AI Summary
5 min readWhy understanding how time works is the biggest mystery in science
"Time is just a number you plug into the equation to tell you what the real thing the system you're trying to study is actually doing," says physicist Jim Al-Khalili. But that simple picture unravels fast. In his book On Time: The Physics That Makes the Universe Tick, Al-Khalili argues that time is not one thing but several contradictory things depending on which branch of physics you consult—and that resolving these contradictions may be the deepest challenge facing modern science.
The ancient divide that still haunts physics
The tension between time-as-real and time-as-illusion goes back to ancient Greece. Heraclitus saw time as a river, real and flowing, carrying us along. Parmenides and his student Zeno argued time was an illusion—Zeno's famous paradoxes were designed to show that motion and change couldn't be real. "That struggle between is time a real thing, is it an illusion, is there something there with time being something real that flows—even today there's a whole discipline called the philosophy of time where people are still trying to understand it," Al-Khalili notes.
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What you'll learn
- 1 (03:05) **Introducing Professor Jim Al-Khalili and the puzzle of time** - The host welcomes the physicist and author to discuss his book *On Time: The Physics That Makes the Universe Tick*.
- 2 (05:58) **The Ancient Greek roots of the time debate: Heraclitus vs. Parmenides** - The discussion traces the fundamental philosophical schism about time's reality back 2,500 years.
- 3 (08:00) **Time as a mere parameter in physics equations** - Al-Khalili explains how time is usually treated as a simple variable in most of physics.
- 4 (09:33) **Einstein's revolution: time as a dimension and the relativity of simultaneity** - Special relativity fundamentally changed the picture of time from Newton's absolute clock to a fourth dimension of spacetime.
- 5 (10:36) **The thermodynamic arrow of time and entropy** - Physics introduces a second, contradictory picture of time: an irreversible arrow pointing from past to future.
- 6 (13:02) **General relativity: how gravity warps time** - Einstein's theory of gravity reveals that time is not just a dimension but a malleable part of the fabric of reality.
- 7 (16:35) **The GPS proof: relativity is a practical necessity** - The most concrete example of time dilation is the global positioning system in your phone.
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Show Notes
When most of us think about time our minds likely turn to thoughts of the second hand that ticks around a clock, or maybe the occasions we’ve been late to catch a bus. But if we stop to think about what time actually is things quickly get more subtle and complicated. Does time only exist in our minds as a psychological illusion, does it really only run forwards and not backwards, and how close is modern physics to helping us to figure out its true nature?
In this episode we’re joined by physicist, best-selling author and BBC presenter Prof Jim Al-Khalili to talk about his latest book, On Time – The Physics That Makes the Universe Tick.
He tells us how thinkers going back as far as ancient Greece have struggled to define what time really is and how it works, how Einstein’s theories tell us that time can run at different rates in different circumstances, and how understanding its true nature maybe key in our search for a theory of everything.
Take your curiosity further with a subscription to BBC Science Focus magazine. Every issue is packed with fascinating insights into the science behind everyday life, the latest breakthroughs and expert analysis, delivered straight to your door. Receive an extra £5 when you subscribe using the code SF5OFF, (minimum spend £20, see full terms and conditions on our website).
https://www.ourmediashop.com/bbc-science-focus-magazine-pod30
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