Mindscape 218 | Raphael Bousso on Black Holes and the Holographic Universe

Patreon: / seanmcarroll
Blog post with audio player, show notes, and transcript: www.preposterousuniverse.com/...
Stephen Hawking’s discoveries of black hole radiation, entropy, and the information-loss problem have both taught us an enormous amount about the relationship between quantum mechanics and gravity, and also left us with some knotty puzzles. One major insight is the holographic principle: the information describing a black hole can be thought of as living on the event horizon (the two-dimensional boundary of the hole), rather than distributed throughout its volume, as normal physics would lead us to expect. Raphael Bousso has made important contributions to our understanding of holography and its implications. We talk about the modern point of view of how gravity relates to quantum mechanics.
Raphael Bousso received his Ph.D. in physics from Cambridge University, where his advisor was Stephen Hawking. He is currently a professor of physics at UC Berkeley. He has made pioneering contributions to our understanding of black hole information, the holographic principle, the string theory landscape, and multiverse cosmology.
Mindscape Podcast playlist: • Mindscape Podcast
Sean Carroll channel: / seancarroll
#podcast #ideas #science #philosophy #culture

[@michaeljfigueroa]

Any chance for a part 2 of this discussion?

[@lucianmihail584]

Excelent episode, i'll love a second part of this disscution. Thank you, Sean!

[@michaeljfigueroa]

Maybe if we ask on Patreon.....!!!

[@Ava31415]

59 years ago, I gave up physics because I could imagine ADS/DS driving me down an insane rabbit hole, but this was fun! Thanks, listened though 3 times, and want to many times more, Can I suggest plugging 2 lapel mics into your phone and hit record when you have that coffee

[@malinkifox2011]

Loved this podcast he uses such simple way of explaining very complex theories

[@spaceinyourface]

I love all these physics podcast.

[@Life_42]

I'm so happy to have stumbled upon this channel! Thanks to StarTalk and Closer To Truth!

[@keatodiet]

I loved how sean grew more and more passive aggressive as the show progressed lol

[@michaeljfigueroa]

Thanks. I enjoyed this one a lot!

[@kquat7899]

Looking forward to this!

[@viktorbarkar8228]

Thank you for your work

[@ddavidjeremy]

If I'm going to get A sufficient understanding of the Holographic Principle someone is gonna have to get out the crayons, write a sing-along and break that thing down "Barney style" for me.

[@fmbgcunha]

Top episode, one of the best.

[@dimitrispapadimitriou5622]

Quite recently ( a couple of months ago), a new preprint from Robert Wald , D. Danielson, G. Satishchandran introduced a new interesting twist that has to do with the black hole information problem. According to this paper, black holes decohere even quantum superpositions of stuff that remains outside the horizon ( for example in orbit around the hole). The implication is that , eventually, black holes ( and perhaps more generally causal horizons ) have the potential to fundamentally decohere almost every quantum superposition in the universe...

[@bjpafa2293]

"... almost every superposition..." is too vague, non even fitting the analogy minimum definition as a figure of style... But, OK, we should be able to answer after reading the paper... 👌

[@marishkagrayson]

Yes, the black holes have been described as “eyes” that decohere all states. I prefer to see the black holes as buttons that hold together (stitched up) “reality”.😅

[@erichodge567]

You know...I won't even pretend to understand one ten thousandth of what is being discussed here, but still I listened entranced for an hour and a half. This is what it must have sounded like when Bohr and Einstein were having their famous arguments, or when Richard Feynman and John Wheeler were hashing it out. Honest, informed debate. What a far cry from our politics at the moment...

[@elwood.downey]

Best episode yet.

[@SubstanceP888]

Debatable.

[@elwood.downey]

@@SubstanceP888 Sure, it depends on why one is here. I'm here as an adjunct to Dr Carroll's Biggest Ideas in the Universe series. The premise there was to pull no punches and talk real physics. But some time ago Dr Carroll wandered off more often into the softer sciences in which I have no interest. That's when I pulled my Patreon support. So I'm always glad when at least this youtube series gets back on track for me.

[@skydweller2049]

What does it mean to have quantum states? as in the black hole has a certain amount of quantum states to it.

