I reached a bit of a watershed recently in my thinking on the question of whether we live in a deterministic universe, and what I see as a the related question of whether we enjoy real freedom of choice.

Like most people who have contemplated the paradox, I had hitherto been dissatisfied with my grasp of the matter, because neither determinism nor its alternative are without contradiction:

  • the notion of determinism seems obviously at odds with our perception that we enjoy freedom of choice.
  • the alternative to determinism - call it indeterminism or free choice, seems obviously at odds with the following understanding of the laws of science: certain "a priori determined facts" combine and interact according to a set of behavioural rules (the laws of physics), to yield a certain outcome. Fixed rules with no probabilistic element leave no room for choice. Probabilistic rules may leave some room for choice - but only insofar as the facts were unknown in advance.

It occurred to me recently that the debate focuses upon the "laws of physics" part, and whether these laws combine all the "a priori determined facts" in a determined way or a probabilistic way.

But in reality, the notion of a fully complete set of "a priori determined facts" is an assumption - a myth in fact - a simplification which we are taught to apply in the classroom. The true reality is that we only ever have some observations and experiences which point more to some "a priori determined universe" than some other such universe. We can never prove with any certainty that the actual determined universe exists aywhere other than in our imaginations. Moreover, nothing is EVER determined. Any supposed "fact" is at risk of us waking up to discover that we dreamt it.

So I am now of the view that it is our assumption that there exists a set of "a priori determined facts" which creates the illusion of determinism. We are, quite simply, assuming determinism, by the way we think about the workings of the universe.

I'm curious how this conclusion from a non-philosopher fits in to the accepted narrative among those more learned than I, on the matter.

  • When you say "a priori determined facts", are you using "determined" in an epistemological sense of something we have learned or discovered (suggested by Moreover, nothing is EVER determined. Any supposed "fact" is at risk of us waking up to discover that we dreamt it), or are you talking about something like a precise statement of "initial conditions" in physics, which could include objective truths about the state of the universe at some past moment which no human ever discovers? (a more ontological meaning of 'determined fact'). Usually determinism is conceived in terms of the latter.
    – Hypnosifl
    Dec 29 '21 at 22:27
  • "the notion of determinism seems obviously at odds with our perception that we enjoy freedom of choice." It doesn't seem obvious to me. In fact, I don't think I have that perception.
    – Chelonian
    Dec 31 '21 at 5:30
  • @Hypnosifl I think I'm contemplating either of your interpretations of "a priori determined facts". To my mind the latter is as much a myth as the former, and heretofore it had been my delusion that "initial conditions" are in some sense fully and unambiguously defined, that led to any ideas of determinism. Once one realises any attempt to define initial conditions is only an approximation, there is no longer any case for determinism. Jan 2 at 22:39
  • @Chelonian If the choice B you are about to make is predetermined, then how can you be free to choose A instead? Jan 2 at 22:43
  • heretofore it had been my delusion that "initial conditions" are in some sense fully and unambiguously defined But if you mean "defined" by humans, then it would be the epistemological interpretation. On the other hand, if we are talking about the ontological interpretation, in general do you believe there can be truths about reality that are not known by any human, and perhaps never will be, like what the surface of a planet in another galaxy is like? Or are you skeptical of any mind-independent physical reality, not just initial conditions?
    – Hypnosifl
    Jan 2 at 23:35

Much of the motivation to reject free will is the common belief that the physical world is deterministic.

However, the physical world is not deterministic -- it instead appears to be stochastic in both classical and quantum physics.

Relative to classical physics, several physicists in the last several decades have been exploring "classical" cases which lead to stochastic solutions. Here is one such reference: https://www.journals.uchicago.edu/doi/full/10.1086/594526?casa_token=jcR7Qn5Ji-cAAAAA:rxtSGXk98L_jfEBttu1Lt2LD3DGjsRXmhk6C_4AcUByNqWdELIjk_3ehV_rhVWe0TM9DbprEJkLj Note the language is not particularly clear, but for every case where "uniqueness fails" or "there is more than one solution" -- that translates into classical physics having multiple possible outcomes to an event, and thus being stochastic rather than deterministic.

Another discovery, a little older but also recent, was that even deterministic models can be unpredictable. This was first discovered in weather models, where a complex weather simulation code, which was entirely deterministic in character, ended up giving radically different predictions when one of its inputs was rounded off at the 4th decimal place. These are now called chaotic systems, and weather is considered a prime example of classical physics "deterministic" chaos in nature.

A good example of chaotic behavior in a much simpler system than a weather model, is this illustration of chaotic behavior from triple pendulums: https://jakevdp.github.io/blog/2017/03/08/triple-pendulum-chaos/ The triple pendulums provide an example where that is not the case, because it is SUCH a sensitive system, that variations on the order of the Heisenberg uncertainty principle in initial state, quickly lead to the sort of chaos this video illustrates. IE -- macro scale chaos phenomena allow quantum stochasm to leverage up to macro-scale stochasm.

