The Supermassive Podcast - What is the Hubble Tension?

Episode Date: February 26, 2026

There's a crisis in cosmology when it comes to understanding a little thing like the acceleration of our universe, aka The Hubble Tension. And in this episode, Izzie Clarke and Dr Becky Smethurst are digging into what this is and (trying to) explain the science behind it. A huge thank you to our guests, (Nobel Prize winning-) Professor Adam Riess from John Hopkins University and Professor Silvia Galli from Institut d'Astrophysique de Paris. Join The Supermassive Club for ad-free listening, forum access, and extra content from the team. And email your questions to [e-mail] or follow us on Instagram, @SupermassivePod.The Supermassive Podcast is a Boffin Media production. The producers are Izzie Clarke and Richard Hollingham. Hosted on Acast. See acast.com/privacy for more information.

There was a huge secret before the release of the data. We've had questions about, is that expansion rate changing with time? How fast is it expanding? What does that imply about the future? Are we looking at limitations of the cosmological model? Hello, welcome to the supermassive podcast from the Royal Astronomical Society. With me, science journalist Izzy Clark and astrophysicist Dr. Becky Smethurst. recently the astronomy community has had a little bit of a shake-up when it comes to understanding

just a little thing like the expansion of the entire universe. There are a few ways to measure this rate of expansion. But in recent years, scientists have been getting different results, which have opened up a big old can of worms when it comes to understanding our universe. You know, like no biggie. I mean, so we are going to attempt to tackle the ins and outs of this. This is what is known as the Hubble Tension. And in this episode, we're going to be digging into what this is

and, you know, trying to explain the science behind it. And are we setting off the Nobel Prize alarm yet? Is he? Woo! Woo! Not for us personally, no, but we are for one of our guests. So I can confirm we have our first Nobel Prize winning guest on the show. That's Professor Adam Rees, who studies the expansion rate with nearby galaxies. And I also spoke with the brilliant Professor Sylvia Galley,

who measures the expansion rate using the cosmic microwave background. So we'll get their thoughts on all of this in a moment. Yeah. Looking forward to both of those interviews. They're so hard. It's okay. Yeah. It was like just going up to those interviews, like please talk to me like I'm five.

What is happening? Thank you. And obviously Dr. Robert Massey from the Royal Astronomical Society is here too. So, Robert, why do we call this the Hubble Tent? who was Hubble and what does he have to do with all of this? Well, I want to start by saying, you know, we should aspire to Becky getting a Nobel Prize someday, but of course it not.

Of all the presenters, all the people on this show. Yeah, one day. Anyway, yeah, so Edwin Hubble was an astronomer. I mean, the Hubble Space Telescope was named after him, right? So it's very significant. He was an astronomer who worked at the Mount Wilson Observatory in California in the 1920s. He used a two and a half meter telescope, which was then the biggest in the world,

to study these stars called Cepheid variables. And they are evolved stars, the stars are reaching the end of their life. They pulsate and change luminosity with a period, a regular period that's related to how bright they are. And that was discovered by Henrietta Swan Levitt. It was also massively distinguished astronomer

in the 1900s. And that means, because we know about that regularity, we can use them to measure distances, I'd like to think of this as like a traffic light analogy, right? So if you look at, say, a traffic lights in the distance, we know that they go, you know, kind of red and red hammer together and green and so on,

if you imagine looking at those at a great distance and seeing the same change, you'd know you were looking at the same thing. It's sort of like that, you know, understanding that the further away something is, the fainter it is and knowing it looking at the same kind of object. Yeah, I like that analogy. I never thought about that.

I always think about it as like crossing the road and you see, like in the dark and you see lights in the distance, you know how far away the car is because of how bright the headlights kind of appear. You know if it's safe to cross the road. That's how I always think about it. So it's fun that we both have road analogy. I don't take credit for this.

I remember a lecture many years ago describe you, but it's one way of measuring distance, right? So they are a very standard way of doing it. Now, it is more complicated, of course, because everything in astronomy often is, but there's, you know, the complication is there's different types of sephids and the measurements are never quite as trivial as you might imagine. But what Hubble did was look for these stars.

And because he had a reasonably big telescope, a very big telescope, by the standards of the time, he was able to look at them in what we now know external galaxies because until that point, the astronomers assumed that the Milky Way was everything, you know, the whole universe was the Milky Way. What Hubble did was to realize that there were very, very distant external galaxies, so massively increased the size of the universe. That was the first thing he did. No biggie.

Yeah, no biggie, exactly. Yeah. So then using that technique, he measured the distances to a larger number of galaxies, I think, you know, a few tens of galaxies. And he also looked at the redshift of those galaxies. Now, that is the dopper effect. It's where if an object is moving away or towards you, the wavelength of the light that emits changes slightly, basically it's stretched out or compressed a bit. And if it's moving towards you, it's slightly bluer. If it's moving away, it's slightly redder. And that gets much more extreme with very, very distant galaxies, but he wasn't able to measure those. Anyway, he realized then that the velocity at which the galaxies are moving away is proportional to their distance. That's Hubble's law, and the Hubble constant is the factor that links the two.

