The story goes that when an apple fell on Isaac Newton’s head, it inspired him to develop the theory of gravitation. What makes that theory significant is that it not only predicts the motion of a falling apple, it explains why the apple moves that way and expands that explanation to cover the movement of the tides, the planets and the stars.

“The greatest achievements in science have been these big leaps forward, when someone like Darwin or Newton is able to explain a lot of previously-gathered information with one theory,” says philosophy professor Andrew Wayne. Kepler, Wayne points out, had determined the orbits of the planets long before Newton came along, and Galileo had developed laws about the movement of pendulums and falling object. “But it was Newton who said ‘this is all because of gravity.’”

While scientists are out there looking for explanations, few of them think a lot about what makes something qualify as explanatory. That’s where Wayne comes in. “What I am examining in my work is how science provides these explanations.” Philosophers have been exploring this question since the 1940s, but Wayne says none of them got it right. He’s remedying that with his new project, which focuses on explanations in the field of physics.

Physics uses models to represent what is happening in a situation. However, don’t look for an exact copy or even something realistic. “The kind of models that physicists are using in their explanations are highly idealized, and in some respects they’re not really an accurate representation of reality,” Wayne explains.

Galileo, for example, developed theories about the movement of a pendulum, but they required the assumptions that the pendulum was not subject to air resistance and that the string or wire had no weight. Under these conditions, Galileo suggested the pendulum would swing back and forth indefinitely, according to his formula.

But in real life, a pendulum swings in shorter and shorter arcs and eventually just hangs there.

Other types of models are even further removed from real situations. Some require imagining that an infinite number of molecules are present, for example.

So how can models that are not accurately representing reality actually explain reality for us? “These models can be explanatory when they are appropriately integrated into the larger theory,” Wayne says. “You might have a model that is built just to fit the system that has been observed. That model might let you make predictions, but it’s not explanatory. It’s how your model relates to the over-arching theory that makes it explanatory.”

Wayne, who studied physics at the University of Toronto before realizing that his interests lay more in the direction of philosophy, is investigating the explanatory aspects of gravitational wave models — an active research area in U of G’s Department of Physics. “What’s interesting is that there are actually two different models that make the same gravitational wave predictions,” says Wayne. “Physicists believe one is explanatory and one is not. They both make the same predictions, but their inner workings are very different – and both are highly idealized.”

One model integrates with the general theory of relativity in a strong way; the other connects to that theory in a weak way. “Some physicists prefer one, and some the other,” Wayne says. His research will examine these models as examples of how physics can effectively explain nature.

“What I’m looking at is how the theory connects to the models,” he says. “Philosophers usually see models as applications of the over-arching theory. But that’s not at all what it is. It’s much more complicated and subtle than that.”

Wayne’s investigations into the explanatory nature of the models used in physics will become a series of articles and a book project. He’s also planning an interdisciplinary workshop that will bring together philosophers and physicists to discuss these issues.