“You’d think they’d tell you up front, “Hey, the evolution of a quantum system depends on stuff like the second derivative of the amplitude distribution, so you can’t possibly break it down into the evolution of individual configurations.”
It’s worse than that; they wait until the 2nd semester to even start talking about time-evolution. They spend the first semester trying to find, for a given Hamiltonian, a set of wavefunctions for which the value of a particular observable, energy (or in a few cases, momentum), is unchanging in time. Time-evolution is presented only as a consequence of either a superposition of time-independent states, or as a changing external potential.
Which really misses the point: the “superposition” is already a valid solution to the full schrodinger equation in it’s own right, and the whole concept of an external potential is a result of our inability to account for each particle in the system at once.
“You’d think they’d tell you up front, “Hey, the evolution of a quantum system depends on stuff like the second derivative of the amplitude distribution, so you can’t possibly break it down into the evolution of individual configurations.” It’s worse than that; they wait until the 2nd semester to even start talking about time-evolution. They spend the first semester trying to find, for a given Hamiltonian, a set of wavefunctions for which the value of a particular observable, energy (or in a few cases, momentum), is unchanging in time. Time-evolution is presented only as a consequence of either a superposition of time-independent states, or as a changing external potential. Which really misses the point: the “superposition” is already a valid solution to the full schrodinger equation in it’s own right, and the whole concept of an external potential is a result of our inability to account for each particle in the system at once.