Now, that also was an insight into the fact that the universe was expanding and, you know, for reasons it will come on to a lot of time, that was obviously a hugely important discovery too, but it then connects with things like today, dark energy and so on and the cosmological constant. The point is that universe is expanding. That was a big insight into that. Now, in modern times, you've got much, much better and more accurate measurements, both of the speed of which galaxies are moving away first. And also, in many cases, at least for the nearby one, their distances, because ironically, the Hubble Space Telescope was used to look at these stars in, galaxies that were further way to refine that. But there is a difference between the measurements of the Hubble constant, the local universe, so using it for nearby galaxies and the value we get by looking at the cosmic microwave background, which is the residual heat that we see that's left over from the Big Bang and sort of like the last point at which we could see it emitted.

It was a slightly complicated explanation, but if you imagine like a cloudy sky, it's like the light being scattered from that surface. And it was scattered from the universe 380,000 years after the Big Bang, and we're seeing that residual heat. And if you imagine, like a cloudy sky, and if you measure, if you look at that, there are patterns in it that tell us something about the structure of the universe. And it then allows us to derive some of the different cosmological concerts, not just the particular cosmological constant we'll talk about. But there is a discrepancy between those two measurements. And that is the Hubble tension. Now, that background was measured with satellites like the Plank Observatory a few years ago, produced a really

detailed map. And so it's tricky. There is a debate about how real it is. There's a debate about the errors on it, but it's certainly intriguing cosmologists. I will defer definitely to people like Becky at this point to get into some of the details of this, but it's an ongoing thing. It's like the idea around maybe the value of dark energy isn't constant. Maybe there's something going on there as well. So cosmology, I don't know if it was fair to say we thought it was settled. I don't think that was true.

But there was an argument about it being precision cosmology and all these nice, neat numbers. And it turns out, as with so much in astronomy, astrophysics in cosmology, it's not quite the case. There's more to this than meets the eye. Yeah. I think when I was starting my PhD, back in 2013, don't work those mats out.

I remember, I'm not going to comment. I remember sort of thinking, I don't want to get into cosmology. It's really boring because everything's, as you were saying, like precision cosmology. It was like measuring, you know, these cosmological values. So basically the numbers that describe

the best model of the universe that we have. That's what we meet when we talk about a cosmological value, right? It was like measuring those values to like what felt like five or six decimal places and I was like, that's really boring.

And so I just didn't want to get into it at all. And now, as you say, it's just completely been blown wide open because almost by doing those precision measurements, we're realising actually these two methods that we thought were super precise and have been getting more and more precise,

now don't agree anymore. And it's really interesting to think what it could be Is it new physics or is it bad data, basically, is what it boils down to? And I think that's a lot of it. Not bad data, but not the best data. There's some discrepancies somewhere, where are they? Sort of trying to get to those.

But I think that's it when it comes to the Hubble tension. People might have seen this called the crisis in cosmology. People really leaning into the drama. But obviously, me just getting carried away with things, I love the idea that is there something we just don't know about the universe? Is there something in the model that we now need to go and look at? Who knows? Right.

Let's look at how scientists are trying to understand this mystery, ease this tension, find out about our universe. And one way to do that is by studying nearby galaxies. And Professor Adam Rees is a professor of physics and astronomy at John Hopkins University and is a distinguished astronomer at the Space Telescope Science Institute. He's also the winner of the Nobel Prize in physics in 2011. So I think he's a pretty good person to speak to about this. We caught up a few weeks ago, and the first question that I asked him was,

what can we understand by studying nearby galaxies and why is he so interested in them? I've always been interested in the big picture, what the universe is, what it's composed of, How old is it? What is its fate? And what's really remarkable is that these are questions that instead of asking a philosopher or a priest, you can address scientifically by making measurements of the motion of the universe. Okay. And so how is it that that can tell us about the universe and the motion of it? What exactly are you looking for? We've known for about a hundred years.

that the universe is expanding. But we've had questions about, is that expansion rate changing with time? How fast is it expanding? What does that imply about the future of the universe? What does it tell us about the composition of the universe? And so the way we determine this is by measuring the distances of galaxies around us. And that tells us how far back in time we are looking, because distance is time because of the delay of light. The speed of light is finite. It's not immediate. And then we measure what's called the red shift.

So that is the stretching of the wavelengths of light due to the expansion of space. That tells us how much the universe has expanded, looking back to different slices of time in the history of the universe. And so with that approach, what does that tell us? What results do you get about the range? of the expansion of the universe. One thing it told us, going back to 1998, is that the expansion is speeding up. It's accelerating. And this is attributed to this mysterious component of the universe called dark energy. And there's very wide agreement on that. In fact, that's the thing we

won the Nobel Prize for. So generally, they don't award you that unless people think it's, something is true. But then more recently, it's become interesting to note that the specific rate at which the universe is expanding, something called the Hubble constant, does not match the other approach to measuring or estimating how fast the universe should be expanding, which is by looking at the radiation left over from the Big Bang. And looking at that radiation and interpreting it in the context of our model of the universe, which is called Lambda CDM, that sort of encapsulates everything we know about the universe. Those two routes don't agree and that's become a real mystery or problem in cosmology. Now, this is probably the million dollar or the million

pound question, but do we know why? I'd rather than the million pounds, I understand the exchange rate, but anyway, go on. Do we have any inkling why? Why is there this discrepancy between the two different approaches of understanding this acceleration? Right. Well, as you said, that is the very big question, and I, you know, I really wish I knew the answer. You know, I work on the measurement side, and so we have been scrutinizing the measurements for about a decade now, very carefully reviewing them and thinking of anything that could go wrong and going down all kinds of rabbit holes to see what that could be. Most recently, we have used the new James Webb Space Telescope to improve. of the observations that were previously made with the Hubble Space Telescope. And these give us much higher resolution, which is great for the kind of measurements that I make.

