A lot of times science advances by incorporating or interpreting old ideas under new scenarios.

For example, Lorentz first proposed the so-called Lorentz transformation, but it was Einstein who correctly interpreted and applied it in his theory of special relativity. Yang and Mills first came up with the SU(2) gauge theory idea for studying nuclear isospin. But it was Glashow, Weinberg, Salam , and ‘t Hooft who found the best application of the idea to the electroweak interaction eventually leading to the most celebrated unification theory (called the Standard Model) for all three gauge interactions of the known elementary particles.

Riemann and others proposed non-Euclidean geometry theory and developed the fantastic mathematical tools accordingly. But it was Einstein who found the most exciting physical application in general relativity for the new math idea.

We do not diminish the importance of the original ideas. But we should not consider the most exciting application of old ideas any less valuable either. We probably all agree that many great breakthroughs, certainly including the above-mentioned most-admired achievements in physics, have occurred by reviving old ideas to a certain extent.

Unfortunately, some people, even as seasoned scientists, still tend to dismiss any new results immediately when they first see old ideas are used. Such rejections have happened in the past and are still occurring nowadays. At those moments, they forgot that some, if not most or all, of the biggest discoveries in the history were done with old ideas.

Sometimes, a bunch of old ideas were mixed in a new proposal like in a new cocktail. And of course, with some new ingredients. The best cocktail might be mixed with the most ingredients/ideas. For example, Einstein’s special relativity was born with the ideas of Galilean relativity and Maxwell’s electromagnetic or light theory. His theory of general relativity was motivated by a host of ideas like Mach’s principle, generalized Galilean relativity (i.e., general covariance), Minkowskian spacetime, Riemannian Geometry, and the variational principle.

The origin of quantum theory was probably more complex: certainly the idea of atomicity and discreteness was critical; formalism of classical mechanics (Lagrangian and Hamiltonian) played a role; Feynman’s path integral formulation became the quantum version of the variational principle, etc.

In particular, the Standard Model was developed on the basis of a set of existing ideas: obviously quantum idea and field theory, Yang-Mills or gauge theory, and the Higgs mechanism that is similar to the mechanism of spontaneous symmetry breaking first applied in the study of superconductivity, among others.

The new mirror matter theory (see here for a popular summary) is no difference as it is also based on a lot of great ideas brewing in the past: parity violation and mirror symmetry, supersymmetry with new understanding, the spontaneous symmetry breaking mechanism, quark condensation, Feynman’s path integral formalism with new principles (i.e., new version of the variational principle), topological transitions, neutral particle (especially neutrino) oscillations, math framework on topological and differential manifold (fibre bundle and group theories), etc.

There are some ingredients indispensable when we prepare food. Similarly, there are some old ideas appearing much more frequently in series of scientific advancements. Some old wine tastes so great for a reason. These golden old ideas keep repeating in the history also for a reason. Because they reflect some truth of the nature. We just need to polish them more in the ever-coming new theories for the next stage of our understanding of the Universe.

Among all, the variational principle is probably the oldest and has a history of at least a few hundred years. It has carried many different names or forms in the history: Fermat’s principle for light propagation, the principle of least action or the action principle for classical mechanics, Feynman’s path integral formalism for quantum theory, etc. This idea might be the very reason why math even works in physics. Its taste may last even longer beyond our imagination.

One could argue that ideas of symmetry and symmetry breaking might have a longer history. But modern versions of mirror symmetry and spontaneous symmetry breaking (including fermionic condensation) are less than 70 years old. During such a short period, on the other hand, they have thrived in many sub-fields of physics and math. The idea of mirror symmetry has been closely related to parity-violation, old mirror matter theories, string theory, and Calabi–Yau manifolds, while the idea of spontaneous symmetry breaking was applied to superconductivity, Higgs mechanism, chiral symmetry breaking, and other phase transition theories.

Supersymmetry and modern forms of topological transitions (e.g., instanton, sphaleron, quarkiton) are probably less than 50 years old. These are relatively new yet hard-to-understand ideas. Better understanding of these ideas and mixing them well with other older ideas, probably in the new mirror matter theory, will certainly help reveal new physics in our beloved Universe.

Are we ready to taste the new cocktail?