Coffee on the terrace, watching the sunrise, thinking of a line from a poem of Dylan Thomas: "The force that through the green fuse drives the flower." The long, long fuse -- through twenty miles or so of blue air, 93 million miles of space, and half-a-million miles of turbulent hydrogen -- to the heart of the sun.
It's hot at the center of the sun. About 15 million Centigrade degrees hot. At 15 million degrees something remarkable happens. Hydrogen nuclei, which carry positive charges, are able to overcome their mutual repulsion and fuse together to form helium. Fuse. That word again! The green fuse. Dylan Thomas was more right than he knew. Fusion is the force that drives the flower.
Every second the sun converts roughly 700 million tons of hydrogen into helium. And the helium weighs less than the original hydrogen. Five million tons less. Matter has disappeared. Matter has been turned into pure energy. The old Einstein equation -- energy equals mass times the speed of light squared. Every second the sun turns five million tons of its own substance into radiant energy.
"The force that through the green fuse drives the flower/ Drives my green age; that blasts the roots of trees/ Is my destroyer." Dylan Thomas was a poet. Einstein was the scientist who unraveled the mystery of fusion in the sun. The two men were contemporaries. They died within a few years of each other in the mid-1950s. They both perceived the essential unity of matter and energy. They both recognized in nature a physical force that drives all things, a force that is both creative and destructive, holy and terrible.