But to people who are looking or hoping for that this would explain the answer, that it would go away with better data that has not occurred. In fact, the JWST data has really confirmed the picture we have with Hubble. And obviously with this, there are a few different ways of studying this and looking into this further. And you're looking at supernovae. So why are they so important within this approach of looking at our local galaxies? Right. So in order to measure the expansion of the universe, you have to look at objects that are in deep space where the universe is actually expanding. So for example, if you focus too close, the nearest galaxy to us is Andromeda. And that one isn't even

moving away from us at all. It's actually moving towards us because the gravity between us and Andromeda is strong and it overwhelms the expansion. So the key is you have to look far out and you have to look at something that you recognize so that you can estimate how far away it is, generally from how bright it appears. And so in our case, exploding stars called Supernovae offer us the best tools for doing this. When I look at a whole galaxy, for instance, I can't tell you whether that's a very far away galaxy that's very, very luminous, and so it looks faint, or whether it looks faint because it's actually very nearby, and it's a little wimpy galaxy. And the problem is galaxies come in all kinds of shapes and sizes.

They're like crowds of people. You don't know. There's not a standard crowd of people. It could be 100 people. It could be a million people. Supernovae, unlike that, are distinct objects that explode. And when they explode, the kind I look at, almost always explode with the same luminosity.

And so like a kind of standard lighthouse, when you see one far away, you can tell how far away it is from how bright it appears. And so that's why I look at supernovae. And so can you tell me what is the rate of expansion that you measure through this approach? Yes. So we use kind of funding units that get closer to the observation. And so the Hubble constant, this expansion rate, clocks in in local measurements at a value of about 73 kilometers per second per megaparsec, which is kind of funny units. But simply put, that says the universe doubles in size once every 10 billion years at the current rate.

The other approach, which starts at the early universe, and then infers how fast the universe ought to be expanding. today, based on the model, gives about 67. And these might sound close. In fact, to many people, they would say, hey, you're only differ by about 10%, you know, good for you. But the problem has, our error bars have gotten very small, and so that we are now somewhere between five and seven times the error bar apart. And so if there's not a problem with the measurements, and as I said, over 10 years of scrutiny, nobody has really found one, then it may imply that we're missing something in our understanding of the universe. Okay, because that's what I was going to ask.

At what point do we look at whether it's observational errors or are we looking at limitations of the cosmological model? Right, right. So certainly the latter is the most exciting possibility and the one that many people are hoping for, but one has to be very careful with the measurements. But having said that, our science community, we don't operate, you know, in a sequence. We all operate in parallel. And so for 10 years,

theorists have been hypothesizing ways that the universe could be different in how these might explain this phenomenon called the Hubble Tension. And there are lots of ideas. Some of them can explain some of the difference, but there's no one idea that is head and shoulders better than the others or appears to, you know, I would say fit like a glove. And so that's why, you know, we haven't jumped on to one idea and said, oh, that's it. We kind of remain in this uncertain mode where we keep circling around the measurements and circling around the ideas, either waiting for a brilliant theory that explains this and presumably other mysteries as well.

That's the important thing for people to understand is science. don't like explanations that just fix up some particular observation. They like theories that explain many things that we're seeing, gives them greater confidence in it. And so that's what we're sort of wrestling with is, you know, we haven't really found a new theory that explains this and then even other conundrums in the universe. And so if we look at that rate of 73 kilometers per second per megaparsec,

with the interesting units as we'll move past that. But what does that tell us about our universe and what is the impact of having a rate of expansion at that rate? Right, right. So, you know, what it literally means is, you know, every time, what's a megaparsec? It's about the distance between us and the nearest galaxy andromeda. So it means, you know, every time you go out a slice further and further,

that slice or shell is more. moving away from us at another 73 kilometers per second, which is actually a very fast speed in general, though not a lot for the universe. It's actually in the units of the inverse of time, which is to say, and as I mentioned earlier, this particular rate says the universe doubles every 10 billion years. And so that's a sort of simpler way to think of it. But I don't think the specific rate is what's interesting here. What's interesting is that our end-to-end test of our understanding of the universe, starting at the beginning versus the end, they don't match. And so when something doesn't match, we wonder, you know, is there some component of the universe that we're

missing or is the physics of the universe somehow different than we thought? And so that's what makes is such an interesting problem because right now, about 96% of the universe, stuff we call dark matter and dark energy in the model, we pretty well acknowledge we don't fully understand. And so, you know, our question is, as we probe the universe and we see other surprises, might that be telling us about those components, whether they're strange or more exotic and somehow than we thought? It's so exciting. And I mean, surely what we call head scratches, those are like, huge.

huge questions to sort of try and dig into it and better understand. So as you mentioned, you're using the James Webb Space Telescope to study this further. So how has that helped or what information has that given you? Right, right. That's a great question. So among the measurements we make, we often look into distant galaxies, peer into them with the James Webb Space Telescope. These are often galaxies that hosted a supernova,

many years ago. And then we look for other types of stars in those galaxies that we recognize that have analogs nearby. And we use those to calibrate the supernovae. That can be challenging because if your telescope doesn't have excellent resolution, then those stars can be blurred together with other stars in the images. It's sort of like if you've ever looked into the eye doctor and you look at an eye chart at different letters and they ask you to read it. And, you know, don't have good enough resolution, then the letters and the parts of the letters blur in some way that you can't tell one from another. So having the James Webb Space Telescope has been like being able to jump two lines down that eye chart and be able to resolve the letters. And so it allowed

us to go back to look at the Hubble Space Telescope images, which, you know, look comparatively blurry compared to James Webb and see that the contribution of other stars was, about what we expected, and so the measurements didn't change, but now it gives us a great deal more confidence in the measurements. Wow, that's amazing. Gosh, that's so much more resolution. And if there's one more question or one more element of it that you just want to understand, do you know what that is?

