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By Root 979 0

about this for a moment and it seems like a very odd thing. Perhaps the most familiar kind of energy is the energy of motion; if someone throws a cricket ball at your face, then it hurts when it hits you. A physicist would say that this is because the cricket ball was given energy by the thrower, and this energy is transferred to your face when your face stops the ball. Mass is a measure of how much stuff an object contains. A cricket ball is more massive than a table-tennis ball, but less massive than a planet. What E = mc2 says is that energy andmass are interchangeable much like dollars and euros are interchangeable, and that the speed of light squared is the exchange rate. How on earth could Einstein have reached this conclusion, and how could the speed of light find its way into an equation about the relationship between energy and mass? We do not assume any prior scientific knowledge and we avoid mathematics as much as possible. Nevertheless, we do aim to offer the reader a genuine explanation (and not merely a description) of the science. In that regard especially, we hope to offer something new.

In the latter parts of the book, we will see how E = mc2 underpins our understanding of the workings of the universe. Why do stars shine? Why is nuclear power so much more efficient than coal or oil? What is mass? This question will lead us into the world of modern particle physics, the Large Hadron Collider at CERN in Geneva, and the hunt for the Higgs particle that may lead to an explanation for the very origin of mass. The book finishes with Einstein’s remarkable discovery that the structure of space and time is ultimately responsible for the force of gravity and the strange idea that the earth is falling “in a straight line” around the sun.

1

Space and Time

What do the words “space” and “time” mean to you? Perhaps you picture space as the blackness between the stars as you turn your gaze toward the sky on a cold winter’s night. Or maybe you see the void between earth and moon sailed by spacecraft clad in golden foil, bedecked with the stars and stripes, piloted into magnificent desolation by shaven-headed explorers with names like Buzz. Time may be the tick of your watch or the reddening of the leaves as the earth’s yearly circuit of the sun tilts northern latitudes toward shade for the 5 billionth time. We all have an intuitive feel for space and time; they are part of the fabric of our existence. We move through space on the surface of our blue world as time ticks by.

During the late years of the nineteenth century, a series of scientific breakthroughs in apparently unrelated fields began to force physicists to reexamine these simple and intuitive pictures of space and time. By the early years of the twentieth century, Albert Einstein’s colleague and tutor Hermann Minkowski was moved to write his now-famous obituary for the ancient arena within which planets orbit and great journeys are made: “From henceforth, space by itself, and time by itself, have vanished into the merest shadows and only a kind of blend of the two exists in its own right.”

What could Minkowski have meant by a blend of space and time? To understand this almost mystical-sounding statement is to understand Einstein’s special theory of relativity—the theory that introduced the world to that most famous of all equations, E = mc2, and placed forever center-stage in our understanding of the fabric of the universe the quantity with the symbol c, the speed of light.

Einstein’s special theory of relativity is at its heart a description of space and time. Central to the theory is the notion of a special speed, a speed beyond which nothing in the universe, no matter how powerful, can accelerate. This speed is the speed of light; 299,792,458 meters per second in the vacuum of empty space. Traveling at this speed, a flash of light beamed out from Earth takes eight minutes to pass by the sun, 100,000 years to cross our own Milky Way galaxy, and over 2 million years to reach our nearest galactic neighbor, Andromeda. Tonight, the largest