Into the Impossible With Brian Keating - Exploring the Mysteries of the Expanding Universe with Adam Riess

Episode Date: July 4, 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! What is the Hubble tension? How does it challenge our current understanding of the universe? Why do different methods of measuring the universe’s expansion yield different results? And does our cosmological model need a complete overhaul?  I had the honor of discussing all this and more with none other than Adam Riess. Riess is a renowned astrophysicist who won the Nobel Prize in Physics for his groundbreaking research on the expansion of the universe. Through extensive measurements and collaborations with other scientists, Riess discovered an intriguing tension in the size of the expansion of the universe, which has been steadily increasing over the last decade. These results, which have reached a significant level of more than 5 sigma, have revealed an unexpected phenomenon: the universe's expansion rate seems to vary depending on whether we start from the beginning shortly after the Big Bang or from the present.  In this episode of Into the Impossible, Riess and I explore the challenges of measuring distances in the universe, the possible role of dark energy, and how this challenges the concept of the cosmological principle.   Tune in! Key Takeaways: 00:00 Intro 01:03 Proving Einstein wrong 06:38 Struggling with experiment results 08:57 What is the Hubble tension?  18:45 Can curiosity be cultivated and sustained?  24:05 Measuring distances in the universe using parallax 32:54 The Hubble tension persists  38:56 Revising the cosmological principle  42:47 Gravitational lensing  51:03 Surprising JWST findings  54:33 Theoretical implications of the Hubble Tension measurements 56:47 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 😀 ! ➡️ 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

These are the best tools that we have. And when we measure it, we get an answer that's somewhat different. And the size of this tension or significance of the difference has grown over 10 years pretty steadily so that we've reached more than 5 sigma. And through duplication of measurements other people have done with other techniques, what has shown up is a funny dichotomy that how fast the universe is expanding seems to depend. on whether you start from the beginning shortly after the Big Bang or whether you start from the present. And, you know, a story shouldn't depend on which end of the story you started. That's how it looks to us. And so that's why a lot of people are suspecting maybe it's the cosmological model itself, the story we tell ourselves to connect the beginning and end.

Any sufficiently advanced technology is indistinguishable from magic. Open the pod bay doors, hell. Welcome everybody to another exciting episode of The Into the Impossible podcast, featuring a friend, an inspiration, a local hero and a global cosmic hero, one of the few people on Earth who proved Einstein wrong and demonstrated that he actually made a blunder by calling his blunder a blunder. We'll get into that. It's my friend Adam Reese, Professor, Bloomberg professor at the John

Hopkins University, which I understand is not a plural, but it's a singular name Jones. And Adam is the Bloomberg professor. He's also known for third place in the Charlie Town Symposium in 2005, which we can get into some information there. There's a person that won that who was supposed to go on to great things in life, including potentially winning a Nobel Prize. We won't speak about him. That's me.

We will speak about the person that did eventually achieve this great. stupendous feat. And that's Adam Reese, of course. So Adam, as you know, when we have guests on the podcast that have written books, we always have a segment called judging books by their covers. In this case, we don't have a book by you. I'm hoping to be your agent and get residuals. But we have a paper that's signed by you. And it is called, well, I'll let you go through it. But we always ask, what is the genesis of the title? How did you come up with it? What was that process like and usually the authors come on say my publicist or publisher told me how to do it this way yeah but in this case i assume you had some input on it and uh and you'll have uh something to say

about it as well as the cover illustration which isn't really here uh but we'll talk about yeah let's talk about figure one okay so adam reese judged the paper by its cover and its title and its and its artwork please uh okay well you know we decided to call this one observational evidence from supernovae for an accelerating universe and a cosmodule constant. And this was a case where we decided to say the whole story in the title in case you never got past the title or even read the abstract. But no, this was our discovery paper. We had observed distant type 1a supernovae. We were using them as tools for measuring distances, also for measuring redshift. So together the two measure the expansion rate of the universe.

we had measured nearby ones, which told us the expansion rate today. We were looking at distant ones to tell us the expansion rate in the past. We were testing the cosmological expectation that the expansion since the Big Bang was slowing down. And instead, we saw that it was speeding up, that it was accelerating. And so that's why it's the first statement. And why is that, to be totally honest, we don't really know for sure. This is generally given the name dark energy, but a specific kind of dark energy, the one with the greatest history, and also the one that's the simplest and sort of mathematically is Einstein's cosmological constant. And so in that title, we said, we see the universe accelerating.

It kind of looks like a cosmological constant. And we'll get in some of the details of what a cosmological constant is in just a bit. But suffice it to say, as I mentioned, that good old Albert here, he, had originally put in a cosmological constant because as we teach our students, he knew that he was made of matter and anything that has a universe that has matter can either contract or expand, but it can't be static. And back then, I used to make fun of them, say, oh, you know, how could he put this in? It's so stupid. But really, back in 1915, 1917, the universe was the Milky Way, right? Correct. So what he did was not that unexpected, even until 1929 when he recanted, so to speak,

which was after the night after he won his double prize himself in 1922. Do you know why he received it in 22? He won the 21 Nobel Prize and he received it in 22. I remember it took him a while to get the message and it took him a while to get there. Yeah. But I also know there was a lot of controversy about giving him the Nobel Prize, even though, you know, he should have won five of them. Exactly.

Right. But going back to his motivation, I mean, the lore is that he had asked a strong of the day, what's the universe, which, as you said, is the Milky Way, what's it doing? And they said, it isn't moving all that much. You know, the velocities of stars was relatively small. And so he took that to mean the universe was static, more or less. So that was a kind of observational constraint. You know, the story could have been quite different if, you know, he had asked them, I don't know, 10 years later and learned that actually the galaxies have red shifts and things are moving apart.

So, you know, he got bad information. And so he kind of made his theory fit that. Yeah. And it's really hard to get back in the mindset of somebody, first of all, in the early 90s before you and your teammate and your competitors. And we'll get into that in some detail, I hope. And, you know, that made sense. And actually, even Hubble's early data were, you know, horrendously noisy.

