What is time, really?

Quick Overview

The video concludes that time is likely an emergent phenomenon, not a fundamental component of the universe, arguing against the notion of absolute time and suggesting that causality might precede the conventional concept of time, exploring theories like Causal Sets and Julian Barbour's Shape Dynamics.

Key Points: Time is not necessarily fundamental; it might emerge from something else, contrasting with the view that time is a fundamental ingredient of the universe. The video explores two main approaches to time: (a) No Time is Special (all moments are equally real), and (b) Construct Physical "Now". Causality First approaches, such as Causal Sets, Hypergraphs, and Causal Fermion Systems, propose that the ordering of events (causality) is fundamental, not time itself. Julian Barbour's Shape Dynamics suggests that what is real is the relationships between particles, not the passage of time, viewing time as an illusion. The concept of "Now" is questioned, as physicists struggle to define it physically, evidenced by the time variable being unobservable in the Schrödinger equation (H|Psi> = i downbar ext{d}t| ext{Psi} angle). The discussion highlights that our subjective experience of time flowing (past remembered, future unknown) does not align with fundamental physics where all moments might exist simultaneously. The video promotes Brilliant.org courses as an effective way to build knowledge, offering subscribers 20% off the annual premium subscription via the link brilliant.org/Sabine.

Context: This video explores the philosophical and physical nature of time, questioning whether time is a fundamental dimension of reality (like space) or if it emerges from underlying structures. It contrasts the standard view of time as a coordinate, as described by Einstein's theories, with alternative theories that prioritize causality or static configurations of reality, referencing key thinkers like Julian Barbour and George Ellis.

Detailed Analysis

The video tackles the profound question, "What is time?", identifying three main interpretations: time as a dimension that separates past from future, time as a coordinate akin to space in Einstein's theories, and time as something we subjectively experience, which may not be physically fundamental. The discussion introduces Einstein's view where time is a coordinate linked to space (spacetime), where changing coordinates does not change the underlying reality, unlike our perception of time flowing. It then pivots to theories suggesting time is emergent, such as Causal Sets, Hypergraphs, and Causal Fermion Systems, which prioritize causality as fundamental. Julian Barbour's 'The End of Time' is cited, proposing that reality consists only of 'shape dynamics'—relationships between particles—and that time is an illusion. The video further investigates the concept of 'Now,' noting that in quantum mechanics (via the Schrödinger equation), the time variable ($t$) is not an observable quantity. It presents two ways to resolve this conundrum: (a) No Time is Special (all moments are equally real, challenging our perception), or (b) Postulating a physical 'Now,' a concept George Ellis suggests is difficult without a fundamental structure for time. The speaker personally favors the causality-first interpretation. Finally, the video concludes by recommending Brilliant.org courses for building intuition in mathematics and science.