Heisenberg's 1925 Quantum Mechanics Paper

Here is a good new video: How Heisenberg Discovered It. There is more detail here.

It is largely on Heisenberg's famous 1925 Umdeutung paper.

In his article, Heisenberg described a new framework for quantum theory that was based on observable parameters (parameters that could be measured in scientific experiments), such as transition probabilities or frequencies associated with quantum jumps in spectral lines, rather than unobservable parameters, like the position or velocity of electrons in electron orbits. Thus, Heisenberg used two indices for his re-interpretation of position, corresponding to initial and final states of quantum jumps. Heisenberg used his framework to successfully explain the energy levels of a one-dimensional anharmonic oscillator.

Mathematically, Heisenberg used non-commutative operators in his new multiplication rule, i.e. generally A B ≠ B A for quantum quantities A and B. This insight would later become the basis for Heisenberg's uncertainty principle.

This theory beme quantum mechanics, and has been well accepted for a century, described in textbooks, and applied to a trillion dollar industry.

The bizarre thing is that now the leading popularizers of quantum mechanics seem to not understand Heisenberg's first paragraph. The latest offender is the Veritasium channel. I have criticized many others on this blog. What they have in common is that they refuse to accept that quantum mechanics is about observables, and argue that the theory must mathematically represent unobservables.

In their jargon, the unobservables are called hidden variables, and the belief that they should be incorporated into the theory is called realism.

The 2022 Nobel Prize was given for the experimental proof that local hidden variables are impossible. John von Neumann had said so in his 1930 treatise, and the experiments were just confirmation of what the textbooks have said since 1930.

Maybe all the textbooks are wrong, but that is like saying that perpetual motion machines are possible, or that rockets can go faster than light. Anyone making such a claim needs to explain how everyone else has been so wrong for so long.

They do not, of course. They mainly give some silly argument about how QM would be hard to understand if it included the unobservables. Of course that is true, because the whole point of QM since 1925 has been to exclude the unobservables.

When you hear people demand realism, they are essentially demanding commuting hidden variables to represent unobservables. The whole point of QM is to avoid such things.

Another trouble point is the supposed quantum nonlocality. I have come to the conclusion that this is a misunderstanding or rejection of probability, and doesn't even have anything to do with QM. If a theory predicts probabilities, as all physical theories do, then it says there is a chance something happens and something else does not happen. Assume that something involves at least two spatially separated events. As soon as you run an experiment and see that something happens, you immediately learn that something else did not happen, and that conclusion is the supposed nonlocality. You can call this nonlocal, but that is silly as the same thing happens in any theory.