Re-running The Universe: Determinism, Indeterminism, Quantum Stuff
[This is part of a set: Thinking]
The philosophical persuasiveness or either determinism or indeterminism has been made foggy by the success of quantum physics, in particular the apparent indeterminate nature of the world, that is the result of quantum physics.
One question that arises is the extent to which we can be sure, or not, that the universe is deterministic. Does ontological determinism hold?
[This follows from another post which assumed determinism for the points made. It ignored quantum stuff.]
From the point of view of a scientist there is the laudable position that we go wherever the evidence leads – and I agree with that. It appears that all the science is telling us that we live in a quantum indeterministic world, but with determinism at the macro level that allows us to make limited predictions.
So, if anyone wants to argue on the basis of evidence, then that’s it. The world is a deterministic+indeterministic mix. But it is indeterminate anyway, epistemologically, to those entities within it.
At our macro level we can still argue that there is a determinism that appears as a result of any quantum event, once it has occurred. Once a particle has had a causal effect on another, to a measurable degree, then the outcome is, within limits, deterministic.
One question that often arises is this. If we ran the universe again, would all the same events occur? The quantum non-determinist would say that, no, it would not, because quantum events are by nature indeterminate and would result in a different outcome.
But, given that we can’t re-run the universe this is a speculative position. Here I give several alternatives that I see. What follows assumes there is some sort of existence of something outside our universe – that our universe is contained in some way, so that the starting conditions can be set up the same way, down to whatever detail one might like to speculate about.
Determinism seems to require causality, otherwise what does it mean for one state to be determined by prior states. On the other hand, if there is a genuine time symmetry, then effects would cause causes, when considering time reversal. A one-way time dimension can also be causal the one way (which is what we perceive), and yet even in this universe Galilean physics is time reversible. Anyway, putting time issues to one side for now, here we go:
1) Indeterminate Universe. In this case there might or might not be causal relationships. It might be the case that there is no causality, just correlation – weak observed correlation. How does a completely indeterminate universe allow for predictability? Maybe it doesn’t. Maybe what we perceive as repeatable predictable outcomes – say from y = mx + c – are just coincidental correlations. If the universe is so indeterminate in actuality, in practice it’s difficult for us to figure that out, to ‘determine’ its indeterminism, as it were. This is somewhat like the reality-solipsism dilemma – we can’t tell the difference. The point though, in the context of this post, is that to re-run this universe with the same starting conditions will result in a different universe each time.
2) Deterministic Universe. In such a universe every event is determined causally by prior events. This is a point of view that might have been held prior to our discovery of the quantum indeterministic nature of the universe. In such a universe it would re-run exactly as it did on a previous run. On the face of it, at the macro level, it seems a reasonable working hypothesis. We observe what we think are deterministic connections on many levels of science, and other than quantum indeterminacy, we’ve observed no evidence against determinism.
3) Quantum Indeterminate Universe. In such a universe, even with identical starting conditions, the re-run would produce a different universe, because of the truly indeterministic nature of quantum events. This seems to be how some scientists view the consequences of quantum physics in our particular universe. But this seems to require some knowledge of facts outside our scope. Consider, if the quantum indeterminacy is, at some other level, actually determinate, but our understanding of physics is mistaken, then how would we tell the difference? Only a re-run of this universe would reveal the true quantum indeterminacy because a different universe would appear on each run.
4) Quantum Determinate Universe. In this universe even the quantum events are determined – though I refuse to speculate on how that might occur. Note though, that to the entities contained within each ‘run’ of that universe the quantum events would still be non-deterministic, because those entities are contained within the re-running universe and are bound by the evolving quantum events that are taking place. So, on each re-run, the inhabitants of the universe are convinced that their universe is non-determinate because of the observed quantum events, and yet on each re-run the very same quantum events are occurring, deterministically, and each re-run produces an identical universe.
Now, (4) is purely speculative of course. But then so are all of these options, because we don’t have a view of our universe from the outside and over re-runs of it. So, I don’t see any justification for being dogmatically committed to any of these views.
Perhaps the important point is that we do not know what our science is telling us about the deep status of our universe. It is all metaphysical speculation. And, I repeat an earlier point, to us it’s all indeterminate anyway. We cannot tell the difference between a determinate and an indeterminate universe if we ar a part of it.