Into the Impossible With Brian Keating - Dark Energy Is Dying: The Cosmological Crisis Nobody's Telling You About

Episode Date: April 3, 2026

Please join my mailing list here 👉 https://briankeating.com/yt to win a meteorite 💥 Brian Keating takes us on an exclusive tour of the Royal Observatory Edinburgh with cosmologist Marcos Pellejero, exploring the mysteries of dark energy and the accelerating universe. From the historic halls where human "computers" shaped the foundations of modern cosmology, to the cutting-edge DESI experiment mapping galaxies across the cosmos, the conversation explores whether dark energy is truly constant—or if our cosmological model is beginning to show cracks. - Key Takeaways: 00:00 "Dark Energy and Cosmic Clues" 04:42 "Light Pollution Ruins Observatories" 07:03 Royal Astronomer's Electric Chair Solution 11:06 "DESI Challenges Vacuum Energy Constant" 15:48 "Advancing Simulations and Synergies" 19:14 "Science and Art: Problem Solving" 20:29 "Exploring Dark Energy's Secrets" - Join this channel to get access to perks like monthly Office Hours: https://www.youtube.com/channel/UCmXH_moPhfkqCk6S3b9RWuw/join 📚 Get my books: Think Like a Nobel Prize Winner, with productivity tips from 9 Nobel Prize winners: https://a.co/d/03ezQFu Focus Like a Nobel Prize Winner, with life-changing interviews with 9 Nobel Prizewinners: https://a.co/d/hi50U9U My tell-all cosmic memoir Losing the Nobel Prize: http://amzn.to/2sa5UpA The first-ever audiobook from Galileo: Dialogue Concerning the Two Chief World Systems: Ptolemaic and Copernican https://a.co/d/iZPi9Un Follow me to ask questions of my guests: 🏄‍♂️ Twitter: https://twitter.com/DrBrianKeating 🔔 Subscribe https://www.youtube.com/DrBrianKeating?sub_confirmation=1 📝 Join my mailing list; just click here http://briankeating.com/list ✍️ Detailed Blog posts here: https://briankeating.com/blog 🎙️ Listen on audio-only platforms: https://briankeating.com/podcast #universe #podcast #briankeating #intotheimpossible #science #astronomy #cosmology #cosmicmicrowavebackground #darkenergy #Galaxysurveys #RoyalObservatoryEdinburgh #hubbletension #universeexploration #cosmicmysteries Learn more about your ad choices. Visit megaphone.fm/adchoices

Some of the strongest evidence that the universe is accelerating doesn't come from one telescope or a single experiment. It comes from a tiny ripple frozen into how galaxies cluster across the cosmos. Today, from the Royal Observatory in Edinburgh, we're following that ripple with cosmologist Marcos Pellehero to see what it really says about dark energy. I'm Brian Keating, and this is an exclusive tour of the Royal Observatory Edinburgh with cosmologist Marcos Pallero. We'll go from this historic telescope to cutting-edge simulations to the DESE experiment, one of the most ambitious galaxy surveys ever built to ask a simple question. Is dark energy really constant? Or is our entire cosmological model starting to crack?

Long before silicon chips, the computers up here weren't machines. They were people. Often they were women hired to comb through photographic plates measuring every faint smudge of light by hand. Their names rarely made it into papers, but their measurements are literally baked into the datasets we still build our modern cosmological models on. This building was designed as a cathedral for starlight. The telescope sits on a massive pier that sinks onto the hill, isolated from the floor,

so footsteps don't shake the images. As our cities grew brighter, places like this became less useful for frontline observing, but the engineering mindset behind them is still the same one we still use today to measure the universe's properties. This is a picture of the family of the Royal Astronomer before this place had no house anymore, okay, for them. Good. Yeah, and this is basically like the idea of, like,

in the old times you would have looked through a telescope like this one, but nowadays, here in the lab, they're building things like this, like these robotic arms to basically place fibers and get some of the light and decrees. the composite and study. This is not far from the Simon's Observatory. That's in the north. Okay, and just one more question.

Sorry, I know that you have been here for quite a long time. Do you see any weird wall in this room? Yes, which one? Why do you think is weird? There are two reasons. Well, it has a picture. Yes, this one is weird, but this is not, this is a door, right? This is not a wall.

