Determinism and scientific laws

by Neil Rickert

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.

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3 Comments to “Determinism and scientific laws”

  1. Neil Rickert: “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.”

    That’s true, but no mechanism in operation within the universe is evidence for determinism even if you understood it completely.

    Determinism deals with states and their transitions.

    If the universe consisted of two photons flying through space at C, you could derive your proof of determinism from that model.

    Their relative position at any point in time would be dependent on a previous point in time and the resulting interaction between their masses.

    Now start adding photons one by one to the universe. No matter where they are, their influence on the others is predictable.

    will always follow and it will always be exactly that state for any given model, even if trillions and trillions of photons are added.

    Our inability to predict because of our less than perfect understanding of the laws of physics, does not change that deterministic quality of our universe.

    always follows in any universe regardless of its size.

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    • That’s true, but no mechanism in operation within the universe is evidence for determinism even if you understood it completely.

      I agree with that. However, we can only observe the universe from within the universe. Unless we can somehow leave the universe, and view it from the outside, we will always be under that constraint. And thus there could never be evidence available to us, that could settle the question of determinism.

      Determinism deals with states and their transitions.

      Be careful with that kind of argument.

      When we discuss computers, or finite automata, or Turing machines, we have a very precisely defined notion of “state” that we can use. But when people talk more broadly of states and transitions, as happens discussions of determinism and in a lot of philosophy of mind, they usually have no coherent definition of what they mean by “state”.

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  2. That should be;

    “State n+1” will always follow “state n” and it will always be exactly that state for any given model, even if trillions and trillions of photons are added.

    and

    “State n+1” always follows “state n” in any universe regardless of its size.

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