Episode 31: Brian Greene on the Multiverse, Inflation, and the String Theory Landscape

String theory was originally proposed as a relatively modest attempt to explain some features of strongly-interacting particles, but before too long developed into an ambitious attempt to unite all the forces of nature into a single theory. The great thing about physics is that your theories don’t always go where you want them to, and string theory has had some twists and turns along the way. One major challenge facing the theory is the fact that there are many different ways to connect the deep principles of the theory to the specifics of a four-dimensional world; all of these may actually exist out there in the world, in the form of a cosmological multiverse. Brian Greene is an accomplished string theorist as well as one of the world’s most successful popularizers and advocates for science. We talk about string theory, its cosmological puzzles and promises, and what the future might hold. (For more general string theory background, check out Episode 18 with Clifford Johnson.)

Brian Greene received his doctorate from Oxford University, and is currently a professor of Physics and Mathematics at Columbia University. His research includes foundational work on topology change, mirror symmetry, and the compactification of extra dimensions. He is the author of several best-selling books, including The Elegant Universe and The Fabric of the Cosmos, both of which were made into TV specials for NOVA. He and Tracy Day are co-founders of the World Science Festival.

[seancarroll]

Hi Folks-- There have been issues with the audio quality on the last few episodes, so these are improved versions. It's easy for me to replace the audio file alone, but the only way to edit a YouTube video is to delete and replace with a new one, so that's what I've done.

[woody]

Two of my favourite physicists and now with improved audio.

[learneraccount]

Sean and Brian are brilliant scientists with incredible communication skills. What a great privilege to hear them conversing together.

[Okla_Soft]

One retort to the Boltzmann brain problem is that even if you accept that your brain is more likely to be a Boltzmann brain, and your mind just popped into existence with your entire life’s memory’s intact, it would have to keep popping into existence repeatedly every instant (quanta) of time after you make the observation. It holds up logically for an instant but the plausibility goes away after some elapsed time of the brain existing. Your reality could only be mirrored by the Boltzmann brain scenario if it continually appeared with each subsequent appearance having to account for the last moments of time that you experienced after it first appeared. This argument was made by Lawrence Krauss I think.

These guys are 2 of the best authors on modern physics, period. Brian’s “The Elegant Universe” is a stunning work, and Sean’s “The Big Picture” is a dizzingly thorough volume on every important concept in science. I treasure all of Brian’s books, have read most of them several times over and I love Sean’s lectures, podcasts and literature. So cool to listen to them have a conversation on string theory.

[JustinWatersJustinWaters]

My first cosmology book was Fabric of the Cosmos by Brian Greene. It was a great book, but the string theory chapter confused me and kind of discouraged my further research into cosmology for a few years because I thought I didn't have enough knowledge of physics to understand the subject. Now I understand much of string theory is speculative. I think to not overwhelm new laymen from researching cosmology, it's important to provide a disclaimer whenever an idea is very speculative. I appreciate a disclaimer was provided at the beginning of this video 0:32.

[johnmcntsh]

This is one of the best. There are people who can communicate well over media and people who have trouble. These two are experts. Thank you

[jjgarrison]

I'm working towards my physics degree and you are one of the reasons why i decided on physics. List includes:Brian Greene, Michio Kaku, the Flash (lol), yourself and a former high school teacher. Keep up the great work and having awesome guest!

[EB-xhii]

Brian is such an eloquent speaker, full of bright ideas and tremendous insights. Sean is a fantastic interviewer that asks truly profound questions of his guests and really challenges them to explain it in layman terms (for dummies like me :) Thank for your podcast Sean and Brian for being such great promoters of science and for explaining challenging cosmological, quantum and physics ideas in an understandable manner.

[igor.t]

A different “Brian Greene” from this side of the equation; I meant to say “this side of microphone”, that is – conversation. Somewhat boyishly rebellious (and I mean it as a compliment), but definitely passionate about his original work. And, yet, quite cool-headed, dispassionate, and realistic about the prospects & in-field probabilities of “his theory of everything” – at the same time. The nicest thing about this talk: a pleasant, dynamic, friendly exchange among two fellow physicists.

[frederickj.]

This one's really a gem in the 'grand overview' department for fundamental physics & cosmology -- where have we been (?)... where are we now (?)... and a little on where we might be going. If you were looking for a Brian Greene science program which *doesn't* "feature" a tedious cacophony of tacky and irrelevant *dumbing it down* style distractions for the masses... and which isn't introduced by, or interspersed with silly episodes of Brian's Shatner-circa-1967 school of bad acting or his pacing around on a stage mello-dramatically pondering the too obvious "big" questions in time wasting fashion... well, *here ya go!*

Ah, that's *much* better! This one's got some meat on its bones and is easily worth the time invested. A great job again by Sean Carroll, keepin' it real.

[whybother]

Thank you Sean for doing this. I wasn't very enthusiastic student in college when it came to physics. But you and Brian encouraged me to actually learn more about modern physics theories. It's truly fascinates me.

[soonfajsk]

Sean Carroll any chance you’ll have Brian Cox on any episode soon? Would be amazing

[travellingnutrino]

33:55 "buttload would be the technical term, right?" hahaha my favorite joke of the conversation. Love these two!

[YAS-dnxn]

Love you guys. Two of my favourite physicts

[bitdribble]

This conversation explains, at high level, many questions I had about the structure and meaning of String Theory

[takefivepaullucido]

Sean, I really enjoyed your podcast with Brian Greene. The two of you have a good chemistry and exchange. I have been a fan of Brian's work for quite some time and his book "The Hidden Reality" which my son bought for me a while back. -- Keep up the great work on your podcasts! -- I think will listen to it again tonight ;)

[jostanton]

Absolutely fantastic, I love mindscape now I have a reason to live.

[davidjimenez]

I was incredibly pleased when I got the alert about a new Mindscape podcast. I was then even more pleased when I saw Brian Greene on this one, as I thought they'd done a second one. But thanks Mr Carroll for doing your best to put out the best content that you can. Loving all of these podcasts, although I'm still quite uncertain about String Theory, but I am curious to see where it goes from here....

[zagreb]

Two best public speakers in science. Next Ed Witten or riot 🤣

[Jesse-cwpv]

Wow just discovered Sean had a pod cast. Been a fan for a while