Many of the numbers that go into the Drake equation can only be guessed at, for example, the factor L, the average lifetime of an advanced civilisation.
According to Drake, the average of people's best estimates suggests that there are about 10,000 technically advanced civilisations spread across our galaxy.
Image: Frank Drake demonstrating his famous equation (credit: Dr Seth Shostak/SPL)
An astrophysicist estimates how many civilisations are out there.
Frank Drake explains how to estimate the number of civilisations in our galaxy.
The Drake equation is designed to estimate the number of detectable alien civilisations in the Milky Way, as Frank Drake explains in this clip.
Frank Drake describes the rhythms found in pulsar signals.
In the late 1960s, Frank Drake describes pulsars and the patterns found in their signals.
Frank Donald Drake (born May 28, 1930) is an American astronomer and astrophysicist. He is most notable as one of the pioneers in the search for extraterrestrial intelligence, including the founding of SETI, mounting the first observational attempts at detecting extraterrestrial communications in 1960 in Project Ozma, developing the Drake equation, and as the creator of the Arecibo Message, a digital encoding of an astronomical and biological description of the Earth and its lifeforms for transmission into the cosmos.