OT: What's New in SETI?

This week's column by Ctein

Recently there have been some interesting scientific developments in the Search for Extraterrestrial Intelligence (a.k.a. SETI) that I picked up at September's "100 Year Starship" Conference in Houston.

No, we haven't found anybody yet. If we had, you wouldn't first be reading about it here! But, the astronomical community has constrained one of the possibilities and thought up a new way to search for others.

This is not a speculative column on the nature of extraterrestrial intelligence and why we have or haven't found evidence for it. I hit that topic two years ago in "Where Are They?" If you're inclined towards comments and questions in that direction, you ought to review that column and the very thoughtful comments from readers that follow it; your concerns may already have been addressed.

First, one specific and negative result. Dyson spheres are either extremely uncommon or entirely nonexistent.

Most of you are asking yourselves, "What the heck is a Dyson sphere?"

Freeman Dyson suggested, half a century ago, that a sufficiently advanced solar-system-spanning civilization (such as we might plausibly become in a few hundred years) might eventually decide to surround its star with a densely packed network of solar collectors to capture most of that sun's output as useful power. There is no reason why that can't be done; it's one of the less fanciful extrapolations of current engineering.

A Dyson sphere is a highly recognizable object with today's telescopes. No natural object has its luminosity characteristics. It would be a compact source with a total brightness equivalent to a star, but with very strong, even dominant emissions in the 10–20 µ infrared. That's simply because the waste heat from all that power consumption still has to get radiated away from the roughly 1 astronomical unit radius sphere.

(Just to be clear, the sphere isn't necessarily a solid structure; in fact that's the least likely form. It's really a very closely spaced array of solar collectors. Doesn't much matter in this discussion.)

We've now done a substantial amount of sky surveying in the mid-infrared. We don't see anything like this. If there are any Dyson spheres out there, they are far fewer than one in a million.

Now on to some more hopeful news.

The trickiest part of SETI has been figuring out what to look for. The Drake equation is a lovely conceptual tool for trying to estimate the number of civilizations that might be out there, but the further you get into the terms of the equation, the more uncertain the numbers are. At this point we have some handle on the number of stars, the number of planets per star, and the percentage of those planets that are nominally habitable (for a loose definition of habitable). But the last terms in the equation have nothing to do with basic science as we know it. They're essentially sociology on unknown creatures: What fraction of civilizations do something that we would detect as communication and how long do they do it for?

The answer, of course, is that we don't have the foggiest idea. We look for what we can look for: radio and optical signals. Does any technology use that for very long? Who knows? We can only look for what we know how to look for, but we have little confidence that we're looking for the right things.

Now there's a new search proposal which gets around that problem entirely. It doesn't look for specific technology or uses of technology, it just looks for civilizations that are large enough to be using a lot of power. And by "a lot" I don't mean much more than we're using today. Maybe a factor of two.

The power consumption of all of humanity, in all forms, is about 1/2000th the power the Earth gets from the sun. Which doesn't sound like a lot, but it's close to an excess that we can detect with current telescopes. Almost all of that power ends up as waste heat that gets radiated away from the planet. The distribution pattern of that radiation, both geographically and spectrally, doesn't look the same as what the planet radiates naturally.

What is elegant about this search aproach is that it doesn't depend on any assumptions about the technology of the civilization, where they get their energy from, how they're using it, how they communicate—none of that. All they have to do is be big enough to be consuming a little more power than we do, and we'd be able to see them.

But how far out, you ask? That's where Colossus comes in. This proposed 75-meter Earth-based telescope uses a novel design that reduces its weight by a factor of five. The cost of a telescope scales pretty well with its weight. This puts Colossus within the reach of the "big astronomy" budgets—that is, under $1 billion.

There's lots of truly nifty astronomy that Colossus can do, but what interests this column is the SETI search. Colossus will be capable of seeing human-scale civilizations out to about 20 parsecs. There are a lot of stars within 20 parsecs of Earth. In fact, based on the Kepler data, it's estimated that there are several hundred Earthlike planets within that sphere.

