Quantum information and the Foundations of Physics: Gravity, Entanglement, and the Road to Quantum Gravity

Overview

A Royal Institution talk presents a information-centered view of physics, arguing that quantum information, not classical probabilities, is the core of physical theory. The speaker explains how quantum waves and complementarity drive the peculiar behaviour of quantum systems and outlines how this view points toward a quantum description of gravity and the next theory of physics.

Key themes

The talk surveys historical ideas from Bohr to Heisenberg and Mott, discusses interpretations such as many-worlds, and describes frontier experiments that probe whether gravity can be quantum. It also touches on testing quantum mechanics with living systems and the philosophical implications of a quantum information based reality.

Foundations through Information

The speaker argues that physics should be understood as information processing, with Shannon information setting the quantitative backbone. Probability is a reflection of missing information in classical physics, but quantum mechanics makes probability intrinsic, enabling quantum information to act as a new kind of medium. The talk emphasizes complementarity, where different quantum information media (for example position and momentum) cannot simultaneously define a single classical information state.

He traces the historical development from Schrödinger's wave equation to Heisenberg's matrix (quantum-number) view, explaining how classical trajectories emerge from quantum processes when the surrounding environment localizes particles through interactions, as in cloud chambers described by Mott. This leads to the central claim that quantum mechanics does not require a collapse or a special observer, and that locality can be preserved when information is treated in quantum terms.

Looking forward, the talk turns to gravity as a potential quantum information channel. A proposed experiment uses macroscopic masses in quantum superpositions to test whether gravity couples to all positions simultaneously and whether gravity itself is quantum. If two nanospheres can be entangled through gravitational interaction, it would indicate gravity is quantum mechanical; if not, it would challenge prevailing assumptions about quantum gravity.

Beyond gravity, the speaker discusses exploring quantum superpositions in living systems, including bacteria and tardigrades, to address whether consciousness or life itself imposes a unique boundary on quantum behaviour. The overarching theme: experimental progress in quantum technologies is opening a frontier that could revise our understanding of space, time, and reality itself.