How to Find ALIEN Dyson Spheres

**SPEAKER_1** (0:00)
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**SPEAKER_2** (0:31)
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**Matt O'Dowd** (1:00)
In our search for alien life forms, we scan the planets and eventually exoplanets for primitive biosignatures. We wait and hope for errant artificial signals to happen by the Earth. But these may not be the best way. Any energy hungry civilization more advanced than our own, may leave an indisputable technological mark on the galaxy. And yes, we're actively searching for those too. Time to update you on the hunt for galactic empires.
Humanity is an energy-hungry species, and that hunger grows exponentially. Fortunately, we have a near-inexhaustible power source raining down from above. We could satisfy humanity's current energy needs by covering a tiny fraction of Earth's surface with solar cells.
And we should probably do that, by the way.
But we can also expand that area indefinitely, not by covering the entire Earth, but by building solar collectors in space. That's a lot of room to expand if we were to cover the entire sphere surrounding the sun with the radius of Earth's orbit, we'd collect all of the sun's light a billion times more than we'd get just by covering the planet in solar cells. The idea of wrapping the sun in solar collectors is not new. It was first proposed by British author Olaf Stapledon in his 1937 story, Star Maker. It was also named the Stapledon Sphere, but only by the guy who was trying to avoid having his own name attached to the idea without success. In 1960 Freeman Dyson was inspired by Stapledon's fiction to propose that a highly advanced civilization might expand to occupy an entire sphere surrounding its home star at the radius of the planet of origin for the purpose of both habitation and energy collection. To Dyson's regret the notion became called the Dyson Sphere. Naturally we've talked about the plausibility of Dyson spheres in the past. Long story short, not plausible as a solid shell, but pretty reasonable actually as a swarm of independent craft, either in orbit around the star or kiting in place on the solar wind. But Freeman Dyson's original paper was not about how to build one of these things, rather about how to find them. If the Dyson sphere or swarm or whatever is a natural stage in the progression of many civilizations, might these be the best way to look for signs of intelligent life?
Let's find out what our search has told us. Earth's biosphere is already a pretty good planet scale solar collector. If you were to observe Earth from a distant solar system, you might notice that it looks strangely dark. It doesn't reflect nearly as much of the sun's light as you'd expect for a globe of water and rock. It's as though that energy is being sucked up. But if you shifted your gaze from visible light to infrared, you'd find all of the missing energy. See, the sun produces a thermal spectrum. Light generated by its 6,000 Kelvin surface is distributed at all wavelengths, but it peaks in the visible part of the spectrum.
And Earth's biosphere, mostly its forest, absorb a fraction of that light and use it to power biological processes. And in the process they warm up, shedding all of that energy as a new thermal spectrum, now at 300 or so Kelvin, with its peak at infrared wavelengths. To spot this spectral shift from another star, you'd have to have an incredibly sensitive telescope to pick the Earth's faint glow from the sun's overwhelming brightness.
But if a civilization has expanded to reprocess a significant fraction of its home star's light, then not only could we detect that shift with our current telescopes, it would be difficult to miss.

**SPEAKER_4** (5:00)
Tomorrow morning is knocking.