Theoretical physicist Brian Greene, best known for his work on string theory, explains how music might have the answer we need to find a unified theory.

**Brian Greene**: Albert Einstein dreamed of finding what he called a Unified Theory. By that he meant a single idea, a single principle, maybe even a single equation that might describe everything in the universe. He worked long and hard many decades to try to find the theory and he never did. Since his passing many physicists haven take up where he left off, and many of us believe then an approach called String Theory may be the Unified Theory that he was looking for. And the basic idea of the unified description of all matter is pretty straightforward. If you take any piece of material, say a piece of wood, cut it in half, cut it in half again, keep on cutting it to ever smaller pieces, the basic question is what’s the smallest piece that you get to? What is the finest uncuttable constituent? Now we all know if you cut fine enough you get molecules, if you cut them up, you get atoms, if you cut them up even further you get other particles, electrons going around the nucleus with neutrons and protons, even though the neutrons and protons are smaller entities called quarks. The conventional idea stopped there. String Theory comes along and says “There may be one more layer of structure: inside an electron, inside a quark, inside any particle you have heard of, according to these ideas, is a little tiny filament. Looks like a tiny little string, that’s why it’s called String Theory, and the little strings can vibrate in different patterns.”

So the idea is that, according to this theory an electron can be a string vibrating in one pattern. You can call it a middle C if you want, by the musical analogy, a quark could be a string vibrating at a different pattern like an A. So the difference between one particle and another is simply the note that its string is playing. And this is the unified description that this theory puts forward: everything can be reduced to the notes these fundamental strings are playing. Now that’s metaphorical. There’s math behind this, that allows us to see all of the key elements of physics can find a home in this description, but in a nutshell that’s what this theory says.