In The God Equation: The Quest for a Theory of Everything (Doubleday, Apr.), 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 thought that the rich diversity of matter could be explained by music. By hitting a lyre string, a vast number of notes or resonances are created, obeying a precise set of mathematical rules. This, he thought, was a simple metaphor which could explain why our world was so beautiful but so complex. Today, if you had a super microscope, you might see that an electron is like a rubber band. But each “note” on this tiny rubber band is actually a subatomic particle. By hitting the string, you can recreate all the subatomic particles. Then physics has been reduced to the harmonies one can write on a vibrating string. Chemistry is the set of all interactions of these strings. The universe is a symphony of strings.
What fascinated you about string theory?
When I was eight years old, I heard a story that changed my life. The news said that a great scientist had just died, but could not finish his greatest work. What could be so difficult that the greatest scientist of our time could not finish it? Later, I found that this was Albert Einstein, and he was attempting to “read the mind of God.” He wanted a single equation that could unify all the laws of nature. To me, it was a breathtaking challenge, to create a “theory of everything.” It was to be the crowning achievement of 2,000 years of science, ever 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 leading, and only, candidate for this fabled theory, string theory.
You write that symmetry “indicates some deep, underlying physical principle about the universe.” What part does symmetry play in the theory?
Beauty, to a physicist, is symmetry. From the glimmering of a shiny crystal or precious jewel to the blazing sunset and the intricate patterns in a kaleidoscope, all possess a gorgeous symmetry—the property that it remains the same even when we rearrange its parts. Symmetry is a powerful tool to unify seemingly unrelated forces. Electricity and magnetism seem so distinct, yet there is a symmetry which can turn electricity into magnetism and vice versa. So the next logical question is: is there a master symmetry which can turn all of the forces of nature into each other? That is where string theory comes in. It has the largest symmetry ever found in physics, called supersymmetry, which can rotate all of the particles of physics into each other.