Monday, January 21, 2008

Meet the Incredibly Strange Boltzmann Brain Problem

It took me three reads of the NY Times article, “Big Brain Theory: Have Cosmologists Lost Theirs?” before it finally made sense. And it’s huge. The piece challenges whether or not “we and the universe are real,” and elegantly explains (in theory) how (what we call) the universe came to be.

Also, I should note it took me about five revisions to create a blog posting here that I think is useful. Really, you need to read the Times piece. But before you do, read this. The purpose of this post is to explain the concepts explored in the article so, hopefully, it will make sense the first time you read it.

This is a story of what we (pretty much know) and what we don’t (or don’t want to) know. So let’s start with what we (pretty much) know.

We know the universe is expanding, that is, galaxies are moving apart from each other. And we know that they’re moving away from each other at increasing speeds.

Now, according to conventional wisdom (because of something called “dark energy”), “this runaway process will last forever,” explains the Times.

So, space is forever expanding at faster and faster speeds.

In the Times column, we learn that “galaxies will eventually be moving apart so quickly that they cannot communicate with one another.” That’s fast. Faster than the speed of light. So fast, that (this is important) the edges of a galaxy “would glow, emitting a feeble spray of elementary particles and radiation, with a temperature of a fraction of a billionth of a degree.”

Within the seething, glowing edges of galaxies hurtling through space, faster than the speed of light, rare fluctuations “big enough to recreate the Big Bang” would occur. According to the Times, “In the fullness of time this process could lead to [an] endless series of recurring universes. Our present universe could be part of that chain.”

How could a new universe expand within a universe? For the same reason galaxies can move faster than the speed of light: it is space that is expanding.

Confused? Here’s an example that should help. Think of space as a piece of saltwater taffy. Now imagine pulling the piece of taffy, and as it stretches, dropping a spot of ink on it. As the taffy expands, so does the ink. That ink is a new universe.

In our universe,
there are something like 80 billion galaxies. If our universe sprouted from the edges of one galaxy in another universe, and ours was the first and only universe to do this, then there are at least 160 billion galaxies. But ours was probably not the first and only universe to do this. There are probably a lot of universes sprouting off the edges of a lot of galaxies going back to whenever this whole incredible process started. One expert told the Times, “In eternal inflation, the number of new bubbles being hatched at any given moment is always growing.”

This brings us to the Boltzmann Brains problem.

Ludwig Boltzmann was a 19th-centry Austrian physicist who described how the universe could (bear with me here, I’m dumbing this down so it makes sense) restore itself after burning out. Given what we know (and I described earlier), the universe doesn’t regenerate in that way. But Boltzmann started cosmologists thinking about the “probabilities in an infinite universe in which everything that can occur, does occur, infinitely many times,” as described by one scientist.

Now, if “everything that can occur, does occur,” what are the most likely things to occur? Simple stuff. We know that because of something called “the second law of thermodynamics.” Simply put, the law states that stuff in nature gets more disorganized as time goes by. For example (again, bear with me, this is a very simple example), you can scramble an egg, but it’s not going to naturally unscramble itself into a more highly organized, egg-in-its-shell if you leave it alone.

So here’s the Boltzmann Brains problem. If nature favors simplicity, and we live in an infinite universe of infinite possibilities, then what’s more likely, that you, the reader, reading this now are “a person with a real past born through billions of years of evolution in an orderly star-spangled cosmos,” or that you’re a very simple, “momentary fluctuation in a field of matter,” or in other words, a brain floating through space imagining an illusory reality.

According to some calculations, there are an “infinite number of free-floating brains for every normal brain, making it ‘infinitely unlikely for us to be normal brains,’” reports the Times.

Of course, this is entirely absurd. But you can’t just ignore it. We’re talking about “a string of logical conclusions” here! It just happens that the logic leads us to a very absurd (or very uncomfortable, if not terrifying) place. So what now? Cosmologists are struggling to eliminate the “freaks” (free-floating brains) from theories. Two reasons. One, I think we’d all like to know that reality is, well, real. And two, what are we missing here? If the logic leads us to an absurd place, maybe the logic is flawed. Or maybe there’s a big something-or-another that we’re missing. And that something-or-another could be something very exciting that unlocks a new era of scientific discovery. Time travel? Teleportation? Interstellar space flight? Perhaps something more modest. Faster computers? Zero-emission energy? A cure for cancer? Whatever it is, the smart money is on something nice and simple.

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I started pound360 to channel my obsession with vitamins, running and the five senses. Eventually, I got bored focusing on all that stuff, so I came back from a one month hiatus in May of 2007 (one year after launching Pound360) and broadened my mumblings here to include all science.