In quantum mechanics the state of a physical system is described by a wavefunction, which provides information about the probabilities of various outcomes, such as finding a particle at a particular location in space. This differs dramatically from classical physics, where a particle is described by a definite position and momentum. As a result, quantum mechanics inherently involves a certain level of uncertainty. A key question is whether this uncertainty reflects a fundamental indeterminacy in reality itself or merely our limited knowledge of the physical system.

One possibility is that reality could be deterministic, and the wavefunction might simply describe statistical properties, much like temperature and pressure describe the collective behavior of gas molecules. In this view, the true state of the system would be governed by hidden variables—deterministic factors that remain unseen yet produce the probabilistic outcomes we observe in quantum experiments. The standard view, however, is that the universe itself is inherently probabilistic. Furthermore, Bell’s theorem famously rules out “local hidden variable” models, suggesting to many that any such model must allow instantaneous causal influences between spatially separated objects. But is this standard picture as definitive as it seems?

In this episode of the podcast, I speak with Rob Spekkens, one of the world’s leading experts on the foundations of quantum mechanics. His research explores the idea that a quantum state may represent a state of incomplete knowledge rather than an objective state of reality. Many of the phenomena commonly associated with quantum mechanics—noncommutativity, interference, entanglement, wave-particle duality, and discrete energy levels—can, as Rob demonstrates, be modeled with classical toy models wherein each system has a determinate physical state but where we have incomplete knowledge of this state.. Rob suggests that quantum mechanics may not be as fundamentally different from classical physics as it initially appears. If we truly want to understand quantum reality, we should focus on isolating and investigating the "thin film" of phenomena that distinguish a quantum from a classical world. That's what we discuss in this episode.

►Watch on YouTube:
https://youtu.be/J2ZIRkfrFlI

►Find out more about Rob's work:
https://perimeterinstitute.ca/people/robert-spekkens

►Follow Rob on Twitter:
@RobertSpekkens

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These conversations are supported by the Andrea von Braun foundation (http://www.avbstiftung.de/), as an exploration of the rich, exciting, connected, scientifically literate, and (most importantly) sustainable future of humanity. The Andrea von Braun Foundation has provided me with full creative freedom with their support. As such, the views expressed in these episodes are my own and those of my guests.

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