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although it was a riff on "spherical cow in a vacuum" - I suppose it's effectively an instance of the fermi paradox

failure to observe dyson spheres and failure to observe any civilization at all has so far been indistinguishable

dyson spheres are easy to look for (infrared sig), you get a testable theory out of it; out of most of the others, you don't

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and

dyson swarms are a way more workable design