Why does quantum mechanics need philosophy?

With his characteristic insight, Randall Munroe presents the amusing graph above. As someone who has had enough years of math (a Ph.D. in math in 2007 and pretty much continuous use of advanced mathematics since then) to understand all these subjects, I find a lot of misconceptions about quantum mechanics, even among those who should know better. For those who don’t have the math, I can only imagine that it must be confusing.

Many Worlds

Many of you know I have had an ongoing battle against the Everettian Many Worlds Interpretation of quantum mechanics. I’m not against multiverses per se although I have sometimes given that impression. Rather, I am against using mathematical abstractions and conveniences as guides to reality. This stems from my larger battle against Platonist Idealism, the idea that abstract, mathematical ideas exist in their own reality. (Max Tegmark is a good example of a proponent of these ideas.)

Mathematics is a useful way of representing reality but there is always a certain amount of sausage making in any mathematical model. I feel like mathematical physicists should know better. My background is in statistical mechanics which, more than any other field of physics, exposes the sausage making for all to see.

Unfortunately, in quantum theory we don’t know what is in the sausage. Quantum theory is in some ways a black box. We put in fields and particles, mass, charge, energy, and so on and out we get are probabilities that match what we see, but a lot of the stuff we put in is not, from any intuitive standpoint, real.

That’s where philosophy comes in. Quantum mechanics says that reality depends on things represented by mathematical objects that are either not real or are unobservable in any direct way. I’m talking about wavefunctions and virtual particles.

How we interpret all of that, lacking better evidence, comes from philosophy. Do we stick to concepts like realism and locality or do we allow those to slip away? Is the universe subjective or objective? Is there a single fixed reality or many? Is there a single universal framework for interpreting results or must we pick and choose from several incompatible ones? Does measurement or observation create reality? Are classical definitions of observables sufficient for quantum physics or must we expand the definition of position, momentum, and spin?

Most interpretations of quantum mechanics, whether complete or incomplete, rely on particular philosophical notions to nail down their interpretation.

Many (I would say most) physicists are uninterested in philosophy and believe it isn’t important. Unfortunately, however, because philosophy is a meta-discipline that defines the assumptions and terminology of any given discipline, everyone needs philosophy, including physicists. If you don’t grapple with philosophical ideas, you will just use what you inherited, which may not make a lot of sense. For lack of metaphysics, you will fight against ill-defined terms and fail to come to grips with what you reality is. For lack of epistemology, you will not know what you can and can’t know and so risk putting too much or too little faith in what you believe. For lack of ethics, you will make Faustian bargains without realizing it or else steer clear of difficult moral decisions in favor of the naive belief that you can avoid all ethical dilemmas through restricting your activities to a few safe areas. For lack of aesthetics, you will fail to examine your own ideas about beauty–how much of physics is about finding the beautiful?

Most physicists would like to embrace just one branch of philosophy: logic.

Part of the problem here is that we have mathematical models for empirical results: ways of “quantizing” classical physics and definitions for new forces and fields that we only observe in a quantum way. Yet, the math suggests there is a lot more going on than we can see.

Naive journalists unfortunately fail to understand a lot of the subtleties here, getting hooked on faster-than-light phenomena or spooky action at a distance, Schrodinger’s cat paradoxes, string theory, and multiverses. The real problem at issue isn’t that quantum mechanics predicts these things but that we don’t understand the metaphysics. We don’t know what is and is not real within the mathematical models we have or how to interpret them if things we can’t see directly are real.

If you look deeply at what we actually can see, it is particles and particle interactions with force fields. All the rest is probability from carrying out the same experiment over and over again or multiple simultaneous experiments.

That is why, coming from classical statistical mechanics, which is all about proposing unrealistic models that give real predictions, I say there is a lot of sausage making going on, whether we explicitly understand the process or not.

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