finds none. In IRAS-based whole-sky upper limit on Dyson Spheres Richard A. Carrigan Jr tells how he searched for Dyson spheres in the IRAS infrared satellite database. The sensitivity ... was enough to find solar-sized Dyson Spheres out to 300 pc, a reach that encompasses a million solar- type stars.

The evidence mounts that technology is scarce.

It does say that four sources were slightly interesting, but the survey does seem to suggest that such things are rare or absent from our part of the galaxy.

One problem with makin these things is that you need to have one already built in order to get enough energy to build one. To take a planet apart to build solar power collectors requires a lot of energy- energy you haven't got because you haven't built the collectors yet. In reality, the construction of an opaque solar power swarm would take a very long time, with very slow growth at first.

It may be that at some point, long before you get to the point of building a full Dyson swarm, a civilisation will find that they run out of patience with the project and find something else to do.

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I would say that this does not indicate that technology is scarce. Dyson spheres are interesting but don't, in my opinion, indicate tech level. Obviously it would take quite an advanced civilization to create one - but there are several possible ways in which an advanced alien may not want to make one.

Its a bit like saying that since we don't get any MP3s from space that obviously no other advanced civilization has music downloads.

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Shame. Interesting article though. Thanks timb.

Not finding evidence of any one particular technology, unless it is very basic (such as radio transmissions), is not much evidence for a lack of technological civilization. Failing to find evidence of any technology is. I posted this as part of my self-appointed role as wet blanket to the star trek lobby.

Well, 300 parsecs is only a tiny bit of the galaxy, much less the Universe. I don't think Dyson spheres would be inevitable for a supertech society anyway.

And in a way, it's probably a good thing that nobody that powerful is close to us; there's no way we could defend ourselves against Dyson-sphere builders.

Good point.

Doesn't eliminate Ringworlds though.

No, but the strength of materials in the real world does.

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Come on... scrith is the wonder-material of tomorrow! Soon you will be barbecuing on a scrith grill! scrith baseball bats! scrith shoes!

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---"Why do things have to suck so bad?" a friend once asked me.
"Because space is a vacuum and that's a lot of suck." I replied.
(Actual quote)---

Bad idea: Do NOT hunt for people who do not want to be found and have technological capability to take apart planets.

"Hey honey, watch me poke this bull with a stick!"

Oh so thats it then. No aliens. (slitting wrists) :-)

Only Niven-type ringworlds, spinning around the main axis for Earthlike gravity. One rotating at close to orbital velocity for a circular orbit with the same radius would only need to have the strength to withstand tidal forces from other objects in the system, and the corrective forces needed to keep it centered and counter any other instabilities due to self gravitation and variation in position around the sun.

And a glass top to keep the air in!

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Todd (Bowie, MD, US, North America, Earth, Sol System, Vega region, Local Bubble, Orion arm, Milky Way Galaxy, Local Group, Virgo A Cluster, Virgo supercluster, the universe in which spock is clean shaven)

Quidquid latine dictum sit, altum sonatur.

personal page: http://blog.astrosketches.info

Yes. Such a ringworld, rotating at near-orbital speed, would have low gravity , so would need to be sealed. A good idea, nevertheless, if you can tolerate low gravity. We call these low-gee rings 'Ribbonworlds' at OA. perhaps because they flap about a bit.

One idea I had was to make the ringworld surface itself a dynamic orbital ring, which would be rotating much faster than orbital speed but would be held in place by a massive, non-rotating outer ring- which would be pulled towards the star by gravity. I haven't worked out any maths for this, however- there may be constraints I haven't considered. Probably the worst problem would be keeping the rings apart magnetically- the level of fine control required might be unfeasible.

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Or it could consist of a string of much-smaller rings rotating for their own gravity.


Actually, it should be possible to make such a thing passively stable, aside from the usual ring instabilities. I've considered it a few times...the main problems I see are electromagnetic drag (very strong fields needed to support what amounts to the surface of a planet, lots of losses...and waste heat), and the sheer quantity of superconducting material required.

edit: look at it the other way around...a maglev rail with habitats racing along it, and the limit of what you achieve by adding habitats over time. Also, they needn't be on the sunward side, but could hang from the rail.

