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Comment by mcarvin | Hacker News Reader

Certain irony about saying that a LAW of physics is not deterministic. Conceded though that determinism does not hold up at the quantum level.

Disagree though that quantum non-determinism translates to non-determinism at the scale we experience [1]. Have never seen a Feynman diagram for a soccer ball. Which is why I feel comfortable saying that if you believe the macro world is deterministic then you cannot also believe there are objective probabilities (unless, as you indicated you are talking about the subatomic world).

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Chaotic macroscopic system + non-determinism at atomic scale = non-determinism at macroscopic scale.

So, e.g., the temperature at the tip of the Eiffel tower on Jan 1, 2014 1pm is non-deterministic.

From a practical approach, the physical world can seem fairly deterministic. If you drop something in a vacuum and nothing hits it, you can say with a great deal of accuracy how long it will take to hit the ground. I don't think that this practical determinism translates to a philosophical determinism.

Determinism does hold up at the quantum level. Quantum mechanics is completely deterministic. Collapsing the wave function to a classic state, is the probabilistic aspect, if any.

I think that quantom mechanics makes us think differently about probability and determinism by giving the mathematical (human created) concept of probability a physical meaning. Similar to the example in intuition 2, a coin toss could be considered determinstic even if we do not try to predict the result. It is pre-determined that given a large enough number of coin tosses, very close to 50% of them would come out heads. Qunatom mechanics makes us consider probability as a physical property inherent in all physical objects. This way of thinking helps reasoning about genetic predisposition as well (which is always probabilistic). Just like any coin is "free" to make a choice, and yet it is certain that they would (almost) precisely split down the middle, so too can genetic predisposition can be said to be both constraining and not constraining at all at the same time.

Admittedly beyond at the limits of what this armchair quantum mechanic can say with confidence but to borrow from Hawkings... probabilities in quantum mechanics "reflect a fundamental randomness in nature" [The Grand Design]. So while quantum theories are testable, they are not always predictive (necessary for determinism).

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