The Elegant Universe

Reading about the Large Hadron Collider reminded me of The Elegant Universe, a wonderful and readable book on string theory by Brian Greene. In the standard model, the fundamental constituents of matter consist of a bewildering menagerie of point particles. String theory takes a different view. It claims that particles are not point-like at all, but when examined at a sufficiently small level of detail actually consist of a tiny one-dimensional vibrating loop---a string. This shift from point particles to one-dimensional strings resolves a deep conflict between the two most successful theories of modern physics: general relativity and quantum mechanics.

Einstein's theory of general relativity provides us with an unparalleled understanding of the universe at the largest scale---at the scale of stars and galaxies and clusters of galaxies. Quantum mechanics provides an unparalleled understanding of the universe at the smallest scale---at the scale of molecules and atoms and sub-atomic particles. Over the last century, scientists have verified the predictions of these theories with unimaginable accuracy. These are truly the two most successful theories of modern physics. There's only one small fly in the ointment: the two theories are incompatible. As currently formulated, they cannot be both right. They conflict when trying to explain what happens at a singularity, such as in a black hole or at the very beginning of the big bang.

String theory resolves this incompatibility. My naive understanding is that string theory does away with the point nature of the fundamental building blocks of matter, and thus eliminates the need to reason about singularities. In fact, within string theory, general relativity and quantum mechanics require one another for the them to make sense.

It's been a while since I read The Elegant Universe, so I can't provide a decent review. But I will say that Part II of the book---which explains general relativity, quantum mechanics, and their incompatibility---is a really great read. It alone is worth the price of admission. Section III---which introduces string theory---was my first introduction to string theory, and it's really well done. Section IV covers more advanced material, and I remember being somewhat lost.

All in all, I highly recommend this book.