Into the Impossible With Brian Keating - Addressing the Biggest Controversies in Modern Cosmology with George Efstathiou [Ep. 436]

Episode Date: July 7, 2024

Join my mailing list https://briankeating.com/list to win a real 4 billion year old meteorite! All .edu emails in the USA 🇺🇸 will WIN! Modern cosmology is full of controversies, challenges, and unresolved tensions. This can, of course, be very frustrating. But it’s also extremely fun!  Especially if we approach these challenges with brilliant minds who aren’t afraid to tackle them head-on.  One such luminary is the renowned George Efstathiou. George is a British astrophysicist and Professor of Astrophysics at the University of Cambridge. He was the first Director of the Kavli Institute for Cosmology at the University of Cambridge from 2008 to 2016.  George joins me today for a cosmological episode in which we look at cosmic acceleration, Hubble tension, Sigma-8 tension, inflation theory, BICEP2, Planck collaboration, and more.  Tune in! Key Takeaways: 00:00:00 Intro 00:04:25 Baseless claims in cosmology  00:13:57 Solving the Hubble tension 00:23:11 Axion-like early dark energy  00:28:03 Primordial magnetic fields  00:30:36 Solving the Sigma-8 tension  00:38:37 Inflation and the Multiverse  00:48:30 BICEP2  00:54:50 Existential question 00:56:42 Outro  — Additional resources: 📝 Get one month of Snipd Premium for free with this link: https://get.snipd.com/Cx7S/brianSnipd Snipd lets you take Smart Notes 🧠 with AI 💡 — it’s my favorite podcast player 😀 ! ➡️ Learn more about George Efstathiou: 💻 Website: https://people.ast.cam.ac.uk/~gpe/ ➡️ Follow me on your fav platforms: ✖️ Twitter: https://twitter.com/DrBrianKeating  🔔 YouTube: https://www.youtube.com/DrBrianKeating?sub_confirmation=1  📝 Join my mailing list: https://briankeating.com/list  ✍️ Check out my blog: https://briankeating.com/cosmic-musings/  🎙️ Follow my podcast: https://briankeating.com/podcast Into the Impossible with Brian Keating is a podcast dedicated to all those who want to explore the universe within and beyond the known. Make sure to subscribe so you never miss an episode! Learn more about your ad choices. Visit megaphone.fm/adchoices

I hate to say it, but cosmology is one of those fields where the mysteries only seem to grow, the more we learn. It can be extremely frustrating, but it's also tons of fun. We're still grasping at the elusive nature of dark matter, wrestling over the persistent Hubble tension and grappling with the puzzle of Bariani symmetry. And most of all, puzzling over one of the most frustrating questions of all, is dark energy truly behind our universe's accelerated expansion? Luckily, today, we are blessed with one of the most brilliant minds in the universe, George of Staddeo, a professor at the University of Cambridge and the first director of the Kavli Institute for Cosmology. Today, he shares some counterintuitive wisdom that absolutely blew me away.

He's joining us today to drop some more big bang-sized truth bombs on us, to address the anxieties, tensions, and curiosities that plague cosmology, but I'll also make it the most fascinating subject manageable. So let's get to it. Any sufficiently advanced technology is indistinguishable from magic. Open the pod bay doors, help. First, I want to ask you, George, I always ask people, what's your favorite day on the calendar for you? I think it might be in September.

But the reason I ask that is because the origin of your birth or of some significant event is always something special. And so I want to ask you about your origin story starting back. some decades ago. So tell me, please, how did, what's your past world line look like? It's quite interesting. My parents were both born in Cyprus and moved into, they moved to the UK after the Second World War. So my father came in 1949 and my mother came a couple of years later and they met in the UK. And at that time, you know, Cyprus was a British colony. And the Brits were looking to the colonies, you know, come to the UK and help rebuild the motherland after the war. So, you know, so that's how my parents ended up here.

So as part of this, you know, quite significant migration of people from former British colonies to Britain. So before then, I mean, my father was, my father's family, they were farmers in Cyprus. And, you know, my father eventually set up a business as, you know, running a fish and chip shop. And so, you know, when I was a kid, I used to work there at the fish and chip shop. So there wasn't a sort of academic background to the family. I was always interested in astronomy. I mean, you know, one of the, you know, I think one of the reasons that I got into astronomy professionally was because I never grew up. You know, you ask these fundamental questions as a child.

And, you know, I'm still working on those fundamental questions, you know. So there wasn't a history of academic, you know, go to university and so on. but I got motivated for a really weird reason that I decided I wanted to go to Oxford and the reason for that, you know, there was a TV program called The Persuaders with Tony Curtis and Roger Moore, so they played these sort of playboys,

sloths solving various, you know, crime problems and so on and so on. And the start of it, the Roger Moore character, Brett Sinclair, was from a wealthy family, went to Oxford. And, you know, from the credits, I thought that's what I want to do. I want to go to Oxford. So it really became a sort of ambition. And eventually, I did end up, you know, going to Oxford. And, you know, then, you know, launched into a research career. When I look at your career, it's kind of what resonates with me is this notion that you're kind of unafraid, you're courageous in your approach to taking on the orthodoxy when necessary and sometimes being slightly controversial or contra.