And he was relying on Henrietta Levitt's data and Vesto Sly. I love the name Vesto. I was going to name one of my kids of Vesto. You know, I named it's not on the top list these days. It's not. Yeah, it hasn't made the list at a while. I get teased a bit at school. It sounds like VESPA.

I don't know. It could be a guy out of a cool thing. But nowadays, you know, we talk about the cosmological constant. We're even trying to measure. Is it varying? Is it dark energy or is it a constant? And we just accept that there's some form of repulsive anti-gravitational force causing galaxies to expand.

But what was it like as an early? graduate student in the 90s, working at Harvard, Bob Kirchner, you know, friend of the show and so forth. Brian Schmidt, past guest on the show. What was it like when you were, you know, dealing with this milieu? You had this expectation. The universe was dominated by matter. It's all we knew about. But it didn't seem like we lived in an open universe. And what was it like to operate in that framework and have the realization that there's something really funny going on in the cosmos? Right. Well, you know, I would like to tell you, glorious things about deep thoughts that, you know, we had or that I had at the time.

But, you know, to be honest, you're doing a measurement and experiment that's hard that people haven't done before. And you just want to get the right answer. You know, that's all you're just kind of obsessed with getting it right and not screwing it up. And so the reality is when we saw that result, my thought was, oh, we screwed this up, you know, and then you have to go through a lot of checks. And yet, you know, you've also learned to avoid confirmation bias, which means that, you know, you don't want to just assume you made a mistake and the first time you see anything sort of go, yeah, okay, that's got to be a mistake or something you really need to get it right. And so, you know, we went through a process of checking things. You know, anytime you make a

measurement, there are certain aspects of the experiment that you're a little uncomfortable with. You think, oh, that's the first thing I'm going to go take a look at. So, you know, there was this obscure thing, astronomers called K corrections, which is really just a fancy term for relativistic corrections, you know, the fact that we're looking at things with larger red shifts. And so redshift has many effects. It, or I should say expansion has many effects. It causes redshift. It causes time dilation. It changes the energy density of photons that you're looking at. There's, I think, five terms altogether. And you've got to get them all right. So usually it's like, oh, do we leave out one of the one plus D terms or did we stick in one too many? And so, you know, you go back

over the whole process when you get an answer that you don't expect. It's peak pollination season, and my business is scaling fast. To keep the nectar flowing, I need a phone plan with top priority data speeds. That's why I chose GoogleFi Wireless. My connections stay strong even when the hive is buzzing. Plus, unlimited plans started $35 a month. Now, that's a deal that doesn't stay. Explore GoogleFi Wireless plans today.

Plus taxes and government fees, Google FiWireless is not subject to data traffic deprioritization during times of high network usage. Now we have that similar situation where we see strange things, although I would classify your discovery as I argue in my first book as a serendipitous discovery because you were looking for the opposite. So that is sort of self-insulating against confirmation bias. Like Penzies and Wilson we were talking about before we start recording, they weren't looking for the CMB. In fact, you know, they were trying to get rid of some noise with the observations of the first telecommunication satellite. So they would have preferred probably originally that it wasn't there in the first place. Now we're in the situation where astronomers are and physicists are trying to explain the so-called Hubble tension. And, you know, I can't resist.

I had on, you know, this famous theory of consciousness individual named David Chalmers at NYU, who's known for what's called the hard problem of consciousness, which is, you know, can you really identify and define what the conscious qualia experiences of another? I had him on. I was like, look, and he's from Australia. So I said, look, if I had on, you know, someone from Sweden and I don't, if I have an ABBA, and I don't ask them to play, you know, dancing queen or something like it. Or if I had an ACDC, because he's Australian. I said, got to play back. Come on, you got to play. So can you please describe it?

This is like you're like you're playing the role of ABBA here, ACDC. You know, four-letter acrony. Yeah, I'll go with ACDC. Okay, cool. Tell me, what is the Hubble tension? And could we be in sort of the opposite domain or look, or everyone's proposing solutions? unlike the purity of your discovery and your colleagues. Right.

Well, so the Hubble tension, let me just back up. The Hubble constant is the rate at which the universe expands today. And if we understand the universe very well, we should be able to translate the rate at which the universe expands at any time in the universe to any other time. That's sort of, in a way, the idea of physics. You know, you throw a ball in the air. And, you know, if you know how fast the ball is traveling at some point, you'll know how fast the ball is traveling at all. points. So observations of the cosmic microwave background, which of course you work on, give us very detailed picture of the universe shortly after the Big Bang. But, you know, that was a long time ago.

You know, some, you know, more than 13 billion years ago told us very specifically what the universe looked like then. And so using the physics of the universe, we should be able to translate that information to how fast the universe is expanding today. I would call this a prediction. But it's a very precise prediction. And so a powerful, you know, I've been calling it an end-to-end test of our understanding of the universe is to measure how fast the universe is expanding, using the best tools that we have. And so for, you know, the last 15 years, we've been doing that, making more and more precise measurements using the Hubble Space Telescope, using Gaia, European Space Agency mission measuring parallaxes, now using the James Webb Space Telescope. So these are, you know, these are the

best tools that we have. And when we measure it, we get an answer that's somewhat different. And the size of this tension or significance of the difference has grown over 10 years pretty steadily so that we've reached more than five sigma difference, five times the size of the mutual error bars. And so that's usually the point in time where physicists, scientists, are willing to check off being unlucky as a possible answer. And so we, I think, have more or less checked that off. And through duplication of measurements, other people have done with other techniques, what has shown up is a funny dichotomy that how fast the universe is expanding seems to depend

on whether you start from the beginning shortly after the Big Bang or whether you start from the present. And, you know, a story shouldn't depend on which end of the story you started. But that's how it looks to us. And so that's why a lot of people are suspecting maybe it's the cosmological model itself, the story we tell ourselves to connect the beginning and end. So, of course, the Hubble constant is the current time evaluation of the time derivative of the scale factor divided by, you know, the scale factor itself evaluated today.

