Be that as it may, prolific science writer and cosmologist Paul Davies has a short piece at the Scientific American blog in which he demurs to the prevailing Zeitgeist on the question of life elsewhere in the cosmos. He writes:
When I was a student in the 1960s almost all scientists believed we are alone in the universe. The search for intelligent life beyond Earth was ridiculed; one might as well have professed an interest in looking for fairies. The focus of skepticism concerned the origin of life, which was widely assumed to have been a chemical fluke of such incredibly low probability it would never have happened twice.It is interesting that so many people have come to believe that life is common in the universe even though so much of what we've learned about the conditions necessary for life to exist anywhere has actually decreased the likelihood that it exists anywhere but here. There are two reasons, I think, for the change in opinion on this question. One is philosophical and the other is scientific, and the latter is pressed into service to reinforce the former.
“The origin of life appears at the moment to be almost a miracle,” was the way Francis Crick described it, “so many are the conditions which would have had to have been satisfied to get it going.” Jacques Monod concurred; in his 1976 book Chance and Necessity he wrote, “Man knows at last that he is alone in the indifferent immensity of the universe, whence which he has emerged by chance.”
Today the pendulum has swung decisively the other way. Many distinguished scientists proclaim that the universe is teeming with life, at least some of it intelligent. The biologist Christian de Duve went so far as to call life “a cosmic imperative.” Yet the science has hardly changed. We are almost as much in the dark today about the pathway from non-life to life as Darwin was when he wrote, “It is mere rubbish thinking at present of the origin of life; one might as well think of the origin of matter.”
Davies touches on the scientific reason:
There is no doubt that SETI – the search for extraterrestrial intelligence – has received a huge fillip from the recent discovery of hundreds of extra-solar planets. Astronomers think there could be billions of earthlike planets in our galaxy alone. Clearly there is no lack of habitable real estate out there.The fact that there are so many planets, some of which might be habitable, floating about in the ether has caused scientists and others to hope that, given so many opportunities, life just has to exist on some of them. This, however, is not necessarily so. If the chances that life could arise through purely mechanistic, physical processes is astronomically high, as some have alleged (though Davies argues that such probabilities can't be determined), then even if there are billions of habitable planets that's still not enough to guarantee that life exists on any of them. Here's Davies:
Another common argument is that the universe is so vast there just has to be life out there somewhere. But what does that statement mean? If we restrict attention to the observable universe there are probably 10^23 planets. Yes, that’s a big number. But it is dwarfed by the odds against forming even simple organic molecules by random chance alone. If the pathway from chemistry to biology is long and complicated, it may well be that less than one in a trillion trillion planets ever spawns life.There's more at the link. I said above that there were, in my opinion, two reasons why many think life exists elsewhere - one scientific, the other philosophical. The philosophical reason is that materialism would be given a shot of adrenalin were life to be found throughout the cosmos, and, since many scientists are materialists, they dearly long for that shot.
If it could be shown that life can be confected wherever suitable conditions exist it would give a psychological boost to the materialist's fundamental claim that no intelligences, divine or otherwise, are necessary to explain life. Of course, logically, even if life were to be found on every other planet in the entire universe it would do nothing to dispel the claim of theists that a divine intelligence was indeed necessary to produce it, but what materialists are hoping for is psychological support for their non-theistic metaphysical assumptions, not logical proof, which is probably unattainable in any case.