Will Colossus find evidence of ETI? Oh, probably not. If it were that common, we'd likely see other signs of it.

Or so we imagine. As my earlier column explained, we really don't have a clue how aliens might think or what they might do.

And that's the whole reason for the survey. We don't have much in the way of clues. If Colossus turns up zip, then that puts another upper limit on the number of such civilizations in our neck of the woods, much as the lack of Dyson spheres put a limit on those kinds of civilizations. It'll tell us a lot more about just how alone we are (or aren't?) in the Universe.

Ctein

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(To see all the comments, click on the "Comments" link below.)
Featured Comments from:

Richard: "It seems to me that we should still be Searching for Terrestrial Intelligence. Once that is found, then perhaps we might disperse with spending trillions of dollars on war and use it instead to start exploring. There is Life out there; one only needs to look up at the stars on a dark night and know you are only seeing a fraction of what's there. Will we be intelligent enough to find it and will we know what to do if we do find it? Great article."

Comments

[Romano]

I think that the saddiest thing I realized when turnef 40 (a while ago... ) was that I will never walk under a different Sun. A kind of very special 40-y-o crisis. I still hope to see a proof in my life that we are not a strange glitch in the Universe. Thanks for the insight.

[Bill]

I have a Dyson vacuum cleaner. He also makes washing machines and hand dryers. Never seen his spheres though :)

[rnewman]

While I believe that SETI is a good program, I have some doubts about a couple of your assumptions.
First, I am not so sure we could detect a Dyson sphere with current telescopes. Any civilization which can build a Dyson sphere will probably also be using thermoelectric conversion to increase efficiency. The generation of IR as waste would be greatly reduced. In space the Seebeck effect would be rather efficient, as the differential temperatures could be very large. Further, depending on how the sphere elements are distributed, they may not show up using the occlusion methods we now use to detect planets.
Second, is the ability to identify life, intelligence or 'civilization'. We currently tend to assume any life will be carbon based as is ours. The case has been made that other lifeforms, based on, for example, silicon, are possible. If such exist, will we be be able to recognize them? Or their artifacts?
As I said, I support SETI, but it is only capable of detection a limited subcategory of the intelligence signals it searches for.

[Another Phil]

Hi Ctein,
I'll have to look into how it can differentiate between civilisation heat output and a highly volcanic planet now!

I like this image of where our TV signals are now (although background noise would hide them);
http://grandrants.files.wordpress.com/2009/07/watching-tv-on-alpha-centauri.png
and this one relating it to our galaxy;
http://i.dailymail.co.uk/i/pix/2012/02/27/article-0-11EF84AB000005DC-183_964x959.jpg

I always thought a Dyson ring ala Larry Niven's Ringworld would be more practical than a sphere.

best wishes phil

[Stan B.]

I'm all for anything and everything that increases our knowledge of what's out there. But if it's proof of intelligent extraterrestrial life that you want, you need not look further than to what's going on right here on terra firma- as this Right Stuff astronaut can attest to...

http://www.youtube.com/watch?v=dvPR8T1o3Dc

http://www.amazon.com/UFOs-Generals-Pilots-Government-Officials/dp/0307716848?tag=vglnkc7117-20

[ctein]

Dear Bill,

Oh, sure you have!

http://g-ec2.images-amazon.com/images/G/01/Home_Garden/A-Plus_Pages/Dyson/DC25-MultiFloor-Ball-Technology._V386852922_.jpg

{VBG}

pax / Ctein

[Kili]

I suppose that all those civilizations, that are more advanced than our own, did already find the way not to let all that energy radiate away as thermal waste or are they in the possession of technologies that require lot les energy for living.

[ctein]

Dear rnewman,

Taking your excellent questions in kind of reverse order....

There's a big difference between searching for extraterrestrial life and searching for ET intelligence. Indeed the search for ET life can only look for, as Bones McCoy would've put it, “Life as we know it, Jim!” Because we have no idea what to look for if it isn't life that uses a chemistry vaguely similar to ours.

