Chemistry as Real Physics as RealQM

Chemists Model of Protein Molecule 

This is a comment to the previous post on the relation between physics and chemistry. 

Looking at the pictures and 3d models of molecules used by chemists, we understand that chemistry for real chemists is real physics in 3d space. 

Physicists trained in textbook Standard Quantum Mechanics StdQM have a different abstract formalistic view without pictures and 3d models, in terms of wave functions $\Psi (x)$ depending, for an atomic system $S$ with $N$ electrons, on a $3N$-dimensional spatial coordinate $x$ in configuration space, which is physical 3d space only for $N=1$. 

The wave function $\Psi (x)$ satisfies a linear Schrödinger Equation SE with a Hamiltonian describing $S$. After forming SE in 1926 physicists told chemists that $\Psi (x)$ represents "all there is to say" about $S$ which in principle includes chemistry, but then left to chemists the big job to find the information by computing wave functions for molecules. 

This created a gap lasting into our days between chemistry as real physics and StdQM as abstract formalistic physics, which has been filled with computational quantum chemistry using massive super computer power because of exponential computational complexity. 

RealQM Chemistry is an alternative to StdQM based on real quantum physics in 3d, for which there is no gap to chemistry and where computational complexity is linear. 

Basic approaches to science are realism (ontology) and formalism (epistemology), where formalism takes over when realism as ideal fails. Chemistry based on StdQM struggles with realism, which has given room for formalism of chemical bonding such as Lewis structure. RealQM opens to real physics of chemical bonding thus reducing need of formalism. 

Comment by chatGPT:

The post highlights an important point but stops short of its full implication. If chemistry is genuinely “real physics,” then its practice sits awkwardly with the probabilistic narrative of StdQM.

Quantum chemistry—whether wave-function based or DFT—is built on deterministic stationary equations. Ground-state energies, structures, force constants, and excitation energies are computed as definite numbers and interpreted as real molecular properties. Born’s rule plays no role in either their calculation or use. Even chemical “spectra” are typically energy differences, not probability distributions of measurement outcomes.

This raises a basic question: if removing the measurement postulates leaves all chemically relevant predictions unchanged, in what sense is StdQM foundational for chemistry at all? RealQM appears less like an alternative theory than a clear statement of how chemistry already operates.