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You may want to look at Kepler's problem solution(en.wikipedia.org/wiki/…), any 2 body system, with mass $m$ and $M$ can be reduced to a fixed mass of $M+m$ and a orbiting mass of $\frac{Mm}{M+m}$, the reduced mass. Such precession is indeed observed relativistically, but for a simple inverse square force it's likely numerical error
If the spring has mass, does it lose energy as heat when being contracted or absorb heat when it contracts? Yes, which means energy is being exchanged with the environment. It's similar as considering a block moving from point A to B with friction. Some energy also goes into rearranging the lattice in the spring, which is also dependent on time
Good point, in the short section I've presented, many many justification steps are ignored. However, the wave function still should have units of $m^{-\frac{1}{2}}$ and total probablity of measuring a particle at any position is 1. P.S. really the momentum eigenvectors are just the position being completely undefined
Yes, there is a problem there, the question is how should I express the extra units, oh and the $kg\frac{m}{s}$ should go inside the inverse root.(oh and the recent edits are just formatting changes, no content added)