus around a neutron star) failed. I simply couldn't suspend my disbelief, but perhaps because major inconsistencies between how it's workings were explained and a storyline that took place within a 'smoke ring' that worked quite differently. It did make me think about whether habitable freefall 'zones' could exist naturally. Beyond the zone between two planets orbiting so close their atmospheres merged, (Robert Forward?) I haven't heard of any.
• May 15th, 2012, 12:02 AM
skeptic
Ken

Maybe if the species involved evolved from anaerobic organisms, so that it needed no gas to breath, it might be possible to get a free fall intelligence living in space. It might be a little difficult to work out the natural ecology, though. The time taken to move to where nutrients were available might mean that such an organism would be living on a much slower time scale to what we use.
• May 15th, 2012, 01:16 PM
Janus
Quote:

Originally Posted by Ken Fabos
John Galt @6 - it sounds plausible to hold atmosphere in centrifugally with high walls but my understanding is that it wouldn't work. I admit I'm not sure of the physical reasons but recall it got a mention by someone with some expertise in atmospheric physics at RealClimate - a diversion during discussing Dr Dyson's views on climate change if I recall correctly. Every molecule moving anti-spinward would tend to lose that outward push? Molecular velocity relative to the strength of that centrifugal push?

Hmm, I don't know if I by that argument. The tangential speed of the ringworld would have to be ~1211 km/sec. The average speed of an air molecule at STP is 0.5 km/sec. Thus an anti-spinward moving air molecule would "weigh" ~ 0.999 times its "rest" weight.

However, the Earth rotates with a tangential speed of ~0.46 km/sec at the equator. An air molecule moving Eastward would add. 0.5 km/sec to this. If you were to compare this molecule's apparent "weight" to that of one at rest with the surface you get a factor of ~0.998.

Thus if you compare the difference in "weight" for a anti-spinward ringworld molecule to to an Eastward moving molecule on the Earth, the Earth molecule weighs less, and the Earth would be more likely to lose its atmosphere due to this than the ringworld would.
• May 15th, 2012, 05:29 PM
Ken Fabos
Janus, I could be wrong. It wouldn't be the first time.

PS - wouldn't the critical factor be the centripetal force which relates to angular velocity rather than the tangential speed? The relationship between tangential speed and radius? Presumably sufficient force to give an equivalent to 1G (or whatever it was for Ringworld). It doesn't mean that you are wrong that atmosphere would act similarly under centrifugal effect as with gravity. I admit to being out of my depth here.