In The Equation of God: The Quest for a Theory of Everything (Doubleday, April), physicist Kaku explores what he calls “the deepest mysteries of space and time” using string theory.

How would you explain string theory in just a few sentences?

The Greek mathematician Pythagoras believed that the rich diversity of matter could be explained by music. By striking a lyre string, a large number of notes or resonances are created, obeying a specific set of mathematical rules. It was, he thought, a simple metaphor that might explain why our world was so beautiful but so complex. Today, if you had a great microscope, you could see that an electron is like a rubber band. But every “note” on that little rubber band is actually a subatomic particle. By hitting the chain, you can recreate all the subatomic particles. So physics was reduced to harmonies that can be written on a vibrating string. Chemistry is the set of all the interactions of these chains. The universe is a symphony of strings.

What fascinated you about string theory?

When I was eight, I heard a story that changed my life. The news said that a great scientist had just died, but couldn’t finish his greatest job. What could be so difficult that the greatest scientist of our time couldn’t finish it? Later, I found out that it was Albert Einstein and that he was trying to “read the mind of God”. He wanted a single equation that could unify all of the laws of nature. For me it was a breathtaking challenge, to create a “theory of everything”. It was to be the crowning achievement of 2000 years of science, since the Greeks asked, “What is the world made of?” I wanted to be part of this revolution. And for the past 50 years, I have worked on the main and sole candidate for this legendary theory, string theory.

You write that symmetry “indicates a deep and underlying physical principle about the universe.” What role does symmetry play in the theory?

Beauty, for a physicist, is symmetry. From the sparkle of a shining crystal or precious piece of jewelry to the blazing sunset and intricate patterns of a kaleidoscope, all possess a magnificent symmetry – the property that it stays the same even when we rearrange its parts. Symmetry is a powerful tool for unifying seemingly independent forces. Electricity and magnetism seem so distinct, but there is a symmetry that can turn electricity into magnetism and vice versa. The next logical question, then, is: is there a master symmetry that can transform all the forces of nature into each other? This is where string theory comes in. It has the greatest symmetry ever found in physics, called supersymmetry, which can rotate all the particles in physics into each other.

A version of this article appeared in the 4/1/2021 issue of Weekly editors under the title: Untangling the universe

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