June 01, 2013
Where Are The Alien Megastructures?

Check out The Hunt for Alien Megastructures by Markus Hammond. Some researchers are looking for signs of Dyson spheres.

To find a Dyson sphere, you need to look for a specific signature of infrared light, emitted at just the right set of wavelengths.

And thatís just what an ongoing project, headed by Dick Carrigan at Fermilab, has been doing.

Will alien species think building Dyson spheres brings the risk of unwanted hostile attentions? My guess is some will think that way. The ones that do not think that way might eventually get wiped out. Though their Dyson spheres would survive perhaps for thousands of years before another race's attack fleet could reach it.

Does the vastness of the expanses between stars make interstellar travel so hard that interstellar attacks are rarely attempted? Or do aggressors send nanobots to carry out their attacks? Also, are Dyson sphere builders likely to be able to repel a nanobot attack?

Share |      Randall Parker, 2013 June 01 04:31 PM 


Comments
JayMan said at June 1, 2013 6:26 PM:

I don't see why a civilization would build a Dyson Sphere. Would we?

Grumbles said at June 1, 2013 7:38 PM:

Where is the profit in launching an attack across interstellar distances?

Brett Bellmore said at June 2, 2013 4:41 AM:

I know that's what I think, when I see a sphere built around a star, making it's entire energy output available for, if necessary, military purposes:

Easy pickings!

Seriously, let us assume a civilization capable of detecting any Dyson spheres, and which is both capable and determined to reach out across interstellar space, and wipe out anybody who builds one. They must have massive capabilities, to be able to deploy, at many light years' distance, resources sufficient to kill off a species which has already achieved K-2 status, and has the entire energy output of a star at it's disposal. They must already be spread across the galaxy. Monitoring all stellar systems locally would be a piece of cake, and wiping out nascent civilizations at a far lower level would be the efficient course of action.

IOW, they'd likely already have found and killed us, and they'd probably have their own Dyson spheres all over the place, to provide power for their genocidal crusade.

We either live in a galaxy where all intelligent life cowers in hiding, fearful of being wiped out if it's noticed, or one where WE are the only intelligent life. I think the latter rather more likely, for this, and other reasons.

Why would a civilization build a Dyson sphere? Because it is the easiest way to have at your disposal all the power necessary to do the things an ambitious civilization wants to do: Teraform planets. Launch a massive interstellar colonizing effort. Power clouds of trillions of space colonies.

Really, it's the logical thing to do, as soon as you're capable of it.

Engineer-Poet said at June 2, 2013 7:58 AM:

Could a more advanced civilization hide their Dyson sphere by faking the spectral signature of a cooler star?  There's plenty of work you can squeeze out of the ΔT between 5700 K Sol and a 2000 K fake red star.

Ambacti said at June 2, 2013 11:17 AM:

I don't think building a Dyson sphere around a yellow star would make sense. If there are Dyson spheres out there, they are on small, long lasting, efficient red dwarves. A big yellow star like ours has poor hydrogen circulation and will blow up in your face after a short few billion years. A nice red dwarf with good hydrogen convection could be mined for trillions of years. Given the economies of scale, it is entirely expedient to achieve almost complete spectral blockage for an already dim red dwarf, killing two birds with one stone. It is impossible to tell with the naked eye, but at least 85% of the stars in the galaxy are red dwarves. If a few hundred million of them were well insulated Dyson spheres, we wouldn't immediately notice their absence. In fact, we have barely got a handle of the exact number of red dwarves in the galaxy, every advancement in telescopes reveals new red dwarves by the barrel load. If I were an astrophysycist with time to burn, i'd do a galaxy wide red dwarf population density census, perhaps after a few decades of looking, some conspicuous dim patches with statistically too few red dwarves might be found.

-don't forget to cite me in your paper :)

Brett Bellmore said at June 2, 2013 1:17 PM:

The reason it would make sense to build a Dyson sphere around a yellow star, is because we happen to be around a yellow star already, and the Dyson sphere would give us the power necessary to go other places. Sure, you might subsequently build around red dwarfs, because they're common and stable.