[@gtziavelis]

holographic principle: have always found it fascinating that a ONE-dimensional point directly behind a black hole from an observer's viewpoint gets promoted to a TWO-dimensional Einstein ring observation, and have never heard an expert talk about this "dimensional upgrade". that is akin to, or if you're imaginative, something like the opposite of, black hole information being encoded on the surface area rather than in the volume, which, in layman's terms, is like a "dimensional downgrade".

[@TheMemesofDestruction]

Perhaps it’s computationally reducible? ^.^

[@ilikenicethings]

Isn’t it because the ring is showing you the same “one dimensional” source as seen from different places in the universe that encircle the distorting mass from your perspective?

[@Littleprinceleon]

A link to any video on this Einstein ring? Thanks

[@simesaid]

To start with, nothing that you've mentioned has anything to do with the holographic principle, or to Hawking radiation either. Second, Einstein rings are created when the light from an entire galaxy is 'bent' around another galaxy that sits between us and the one further away. Now, most, if not all, galaxies (including the Milky Way's) _do_ happen to have a supermassive black hole at their centre, but Einstein rings are purely gravitational in nature and black holes aren't strictly needed for them to be created - any sufficiently massive object (or collection of objects) will do. Lastly, there is no "dimensional upgrade". There is 2D light coming from a distant galaxy, and you see a 2D Einstein ring as that lights trajectory (travelling on geodesic 'straight lines') is 'bent' around a closer galaxy. There is no 1D. Electrons are described in physics as being _point_ particles - and points _are_ 1D, but that's about the only time you'll ever hear about 1D objects. We live in a 3D universe, and thus everything we can see is 2D, even if something _looks_ 1D, upon closer examination it will turn out to actually be 2D. Hope that helps a bit. Einstein rings are actually pretty cool, because the phenomena allows us to see _very_ old galaxies that are _very_ far away and that would ordinarily be invisible to us as they lie behind other galaxy structures! Good luck with your physics journey, have a great day!

[@hugegamer5988]

@@simesaid point particles aren’t even strictly points. Beneath the plank length size loses meaning as we know it. Further, with the probability of interaction being a cloud in quantum mechanics explicit classical size as we know it does not exist.

[@bendavis2234]

When he said that “physics doesn’t concern itself with the question of what is real” I’m can feel Sean holding back on his opinion of the matter.

[@HonkletonDonkleton]

Because that's philosophy. Science is concerned with testing hypothesis via experimentation, that's all

[@bendavis2234]

@@HonkletonDonkleton Yep it is philosophy, no doubt. Seeing that Sean now has a chair in philosophy, I'm not sure that he would back away from the question because of that.

[@tiborkoos188]

I wish you continues the debate whether one of 2 equivalent alternative models can be considered as more reflective of reality. Especially Sean's point about the relative ease of evolving one versus the other form or representation. BTW, the evolution of representation of space in the MEC is am amazing fact. And interestingly that is 2D not 3D ! (not that this fact has anything to do with with the ADC thing, the mind as a whole has a 3D space model).

[@user-gj7vp6wk3e]

WHAT EXACTLY IS AN ERGOSPHERE?

[@vasyakalistrov8184]

everything we found probably is emergent except maybe time... we need some strong emergency theories on different levels of emergency/complexity

[@portalsandmagicghostnumbercube]

There needs to be an amended Invisible/Holographic Principle of the Multiverse. A duality within a duality. A dual pair track of parallel principles. Two sides of the same coin. The Holographic Principle works well in individual universes, but a more complete Invisible/Holographic Principle would go beyond the curtain of our observable cosmos and into the multiverse.

[@portalsandmagicghostnumbercube]

@@karagi101 The duality between the 1. invisible and holographic (the 2. Bound and 3. Bulk) duality within a duality. It really is a trinity.

[@portalsandmagicghostnumbercube]

@@karagi101 hmmm.🤔

[@bryandraughn9830]

Isn't gravity weird enough to grab hold of empty space and "bend" it somehow? It's always struck me as odd that this is a given. Doesn't anyone at least have some hypothesis for how mass might do such a thing? Why should empty space care at all about an object being there? If the gravitational "field" exists everywhere to begin with, that helps, but ive not heard it described that way. Why would the gravitational field affect space when all of the others only affect particles? Gravity is extremely weird.