For modern physics, the founders of quantum theory embraced stochasm. This is called the Copenhagen "interpretation" of Quantum mechanics. Not all their peers wanted to accept stochasm in the universe, leading to a proliferation of efforts to reinterpret QM non-stochastically.
The two key legs of stochasm have been Heisenberg's Uncertainty Principle, which notes that one cannot actually discover the product of pairs of terms to less than a certain uncertainty content. The clearest product to illustrate this is time and momentum. https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Quantum_Mechanics/02._Fundamental_Concepts_of_Quantum_Mechanics/Heisenberg%27s_Uncertainty_Principle If we cannot know either the initial or final states of a system precisely, that brings not just predictability into question, but Heisenberg thought the entire concept of causation was now suspect.

The other leg has been quantum mechanics -- that the behavior of elementary particles is like waves, that decompose into particles for interaction purposes at stochastic locations within the wave-field. One of the clearer aspects of quantum mechanics, is that the decay of a single radioactive atom -- will not occur at a predictable time but will occur randomly based on its "half-life". The developers of QM recognized that this is a violation of not just determinism, but also of normal understandings of causation.

Einstein was one of the major leaders in the effort to challenge the stochastic nature of QM. He postulated a set of alternative interpretations of QM observations, which failed test after test. His final effort was the concept if intrinsically hidden variables, unable to ever be observed. He got grief over this, as he seemed to be violating one of the key aspects of science-- refutability of one's theories. But Einstein, as a good scientist, pushed for ways to test his "interpretations" vs Copenhagen. Note if tests can distinguish between them, alternative "interpretations" are actually alternative theories. All of Einstein's alternative "interpretations" have been refuted by these tests.

A list of most of the "interpretations" is here; https://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics. Note that the only two "interpretations" labeled non stochastic are many worlds and Bohm-DeBroglie. Bohm's is a hidden variable model, with global rather than local hidden variables. What that means is that every event is influenced by every other object in the universe, regardless of distance, and regardless of speed of light limits. Bohm sacrificed compatibility with General Relativity, for the comfort of a deterministic model. It has now been fairly widely recognized that Bohm's theory is different from QM, and it is often now described as Bohmian Mechanics. The results of test cases to date, have been strongly trending against Bohm and in favor of Copenhagen; http://settheory.net/Bohm https://www.physicsforums.com/threads/back-pedaling-on-bohm.905194/. Bohm -- has not been widely considered refuted yet -- but these observations and test cases have drastically dampened enthusiasm for Bohm's theory.

Many Worlds postulates that for every quantum event, all possible outcomes occur, and the universe splits to create alternate non-interacting universes for each possible outcome. Many Worlds is claimed to be a "deterministic" theory per the Wiki page, and many advocates. But this does not appear to be the case. For any observer, there will only be one outcome to any event, and that outcome is not deterministic, but stochastic. Postulating that other observers exist, and that all possible outcomes are observed between the theoretical collection of all of them -- still leaves each of them as a single observer, experiencing a stochastic event. Per the standard for determinism set for classical physics -- LaPlace's Demon could neither know the current state of the universe (it would still be limited by Heisenberg Uncertainty Principle), nor could it predict the outcome of any measurement (echoing Earman's language relative to classical physics, "there is not a singular solution"). "All of the Above" is not determinism. Plus -- postulating excess universes that are undetectable in principle -- is a violation of science basics, for which Einstein received justified grief.

Additionally, Many Worlds, from a pragmatic causal point of view-- explicitly abandons causation and cannot even adopt the envelope/probability approach that plausibly can encompass chaos events. This is because probability between the worlds becomes a nonsense concept -- all of them exist, and there is no "bandwidth" feature to these different universes that can distinguish "frequency". Putting this in personal terms, I could in the next 20 minutes, complete this entry, and post it, abandon the project and play video games instead, or walk next door and murder the neighbor family. All are possible, none are any more "caused" than the other, and each occur in SOME world per MW "interpretation". sSuch a radical elimination of the concept of causation, is not what most determinists are looking for, and the popularity of the MW interpretation is likely due to its non-physics adherents not understanding how it destroys any coherence to causation.

Bohm is to be heading down the path of refutation that Einstein's hidden variable theories followed, and MW is not really a deterministic model. Quantum mechanics is intrinsically indeterministic. Combined with both the indeterminism in classical physics, and the intrinsic unpredictability of chaos phenomenon (and actual indeterminism once one includes Heisenberg's uncertainty), leads to a definitive answer -- the "laws of physics" do not support determinism.

Whether this allows free will or not -- is another question.


There is no paradox. There is no determinism.

The problem with determinism is that it does not explain how the Universe was shaped, how the initial conditions were set, why did it turn out this way and not in any other way. Instead, it only denies both methods of determining anything: probabilistic randomness and intentional design.

In determinism, nothing can happen by choice or by chance. Therefore in determinism nothing can happen at all.

Only the laws of physics are acceptable "a priori determined facts". But the laws of physics can only determine the effect if there is a cause. The laws alone cannot determine anything.

  • Your answer appears to predicate "determinism is contradictory" upon the premise that "initial conditions are required." But it is unclear to me that initial conditions are required. Why must we have a determined set of initial conditions? Dec 3 '21 at 10:31
  • If there are no initial conditions, there are no subsequent conditions either. If there is no cause, there is no effect. Dec 3 '21 at 12:32

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