"Where Is Everybody?"
During a lunch in 1950, physicist Enrico Fermi asked, "Where is everybody?" given the billions of stars in our galaxy, many with Earth-like planets, intelligent life should be common. Civilizations should have colonized the galaxy by now. Yet, we see no signs, hear no signals. This contradiction is the Fermi Paradox.
Frank Drake formulated an equation to estimate the number of active, communicative civilizations. N = R* × fp × ne × fl × fi × fc × L. The most critical variable is 'L'—the length of time a civilization survives before destroying itself.
One explanation is the Great Filter—a barrier to evolution that makes intelligent life extremely rare. Have we already passed it (origin of life is rare)? Or does it lie ahead (civilizations inevitably destroy themselves with nukes or AI)?
Another chilling theory is the 'Dark Forest' hypothesis: civilizations hide to avoid being destroyed by hostile advanced species. Broadcasting our existence might be suicide.