Topics Physics

Question If quantum mechanics or other fundamental theories of physics have it that small physical entities which make up everything else do not behave deterministically, does that indeterminism inherited by all other larger entities, whether those are molecules, gases, instantiated computer programs, and people? In general, does indetermism on one "lower" physical level imply indetermism on a "higher" one?

Accepted:
April 8, 2009

Comments

The answer to the general question is that indeterminism at the "lower" level doesn't have to mean indeterminism at "higher" levels. Here's an abstract way to think about it. Suppose some theory has a set of possible states -- call it S -- and a strict deterministic law governing how the states change over time. Let's suppose that this theory is both true and know to be true. But suppose, unbeknownst to us, each of the states in S can be realized in many different ways, at some sub-microscopic level that we don't have access to. And suppose that even though the law that tells us how we get from one state in S to another is deterministic, there's no deterministic law governing exactlywhich way states in S will be realized as the system moves from one state to another.We might never have any reason to believe any such thing, but it could be true all the same.

That's one story about how indeterminism at the micro level might not infect the macro level. Another way is a "for all practical purposes" version. There might be all sorts of blooming and buzzing at the fine-grained level, but all that might average out so that things at the macro level are extremely unlikely to depart from some deterministic rule. Thermodynamic systems are typically like that; the thermodynamic laws hold "for all practical purposes" even though what's going on under the hood is (or may be) indeterministic, and even though there is a teeny tiny probability that your cup of coffee will spontaneously freeze.

As for quantum indeterminacy, it certainly can infect the macro-world. Indeed, it does so every time someone in a lab performs a quantum mechanical measurement. (What the instrumnet registers depends, crudely, on which way the quantum jumps.) But there are good quantum stories about why most of the time, in most circumstances, macroscopic things behave deterministically to a very good approximation