A non-probabilistic quantum theory produces unpredictable results

Lisa Zyga in Phys.org:

Quantum measurements are often inherently unpredictable, yet the usual way in which quantum theory accounts for unpredictability has long been viewed as somewhat unsatisfactory. In a new study, University of Oxford physicist Chiara Marletto has developed an alternative way to account for the unpredictability observed in quantum measurements by using the recently proposed theory of superinformation—a theory that is inherently non-probabilistic. The new perspective may lead to new possibilities in the search for a successor to quantum theory.

The unpredictability observed in quantum experiments is one of the unique features of the quantum world that sets it apart from classical physics. One prominent example of quantum unpredictability is the double-slit experiment: When sending a stream of particles (such as photons or electrons) through two small slits in a plate, the individual particles are detected at different locations on a screen behind the plate. Although it's possible to predict the probability of a particle impacting at a certain location, it's not possible to predict specifically where any individual particle will end up.

Traditionally, this apparent probabilistic behavior that is observed in experiments has been accounted for in quantum theory by using the Born rule. In 1926, the German physicist Max Born developed this rule to determine the probability of finding a quantum object at a certain location—or more generally, the probability that any measurement on a quantum system will produce a particular observed outcome, depending on the quantum state of the object.

The Born rule is a unique part of quantum theory in that it is the only stochastic, or randomly determined, element in quantum theory. The Born rule has basically been added by fiat on top of a theory that is otherwise deterministic.

More here. [Thanks to Farrukh Azfar.]