What is it if you could just click your fingers and get an answer? What do you think it would be? I mean, at the heart of all of this, I'm still most intrigued by dark energy, this stuff that we helped discover in 1998. What is it? What is its nature? How does it operate? So ultimately, my biggest wish is that all of these tensions and questions tie together, that they

ultimately are revealed by some new discovery or theory that comes up over the next few years, hopefully while I'm still active in this field, because these things can. You know, you could learn the answer tomorrow or it could be a century. It's hard to know. Thank you to Adam Reese, who can also add a first Nobel Prize winning guest on the Supermaster podcast to his long list of much better accolades, I think. I'm sure that's top of his list. Yeah, absolutely. Yeah, for sure.

I mean, obviously. But Becky, there's also another group using nearby galaxies. and even they get a slightly different result from Adam's approach, right? So what's going on there? Yeah, this also adds a little bit of confusion to the whole problem because we've got the main issue is that, you know, the results from measuring the expansion rate directly from galaxies gives us one answer, and then by using the cosmic microwave background

and fitting a big model to the universe, we get a different answer. But also, there's different answers when you do things directly and measure it locally. So there is another, there's a few groups doing this. I think one of the biggest ones, along with Adam Rees' group, is Wendy Friedman's group as well. They're doing something ever so slightly different that complements what the Rees group is doing. So, for example, the Rees group is using like the Seffod variables, right, that we spoke about. They're like the OG, the original, what we call standard candle, right, that has a set brightness that we know. And so because we know how bright it is, roughly, we know what distance it is.

And yes, there is a load of assumptions that come into there. This thing is all a bit of a big house of cards in terms of working out these distances. But there are other standard candles that we can use. Yeah. That are really sort of like a more modern sort of discovery. There's things called TP AGB stars. Love it.

Thermally pulsating AGB stars. There's tip of the red giant branch stars, which is all sort of like stars in a very specific stage of their evolution. And again, because they're in such a very specific stage, and they gave out very specific, like, colors and spreads of light in those specific stages. We can recognize them, and we know what their brightness should be from the physics modeling of them that we've done. And so with those, we can then say, okay, well, let's ignore the sephids. Let's use these stars to work out the distances to those galaxies and then work out what the hobble constant is,

this rate of expansion, you know, now. And when you do that, you always get an ever as a slightly different result. Okay. Right? Little, teeny tiny. difference, okay. Yeah. And again, all of this work is built on sort of this house of cards of assumptions to get you there in terms of like, we assume it's this brightness, we suit you, and therefore at this distance, et cetera, et cetera. And so there is an argument that one of the

reasons for this tension is because there's something wrong in that big list of assumptions that you've done. And of course, then an extra complexity comes from how you, you know, account for dust in the way to those stars that's reducing the light. And, things like that that we then detect. And so there's been big pushes to like reanalyze a load of old data as well with sort of modern techniques. And so Wendy Friedman's group is kind of arguing that when they now do this with lots of different standard candles, they actually get a result that does agree with the cosmic

microwave background results, assuming this big model of the universe. And so they're saying, well, the problem's kind of gone away. Okay. Whereas Adam Reese's group is still saying, actually, no, we still think. the problem is there. Now, it could be because the problem is with this effort. Right? And there could be some big assumption there.

This big crowding problem could be an issue for all of these methods where you can't quite isolate the light from just the one star either. You're getting like blending from other stars nearby. There could be issues with dust in the foreground. There could be all sorts of problems. But it's interesting to see that with different standard candles, maybe there's, there isn't an issue. But again, this is such.

difficult, so many step science. This is not a simple sort of, you know, quite as it was when Hubble was doing it, where he was like, measure, you know, the Red Ship measures some rough distance and do. You know, it's really getting into the weeds. So I'm really interested to see what's going to come out of all of this. I think JWST was sort of, the James Space Telescope, really lauded as like the savior for this problem. It was like, it will resolve the crowding problem.

We will be able to resolve individual. stars, we'll be able to get better distances, we'll be able to, you know, see more individual stars in more distant galaxies and things like that. But if anything, I think it's caused more problems. It's not because of more problems. It's raised a lot more questions. It's not been the quite simple solution. I think people were hoping that it would be, which is why I'm kind of thinking it could be an amalgamation of both of these things where we've said it's either new physics or it's something wrong with the data. And I think there could be a little bit of both aspects in there.

Yeah. Maybe I'm managing my bets. I don't know. Like, okay, and I guess it's one of those things. Like, as technology gets better, as our measurement approaches advance, we get more and more data, so there's more and more to scrutinize. Is that part of it as well? A little bit.

