Scientific determinism

In his book, A Brief History Of Time, Hawking says 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.

Karl Popper's book The Open Universe: An Argument For Indeterminism argues that in its strongest version, scientific determinism makes a very strong assertion, that "all events are in principle predictable". The qualifier "in principle" can lead to persistent arguments.

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)