I always tell my students, you know, the Hubble parameter is the second most important number in all of cosmology. If you had just one choice, though, I'd say take A of T, take the scale factor from which you can get everything either kinematically or otherwise. But I can't resist because you're here. And because my students, you know, when I asked them, well, like, the first derivative of the scale factor is the Hubble constant, is proportional to Hubble parameter. The second derivative is the Q-0 deceleration parameter, which you thought would be decelerating

back in the 90s. It's even named the deceleration parameter. The expectation is built right into the name. And maybe it's true because the very early times it was decided. But then the third derivative, I asked my students, I was like, I can't remember. And they said, jerk, jerk. I was like, how dare you? How dare you call me a jerk?

What could we learn, if anything, from the third derivative? I was thinking, you can write down the third derivative in Newtonian mechanics of a particle just moving around and maybe it has a rate of change of acceleration. But what physically would it correspond to? Would it lead to another parameter? Could it tell us about a resolution of the Hubble tension? Could it tell us about dark energy in some way? Or what could it tell us if we could measure?

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It really helps. Thanks a lot. Now back to the show. I mean, so in principle, it's the transition. that we see between the universe decelerating and accelerating. You know, it's very surprising that there is a transition that we can witness in our, you know, recent cosmic history. I mean, it's very hard to understand because, you know, if it's a cosmological constant dark energy,

the universe will just continue this way for trillions of years. So the transition was quite recent. This is called the why now problem. But going back to the cosmic jerk, you know, it's possible different conceptualizations. of what dark energy could be, could give you different values for the jerk. The cosmological constant tells us that it should be one in kind of dimensionless units. So I think it's another one of these fundamental tests that you need to do. Anytime you have a theory that you're not totally confident in, maybe it's phenomenological, if it tells you something you should see, you should go

look at that. You know, you should measure it as best as you can. And so, you know, I would just put this on that list of things that, you know, you should check. There could be a surprise. This is, you know, how we test theories. Did it ever, you and I were talking over dinner last night about, you know, the different types of scientists. You know, some are more curious. Some treat what we do as cosmologists, you know, work a day. You know, they packed their lunch bucket every day and come to work and so forth. But others think contemplate the deepest possible topics and concepts in all of science. You know, I pointed out to my students on the first day of cosmology. If you go to Wikipedia and you type in science, the first image that comes up is a

picture from the WMAP team of the famous evolution of the universe is seen from some God's Eye perspective, if you will. So that means that it's sort of paradigmatic. And a huge swath of the phase space of the universe's history is that afflicted and affected by dark energy. Do you ever stop and think about it? I know we're kind of, you're at MIT grad. You're at MIT grad you guys are you know very very serious but you ever think what are the implications of this i mean as you said trillions of years of evolution why here why now um does it ever overwhelm you just as a human being does it ever like affect you that wow i'm in the same kind of category of people that first knew some fundamental truth about the universe and has it affected you just as a

human being as a parent right etc um i feel like the awe that i get thinking about the universe is very closely connected to the same awe I felt as a kid just looking up into the sky, you know, just looking up at the stars and the blackness and thinking about, you know, how far away things are. And, you know, my parents telling me things that you see are millions of light years away. That means that the light is reaching from millions of years ago. I remember my dad telling me, you know, some of those stars might not even be there anymore that you're seeing. And I was just trying to picture, what does that mean? Like there's some beam of light. It's headed to me and it doesn't have a back end to it anymore.

That's so crazy. And, you know, so I would say the awe that I feel is the same awe that other people experience who have really looked up at space and have had that feeling. And I'll admit, there are people who don't look up, who are, you know, not so fascinated by that. This is, I sort of divide the world to some people are curious and some people are not curious. You can almost divide people up. And the people who are not curious, it's hard to describe to them curiosity. and the people who are curious experience awe like that, you know, on a fairly regular basis.

And so, you know, I just consider myself lucky that I get to combine the work that I do with that curious awe feeling. So a lot of times we kind of devolve on this podcast into, you know, religious or theological topics. We're not going to get too religious or theological. But there's a series of essays written by Rabbi Jonathan Sachs, who was the chief rabbi of the British Commonwealth until he died sadly a couple years ago. too early and he used to talk about so-called peak experiences which is a concept from

psychology that when you have when you see the Grand Canyon when you see a sunset when you see this or yeah yeah people have awe and they want to have some source of gratitude to displace that feeling of all towards or project towards a source of gratitude obviously for a rabbi he's talking about God and some almighty power it could be nature it could be whatever you like but humans love to have some sort of prima facie mover that that causes them to experience the feeling of gratitude. I believe that as scientists, we become inured to such feelings because we witness it every day when you start thinking about, well, if one of these parameters was changed by a tiny little bit, we wouldn't be here wondering,

why does it have the value that it has? I wonder, you know, is there any way that you can cultivate, you know, you have children, I have children? Can we cultivate the maintenance, not just the insipient, the original curiosity all kids have, right? But how do you sustain it? Because you're right like some of my colleagues in this very building I won't say who you know I'll say like I'll have them over for dinner or whatever I'll look at a constellation and I'll say what do you what do you make of that constellation I don't know what that is right and I always joke like oh yeah if you study geography I wouldn't expect you to know what Mexico is you know it's just like it's just your freaking job you're astro namer right but but tell me is there a way to to you know to inculcate but also to maintain sustain or is it really innate in the human being you know individual I mean I think you know any time you spend a lot of time looking at one thing, even if it was something that gave you awe, you know, even if you're the, you know, tour guide of the Grand Canyon, you know, at some point, you know, you get used to it a little bit so that you're not like each day like, oh my God,

look at that. That's true. I have to, sorry to interrupt you, but every so often I take one of my kids, you know, I pretend I'm a good dad. I take them on a field trip. And there was a field trip about three or four years ago before COVID at SeaWorld here in lovely San Diego. Come and visit. Lovely downtown San Diego.