And, don't envision some massive rigid sphere; A Dyson sphere would be built as a statite array, lightweight units independently supported by light pressure. The entire sphere would be no more massive than a moderate sized asteroid. We could probably start building one before the end of the century, no unobtainium required.

Engineer-Poet said at June 2, 2013 2:31 PM:

Statites not required either.  Building the first set as an orbiting band between Earth and Sol to provide some shade could help if climate control is necessary.  If you don't want that any more, you use light pressure to change their orbital plane slightly.

Brett Bellmore said at June 2, 2013 2:54 PM:

I don't think they'd start out as statites. The problem with statites, as classically conceived, is that you can't really use most of the light hitting them. If you absorb light on the sunward side, and radiate it as power on the other, it provides no net lift!

But a closed array of statites around a star would build up reflected/re-radiated light inside, and act like a balloon inflated with photon gas. Assuming that the sunward surface had a 90% albedo, the light pressure will increase 10 fold, allowing the full radiated power of the sun to be available for power production, while the statite can be built much more robustly.

You'd start out with the statites functioning as solar power satellites, in orbit around the equator, then build towards the polls, inclining the satellites to compensate for the axial component of the pull. As you started to approach closure, you could slow the orbital velocity as the light pressure increased, ending up at a standstill when closure reached 100%.

Only near the end of the process would they be functioning as genuine statites.

Kudzu Bob said at June 2, 2013 3:12 PM:

Where is the profit in launching an attack across interstellar distances?

Don't be naive. The profit is in building interstellar battle cruisers, not in using them. The Emperor in Star Wars may not have gotten much bang for the buck out of his fancy Death Star, but you can be sure that the well-connected corporation that won the bid did quite well for itself. And after a bunch of kids blow the damned thing up, does Palpatine have the entire board of directors executed? No, he lets them con him into constructing another moon-sized space station instead. That sounds about right.

Engineer-Poet said at June 2, 2013 11:13 PM:
a closed array of statites around a star would build up reflected/re-radiated light inside, and act like a balloon inflated with photon gas.

It might be best to use waste heat for the photon gas, rather than reflecting (and diffusing) incoming light.  Ten sun's worth of IR takes you to 700 K.

Might it be worthwhile to use reflected light to boil off the outer layers of the Sun, reducing its mass and extending its lifespan?  That certainly requires an extremely long time horizon; no pol in a democratic regime is going to vote for it over bread and circuses.

A Sunshade power system could just sit at the Earth-Sun L1 point.

Phillep Harding said at June 3, 2013 10:27 AM:

EP, No politician, even with multiple thousand year life spans.

Randall Parker said at June 3, 2013 8:57 PM:

Grumbles,

Lots of people do lots of things for reasons other than profit. Imagine a species that thinks it should be the only intelligent species in the universe and that any other intelligent species is an offense against their god. Or imagine a species that gets great joy from hunting and killing. Or imagine a species that just wants to spread itself all over and considers all other intelligent species an obstacle in their plans. Another motive: fear. If you think all other intelligent species are hostile to your species then kill them.

Brett Bellmore said at June 4, 2013 9:34 AM:

Yeah, I'm just pointing out that, rationally, in that scenario, we'd already be long since dead. So we know we're not living in that scenario.

Ambacti said at June 5, 2013 9:24 AM:

If humans get out into interstellar space, woe be upon any creature more primitive than we. We should not expect anymore restraint from alien life than we ourselves would show. Given the fact that our presence is known within a radius of only about 100 light years, it is too soon to rule out the possibility that the galaxy is crawling with million IQ space nazis looking to exterminate all uppity untermenschen. If this is in fact the case, we most likely won't even see the end coming, no alien battleships will come into orbit. What we can eventually expect is a bombardment by relativistic low-observability a.i. guided anti-matter powered cruise missiles. Some would argue that if the intention to suppress all other intelligent life existed, the best course of action would be to flood the galaxy with self-replicating hunter-killer drones. I have my doubts about this method, splattering your hard earned technical knowhow across the galaxy is foolhardy. An equipment failure or enemy subversion is always possible, potentially causing a serious pain in the ass. I think a relativistic projectile would minimize the risks of capture posed by technical breakdown or subversion.

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