Geoff Marcy has spent the better part of his career peering into the depths of space in the search…
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Top image: Star Trek: The Next Generation, "Relics" features a Dyson sphere. 

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Very quickly, a Dyson sphere is is a hypothetical megastructure envisaged by physicist Freeman Dyson that would be roughly the size of a planetary orbit and consist of a massive array of solar collectors.  It would be the solar panel to end all solar panels, a massive object capable of fueling a civilization with all the energy it could ever possibly need - 4x10^26 W to be exact. 

Given the extreme benefits and relative ease of building such a structure, many futurists speculate that Dyson spheres are a common fixture of the Galaxy, a logical end-point for an advanced, machine-based civilization.  The general thinking is that an advanced civilization would use all the power produced by their sun to fuel their massive computational projects, which could include uploading all of their consciousness into a digital substrate.  Furthermore, the Great Silence may indicate that advanced civilizations aren't really interested in taking interstellar vacations, preferring to stay at home where the action is. 

We are closer to being able to build a Dyson Sphere than we think.  By enveloping the sun in a…
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While it might seem reasonable that SETI look for Dyson spheres, the organization has made no serious attempt to do so.  It's the kind of thing that's only been done by a few dedicated folks and amateurs.  But that's looking to change, as SETI revises its sense of the future. 

SETI's reluctance

Up up until very recently SETI has been hesitant to supplement its traditional strategy of scouring the heavens for radio signals.  But as we head deeper into the 21st century, and as our conceptions of what an advanced intelligence might look like, SETI is starting to come around to the idea of trying other strategies. 

That includes expanding our notions of what other civilizations might look like.  For example, in a recent conversation with io9, SETI Institute's Seth Shostak conceded that the "vast majority of life in the Galaxy is very likely to be machine-based."  As we already noted, the power generated by a Dyson sphere could be very useful to a cybernetic intelligence. 

Similarly, NASA's Stephen J. Dick has argued that we likely live in a "post-biological universe," in which digital existence has largely trumped the biological.  He makes the case that we may become (or spawn) a postbiological species — one that has "evolved beyond flesh-and-blood intelligence to artificial intelligence" and is a "product of cultural rather than biological evolution."  He believes that this possibility hasn't been given the attention it deserves, nor has it been carried to its logical conclusion.  Consequently, Dick argues that we need to apply more long-term thinking when contemplating the problem of our future and that of intelligence in the universe. 

Thus, Dick's insight also suggests that we should be looking for Dyson spheres and other megascale artifacts. 

Bring on Dysonian SETI

Given that SETI has been listening for radio signals for the past half century with no results, and in consideration of the widening array of target options, it's time that SETI update their thinking.  This has given rise to the "Dysonian SETI" approach, a new methodology that would involve a wider set of search parameters and assumptions. 

The expansion of SETI into these areas would significantly expand the overall process, greatly increasing the chance that we might detect signs of advanced alien life. 

How to find a Dyson sphere

It's one thing to talk about looking for a Dyson sphere, it's another thing to find one. 

At first blush it sounds impossible: how could we possibly detect something that's practically invisible?  For sure, given that the shell absorbs virtually all of the host star's solar output, the spot in space where the Dyson sphere should be would be completely dark.  And it is.  Except for one very important thing: It's still giving off heat. 

Every star radiates something pretty close to a blackbody spectrum.  But if a star's radiation is captured by say, a Dyson sphere, and then re-radiated back out at a distance of around 1 AU, it would re-emerge at a much lower temperature — a few hundred Kelvin to be exact.  Freeman Dyson himself knew this, which is why he suggested that we scan the heavens for blackbody objects radiating in the far infrared around 10 microns in wavelength. 

Of course, detecting such a signature wouldn't guarantee that what we've detected is a Dyson sphere.  But it would sure make us think, wouldn't it?  Such a discovery would not only be monumental for science, it would be a powerful indication that we ourselves might also build such a thing someday.