Dyson Spheres

[Michael Hopcroft]

One of the most impressive astro-engineering feats ever concieved (but obviously not attempted) by man is the Dyson Sphere. This is basically a huge shell constructed around a star that enables the use of all the star's emitted energy. it would also allow for an almost-unimaginable interior surface area which could support an enormous population.

 

It is the sort of theoretical construst that has enormous potential for use in a HERO campaign. so here are some questions and possibilities:

 

1. Because a Dyson Sphere is a solid object that completely surrounds a star, detectiong one from the outside would be difficult nat bbest -- especially if its makers wanted it to be hard. would a starship find any evidence that the thing is there by any means short of collision?

 

2. Once the sphere is constructed and inhabited, would it require further attention from its makers?

 

3. If one's world is a Dyson Sphere, how would one's life be different?

[DrFaust]

Re: Dyson Spheres

 

3. If one's world is a Dyson Sphere' date=' how would one's life be different?[/quote']

 

No over-crowding. In fact, there'd probably be vastly vast tracts of wilderness.

 

Travel and transport of materials might be a problem -- but then, you're talking about a civilization that's built a Dyson sphere, so probably they've already sorted long distance travel.

 

For a species that's spent most of its history living on the outside of a sphere, adjusting to the interior might take a while. Some people might develop an odd sort of vertigo -- but then, the curve of something as large as a Dyson sphere would probably be imperceptible to the human eye.

 

I still think it would be weird to look up and see land overhead, however distant.

[Erkenfresh]

Re: Dyson Spheres

 

3) I don't think you would see the land on the other side. I think the main thing to get used to would be the constant daylight. The creators would need to build some sort of roating hemispheric shield to give 12 hour days and nights to everyone (or whatever day interval suits everyone).

 

I imagine the travel inside the sphere would be built into the shell of the sphere, like a subway, or on the outside of the sphere with no wind resistance. If you needed to go to the opposite side, air travel inside the sphere seems likely.

 

1) How would anyone detect it from the outside? Well certainly, I'd imagine plenty of energy seeps out of the sphere either in the form of heat or radiation. What would the sphere do with excess energy anyway? It's gotta go somewhere. This energy output should be detectable outside the sphere.

 

2) I bet maintenance would be quite painful. But, this could be handled by a mechanic every 10-20 square miles or so. Granted, that's a lot of mechanics, but the pay would probably be very nice.

[Michael Hopcroft]

Re: Dyson Spheres

 

3) I don't think you would see the land on the other side. I think the main thing to get used to would be the constant daylight. The creators would need to build some sort of roating hemispheric shield to give 12 hour days and nights to everyone (or whatever day interval suits everyone).

 

Still, if all-daylight all-the-time is all you've ever known it wouldn't be as much of a problem. Although someone from outside the spehere, should they be able to get in, would intially be disconcerted and wonder when they should sleep.

 

I imagine the travel inside the sphere would be built into the shell of the sphere, like a subway, or on the outside of the sphere with no wind resistance. If you needed to go to the opposite side, air travel inside the sphere seems likely.

 

Except that, since the fundamental properties of the star don't change, you can't have atmosphere clean through. what you would have is a layer of atmosphere covering the interior of the sphere and hard vaccuum beyond. You could use a space-worthy craft to get from one side of the sphere to another in a hurry, but it would require some tricky navigation due to the natural gravity of the star.

 

1) How would anyone detect it from the outside? Well certainly, I'd imagine plenty of energy seeps out of the sphere either in the form of heat or radiation. What would the sphere do with excess energy anyway? It's gotta go somewhere. This energy output should be detectable outside the sphere.

 

But if that energy is being stored and collected within the sphere (which is part of the point of building the Dyson Sphere in the first place), then nothing would be there to vent and the problem of ships from outside bumping into the sphere remains.

 

2) I bet maintenance would be quite painful. But, this could be handled by a mechanic every 10-20 square miles or so. Granted, that's a lot of mechanics, but the pay would probably be very nice.

But, here is a collary to the problem: if the sphere outlasts those who made it, but there is life inside it still, then things get really interesting. This is a construct that is designed to last millions of years.

[Curufea]

Re: Dyson Spheres

 

Solar winds and solar flares would cause considerable havok, as the energy would have nowhere to dissipate but into the shell.

 

Plus, you would need artificial gravity generation and artificial shielding against radiation.

