Cellular Automata - the key to physics? Pthppptt.

There's a book review on Salon of Decoding the Universe: How the New Science of Information Is Explaining Everything in the Cosmos, From Our Brains to Black Holes, which really gave my pseudo-math detector a nasty kick.

Now, to be clear: I haven't read the book. I'll probably take a look at it next time I'm in a bookstore. I'm not criticizing the book (yet). All I'm doing is snarking the review. But it's enough to set my teeth on edge.

The book is about the idea that the universe behaves a lot like a cellular automaton. This is a cool idea. To my knowledge, it was first suggested by Marvin Minsky sometime back in the late seventies. There's a lot to like about the idea; it has a very clean intuitive feel, and provides some intuition for explaining things like time dilation. (Short form: think of a object moving around through space as a little program moving around between points in a lattice of CAs. Each cellular computation quantum, the object/program can do one thing: move, or do some bit of computation to describe what's happening on/in the object. The quanta spent doing computation about the object are subjective time to something on/in the object. The faster it moves, the fewer quanta are getting spent on computing subjecting time - and voila, time dilation. )

Of course, this doesn't actually match the *math* of how relativity works very well. The math of relativity is a complicated structure that shows that no matter what frame of reference you choose, things work the same way: there is *no* right frame. There is no such thing as a single objective correct way of looking at things. For example, think about a simple situation where you have two particles, one of which is stationary, and one of which is moving at .9c.

There's no way to distinguish that from a situation where the particle that you said was moving at .9c, and the particle that you said was stationary was actually moving at .9c. And there's no way of distinguishing that from a situation where both particles are moving at .45c. In fact, any or all of them are perfectly valid descriptions of the situation. It is not the case that there is one view that is right - they are all equally right. (This is very hard to comprehend. I don't pretend to have a very good intuitive grasp of how it works. But the math has been worked out, and tested in great detail against physical models, and it's proved out magnificently. )

That doesn't work in the CA model. In the CA model, there is one object that is stationary, and one that is moving - and there is a huge difference between the two.

The real math of relativity and quantum mechanics has never been worked out in CA. In fact, every effort to come up with a cellular automaton that models even limited aspects of reality has failed, miserably. Steve Wolfram discusses the idea at great length in "A New Kind of Science" - but doesn't manage to come up with a really accurate model of gravity. John Case at the U of Delaware, my alma mater, has done some very cool work on modeling things using a tetrahedral 3d CA - but has not yet come particurlarly close to being able to do efficient accurate models of anything interesting.

Back to the review.

The review goes into a pile of pseudo-philosophical rubbish about how "information is as physical as matter":

"Information is physical. Information is not just an abstract concept, and it is not just facts or figures, dates or names. It is a concrete property of matter and energy which is quantifiable and measurable. It is every bit as real as the weight of a chunk of lead or the energy stored in an atomic warhead, and just like mass and energy, information is subject to a set of physical laws that dictate how it can behave."

It's the same kind of gibberish that creationists use to explain how "information can't be created". Very touchy-feely, with examples about the wonders of how the reviewer finally comprehends how her candy thermometer works.

But....

For all of her discussion, she never mentions what CA has to do with it. She's reviewing a book on a mathematical model of physics based on a simple idea - and she never bothers to talk about just what that model is!

What does she, or the author of the book mean by the physical reality of information? I know what classic CA means by it: that reality is nothing more that the data defining the states in a huge CA lattice. But that's not what the reviewer means - just read her explanation of how she understands it:

was contemplating this the other day while using a candy thermometer to figure out if the sugar syrup I was boiling had become hot enough to add to a bowl of whipped egg whites. Reading the numbers on the thermometer might seem to the casual eye like a nonphysical transmission of information, even though energy from the electric company was used to generate the light bouncing off the thermometer and into my eyes and energy from my lunch powered the neurons that fired in my brain as I read it.

But what intrigued me most about the experience was the realization that while "240 degrees" was the information I thought I was getting from the thermometer, it was really the mercury in the device that told me what I needed to know. It borrowed a little heat from the boiling syrup and expanded up the glass tube of the thermometer to give me the news. The increase in the temperature and the volume of that mercury was the true source of the information (about the heat of the syrup). My seven-minute frosting was a classic illustration of information in action!

Does the reviewer know what a CA is? Sure doesn't seem like it. Does she care? Sure doesn't seem like it. So what's she doing writing a review of what a brilliant job the author of the book does at explaining math?