[@dimitrispapadimitriou5622]

52:00 The problem is that , generically, there is no way for an external observer to define were the event horizon of a black hole is with any local experiment. Event horizons are global properties of spacetime, you need to know the entire history of the future to decide how big a black hole will be eventually... "Stretched horizons", besides the fact that they're coordinate dependent ( so they don't have any fundamental significance) are also meaningless in realistic situations, for example in the case of merging black holes.

[@hugegamer5988]

How local? You can test the local curvature of spacetime, by measuring spaghettification and the ansitropy in the local ambient cosmic microwave background radiation. You can calculate the time to the horizon by the time it takes you to be causally disconnected from the CMB and the mass by the amount of spaghettification with respect to the rate of CMB shift.

[@dimitrispapadimitriou5622]

@@hugegamer5988 You forgot that real black holes are not static or stationary. They're growing by consuming stuff/ radiation , they merge with other black holes etc. Their horizons that we observe are "apparent" or dynamical horizons, not the absolute event horizons. So, defining a timelike "stretched horizon", that lies just outside the "global Event horizon" needs knowledge of tne future history of spacetime, generically. Black holes are not isolated, as in theoretical papers, where it is assumed that they're asymptotically stationary...

[@hugegamer5988]

@@dimitrispapadimitriou5622 they don’t assume the horizon is asymptotically stationary instead they assume that infalling mass updates the horizon the speed of light causing the surface to ring its measurable during large mergers

[@dimitrispapadimitriou5622]

@@hugegamer5988 The whole thing about " black hole complementarity" is based on the concept of the "stretched horizons". As i already said, these notions of "stretched horizons" are basically meaningless when you have e.g. merging black holes... Before merging, the horizons of the holes are "apparent", they're not "event horizons". Stretched horizons are coordinate dependent. They don't have any " fundamental" physical meaning...

[@hugegamer5988]

@@dimitrispapadimitriou5622 I believe you have failed to understand correctly. From basic quantum mechanics we know the stretched infalling spacetime lengthens the wavelength to larger than the observed universe while with Heisenberg uncertainty we know the momentum is unfathomably large and these along with other basic postulates in quantum mechanics is what gives a physical spatial basis for maintaining a 2 dimensional surface that preserves information such as quantum states and entanglement. No need to see into the future any more than quantum mechanics currently does as measured on the benchtop.

[@waylayin6159]

I figuered out how to get information out of a black hole. You take someone they go in head fiirst. And then they use sign language! And do that as fast as they can on what they see before they are in it completely

[@waylayin6159]

@@karagi101 American!

[@JAYMOAP]

Legend 👌

[@EWischan]

Kylo Ren: "More"

[@spaceinyourface]

I wonder what asking gravity nicely really means. Probably lots of maths ey !!

[@bencegyurky1596]

Gravitiy is nothing. In the infinite realm only relative vacuums exist.But you can name it to absolute vacuum if you don't mind.

[@spaceinyourface]

@@bencegyurky1596 Cool,,,case closed,,,physicists can now rejoice in your wisdom.

[@diamon999]

I got a bit confused about the elphant at the centre of the universe. Sorry ;)

[@F_L_U_X]

:)

[@johnrowson2253]

( My girlfriend is either in protective custody, or past ? ). I confess that was an issue here, but I wonder why ? , and if that question is productive in answering further queries ? it being what distracts me from working on what ‘spearheads’ what curiosity I have. When will the QM ( volume 2 ) be in print ? Thanks

[@user-sf2ed4ek3c]

6 missed calls from Eric Weinstein.

[@emilylowrance7930]

you won't get far by being humble, is that physics only?

[@johnrowson2253]

Sorry

[@thorntontarr2894]

@10:50 or so, " unfortunately, not including the one in which we seem to be living" says it all about this podcast. Moving on.

[@imadetheuniverse4fun]

you're... disappointed that this podcast didn't solve quantum+gravity? lol

[@lionturtle1972]

1:09:15 or maybe Quantum Mechanics is Bullshit.

[@jonnymoney1071]

starts at 4:50