If we’re right that there are 100,000 or more intelligent civilizations in our galaxy, and even a fraction of them are sending out radio waves or laser beams or other modes of attempting to contact others, shouldn’t SETI’s satellite array pick up all kinds of signals?
But it hasn’t. Not one. Ever.
Where is everybody?
That question (or a variant of it) is known as The Fermi Paradox, and the above quote is taken from this rather nice and very readable article which outlines some of the big questions and possible answers.
Many thanks to Michael Fraser for the link.