Episode 2: Carlo Rovelli on Quantum Mechanics, Spacetime, and Reality

Quantum mechanics and general relativity are the two great triumphs of twentieth-century theoretical physics. Unfortunately, they don't play well together -- despite years of effort, we currently lack a completely successful quantum theory of gravity, although there are some promising ideas out there. Carlo Rovelli is a pioneer of one of those ideas, loop quantum gravity, as well as the bestselling author of such books as Seven Brief Lessons on Physics and the recent The Order of Time. We talk about how to make progress on this knotty problem, including whether string theory will play a role (Carlo thinks not).

Carlo Rovelli is a professor of theoretical physics at the Centre de Physique Théorique de Luminy of Aix-Marseille University in France. In 1988, he and Abhay Ashtekar and Lee Smolin introduced the idea of loop quantum gravity. He is also the author of the "relational" interpretation of quantum mechanics.

[seancarroll]

Four podcasts are dropping this week, in honor of our launch! After that, one every week or two (depending on how popular it gets).

[urspeterkaelin]

Although not a physicist, just a lawyer, although not a native English speaker, just a Swiss German, your lectures help me in enlarging my bumble knowledge of, among others, physics in me older years. I am outmost thankful.

[DanielFoland]

There is no debate, this podcast is awesome

[Starlite]

Please, more episodes with Dr. Rovelli going deeper into Loop Quantum Gravity. This was a really good one!

[semidemiurge]

That you keep the discussion at a high level and make us do serious work to follow/understand is so refreshing and very much appreciated.

[PavelSTL]

Professor Carroll, can you please dedicate a portion of your podcast explaining your choice for the many world interpretation of QM for the layman. I get the impression that "many worlds" is simply choosing the lesser of the two evils, where the other one is to conveniently discard the other possibility of the wave function collapse. So is it just a temporary "solution" until a better theory comes along, or do you actually think the many worlds is accurately modeling "reality" as we know it? And while the many worlds is mathematically elegant, intuitively it's hard to swallow. I do agree with Rovelli that it comes with heavy ontology, and it's not the fact of the many worlds itself, it's the implications. Our way of reasoning in everything we do in life, including classical theories, is structured to think along a tempo-spatial *causal* line. I don't want to put a gun to my head because there's high likelihood of me getting killed, plain simple. I don't see how you can justify clearly bad decisions in the many worlds framework. After all, all possibilities will be realized, including me being still alive. Does the notion of cause and effect retire from the conversation? I'm afraid more explaining work needs to be done besides simply saying our intuition didn't evolve to do theoretical physics. How does the many worlds make a difference, if any, in how we interact with the world?

[danielskipperrasmussen]

Ed Witten as a guest would be rare and unique.

[metallife]

Sean thank you for making these. These past two podcasts are packed full of value and insight, like an oasis in the barren landscape of word vomit podcasts

[ZachMatics]

I would absolutely love it if you could explain the implications and inner-workings of the double slit quantum eraser experiment. Thank you. Sharing this with the people around me.

[TheSonicfrog]

Great interview with Carlo Rovelli! These are exciting times and Carlo is a fantastic 'splainer of all things physics, as is Sean. I highly recommend both Carlo's recent books, as I do Sean's from Eternity to Here.

[BFSearle]

Came here from your conversation on Joe Rogan. Loving the podcast - right up the alley with what I'm interested in! Keep up the good work!

[antonioda]

i like how physics is becoming popular and actually changing the common sense about reality we had in last century. i think there is something really new coming from it in arts, literature, and human expression in general. it's good because we are now living in a pretty dull era

[FeistyJackball]

Very glad you've decided to do this Sean! It's really solid. Well done man! Broadcasting far and wide...

[KeithCooper-Albuquerque]

Excellent once again Sean! These podcasts are just wonderful! The comments show a very nice caliber of listeners who have some level of understanding these complex topics. I am looking forward to many more of these sir! Carlo Rovelli was a wonderful guest as well!

[pimwiersinga]

Fascinating conversation... full of clarity.

[lylasolis]

So glad to have found your podcast (this episode in particular) right after watching the Joe Rogan Experience episode you were on last year. You have sparked my interest in quantum physics! Can't wait for all the new episodes to come; all 4 that I have listened to so far have been great.
Thanks!

[oatlord]

Sean, I have a black hole question. How close to the event horizon or the physical black hole do you get before the gravity differences between head and feet begin to cause joint pain?

Before the event horizon or after?

[DevanMccallister]

Can someone explain this to me. I watched a video with Carlo and he talked about black holes and that the star still resides deep inside the black hole. Not the singularity. Actual star. I never heard that before.

[davebowles]

I found out about you through a Joe Rogan podcast and then looked for your podcast. I listened to the first and now listening to this one. I also subscribed and am just fascinated by all this. Keep them coming. These are awesome. Thank you!

[dwinsemius]

Having trouble understanding why the EM field can be measured in an arbitrarily small volume of phase space, but that the gravity field cannot. (Was not previously aware of the "Landau error".) Wouldn't the energy in the EM field have mass and cause a black hole in the gravity-space field? Don't these fields share a phase space? Did I hear these arguments incorrectly?