Once you do get to the scale of atoms and smaller, things certainly do get counterintuitive and distinctly nonclassical. We have seen many examples now. Particle position gets blurry. Particles seem to be governed by invisible wave functions. Particles interfere with themselves after passing through or around obstacles. We can’t tell which slit the photon or electron went through, and the whole idea of a trajectory is useless. Electrons jump from one energy level to another spontaneously and instantly. Particles appear and disappear out of thin air. Trying to get any information about a particle necessarily disturbs it, adding more randomness to the situation.
All of this randomness puts in jeopardy the two kinds of determinism that were hallmarks of science during the classical age. In the quantum world, the most complete knowledge possible about the state of a physical system is no longer sufficient to determine exactly how it will be in the future. We can’t know both a particle’s position and momentum at the same time, so no physical law could possibly predict where it will be at all future times. Absolute predictive determinism is not a feature of quantum physics. We will simply have to settle for determining probabilities of future events occurring.
QUANTUM QUOTE
Because all experiments are subject to the laws of quantum mechanics … it follows that quantum mechanics establishes the final failure of causality.
—Werner Heisenberg
Is it the same for causal determinism? This is a somewhat more philosophical question, but certainly one worth asking. If the result of any experiment or any measurement can only be a set of probabilities, what can we say about the causes of the results we actually observe? We are running into severe limits on what we can know. Are these temporary boundaries, awaiting an even deeper understanding of nature? Or, is this all there is? We delve into questions like this, but in the meantime we have more work to do to complete our understanding of modern quantum physics.
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