Once upon a time matter and energy were thought to be two different things. That has changed. The advent of the atomic age has demonstrated beyond all reasonable doubt that matter is simply another form of energy, one among many. In fact, there is really only one fundamental substance out of which every material thing is made: energy. Light is energy. Heat is energy. A magnetic field is energy. Gravity is energy. An atom is energy, as is a proton or a quark. A Dodge Caravan is energy. So is a pencil. The only thing that makes each of these different from the others is the physical,
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