 

And, just to be pedantic, and someone will mention it sooner or later - a Dyson sphere is a number of platforms arranged spherically around a star, not a solid shell. It's science fiction stories that have made it more commonly thought of as a solid shell.

 

back on topic-

Excess energy would be vented as heat into space.

There is always excess energy - no transferrance between types of energy is done without some loss.

The Sphere would be detectable because radiation does not pass through it. Radio telescopes would see an empty spot where there should be noise from stars behind it. Pretty similar to how we detect extrasolar planets now.

 

Storms would be a major problem unless they had weather control. Otherwise we're talking vast areas in which wind can create coriolis forces.

 

Like the Ringworld - it would need an active defense against meteors, or it would be holed.

 

Evolution, like the Ringworld, would have a very big playground - there would be many species and subspecies that would never occur on a planet.

 

There are no new resources, so infrastructure would have to be planed around existing resources. Unless they started raiding other systems. Which is possible - if you can build a Dyson Sphere, you can move a star.

[austenandrews]

Re: Dyson Spheres

 

(Edit: Oh great, I get to follow Curufea and look like a chump. )

 

1. Because a Dyson Sphere is a solid object that completely surrounds a star' date=' detectiong one from the outside would be difficult nat bbest -- especially if its makers wanted it to be hard. would a starship find any evidence that the thing is there by any means short of collision?[/quote']

- Since the sphere blocks light, the "dark spot" should be readily detectable. Transparency could probably be spoofed as camoflage.

- The exterior surface should reflect radiation. Presumably this could also be eliminated by technology.

- External objects will impact the surface and release detectable energy. Could be masked by absorbing incoming objects.

- Also the star has a gigantic gravity field, which could only be eliminated by the most rubbery of science. If the sphere is perfect, though, the gravity signature may not reveal its presence.

 

One point to note - a Dyson sphere doesn't have to be a single, solid construct. It can (and probably would) be made up of smaller parts.

 

2. Once the sphere is constructed and inhabited, would it require further attention from its makers?

My understanding is that Dyson spheres are not stable. That is, while a ringworld can be put in a stable orbit, a contiguous sphere can't "orbit" something inside of it. So if your sphere is basically one monolithic construct, some sort of propulsion must be used to keep it from wobbling.

 

Off the top of my head, this could be remedied by making the sphere out of concentric ringworlds that span the entire 360 arc perpendicular to the ecliptic. (Just make sure you space them apart radially so they don't crash together, which would be messy.)

 

3. If one's world is a Dyson Sphere, how would one's life be different?

Depends. If we're talking about a monolithic sphere, you can't spin it for centripetal gravity like you can a ringworld. At best you could spin it and treat the equator like a ringworld, with gravity decreasing as you near the poles. My point is, a Dyson sphere by itself would not be Pellucidor on a stellar scale. You couldn't stand on the inside surface except at the equator (or whatever latitudes gravity is tolerable). Now if your "sphere" is made of freestanding ringworlds, each could have its own centripetal gravity. Alternately you can handwave a solution with artificial gravity. Or you could have the thickness of the "shell" be sufficient to generate its own livable gravity (though I'd hate to see the mass calculations on that monster). Or simply have everyone live in microgravity, attached in various ways to the inner surface.

 

(Of course one could also live on the outside of the sphere, but that doesn't sound like the direction you're going.)

 

From the inside surface, you wouldn't see the stars. You'd have unending sunlight (though if the sphere were made of ringworlds, they could be segmented so that inner rings provide periodic shade for outer ones - assuming of course the builders cared about light-dark cycles). There would have to be a mechanism for keeping solar radiation from just building up and cooking the inner surface.

 

Space travel would be very common, if one wants to jump to different points inside the sphere. On a more planetary scale, navigationally it'd essentially be a "flat earth" making air travel simpler.

[Old Man]

Re: Dyson Spheres

 

But if that energy is being stored and collected within the sphere (which is part of the point of building the Dyson Sphere in the first place)' date=' then nothing would be there to vent and the problem of ships from outside bumping into the sphere remains.[/quote']

 

Complete absorption of that energy is unlikely at best, and even if it were being 'completely' absorbed, where would it go? I would expect the sphere to at least emit blackbody radiation. Of course, since we are discussing SF, you could always decide that the sphere builders' technology is indistinguishable from magic, and then you have your invisible sphere... but I don't think such a thing is actually possible in your reality.

