There is exchange of all things for fire and of fire for all things, as there is of wares for gold and of gold for wares.

-- Heraclitus of Ephesus (c. 540 B.C.E. - c. 480 B.C.E.)

In classical physics, everything in the universe is made of either matter or energy. What makes matter special is mass; you can weigh it, something you can't do with light.

Modern physics reduced matter down to atoms, then to protons, neutrons, and electrons, then again to quarks, leptons and other oddly-named particles. Albert Einstein entered the scene with his famous theories of relativity, and these tiny particles suddenly looked much different from classical physics' black-and-white division of matter and energy.

Einstein's theories led to the famous equation, e = mc2, which says that energy and mass are actually two different forms of the same thing. Mass and matter might better be looked at as a form of very dense energy. In fact, mass can be converted to energy, and vice versa. (Humanity chooses to use this knowledge to make nuclear bombs, but is that Albert's fault?)

The sophisticated realist, long since having realized that things are not what they seem, now looks around and sees only energy. The diversity of the entire universe (not to mention the room where I'm now sitting) is simply an uneven distribution of swirling energy, created by combinations of a very small number of very tiny forms. This recognition barely rocks the boat compared to what else has been found.

Next: Making Waves

For Further Exploration

The technically minded and curious can browse these sources elsewhere on the Web: