Warning: I am taking a modern physics course, and haven't taken QM. I know nothing of "commutators, operators, hilbert spaces, etc."(adsbygoogle = window.adsbygoogle || []).push({});

I understand ##\Delta E \Delta t >= \hbar /2 ## to mean that I can't know the energy of a system and the time at which that energy takes place exactly. These two are fuzzy, so to speak.

However, when deriving the particle in a box wavefunction in 1D or 3D, you get sharp values for the energy of the system. At the same time that wavefunction is clearly a function of time and therefore I can know both ##E## and ##t## with precision. Why isn't this in contradiction with the E/t uncertainty principle?

Also I've seen some proofs that state that ##\vec{L}## can't be known because it would violate the p/x uncertainty principle. But why does this mean that I can't knowtwocomponents of ##\vec{L}## with precision? I mean, the natural implication of not knowingLwith certainty, would be that its 3 components aren't known. I don't see the importance of 2 components here...

Thanks!

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# Understanding E/t uncertainty and ##\vec{L}## uncertainty

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