It could be sooner than you think.
It spells inescapable doom for intelligent life in the far, far future. No matter where you are located, the rest of the universe would eventually be receding from you at the speed of light, slipping forever beyond the horizon of knowability. Meanwhile, the shrinking region of space still accessible to you will fill up with a kind of insidious radiation that would eventually choke off information processing—and with it, the very possibility of thought. We seem to be headed not for a Big Crunch or a Big Chill but something far nastier: a Big Crackup. "All our knowledge, civilization and culture are destined to be forgotten," one prominent cosmologist has declared to the press. It looks as if little Alvy Singer was right after all. The universe is going to "break apart," and that will indeed mean the end of everything—even Brooklyn.
Even more interesting is this idea from Freeman Dyson:
Suppose the acceleration does turn out to be temporary and the future universe settles into a nice cruise-control expansion. What could our descendants possibly look like a trillion trillion trillion years from now, when the stars have disappeared and the universe is dark and freezing and so diffuse that it's practically empty? What will they be made of?
"The most plausible answer," Dyson said, "is that conscious life will take the form of interstellar dust clouds." He was alluding to the kind of inorganic life forms imagined by the late astronomer Sir Fred Hoyle in his 1957 science fiction novel, The Black Cloud. "An ever-expanding network of charged dust particles, communicating by electromagnetic forces, has all the complexity necessary for thinking an infinite number of novel thoughts."
How, I objected, can we really imagine such a wispy thing, spread out over billions of light-years of space, being conscious?
"Well," he said, "how do you imagine a couple of kilograms of protoplasm in someone's skull being conscious? We have no idea how that works either."
Lawrence Krauss, the most famous professor at my dear old alma mater, makes an appearance as well, with a more pessimistic ake:
"We appear to be living in the worst of all possible universes," Krauss told me, clearly relishing the note of anti-Leibnizian pessimism he struck. "If the runaway expansion keeps going, our knowledge will actually decrease as time passes. The rest of the universe will be literally disappearing before our very eyes surprisingly soon—in the next ten or twenty billion years. And life is doomed — even Freeman Dyson accepts that. But the good news is that we can't prove we're living in the worst of all possible universes. No finite set of data will ever enable us to predict the fate of the cosmos with certainty. And, in fact, that doesn't really matter. Because, unlike Freeman, I think that we're doomed even if the runaway phase turns out to be only temporary."