Without worrying about free will, here’s a quick look at determinism and indeterminism.

Determinism

Determinism effectively says that whatever happens in a causal chain results from what has happened before. If we could turn back time, the events would unfold identically.

In a deterministic universe, borrowing from Peter van Inwagen’s example, if Sally has to choose between Julliard and Harvard, if she ‘chooses’ Harvard, the first time, and subsequent instance would see her making the same choice.

Indeterminism

Indeterminism effectively says, that whatever happens in a causal chain results from what has happened before. However, random events could alter the outcome. If we could turn back time, although events could unfold identically, they don’t have to.

In an indeterministic universe, borrowing again from Peter van Inwagen’s example, if Sally has to choose between Julliard and Harvard, if she ‘chooses’ Harvard, the first time, a subsequent instance might see her choosing Harvard again, but she might also choose Julliard. Since we have not entered free will into the arena, her choice was indeterminate but based on something entirely outside of her control. At some point, RNG entered the picture and tossed a 1 instead of a 0 thereby sealing her fate, as it were.

Again, absent the notion of free will, perhaps Sally was particularly inspired by a music teacher or a musician. Perhaps she just watched the Johnny Depp and Amber Heard trial and was compelled to fight for justice. Perhaps she was hungry or full. Perhaps she was stuck in traffic. Perhaps she was deciding during shark week.

Groundhog Day and Butterfly Effect

Another popular trope is that if we could rewind time, we could either effect change in the rerun through learning or just altering the past. We’ve seen this played out in movies like Groundhog Day, Butterfly Effect, the Back to the Future series, and so on. Time travel stories present several thought experiments that clearly play on the concept that we do have power over our environment. We’ll save this narrative for another day.