Study Design II: Physics Research

I’m going to give a specific example of an actual design from an actual study in moral psychology research in part III, but I thought that, both for continuity’s sake and to emphasize the fact that there is no The Scientific Method, I’d say a bit about research designs in a totally different set of fields.

Most people know about CERN’s LHC. In a previous post, I described how tests on the so-called “God Particle”, the Higgs, continue despite the fact that researchers declared it found in 2012. Unfortunately, the kind of experimental designs in quantum and particle physics are too technical to explain in any decent detail, so I will suffice with a partial explanation and an older, simpler experimental design.

Quantum Mechanics: Where “physical systems” are mathematical objects
The following is the most concise and general description of all experiments in quantum mechanics of which I am aware:
QM measurement (Stapp)
(from Stapp’s Mind, Matter, and Quantum Mechanics, 3rd Ed.)

Great. So, what on earth does that mean? A fundamental issue in quantum theory is measurement. Many people are aware that any measurement of quantum systems will disturb the system (the uncertainty principle). What is less well known is that we can’t measure a system without preparing it (i.e., whether we are crashing cars for safety tests or using ion traps to “control” subatomic particles, we have to set-up the system so that we can run it and measure the outcome). You may think “ok, but ‘duh’ with a side of ‘so what’?” and I wouldn’t blame you. But if you think about what preparation entails, you might realize that in order to prepare a quantum system we have to fundamentally “disturb” the system. To simplify, I’ll use let’s watch an experiment:

So we detect individual electrons as if they were particles, but the pattern formed (the interference pattern) cannot be formed by particles. Particles have a well-defined location and trajectory. That pattern is only possible if the electrons somehow interfere with themselves, such that they are not localized until we detect them, and prior to detection they weren’t following any path.

Strange as this is, it skips over a central problem: in order to get electrons to go anywhere, we have to mess them up. That means we don’t actually know where they started out and in which direction they were going. In order to accurately predict how the electrons will be distributed, we prepare our system and then translate the way we prepared it into math(a wave-function) that not only doesn’t accurately tell us the initial state of the electrons, it doesn’t even correspond to any electrons. It’s a system that “lives” in an abstract mathematical space (Hilbert space, a complex and usually infinite-dimensional space), and, given a specific manner of preparation it allows us to calculate the probability of particular measurement outcomes. Stapp’s quote above is essentially saying just that: quantum theory describes systems statistically, and the particular statistical descriptions depend upon the manner of preparation and the type of system. What we call the state of the system is really a mathematical function, and we do not know how it corresponds to physical reality.

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