[McCoy]

Re: Dyson Spheres

 

As Curufea and austenandrews have mentioned, Dr. Freeman John Dyson original idea (http://www.islandone.org/LEOBiblio/SETI1.HTM) was not a solid structure, but a shell of satelites that effectively harvested 100% of the solar output.

 

The solid structure would probably be more than a couple solar masses. Even a Ringworld would require not only all the metals in the native system, but a couple of neighboring ones as well.

[McCoy]

Re: Dyson Spheres

 

Complete absorption of that energy is unlikely at best' date=' and even if it were being 'completely' absorbed, where would it go? I would expect the sphere to at least emit blackbody radiation. Of course, since we are discussing SF, you could always decide that the sphere builders' technology is indistinguishable from magic, and then you have your invisible sphere... but I don't think such a thing is actually possible in your reality.[/quote']

Dr. Dyson suggested looking in the 10-micron range. Cancer could answer this better, but IIRC, from a distance and with no companion star to provide a mass check a body whose radiation peaked in the IR would probably be assumed to be a brown dwarf, a super-Jupiter where fussion never started.

[austenandrews]

Re: Dyson Spheres

 

Are a star's emissions essentially uniform over its surface? If not, wouldn't uneven emissions knock the sphere out of position?

[fwcain]

Re: Dyson Spheres

 

One of the most impressive astro-engineering feats ever concieved ... is the Dyson Sphere. This is basically a huge shell constructed around a star that enables the use of all the star's emitted energy.

Uhhh...

 

And' date=' just to be pedantic...a Dyson sphere is a number of platforms arranged spherically around a star, not a solid shell. It's science fiction stories that have made it more commonly thought of as a solid shell.[/quote']OK, someone else did catch this... (Never mind, nothing to see here, move along, these aren't the droids you're looking for...)

 

Franklin

[Dr. Anomaly]

Re: Dyson Spheres

 

My understanding is that Dyson spheres are not stable. That is' date=' while a ringworld can be put in a stable orbit, a contiguous sphere can't "orbit" something inside of it. So if your sphere is basically one monolithic construct, some sort of propulsion must be used to keep it from wobbling.[/quote']

Actually, a ringworld isn't stable, either. After this was pointed out to him, Niven actually used that as a plot point in his series.

[austenandrews]

Re: Dyson Spheres

 

Actually' date=' a ringworld isn't stable, either. After this was pointed out to him, Niven actually used that as a plot point in his series.[/quote']

D'oh. That's what I get for only reading the first one.

[keithcurtis]

Re: Dyson Spheres

 

{WARNING TYPE=PEDANTIC}

Uhm, actually, no, that wasn't the idea originally proposed by Dr. Dyson. His original idea can be described as a cloud of satellites, all with an orbital radius of about one A.U. about a star. It was the sci-fi writers who later took Dr. Dyson's idea and turned it into a solid structure...

{/WARNING}

 

Franklin

As was mentioned several times in the posts above.

 

Keith ";)" Curtis

[Egyptoid]

Re: Dyson Spheres

 

megascale is cheap nowadays.

[Cancer]

Re: Dyson Spheres

 

If your tech follows conservation of energy (which isn't a given in a sci-fi campaign), then a spherical shell that absorbs all the energy from a star contained inside will warm up so that the energy flux it collects from the star is balanced by the energy lost to the outside. Your engineering may collect some of the energy and sequester it into another form (create bulk antimatter from energy for use as starship fuel? channel lots of it into a "cooling laser" as featured in David Brin's Sundiver? convert all the waste heat to neutrinos and radiate those?), but failing that, then the outside of the shell will warm up to a termperature that can be computed quite simply:

 

T shell = T star * sqrt( R star / R shell )

 

Where T star is the surface temperature of the star (for the Sun, this is 5800 Kelvin), R star is the radius of the star, and R shell is the radius of the shell. If you're surrounding the Sun (T = 5800K) and you want T shell = 288K (15 C, current Earth surface), then you get R shell = 406 R star. Since 1 AU is about 215 solar radii, that means a shell radius of about 1.9 AU. (This is bigger than 1 AU because the Earth reflects a good fraction of the input solar luminosity without absorbing it and so that part's lost and doesn't go to heating up the planet, but in a Dyson sphere that reflected radiation ends up being absorbed sometime, somewhere in the sphere.)

 

The material of the shell, at equilibrium, is about the same temperature on the inside and out.

