Scientific determinism
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Physicists have sometimes used the term "determinism" in a special way that people such as Karl Popper and Stephen Hawking have called scientific determinism.
Popper insisted that the term "scientific" can only be applied to statements that are falsifiable. Popper's book The Open Universe: An Argument For Indeterminism defines scientific determinism as the claim that ...any event can be rationally predicted, with any desired degree of precision, if we are given a sufficiently precise description of past events, together with all the laws of nature, a notion that Popper asserted was both falsifiable and adequately falsified by modern scientific knowledge.
In his book, A Brief History of Time, Hawking claims that predictability is required for "scientific determinism" (start of chapter 4). He defines "scientific determinism" as meaning: "something that will happen in the future can be predicted."
Since many limitations on predictability are now known (for a partial list see: quantum indeterminacy), most people who argue for determinism do not argue in favor of a strong version of scientific determinism. For example, a weaker type of determinism is one that only implies a unique, mechanical course for the universe with future events being caused by past events.
Hawking admits that even the uncertainty principle does not absolutely rule-out a kind of determinism "in principle", and says that quantum mechanics may very well allow the universe to be deterministic. He wrote:
- "These quantum theories are deterministic in the sense that they give laws for the evolution of the wave with time. Thus if one knows the wave at one time, one can calculate it at any other time. The unpredictable, random element comes in only when we try to interpret the wave in terms of the positions and velocities of particles. But maybe this is our mistake: maybe there are no positions and velocities, but only waves. It is just that we try to fit the waves to our preconceived ideas of positions and velocities. The resulting mismatch is the cause of the apparent unpredictability." (conclusions section of A Brief History Of Time)