Conversely, SETI doesn't need to know anything about the physical nature of the life–– carbon vs. silicon, organic vs. inorganic –– but it has to make some broad assumptions about how that life behaves. So an entirely different set of search criteria and parameters come to play.

I think you're misunderstanding how an IR SETI search works. Virtually all energy consumption ultimately degrades down to EM radiation, that's just the way physics and thermodynamics works. Most of it, the vast majority, ultimately goes to heat, after you've extracted all the useful entropy differentials from it. There's just no way around that. It's not about how efficiently you capture or convert the natural power in the first place. You could have solar cells that were 100% efficient here on earth and after we got done using the energy, to run our appliances, our cars, our factories and light our lights, 99% of it would still end up as simple thermal energy.

The only way to avoid that is to actually throw away most of the usable power and NOT utilize it. Which is obviously counter to the point of the whole thing. The more efficiently you're using the natural resource, the more of it ends up as, ultimately, discarded heat.

That heat has to go into equilibrium with the surrounding space. If it doesn't, your environment just gets hotter and hotter and hotter. It's that equilibrium heat that produces the 10-20 µ infrared signature. You are correct that a small fill factor produces a much smaller signature. And, of course, if the fill factor is low enough, comparable merely to the diameter of a planet, you can't tell that excess thermal radiation from the natural thermal radiation of a planet. But the whole idea of a Dyson sphere is that it's a very advanced civilization that wants to use a significant fraction of the output of their star, at least several percent.

Of course there's no guarantee that some alien intelligence does build large, energy-hungry civilizations like we do. It's just that it's still a much broader criterion than trying to guess exactly what kind of communications/technology they operate with. No matter what you're using, it generates waste heat.

pax \ Ctein
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[ctein]

Dear Phil,

I'm the fellow, by the way, who calculated EXACTLY how unstable Larry Niven's Ringworld was. The qualitative answer is **very**-- quantum fluctuations alone will cause it to collide with its parent star in one generation. It's like the problem of balancing a pencil on its point; as soon as it starts to go the least bit out of balance, the process snowballs.

Back to your observation: Differentiating the natural signals from the unnatural ones is, of course, a big part of the design. But that has a silver lining.

Keppler was faced with the same problem–– it looked for planetary occultations by detecting a slight fluctuation in the brightness of the star. But lots of things can make stars fluctuate in brightness; flare activity, natural kinds of pulsations or stellar vibrations, even a decent sized sunspot group dims the output of a star by more than the silhouette of a planet passing in front of it.

All of these things have identifiably different characteristics from a planet transit. For example, a sunspot group takes approximately half the rotation period of the star to traverse the field of view and the dimming effect fades in and out more gradually. A planet transit takes hours and the shadowing is a pretty sharp-edged event.

The silver lining, which is a pretty big one, is that we are learning a HUGE amount about how other stars behave from these non-planetary variations that Kepler sent back. All sorts of stellar characteristics that we could not previously measure––incidence of large sunspots, how many stars are slightly variable, things like that. It's not the headline-making news, but astronomically it's as valuable as the planetary detections.

Similarly, sorting out the infrared signatures for extrasolar planets WILL tell us a huge amount about their geological processes, their atmospheric composition, and a bunch of other stuff.

Colossus is primarily useful for a huge amount of valuable astronomy. It's entirely worthwhile project. It just happens that one of the things it can do is put some real constraints on the prevalence of nearby civilizations comparable in size to our own.

pax \ Ctein
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[Del Kimbler]

Most of what I know about alien intelligence I learned from Larry Niven, who also expounded a novel variant of the Dyson Sphere, as you might know. Interesting how science catches up to science fiction. That is one of the things that keeps me reading both. Thanks for giving my brain a nudge in a slightly different direction.

[Al Patterson.]

We don't see them because they aren't using Dyson spheres, they are using Ringworlds, which are harder to detect...

[John Camp]

It's very likely that even the most advanced civilization wouldn't need the energy from a Dyson sphere. What would they use it for?

