The Sciences

OO's and BB's

Cosmic VarianceBy JoAnne HewettFeb 21, 2007 8:02 AM


Sign up for our email newsletter for the latest science news

One nice thing about being a scientist, or at least an academic one, is that occaisionally you get your mind blown without any drugs or anything. Someone comes along and just pulls the rug completely out from under you - a total Denial of Reality Attack - and then you are left on your own to pick up the pieces. Today at UC Davis we had a seminar from Don Page of the University of Alberta. The title and abstract of this talk sounded like science fiction, so I reproduce it here:

Don Page, University of Alberta Title: Is Our Universe Decaying at an Astronomical Rate? Abstract: Unless our universe is decaying at an astronomical rate (i.e., on the present cosmological timescale of Gigayears, rather than on the quantum recurrence timescale of googolplexes), it would apparently produce an infinite number of observers per comoving volume by thermal or vacuum fluctuations (Boltzmann brains). If the number of ordinary observers per comoving volume is finite, this scenario seems to imply zero likelihood for us to be ordinary observers and minuscule likelihoods for our actual observations. Hence, our observations suggest that this scenario is incorrect and that perhaps our universe is decaying at an astronomical rate.

Boltzmann brains? WTF? Intrigued, I went. This is a well-respected, highly-cited cosmologist after all. A former student of Stephen Hawking, no less. The jargon in the abstract, though bizarre, had a certain je ne sais quoi... The idea Don put forward is this: there's us, the ordinary observers (OO's) in the world, who have achieved a certain stature after billions of years of evolution in the universe, and are now capable of making quite refined (or so we think) observations of the universe. Andre Linde called OO's "just honest folk like us." We've made it as a species, man- and womankind, and we're figuring ou the really deep things that are going on like the Big Bang, genetics, and all the rest. Then, though, there are the BB's in the universe: Boltzmann Brains. Random fluctuations of the fabric of spacetime itself which, most of the time, are rather insignificant puffs which evaporate immediately. But sometimes they stick around. More rarely, they are complex. Sometimes (very very rarely) they are really quite as complex as us human types. (Actually, "very very rarely" does not quite convey just how rare we are talking now.) And sometimes these vacuum quantum fluctuations attain the status of actual observers in the world. But, the rarest of them all, the BB's, are able to (however briefly) make actual observations in the universe which are, in fact, "not erroneous" as Don Page put it. The man was a compelling speaker, and soon I realized there was an actual intellecutal debate underway in the high end of the cosmology/high energy community as to what the role of these BB's might be in the universe, in the very far (or maybe not so far) future. We have a certain prejudice that, well, there just aren't so many of them out there at this stage of the game, 14 billion years after the Big Bang. We'd like to think that we have the stage at the moment, we OO's, um, assuming there are in fact more of us out there. (Any other non-human OO's out there, could you let us know, please that you are listening? We have a few questions for you...) The thing is, when you start talking about very very...very rare things like Boltzmann Brains, you are talking about REALLY long times. Much longer than we've had on earth (and I mean 4.5 billion years) by many orders of magnitude. Numbers like 10 to the 60th years were being batted around like it was next week in this talk. By those times, all the stars and all the galaxies have gone out, and gone cold, and space has continued to expand exponentially and things are long past looking pretty bleak for the OO's still around, who (we presume) need heat and light and at least a little energy of some sort to survive, even if we are talking about very slow machine intelligence (even slower than humans for example). So eventually, the mere fact that there is, at these long times, just oodles of space in the universe means that the BB's become more and more common (even if they are rare) and eventually dominate the, uh, intellectual landscape of the universe. Of course this immediately raises all sorts of questions, such as mind/matter duality, the nature of reality and consciousness and multiple consciousnesses, perceived versus objective independent reality. Not to mention whether our "universe" is the only one. Okay, I'll stop now... Well, at this point in the talk, being new to this and my mind already quite blown, I had trouble keeping the thread. Somehow or other Don seemed to conclude that a BB-dominated universe was absurd (though are we sure we're not in one already?) and then posited a radically different spacetime metric, an Anti-deSitter space, which he seemed to think might contain the problem. But then he hit another question which was the title of the talk: must the universe be decaying more rapidly than we expect? I am mangling this horribly, and of course before writing this I took just a glimpse at the already voluminous amount of literature on this topic, and realized that I have a lot of reading to do, both blog and academic. So it's best I stop and let you all go look up Botzmann Brains, as I will, and do some more reading. Sigh. The Ultimate Fate of the Universe is of course a nice escape from our quotidian grind. But, as Lenny Susskind wrote in his inscription to us in his book The Cosmic Landscape, at a signing last fall in Davis, "Hey, things could be worse!" (And, Lo! They were worse...)

1 free article left
Want More? Get unlimited access for as low as $1.99/month

Already a subscriber?

Register or Log In

1 free articleSubscribe
Discover Magazine Logo
Want more?

Keep reading for as low as $1.99!


Already a subscriber?

Register or Log In

More From Discover
Recommendations From Our Store
Shop Now
Stay Curious
Our List

Sign up for our weekly science updates.

To The Magazine

Save up to 70% off the cover price when you subscribe to Discover magazine.

Copyright © 2021 Kalmbach Media Co.