I am just starting out in self-study for quantum theory, so forgive me if my question seems elementary or completely misguided. In quantum mechanics, every wave function ψ can be decomposed into a linear combination of basis functions in the following manner:(adsbygoogle = window.adsbygoogle || []).push({});

[itex]\Psi = \Sigma{c_{n}\Psi_{n}}[/itex]

Now, [itex]\left|c_n\right|^2[/itex] is the probability of finding an energy E_n upon measurement. For a single particle, it seems that conservation of energy would then require E_n upon all subsequent measurements, and therefore should have "collapsed" into a basis state for as long as the particle is in an infinite well. However, I hear that this is true only "immediately after", and that the Schrodinger equation will require the particle to evolve back into a superposition state. However, this does not sit comfortably with me, as it would seem possible now to measure a different energy E_m corresponding to a different basis state, thereby failing to conserve energy. I know that a "weaker" version of energy conservation holds as <H> (the expectation value of the Hamiltonian) remains constant through time, but is it possible, for a single particle, to measure different energy in two successive measurement while it is in the same state? Doesn't this violate energy conservation? Any illumination would help.

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# Question About State Collapse and Energy Measurements in Infinite Well

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