 

The outside of the shell will radiate like a black body, and the peak radiation curve for 288k is at about a wavelength of 10 microns, which McCoy mentioned above. You can't observe this very well from the ground, but it's pretty easy from space nowadays.

 

This simplistic argument holds as long you're intercepting all the stellar luminosity and letting the waste radiate as normal electromagnetic radiation ... doesn't matter if the shell is a monolithic object or a fleet of satellites.

 

So to find Dyson spheres, you look for things with 1 solar luminosity radiating with a more-or-less single temperature of about 290K. They'll be distinctive; there aren't many natural astrophysical sources that do that.

[Nyrath]

Re: Dyson Spheres

 

Dr. Dyson suggested looking in the 10-micron range. Cancer could answer this better' date=' but IIRC, from a distance and with no companion star to provide a mass check a body whose radiation peaked in the IR would probably be assumed to be a brown dwarf, a super-Jupiter where fussion never started.[/quote']

Roger the 10-micron infrared radiation. I've seen some references that suggest some kinds of Dyson sphere might be mistaken for a red-giant type star by a casual sky survey.

 

The other factor to keep in mind is that with the science-fictional giant-hollow-sphere kind of "Dyson" sphere, the blasted thing has a surface area of approximately one billion Earths. How many interstellar empires that you've read about have one billion planets?

 

Dyson Spheres at Wikipedia

http://en.wikipedia.org/wiki/Dyson_sphere

 

Dyson Sphere FAQ

http://www.nada.kth.se/~asa/dysonFAQ.html

 

Megascale structures

http://en.wikipedia.org/wiki/Megastructure

note the Alderson Disk

http://en.wikipedia.org/wiki/Alderson_Disc

[Teflon Billy]

Re: Dyson Spheres

 

If your tech follows conservation of energy (which isn't a given in a sci-fi campaign)' date=' then a spherical shell that absorbs all the energy from a star contained inside will warm up so that the energy flux it collects from the star is balanced by the energy lost to the outside. Your engineering may collect some of the energy and sequester it into another form (create bulk antimatter from energy for use as starship fuel? channel lots of it into a "cooling laser" as featured in David Brin's [i']Sundiver[/i]? convert all the waste heat to neutrinos and radiate those?), but failing that, then the outside of the shell will warm up to a termperature that can be computed quite simply:

 

T shell = T star * sqrt( R star / R shell )

 

Where T star is the surface temperature of the star (for the Sun, this is 5800 Kelvin), R star is the radius of the star, and R shell is the radius of the shell. If you're surrounding the Sun (T = 5800K) and you want T shell = 288K (15 C, current Earth surface), then you get R shell = 406 R star. Since 1 AU is about 215 solar radii, that means a shell radius of about 1.9 AU. (This is bigger than 1 AU because the Earth reflects a good fraction of the input solar luminosity without absorbing it and so that part's lost and doesn't go to heating up the planet, but in a Dyson sphere that reflected radiation ends up being absorbed sometime, somewhere in the sphere.)

 

The material of the shell, at equilibrium, is about the same temperature on the inside and out.

 

The outside of the shell will radiate like a black body, and the peak radiation curve for 288k is at about a wavelength of 10 microns, which McCoy mentioned above. You can't observe this very well from the ground, but it's pretty easy from space nowadays.

 

This simplistic argument holds as long you're intercepting all the stellar luminosity and letting the waste radiate as normal electromagnetic radiation ... doesn't matter if the shell is a monolithic object or a fleet of satellites.

 

So to find Dyson spheres, you look for things with 1 solar luminosity radiating with a more-or-less single temperature of about 290K. They'll be distinctive; there aren't many natural astrophysical sources that do that.

The problem is that there is no gravity on the inside surface. You wouldn't have vast tracts of land, you'd have vast tracts of corridors ala the Death Star with the star below the floor.

 

Would you construct vast warehouses with sun lamps?

 

This is the reason that for my fantasy world the sphere is on a demiplane that has as part of its physics an anti-gravity force that orginates at the center of the star and grows from zero to kg*9.8m/s^2 at the surface of the sphere.

 

Would there be any stable lagrange points in such an arrangement? I wonder.

 

TB

[Cancer]

Re: Dyson Spheres

 

Yeah, gravity is a fundamental problem. Radiation and energy balance is easy, so I answered the easy question.

