Rethinking Time in Physics: Entropy, Clocks, and the Arrow of Time

The video challenges the idea of a single universal time, arguing that time is the collective behaviour of many clocks and is defined by entropy growth. It explains that in general relativity there is no unique time variable and that clocks measure differences in gravitational fields between events. In quantum mechanics, time can be treated as a derived concept rather than a fundamental variable. The only true arrow of time emerges from thermodynamics and the second law, while our human experience of time is linked to memory, heat, and perception. The talk emphasizes the multiplicity of times in the universe and invites a broader, more complex view of time beyond an ever-ticking clock.

Rethinking Time in Physics

Time is not a single, universal variable but a tapestry woven from many clocks and their interactions. The speaker argues that fundamental equations of physics are largely time symmetric, yet our experience of time flows in one direction because of entropy growth. In this framework, what we call time is a bookkeeping label attached to sequences of events and changes across the universe, not a pre existing external clock.

Relativity and Clocks

In general relativity, there is no unique time coordinate that applies everywhere. Different clocks tick at different rates depending on their position in the gravitational field and their motion. The essential idea is that the clock is measuring a physical quantity tied to the gravitational field between events, rather than a universal time flow. The Schrödinger equation can be formulated without designating a separate time parameter, focusing instead on the relational aspects of clocks and measurements.

Quantum Mechanics and Time

The quantum description can be coherent with multiple time notions. Rather than introducing a preferred time variable, quantum gravity formulations often eliminate time as an independent variable and rely on clocks and correlations between physical quantities to describe evolution.

Entropy and the Arrow of Time

The direction of time at the macroscopic level emerges from thermodynamics. The second law is statistical, arising from the tendency of systems to move toward higher entropy states. Time oriented phenomena such as heat and temperature are naturally tied to entropy and energy flows, which gives us a perceived time direction even though the underlying laws are time reversible in many cases.

Perception, Memory, and Humanity

Our sense of time flowing is intimately connected to memory, anticipation, and energy consumption. The lecture uses intuitive examples, such as a breaking glass or a hot cup of water, to illustrate how entropy underpins time oriented experiences. It also points out that we are themselves time oriented beings, like candles burning energy and generating heat.

Conclusion: Embracing Multiplicity

The talk culminates in the idea that there is no single cosmic clock, but a multiplicity of times that coexist. Recognizing this multiplicity helps us understand physics more deeply and navigate the complexity of scientific description and human experience. Time is not an external flow but a property of the evolving universe shaped by entropy and the relational dynamics of clocks.