The Boltzmann Brain Controversy

The recent article in the New York Times has raised the question – Have Cosmologists lost their minds?

It’s hard to discuss cosmology except at the most elementary levels succinctly. The issues involved multiply and then multiply in complexity very rapidly. The issue of the moment, discussed in so many physics and astronomy blog pages of late that I lost count, is about something called the Boltzmann Brain.

There is a decent 25 word or less type explanation of the concept in wikipedia, but I’ll try to sketch it out in my own words (if only to clarify the ideas in my own mind). It goes like this – One concept of our universe is that it is something that just happens every so often. Mere, random chance. We and everything else can be considered just a random organization that appeared in one universe of an infinitely large number of universes, each different and each with its own set of physical laws. Some of those universes contain conscious and self-aware beings, and most don’t. The ones that do must, of necessity, have physical laws that permit consciousness and self-awareness, so the fact that we find ourselves in a universe so ideally made to permit our existence is not surprising. It’s a selection effect. The only universe an intelligent observer is going to see is one that permits intelligent observers.
But there is a paradox – In an infinite universe (or universe of universes), that which can happen, will happen. And it will happen an infinite number of times. There will be another you somewhere, and in fact, there’s lots of them, along with the desk and computer you’re sitting at. This is a problem because the second law of thermodynamics says that it’s much easier (and therefore much more likely) that there is a you without the computer and desk. In fact, the universe is much more likely to have you without all the extraneous stuff, like planets and bodies, and be overwhelmingly populated with sub-universes that have only free-floating, self-aware consciousnesses that are you (which are called for historical reasons, Boltzmann Brains). The fact that you have all the extra stuff in the universe that you don’t apparently need is just one of those things, but it’s also extremely rare. We shouldn’t find all this ordered stuff in the universe, but we do.

And now you can see why the NYT asks if cosmologists have lost their minds. This is where the theories take them, seriously. We’re not talking about mistakes here, in the sense of someone adding two and two and writing five when they knew better, but about things that are self-contradictory. It starts by assuming that we are not unusual and proceeds to prove the opposite, all perfectly logically. It’s more than troubling to cosmologists everywhere because they used to rely (a lot) on Occam’s Razor, which they now want to throw out the window.

Now I’ve intentionally not used words like entropy and randomness here, but Luboš Motl does not.

I argued that some people overestimate the importance of the time-reversal-symmetric microscopic laws relatively to other important facts about the Cosmos we know – such as the difference between the future and the past. But there is one more reason why many people have a problem with this obvious insight. This reason is called religion:

  • the idea of special initial conditions reminds us of God, and because these people really hate the idea of God, they also hate the idea of special initial conditions
  • It’s one of many examples showing that a left-wing or anti-religious bias can lead to as unscientific ideas as a right-wing or religious bias.

As a Christian athetist, I am no real believer but if special initial conditions were offered as a definition of God, then I would argue that God has been experimentally proven beyond any reasonable doubt.

Ooooffff. Cosmology cannot avoid the issue of God. It even starts to look like the more mankind discovers about the nature of the universe, the more mankind starts to understand the necessity of God. If there ever was the notion that physics or science could offer explanations that removed that necessity, further investigation shows that particular notion was wrong.

It’s an incredibly large and maybe even inspiring topic. Many more references can be found at :Cosmic Variance and again here, at Darwiniana (a very good synopsis, btw), and some original material at arXiv.

Sigh – And even as I read over the referenced articles (again), I feel the need to expand a bit, based on one paragraph by Sean Carroll. He properly notes that another way of looking at the problem is to realize that our physics says it’s likely our universe is going to spend most of eternity in a totally disordered state (at maximal entropy). Compared to that span to time, the few billion years we’ve spent so far moving to that state is indeed an unusual way for the universe to be. That doesn’t make it remarkable, however.

So what are we to conclude? That our observed universe is not a statistical fluctuation around a thermal equilibrium state. That’s very important to know, but doesn’t pin down the truth. If the universe is eternal, and has a maximum value for its entropy, then we it would (almost always) be in thermal equilibrium. Therefore, either it’s not eternal, or there is no state of maximum entropy. I personally believe the latter, but there’s plenty of work to be done before we have any of this pinned down.

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