How do you say it there? I don't say controversy, but do you say controversial? When I was in the UK last summer, you were busy, and I should mention you're one of the treasured members of the Simon's Observatory External Advisory Committee, which is something that we lacked with our bicep experiment. We didn't have guardrails, checks and balances. We didn't have a kitchen cabinet or war cabinet, however you want to phrase it. And so your insights have been invaluable there. But I want to ask you, you're kind of known for, taking on these grand challenges, when you look at something, which I spoke about this summer

at the Royal Institution, which was the question, was there a big bang? There's a lot of kind of commentary from many people, some are experts, some are not, that either the big bang didn't happen or that it happened essentially twice as long ago as we naive cosmologists would assume. How do you separate the orthodox kind of challenges that you are taking on with anomalous? and Hubble tensions and Sigma 8 tensions and stuff that we'll get into. How do you separate that from what might be considered to be, you know, baseless claims about the non-existence of the Big Bang? And as I made a joke, I said, you know, if there's no Big Bang,

you don't need a big banger. And I showed a big, big sausage. Yeah, so go ahead. So on controversy, you know, I mean, I don't court controversy. And in fact, the people have accused me of being fought to. two orthodox. I defend the standard model of cosmology Lambda CDM to the death. And so, you know, I mean, you just have to look at some recent articles like the one by

Brent Tully, where he actually names me as, you know, as somebody who has, reminds him of Sandwich and Tamar who wouldn't accept the key project, Vanu's the, the, key project, the value of the Hubble concert. So I probably don't talk about the Hubble Cons. So I think it depends on your point of view. I mean, the problem with that is that people don't

I think understand when we got plant data of how extensively I tried to break the land CDM model. And I just couldn't do it.

It just wasn't possible. So, you know, it's not, it's not for want of defending a particular cosmology. It was the, I'd have loved, I mean, you know, you know, you, you know, in science that, you know, you do big experiments and you, you know, you find a massive discrepancy with, you know, what everybody accepts. Then that's a big result. Okay. So, you know, it wasn't for one to try it. But as for, I'm actually worried and I'm wondering whether it's a function of age, actually, about people getting a lot of publicity for very weak, more outlandish ideas.

And this is an increasing trend. I encountered this just this week because you've probably seen articles or, you know, reports of the discovery of a big ring in the sky. Now, this is MG2 absorbs, so absorption lines from quasar spectra. And, you know, this has been reported as an enormous structure in the universe that, you know, disagrees with the standard model. Just look at the data. It's incredibly sparse, you know? I mean, I don't think that there's a, you know, it's very difficult when you're dealing with sparse data.

It's always difficult to deal with look elsewhere effects. You see a pattern and, you know, how do you assign the significance to once you've seen it? And when I first looked at the picture of the MG2 absorber distribution on the sky, I wondered, which ring are they talking about? Because I could see, Sev. But this has made it, you know, into new scientists, into, you know, sky telescope here in the US. And, you know, it seems to me.

you know, incredibly weak. And then you can get even more outlandish theoretical ideas. I mean, the observational thing, okay, fair enough, they've pointed this out, but, you know, it's not very convincing. But then on the theory side, just have a look at some of the things that have, you know, appeared recently.

Like, you know, we make a model based on Mond, that changes the growth rate, the fluctuations that we can get enormous voids. and that this fits in with the big ring and, you know, the voids can explain the anomalous value of the Hubble constant and so on. And now you get into really outlandish ideas and it's published. Yes. So, you know, and this, this worries me because it's creating, you know, that's, the idea, that is, that idea, that idea conflicts with so many things that. know. But it's, yet, I was asked to comment by a journalist, you know, from New Scientist about, about the Mond paper. And I was very busy and I just wrote back quickly saying,

really, new scientists, there's plenty of good science that new scientists could be reporting. Why are you giving it a fuel to these kinds of ideas? And I said, you know, we, if we live in a world where people have created alternative realities, you know, politicians have created alternative reality, we really shouldn't be doing this as scientists, okay? So, so the journalist didn't take kindly to that remark, but it does bother me. It does bother me. There are these sort of alternative realities. And, you know, you can't engage when it becomes, when the, you know, different perceptions, perceptions are so different. you can't engage. We've always, we're struggling, as cosmologists as scientists, we're always struggling with the fact that there are some observations that don't fear. Okay, I mean, a quote that I've used for decades, it is apparently attributed to Francis Crick.

