A couple of weeks ago I received a letter in Spanish. I don't know Spanish. I was staring at the text, trying and failing to make sense of it by using my primitive French, when my teenage daughter wandered by. She picked up my letter and cockily gave me a quick translation.

I was both pleased and annoyed - aren't I supposed to know more than my children? - but the experience started me thinking: about language, and the importance of the right language if you want to do science in general, and physics in particular.

Of course, every science has its own special vocabulary, but so does every other subject you care to mention. Partly it's for convenience, although sometimes I suspect it's a form of job security. Phrases like "stillicide rights," "otitis mycotica,"and "demultiplexer" all have perfectly good English equivalents,but they also serve to sort out the insiders from the outsiders.

One subject, though, is more like an entire language than a special vocabulary, and we lack good English equivalents for almost all its significant statements. I am referring to mathematics; and, like it or not, modern physics depends so heavily on mathematics that non-mathematical versions of the subject mean very little. To work in physics today, you have to know the language of mathematics, and the appropriate math vocabulary and methods must already exist.

On the face of it, you might think this would make physics an impossibly difficult subject. What happens if you are studying some aspect of the universe, and the piece of mathematical language that you need for its description has not yet been invented? In that case you will be out of luck. But oddly -almost uncannily - throughout history, the mathematics had already been discovered before it was needed in physics.

For example, in the seventeenth century, Kepler wanted to show that planets revolved around the Sun not in perfect circles, but in other more complex geometrical figures. No problem. TheGreeks, fifteen hundred years earlier, had proved hundreds of results about conic sections, including everything Kepler needed to know about the ellipses in which planets move. Two hundred years later, Maxwell wanted to translate Michael Faraday's experiments into a formal theory. The necessary mathematics, of partial differential equations, was sitting there waiting for him. And, to give one more example, when Einstein's theory of general relativity needed a precise way to describe the properties of curved space, the right mathematics had been created by Riemann and others and was already in the text books.

Of course, there can be no guarantee that the mathematical tools and language you want will be there when you need it. And that brings me to the central point of this column. One of the hottest subjects in physics today is the "Theory of Everything,"or TOE. The "Everything" promised here is highly limited. It won't tell you how a flower grows, or explain the IRS tax codes. But a TOE, if successful, will pull together all the known basic forces of physics into one integrated set of equations.

Now for the tricky bit. The most promising efforts to create aTOE involve something known as string theory, and they call for a description of space and time far more complicated than the height-width-length-time we find adequate for most purposes. The associated mathematics is fiendishly difficult, and is not just sitting in the reference books waiting to be applied.

New tools are being created, by the same people doing the physics, and it is quite likely that these will prove inadequate. The answers may just have to wait, until, ten or fifty years from now, the right mathematical language has been evolved and can be applied.

It's one of my minor personal nightmares. Mathematics, more than almost any other subject, is a game played best by the young. Suppose that, five or fifteen years from now, we have a TOE that explains everything from quarks to quasars in a single consistent set of equations. It will, almost certainly, require for its understanding some new mathematical language. By that time I may just be too old or set in my ways ever to learn what's needed.

It's a dismal prospect. You wait your whole life for something, and then when it finally comes along you find you can't understand it.

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