The physicist Antony Valentini recently argued in IAI News that quantum mechanics is a straightforward—though incomplete—description of material reality. Today, philosopher and former Director of Research at the renowned French National Center for Scientific Research, Michel Bitbol, makes the opposing case. Scientists, he argues, mistakenly assume that quantum mechanics must either be an incomplete description of a deterministic reality or a complete description of a genuinely random reality. A third option, too often ignored, is that quantum mechanics is not a description of external reality at all, but a tool for predicting our “creation” of our own experiences and ideas of reality. The randomness in quantum theory is a measure of the freedom we have in so creating our world.

So many stunning technological achievements stem from quantum physics that it is difficult to believe it rests on a set of negative features. Here are three of them:

Unpredictability: Individual events at the microscopic scale are generally unpredictable, except to the limited extent permitted by probabilistic estimates.

Indeterminacy: Certain pairs of properties of a particle, such as its position and momentum, cannot be known simultaneously with arbitrary precision (“Heisenberg’s ‘uncertainty’ relations” or “Heisenberg’s indeterminacy principle”).

Informational boundedness: According to an axiom proposed as a basis for deriving the formalism of quantum mechanics, “there is a maximum amount of relevant information that can be extracted from a physical system.”

To the satisfaction of physicists, these negative features do not hinder the theory’s predictive power and explanatory capacity; they are precisely what enable its extraordinary quantitative successes. One of its most remarkable accomplishments is the prediction of a nonzero minimum energy, which follows from Heisenberg’s indeterminacy. This implies, among other things, that even the vacuum exerts measurable pressure on closely spaced conducting plates, a phenomenon known as the Casimir effect.

But philosophers, and many of the physicists of the time who were philosophers at heart, sought to look beyond the theory’s practical successes and understand the meaning of its negative features. Accordingly, in the formative period of quantum theory a century ago, the debate among its pioneers focused largely on the origin of the “indeterminism” that appeared to permeate it.

The options seemed simple and aligned with the ordinary dualistic theory of knowledge: the source of indeterminacy was sought in either the subject or the object, the human observer or the observed world, finite knowledge or an inexhaustible reality. Accordingly, when the chance occurrence of individual events was at issue during the famous Solvay Conference in Brussels, which brought together the creators of quantum mechanics in October 1927, some invoked a “choice of the observer,” whereas others spoke of a “choice of nature.” The dilemma was also reflected in the three words Heisenberg hesitantly used to characterize his relations: do they express merely our uncertainty (Unsicherheit) or imprecision (Ungenauigkeit) about a reality that is otherwise determined? Or do they reveal a genuine indeterminacy (Unbestimmtheit) of nature?