So far in Uncertainty Wednesday, I have introduced a framework in which I attribute uncertainty to limits on observations and explanations of reality. That was followed by a series of posts detailing such limits on observations, including fundamental limits, resolution, measurement error, cost and impact. Then a brief explanation of explanations, followed by fundamental limits on explanations and incompleteness.
Now here comes a big question. What about reality itself? Is it a source of uncertainty also? Asked differently: even if we hypothetically had perfect observations and perfect explanations (despite knowing already that’s not possible), would there still be uncertainty just coming from reality itself?
People who answer this in the affirmative will generally point to quantum mechanics and the seemingly probabilistic behavior of particles at the quantum level. For instance, the spin of a particle is quantized, meaning one can experimentally observe only specific quantities (and no intermediate ones between those). Furthermore, depending on the alignment of the measurement to the spin of the particle, the result of the measurement will be random between different spin values.
Albert Einstein famously didn’t like this aspect of quantum mechanics and repeatedly said and wrote variants of
God does not play dice.
To which Niels Bohr (or Enrico Fermi) may have replied “Einstein, stop telling God what to do with his dice” (adding a bit of uncertainty on quotes here …)
It is now a hundred plus years later and this discussion still has not been settled. The main Wikipedia page on “Interpretations of Quantum Mechanics” lists 17 different interpretation and the separate page on “Minority Interpretations” lists a bunch more. Even the existence of two separate pages is a hint at how unsettled this question is.
There are interpretations of quantum mechanics that treat the probabilities as inherent in reality itself and others which argue that it arises solely as a result of observations (and thus can be seen as a limit on observations). An example of a non-probabilistic interpretation is the many worlds one (e.g. Everett) where every outcome actually exists and the totality of all worlds is always certain, it just so happens that you don’t know ex-ante which of those worlds you will be in, which means reality from the perspective of a single observer appears random. For a more recent non-probabilistic interpretation that does not rely on multiple worlds see the work by Chiara Marletto on the Constructor Theory of Probability.
So the answer is: we don’t know. Reality may have inherent uncertainty and it may not. I would add that we should be open to the possibility that settling this question one way or another may actually be impossible. There is nothing that assures us that the question “does reality have inherent uncertainty?” is in fact answerable (which is also related to the simulation hypothesis).
For the purposes of Uncertainty Wednesday I will treat reality has having no inherent uncertainty. All uncertainty then arises from limitations on observations and explanations.
PS An important aside: the existence of uncertainty as an emergent property on top of a reality without inherent uncertainty, is enough to allow for the existence of free will (again as an emergent property of a collection of humans, not instantaneously for any individual).
