Recent posts recall that the accepted canon/standard of Quantum Mechanics QM as Schrödinger's equation for an atomic system with N electrons, is a linear partial differential equation in terms of a multidimensional complex-valued wave function \Psi (x1,x2,...,xN,t) depending on N three-dimensional space variables x1, x2,...,xN and a time variable t. The equation arises as an ad hoc mathematical generalisation of Schrödinger's equation for a Hydrogen atom with one electron (N=1), which can be given a direct physical meaning with the wave function representing an electron density.
The basic question QM concerns the physical meaning of the wave function for N>1. The accepted answer coined as the Copenhagen Interpretation CI imprinted into the canon by Born followed by Bohr, is that \vert\Psi (x1,....,xN,t)\vert^2 represents a probability density for an electron configuration described by the coordinates (x1,...,xN,t). But a probability density does not describe any state of physics and QM still after 100 years remains a mystery as acknowledged by all prominent physicists.
To a mathematical mind the ad hoc generalisation is direct, and so physicists impressed by mathematics have been forced to accept it as true physics, although mysterious. So instead of searching for a generalisation with physical meaning (see Real Quantum Mechanics), all efforts have gone into loading the multi-dimensional wave function \Psi (x1,x2,...,xN,t) with (some) physical meaning.
To this end physicists have come up with the idea to distinguish between wave functions which are symmetric in the variables (x1,...,xN) (augmented by a two-valued spin variable) supposed to represent boson (photon) and anti-symmetric supposed to represent fermion (such as electron and proton), with any particle being either a boson or fermion. Anti-symmetry was crafted so as to prevent two electrons with the same spin to be at the same place in space-time, expressed as Pauli’s Exclusion Principle.
With this perspective a God creating the world of physics must have been mathematician and not physicist. First He created multidimensional wave functions, which is a very rich Universe, and then He decided that only symmetric or anti-symmetric wave functions would represent actual physics, asking systems of particles to keep track of symmetry or antisymmetry. But a mathematician cannot create physics, only at best model physics in terms of mathematics and computation. God must have been also physicist with richer tools for creation than mathematical symbols on a paper. And then He would not have been satisfied with a purely mathematical Universe designed by mathematicians like the CI of QM...
To sum up: Standard QM for a many-electron system is based on a linear wave equation for a multi-dimensional complex-valued wave function arising from a generalisation of Schrödinger's equation for a Hydrogen atom according to purely mathematical principles. The following questions present themselves as the fundamental conundrums of modern physics:
- Why is the wave equation for a system scalar-valued and not vector-valued?
- Why is the equation linear and thus allowing superposition? Physics is rarely linear.
- What physics is captured by the multi-dimensional wave function? Do electrons play dice?
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