Yeah, exactly. Like what was Fuzzy Blobs is now resolved with JadWST and things like that. So there is an aspect to that. And sometimes, you know, you think, well, is more data better because then you'll, you'll get better statistics or is more data just, well, if we're doing a slightly wrong analysis on more data, then it's always going to, you know, we don't know that it's necessarily wrong because there's some assumption in the bigger house of cards, you know, then that's where, you know, sort of a big issue might lie. So it's interesting thing. And it could not just,

it might not just be the, you know, the local galaxies ones that we have an issue with the data. It could also be the Cosmic Microw background and how we've analyzed that, which, you know, I'm hoping we're going to hear about very soon. We've covered measuring this expansion rate from using nearby galaxies. But another approach is to study the cosmic microwave background, aka the CMB, aka the Echo of the Big Bang. Professor Sylvia Galley is from the Institute of Astrophysics in Paris. She's a cosmologist, so she's interested in studying the universe,

how it was born and how it evolved. And she told me what the cosmic microwave background control. show us. The cosmic macro background is the most ancient light that we can observe in the universe. It comes from an epoch when the universe was very, very young. It was only 400,000 years old and consider that today the universe is almost 14 billion years old. It's an extraordinary source of information about many different aspects of our universe. So it tells us what was the state of our universe when it was extremely young. The structures that we observed today in the universe, such as galaxies and so on, didn't exist.

We only had like a primordial soup of matter, of electrons and protons and photons that were all mixed together. So it tells us about how the universe was when it was very young. And also it gives us information about what happened later because then he had to travel for more. more than 13 billion years before arriving to us. So we have information about all of the path that it went through. So what fascinates me about this is that it's this incredible tool to study the universe as a whole. And obviously this episode is all about the Hubble tension. So what does it tell us about the universe?

The CNB is indirectly sensitive to how fast the universe is. expanding today. What's fascinating about it is that it has a average temperature which is very very low. It's about 2.7 degrees above the absolute zero. It has a super tiny variations of temperatures in different directions of the sky and one of the interesting things about these variations is that they have characteristic scale which is imprinted in these maps of temperature that that we can build of this radiation. And depending on how far the CMB is from us,

this characteristic scale will be smaller or larger. And so by measuring this characteristic scale and by measuring other statistical properties of this radiation, we can infer the distance. And then clearly the distance between us and the moment when the CNB formed depends on how fast the new universe expanding, by how much the universe expanded and so on. So we are indirectly sensitive to how fast the universe expands.

And we know that from measuring sephids, which is a typo start, that gives us one measurement. And looking at the cosmic microwave background gives us another. So how are you measuring that? What was that process? So we had some measurements in the early 2000, 2010s, very good measurements from supernovae. And then in 2013, we had the first release of the Planck satellite data, so CMB data. But for the first time, showed a value of this expansion rate of the universe from the CMB, which was lower than what the supernovae were telling us. The supernovae were around 73, 74, kilometers per second per megaparsec, whatever that means. With Planck, we had something around 67.3 at the time.

But, you know, the error bars were, at the time, were large enough that one could say, okay, it's a statistical fluctuation. You know, these measurements have noise. So it was, you know, like an interesting difference, but it was not yet huge. But this modern problem started with the release of the Planck results in 2013. Then we had the second release in 2015 and the third release in 2018. and the error bars for Planck just shrink entered on that value. For the supernovae, it was the same. They had new releases and the aerobars just shrinked.

And today, we are with the situation that the measurements are really different with super tiny arrowbars. So the problem is really there. It's not a statistical fluctuation. And I just want to jump in on that because this is where error bars are really quite important. So these are the things that give us a range from a result, right? So we might say, okay, by using these supernovae, we get a measurement of 73 kilometres per second per megaparsec, with quite big error bars. So if they were to eight figures on either side, if you got a measurement of 67 using the cosmic microwave background, that would be within the error bars.

And you've got that crossover and they're aligned. So this is the thing, isn't it? It's the fact that the error bars have shrunk down. There's not that overlay and that sort of wiggle room for measurements. So how are you feeling and what were you thinking when those results came through? Yeah, I must say I really remember before publishing the first Planck results. So there was a huge secret about the Planck results before the release of the data, we realized, you know, we were like, the world doesn't know what we know right now. It's not as low,

you know. I mean, I remember the excitement of, oh my God, you know, we are about to say that we might have a problem. And then, I mean, the problem just became bigger and bigger, right? And it became the more and more interesting. I think ruling out of the fact that this can just be a statistical fluctuation was important. And for many years, you know, we worked towards that goal on one hand. The second goal was clearly, I mean, there are two other hypotheses. The way we do the measurements is either of the two measurements is wrong. And I can tell you more about why I think the CNB side is very sound. Or there is really something fundamental we don't understand about the universe, which is clearly the most exciting hypothesis. Yeah, absolutely. And you mentioned earlier that you think the

CNB approach is pretty sound. Why is that? And what do you think then is causing this discrepancy? First of all, the plank result went under an incredible amount of scrutiny within the collaboration, but also outside the collaboration. There are people that have, you know, reproduced the analysis with different techniques and so on. And, you know, in all these years, the results haven't moved. The second most important is that 2025 was very important for these. this goal is that we have two other almost independent CMB experiments, which are the Atacama Cosmology Telescope Act, and the South Pole Telescope, which I have the pleasure to be part of.

