This is a followup to my earlier post on free will. The debates around free will usually relate it to determinism. And some people seem to believe that science shows that we are in a deterministic universe. As one of the comments to Jerry Coyne’s post suggests, if we are scientists, then we should be devising experiment tests to help us determine whether our universe is deterministic. And, much like that commenter, I am unable to conceive of how it could be tested. That ought to suggest that “determinism” itself is not a well defined idea.
Determinists seem to base their determinism on the fact that our scientific laws are deterministic. But that is surely a mistake. We prefer deterministic laws, because those are the most useful for making predictions. If the deterministic law is slightly off, then our predictions will be slightly off. Being able to make predictions that are close, but not quite exact, is already quite useful. So we should prefer deterministic laws that are slightly off, over indeterministic laws that are completely correct but that cannot make predictions because of their indeterminism.
As an illustration, consider the gas laws from physics. These are deterministic, and very useful for making predictions. The physicists actually call them the “ideal gas laws,” for they are completely correct only about an imaginary ideal gas. They are not quite correct about real gases. Philosopher of science Nancy Cartwright has argued that many of the laws of physics are idealizations, rather than correct descriptions. And if the deterministic laws of physics are actually idealizations, then they do not constitute actual evidence for the belief that the universe itself is deterministic.