If alien civilizations exist throughout the universe, many have had billions of years to develop technology, expand their population and energy supplies, and travel across their galaxies. Kardashev classified hypothetical advanced civilizations by the magnitude of their power supply, with Type II civilizations harnessing most of the energy output of their host star, and Type III civilizations using most of the power in their galaxy. As Dyson pointed out in 1960, the waste heat emitted by a such civilizations would easily overwhelm that of their host star or galaxy, distinguishing them from "normal" astrophysical sources. This approach to SETI makes few assumptions about the behavior of alien civilizations, primarily: conservation of energy, the laws of thermodynamics, and that given the age of the Universe aliens have had time to develop very large energy supplies.
The WISE all-sky mid-infrared survey has dramatically improved our ability to detect such civilizations and to distinguish them from "natural" astrophysical sources. I will discuss our team's efforts to identify candidate Type II civilizations in the Milky Way and Type III civilizations throughout the low-redshift universe. Because the scope and assumptions of this approach are complementary to those of telecommunication SETI, a null result has the potential to rule out broad classes of proposed resolutions to the Fermi-Hart Paradox, particularly those that invoke organization of advanced alien species across the Milky Way.