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.