316 | Niayesh Afshordi and Phil Halper
Sean Carroll's Mindscape: Science, Society, Philosophy, Culture, Arts, and Ideas
Sean Carroll | Wondery
4.8 • 4.4K Ratings
🗓️ 26 May 2025
⏱️ 89 minutes
🧾️ Download transcript
Summary
Einstein's general theory of relativity, plus some reasonable assumptions about the universe and what it's made of, has a remarkable implication: that as we trace cosmic evolution into the far past, we ultimately hit a singularity of infinite density and curvature, the Big Bang. Did that really happen? Einstein's theory is classical, after all, and the world is quantum. And whose to say what assumptions are reasonable? Niayesh Afshordi and Phil Halper have written a new book, Battle of the Big Bang: The New Tales of Our Cosmic Origins, that surveys all of the mind-bending possibilities.
Blog post with transcript: https://www.preposterousuniverse.com/podcast/2025/05/26/316-niayesh-afshordi-and-phil-halper-on-the-big-bang-and-before/
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Niayesh Afshordi received a Ph.D. in astrophysics from Princeton University. He is currently a professor of physics and astronomy at the University of Waterloo, and associate faculty in the cosmology and gravitation group at the Perimeter Institute for Theoretical Physics.
Phil Halper is a science communicator and a fellow of the Royal Astronomical Society. His astronomy images have been featured in major media outlets including The Washington Post, the BBC, and The Guardian, and he has published several papers in peer-reviewed journals.
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Transcript
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| 0:00.0 | Hello, everyone, welcome to the Mindscape Podcast. I'm your host, Sean Carroll. One of the downsides, |
| 0:05.1 | there aren't that many, but one of the downsides of being a cosmologist is that sometimes when |
| 0:11.6 | your fellow cosmologists try to explain the important ideas of your field to the rest of the world, |
| 0:17.3 | they cut corners now and then, or they take shortcuts, use different jargon words |
| 0:23.3 | in specific ways, and not everything always becomes clear. A classic example of this is the |
| 0:29.1 | phrase, the Big Bang. As I've said various times on Ask Me Anything and elsewhere in the podcast, |
| 0:36.2 | the Big Bang phrase means different things to different |
| 0:39.2 | people. To some people, it means the event, the moment in time when the universe was singular |
| 0:45.6 | at the beginning, T equal zero, time equals zero, as predicted by classical general relativity. |
| 0:52.2 | To other people, since classical general relativity is not correct, |
| 0:56.0 | and that Big Bang singularity is just a breakdown of our understanding, they use the phrase |
| 1:01.4 | big bang to mean the hot, dense, rapidly expanding super early phase that the universe was in. |
| 1:09.4 | People who believe in inflationary cosmology will sometimes use |
| 1:12.7 | the phrase Big Bang to mean whatever happened before inflation. Other people who believe in |
| 1:17.9 | inflationary cosmology will use the phrase Big Bang to mean what happened right after |
| 1:22.4 | inflation when the universe reheats into matter and energy. Many people will use the Big Bang to be the whole model of the universe reheats into matter and energy. |
| 1:33.9 | Many people will use the Big Bang to be the whole model of the universe, the whole last 14 billion years, plus whatever happens in the future. That's the Big Bang model. All of these are perfectly |
| 1:39.8 | valid concepts, but they really do deserve different names. One of the simplifications that really |
| 1:45.1 | gets in the way is the idea that because in classical general relativity, the Big Bang is a singularity |
| 1:52.0 | and therefore a boundary to space time, that there can't be anything before the Big Bang. But as we |
| 1:58.8 | said, the Big Bang story in general relativity can't be complete because |
| 2:03.2 | general relativity itself is not complete. It does not include quantum mechanics. So the only |
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