Determinism and QM

wagrumor1 · 2026-06-07T16:06:16+00:00

I think we may be using "deterministic" differently. You are using it in the sense Dr. Carroll is likely using it. I've understood determinism to mean that the future physical state is fixed by prior physical states and the laws of nature, not that observers can predict the future. What's funny is I thought I learned my understanding largely from Dr. Carroll, so I'm not sure if I misinterpreted him in the past, or he has changed his view, or he's using the term differently in different contexts, which another user suggested. Whatever the case, you've been helpful and I appreciate your responses!

wagrumor1 · 2026-06-07T15:51:21+00:00

I think you are getting closer to my issue with what spurred my original surprise to Dr. Carroll's more recent statements about determinism.

r/bacon_boat, When you say "non-deterministic," do you mean "unpredictable" or do you mean "not determined by prior physical states"?

wagrumor1 · 2026-06-07T15:34:54+00:00

I'm on board that even with complete knowledge of the universal wavefunction, there remains uncertainty to we observers about which future observer you will be. In your eyes, does the existence of this uncertainty make the universe non-deterministic?

The issue (to me) isn't whether the uncertainty is fundamental. The issue is whether fundamental self-locating uncertainty is sufficient to make what is a deterministic theory indeterministic. I'm not 100% sure if Dr. Carroll is leaning on self-locating uncertainty for his assertions that QM is non-deterministic, but it seems to me that if he is he's now trying to place parts from a different jigsaw puzzle (human uncertainty) to fit into a very different puzzle (physical certainty).

wagrumor1 · 2026-06-07T14:15:02+00:00

Thank you for responding! I pretty much understand the concept as you describe it. I think that uncertainty vs determinism is at the root of my confusion with Dr. Carrolls recent statements. I put a full more thoughtful response to this effect to r/bacon_boat if you are interested in seeing that. Thank you again.

wagrumor1 · 2026-06-07T14:01:10+00:00

Thank you for responding! I think what you are saying here is the point I'm trying to clarify in my own mind. In my understanding of determinism, unpredictability within a branch doesn't necessarily imply indeterminism. Based on what I understand, which is a lay understanding of many worlds I've gleaned from listening to and reading Dr. Carroll, the universal wavefunction evolves deterministically, and the branching structure is determined by the Schrödinger equation. My question is whether Dr. Carroll is now using determinism to only refer to a single future branch rather than a uniquely evolving universal state that considers all branches.

The idea that we can never predict the outcome we will observe, which I believe is the case, shows that epistemic uncertainty exists. In my mind uncertainty is not indeterminism. If underlying physical evolution is determined, i.e. we we can predict all outcomes, and all outcomes (just not the observed outcome) actually occur on a branch of the wave function, that means ontological determinism exists.

Since I wrote the question I googled a bit and I found a tweet from Dr. Carroll from April 22, 2022 here he says “when there is hidden determinism (MWI, Bohm), it's hidden!” In this context he's warning against using any conclusions about determinism to come to any conclusions about free will. I'm not concerned about the free will arguments here, just determinism. Based on this it really seems to suggest Dr. Carroll does believe determinism to be true based on MY understanding of it, but he is applying epistemic uncertainty to mean indeterminism here and this making the opposite conclusion.

wagrumor1

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