Quantum theory appears to allow some kind of connection between entangled particles, but not enough to send messages. Antony Valentini argues this is a conspiracy: there must be something deeper than quantum, where nonlocality can actually be used to send messages, but it is hidden from view in standard quantum experiments. In this episode of the Quantum Foundations Podcast, Valentini uses Pilot-wave theory to explain the physics of the nonlocal subquantum world. He discusses various ways that the theory could be experimentally tested, by looking for signatures of violations of the Born rule in extreme environments, such as the early universe. He also discusses the radical technological implications of subquantum physics, if we were able to harness it.

Valentini recently released a book for a general audience explaining these ideas, "Beyond the Quantum: A Quest for the Origin and Hidden Meaning of Quantum Mechanics".

What if quantum particles have no gravity? In this episode of the Quantum Foundations Podcast, Professor Gerard Milburn explains how this radical idea could solve open problems in quantum theory and lead towards a theory of quantum gravity. It comes with extreme consequences for quantum measurements; the formation of black holes; and even the beginning of the universe. From a new understanding of Bell experiments to a cosmological arrow of time, find out if dropping gravity from the equation could be the start of transforming the field of quantum science and technology.

If there really is a quantum reality for every possible outcome of a measurement, then where do measurement probabilities come from? Dr Tony Short at the University of Bristol has used a set of intuitive assumptions to derive probability in a quantum multiverse. In this episode we discuss his motivations for exploring the many-worlds interpretation; what his assumptions are and how they lead to the Born rule for measurement probabilities; and how these ideas fit within the broader landscape of research in quantum foundations, probability and the many-worlds interpretation. 

The notion of true quantum nonlocality is absurd. Prof Tim Palmer from the University of Oxford suggests that there is a hidden assumption in standard quantum mechanics, and dropping it will save us from this absurdity. Namely, the reality of counterfactuals: the physics of what could have happened but did not. Inspired by chaos theory and the fractal structure widespread in atmospheric physics, Palmer has developed a new underlying structure for quantum theory, with radical implications for our fundamental principles of quantum physics; the limits of quantum computation; and perhaps even the search for quantum gravity.

What if you could put an observer in superposition on a quantum computer? Dr Will Zeng suggests that this experiment could stretch standard quantum theory so far that it might break — and radically update our understanding of physical reality. However, today's proof-of-principle experiments on quantum computers use single qubits to model observers. Zeng explains how a new programme of research aims to quantify "observer-ness" and conduct experiments with increasingly realistic observers, pushing quantum computers to the limits until they can run actual quantum Artificial General Intelligence experiments.

Our most far-reaching principles of physics are not about what changes, but what stays the same: conservation laws. In this episode of the Quantum Foundations Podcast, Dr Chiara Marletto from the University of Oxford explains how such principles enable discovery of new physical phenomena; their central role in thermodynamics; controversies about how they hold up in quantum mechanics; and how they can be used to formulate results about future theories of physics beyond quantum.

You’ve heard of cryptography. Perhaps quantum cryptography too. Maybe even post-quantum cryptography. But what about *quantum post-quantum cryptography*?! When this came up in conversation with Oxford Computer Scientist Matthew Gray recently, I’d never heard of it. I wanted to know more, so I invited him for a podcast. Turns out, there’s a whole world of layers to unravel linking quantum and cryptography — or even multiple worlds… In this discussion, we dip into those, and how this all relates to “metacomplexity” problems: the hardness of figuring out the hardness of a problem. Listen to this episode if you want to experience your perception of how quantum computing meets cryptography shift from monochrome to technicolour, as we push cryptography to its limits through the lens of fundamental assumptions about computation, quantum physics and reality.

What if time isn’t fundamental — but emerges from quantum mechanics itself? In this episode, Dr Simone Rijavec explains how a timeless quantum universe can still give rise to the illusion of time flowing. We unpack the Wheeler–DeWitt equation, the Page–Wootters model of relational time, and how these ideas connect to the multiverse and quantum gravity. Dr Rijavec is a postdoctoral researcher at Tel Aviv University and former PhD researcher at the University of Oxford.

From the Big Bang puzzles to testing if the early universe was quantum entangled — physicist Dr Aditya Iyer, from the University of Oxford, explains how quantum phenomena are key to understanding cosmology, gravity and even how it's possible we exist at all.

What if we don't need quantum mechanics to express the key properties of quantum information? Join me for a deep-dive into the Constructor Theory of information with Dr Chiara Marletto, Research Fellow at the University of Oxford.

Constructor Theory is a research programme proposed by Prof. David Deutsch in 2012, and further developed by Deutsch and Marletto, and collaborators, since then. The theory aims to unify various strands of physics, and solve open problems — and the key motivation and starting point is a new conception of the laws of physics surrounding information.

In this podcast, we discuss what constructor theory is; how it expresses laws about classical and quantum information; applications to e.g. tests of quantum gravity and quantum field theory; the role of locality and subsystems in the testability of physics; and taking fundamental physics back to the roots of the early days of quantum information theory.