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

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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).

[@RareshVladBunea]

The more the better! Keep them coming. We need your unique conversation skills, tone, and civility. Thank you!

[@jamesward35]

sean this is going to get massive don't you worry about it. people should be paying to hear the knowledge you have amassed

[@pansepot1490]

Thanks for explaining. I haven't had time to watch the first one and when I saw the second I thought there's no way I can possibly keep up with this frequency of upload.

[@seanmeadows2499]

Great! I hope a lot of people tune in. I agree with a lot of the other commenters, that the addition of video would increase your viewership/listenership substantially. The technical barriers to doing video podcasts are fairly low now and there are a ton of potential guests that are already in SoCal area or will be passing through that could meet at your office or at a basic studio to record the episode. Your message and understanding is really valuable, so I’ll be thrilled to see you be as successful in this medium as possible. I have web dev and some audio/video experience, in SoCal, and would happy to assist pro bono.

[@IoNessunoMolti]

Fantastic, and BTW I loved this one!

[@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

[@mrloop1530]

Okay

[@PerryUK]

Prove it!

[@shepardzane30]

sorry to be so off topic but does any of you know of a trick to log back into an Instagram account?? I was dumb lost the account password. I would love any tricks you can give me!

[@ianmoshe227]

@Shepard Zane instablaster ;)

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@Ian Moshe Thanks for your reply. I got to the site through google and I'm waiting for the hacking stuff atm. I see it takes a while so I will get back to you later when my account password hopefully is recovered.

[@Starlite4321]

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

[@metal4life543]

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

[@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.

[@paxdriver]

The only podcast ever where Lee Smolin gets named dropped lol love your work Sean, thanks to you and Caltech for all the public engagement like this. Your efforts are greatly appreciated

[@danielskipperrasmussen161]

Ed Witten as a guest would be rare and unique.

[@noahway13]

I watch many of this type of videos, but I have never seen him as a guest. Does he do videos, or have I just missed him?

[@nias2631]

For what it's worth I went to one of his talks years ago. I do not have the impression he would discuss physics anywhere near a general audiences level... The math would retain meaning better than any words.

[@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!

[@antonioda3744]

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

[@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?

[@cammo777]

@Oners82 You're not Professor Carroll.

[@roqsteady5290]

@Oners82 : Spot on explanation of what Sean Carroll is saying and is certainly a very compelling argument IMOP. There is some difficulty, I think, as to whether other worlds have the same ontological status as this one (as David Deutsch seems to suggest - see "Fabric of Reality") or whether at least some of those other worlds will fade out as they become more and more bizarre - compare Feynman's explanation of how a light beam actually goes every which way between two points, but appears to go in a straight line because many paths cancel out (in his book QED).

[@FeistyJackball]

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

[@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.

[@AaronBowley]

hey I know some people will be like woah you just posted yesterday but wow I would NOT MIND A PODCAST EVERY DAY like seriously I’d rather listen to SC ask questions every day than basically anything else so LETS GO

[@keithinadhd6693]

I am loving this podcast! Thank you for it.

[@vckamath]

This podcast is essential. Please keep this going.

[@pimwiersinga8822]

Fascinating conversation... full of clarity.

[@weinhold0204]

Thanks for hosting this podcast Sean. I've always loved your interviews and talks on other shows. I can't wait to see what other amazing guests you'll have on!

[@alachance2010]

Very Happy you are starting this podcast! Thanks Sean!

[@darrenbrown7037]

Great podcast, so glad you have decided to do this. I would love to hear you speak with Brian Cox.

[@davebowles1957]

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!

[@GeorgeGrigalashvili]

Please do record videos as well!

[@oviros]

yes,a Joe Rogan format type would be awesome.Monologues or dialogues would enrich every viewer.

[@alangarland8571]

How would that improve it?

[@alucard0712]

@@alangarland8571 I can watch it instead of just listening?

[@larsalfredhenrikstahlin8012]

yes!

[@ggrthemostgodless8713]

Nope... he cannot do that as easily as this format, why?? because he has his mini podcast pack he carries around wherever he goes to talk to interesting people (he mentioned this at his Joe Rogan sitting), I imagine that he would have to carry at least two cases of equipment if he wants to include video, plus SOME people are more self conscious with video than just audio. If the choice is this or nothing, I think most of us would rather have this.

