I don’t know about you, but I’ve been feeling pretty depressed about the ultimate fate of the universe lately. All this damn dark energy accelerating everything —

For w=-3/2, the Milky Way will get stripped roughly 60 million years before the Big Rip. Curiously, when this occurs the horizon will still be ~70 Mpc, so there may still be other observable galaxies that we will also see stripped apart (although given the time delay from distant objects, we will see the Milky Way destroyed first). A few months before the end of time, the Earth will be ripped from the Sun, and ~30 minutes before the end the Earth will fall apart. . . molecules and then atoms will be torn apart roughly 10-19 seconds before the end, and then nuclei and nucleons will get dissociated in the remaining interval. . . . .

The end of structure, from cosmic, macroscopic scales down to the microscopic, leads us to remark that our present epoch is unique from the viewpoint that at no other time are non-linear structures possible. When the phantom energy becomes strong enough, gravitational instability no longer works and the Universe becomes homogeneous. Eventually, individual particles become isolated: points separated by a distance greater than 3δt(1+w)/(1+3w) at a time trip-δt cannot communicate before the Big Rip. Therefore, the dominance of the phantom energy signals the end of our brief era of cosmic structure . . .

(Caldwell, Kamionkowski, and Weinberg, “Phantom Energy and Cosmic Doomsday”)

— it’s like the post-Einstein, post-Hubble version of the last chapter (chronologically speaking) of The Time Machine:

The darkness grew apace; a cold wind began to blow in freshening gusts from the east, and the showering white flakes in the air increased in number. From the edge of the sea came a ripple and whisper. Beyond these lifeless sounds the world was silent. Silent? It would be hard to convey the stillness of it. All the sounds of man, the bleating of sheep, the cries of birds, the hum of insects, the stir that makes the background of our lives — all that was over. As the darkness thickened, the eddying flakes grew more abundant, dancing before my eyes; and the cold of the air more intense. At last, one by one, swiftly, one after the other, the white peaks of the distant hills vanished into blackness. The breeze rose to a moaning wind. I saw the black central shadow of the eclipse sweeping towards me. In another moment the pale stars alone were visible. All else was rayless obscurity.

Then a few weeks ago, as part of my ongoing plan to clear my bookshelves by taking boxes full of books in categories J, L, M, and N down to the used book store and trading them in for a much smaller number of more expensive books (it’s kind of a Zeno’s Paradox thing), I picked up Infinite Worlds: An Illustrated Voyage to Planets beyond Our Sun. And what do I find out, in between all the pretty pictures of hot Jupiters and pulsar planets? That most of the stars that will ever exist have already been formed, and that even if the universe’s rate of expansion isn’t accelerating, in another 10 trillion years we’ll have drawn down our whole account in the cosmic hydrogen bank, and Stelliferous Era will be over. That most of the history of the universe, like 1040 years of it, is going to be spent sitting in the dark waiting for protons to decay. (And even when they do, it’s not very exciting.)

So I was pleased to run across this post from Sean Carroll (of the U of Chicago’s Enrico Fermi Institute, and one of the brains in the vat powering Cosmic Variance — which if you’ve read this far without your eyes glazing over, you probably should be reading):

So when we evolve to “empty space,” there is still some energy pushing the universe around; the resulting spacetime is called “de Sitter space.” Along with this energy comes a small nonzero temperature, which keeps all the fields in the universe gently fluctuating. Gentle or not, however, if we wait long enough we will find a really big fluctuation — one that is large enough to make inflation spontaneously begin. In other words, we are suggesting (although it's not original with us) that de Sitter space is unstable; it doesn’t last forever, but eventually starts inflating here and there. These little inflationary patches will ultimately convert into ordinary matter and radiation, leaving behind universes just like our own.

(Yay!)

And here is the fun part: this story can be told either forward or backward in time. In other words, you give me some state of the universe, chosen however you like. (Maybe you calculated the wavefunction of the universe, who knows.) I evolve it using the laws of physics. If Jennie and I are correct, it first empties out into a cold de Sitter space, dominated by a tiny shred of dark energy. But eventually we get lucky, and a small patch of inflating universe is born within this de Sitter background. This will happen at different places and times, give rise to a fractal distribution of spacetime geometry in the far future. And I can do the same thing going backwards in time from the initial state you gave me; the generic evolution is the same. It will empty out, and eventually begin to spontaneously inflate. So in the super-far past of our universe, before our “Big Bang” (which is nothing special in this picture), we will find other Big Bangs for which the arrow of time is running in the opposite direction. On the very largest scales, the entire universe is symmetric with respect to time.

So, you creationists: leave evolution to the Flying Spaghetti Monster. Instead, thank God for vacuum fluctuations.

Still: I wish the cosmologists would hurry up and sort this stuff out. Heat death, Big Rip, brane collisions — how am I supposed to write my space opera if I don’t know how the universe is supposed to end?

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Update: Did I say most of the history of the universe is spent sitting in the dark waiting for protons to decay? I meant most of the history of the universe is spent sitting in the dark waiting for black holes to decay. Which takes even longer. Like, somewhere between 1083 and 10131 years, according to the University of Michigan.

And when you’re done with that, you can occupy yourself waiting for nothing.

Forever.

It’s like Sartre’s recipe for tuna casserole.

Except: Vacuum fluctuations! Yay!

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P.S. Justine — does this help? Or still bored?