Contrastive explanation
Many people mistakenly claim that the radioactive decay of a single atom is not just unpredictable but inherently random: an atom that actually decayed at time t might not have decayed at t given exactly the same prior conditions. Determinism rejects this claim. Here’s one reason why.
If the atom decayed randomly at t, then there’s eventually no contrastive explanation of why it did: no reason why the atom decayed at t rather than not. Even if we’re told the atom had a 90% chance of decaying at t, that doesn’t answer the question “Why did the 90% likely outcome happen rather than the 10% likely outcome?” Of course, responding with “Because it was nine times more likely” doesn’t answer the question either. Why did the much more likely outcome happen when the much less likely outcome could have happened instead?
Sooner or later, the friends of randomness ‒ indeterminists ‒ must say, flatly, “It just did, end of story.” But why end the story there rather than at some earlier stage? Here indeterminists give two responses: (1) “Earlier in the story, we had contrastive explanations to give, but now we don’t,” and (2) “Explanations have to run out eventually.”
Response (1) just reports our current level of explanatory success, which implies nothing about randomness in the world. After all, countless phenomena have contrastive explanations that eluded science until they were eventually found. Response (2) is just false. While any single explanation must be finitely long to be useful to us, there’s no reason to think that explanation itself must be a finite resource. Indeed, if you rule out an infinite regress of explanations, then you’re stuck with either brute facts ‒ “It just did, end of story” ‒ or explanatory circles whose own existence would be a brute fact. See section 4.3 of my book for details.