[@Foneio]

I've been waiting so long for Sean Carroll to do a podcast! KZbin has delivered the goods.

[@MickShredLord]

Sean, thank yooooou for starting your own podcast! I already have the feeling it's is going to be in my top five.

[@lylasolis3701]

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!

[@Rayemode]

So refreshing to hear a pod like this! Keep it going!

[@comptoncity2]

You definitely need to go full video. It will take your podcasts to the next level. Loved it btw

[@JeffreyMW1]

Thank you, thank you, thank you. Great stuff in these podcasts. Can't wait to listen to you and your next guest.

[@gregspradlin290]

Love this content and will definitely be listening to future episodes. Don't mind the no video thing at all, as I'm listening to these while doing other things.

[@ameremortal]

I’m personally very happy that you read your own audiobooks.

[@Craznar]

Already, I'm still only half way though the last one. Wait - he is travelling at close to light speeds, it just APPEARS to us that they are coming in fast :)

[@mikelevitz1266]

Wonderful lecturer. A rock star!

[@MrHomniel]

This podcast is fantastic! Makes me want to pick up my old books and calculate the universe :)

[@Ayal137]

Please do not stop podcasting

[@cashhaaser6787]

Sean: I am a big fan of yours. I admire (and envy) what a great communicator you are. I enjoy this podcast as well. I can see why you have the office of R.F)!

[@roodborstkalf9664]

Very good podcast. Rovelli emphasized correctly that it is a big deal that evidence for supersymmetry haven't shown up yet in the CERN experiments

[@SynysterGates70]

Amazing Podcast, Sean! I specifically love the intro where you give us some backgrond information on the guest and their area of expertise. Really helps fully digest the whole podcast. Cheers!

[@leonenriquez5031]

You cannot be "a realist about reality" because the whole aim of physics is to establish what physical reality is, so you don't have the ground to be a realist to start with. That's precisely what you are looking for: the ground where you can actually asume a realist position. If that ground does not pertain to the category of the actual, then your realist position can't be what you say it is, Sean. It's not realism but idealism, which is what you are trying to avoid.

[@classickettlebell2035]

Thanks for the great podcast Sean Carroll 🙂🙂

[@RobbertJan]

Such an interesting conversation, wish it was longer!

[@JPeraltavideos]

Gracias por este podcast. Ojalá tuviera subs en Español para alcanzar a más personas

[@aquaperro]

Maybe it's just me, but when I think of the Speed of Light in terms of Speed of Time, things tend to make more sense.

[@madderhat5852]

Great talk on the most recent thoughts about the subject.

[@vitaly2432]

So glad you started this podcast! Would be great if you made an episode on Many-worlds interpretation some time. I'd like to know why it's your favourite. What good reasons do you think you have for supporting this theory and not some other?

[@Quakez0r]

I have gardening to do today. This will make it far more enjoyable :)

[@1Anthonyjp1]

Please show you talking with the person you are interviewing. A picture on for and hour does not do justice to a podcast on KZbin. Love your work! Video is needed!!! Thank you for educating all of us.

[@jonseltzer321]

Awesome, didn't want it to end.

[@ameremortal]

Excellent discussion.

[@smotpoker81]

Sean, you rock bro. Me, You, and Hugh. That's the name of my unwritten script. It'll be terrible. You'll love it.

[@cashkaval]

Just finished listening to the 1st one.

[@RandyH524]

Love you Sean. So happy you started a podcast! Subscribed!

[@DavidRuizTijerina]

I'd love to see Sean interview people with a different perspective on the physics of gravity and space-time than the ones that already get so much publicity (string theory, for example). Grigory Volovik and Xiao-Gang Wen have amazing results for the emergence of both particles and forces from underlying strongly-correlated degrees of freedom. I think interviewing them would be refreshing for a lot of listeners.

