366 | Jim Al-Khalili on Time, Quantum, Biology, and Cosmology
August 31, 2026
AI Summary
5 min readIn 2010, when Sean Carroll published From Eternity to Here, the subtitle landed on "the quest for the ultimate theory of time"—a nod to a publishing trend for "quest" books. Carroll notes that the quest is not over, which is why physicist and science communicator Jim Al-Khalili’s new book On Time can cover similar ground while offering a genuinely different perspective. Al-Khalili does not shy away from the deepest puzzles: whether time is real, why it has a direction, and how quantum mechanics and biology complicate the picture. But he also brings a distinctive stance—one that treats irreversibility as more fundamental than the time-symmetric equations physicists usually start with.
Time as Real, Directed, and Tangible
Continue reading the full summary in the app — free to try.
Read Full Summary →Free • No credit card required
Never miss an episode of Sean Carroll's Mindscape: Science, Society, Philosophy, Culture, Arts, and Ideas
Get every new episode summarized in your inbox — free, ~5 minutes to read.
No spam. Unsubscribe anytime.
What you'll learn
- 1 (04:44) **What Is Time?** - Jim defines time as a real, tangible part of 4D spacetime with a baked-in direction, and distinguishes physical time from psychological time.
- 2 (08:01) **Time Exists vs. Time as a Tool** - Jim affirms time is real, not just a human tool, and explains his late-career shift to foundational questions.
- 3 (15:27) **Presentism vs. Eternalism** - Jim leans toward eternalism (all times exist equally) due to his training in relativity.
- 4 (18:52) **The Arrow of Time: The Conventional Story** - Jim outlines the traditional view that fundamental laws are time-symmetric, while the Second Law of Thermodynamics gives time a direction.
- 5 (21:51) **Jim's Alternative: Irreversibility as Fundamental** - Jim argues that irreversibility is more fundamental than time-symmetric laws, because no system is truly isolated.
- 6 (30:37) **The Past Hypothesis** - Jim explains the conventional past hypothesis: the universe started in a very low-entropy state at the Big Bang, which explains why entropy increases.
- 7 (36:37) **From Low Entropy to Human Experience** - Jim discusses the gap between the Big Bang's low entropy and our perception of time's flow.
+ Full timestamped outline available in the app
Guests on this episode
Show Notes
Everyone lives through time, but we continue to struggle to fully understand it. We remain unsure whether time is fundamental or emergent, why it has an arrow pointing from past to future, and how that arrow connects to our experience of time's passage. Jim Al-Khalili's new book is On Time: The Physics that Makes the Universe Tick. We discuss what time is at the most basic level, and how it connects to open questions in biology, cosmology, and quantum mechanics.
Mindscape listeners can try StatsKey Pro free for one month with code MINDSCAPE. After that, it's $4.99 per month unless canceled. #ad
Support Mindscape on Patreon.
Jim Al-Khalili received his Ph.D. in physics from the University of Surrey. He is currently Distinguished Emeritus Professor of Physics at Surrey. He is a Fellow of the Royal Society, and has served as past president of the British Science Association. He has been awarded the Michael Faraday Prize by the Royal Society, and has been appointed an appointed Officer of the Order of the British Empire.
More from this podcast
Sean Carroll's Mindscape: Science, Society, Philosophy, Culture, Arts, and Ideas →