|MadSci Network: Physics|
Jennifer - this turns out to be a pretty profound question, so I'll just sketch out an answer here. Light is not matter at all - it is a form of energy. More specficially, it's a form of electromagnetic radiation. The ordinary matter that we are made of consists of particles called electrons, neutrons, and protons. These particles have mass and, in the case of protons and electrons, electric charge. Light can be tought of as being made of particles called photons, which have no mass and no electric charge. Some other forms of electromagnetic radiation include radio waves, X-rays, and gamma rays. (Side note: the "radiation" that comes from radioactive atoms is sometimes matter and sometimes energy. The confusing name was given before people understood radioactivity.) But that's not the end of the story. It turns out that matter can be turned into energy and vice versa. This is what happens in nuclear reactions, and is what Einstein's famous formula E=mc^2 refers to. There is lots more to be said on this topic, and you can find information about it in any physics textbook. A book with a bunch of good, short essays on this topic is "The World Treasury of Physics, Mathematics, and Astronomy", and almost any popular physics book will talk about matter and energy to some extent. An interesting book with a different slant on the topic is "Catching the Light: the entwined history of light and mind" by Zajonc. Pauline
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