Physics does not predict rigid trajectories

Free will is mostly a philosophical issue, but some of the arguments are subject to scientific analysis. Jerry Coyne writes:

The fact that articles keep coming out assuring us that we do have free will, yet each assurance is based on a different premise, tells us that the philosophical debate will never end. Yet I consider it already ended by science: we do not have libertarian free will because our thoughts and our actions are decided by the laws of physics and not by some numinous “will” that interacts with matter in ways that physicist Sean Carroll has said is impossible. Ergo the appearance of compatibilists, who admit that yes, determinism rules, and at any one moment we can behave only one way—a way determined by physical law—but nevertheless we have other kinds of free will compatible with determinism.

That, of course, won’t satisfy the majority of people who do believe in libertarian you-can-do-otherwise free will, among these the many religionists whose faith absolutely depends on our being able to choose our path of life and our savior, and your salvation depends on making the right choice (Calvinists and their analogues are an exception). Compatibilists, when they tell us that nobody really believes in libertarian free will, are simply wrong: surveys show otherwise, and there are all those believers.

No, this is just wrong. The laws of physics are not so deterministic as to rule out libertarian free will.

I recently criticized Sean M. Carroll on free will.

Coyne is responding to this essay:

We need not think about the fundamental laws of physics as rails directing reality along a rigid trajectory. Rather, we can think of them as constraints on what kinds of physical transformations are possible and impossible. ...

Famous ‘free will sceptics’ like Jerry Coyne and Sam Harris are rightly worried about ditching the concept of physical determinism. In their view, the only alternative is a mysticism allowing for all kinds of silly miracles and supernatural beings. ... we still live in a universe governed by timeless, fixed laws — it’s just that these laws do not dictate by themselves how exactly the future will unfold.

..., we don’t need to accept the notion that the universe evolves according to some predetermined plan, set in stone from the beginning of time. Our best theories of physics don’t require it, and our best ethical, psychological, and political theories must reject it.

The essay refers to this 2014 paper for theoretical support. That paper is sympathetic to many-worlds theory, which is another can of worms.

Regardless, it is true that the laws of physics impose contraints on motions, and not rigid trajectories.

In a freshman physics textbook, you might see an exercise that calculates the trajectory of a cannonball, and that may seem to have infinite precision. But that is just the simplified freshman version. If you apply the laws of physics properly, you find that the forces, masses, and other parameters can only be known to be in some range of values, and the predicted trajectory is really a contraint on a range of possible trajectories.

Calvinists and academic atheists aren't the only exceptions to believing in free will. So do Moslems, and a lot of Protestant theologians.