You'll get a commission. You get a free sign copy of that. And I got there 15 minutes early. I'm a good dad. And I was a chaperone. And there's a huge roller coaster there. I forget the name of it. Stuart,

I don't know if you know the name of it. But let me know what it's called the lightning or whatever. So there's some huge roller coaster. And there's a guy whose job it is to go on the roller coaster by himself every morning and make sure he's not going to die. And I always bring my telescopes and binoculars wherever I go, as I'm sure you do. And I, like, zoomed in on him. And the guy was, like, a stoic. He was, like, almost like, angry.

He was, like, totally oblivious to it. So you're right. Yeah, the chore guy of the grand cat, it's a great analogy. And, you know, I would say in my example, in particular, you know, I've been looking at images from the Hubble Space Telescope for about 20 years. Yeah, right. And I know conceptually, intellectually, that they are fantastic. But I am so used to what there should look like that occasionally I'll get one. and I'll be like, that one's a little out of focus, I think.

That one's not so sharp. And so I got to experience awe all over again this past year when we launched the James Webb Space Telescope. And I'm now looking at the same things that I've studied, stared at, whatever, with Hubble. And along comes James Webb and awe comes right back to me in that experience. I'm now looking at images from James Webb Space Telescope. And I have double awe in that, you know, I was really skeptical that this thing was going to work. And so it's like, you mean that thing actually worked?

And you mean this is, I can actually see like this? And so it's just spectacular. Wow. So getting those experiences. All it requires is a new $10 billion telescope every 20 years. We're a bigger Grand King in and we'll all be right back. I've heard that the Mariner trench on Mars is quite nice. So let's talk about your web paper.

I read it earlier today. And I'm, you know, I can really say because I'm a cosmologist. So what the hell do I know about Sepheid variables? But I was really interested to read this paper. First of all, you're an excellent writer. You know that. That's why I want to be and get the royalties and residuals from your upcoming books in perpetuity. Stay tuned for that announcement next time, Adam is in town.

Just to be clear, my papers are free. The telescopes are taxpayers' work, and we don't. That's right. This is free, but the signed one, that'll cost you. And I should mention also that you're here to deliver the DASHN lecture, which is a prize lecture that we offer to the most renowned physicist and cosmologists around the world and astronomers and you follow in a grand tradition. Barry Barish came a few years back and we've had Andrea Gazz and many other,

you know, luminaries, both astronomical and otherwise. But I read this paper and with one of your students from just this year, initial observations, Cepheid variables. And what was interesting and fascinating to me is you were basically using it, if I'm not wrong, to compare measurements made from a supernova that's like your father's light from a star that may not appear. It was from a supernova that popped off in. in the year 2012.

Talk about that. What kind of supernova is it? What is that? And how do you use something that's gone now? How could web observe something that's not here? Right, right, right. So, you know, going back to the Greeks, the Greeks first taught us about triangles,

which are very useful. And they taught us how to measure parallax, which is something we do naturally with our eyes, which is to build a triangle in space, a virtual triangle. And if you can get to get a view from two different spots on the triangle, right? You can measure the angle through which a distant object moves, and that completes the triangle. That angle is the enclosed angle. If you can measure what we call the baseline, the separation between your two points of view, then basic trigonometry tells you the

length of that triangle, tells you the distance. And so in an ideal world, we would go out and we would look at everything with using parallax. And in our case, parallax, we obtained by waiting six months for the Earth to move from one side of its orbit to the other. That makes our triangle. The problem is, unfortunately, that things are really far away in the universe. They're really shockingly far away. In fact, if I could just say, this is one of the main reasons in the beginning that the Greeks disputed the idea that the Earth moved around the sun was because they reasoned if that were the case, then as they looked out at distant things like stars, you know, what we see as constellations would change their shape over the course of the year

because, you know, we would move and, you know, and so they couldn't see any what we would call parallax. And so they said, therefore, the Earth is not moving. And so what they just couldn't imagine was just how far away things are. There was parallax. It was just too small to see. And so over the years, we've gotten much better at measuring parallax, primarily with space missions. But even with the greatest space mission, which right now is Gaia, European Space Agency mission, we cannot measure parallax outside the Milky Way. Okay. So if we want to measure distances even longer range, we have to measure the parallaxes of certain kinds of stars in the Milky Way whose characteristics allow us to recognize them in other galaxies so that when we see one,

we could say, oh, that's just like this star nearby that I measured the parallax for. It's just far away. Its brightness will tell me how far away it is. And so there's a certain class of star called a Cepheid variable that has been our gold standard of measuring distances to galaxies since Henrietta Swan Levitt first recognized them in the small magillanic cloud more than a hundred years ago. So this is, you know, we don't get the invention of new kinds of stars all the time, so we sort of, you know, in many cases, we use what was known just with better technology. And so the wonderful thing about these Cepheid variables is, first of all,

they're super giant stars, not just regular stars. They are among the most luminous stars that exist. And so that means that not only do you have a standard candle, but your standard candle is a lighthouse. It's really powerful. So we can measure really long-range distances. And the other thing that makes them very handy is they vary in their brightness. Now, that might sound annoying, like, oh, you told me you want a standard candle. You want a variable candle? Well, no, their mean, the average brightness they have is the standard candle.

But the fact that they vary and the period that their variation occurs over scales with the mass. or luminosity of the star so that by measuring the period, we can actually tell just how luminous that standard candle is. So it customizes or standardizes the measurement. And so we find with Cepheid variables, we can measure distances with one star that are good to just like 3%. And so now what we do is we use the Hubble Space Telescope to measure the distance to galaxies with Cepheid variables,

but we pick special galaxies. We pick ones that recently hosted a Type 1A super, supernova. And the reason is because sepheid variables will only carry you so far, tens of megaparsecs. Type 1a supernovae, which are Chandrae-Car mass white dwarfs, are much more luminous than sephiate variables. They reach 5 billion solar luminosities. And so with powerful telescopes, we can see them all the way out to Redshift 2, maybe even beyond. And so this forms what we call the cosmic distance ladder, the ability to measure the parallax to a kind of a star to measure its luminosity, see that star in a galaxy that hosted a type 1a supernova to calibrate it, and then see type 1a supernovae about as far as you need to. And so we use this to gauge the expansion rate of the universe.

