In a depressing twist of fate, it turns out what we thought was universal background microwave radiation was just red-shifted IR from the huge number of Dyson structures in our neighborhood.Hmm the whole Concept of the Dyson structures (Swarm, Sphere, Ring) was put forward because they would emit a lot of Infrared radiation. Enough for our pre-FTL society to detect.
Aliens were everywhere, they just didn't feel like talking to us.
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