The Principle of Least Action: Feynman's Physics Explained
Like mechanics, all of electrodynamics can be summed up in one powerful principle: least action. The motion of a charged particle and the behavior of the field can both be found by choosing the configuration that makes a quantity called the 'action' stationary. This abstract, beautiful idea is the foundation of modern field theory, including quantum electrodynamics — and it suggests Nature is, in some deep sense, economical.
The big idea
Nature acts economically — it chooses the path of stationary action.
Think about it
Why is it remarkable that so much physics can be stated as 'Nature minimizes (or balances) a single quantity'?
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