Since the dawn of the scientific age when telescopes revealed the existence of planets other than our own, humankind began asking questions and fantasizing about whether Earth holds the only complex and intelligent life in the universe. All sorts of opinions have been circling around for a long time, and even a simple Google search reveals hundreds of thousands of items on the subject.
Professor Andrew Watson from the University of East Anglia has derived some mathematical models (pdf) in an attempt to show the likelihood that any intelligent life outside our planet is highly improbable. His main point comes from his theory that it took several very difficult evolutionary steps to get us to where we are, and these steps took 4 billion years, only developing intelligent life near the end of Earth’s total habitability range. This range is based on the effects the sun will have as it expands in the next few billion years. These unlikely combinations of events lead Professor Watson to conclude that intelligent life on other planets is extremely unlikely. He states, “At present, Earth is the only example we have of a planet with life. If we learned the planet would be habitable for a set period and that we had evolved early in this period, then even with a sample of one, we’d suspect that evolution from simple to complex and intelligent life was quite likely to occur. By contrast, we now believe that we evolved late in the habitable period, and this suggests that our evolution is rather unlikely. In fact, the timing of events is consistent with it being very rare indeed.”