Avi Loeb, who's one of the most creative people in my field, posted a paper yesterday exploring the likelihood of life in the universe as a function of time. He and his two collaborators argue that life is far more likely to arise in the distant future of the universe than it is today. Why?
It's mostly a question of time. The universe is 14 billion years old, but if we extrapolate forward by many trillions of years, there's just more opportunity for life to arise in that much larger span of future time than in the time we've had so far. The Sun will burn out long before then -- it's already halfway through its expected lifespan. (Don't panic! There's still time for that last-minute order to Amazon). But low-mass dwarf stars, much smaller than the Sun, are the subcompact cars of the universe -- they don't burn through their nuclear fuel as wastefully, so they'll survive trillions of years into the future. Loeb and collaborators argue that life is most likely to arise in the distant future on planets orbiting these stars.
A problem with this scenario is that we don't know if planetary systems around dwarf stars are suitable places for life. Dwarf stars are much cooler than the sun, so planets have to be much closer in, where tidal forces are a lot stronger. These stars also tend to fluctuate more in their brightness than do Sun-like stars. But as scientists begin looking for signatures of life on planets orbiting other stars, we may soon find out whether dwarf star planets are the preferred places for life to exist, or if they're mostly just lifeless rocks.