I think it's very likely that we (on earth) are approaching the limits of heat-generating technology, and that there will be few big increases in the future. I think we're near the end of physics, if not chemistry, and there are no big "practical" surprises left out there. If that's so -- if we're reaching the point where our technological jumps will be the equivalent of going from the iPhone 5 to the iPhone 5s -- then other civilizations might forever be below our horizon.

What kind of civilizations might be out there is somewhat beside the point in this SETI/Dyson Sphere idea, because we are not (and can't) look for *any* civilization, but only certain kinds of civilizations. At the present state of the art (or in almost any conceivable state of the art) we would not be able to detect a non-technological, psychology-based civilization among whale-like creatures on a water world. Given that many civilizations may be fundamentally undetectable, and that many planets may never achieve or have already passed through the technological period, then planets such as ours, in this moment, may be truly rare.

It's possible that what we were trying to detect with SETI (broadcast electromagnetic signals) may exist for only an extremely short time -- most earth-based military signals have now gone underground, via cabling, because they are harder to detect that way, and are more accurate. It's not impossible to believe that eventually all signals (radio, TV, etc.) will be cabled for efficiency's sake, and that broadcast signals could become a thing of the past.

[Another Phil]

thanks Ctein,
Quantum fluctuations appear to be destroying my washing machine - and I thought it was a bearing...

rgds phil

[Ed]

Personally I have not met any intelligent creature on earth (appart from the odd dolphin).....you're not calling the ape descendent bipedal planet ravashing creature intelligent are you?

Greets, Ed.

[Ed]

Keppler was faced with the same problem–– it looked for planetary occultations by detecting a slight fluctuation in the brightness of the star.

Eh, Keppler was a he....in my mind, untill I found out you were referring to the satelite not the astronomer, weird, usually satelites do not face problems, there operators however do from time to time.

Greets, Ed

[Ed]

Couldn't a ringworld be stabelised by some sheppard moons......much in the way as the rings of the planet some humans seem to call Sani are?

Greets, Ed.

[ctein]

Dear Ed,

Sorry, did not mean to create any confusion. The normal conventions here for writing about space programs are that sometimes you just refer to them by name, as shorthand. So, I could write, in an article on the early space program, “The Apollo program engineers faced major design problems…” or “The Apollo program faced major design problems…” or “Apollo faced major design problems…” and they'd all be read the same way. But that assumes the readers know what the Apollo space program is. I assumed that anyone reading my column would be familiar with the Keppler space mission. That wasn't a proper assumption.

Re: Ringworld, you're making the same mistake that Larry did. Ringworld is a solid body, which means it's not actually orbiting its sun. The fact that it's spinning is irrelevant to the physics. It's just a giant ring with the sun at the center. The moment anything makes it drift slightly off center the side a little bit closer to the star gets pulled more strongly by the star's gravity than the side further away, and the process accelerates. Shepherd moons don't fix that. They work for Saturn's rings because Saturn's rings aren't solid discs, they're just a whole bunch of independent particles in similar orbits.

Fred Hollander was the first to point this out, very shortly after Ringworld was published. It was just assumed that for something as huge as this, the instability times would be measured in millennia if not millions of years. It took five years for someone to get around to doing the actual calculations, namely me. It turned out that, no, the instability time was more on the scale of the orbital period.

When I told Larry this, he didn't really believe it. He was pretty convinced there must have been an error in my modeling. Then, a short time after that, Dan Alderson came up with the same results by an entirely different mathematical approach. That convinced Larry, and he had to go back and substantially revise his ideas for Ringworld Engineers. He was very gracious about it (I fear I would've been a lot more grumpy) and gave us a nice acknowledgment.

pax \ Ctein
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[Ed]

No, no I know about Kepler the now (nearly, it might be used to look for planets around white dwarfs) defunct satelite (that was lauched years behind scedule).....just that in my mind Kepler is a scientist first and a satelite later. So my cognitive cortex was a bit thrown of kilter by the "it".

Greets, Ed.