and he said that, you know, if your theory agrees with all of the observations, that it's bound to be wrong, because at any one time some of the observations will be wrong. So that's the, so what we're struggling is trying to make sense of things we don't know, you know, whether, you know, this particular observation is right, you know, this isn't right. so we're constantly mud wrestling we're having to make these judgment calls so on the theory side we have

you know over the many many years developed this kind of intuitive feel that you know an elegant idea is likely to be more right than walk up lots of bells and whisters than we could adjust take it

So simplicity and beauty is a guide to assessing theories. And, of course, you can phrase that thing, you know, that concepts in a statistical jargon if you want to. But on the observational side, it's then a judgment call, very subjective judgment call on what to ignore and what not to. And that's where we get a lot of controphacy. Hey there, fellow explorers of the universe. I hope you're enjoying this cosmological voyage with none other than my hero, George F. Stadio himself. It was a really fun interview, and I hope you appreciate that I don't always bring guests that are household names like Neil deGrasse Tyson or Ryan Green or Sam Harris. Sometimes I bring lesser known individuals,

but they're not lesser luminaries. These are some of the most brilliant minds in the known universe. If you want more of them, please do join this channel. Please do subscribe. Subscribe to this channel or follow the podcast on your podcast app player of choice. Only about half of you are doing it, and that's a number even more mysterious to me than the puzzle of dark energy. So once you do it, that'll clear up that dark matter for me and allow us to get back to having more exciting conversations just like this. Now back to George. Very underappreciation. It's peak pollination season, and my business is scaling fast.

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You can, I mean, in the social sciences, there's at least a name for it, you know, P hacking. we don't really have that. But there is a tension in that we, no pun intended, that we have a singular cosmos, you know, at least for now, I want to talk about the multiverse later, but there is but one cosmos. There is but one universe from which to draw information experimentally and empirically. So when you're in such a situation, unlike even astronomers who have, you know, literally 10 to the 20, you know, stars in the observable universe, we only have one universe.

one universe to study. So I was found that that puts us at a disadvantage in that we kind of tend to overinterpret things. And maybe, just maybe, we're reaching here to find tensions and and so forth where they're not. And I guess I wanted to pivot to the Hubble tension. I've had Adam Reese on many times. And I wondered, you know, it would be it would be impolite if I didn't allow you as one of the foremost experts in this to explain it from a technical point of view. My audience is highly technical, the most brilliant audience in the known universe. So please, start with the high level. As a professional, as someone working in this front, we see respected astronomers, the disagreeing.

I've often said we have so many tensions that we need a good therapist for the field. How do you view the Hubble tension? The Hubble tension is a really... It's a really interesting. It's a really interesting problem. You know, let me say at the moment that, you know, I don't know the section. I mean, you know, I'm agnostic. So what I do have is a tremendous amount of respect for Adam Rees and his team

and the work that they've done, you know, the, the, so, you know, I think they've, they've done beautiful, beautiful observations, lots of consistency checks. and so on and so on. So, but just to explain my perspective, we have a standard model of cosmology that's specified by six parameters and it fits a range of observations beautifully. And in particular, the cosmic microwave background.

So from observations of the cosmic microwave background, this model gives us a value of the Hubble constant of about 67.5 plus this about a half. and then Adam Reese with direct kind of the detection measuring the distance scale with a distance ladder. So this uses a combination of geometric distance anchors, then Cephys to bootstrap out to

so Cepheid measurements of galaxies that hostes it as Type 1A Supernovae, and then you go to cosmological distances, assuming that supernovae is standard caps. So it's quite an elaborate distance ladder, and they get 73 plus or minus 1. So the tension, the discrepancy is 5-sign. Now, the reasons I think that you have run into difficulties is that, you know,

the Cosmobile of Microw background, those results for that model is secure because we have, you know, at, you know, predecessor of signs, and the same. South Pole Telescope with independent measurements of the cosmic microwave background, independently if planet they give the same. So there isn't a problem with the observations of the cosmic microof background. So I think that side is secure. Then what you can do is you can construct an inverse distance ladder. If you have measurements, another geometrical measurement, So from galaxy surveys, you can measure a geometric scale that comes from the oscillations of barons when the universe was highly ionized. That gives you another geometric distance specimen.

And then you can infer from, you know, if you calibrate the B.A. on measurements using the C&B, you can infer a value of the Hubble constant. So that's called an inverse distance later. that gives you about 68 consistent with the cosmic microwave background. It depends on a normalization which tells you

the physical scale of these oscillations. So you can argue that maybe that's wrong and that's most of the so-called solutions of the Hubble Tension of all to that scale. So it's the maximum distance that

sound waves can travel from the beginning of the universe to the time of recombination. So we call it the sound horizon. But independent of any sort of, you know, measurement of the sound horizon, you can use primordial ducythesis

and infer a sound horizon. And that also agrees with, you know, the CMB. So you have a situation you've got to try and come up with a mechanism for the sound horizon, and then you have to fiddle around with nucleus synthesis. And if you don't, then you have this problem. So you can't modify the late-time physics.