I like to call that idea a 'necklace'. This idea comes quite close to Olaf Stapledon's original idea of 'strings of artificial worlds, surrounding a star' which, I believe, inspired Dyson in the first place.
But necklaces, and their slightly more substantial cousins, topopoli (macaroni worlds) would be difficult to see in the infrared, I would imagine.

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Now Clarke might have had the right idea--forget making an optimal place for your body to live, utilizing solar energy to the fullest. Get rid of your body and exist as an energy being in the universe, a la 2001! You can even leave monoliths all around to freak corporeal beings out.

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Todd (Bowie, MD, US, North America, Earth, Sol System, Vega region, Local Bubble, Orion arm, Milky Way Galaxy, Local Group, Virgo A Cluster, Virgo supercluster, the universe in which spock is clean shaven)

Quidquid latine dictum sit, altum sonatur.

personal page: http://blog.astrosketches.info

we might as well be pre-victorian english imagining aliens would build space houses out of bricks, and fly in bullets shot out of a giant blunderbuss.

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plenty of woo, at the hotel hoagaland...

or imagining fairies at the bottom of the garden.

Clarke also described the monoliths self replicating in order to convert a gas giant (Jupiter) into a miniature star; if that isn't megaengineering, I don't know what is.

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Adding another 79 Jupiter masses to Jupiter would be giga-engineering, I think.

well--the monolith's I believe "pressurized" Jupiter (i.e. changed the "laws of stellar physics"--the emergent ones, not the fundamental ones). Unless I misunderstood.

(actually since they can be used for teleportation, it would make sense to just dump, say, a real star into Jupiter this way! Take one 160 Jupiter masses, put a monolith in each, and let the two equalize)

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Todd (Bowie, MD, US, North America, Earth, Sol System, Vega region, Local Bubble, Orion arm, Milky Way Galaxy, Local Group, Virgo A Cluster, Virgo supercluster, the universe in which spock is clean shaven)

Quidquid latine dictum sit, altum sonatur.

personal page: http://blog.astrosketches.info

The monoliths 'stellified' Jupiter by changing its density until fusion started at the core. They seem to have done this by sucking in the atmosphere of Jupiter and changing it into something denser; iron perhaps. The increased density increased the gravity of the planet until fusion started at the core.

Incidentally, if they did change hydrogen and helium into iron using fusion that in itself would produce much more heat than the hydrogen fusion that Clarke described; transmutation of elements up to iron is exothermic- its just a little difficult to achieve...

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How so? Per unit input mass, the curve of binding energy shows that the H-->He transformation releases about 3/4 of the energy you'd get by going all the way to iron.

Its a while since I went to school, but I think three quarters is less than one. Maybe much more was an over-statement, but H->Fe definitely releases more energy than H->He.

Just because they are building Dyson sphere's doesn;t mean they are hiding. Just trying to maximize their stars energy for their own use.

But I agree, if we were to discover some ET species that was obviously trying to hide itself, and seemed to have the technology to hide itself, would be best to leave em alone.

I am thinking of finding a hornets nest, but you haven't alerted them as to your presence. Move slowly and back away!

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I've thought along similar lines. I wanted to make something close to a Niven-like 1 AU radius ringworld out of conventional materials that way, with a single "at rest" ring and two counter-spinning rings sitting on it, but the strength requirement still gets ridiculous unless the spin rings are very low mass, or don't provide anything close to 1 G on the inner surface. And then there are the losses you mention.

For the shadow squares, though, I'd replace the passive system with an active one: An array of squares in orbit between the ring and the sun, individually small, that could change angle to the sun, or opacity, essentially acting like a digital light filter on a massive scale. It would be more flexible than the passive shadow square system.

Ultimately, though, it's just easier to make small habitats than giant ones.

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Disclaimer: Avatar is not an official NASA image and does not imply any specific interplanetary or interstellar capability.

The Leif Ericson Cruiser

Here's one kind of ring around a star that could be made using conventional materials
The Rungworld

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To be honest, I didn't know that. Thanks.

Clarke expected that Jupiter would shine for millennia, if not for millions of years, through hydrogen fusion, once its density had been increased - that process would be a slow, steady luminosity.
However the process of transmutation which (presumably) produced the increase in density occured over a period of a few days (or weeks at most) during which time Jupiter would have shone like a little supernova.

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