How to think like a physicist

academics physics
By Adam T.

Ptolemy, the Alexandrian polymath, proposed a model of the universe as a series of concentric spheres. The Earth was the central sphere1 with the sun and stars existing on spheres farther from the center. This is known as a geocentric model, and it was designed to explain the motion of heavenly bodies in the night sky. It was the dominant idea in western astronomy until the time of Copernicus who, as we are usually taught, “proved” that the Earth in fact revolves around the sun. Eventually Galileo was imprisoned by the Catholic Church for promulgating this heliocentric model, leading him to utter the famous and likely apocryphal phrase “Eppur si muove” or “And yet it moves.” Galileo’s point here is that, regardless of whether he recants, the nature of physical reality will remain unchanged. 

Galileo is at least half right. The laws of nature certainly do not change based on what we say. But Galileo did not have evidence to support his implicit claim that the old geocentric model was wrong. Instead, he and Copernicus had accumulated evidence that the new model was simpler. For example, using the heliocentric model, we can write a single equation that is obeyed by all orbits of all bodies within our solar system.2 We could also, however, use a geocentric model to write a series of equations that are also obeyed by all orbits of all bodies within our solar system. The heliocentric model is not more correct than the geocentric one, but you can bet that the heliocentric model will be considerably easier to use.  

This notion of ease of use turns out to be absolutely vital in modern physics, especially in my field of quantum mechanics, because there are myriad ways of understanding the same system. Most of the time, it is impossible to say which of these, if any, are more “true” than the others. Instead, we use the model(s) that will most easily answer the questions we are asking. Choosing and/or building these models is of course not trivial. We study for years to learn the contexts in which certain effects can be ignored while others must be included. We can and often do prove our models wrong, but we never get to know that we are truly right.  

To think like a physicist, then, one must abandon any quest for a higher truth. One must accept that there can be many ways of understanding the same phenomenon and that, as long as these models are consistent with experiment, none is truer than any other. There is great irony in this, since many are drawn to physics by the pursuit of truth. Perhaps a keen sense of irony helps make some physicists great. As Einstein said, “To punish me for my contempt of authority, Fate has made me an authority myself.” 

Adam holds a BA in Physics from Washington University in St. Louis (2013) and PhD in Physics from MIT (2024). He has worked as an engineer and data scientist.

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