Friday, May 15, 2015

Life in the Far Future of the Universe

Could life survive arbitrarily far into the distant future? One hundred trillion years from now, all of the stars will burn out, and the universe will suffer a long, slow decline into darkness. This inevitable decay is predicted by the second law of thermodynamics, which says that entropy always increases.

Entropy is one of those things that everyone talks about, but very few people really understand. Since I don't belong to the latter category, I'll restate the second law in simpler terms:  the second law of thermodynamics is nature's version of the income tax. Whenever you do work, the universe, just like the government, takes a cut.

Energy is always conserved, but useable energy, like the energy stored in coal or gas, always gets converted into useless energy, such as heat radiated into space. So the amount of useable energy in the universe inevitably declines with time, until there's nothing left to support life.

Freeman Dyson, who also came up with the idea of the Dyson sphere, was the first person to think seriously about whether living creatures could survive in the cold and dark of a dying universe.
A Dyson sphere, which is not the subject of this post

Back in the late 1970s, Dyson pointed out that our distant descendants could slow down their metabolism as the universe ages, using less and less energy as time goes on. As these creatures slowed down the rate at which they experience time (the Galapagos tortoise strategy), they could stretch out their subjective lifespans to be infinitely long. (I wrote a report on Dyson's paper in college -- it was one of the things that first got me interested in pursuing cosmology).

The discovery of the dark energy driving an accelerated expansion of the universe threw a wet blanket on Dyson's ideas. What's the problem? At any given time, you can't see everything in the universe -- if you multiply the age of the universe by the speed of light, it gives you the farthest distance that any information can travel since the beginning of time. This distance, called the horizon distance, fixes the usable size of the universe for any creatures living in it. Lawrence Krauss and Glenn Starkmann pointed out that the acceleration of the universe drives information outside of this horizon. Even if creatures could extend their lifespans forever, the amount of information available inside of the horizon is finite. So if these denizens of the distant future found a way to live forever, they would eventually run out of new things to experience. Imagine watching reruns of Gilligans Island over and over again...forever (a not inaccurate description of my own childhood).

It was this paper by Krauss and Starkman that inspired me to write the short story, "Extra Innings," which you can read in my previous post. I was trying to imagine how our distant descendants might react when they finally realized that they couldn't live forever. (Of course, I also threw in a few of my own experiences).  But the story doesn't end there. My own short story got me interested again in the general subject of the distant future of the universe, and when Krauss visited on a sabbatical, we wrote a paper on the idea that accelerated expansion of the universe would, in the future, erase all evidence for the big bang, so that our descendants might have no idea of the true nature of the universe. This is a rare example of science fiction inspiring scientific research, rather than the other way around. We developed this idea into a popular-level article for Scientific American. A few years later, I was reading a short story called "Turing's Apples" by the British author Stephen Baxter, and I ran across some ideas that looked like they were inspired by the Scientific American article.  Baxter confirmed that the story had, in fact, been inspired by our article.

So Baxter's "Turing's Apples" was inspired by a popular science article, which was derived from a scientific paper, which was inspired by a short SF story, which was based on a scientific paper.  See, cosmology does have useful applications.


robk said...

that was great short story from isaac asimow "the last question" or something like that where is very ironic answer for end of universe :)

Robert Scherrer said...

Yes, it's "The Last Question" - one of Asimov's most famous short stories. There's a similar (even shorter) story by Fredric Brown called "Answer" - you can easily find it online.