[@AntonioSanchez-yl9wj]

Sean, first, your podcast is great. Thanks for the initiative. We have discovered that you are also a great host, always putting in the right context questions (and answers). Carlo Rovelli: Quantum Gravity is a terrific matter (Carlos´ specialisation) but the discussion I would have loved to listen is about THE ARROW OF TIME. Both of you have strong positions about this subject. What do you think about the PERSPECTIVAL thesis of Carlo? You probably had this discussion in private with him. Please, create a podcast about this matter, in general. Cheers. Antonio

[@tookie36]

"I see our direct experience of reality is tremendously overrated frankly" hilarious :)

[@mutleyeng]

this would be an ideal vehicle for moving naturalism forward ... you can use that if you like

[@ThePhysicsConnection]

More of these please!

[@GodlessPhilosopher]

You're awesome. I love your work. You should totally interview fellow Everettian and philosophy of physics, David Wallace!

[@filippobonaventura8801]

Great podcast. Thank you so much.

[@kengounited]

You have a great voice, Sean!

[@billnorris5318]

Good show Sean... the imagery of interlinked quantum gravity loops is attractive but it lead me to wonder would this net-like structure exist in two demensions,or three ? I get the fact that they themselves, would BE spacetime, but interesting differences are suggested by both models.

[@Calkil64]

This is amazing! Good job!

[@JayronWhitehaus]

"[Einstein] was best at doing mistakes and getting results, maybe the things go together" -Carlo Rovelli

[@derre98]

Presumambly Carlo was talking about this paper: arxiv.org/pdf/1707.06050.pdf. Just in case someone was interested.

[@markakroll]

When I move from point A to point B, do I move through space, or does space move through me? Your answer will be leveraged with reconciliation with 'local' causal shared symmetry which necessitates [differential time: t'] for any object that exhibit mass.

[@mrcrowly11]

Love the podcast so far! See it you can get David Deutsch!

[@guntersostaric2333]

The many world interpretation by Everett: EVERY image surrounds a complete universe

[@stevenniven4788]

Sean Carroll is well worth listening to and I urge you all to read his books

[@seriouskaraoke879]

Man, you're not messing around. One a day.

[@sofiazulfan9550]

thank you

[@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.

[@Rodo1802]

I’m so happy!

[@thedeemon]

Very nice. Thanks a lot!

[@Raw799]

Sean, I love your fresh podcast. It would be awesome if you had Nima Arkani-Hamed on. Would love to hear you two exchange ideas.

[@chrisrecord5625]

It's interesting to try to think about cognitive dissonance in relation to new perspectives on gravity from Verlinde (Emergent gravity??) to Rovelli and Smolin (Loop) to MOND, etc., but I am going with Robinson's science fiction book, Mars Trilogy, that merges Loop Quantum Gravity and String Theory into one, if Cumberbatch reads the audio version.

[@binaryalgorithm]

So string theory suffers from "preferential attachment", as do certain other theories. This is the human bias toward the popular idea, but it doesn't match the credence afforded by actual experimentation. I love how Sean also teaches us how to think about our ideas so we have a proper "meta" when looking at physics.

[@soundman4062]

Get tom Campbell On The show. Keep doing podcast. Love it🙂

[@chromabotia]

Great podcasts Sean, thank you. You touched on something that is of great interest to me. Super Symmetry. We have had one major energy upgrade at CERN and there have been NO detections of super symmetric particles. Yes, they could exist at higher energies. But what if they don't show up? If super symmetry is dead, would this not mean big problems for the standard model? Thanks...

[@billnorris5318]

Gully Foyle ..it would cause a MAJOR reassessment of many theories BASED on supersymmetry, but remember,..as beautiful as supersymmetry is , it is not per se, the standard model but a potential extension of it...sadly too,, because the theory is so elegant..

[@1p6t1gms]

Wazoo, the idiom and not the other, I am going to need a repeat listen if not more, maybe one or two of the books will help.

[@AlexHumbug42]

My head hurts with this one 😅

[@TripToTrappist1]

YES A PHYSICS PODCAST THANK YOOUUUUUUU MAKE SURE TO LIKE AND SUBSCRIBE, PEOPLE

[@TheMemesofDestruction]

1:08:20 - It’s coming. Publishing now and full formalization by the end of this upcoming Academic year. Eyes on Berkeley, imo.