And how well do we have to know? I'm, you know, taught this, obviously, you know, only a fraction as well as you could convey. But, you know, it occurred to me that, well, the sephiads are, you know, it's a nuclear power plant in space. And we know very little about our own sun and how much could individual intrinsic variations, which for the cognizante, systematic variations in a sephiate versus systematic variations in white dwarf stars or in these type 1a supernovae where, you know, is there any dependence on the companion to the white dwarf? So first of all, white dwarf is this weird material called degenerate matter, which when you add more to, you. it, it gets smaller, which is kind of strange, right? It's nuclear matter. Is the end point of what our sun will get to?

I always forget it. It won't reach the Changer Saker Mass. No, not the Chandra Sanger Sanger Sanger K, but will it be a white dwarf? It will be a white dwarf. Which is basically a carbon. It's a pure diamond, basically, right? But it's not undergoing thermonuclear fusion anymore, so it's just like a junk of this material. So is it possible that, you know, we could explain some of the Hubble tension for nuclear physics side?

Assume you're perfect. Everything you do is perfect. But because we not understand either the sepheed, you know, intrinsic properties of the nuclear reactions going on a sepheed or in the companion to a white dwarf. Are there opportunities to explain the Hubble tension? Right. So observational cosmology, sort of the way, at least I practice it, is based on empirical calibration of these tools. So we start out with theory and we say, oh, type 1A supernova, Chander Seikar mass explosion. Okay, that should be a pretty good standard.

channel, let me start there. Or Cepheid variable, okay, we understand pulsations. We understand the opacity mechanism that drives this. We understand that this ought to be a good standard candle. Let me start there. And then we develop what we call training sets, which are basically large samples where we know the answer, where we know what they should look like. So, for example, for Cepheid variables, you might look at a galaxy that has many hundreds of them. And now you know they're effectively all at the same distance from us. So now you look for empirical characteristics that might change or correlate with their indicating that that galaxy is a little too far, a little too close. And so you train your measurements to sort of account for those.

And so we've done that with type 1A supernovae. That was something I worked on in my thesis. It turns out the light curve shape of the type 1A supernova tells you whether it's a little more luminous or less luminous. The color tells you whether it's been affected by dust or not. you correct for that. The same thing with Cepheid variables. We look at many of them in a galaxy and we correlate the metallicity, the chemical abundance of the Cepheid variable with its luminosity. We calibrate that out. We make our measurements in the near infrared to avoid the effects of dust. So there's no step of sort of theoretical input where we would say, oh, if some process in the

star convection or conduction is occurring differently than we thought, that isn't actually what we do, we do this empirically, but most importantly, it's purely differentially. So we're always comparing, as I said, we're starting out with parallax. That's where the distance knowledge comes in. That's the geometry. Stable-based, correct. And then everything after that is ensuring that the object that you're measuring at one location where you measure parallax is the same as the object you're measuring far away. And so you measure everything you can about it. If you can explain all of the dispersion, the scatter as understandable experimental errors. And if there's nothing left over, then you have a lot of confidence there as well. And so that's, you know, that's more or less the

process. And at some point, at the end of the day, we have to rely on something we call the cosmological principle, which more or less says that we are not in a special place in the universe. There are no special places. And so once I've made measurements of these properties, there's no reason a supernova or a sephiate variable should be different than another one just because it's in a different place in space, right? Because if we couldn't assume that, we'd have to sort of give up on doing all experiments. Instead, we say, we'll assume that. And then if everything is crazy and nothing makes sense, we may revisit that. But, you know, it's worked pretty well so far.

So in this paper in the Appjah, in 2023, with your student, you talk about this effect that you call like biasing bright. What does that refer to? Is the Hubble bias dim compared to the web? First of all, you're using a specific package of instrumentation on the web that's different from the Hubble in a far different wavelength regime. So what does it mean that this bias price? Should we trust you at all? Right, right. You have biases.

So, you know, in 1998, when we saw that the universe was accelerating, right? It's a chain of measurements, but the new measurement, the thing that, you know, hadn't been done before was looking at distant supernovae. and they were fainter than you would have expected if the universe wasn't accelerating. So in those days, we thought, is there a reason supernovae could be fainter? You know, you think in the direction of what seems surprising. In the present case, we look at the Hubble tension, and one way to look at it is to say, oh, the sephiids look brighter in galaxies that host type 1A supernovae than I would have expected if there wasn't this Hubble tension.

So is there a way I can understand that they are brighter than there? they really are, that they just look brighter, okay? And so we look for that with the James Webb Space Telescope because James Webb has such a better resolution that, you know, maybe it could have shown us if there was something else kind of snuggled up to the Cepheid variable that was adding light and biasing it bright.

And so with the great resolution of the James Webb Space Telescope, and I'm gonna talk more about this in my talk today, we have reached the limit where we can really see down to the background where there's nothing else around. And so far, the Cepheid variables don't look any different than they look like with the Hubble Space Telescope. Now we're using a much more powerful telescope, much greater sensitivity. And to some people, this might seem boring, like, oh, wow, you do a measurement and then you go out into another telescope and you just do it again. And it's like, yeah, that's what we do.

Because they have very different systematics. Yeah, they have very different systematics. It's hard to tell a story that the, you know, the effect wouldn't go away. you looked at with a telescope with a better resolution or greater sensitivity or a different wavelength or things like that. So, you know, the real test of experimental result is, you know, it doesn't matter who's looking at it with which telescope or what. It's a fundamental truth. It's on the sky. And so so far, you know, the Hubble tension seems to be passing that test. So it's a persisting, which is, which is, you know, on one hand, it's disappointing because you don't have a resolution, but on the other hand, it's really inspiring because maybe you'll be

the person out there watching this that can add to our knowledge and maybe resolve it or maybe discover, maybe there's something we don't understand intrinsically about gravity, about C-Saintime, about Lorenz and variants, all sorts of things. And it's important, I think, to point out to people, you know, when cosmologists say, oh, we have a model of the universe, oh, we understand the universe. You know, you have to understand that our, what we call model, really is a description of the universe rather than maybe a deep physical understanding of. And so, you know, we have dark energy.