You can't modify the early-time physics, and so you're cool. So that's why, from the theoretical point of view, it's really interesting because it's difficult to know how you can solve this problem. So a lot of people have looked at solutions that alter the physics somewhere in the middle. So you can imagine, so this is a class of models called early dark energy. You can imagine having a field. I mean, I discussed this sort of thing within the plant collaboration a long time again. I called it the confusion field because its only purpose in life is to confuse us about the values that the Hubbock said it as a joke.

but people have studied these models and recently I wrote a paper with Vivienne Poulin and Eric Rosenberg where we use an improved analysis as a plank satellite and it really disfavors it. That doesn't work. So I don't see any good solution. So could it be a problem with the Cephy in the last year or so? The, and recent collaborators have got data on maybe five now galaxies observed with James Webb Space Telescope.

And, you know, at, so with James Way, at these, you know, infrared wavelengths, the resolution is so much better than the Hubble Space Telescope, the photometry is much easier. and they find exactly the same answers as they did with the Hubble Space Telescope. So there's no obvious problem with the photobotry. So if they're wrong, then it's a real conspiracy of a number of things that, you know, have evaded, you know, tests. So the bit becomes contrived. I mean, so, you know, I was in Munich giving a series of lectures last summer. And coincidentally, Adam Rees and our colleagues were in Munich, and there was a separate conference on the distance scale, and they called me in and showed

me the new JWST results. I was sort of flattered that they wanted my seal of approval, you know, in some way. And there's any of this stuff, and then they said, well, what do you think? And I said, I mean, it's really impressive. so I'm going to I'm just going to park the Hubble Trench and their reaction was what? You think you're going to park our data?

Yeah. I said, well, you know, we need a theoretical framework to interpret things and I just don't know what to do with it, you know. So we're going to park it. Don't feel too bad about it because, you know, in our standard model of cosmology, we've parked the problem of dark matter, we've parted the problem of dark energy, and we've parked the problem of inflation. So there's just another thing to buy.

you know. So, but it is frustrating. It's, I would, I would really like to know, uh, the answer. If it's, if it's a theory, if, if theory is wrong, then it's wrong in a really bizarre way that our universe mimics Lambda CDR, you know, really exquisite. Uh, though, you know, it's, it's, it's just an uncanny. So very profound, if it is a theoretical explanation, if it's a data issue, then I don't know what sort of data issue it could be. When we look at some of your recent papers, including one of my favorite, to H-0 or not to H-0, and then that investigated whether late-time physics could account for it, the resolve the Hubble Tension, finding that, no, it couldn't.

So let's say you get a letter from God and God tells you to accept what Sir Arthur Eddington, I believe your countryman once said, never trust an experiment until it's been confirmed by a theory. It seems like you in that paper and with your colleagues and students have ruled out at least half of the available parameter space or in a binary sense, but probably in terms of the elapsed time since the universe is history, it's probably 99.9% of parameter space. So what hope is there other than to look at early times? And that's where I want to turn next. Your papers on Axion like Dark Energy.

How could that potentially solve it? And then I'll present you with a couple of my favorite. I just think it's also. Yeah, it really. I should say, George, by the way, this is what I love about you. You're not afraid to propose bold ideas. You're not afraid to mix it up with your colleagues, but you're equally likely to say that you're likely to be wrong. And I think just for my students out there, there's hundreds of thousands of students that listen to this. That's the mark of a good

scientist. Not to say, yes, aha, eureka, I have found it as, you know, as, as, as, as, as, as, as, as Archimedes would say. But no, to say, wow, that's really weird and I'm doing my best here. And I don't know. I don't know are the three most important words for a scientist. But we'll get into education later. It's maybe a consequence of a very long career in which I've been wrong lots of times. Learn from experience.

But there is an important point which is to always maintain a level of modesty because I'm not as clever as the universe. you know. So what I think doesn't really matter. You know, I mean, you know, things could be much stranger.

And that's what's frustrating because I can't imagine, I can't imagine, you know, how this problem can be solved. But you say axions are not likely, even though this is something that people. I mean, it's introducing a new field and it really is. the only purpose of it is to confuse us about the value of the Hubble Cons, because one of the features, it can't be a sort of standard axiom like potential. You have to make it,

you have to adjust the potential so that this component becomes dynamically negligible at the present day. Otherwise, you'd have another, you'd be able to rule it out from late-time measurements. So you have to start playing around with the potential, so it really does just affect the sound horizon. and the models don't work very well anyway.

