[cgriswald]

That is physically impossible unless there is new physics in that hypothetical design. All physical objects radiate heat and a Dyson sphere in particular would be trivial to detect. You look take a picture of the sky in infrared and in the visible spectrum. If you find an infrared source but no associated visible star you’ve got a strong candidate for being a Dyson sphere. Such searches have actually been conducted.

Other megastructures might be discovered through the same methods as exoplanets.

[JPLeRouzic]

> If you find an infrared source but no associated visible star you’ve got a strong candidate for being a Dyson sphere

You mean like brown dwarfs?

[cgriswald]

Yes, but a Dyson sphere, even around a red dwarf, would be far more luminous in the infrared than a brown dwarf. It would also have a different spectrographic signature, and importantly its heat distribution would appear artificial.