This article is insane. Or rather, the conclusion the article discusses is insane. And I'm a little put off to be reading about the "Boltzmann Brain" when I've read book after book about cosmology and never heard of such a thing. This leads me to believe, though the article doesn't quite say so, that this concept is one that has been adopted by various cosmologists as an amusing or frightening result of their present theories. Given the fact that Ludwig Boltzmann died long before quantum theory arose, and thus could not possibly know or understand how quantum fluctuations could possibly give rise to organized systems at random. In fact, if you read this article at Wikipedia you'll see that this is true, and that Boltzmann's "paradox" has everything to do with classical physics' understanding of random fluctuations in an otherwise fairly disorderly universe. And although quantum theory requires that particles arise randomly in the void of the universe, that is certainly not what Boltzmann had in mind when he created this paradox. Also, there's an anthropic elements to Boltzmann's paradox, in that for us to observe conditions of low entropy, we must be products of those conditions of low entropy, and that has little to do with modern quantum theory anyway. So it would appear to me at least that this paradox was probably remembered by some physicist or grad student somewhere who thought it would graft nicely on to our present explanations for why the universe is as ordered as it is, at least on the local level.
Also, I don't like the emphasis on the paradox anyway, as the article implies that the natural result of quantum fluctuation is an infinite number of self-arising, self-aware entities floating out in the universe. It's more likely that quantum fluctuations, over an infinite amount of time, will product all kinds of random ordered objects, including mundane objects like pianos or bizarre things we have no awareness or understanding of. So the author of the article wants to focus on the anthropic element of the Boltzmann paradox, but fails to really discuss that quantum theory says any ordered object can arise randomly in the universe. They do allude to that, when one scientists says it's more likely a whole other universe would be created than a naked brain floating in space. But by whose calculations are we coming up with these odds? Here's one quote I liked: "People have their own favorite measures of probability in the multiverse, said Raphael Buosso of the University of California, Berkeley. 'So Boltzmann brains are just one example of how measures can predict nonsense; anytime your measure predicts that something we see has extremely small probability, you can throw it out,' he wrote in an e-mail message." Indeed. In fact, this whole article really is only saying that in a universe that expands forever, spinning off into an infinite number of other non-observable universes, each subject to quantum fluctuation, then any and everything is not only possible, but must happen at some point. Which is really not all that interesting or surprising. You don't even need quantum theory for it. Just imagine a universe that lives forever, where anything can happen, and there you go. And that's really all their talking about here, the implications of a universe where things can arise at random. But that means absolutely nothing to you and me here, or to our planet, or our solar system or galaxy, or even our own particular universe, which would be a small enough sample of the multiverse so that incredibly bizarre things are not likely to happen at random where we're going to notice. Yes, in an infinitely old universe where anything can happen, an exact replica of you could arise somewhere that has all of the same memories that you had during life. The implications of such theorizing are fascinating in deed. What if somewhere infinitely far ahead in the future an exact replica is created of you, with all your present memories, on a planet just like Earth? Is that you? Have you been reincarnated? But if you're holding out hope for quantum physics to grant you eternal life...well, don't hold your breath.
Anyway, I personally subscribe to the theory that if your theory produces absolutely insane results, then there's something wrong with your math. We do not sufficiently understand what dark energy is, or why it exists or whether it is even the real reason why our universe is constantly being pushed to expand, or what happens to dark energy and that expansion in the end. I'd prefer to get a handle on those questions before entertaining the idea of how many random brains will appear in an otherwise dead universe.