And actually, my group led the analysis that we published in June. Both of these experiments measure, again, the Hubble Custent from the CMB and find agreement with the results of Blanc, with statistical uncertainties that are becoming comparable to the one of Planck. So these ground-based experiments measure the CMB at higher resolution in respect to Planck. So we are sensitive to characteristics of the CNB, which are smaller at smaller angular scales. We are more sensitive in polarization. So in some way, it's a different range of the CNB measurements, and still we get the same answer.

So which is incredible, right? I mean, it's three different experiments, different techniques on the ground, on satellite, different teams, right? Different teams, which is very important and we get the same answer. And just very quickly, finally, what excites you about the future of this work and this conundrum? So I think the super exciting thing is that people are very creative. So we thank our theorist friends that are on this problem. and there are continuously new ideas of how to solve this.

And the super exciting thing is about how much more data is coming. So I'm personally involved in keeping this adventure with the South Pole Telescope. We have plenty of new data releases that are upcoming these year and then next years. And just what? I mean, clearly, I think while the CNB measurement is extremely sound, I think the supernova part as well, I mean, they've been under an incredible amount of scrutiny from the community, and no one has found so far like a clear way of saying, okay, the measurement is wrong. But I think we are still waiting

for an independent measurement, which is as sound and as well understood as the supernovae and the safades to confirm that results. So that would, I think for the next year's, that's also what we are waiting for. This is the supermassive podcast from the Royal Astronomical Society with me, astrophysicist Dr. Becky Smythurst and science journalist Izzy Clark. So I want to take a quick break from this cosmological conundrum to talk about another one that I've heard which has come from the Royal Astronomical Society. So Robert, explain yourself, please. It's come directly from you, Robert. Don't blame me.

I saw this press release. for a new study that was titled, Dark Matter, not a black hole, could power the Milky Way's heart. So what's going on there? Because we've also had a few emails from listeners, being like, please, can you talk about this at the podcast? So let's go.

Yeah, that was timely, wasn't it? I actually saw the draft of the release, and I thought, oh, that's quite exciting. That's quite a thing. But, yeah, sadly, I can't take any credit for it whatsoever. However, it comes from this Argentinian-Igerman research group. Astronomy is brilliant, All these teams working across boundaries, led by Valentina Crespi.

She's at the Institute of Astrophysics La Plata, and she is Gaia data to understand the distribution of dark matter in the Milky Way. So dark matter is sort of actually more like invisible and mostly transparent matter. The stuff we don't know what it is, that what is it, quarter of the universe we don't understand, as opposed to dark energy, which is an even bigger chunk of the universe, we don't understand. Anyway, the group suggests that instead of having a black hole at the centre of the Milky Way, there's a big ball of dark matter.

Now, I thought about this and I thought that sounds completely mad, but then I thought really very large black holes at some level sound quite mad as well. So we can kind of pick our bonkersness when it comes to the things in the middle of galaxies. Their idea is it's made up of fermions, so light kind of dark matter, things like electrons and the quarks you find in the nuclei of atoms inside protons and neutrons. And they say that's the explanation for the movement of stars, the fast movement of stars that we see around the center of the galaxy. Now, in fairness, they actually say that it's difficult to distinguish between whether it's a black hole or a dark matable.

So they're just putting it out there that this could be a dark matable. And they suggest that the event horizon telescope, if you remember some years ago, there were those pictures. Big orange donut. Exactly, big orange donuts, the middle of, what was it, Messier, 81. 87 and the Milky Way and these beautiful, not many pixels, but these beautiful images just hinting at the picture of a black hole. surroundings. And so they actually say that could be the shadow of a dark matter core. Now that's, that's where it starts to get a little hard conceptually, admittedly. But they then say, well, if we have the VLT, the up and running very large telescope in Chile, as opposed to the

extremely large telescope that will come on stream in a couple of years' time, that can operate with nearby instruments to make what's called an optical interferometer. So like radio observatories work by aligning lots of radio dishes together, you can do it with optical. It's just a bit harder. And that can get ultra-sharp images and they say you could test it looking for this so-called photon ring, which is where the gravity of a black hole blends light into circles. And they predict that wouldn't be there with the dark matter ball, but it wouldn't be there with a black hole. So we'll see. I think the other point about it was that if the dark matter is sufficiently, if there's enough dark matter, that would collapse into a black hole as well. So it's slightly

mind-blown. We will see, I guess. You know, it's an intriguing idea. But yeah, who knows? I think they were just putting it out there and saying there's dark matter distributed through the Milky Way and maybe, therefore, there's just a lot of it. the middle. I mean, Becky, I can see you sort of pursing your lips here. Exactly. Hey, what are you from this, Debbie? I read the paper. It's a great paper. I think what was interesting about how it was then put out into the mainstream media world. I think lost a lot of sort of like intricacies

of this. First of all, it's not a new idea. And this was sort of like, I think, you know, sort of talked about on the news. It's like, whoa, oh, radical idea. No. People have been argued about what's at the central of the Milky Way for years, right? Like, is it a supermassive black hole? Is it a swarm of black holes? Is it just dark matter? And I think what's really interesting here is just to get across the idea that the reason we can't always tell is because it would be the same mass as a supermass of black hole. It just wouldn't be like super crazy dense like a black hole would have to be. Okay. Instead, it would be spread out over a larger area. And so what they were testing was sort of saying, okay, well, if it's spread out versus super dense, that will actually give us, you know,

