Our civilization consumes more and more energy as it progresses. Consider that the total ouput from the Sun is about 4 x 1026 W, of which the illuminated Earth intercepts a small fraction (10-9). With our accelerated energy consumption rate, we would soon use that whole illuminated Earth energy. Given the cosmic timescale (see G. V. Coyne in this proceedings), there is plenty of room for other civilizations to have been born well before ours. These more advanced civilizations would require unthinkable amounts of energy. Freeman (1960) proposed that advanced civilizations would have the means to use all the energy of their parent stars by building A.U. size shells around them. Using the laws of thermodynamics he predicted how these “Dyson spheres” could be observed, even without knowing the nature of these objects. Whole or partial Dyson spheres would dim the original stellar light, and radiate in the IR (at about 10 μm).