[@schmetterling4477]

What is coming? A load of bullshit? :-)

[@TheMemesofDestruction]

@@schmetterling4477 Field Theory Unified. ^.^ - kzbin.info/www/bejne/bWLNfJuKdrWXncU -

[@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?

[@naimulhaq9626]

The double slit experiment shows how observation/measurement (here called 'interaction') turns waves and fields into particles. That indeed is what is claimed as 'no one understand', the most shocking aspect of QM, but also establishes the power of 'observation/interaction'. The shocking part comes from the fact that if Feynman's QF can be observed (by whoever), then we would not have to struggle to construct particles from the field, we could get a free lunch, because that would imply a conscious observer. Rather effortlessly arriving at 'intelligent design'. that can be charged for fine tuning creation (we had no clue about). Leading effortless acceptance of 'divine purpose'.

[@speider]

Naimul Haq it's called iteraction because QM measurements ARE interactions. It's like finding a ball in a dark room by hurling other balls towards it until you hear a thunk.

[@naimulhaq9626]

Front line physics aims to discover how QF can simulate consciousness. When do you hear a thunk when the ball hits a wave/field?

[@metacarpitan]

Im already excited. Quantum was my favourite module. Can you do something on QED? That would be cool.

[@chrisbovenschulte6854]

Hey Sean, please do an episode on quantum Darwinism.

[@lukewalker7412]

love Sean !

[@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?

[@JAckQi888]

Thankyou SC :)

[@joshua3171]

july 2018 dam only seems like yesterday

[@t3hgir]

Sean, what are some implications of the LHC not finding evidence for SUSY? Do you we simply probe at higher energies? I know you and Carlo touch on this near the end of but wanted to hear your thoughts directly.

[@AmiyaSarkar]

Amazing! I really loved the quantization of the Gravity part @ 30-35 minutes. However, i was astonished to not find a choice both are wrong and yet both are right @ 1:05. Don't you believe what you say, sir?

[@robertw1871]

I believe we are in an epoch in physics that’s a progression from Newton to Einstein to something else, perhaps, two or three more revolutionary ideas will come in the centuries ahead. I’m thinking it’s so difficult to quantize gravity because it doesn’t need to be, maybe QM is just fantastic mathematics that’s brilliant at approximating, statistically, the fundamental reality. Is instrumentation failing us? Do we really understand how electronics and materials are behaving? What if time itself isn’t just a simple geometry, perhaps it’s multidimensional, where feilds can obtain superluminal properties, a place where feilds move much faster than we observe even if momentarily, such a property could seem quantum in appearance if unnoticed. Clearly speculation, but I can’t help feel we aren’t yet near the ultimate answer. The bizarre nature of QM seems to be stemming from humanity, possibly we aren’t yet ready to see the universe on its terms, without the haze of human experience. Sadly, if history repeats, it might be centuries before the next Einstein emerges. We all hope Sean will figure it out and explain it to us.

[@AbhiAnand-vn4rq]

Thanks Sean. Do you think the speed of light has ever varied over time?

[@YourMakingMeNervous]

Can you talk with Nima Arkani-Hamed? I'm really intrigued by the amplituhedron and EFThedron.

[@noahway13]

I am not smart enough to get this without a video.

[@bariizlam638]

I've always said that AdS/CFT is the sheezneeeetttt!!! besides Er=EPR as a holographic principle where black hole entropy in a singularity is my Jam bitches!!!

[@istvansipos9940]

he starts his sentences at a volume, then gets less and less loud. then comes the next sentence... it was a pain to listen to this guest, especially with a headset (without it, too). If another guest does this for some reason (perhaps no experience with a mic), pleeeaase, let him / her know early on.

[@Bix12]

Wasn't there an idea floating around that gravity exists across all 10 dimensions, and we experience only that portion of gravity which manages to "leak" into this dimension?

[@Bix12]

This was written at the outset of this podcast, so if it is discussed by these gents do not treat me mean.

[@smotpoker81]

You should host a 2nd conference on naturalism. If you need another speaker, ole smotpoker is always available for his standard fee.