[austenandrews]

Re: Dyson Spheres

 

The other factor to keep in mind is that with the science-fictional giant-hollow-sphere kind of "Dyson" sphere' date=' the blasted thing has a surface area of approximately one billion Earths. How many interstellar empires that you've read about have one billion planets?[/quote']

That's part of the intrigue. What exactly happens to all that surface? Why would it be worth maintaining all that surface if most of it isn't used?

 

The natural inclination is to rectify the inherent improbability of a sphere by using most of the surface area to house insanely huge machinery to run it. Spin the whole thing, set the story on the Earth-gravity equator and allow the ungodly amounts of power to justify pretty much any terraforming project you can imagine.

 

Still, even if the usable surface is whittled down to a few hundred million Earths, that's still enough space for every human alive today to control ten million square miles of land (that's three times the area of the US) or a few hundred million intelligent species to control a planet-size region each.

[Guest Schwarzwald]

Re: Dyson Spheres

 

Another issue is why people would build a DS. I mean the main idea that Dyson had was to collect all the energy output of a star, but what would you do with it all, run a trillion TV's or blowdryers? The point of the original DS was to harvest energy with a layer of solar collectors.

 

Later revisions brought up the idea of a solid shell with living space on the inside, which provides an easily understood reason for one: Living space for an unlimited population.

 

So in that case you'd have all that energy running trillions of TV sets and blowdryers.

 

In the former case, of the sphere being nothing but energy collectors, again one wonders what they'd do with all that power. Use it to produce anti-matter on a megascale to power starships? Maybe. Use it to power things like particle colliders to do research on high energy physics? Power a time machine?

 

In some ways, I can't help thinking that if people have a dyson sphere built for energy collection, we might someday be able to detect what they're doing with the energy rather than the DS itself.

 

Another idea for a DS might be as a protected habitat in case something like a 'core explosion' happens at the core of the galaxy, showering the rest of it with enough hard radiation to make it uninhabitable. This was proposed by Niven in his known space books and like many of Niven's predictions is highly unlikely, but then again you never know. If such an explosion was going to happen or was happening, maybe someone built a DS to create a habitat that was shielded against the radiation from the core explosion.

 

As a side to this issue, tho an important side, I think you'll agree, let's think on the kinds of technology it would take to make a DS. Large scale transmutation might be required, think of what that would imply. Likewise, I think you're need massive numbers of Von Neuman machines to do most of the actual work, those would imply great leaps in AI and cybernetic technology. Nanotech on a massive scale might be useful, but could be subsumed into the Von Neuman machine technology.

 

Naturally advances in space technology, as in efficient drives, are the first step. if you want to live inside it artificial gravity on a huge scale would be nice.

[Cancer]

Re: Dyson Spheres

 

I wouldn't be concerned about a galactic core explosion. We know what causes them (it wasn't known at the time Niven wrote most of the Known Space stories), we can now tell if it is going to happen here. It's not, or at least it's not in the next billion years or so, at which point I stop worrying. Given that multicellular life on Earth has only been around for about 700 million years....

 

Besides, if you make a sphere, you'll just grow to fill it, unless your growth is limited by some other resource.

[Metaphysician]

Re: Dyson Spheres

 

About the only reason I can see for building a Dyson Sphere ( outside of "because we can" as practiced by a truly godlike alien race ) is the energy collection. Anybody who could actually build a Dyson Sphere, would be better off colonizing other planets for population space. OTOH, the concentric ringworld idea would probably work better, as not only would they be more stable and possess 'gravity,' there would be intermediate benefit during construction.

[Guest Schwarzwald]

Re: Dyson Spheres

 

Here's a link to a thread I did months ago with a link to a site discussing possible DS' that have been detected by modern astronomy.

 

http://herogames.com/forums/showthread.php?t=43887&highlight=dyson

 

BTW, I kinda hope there are no DS' anywhere, as I can't help thinking that building one implies that FTL travel is impossible in this universe, and I think that would really suck. I mean, why build a DS if you have FTL?

[Nyrath]

Re: Dyson Spheres

 

About the only reason I can see for building a Dyson Sphere ( outside of "because we can" as practiced by a truly godlike alien race ) is the energy collection.

There is one other good reason, but it is a bad one for game campaign purposes.

A Dyson sphere can be used to make a Matrioshka brain. Such a thing would be even more unwelcome in your campaign than a visit from The Q continuum.