In November 2013 astronomers estimated that 22±8% of Sun-like stars have an Earth-sized planet in the habitable zone. Assuming 200 billion stars in the Milky Way, that would be 11 billion potentially habitable Earths, rising to 40 billion if red dwarfs are included.
40 billion! Imagine that. That’s just in our galaxy. According to the best estimates of astronomers there are at least one hundred billion galaxies in the observable universe. That could be 4,000,000,000,000,000,000,000 Earth like planets I think. I might have missed an order of magnitude.
Our story begins during the summer of 1951. A nucleus of physicists (most veterans of the Manhattan Project) had reassembled at Los Alamos to create the hydrogen bomb– Bethe, Fermi, Gamow, Garwin, Teller. During lunches at the Fuller Lodge, Fermi loved to pose rhetorical questions, which he then proceeded to answer. They group had been joking about the recent UFO reports, when, out of the blue, Fermi asked “Don’t you ever wonder where everybody is?”
Fermi concluded, if interstellar travel is possible, it ought to be positively crowded out there.
However, the question had been asked and continued to beg for an answer. In 1961, Frank Drake, an American astronomer developed the Drake equation. This equation gave an estimate of the number of civilizations in our galaxy with which radio-communication might be possible. The equation itself isn’t particularly useful. Too many unknowns.
Back in 1961, there was no way to estimate the number of planets that could support life. Today from the exoplanet research we know that there could be 40 billion such planets. That still leaves the following variables to consider:
- fl = the fraction of planets that could support life that actually develop life at some point
- fi = the fraction of planets with life that develop intelligent life (civilizations)
- fc = the fraction of civilizations that develop a radio communication
- L = the length of time for which such civilizations release detectable signals into space.
In 1961, Drake made estimates for all the factors and concluded that there could be twenty such civilizations in our Galaxy. However, it all depends on what you guess. Even today, the equation can produce a result from a low of 2 to a high of 280,000,000. In other words, we don’t know.
Is the Earth such a rare combination of conditions that it is unique in the Universe?
Have other intelligences arisen, but found that space travel was too expensive, and didn’t bother to broadcast by radio?
Have other intelligences arisen, but the lifespan of technological civilizations is too short for communication? This resolution leads to the conclusion that technological civilizations doom themselves.
In other words, we don’t know.
To see some of my short stories go to www.edwardmcdermott.net