And the motivation for the project with Vivian and Eric was that if you have a theoretical idea that is, you know, two and a half sigma, it's disfavored at, say, the two and a half sigma level, you don't have to make much of an improvement in the data to turn that into a three and a half sigma level, because you're already on the tail. You should always be on the lookout for theories or things that are nearly ruled out. Because if you find things that are nearly ruled out, you can maybe do something. And, you know, if you're already on the tail, you can do something that just pushes it over the edge. So that's what happens with early dark energy.

It's, you know, it wasn't favoured to begin with. and then you make him, you know, improves the analysis of Planck and it becomes even more strongly disfavored. And that's another thing that really bugs me because, you know, since, you know, Plank collaboration disbanded in 2018. And then I started some projects of trying to squeeze more out of Banked. and everything that I've done on this has just made the data, it brought the data into even closer agreement with the six parameter lambda CDM model. So no sort of anomaly or hint of something that was, you know, looked to be two and a half signet here or whatever.

None of that has got stronger. When I look at the Hubble tension is not really, you know, where the bread is buttered around the Keating household. I'm more interested in much more, you know, kind of primitive and primordial concerns, although it's obviously incredibly interesting. My favorite one is primordial magnetism, a primordial magnetic fields. And I want to segue into that because, you know, when do I have a chance to talk to an eminent expert who's written about all sorts of things?

But the reason I like magnetic fields is because it's the only thing. It's the only thing it doesn't require new physics. We would especially be secure as, you know, having, lectured in the place where Michael Faraday did his work on magnetic fields and the Faraday effect and all sorts of other cool things, to have the, you know, the combination of Lambda CDM with early magnetic fields that themselves could reduce the sound horizon. So first, if you could opine upon that, I like it because it, as I say, it doesn't rely on chameleon fields or evolving dark energy that's not a cosmological constant, which we have no evidence for. So what,

What do you think about this as a, you know, kind of a field? It doesn't seem to get much attention. My good friend, Levin-Pagosian. I mean, we had, in the plant papers, we had, you know, some, you know, some, you know, some analyses that, you know, set constraints on primordial magnetic field. So, so, but there was, there was no evidence for, you know, primordial magnetic fields. problem. I mean, it is an area that, you know, I haven't, I myself, I haven't worked on. And I think primarily it's because, you know, I've had a background in, you know, sort of, in a galaxy formation as well.

And, you know, I used to work on one of those sorts of problems. And the idea that you need, I was never, never brought into the idea that you needed prim prim. primordial magnetic fields to seed the magnetic fields in galaxies. I always thought that the primordial magnetic fields that you would have would be very small anyway.

But you can generate the magnetic fields, you know, spontaneous and then amplify them, you know, through a galactic dynamo. So, so I wasn't, you know, ever did, I never brought into the idea

that you needed primordial magnetic fields. So in terms of another tension, and another reason I sort of favored the, you know, magnetism playing summer all was that there would be potentially a concomitant solution of the Sigma 8 tension. Can you talk about that, which of the two tensions, you know, obviously Hubble gets a lot more attention from its tension. But talk about Sigma 8 and why, again, how, you know, magnetism seems like, you know, it could do two, you know, it could be the peanut butter and chocolate that solves two problems at once. But I'm sensing a little bit of pessimism on your part. Well, I think that the signal at tension will be, we will pretty much know the solution that basically definitively in a few months. How so?

So, okay, so just to explain, I mean, the signal rate tension is that some measurements give, so sigma rate is a parameter that depends on the outstief of matter fluctuation at the present day and the value of the matter density parameter. So gravitational lensing measures a particular combination reasonably accurately. And so this combination of parameters turns out to be low from gravitational lensing. So people have interpreted it as some sort of late-time effects that at late times, the fluctuations have grown less slowly, more slowly than predicted by Lambda C. maybe there's some modification to gravity, something that affects the growth rates and so and so.

That's the tension, okay? So is it a late-time effect? Well, you know, I worried about this because the, so I think it's a good example of where I was motivated by patterns in the data. So is there something wrong with the growth rate, the fluctuations at late times? Well, if we look at some things that I think are uncontroversial, we measure gravitational lensing from the cosmic microwave background, and we measure it really accurately now. And there's no evidence for any change in the gross one. Okay, it's also, I mean, it's also interesting because in modified theories of gravity, you know, photons see a different potential. compared to the matter.

Depending on the type of modification to gravity, whereas in general relativity, they see exactly the same potential. So there's no evidence for anything that departs from general relativity. Photons are doing what they should be doing according to general relativity. So that says,

and now that's sampling things down to Redshift of about two. There's no evidence of any discrepancy there. From Galaxy Redshift service, you can measure the rate of gross fluctuations by looking at the anisotropy of the galaxy distribution in redshift space. You can measure redshift space distortion.