We don't understand the nature of that. yet. We have dark matter. You know, it's, we think it's a particle. We don't know the properties of the particle. We don't know if it has collisions, if it decays, if it's stable, if it interacts. And so we take some very vanilla guesses about that. And so when we see tensions, really all we're saying is we see some measurement that doesn't match the most vanilla guess for our understanding of the universe. And so that might simply mean that there's a wrinkle to our understanding of the universe that something is not totally vanilla, it's pistachio or something. And so, you know, it's, sometimes I think people get the idea like we're upset or disturbed,

everything should fit and we got to, you know, get a hammer and nail down this nail and get everything to stick. And I would say just the opposite. I would say, you know, tensions are our opportunities. You know, the story of science always is you have a paradigm, you have a model, you know, most models are useful, but they're not correct. And so you use the, you use the the model as a tool to make predictions, and then eventually when your measurements get good enough, you break the model because it's not good enough for that measurement, and then you learn something. So, you know, at worst, I would say we're going through that standard process that is usually very enlightening.

Yeah, it's like when they turn on the large Hadron Collider, they first calibrate and they discover all the previous 70 Nobel Prizes. Speaking of Nobel Prize, you were kind enough to loan me your Nobel Prize. Thank you so much for doing that. I'm never bringing it. Don't eat that. I don't eat that. I remember the day that you won it because I was giving a colloquium of the East Coast

at my alma mater at Brown University. And I remember reading in the newspaper a comment from your momata, your thesis advisor, Bob Kirchner. And I remember he was asked, what's the strongest force in the universe? It's not gravity. It's jealousy. I asked Brian Schmidt this. What did he mean? What was he talking about this?

What do you think, I've never asked him. I should ask Bob, but I haven't. He's been busy with his telescope projects and with the Gordon Moore Foundation. Why do you think he meant by that statement? Well, so I remember when he said that. And to be very clear, actually said it when we were still doing that work. It wasn't at the time of the Nobel Prize. It was actually at the time when there were two teams that were competing to make these measurements.

It was in a New York Times article. Yes. And in the late 1990s. And, you know, what he meant in some ways is there's a history in not just science, but in all areas of life, I think, for there to be competition. Competition can sometimes drive excellence. It can also drive, I think you've written about in your book. It can drive people to maybe even make mistakes. But whichever it drives, I guess you can't ignore the fact that it is a powerful force in people.

Yeah. And it does animate. And it could be used, you know, in Judaism, we have this concept of the Yatesur-Hara, the Yateshar Tov, you know, the thing that makes you do good, your good inclination. In Buddhist tradition, there's the Yang and the Yang, and they have different elements of each one in a synergistic fashion. You mentioned the cosmological principle, and I can't resist because, you know, how often do we get together in person? It's been four years since we just were in person, let alone we do a podcast again. But there have been claims that maybe the cosmological principle needs a revision. Maybe it's wrong. There's a five-sigma tension, according to Subir Sarkar, who I mentioned in my book, he wasn't super happy with the way I referred to him, but there's no offense.

Subir, I hope you're watching. I hope you'll come on the podcast at some point. But he is claimed, among other things, not only is the cosmological, you know, principle in need of revision or perhaps wrong, but that dark energy is certainly not the way the consensus has put it, that there is, we don't understand dark energy, is, I think the claim. that he's made. And he's also made claims about, you know, inflation and other things. So, you know, he has, but he's an eminent scientist. He's head of the theoretical physics division, I think, at Oxford. What do you make of these claims, not him specifically, obviously? The claims about the cosmological principle. Yeah, but the cosmological principle might need revision based on the asymmetry of different radio sources versus the CNB dipole and so. I mean, I could tell you the evidence or the data where people have claimed that there's anisotropy of objects in space.

I found not convincing. I'm particularly familiar with supernovae. And so I don't think there is any good evidence, at least not strong evidence, that space is antisotropic. And so that's important in that I don't see the evidence for any violation of the cosmological principle. You know, having said that, I mean, it's something you always have to keep in the back of your mind because, you know, it's not a principle handed, you know, to us on a silver plate that says first start with this. But, you know, when you think about what it means to get rid of the cosmological principle, you almost have to go back to the beginning of like, can we do experiments? Can we look out in space and infer things?

You know, when ancients first looked up at the stars, right? They had to figure out, are those just holes in the firmament through which light passes? Are they real physical objects, right? And so they did experiments. They looked at stars, and over time they noticed, gee, they collect together. That's what would happen if there was gravity. And then they observed some, hey, they're moving around each other. Okay, holes in the firmament wouldn't do that.

However, some clever person could come along and say, yes, but very creative God or somebody who wants to mess with us. And so at some point, you decide, you know, I'm going to go with the physical explanation of what I see out there. And the cosmological principle is a lot like that, too. I'm going to assume that there's not a special place in space, that everywhere is the same, and I can do experiments now. I can learn things in one location, and I can apply them in a different location.

And, you know, that's such a logical and rational way to proceed, so powerful that, you know, it's the last thing I would give up. I like, it would be right up there with like, oh, we can't do math, by the way, as we try to explore science, you know. Right. We don't know if math applies out there either. Although, to be fair, you know, there was something that you can have too much of a good thing, and there was a proposal by Bondi and gold and others, including the former occupant of this office, Jeffrey Burbage, the quasi-steady state cosmology that Jeff used to champion had on giant narlacar, who is Hoyle's best student. He's still doing well and living in India, and we had a great podcast. But does he still believe steady state? Oh, yeah. You said this place was steps from the water. We just haven't found the steps yet.

