In 1961 a young radio astronomer named Frank Drake came up with a formula to estimate how many planets in our galaxy may be home to intelligent life.
It became known as the Drake Equation, and when its inventor factored in the number of stars, the percentage likely to have planets around them, the percentage of those planets likely to be right for life, and so forth, he concluded the universe must be teeming with sentient beings.
The Drake Equation looks like this...
...and there's an explanation of the variables in it HERE. Take a look at the calculator on the right (or at THIS ONE) if you want to play exobiologist yourself. If you're like Drake, you'll conclude that there are myriad civilizations out there trying to get in touch with us.
But are there? We haven't heard from them, hard as Drake and his colleagues have worked at SETI, the Search for ExtraTerrestrial Intelligence.
Now comes Dr. Andrew Watson, a climate scientist at the University of East Anglia in Great Britain, who says the odds of finding beings like us elsewhere is very, very low -- perhaps as little as 0.01 percent over the four billion years that a given planet like ours is likely to be friendly to life. (Hat tip to Tuan Nguyen of our staff for catching this.)
Watson is hardly alone in his belief; Don Brownlee and Peter Ward wrote a book called "Rare Earth" in 2000, in which they argued that our planet was extremely unusual--not only did it have liquid water, not only was it the right size to hold an atmosphere, but it also had a giant neighbor (Jupiter) to draw away asteroids and other debris that might otherwise have pummeled it as the Solar System formed. Find a good discussion with them, Drake and others, HERE.
The factor Watson introduces to the argument is that, as he argues, there's a finite window for life on Earth--and we came into being relatively late in that window. The Sun is slowly growing in intensity (no, lest we digress in that direction, not enough to explain the warming of recent decades), so that Earth has "only" (his quotes, not mine) about a billion years before it gets fried.
"Structurally complex life is separated from prokaryotes [probably the Earth's first living cells] by several very unlikely steps and, hence, will be much less common than prokaryotes," he writes in the journal Astrobiology. "Intelligence is one further unlikely step, so it is much less common still."
Bummer, eh? But Dr. Drake's disciples at SETI keep up their work, funded largely by such benefactors as the Microsoft co-founder Paul Allen. Maybe someday they will prove the Watsons of the world wrong.