In the sixth century b.c.-twenty-five hundred years before Einstein-Heraclitus of Ephesus declared that energy is the essence of matter, that everything becomes energy in flux, in relativity. His great book, On Nature , the world's first coherent philosophical treatise and touchstone for Plato, Aristotle, and Marcus Aurelius, has long been lost to history-but its surviving fragments have for thousands of years...
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