know, sort of like a different behavior of the stars really close in towards the center of the galaxy, because they would get pulled on slightly differently by gravity if it was sort of all the mass was diffuse rather than super dense. And it does cause a very, very small, but supposedly measurable difference. And I think the issue is that we don't have the positions of the stars accurately enough to be able to actually test that measurable difference at the moment. Like with the data we have, we can't tell which is a better fit model, the dark matter cloud, or the black hole. And so that's what they're sort of saying. They're not saying like it's doubt matter. It's saying, hey, actually, we can't actually tell. And the whole thing about, oh, okay, the dark matter

could reproduce what the event horizon telescope has seen. It was a little bit kind of like a just so kind of scenario. It was like, in certain specific types of dark matter models, you could reproduce it and things like that. So I think it does have, like it's not quite as clear cut as like it's necessarily perhaps people have read. And so I think it's really interesting though that they've sort of like suggested that test of like trying to, you know, see if we can observe a photon ring. But that's been on people's radar for years, you know, of trying to sort of definitively prove that, you know, it is what we're seeing in the center of galaxies and things like if we can get it for the Milky Way. So I think it's really cool because if, you know,

but it's one of those things though. If the VLT looks and doesn't see anything, we'll be like, oh, we just, we don't really have the power to be able to see it, right? We don't have the instrument rather than being able to say clear-cut, it's definitely one of the other. Like, I think only if we actually detect a photon ring, will we definitely be able to say it's like a black hole. It's one of those scenarios as well. So it's quite frustrating in that aspect. Okay. All right then. Thanks, guys. Let's get on to some questions about the Hubble tension. Becky, we've had this great question from long-time listener Yandri. Hi, Yandri. And he's just started an undergrad in astrophysics and says that throughout high school,

the Supermassive podcast was a big inspiration for me to pursue astrophysics. That's so nice. That's amazing. Gold star for everybody. Gold star for Yandri. Gold star for us. Becky will help you with your coursework anyway. Been there, done that.

Not doing it again. Becky, this is Yandri's question. He says, could the crisis in cosmology be an indicator of dark energy being non-constant throughout the universe's history? My reasoning is that since we are using the cosmic microwave background, which is from a very early period in the universe, maybe the result of the rate of expansion from that era

is different from the results gathered from the present because dark energy is behaving differently now. I remember hearing about a scientific paper that came out not too long ago that proposed that dark energy could be weakening, could this tie into it. Well, that is a great question, Yandri. And yes, this could definitely be one of the things that falls under the category. degree of like new idea in physics to explain this Hubble tension or crisis in cosmology. Because there's been, yeah, lots of results suggesting dark energy could be changing with time.

So let's take a step back so we understand this. So first of all, Hubble came along and discovered the universe is expanding. And there was that nice correlation between, you know, the distance away and the speed that galaxies were moving. So you've got this nice proportional line between the two. So you assume the expansion is constant. And that's how we ended up with the Hubble constant. Adam Reese and Co. come along in sort of like the late 90s, and they push it out to greater distances and actually find the line isn't a straight line anymore, and it moves, and therefore the universe is accelerating, right?

The expansion is not constant anymore. And we don't know what's causing this accelerated expansion of the universe, but we call it dark energy, and we just say that's the thing that's causing it. And again, we assume it's constant. we assume a constant acceleration rate. And with that assumption is how you get from Plank observing the cosmic microwave background to calculating what is the expansion rate today, right? Because you base your model of the universe on it having a constant acceleration rate, constant dark energy.

But now, recent results have come from DESE, the dark energy spectroscopic instrument, which is like mapping the positions of galaxies over a huge volume. so out to great distances. And they're saying, actually when you do that, the acceleration also appears not to be constant. So the thing causing the acceleration, dark energy also not constant.

It's changing with time. So the universe is actually, if the physics term of it is jerking, right? So it's speed, acceleration, jerk, right? So we assumed the speed was constant. It wasn't. We assumed the acceleration when that was discovered was constant. It wasn't.

Now we're like, okay, is the universe jerking? Watch it just be endlessly cyclical and the jerk isn't constant either. But anyway. So now we think maybe that is the case. There is some tentative evidence that is what's going on. Desi is still working on this. There'll be probably some insight from Euclid when we get that survey, the new space telescope that's gone up as well.

Lots of lots and lots of instruments are going to be focused on this. So if that is the case and the universe is jerking, right? And the acceleration is not constant. then that assumption that you make to map what's going on with the cosmic microwave background to the structure we see today and we assume there's constant acceleration in that time, that's going to be wrong, right? And it's based on a faulty assumption and you're going to get the wrong answer for what's the acceleration rate of the universe today then.

So you've now got people posing what are called W0WA CDM models. So our current best model of the universe is Lambda CDM, which is like constant dark energy. this is now not constant dark energy. W is like the letter we use for dark energy in physics. W0 meaning W now, dark energy now, and WA meaning it can change with time because A is the scale factor. I won't get into it.

But basically, I read it as WoWW models. I don't know if cosmologists do that, but I'm like, whoaa CDM, great, wow, you know, that kind of a wow. Inself Owen Wilson. It is, it is. Or the totally addicted to bass song from the 19, the wow wow. I read it as that. Anyway.

