Given what I suspect is my mediocre performance on our first midterm exam for Quantum Theory, I know now why and how String Theory has such a stranglehold upon Physics. ‘Suspect’ because although to date, we have yet to receive back our midterm results, I am mature and experienced enough to know how I performed on an exam, which in hindsight was fair. I realize my mistake was treating Quantum Mechanics as a physics course. Oh, granted the class falls under the rubric of Physics, but the course is not a physics class.

    Physics is about studying the concepts that underscore observable physical phenomena and applying mathematics as a descriptor towards finding values for properties and states of such physical phenomena e.g. mass, charge density, energy, speed, etc.. Physics problem sets and exam questions challenge the student at finding particular values for a given set-up and particular given known quantities. Not so in QM where the central repeated exercise is solving the same damn equation (Schrödinger’s, of course) for varying scenarios e.g. infinite well, step function, with or without angular momentum, considering full 3D case vs. 1-D. The whole enterprise of QM is about doing the math to determine what the wave function is which represents — here is the only true concept in QM, a particle’s probability distribution. In the end, we are just doing math. Contrary to usual physics exam, where we are allowed a cheat sheet of physics formulae, our instructor forebodes that and using calculators. On the exam, there were no standard equations for us to use as one may expect. We were expected to recall from memory the correct formula to apply. Well, that is what a mathematics exam does. When approaching, say, second semester calculus, a student is expected to memorize all the substitutions and trig identities necessary for evaluating the stock set of integrals. That is how it was on this “physics” exam; just remember what equation to use for what situation and solve, nothing about actually finding the value of speed, energy, or temperature value.

    Goes a lot to explain the old joke about Quantum Mechanics: After the first time taking QM, you do not understand. After the second time, you still do not understand. But when you end up teaching, you just get used to it. The chief reason why no one understands QM is because there is no physical intuition attached to QM. (Grifftiths says as much in the 2nd edition of his undergraduate text.)

    Here is how String Theory has survived. Physicists having passed through QM are accustomed with the idea of letting the mathematics take over and leaving the physics behind. There is a certain expectation that one is not going to understand, so as long as they are able to do the math, then they will be fine. ST has its origin from an adoption of some random equations found in a random math text. Absent of experimental validation, String Theorists are comfortable with doing just mathematics, which sometimes agrees with Classical notions, which is why most physicists support ST. Although I am skeptical of String Theory, I am not of Quantum Mechanics.

Just today in the first half of lecture, we learned of Ehrenfest’s Theorems — N.B. the borrowing of mathematical vocabulary, ‘theorem’ instead saying ‘law’ or ‘theory’, whose derivation showed an explicit link between Classical Mechanics and Quantum informing the learner the crossover point and how QM agrees with CM.

    The upshot is, unlike General Relativity which like traditional physics involves applying mathematics to determine the properties of given physical states, Quantum Mechanics must be approached as a math class. Memorize formulae as you go through the class and know when to use what equation when. There is nothing conceptual that needs to studying, least of all, any physics.