Yes, exactly. So welcome to the dome. So do you see something we have in this dome with respect to other domes that you might have seen? It's not a dome, exactly. It's like a cylinder, right? And this relates to what I was saying before that they were not trying to do a functional building. They were trying to do a beautiful building, right? And then they were thinking on building something that was like a cathedral for science. So the idea, a cathedral needs towers, right?

So this is, again, like this is quite old. And when I was telling you what will we find at the end of that weird wall, the reason is this thing. Okay. So this is square here goes all the way down and into the hill. Okay. And it is separated from the rest of the building because you need to do like very precise observations. And if this is connected to the rest of the building, then if the building moves, this moves, right?

And you want to avoid that. So basically what you do is you create a pyramid, right? That goes, that takes it, puts its roots to the, like deep into the, into the mountain. And it moves at the least you can, right? This specific telescope is from what's built in Newcastle in 19, it's written here, in 1928. Okay, so it's not as old as the building. This would not be the first telescope. that was here, but it's quite odd.

And what's the diamond or mark on? So this was, I think this is a 40 centimeters one. So this is the primary miller. Oh, 40 centimeters, I don't know, in inches. I have no idea from that. It's less than, say 18 inches? 18 inches, yeah. Okay.

Yes, I could. If you say so five feet. So, actually, so have, I mean, I guess you know quite a lot about, about, about telescopes already. The primary mirror is not here anymore. The secondary mirror, which is up there, you can still see it. That's there.

And the detector is completely missing, right? This is empty. Now, what's the reason for this? Well, it's the same, basically the same reason why the original observatory was completely useless by the mid-19th century, which is the cities in Europe

started being lighted, with electric lights and not candles as had happened before. So no fire anymore. Okay. So they basically, they were like very, very bright. And if you had an observatory close to the city center, then you couldn't, you could see nothing, right, of the night sky. So they built this one far away from the city, but the city grew, right?

So at some point, the light pollution of the city made this observatory useless, not useless, but in comparison to other. observatory is basically useless. Okay? So basically for the last, yeah, no, like for the, now it's not anymore, but since 1975 or so, this was used for checking the stability of detectors. So they were building detectors in the lab in the other building.

They will put them here and then they will shake them basically to see if there were any loose pieces that they had forgotten or something like that. Yeah, so that's basically how this works. But you have to think about an astronomer in 1895, okay, basically coming here with a candle, right? And then do you want me to show you how they will open the dome? It's very cool because it's just with robs and there's no technology, no weird technology have been in here.

Come with me, let me show you. So do you see the wheels? The wheels are all around the dome. So those would be used to actually rotate the dome, okay? And then you will have to open this and it is... Very heavy. It is as simple as this even though it's a bit heavy, yes. But that's the way one would open the dome.

Yeah, yeah, very cool, very huge to the very neat. Now, what does he want to open it like up there straight out? Yeah, so the thing is that there's two, right? So one is this one, the other one is that one. That one will go, do you see all of, all of the levels there? And so you will have to use those. So basically what I was telling is that the moment, okay, so these finders, okay, so the small telescopes, the ones that basically tell you where, like, in which way you're looking at, right?

Are very high, right? So in the moment you tilt this, they are even higher. So to reach them, you will have to go up a ladder, okay? And the royal astronomer will have to go up a ladder. And he couldn't have his royal astronomer as going up a ladder because he was the royal astronomer, right? So he asked for this to be built, okay? Which is an electric chair, but a good kind of electric chair, okay?

So the one in which you will sit down and then you will press the button, and then this will elevate you. Okay. And then you can do observations without having to be up the ladder and so-and-so-wa, which is very cool. If you just threw galaxies into the universe at random, you'd get a smooth fog of matter. But when you actually map them, you see a faint preference, a ring, a scale of about 150 megaparses left over from sound waves in the early universe. But these patterns are called barion acoustic oscillations,

and they behave like a cosmic ruler for measuring how far. fast the universe has been expanding. So first of all, what's a barrier on acoustic oscillation, Marker? Well, acoustic oscillations, well, first of all, the way I like to think about them, how galaxies are distributed in the universe, okay? Because they don't follow just random patterns. They have, like, very distinctive patterns. And the first one that catches your eye is basically this cosmic web that you know about. It's a secondary answer, which is, like, yes, closer. But also, when you are at a distance of around 150 megaparsecs, then you find, again, a greater likelihood of finding a galaxy.

