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How could the vacuum, which has nothing in it, have any energy at all? The answer comes from another equation: Einstein's famous E=mc^2. This simple formula relates mass and energy: the mass of an object is equivalent to a certain amount of energy. (In fact, particle physics don't measure the mass of the electron, say, in kilograms or pounds or any of the usual units of mass or weight. They say that the electron's rest mass is .511 MeV [million electron volts]- a lump of energy.) The fluctuation in the energy in the vacuum is the same thing as a fluctuation in the amount of mass. Particles are constantly winking in and out of existence, like tiny Cheshire cats. The vacuum is never truly empty. Instead, it is seething with these virtual particles; at every point in space, an infinite number are happily popping up and disappearing. This is the zero-point energy, an infinity in the formulas of quantum theory. Interpreted strictly, the zero-point energy is limitless. According to the equations of quantum mechanics, more power than is stored in all the coal mines, oil fields, and nuclear weapons in the world is sitting in the space inside your toaster.
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