I&#x27;m unconvinced by the Kardashev assumption that energy is the limiting factor for civilisation.<p>It&#x27;s more likely that beyond a certain point you have all the energy you can use, and the limiting factor becomes collective intelligence.<p>I&#x27;d guess that in the same way that processors keep getting more efficient, so do civilisations. At the highest levels the energy signature of a civilisation is virtually indistinguishable from the cosmic microwave background - if it&#x27;s observable at all.