📡 The Signal

Timeline

• 1896 — Nikola Tesla suggests using radio to contact Mars
• 1924 — National Radio Silence Day to listen for Martian signals
• 1959 — Cocconi & Morrison publish "Searching for Interstellar Communications"
• 1960 — Frank Drake conducts Project Ozma, first modern SETI search
• 1961 — Drake Equation formulated to estimate communicating civilizations
• 1967 — First pulsar discovered, briefly suspected alien
• 1974 — Arecibo Message broadcast toward M13 globular cluster
• 1977 — Wow! Signal detected at Big Ear Observatory
• 1984 — SETI Institute founded
• 1992 — NASA SETI program begins (defunded after 1 year)
• 1995 — First exoplanet discovered around sun-like star (51 Pegasi b)
• 1999 — SETI@home launches, enabling citizen science
• 2015 — Breakthrough Listen initiative begins ($100M commitment)
• 2017 — Interstellar object 'Oumuamua passes through solar system
• 2020 — BLC1 signal detected from Proxima Centauri direction

The Drake Equation

N = R* × fp × ne × fl × fi × fc × L

Where N is the number of civilizations we might communicate with:

• R* — Rate of star formation
• fp — Fraction of stars with planets
• ne — Number of habitable planets per system
• fl — Fraction that develop life
• fi — Fraction that develop intelligence
• fc — Fraction that develop detectable technology
• L — Length of time civilizations transmit

Depending on estimates, N ranges from 1 (we're alone) to millions.

The Fermi Paradox

"Where is everybody?"

Enrico Fermi's famous question haunts the search. If the universe is so vast and old, why haven't we found evidence of other civilizations? Possible answers range from the "Great Filter" (something destroys civilizations) to the "Zoo Hypothesis" (they're watching but not interfering) to the simplest explanation: space is very big and very quiet.