How much did we save? Enough. Enough to get lost. Or you could book a stay with Hilton. Welcome to your oceanfront room. Just steps from the water. The Hilton sale is on now. Book on Hilton.com or the Hilton app

and save up to 20% to get the stay you expected. When you want savings, not surprises. It matters where you stay. Hilton, for the stay. Oh, absolutely. Yeah. And part of that is just, you know, he thinks you can't have too much of a good thing. So he not only adds invariance and Lawrence boost and so forth, but time invariance

and that the universe should be the perfect cosmological principle that they invoked was that the universe was time translation invariant, therefore it didn't have a singular origin, a singular event. So you're right, though. I think, yeah, that would be, and that's why I've gotten interested in these Lawrence and variance violation test and things we helped to do with the Simon's Observatory and maybe even optical telescopes on Earth, looking for variation in time of flight of different objects. And so I want to turn to an article you were quoted in just yesterday I read it with in physics world, maybe.

And it was about measuring the Hubble constant using gravitational time delays and gravitational lensing. Can you talk about lensing? Another thing that Einstein predicted, he had to recant it. I mean, he was wrong. He said it would never be discovered like gravitational waves. Barry Barish's Fort-A. What we're saying about gravitational waves? Wow.

He didn't think we could detect them. I remember my favorite story about Lensing before I stopped interrupting you. It was that he, back in the day, if you were Einstein, you could write to nature. And the article starts off with a few, a little while ago, a Mr. Mandel came to me asking if I could do a little calculation. And this is published and the audience like, I never see gravitational lensing. So what is Lensing? I'm going to tell you about the Hubble concert. What the heck does that have to do with it?

So when we look at Obfittance, far away, we are looking through a lot of space, and there's often matter in that space. And as Einstein showed, matter bends light. And so balls of matter, large groupings of matter, can act not just bending light, but since they're compact and in one spot, they can actually act like a lens, very analogous to a lens. And so what that means is, like a lens, you have rays of light that leave a distant object. And of course, the one that's headed direct. at you may go to you, but there are ones that were diverging. They are going to go away and you will never see those. They're headed off to other observers. This bottle of vodka. Exactly. It's bottle of vodka.

So, you know, the heavy objects bend those rays of light that were headed in different directions back to the line of sight of the observer. And so you may see multiple images from those different rays of light that were headed otherwise. You might see as if you have perfect symmetry of the system where you have, you know, that ball of matter that's acting like a lenses directly between you and the distant object. You can get a lot of rays of light that turn into an actual ring. It's called an Einstein ring. And so these are fascinating objects to study gravity. They're beautiful objects.

And because those different paths of light that head to us have different lengths in space, it takes light different times to travel from the object to us. And so if the background source that you're looking at actually varies in some way, if some event occurs, a supernova or a quasar, gulps of matter, and changes its brightness, then you may see that event occur in the different images at different times. And so if you have different path lengths and you understand the speed of light and you measure the time differential between them, it gives you information about distances.

And anytime you say distances, you know, you have the potential to measure the expansion rate of the universe because you're measuring, you know, you know, red shift and you know distance. So that's the great thing about these lens systems is they're great laboratories for gravity. The tricky business is you have to have an understanding of exactly what kind of matter, sorry, how it's distributed along the line of sight. And, you know, we don't have perfect ideas right now of how matters distributed. There's dark matter, of course, dark matters in halos. Those halos have a shape. And, you know, we argue a little bit about what that shape is. So there's a fair bit of what we call model uncertainty in trying to go from observations of

lensed objects with time delays to a value of the Hubble constant. So I would say these are very early days in playing that game. And so it was a paper reported. a week ago of the first multibly imaged supernova called Refstahl, where you can measure the different images of the supernova, and you can try to infer distances. And I think it's very exciting and interesting work. But, you know, looking at it, the hardest part by far is the modeling. And so, as I recall, they had eight or ten different models attempt to model this. If I can use an analogy, I think it's a little bit like hurricane modeling.

Have you ever seen, you know, people try to predict where a hurricane's going to make landfall? Yeah. And so, you know, you're going, all right, well, let me feed in the wind speed at San Juan and how fast it was going when it passed Cuba. And then you see these spaghetti models that predict all these different places. So I would say at this moment in time, the uncertainty is dominated by the range of models and what they predict. And so I think, you know, the lesson here is that this is a capability that is being developed. And with more objects like this, we will probably learn better how to model these systems. Just the same way that, you know, you like a nice, large data set of hurricanes and actually to know where they made landfall to teach your models.

So I think that process is ongoing. Wow, that's excellent. So you at Johns Hopkins, now we're going to have a little comic relief maybe from all the nerding out we've done. So you are the Bloomberg professor of physics at Johns Hopkins University. What does the former mayor of New York have to? Why does he have an interest in cosmology and supernovae? What could he possibly have? First of all, what's he like? He's one of the richest human beings have ever walked the planet. What does he like as a person? And can you get him on the show? Right. So I've been fortunate to meet him a couple of times. And I could tell you, I was really surprised. I thought, you know, this would be somebody to, you know, mostly focused on, you know, business and philanthropy. And all he wanted to talk to me about was physics. You know, he was intensely curious. He was well read. He wanted to talk about quantum entanglement.

He was interested in cosmology. He wanted to look through our telescope. You know, this is what he was interested in. And so, you know, I was extremely impressed because my, you know, well of knowledge is not, I think, nearly as vast as his is. But, you know, he's quite passionate about many, many different subjects. You know, it also related to this is, you know, he went to Johns Hopkins University. And so, you know, he's grateful for the education he received there. As, you know, many people are grateful for the educations they received in many universities.

And so he's given back quite a lot. We talked over dinner last night about future of education and, yeah, whether we'll be replaced by, you know, super artificial intelligence. Are you nervous? Are you concerned about your job security? I would, yeah, that would be all right with me. Okay. I'll go about as far as I can go and then AI can take over. No, I mean, look, I think, you know, the most.

optimistic take I could say on this is hopefully you know AI will do things for us that will leave our minds free to do you know more challenging things more interesting things things were more curious about or or are more compelling in some way and so you know I've already started using chat GBT you know write me a little code for this or you know write me a draft letter of that or something like that and so you know it's it's a tool I mean you know people I know are quite worried they It could be used in negative ways. And I know that that is the case.

