366 | Jim Al-Khalili on Time, Quantum, Biology, and Cosmology

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**Sean Carroll** (1:00)
Hello everyone and welcome to the Mindscape Podcast. I'm your host, Sean Carroll.
A long time ago, 15 or more years ago now, when I was writing my first trade book, From Eternity to Here, we were talking about the title. We liked the actual title, right? From Eternity to Here. I think that either Jennifer came up with it or we brainstormed it together. I forget, but that seemed to both be fun and also fit what was actually in the book. Then of course, you need a subtitle because you're cute with the title, right? And when you're cute with the title, you need the subtitle to actually explain what the book is actually about. So I was talking about that with my publisher, Stephen Morrow, and eventually he mentioned that the word quest was very popular in publishing circles at that moment in time. Publishing goes through all these various fads and phases, and at the moment, they thought that books that were about quests were really selling well. So the subtitle ended up The Quest for the Ultimate Theory of Time, which is a perfectly decent subtitle. And especially decent, especially appropriate, because the quest is not over yet, right? I was not proposing in that book to answer all the questions that one might have about the nature of time. I discussed the questions, and we talked about various possibilities, but clearly with an eye to saying there's a lot left to be done, which I bring up now because today's guest, Jim Al-Khalili, has a new book out called On Time, and his subtitle is The Physics That Makes the Universe Tick. So it's a very similar theme to what I wrote, and it was more than 15 years ago now, in From Eternity to Here, but there has been progress since then. And of course, even absent any progress, two physicists thinking about the same general area, especially one as big as this, are going to have their own angles on it. So Jim is a very accomplished both physicist and communicator. His topic is something that I've talked about already on this podcast. You've heard me talk about it. I wrote books about it, etc. So this is an excuse or an opportunity if you want for me to play dumb, to pretend I don't have strong opinions about the nature of time and how it works, to get a different perspective because I'm a huge believer that no one person is ever going to be able to state or explain things in the perfect way for every member of the audience. Hearing it in different ways is interesting. And also, I have a lot of questions that I don't know the answer to that I think are really interesting research level problems. I'm trying to think about them, make progress on them. It's always fun and useful to talk to another physicist who's thinking about the same problems. So let's go.
Jim Al-Khalili, welcome to the Mindscape Podcast.

**Jim Al-Khalili** (4:00)
Hi, Sean. Pleasure to be here.

**Sean Carroll** (4:02)
We're talking about a topic dear to my heart as well as to yours. So I'm not going to be reluctant to load you with all the tough questions. So let's start with, what is time?

**Jim Al-Khalili** (4:15)
Okay.
It's a tough question because it's one that we've been thinking, we, humanity has been thinking about for millennia. Going all the way back to the ancient Greeks, there were big philosophical debates about whether time was real, whether it's an illusion, whether it flows. And the more we've understood about the workings of nature, I guess, just the more complicated the answer becomes about the nature of time, not just is it real? Is it all an illusion? Is it just in our heads? But also within physics, what do we mean by time and how it enters different areas of physics in different ways? So in a sense, we know a lot more about time than certainly I would like to think more about the nature of time than the ancient Greeks, but we may not be that much closer to answering the ultimate question.