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Albert Einstein said: "God is subtle; malicious He is not."
From the recent history of fundamental science, let us find out whether God is really subtle.
In the 1960-70's, many ideas to explore the strongly interacting particles (hadrons) were explored. The top idea was S-matrix theory.
G F Chew and his followers believed that from some basic notions the S-matrix for hadrons can be determined. Bootstrap, dispersion relations and nuclear democracy were some of the ideas that were developed. But, this approach reached a dead-end; S-matrix was given up.
Murray Gell-Mann's Current Algebra seemed more successful. Hirotaka Sugawara, in a landmark paper, succeeded in constructing the energy-momentum tensor in terms of currents. But using the hadronic currents alone, it was not possible to understand the strong interactions.
Is it possible to understand hadronic dynamics using infinite-component wave equations? Some tried this approach, but did not succeed.
For a long time I thought that quarks (the presumed constituents of
hadrons) and leptons are the same. That appeared to be the reason for the hadrons and leptons to have the same current algebra. I tried to find out how leptons that have only weak and electromagnetic interactions behave like strongly interacting quarks, but could not do it.
During the years 1967-70, I was trying to generate strong interaction from weak interaction. T D Lee showed how the divergences of Fermi theory of weak interactions behave like strong interaction. After that, Gell-Mann, Goldberger, Kroll and Karplus made a detailed analysis of this.
I tried to use the divergences in Weinberg's Yang-Mills theory of weak interactions to generate strong interactions. In 1971, t'Hooft showed that Weinberg's theory is renormalizable. So there was no divergence in weak interaction theory!
Thus, no subtle idea was suitable for strong interaction. Hadrons such as proton, neutron and pion are built out of quarks which are the fundamental triplets of Sakata-Gell-Mann SU(3). Scientists (including Gell-Mann) hesitated to accept this simple truth.
During Gell-Mann's Bangalore lectures in 1961, Richard Dalitz raised the question why Gell-Mann left out the fundamental triplet of SU(3).Gell-Mann did not answer this question. I have described this "Bangalore Incident"
in many of my essays.
After the success of Yang-Mills theory for describing electroweak interactions, it seemed childish to use the same Yang-Mills theory for strong interactions. But that is what happened. Quantum Chromodynamics which proved to be the correct theory for strong interactions is a Yang-Mills theory.
Therefore, the dynamics of all the three fundamental forces, electromagnetic, weak and strong, are based on Yang-Mills theory.
This is the Standard Model.
After the experimental discovery of Neutral Current Weak interaction, I thought that Nature will throw up a surprise. I thought that the SU(2)XU(1) symmetry will be implemented in a subtle way without the gauge bosons. But gauge bosons were discovered with the masses predicted in gauge theory.
Finally, I expected that spontaneous symmetry breaking will be more subtle than the Higgs-Kibble mechanism and that there is no Higgs boson. But Higgs boson was experimentally discovered in 2012.
This is the reason for raising the question: "Is God subtle?"
Standard Model is not the end of fundamental research. When we probe deeper in our "Inward Bound Journey", the subtle ideas may be needed.