What is time?

This episode of The Naked Scientist podcast explores the multifaceted nature of time, from its historical development to its biological and psychological dimensions. Host Chris Smith begins with a journey through the origins of standardized time, highlighting how Greenwich Mean Time became the global reference point after the 1884 International Meridian Conference. The discussion reveals how the rise of railways necessitated a unified time system, leading to the adoption of 'railway time' and eventually legal standardization in Britain. The episode then delves into the invention of daylight saving time by William Willett, its wartime adoption, and the ongoing debate over its benefits. On the psychological front, Ruth Ogden from Liverpool John Moores University explains how our perception of time is shaped by attention, memory, arousal, and emotional state—why waiting feels slow while enjoyable moments fly by. She also examines why time seems to accelerate with age, attributing it not just to the mathematical relativity of years, but to the increasing time pressure and lack of free time in adulthood. The biological aspect is explored through Eva Winnebeck of the University of Surrey, who details how every cell in our body contains a circadian clock synchronized by the brain's suprachiasmatic nucleus. These clocks regulate sleep, metabolism, and hormone levels, and their desynchronization during jet lag or shift work can lead to physical discomfort. Finally, the episode turns to the future of timekeeping, with Setnam Shema from the UK's National Physical Laboratory explaining how atomic clocks based on cesium atoms have redefined the second and enabled modern technologies like GPS and financial trading. However, the growing incompatibility between atomic time and Earth’s irregular rotation has led to proposals to abolish leap seconds, potentially severing the link between time and the sun’s position. The episode concludes with a reflection on how deeply time shapes our lives—scientifically, biologically, and subjectively.