Probability Amplitudes: Feynman's Physics Explained
Quantum mechanics never predicts a single outcome with certainty; it predicts probabilities, computed from a new kind of number called a probability amplitude, which is complex. The rule: if an event can happen in several alternative ways, add the amplitudes for each way, then take the absolute square of the total to get the probability. It is this adding of amplitudes — before squaring — that produces interference.
The big idea
Add the amplitudes, then square — that's where interference comes from.
Think about it
Why does it matter so much whether you add probabilities directly, or add amplitudes first and square afterward?
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