The Dependence of Amplitudes on Time: Feynman's Physics Explained
How do quantum states change over time? The amplitudes to be in different base states evolve according to equations governed by a grid of numbers called the Hamiltonian, which encodes all the system's physics. If a state has a definite energy, its amplitudes do not change in size — only their phases rotate together at a frequency set by the energy. That is what we mean by a stationary state.
The big idea
Energy sets the rhythm at which a quantum state's phase rotates.
Think about it
Why can a state with definite energy be called 'stationary' even though its phase is constantly rotating?
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