In his letter, Harry J. Lipkin says, essentially, that no fundamentally new theory in physics has emerged for the past 50 years. Many physicists will disagree.
A specific exception to Lipkin’s premise can be found in the Yang–Mills theory of 1954 as an extension of Maxwell’s equations. The theoretical Standard Model that Lipkin describes as hindsight is based on Yang–Mills particles (gluons; see Frank Wilczek, Physics Today, August 2000, page 22), in conjunction with symmetry breaking mechanisms. The past 50 years of particle physics might then be seen as an experimental search into the validity of Yang–Mills theory and its renormalization. Furthermore, Lipkin’s examples of great accomplishments in experimental physics were all taken from particle physics. The debate hardly stops with particles.
Having described such experiments, Lipkin then confuses theory with serendipity. Everyone knows that serendipity (“who-ordered-that”) is an unstated part of any exploration initiative that searches where no one has looked before. NASA addresses it, sometimes explicitly. However, it is rarely stated because taxpayers don’t like to fund it.
Physics is a model or paradigm where theory and experiment must work together. It is a search for understanding. A prominent goal is completeness and consistency, which is where theory plays its role. Theory is also important because it defines what is “observable” and what is “unobservable.” The observable is where experimentalists find fame and fortune. The unobservable includes such things as axioms, boundary conditions, postulates in relativity, and Hilbert space. Take the most important concept in wave mechanics, the wavefunction ψ. It is unobservable. Is Lipkin looking for that experimentally?
The unobservable part of physics, the part that experimentalists can never measure, is fundamental to completeness. In a sense, it is metaphysics. Without it and the theorists who define it, Lipkin’s world would be incomplete and inconsistent.
