Einstein’s description of curved space-time doesn’t easily mesh with a universe made up of quantum wavefunctions. Theoretical physicist Sean Carroll discusses the quest for quantum gravity with host Steven Strogatz.
General relativity and quantum mechanics are the two most successful conceptual breakthroughs of modern physics, but Einstein’s description of gravity as a curvature in space-time doesn’t easily mesh with a universe made up of quantum wavefunctions. Recent work that tries to bring those theories together is revealing some mind-bending truths. In this episode, the physicist and author Sean Carroll talks with host Steven Strogatz about how space and time might be emergent properties of quantum reality, not fundamental parts of it..
Listen on Apple Podcasts, Spotify, Google Podcasts, Stitcher, TuneIn or your favorite podcasting app, or you can stream it from Quanta.
Transcript
Steven Strogatz (00:03): I’m Steve Strogatz, and this is The Joy of Why, a podcast from Quanta Magazine that takes you into some of the biggest unanswered questions in science and math today. In this episode, we’re going to be discussing the mysteries of space and time, and gravity, too. What’s so mysterious about them?
Well, it turns out they get really weird when we look at them at their deepest levels, at a super subatomic scale, where the quantum nature of gravity starts to kick in and become crucial. Of course, none of us have any direct experience with space and time and gravity at this unbelievably small scale. Up here, at the scale of everyday life, space and time seem perfectly smooth and continuous. And gravity is very well described by Isaac Newton’s classic theory, a theory that’s been around for over 300 years now.
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(00:53) But then, about 100 years ago, things started to get strange. Albert Einstein taught us that space and time could warp and bend like a piece of fabric. This warping of the space-time continuum is what we experience as gravity. But Einstein’s theory is mainly concerned with the largest scales of nature, the scale of stars, galaxies and the whole universe. It doesn’t really have much to say about space and time at the very smallest scales.
And that’s where the trouble really starts. Down there, nature is governed by quantum mechanics. This amazingly powerful theory has been shown to account for all the forces of nature, except gravity. When physicists try to apply quantum theory to gravity, they find that space and time become almost unrecognizable. They seem to start fluctuating wildly. It’s almost like space and time fall apart. Their smoothness breaks down completely, and that’s totally incompatible with the picture in Einstein’s theory.
(01:54) As physicists try to make sense of all of this, some of them are coming to the conclusion that space and time may not be as fundamental as we always imagined. They’re starting to seem more like byproducts of something even deeper, something unfamiliar and quantum mechanical. But what could that something be? Joining me now to discuss all this is Sean Carroll, a theoretical physicist who hosts his own podcast, Mindscape. Sean spent years as a research professor of physics at Caltech [California Institute of Technology], but he is now moving to Johns Hopkins as the Homewood Professor of Natural Philosophy. He’s also an external professor at the Santa Fe Institute. But no matter where he is, Sean studies deep questions about quantum mechanics, gravity, time and cosmology. He’s the author of several books, including his most recent, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime. Sean, thank you so much for joining us today.