When you have these kind of patterns, it's usually the reason why they appear is because you have some kind of border or frontier. Turning DAO into numbers isn't just about counting galaxies. You have to know what the universe should look like if your dark energy theory is right. That means running huge in-body simulations. And Marcus works on emulators that use neural networks to mimic those simulations in a fraction of the time. So he can explore many more possible universes than ever before. So one of the main problems to study the distribution of galaxies nowadays

is that the gravity formation is very non-linear. And by this I mean that it comes with loads of complications to solve the equations. So the only analytical solutions that we have are those for the linear theories, okay, in the linear regime, which are like the regime of the very biggest case. In our simplest model, dark energy is just a constant, a fixed energy of the vacuum that never changes. But Desi is starting to whisper something awkward. Is it true, Kyle, that as our colleagues, my friends and colleagues, Suzanne Staggs, Mark Demlin, Lyman Page, I've demonstrated David Sperf. very clearly that the Lambda is unavoidable, or some version of dark energy is unavoidable using the CMB alone.

I think that's true right, Dan. Is it also true from BAA alone? You can derive the imperative of dark energy's existence. Yeah, that is definitely true for BAA alone as well. Our models, if we were to throw out any version of dark energy, would basically be impossible to describe the measurements we see over the rate of range. We make the measurements. We see a preference for something like 70% of the current energy contents.

being dark energy, and that's hard to get around. The data seem more comfortable if dark energy evolves over time. And when you combine that with the fact that cosmology wants neutrinos to be almost massless, while particle physics insist that they aren't, you get a serious tension in our best theory of the cosmos. Theoretically, it makes out of sense that is a constant, right? Because if you think of it as the energy of the vacuum, then the more volume there is, the more vacuum there is, it all compensates and then you get a constant.

So it makes out of sense. but the latest results from DESE and being part of the DESE collaboration, I trust them. Yeah. Because I know that they have very, very, you know, very, you know, very tiki in how to show the results and so on. That's those seems to show that there's a strong,

yeah, but there's like strong evidences from DESE to actually departure of this. And I think like the most, okay, to me, the most interesting part is that cosmology has very few predictions that they can make that can be checked with other kind of areas in physics, for example, particle physics. And there's one prediction that Cosmovi has, which is that we can measure the mass of the neutrinos. Okay? And if you go to the latest results from BAO and DESE and you combine them with other supernova results and so on, you find out that there's strong evidence to actually

having massless neutrinos in the universe. But particle physics experiments tell you that they cannot be mass, massless, right? They have to have a mass. So there's a tension here. There's a paradox here. Like there's a misunderstanding between these two areas of science. And the only, exactly, inconsistency. And the only way of reconciling those two seems to be opening our framework to new ideas on what dark energy could be. And right now, it seems that that's the most compelling way of moving forward, right? Because there are other ways in which you will actually lose this, these constraints, but none of them actually move your measurements. They just make them less accurate. But this one actually moves your measurements in the right direction. This one being

the dark energy. Exactly. So having a dark energy that is not really constant in time, but evokes. The Hubble tension, the fact that different models measuring the expansion rate disagree, might end up being systematic error, or it might be a sign of new physics. The only way to know for sure is to redo the key experiments with ever more careful data. That's part of what surveys like D-E-S and the upcoming LSS are designed to do. So tell me about the Hubble Tension. What is the, because you found there was also some discrepancy depending on what value is the hollow. Yeah, so the Havilt Tension, I don't have a good answer on like what could be happening with

the Havilt Tension. Everything seems to show that it might be due to systematics, but again, I'm not an expert. Do we need more data for both things? Do we need more? I think we need more consistent. maybe that's that's the thing right maybe we have we we need to to redo some of the things that we have done already and I know that this is not very attractive and no one really wants to do this right yeah but but sometimes you have to repeat some some of the experiments and this is being done

by the de s collaboration for example they have like their own set of supernovae and and also the LSD is going to have the own set of supernovae and and again I know that this is not like a very attractive in some way but it's the only way forward To test any model of dark energy, you need to know what the universe's large-scale structure should look like if your model is correct. That's what so-called N-body simulations do. They throw billions of particles into an expanding universe and let gravity sculpt the cosmic web, and then we compare it to what we actually see. Explain first for a layperson, what is an N-body simulation. How do you actually do it?

Do it a laptop, an iPhone? How do you do it? Sure, sure. So they are usually done in supercomputers, right? the big ones there are in supercomputers. And an end-body simulation is basically just a simulation of a very homogeneous universe that evolves with time according to a mixture between Newton's laws and GR, general relativity laws. So basically Newton's laws on an expanding universe.

