|MadSci Network: Physics|
It is too simplistic to say that "matter and energy are interchangeable". What Einstein's formula, E=mc^2, means is that mass is a form of energy. It does not mean that matter is an electromagnetic wave. In quantum mechanics, the wave equation for a massive particle is different from the wave equation for a massless photon. When electromagnetic waves of different frequencies overlap in vacuum, the interaction between them is very weak. There are many interesting effects which can be seen by allowing waves of different frequencies to interact with atoms at the same time, however. You might enjoy reading the book "QED: The Strange Theory of Light and Matter", by Richard Feynman.
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