Those measurements also don't conflict with the standard model. There's no evidence of any funny behavior there. So this was suggestive that maybe it's not a late-time effect, but maybe something else. And then if you look at what's different from gravitational lensing, then what you see is that it's sensitive to small-scale structure, and it's sensitive to structure on such small scales

that the rearrangement of matter caused by active galactic nuclei and other energy injection mechanisms associated with structure formation, can rearrange matters. So maybe there's no problem and that it's just the effects of energy injection from structure formation and alternative possibilities

that maybe there's some funny property of the dark matter. But the point is that you're measuring things on different scales. So is it a early time, late time effect or is it a small scale, large scale effect? With my colleague, Alex Amol, we wrote a

a paper where we said, well, we can, here's what you would need to do to the nonlinear spectrum to make it fit. And then it becomes a question of, you know,

disentangling it. Well, since then, there have been some very interesting developments. At lensing, lensing, you know, measured, the lensing of the cosmic microwave background, you can cross-correlate that

with galaxy, redshifts with either galaxy redshift service or with galaxy catalogs and this gives you a sort of handle on tomography. It means that you can test

the gross rate of fluctuations at a lower redshift than the mean redshift of the lensing effect from the CMBU line. Those analyses that have been done just in the last few months

they agree nicely with the standard Lambda CDN Aspology. There are also, just in the last couple of months, two analyses looking at the numbers of which clusters of galaxies. So this is based on Erosita, an x-ray satellite,

where people have looked at Erosita of clusters that are calibrated using gravitational lensing, their masses are calibrated using gravitational lens. And then another

analysis which uses chandra x-ray measurements and again, weak gravitational lensing mass calibrations.

Those agree with the amplitude of the fluctuations expected from the Lambda CDM cosmology. And so

in a matter of months, we'll see the results from the DESE Redshift server, which will improve the measurements of these distortions in redshift measured from the Galaxy distribution.

And I don't know the results, but they should clinch it. Overlapping the redshift range as the lensing is sensitive to. So I'm hopeful that we'll have an answer of whether it's early time late-time physics, you know, and so. And as you said, the tension is not as strong as the Hubble tension.

And so the solutions might not need to be particularly radical. Hey, it's me, your explorer of the universe from an experimental angle. I hope you're enjoying this conversation with George. And I want you to know, I write about my conversations every single week in my Monday magic mailing messages. It's a lot of M's, but it's for good use because I share with you. the most mesmerizing ideas in all of science, technology, engineering, and math, and sometimes I do great giveaways. Like each month I give away a meteorite, a real piece of not dark matter, but ordinary barionic matter from our early solar system. And you can win one too if you go to

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When you want savings, not surprises. It matters where you stay. Hilton, for the stay. Another topic that is obviously near and dear to your heart and my heart as well is inflation. And there's also some richness with controversy there as well. And I'm thinking of a couple of things. One is maybe late time and actually came from the Planck dataset, which was a hint for negative curvature.

I think Melchiori's group and others have looked at this. So what is your take on this, the robustness of this measurement? So I recall it's a very small negative number, negative fraction of a percent, but it's more than a few sigma, so they take it seriously. How seriously do you take it, if at all? You're shaking your head. Not very seriously. As you know, with the microwave background,

you have a geometrical degeneracy. So there's a very strong degeneracy that just from the microwave background measurements alone, the only thing that breaks that degeneracy is the lensing of the cosmic microwave background. You are allowed a large range of curvages. But it's asymmetric, so it extends into positively curved universes. The difficulty that, you know, some people have said that, you know, is 99, percent or whatever it is, some, you know, huge probability that the universe is not spatially flat, exactly spatially flat.

Significant, you know, curvature detected at 99 send level. But the problem with that is that you're very sensitive to, when you do this, you're very sensitive to prior choices. And I mean, I've written about this, that, that, it's really badly motivated to do analyses based on a flat prior. In other good coverage, flat prior at the present day. I mean, choose a flat prior recombination and see what you get. So that's poorly motivated.

So when you do this kind of... And the other thing is that there's been a massive shift over my career in the way you do statistics when I was, you know, it was first coming into the field, the statistical Bible was Kendall Stewart, which was full of, you know, frequentist tests and, you know, student-te tests and all the sort of traditional stuff. And there's been a big shift to Bayesian statistics. So, and, you know, it's not surprising because, you know, if you've got Bayes theorem,

at a big computer you can solve any problem. But the problem is how do you interpret Bayesian statistics and on this, you should not be a fundamentalist basing because priors matter. And they matter when you've got large degeneracies. In the case of early dark energy that we talked about, earlier there's a big degeneracy that you can, you know, these models are that you're compensating for a change,

changes in the Hubble constant by changing the slope of the fluctuation spectrum. So there's that big degeneracy there. And in the case of curvature, you have a geometrical degeneracy that from the CMB alone gives you a large degeneracy direction. So in that situation, you would be sensitive to priors, and numbers like 99% of evidence in favor of curved universes are. strongly, strongly dependent on the prior choices. So in problems like that, do a profile likelihood.

