  We motivate the \^G infrared search for extraterrestrial civilizations with
large energy supplies. We discuss some philosophical difficulties of SETI, and
how communication SETI circumvents them. We review "Dysonian SETI", the search
for artifacts of alien civilizations, and find that it is highly complementary
to traditional communication SETI; the two together might succeed where either
one, alone, has not. We discuss the argument of Hart (1975) that spacefaring
life in the Milky Way should be either galaxy-spanning or non-existent, and
examine a portion of his argument that we dub the "monocultural fallacy". We
discuss some rebuttals to Hart that invoke sustainability and predict long
Galaxy colonization timescales. We find that the maximum Galaxy colonization
timescale is actually much shorter than previous work has found ($< 10^9$ yr),
and that many "sustainability" counter-arguments to Hart's thesis suffer from
the monocultural fallacy. We extend Hart's argument to alien energy supplies,
and argue that detectably large energy supplies can plausibly be expected to
exist because life has potential for exponential growth until checked by
resource or other limitations, and intelligence implies the ability to overcome
such limitations. As such, if Hart's thesis is correct then searches for large
alien civilizations in other galaxies may be fruitful; if it is incorrect, then
searches for civilizations within the Milky Way are more likely to succeed than
Hart argued. We review some past Dysonian SETI efforts, and discuss the promise
of new mid-infrared surveys, such as that of WISE.

Popular Physics;Astrophysics of Galaxies