How Quantum Models Work

by David Kordahl

A notable theorist visits a notable laboratory (Stephen Hawking at CERN, 2013)

The science lab and the theory suite

If you spend any time doing science, you might notice that some things change when you close the door to the lab and walk into the theory suite.

In the laboratory, surprising things happen, no doubt about it. Depending on the type of lab you’re working in, you might see liquid nitrogen boiling out from a container, solutions changing color only near their surfaces, or microorganisms unexpectedly mutating. But once roughly the same thing happens a few times in a row, the conventional scientific attitude is to suppose that you can make sense of these observations. Sure, you can still expect a few outliers that don’t follow the usual trends, but there’s nothing in the laboratory that forces one to take any strong metaphysical positions. The surprises, instead, are of the sort that might lead someone to ask, Can I see that again? What conditions would allow this surprise to reoccur?

Of course, the ideas discussed back in the theory suite are, in some indirect way, just codified responses to old observational surprises. But scientists—at least, young scientists—rarely think in such pragmatic terms. Most young scientists are cradle realists, and start out with the impression that there is quite a cozy relationship between the entities they invoke in the theory suite and the observations they make back in the lab. This can be quite confusing, since connecting theory to observation is rarely so straightforward as simply calculating from first principles.

The types of experiments I’ve had been able to observe most closely involve electron microscopes. For many cases where electron microscopes are involved, workers will use quantum models to describe the observations. I’ve written about quantum models a few times before, but I haven’t discussed much about how quantum physics models differ from their classical physics counterparts. Last summer, I worked out a simple, concrete example in detail, and this column will discuss the upshot of that, leaving out the details. If you’ve ever wondered, how exactly do quantum models work?—or even if you haven’t wondered, but are wondering now that I mention it—well, read on. Read more »