Sean Carroll's Mindscape: Science, Society, Philosophy, Culture, Arts, and Ideas
300 | Solo: Does Time Exist?
Mon, 06 Jan 2025
A new year, and a new centennial -- 300 (regularly-numbered) episodes of Mindscape! Our tradition is to have a solo episode, and what better topic than the nature of time? Physicists and philosophers have so frequently suggested that time is some kind of illusion that it's become almost passé to believe that it might be fundamental. This is an issue where, despite the form of the question, physics has important things to say that most philosophers haven't yet caught up to. I will talk about ideas from quantum mechanics and quantum gravity that bear on the question of whether time is emergent or fundamental, and the implications of each possibility.Support Mindscape on Patreon.Blog post with transcript: https://www.preposterousuniverse.com/podcast/2025/01/06/300-solo-does-time-exist/Some of the papers discussed herein:Carroll (2008), "What If Time Really Exists?"Dyson, Kleban, and Susskind (2002), "Disturbing Implications of a Cosmological Constant."Albrecht and Sorbo (2004), "Can the Universe Afford Inflation?"Boddy, Carroll, and Pollack (2014), "De Sitter Space Without Dynamical Quantum Fluctuations."Lloyd (2016), "Decoherent Histories Approach to the Cosmological Measure Problem."Page and Wootters (1983), "Evolution Without Evolution: Dynamics Described by Stationary Observables."Albrecht (1994), "The Theory of Everything vs the Theory of Anything."Albrecht and Iglesias (2007), "The Clock Ambiguity and the Emergence of Physical Laws."See Privacy Policy at https://art19.com/privacy and California Privacy Notice at https://art19.com/privacy#do-not-sell-my-info.
Full Episode
Hello, everyone. Welcome to the Mindscape Podcast. I'm your host, Sean Carroll. Welcome to a new year by the conventional calendar, of course, 2025, but also this first podcast episode of 2025 is episode 300. And looking back on previous episodes that ended with 00, that is to say 100 and 200, I did some solo episode of some sort to celebrate the little milestone.
I mean, it's a pretty big milestone. We have a lot more than 300 episodes because many episodes don't get numbers. The AMAs don't get numbers. Holiday messages don't get numbers, special episodes, et cetera. But still, having 300 even numbered episodes is pretty darn good. We've been doing it for a while, longer than I might have guessed at the very beginning.
So what to do for a solo episode to start things out? I mean, in some sense, I've already been talking too much. I did the Hits and Misses holiday message, which went on for a long while. I did a previous solo episode about emergence not too long ago. But OK, there's a tradition. And when there's a tradition, we might as well stick to it.
But I do worry about doing too many solo episodes because I'm not an expert in that many things. I don't want to do a solo episode just on me ranting about things. I think it's OK to admit that one is not an expert on everything or even one doesn't have interesting things to say about every issue out there.
Sometimes it's better just to listen to other people, which is why we have the format of Mindscape as we have it. But I do have some things that I know something about. So I couldn't decide. So what I did is I went on to Patreon, where we have our wonderful Patreon supporters for Mindscape. You yourself could be a Patreon supporter if you just go to patreon.com slash Sean M. Carroll.
And, of course, Patreon supporters get ad-free versions of the podcast. They get to ask questions for the AMAs and occasional other benefits, like I asked them what solo episode should I do. And I did have some ideas, and I took suggestions also. And the idea that I had that eventually won out by the vote, and I think it's a perfectly good one, is, is time real?
Now, just to not keep you in suspense, yes, the answer is yes, time is real. But there are people in modern physics and philosophy who question whether time is real. In fact, I once wrote a paper almost as a joke, but I mean, the title was a joke. The paper was not a joke, I don't like to think, but the title was, What If Time Really Exists?
because it has become so common in physics to not only say, well, maybe time is not fundamental, maybe time isn't even real, maybe it's an illusion, but to also pat yourself on the back for thinking this is a profound thought, even though many, many other people have already had this thought also. I don't think time is an illusion. I think it is absolutely real. It might not be fundamental.
As we've often stressed on the podcast, one should think of things that are emergent as nevertheless real. You know, the table in front of me is real, even though there are no tables in the standard model of particle physics. The idea of a table is an approximate higher level description that has a lot of causal and explanatory power. Maybe time is like that.
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