That's the thing that you should do. March down the degeneracy direction and look at how Kise Square is changing. And if you do that, it doesn't change right. So that's why I don't take these things very seriously. The other thing is that when you've got large degeneracies, combine with something that breaks the degeneracy. And this is easy to do, the CMB,

combined with barren acoustic oscillations, with direct measurements of the CMB lensing potential, you break the degeneracy, and then you get exquisite limits. The university is spatially flat to, you know, a decision of, you know, a few parts in 10 to the three. I don't take that. But you referred to the WMAT thing. Yeah. So we're talking the 20th anniversary of your low anomalies. Yes.

This was great. So the WMAP results came out. There was some evidence that there was a lack of correlations on large scales compared to what you'd expect in a dark matter theory of inflationary theory. So when I saw that, I thought, well, maybe you can relate that to some scale. and the obvious scan is curvature. Okay, so I've read a quick paper trying to relate it to the curvature scheme and what this would imply.

And then I followed it up with another paper on the Maxim likelihood measurement, and that convinced me that it wasn't really very significant. However, there are peculiarities, there are so-called anomalies, on large angular scales. They've been examined in great detail. There's a really, really comprehensive paper by Ben Vandal,

from collaborators a few years ago that looked at a range of statistics, Earthenomalies. So this included correlations in the coefficients of multiple decompositions of the large scale distribution on the sky. And the conclusion is that There isn't anything significant.

I mean, there are anomalies, but they're not mind-blowingly significant. They're sort of a two and a half sigma level. So I think that even the most die-hard inflationary theory, you know, looking at the observations would say our universe looks a bit odd on the large scale. But it's not so odd that, you know, that people have said that really challenge theory. It's just odd, you know. But it'd be telling us something interesting.

And, you know, the question is, you know, can, you know, very, very difficult to make progress with something like this. Pivoting back as we come to the top of the hour, the other controversy that arises with inflation is the sort of concomitant expectation or production of the multiverse. I've had on Andre Linday and Paul Steinhart, Neil Turrock. many, many other people talking, debating Will Kinney, pro multiverse, Andrei Linday as well, and then many opponents to it, like Paul Sternhard, as I mentioned. Talk to me about your impression. Is this really the purview of a cosmologist? I always say, you know, kind of jokingly, that, you know, expecting a cosmologist to opine on the origin of the universe is like asking a, you know, zoologist to talk about the origin of life. You know, they're related.

And you might expect them to answer the question more than a zoologist can answer a question about cosmology. But is the origin of the universe, is the origin of time, is the existence of a pre-existing or simultaneously existing universe? Is that part of the project of cosmology that you and I practice? The multiverse, the difficulty with the multiverse is that nobody, we don't have the theoretical, background and machinery to say what happens in each of the multiverse. So we can't put a measure of the multiverse. And that means that you can't predict anything. So the thing that, I mean, the aspect that the poor Steinhart,

Neuturo really dislike is that if you don't, if you cannot assign the measure to the multiverse, then your theories don't lack predictability. And therefore, you know, you don't know what you're doing. That problem is a really significant problem. So, you know, it's not crazy at all to be critical of the multiverse because it raises problems that we don't understand. Now, does that mean that inflation is wrong? and that's where I would

disagree with Paul Steinhart and Neil. I don't think that that means that inflation is wrong. It just means we don't, you know, inflation is a, you know, we don't understand important aspects about inflation. I think with inflation,

Ed Whitten puts it very succinctly that, you know, inflation is, is attractive because for the amount of physics that you put in, you get a lot out and you risk you to get a lot out. So does it mean it's right? Well, we don't know.

Are there problems with the multiverse? Absolutely there are problems. Undeniable problems with the multibus. March 7th, March 17th, rather. And that was a very, very, very important day in my life. Because that was the day 10 years ago, we released the Bicep 2 results. and I think we're coming on a decade of it. I never, you know, we talk, you know, about nuts and bolts and funding and all sorts of requests and stuff that we on the Simon's Observatory Experimentalist team and analysis team make to the external advisory committee that you're a key member of.