I think, you know, it's hard to think of an advancement in technology that didn't have this sort of, you know, double-edged sword to it. Like, you know, this could be used in wonderful ways. And you know, this could be used in terrible ways. Right. And, you know, ever since we invented the wheel, you know, that has been possible. And astronomers, as past guest, Neil deGress Tyson has pointed out, you know, they're always intimately connected to war as accessory to war as. Yeah. Anything people want to do, they will use the new technology for.

So we'll wrap up pretty shortly because you have to get ready for your talk. I thought this was the time. Wait, yeah, I know. I don't want to burn out your vocal cords, but you've got such a malefluous voice. I'm not too worried about that. The last question I ask about is this controversy, which you, because you're so intelligent, you avoid social media like the plague. But on social media this summer, there was a huge, yeah, brouhaha, the Big Bang never happened,

proven by the James Webb Space Telescope. But this also cost a little bit less than $10 billion, by the way, for my undergrad. to make that 3D printer. Tell me, this concept that the Big Bang never happened because we see objects at greater Redshift. Redshift, the record now is 12 or something like that. 13. 13.

It's insane. And change. So how is that compatible? How could you possibly have a Big Bang unless the Big Bang never happened and the universe is. Right. So the issue really is as we look further back with the James Webb Space Telescope, we look to when the universe was very young, when objects were first forming. And we have expectations of what those objects should look like.

They should look like younger versions of what we see today. We have models and understanding of how they grew to the size they did, how they developed. And so it would be like, you know, like saying, hey, I've never seen your baby pictures, but let's take a look at them. And I expect you're smaller and you're cuter and stuff like that. You'd be wrong in my case. But anyway, but, you know, you have expectations. So, you know, if I saw a picture of you, you're two years old and you have a full beard, right? I'd go, oh, this doesn't make sense or something.

Maybe you weren't born when I thought you were. Benjamin Button effect is gone. So, you know, that's a kind of an overstatement of the fact that, you know, when we've looked out at distant galaxies, some of the earliest ones, astronomers have been surprised. They have looked more massive. They have looked further developed than we thought. And so some initial reactions were, oh, something's wrong with our understanding of the Big Bang. And what we really mean is the time interval that the Big Bang allows. from beginning to those galaxies only a couple hundred million years.

Some astronomers are saying that doesn't seem like enough time for those to form. So there's a couple things you have to think about to take a pause with that. First is, this is hard. And so in particular, we recognize that whenever we look out at things, we see the rarest of objects. We see the brightest, we see the biggest. And so we have to take into account something we call selection effects. You know, you look at a crowd, and you see the things. the tallest people. If you think everybody is that tall, you're going to get confused. So we have to

do that science carefully. And also, we've only looking at a little bit of sky with the James Webb Space Telescope. We haven't yet done the big, wide, deep fields, and we're going to get much better information. So I think it's fair to say the initial look is surprising. Things do look more massive and developed, whether that is enough to break our understanding or tweak our understanding, whether it teaches us about some processes that occurred faster than we expected, or whether it actually teaches us something, even about gravity is occurring differently. You know, I like to kind of take an open mind with it. Let's collect the data. You know, if somebody is jumping to the conclusion that the Big Bang didn't happen, then they probably already had that as their agenda to say that

at the first moment of something. But, you know, this is a beautiful process, this discovery process, but it takes time. You can't just take a picture and immediately know what it means. So, you know, would tell people, you know, check back on this story in six months in a year. In two years, we'll know more. Great. So that brings us beautifully to the final question in the same article where you're mentioned, our friend of astrophysics, Roger Blanford. He says that he's optimistic, that someday this will wrap up one way or another. And he said, it's a knowable thing. That's a resolution to the Hubble Tension. The universe is cooperative in this sense. I was kind of struck. I felt that was a little bit, I don't know what the right way. Yeah.

Aliana or what you'd say, but I'm curious what Adam, what you would say. Because I don't think nature's under any obligation to cooperate with us whatsoever. So what do you think? First of all, are you optimistic as Rogers? So I would answer this from both an empirical and a theoretical standpoint. So from an empirical standpoint, do I believe that we ought to be able to measure how fast the universe is expanding today, that we ought to be able to predict how fast it's expanding from the customer wave background? and we should expect those two to meet.

Yeah, I think that from an empirical standpoint, there's nothing in that measurement process where I say, well, that's impossible and nobody can do that. Now, you know, could we make the measurements better? Absolutely. Will the new facilities teach us things? James Webb, LIGO, future Gaia data releases,

CMB experiments that are going to be extended, like S4, Simon's Observatory. These will weigh in on this and teach us new things. But this is a doable problem. That doesn't worry me. The theoretical implications, what's actually going on may be beyond us. It may not be beyond us. It's hard to predict.

You know, when astronomers noticed that the orbit of Mercury was processing, right? They could measure that thing all day long. They could say, could there be another planet out there, Vulcan that's causing this? We'll look for that. And, you know, ultimately they didn't find it, right? I'm still holding out hope. Who can, you know, who could say, well, maybe somebody will come along. and develop a new theory of gravity, general relativity, and it will explain this, right?

You couldn't sit down and say that'll happen in one year, 10 years, 100 years, 10,000 years, or never. And so that's the part that I'm, you know, not sure if there's something deep and fundamental going on and it takes a deep insight and what time scale we will have on. I just, it's very difficult to predict. Well, speaking of deep things, Adam, your deep intellect has been an inspiration to me for as long as I've known you, uh, continues to be. We, I learned so much every time I'm with you. I wish you could be out here permanently. We'll talk about that later. Uh, you know, maybe we'll slip another one of these. That's delicious. Pretty big. You like that. Yeah. Uh, yeah. Uh, we treat our visitors here

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