And it evolves only through gravity. And it tells you what is going to be the gravitational potential, so what is going to be the structures that you expect to see in the labor. to see in the late universe. And it solves the equations exactly. But for a given set of initial conditions, that's the... James Clerk Maxwell, Peter Higgs,

and the astronomers who built this place. We're all chasing different versions of the same question. What is the universe really made of? And how does it really behave? Marcos does it with simulations, surveys, and machine learning instead of brass and glass.

But the mind's that is still the same. Take a vague intuition and carve it into something the universe can't ignore. So what do we need more of? More galaxies, more observations, more CPU, what do we need more of? Well, we need more of everything. I mean, if you ask me, more of everything.

But so simulations I think we have, I mean like we have plenty. Of course, like the bigger they are the better. But we have techniques to actually do this and body simulations quick enough that I think that's not a bottleneck anymore. It used to be, but not anymore, right? But we also need like machine learning techniques and artificial intelligence techniques to actually use them in the smartest way for that.

And for that, in the synergies between the computing science departments, and the cosmology department, a bottlenecks that we have there are in simulations are more related to hydrodynamic and superlitions, which are the simulations in which it's not only gravity evolving, is gravity plus the pressure from galaxies, explosions of plasma, exactly, so star formation and so on, right? Those are very far from being converged.

So if you run two similar approaches, the outcomes will be completely contradictory. Okay, so they will basically predict opposite. which is something that is very annoying, right? Yeah, exactly. Because then you don't know which university is living, right? So this observatory, there's the Higgs Center that we're at right now. Yeah.

Did you meet Peter Higgs? Did you know Peter Hales? He died? No, I didn't. I moved here, not very, okay, so basically one year before he died. And, well, he was not coming anymore, right? To wait. The quick history here, was Maxwell ever here?

was there? Right? Maxwell is one of my, like, heroes in history because it doesn't seem that he was also like a very good scientist, apparently he was also like

a nice person. Ah, Edinburgh, the city where I first chased light through the mist. At 14, I was already puzzling over the mathematics of curves and colors. Scribling equation.

Didn't pass every exam, mind you. Cambridge nearly said no. But curiosity is a stubborn thing. It carried. me from these cobbled streets to the laws that would bind electricity and magnetism forever. Funny, isn't it?

As my friend, Professor Brian Keating always says, A, B, C, always be curious. So he was born here, and you can actually visit the house where he was born. He wanted to come here, but at the time he had not made his most brilliant contributions to physics, right? And he was actually not accepted in the university. A friend of his was accepted. And at the very beginning, I thought like, oh, who would say no to Maxwell, right? But then you realize that they were actually very good friends since they were kids. And they were part of like this club in which they solved mathematical problems together and so on.

And then you think like, I know, actually, everybody was sad. Probably Maxwell was happy that his friend goes to start position. And he went on to get so. So how does it feel to work in a place like this with all this history, castles, copper. And then you're doing some of the most modern, large-scale simulation ever done, the tundering, the most mysterious force in the universe,

dark energy. I know, I know. I don't see any big leap in that sense, right? So in the end, like, I mean, it sounds very old when you tell these stories and so on, but they were dealing with the same kind of problem. How to make a bigger building and, like, how to make a bigger simulation.

Exactly, like bigger telescope, how to, I don't know, like in the end, it's, it's a very similar mind framework. And it's like a problem-solving framework, right? When you have a problem and you want to find a solution, it's like the brain works in a very similar ways. It's not like music, for example, right? In music, you don't have a very well-defined problem, right? You just have like an intuition, what could work and what could use, right? And, but yeah, and science is a bit like a mixture of those two are, right? Like problem solving and a little bit of inspiration.

And when you live in a place where there's so many artistic stuff, like, around you, then you find out that science and arts are not that different and that you need inspiration from both of them, right? Which is like the cool thing. That's beautiful. Thank you. From this hilltop in Edinburgh to the edge of the observable universe, barren acoustic oscillations and DESE are forcing us to ask whether dark energy is really constant

or whether our entire cosmological model is starting to bend. A huge thanks to Marcos and the Royal Observatory of Edinburgh for opening their doors. If you want to go deeper into DESE and Dark Energy, check out my conversations with DESE, past spokesperson Kyle Dawson, and Nobel laureate Adam Reese. They're linked right here. See you next time. I'm Into the Impossible. And don't forget to like comment and subscribe.

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