But we really never talked about, you know, what was going through your mind when we released these results? And have you tried to portray some of what I thought about. about your impressions of the affair in my book, losing the Nobel Prize. I don't know if I quoted you appropriately, but we were sort of terrified of you and the Planck satellite just on the internals, and we had read a paper, and I mentioned this in the book, by you. I think you're the first author, forecasting in 2009 or 2010, right when Bicep 2 went online at the South Pole,

that you would achieve a level that would able, Plank to detect what we claimed as R.2 at 4 or 5 Sigma. And in the end, I think you recently had a paper about B modes from Plank at Lowell's. We'll talk about that maybe at the very end. But what was going through your mind when we released that and kind of on the inside as a professional competitor? It became very clear, you know, during the early stages of Planck that these forecasts were wildly untimistic. there were systematic effects in Planck that would limit our ability to set tight limits on B modes. I mean, it's sort of mundane stuff, if you like, that the way that the signals, the ballometer signals were converted, you know, from analog signal to a digital signal,

to use systematics in the data that were difficult to disentangle from mother systematics. So, you know,

the polarisation is a differencing measurement trying to measure a very small signal and if you've got fluctuations in your detection baseline,

then, you know, that's a severe problem. There was heroic efforts to remove these systematics and in the end with plank you can set a limit of a tensor to scale a ratio

of about 0.3 or whatever a little bit higher than the bicep detection now when the bicec detection was first and else I mean I was really I was really taken with the shape of the spectrum and that it fitted

climate or gravitational waves. The aptitude was high because we'd already set limits on simple months of inflation and the point two was high compared to the plague results. There was then a flurry of papers, you know, really just quite low-grade papers

explaining, you know, modestly and so, but but then our dust colleagues, we had a telecon, our dust colleagues said, you know, look, that region, it could all be dust. And, you know, this isn't very difficult because, you know, to check with, because, you know, we had 353 gigahertz polarization. And so became very clear that dust was a problem. But 353 was not high enough signal to noise to clinch it.

So that's when we proposed the Bicep plant collaboration so that we could do the cross correlations because then if you do the cross correlations with the bicep data, you prove the signal to noise, and then that clinched it as, you know, dust could explain the entire signal. It was really interesting because because, you know, with the announcement, I thought, this, if it's correct, this is soap, this is, you know, really, really great.

And it was a shame that it didn't pan out. But, you know, that's science. Now, what is the value, the tensor to scale ratio? Who knows? You know, you could struggle for the next 10 years. and not make a discovery. Yeah, we may indeed. But luckily with the Simon's Observatory,

we have many ancillary, and quite frankly, just as interesting science quarries, and you are undoubtedly going to play a key role and making sure we stay on the right track. There's still an incredible amount. One of the things that I like about the Cosmian microwave background is that, yeah, You can make the measurements that on the whole, the interpretation is quite, you know, is simpler than looking at astrophysical object.

So you should milk it for as much as you can, you know. And, you know, you will, you know, with Simons, you'll end up with foreground modeling, confiscated foreground modelling for lensing and, you know, other things that, you know, you have to deal with. to extract the science. But it's still one of the best probes of cosmology, one of the best tests of cosmology that we have. There's a lot of information to be gained. Absolutely. So, George, I have a tradition on this podcast that I always ask one kind of metaphysical or existential question

or more, sometimes inspired by Sir Arthur C. Clark, who gave us the name of this podcast by saying the only way of determining the limits of the possible is to transcend those limits and go into the impossible. But instead, I'm going to use one of his other favorite quotes, which is any sufficiently advanced technology, is indistinguishable from magic. And I want to get your reaction to what Richard Feynman called the cataclysm question. And he would ask scientists to tell him, what would be the most important or interesting or most power-packed phrase or knowledge that human beings in our whole species history have gleaned about the universe such that we could really say that we accomplish something magical. I want to ask you, if you were to make

sort of a time capsule, a billboard for planet Earth, what would you say is the most important, interesting, fascinating discovery, whether it be in science or in life, anything you want? What would be something you'd put on a time capsule to last for all eternity? I think that the most miraculous thing from my perspective, and it's incredible that we have observational evidence to support it, is that the entire observable universe, you know, everything that we see, you know, with our big telescopes and everything, our entire observable universe, has, how we see, our entire observable universe, has, how. has a quantum origin, you know, that quantum mechanics have affected, you know, the very large escape. And that is, you know, that's an astonishing. I find this here is astonishing. Well, no.

If a civilization hasn't figured that out, then that's a good thing to know. George, this has been such a delight, professor at University of Cambridge, first director of the Cavilly Institute for Cosmology. leader of the plank science team, just an all-around mentor and friend of the cosmos. I want to thank you so much for staying up late over there in the UK. I really appreciate it. I know you've had a long day. And I just want to say I appreciate so much your work on behalf of getting things right. We can't afford to make another mistake in this field.

And it's absolutely crucial that you and all the good-natured and good-hearted and good-intentioned people will hold the experimentalist's feet to the fire, but also accept criticism. from us when we do mount it because I think only in that kind of partnership can we achieve a conciliance that allows us to really solve the most fascinating mysteries I think that human brains can contemplate which is how did our universe get to be the way it is thank you very much yama va resort and casino at san manuel is california's number one entertainment destination for today's superstars catch the Jonas brothers return to the yama va theater stage on april 30th the powerful vocals of demi lavato on may 17th and the signature southern country rock

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