So that's what people are working on now is these wow what models, right? Changing, acceleration changing with time. The problem is until we know that behavior of how the acceleration rate is changing with time, hopefully coming from these big surveys that are going to map galaxy positions and things. And obviously from the gaps between them is how you track it. A 3D, you know, distances between them changing with time. You can't get like an accurate or reliable estimate. of the expansion rate now

unless you have that information. It's another little house of cards, right? Plus the models kind of need fleshing out because people have spent decades working on Lambda CDM and now it's like, oh, we need to change things and how does that ripple effect through everything else and what we change? So I think we're, I mean, I would say a few years,

but maybe even like a decade or two out from understanding this fully and actually whether it is the issue to solve this Hubble tension as well. maybe even Yandri will be doing, you know, maybe you're doing your PhD in this in the future. I don't know. Maybe you'll be the one to crack it.

Who knows? Or part of a probably giant team that eventually all come together to crack it, right, from all across the world, because that is what it's going to take. Yeah. Yeah. Oh, great question, Yandri.

Thank you for that. Robert, Stephen Bryant in Australia says, Hi, supermassive, love the podcast. I've noticed that Einstein's cosmological constant seems to be in favour again as the explanation for the expectation for the expanding universe. My understanding is that Einstein discarded the cosmological constant

once the universe was found to be expanding. So how does this help explain our current understanding of the model of the universe? Is it exactly the same as Einstein's original or has it been adapted? Yeah, thanks, Stephen. And you're right about Einstein. So he introduced the cosmological constant

for his theory of general relativity, the theory of general relativity that's so important. And it was put in to make the universe static, so having this kind of repellent component rather than collapsing under the force of gravity. Because when Einstein published his theory of general relativity, we weren't talking about an expanding universe. There was no idea of a big bang or anything like that. So when it was found to be expanding, then yes, the constant was dropped because it was no longer seen to be necessary, you know, nice expanding universe and all the rest of it. And astronomers then spent, I think,

about 60 years debating more or less whether the universe was going to expand forever, the rate at which you would do that, or perhaps it would collapse in a big crunch. It was quite a popular idea when I was a lot younger. So it was reintroduced because of our Nobel Prize. I mean, against Adam Reese and his team, he worked with Saul Permuda and Brian Schmidt. They observed supernovae in the late 1990s. They realized from those observations that the expansion of the universe was accelerating, and they won the Nobel Prize for that.

And that effectively reintroduced Einstein's cosmological constant this time, the lambda bit, the dark energy, this stuff we don't really understand. You know, we know it's there, or it might be getting, we don't even know whether it's really constant actually. So that's a kind of a part of it that Becky was talking about too. But in any case, yes, that's driving the expansion of the cosmos to get faster. It's broadly speaking, what Einstein had in mind. It's just that Einstein believed in a, at least at the outset, in a kind of static universe.

I guess I'm not sure how people at that time thought about the origin and end of the universe, but they certainly didn't have the idea that it started in the 1910s, the idea that it started very, very small and then expanded in the way that we now know it did. So that's the real distinction, I guess. But yeah, the premise is not that different. And it was really weird to have something disappear for six decades and then to be reintroduced again. That was all like the 1930s and 40s, I think. Like we talk about the great debates in physics.

One was sort of like, you know, the Hubble debate about our galaxies outside the Milky Way or not, or are the islands of just like gas in the Milky Way? And the next great debate was like, is the universe like a, I think it was described as like a cosmic egg, you know, just like a little ball. that's been there forever, you know, or is it this, you know, the big bang that it was eventually dubbed by Hoyle as well as almost like a slur against the idea.

Exactly, yeah. Back in Einstein's time, it was decades before that debate. So, yeah, it's interesting to think how just from a bit of like, huh, the maths doesn't work, you know. I can't introduce this term. I'll put it in. He goes, oh, that was stupid, wasn't it?

And now everyone's like, oh, put it back in. There's your Lambda CDM. There's your constant acceleration rate. But now, Maybe, you know, we'll do away with Lambda for the woeers as well. The wow our models. So who knows?

Maybe it will end up being as great as splendor, you know? Exactly. And it all will be in their headlines. Well, I was going to say, who knows where cosmology will be in a century's time. But, you know, it's the, yeah, and Hoyle had the idea the steady state universe. So expanding, but then matter just appearing from nowhere. And it was what, it was a few hydrogen atoms per cubic meter per year. So it sort of seemed reasonable.

And also something you'd really struggled to measure. So his idea just was that. the universe got bigger and then galaxies and stars appeared to fill in the gaps. Yeah, but he was very dismissive at the whole big bang, as you say, Becky. Yeah. I'm just really laughing about the fact that maybe that will be, when we finally figure out the Hubble tension and we finally figure out the crisis in cosmology and like we maybe like settle on the fact that, yeah, we don't have a Lambda CDM, we have a wow, wow,

model, CDM model or whatever it is. The headline will be like, turns out Einstein was right. Lambda was his greatest blunder. And that'll be like the spin that the headlines will put on it. And yeah, it would be very funny, I think. Oh, gosh. And if you want to, I was just thinking about this, we should probably also flag that we did an episode on the end of the universe

quite a while ago. So if people have more universe questions, then maybe give that one a listen. But thank you to everyone that sent in questions. Keep them coming. You can email podcast at rass.ac.org or find us on Instagram at supermassive pod. a lot of these questions were too long that people had to go into the DMs to be like, I have things today. But I think this topic in general is just so interesting because it shows what research can achieve, explore and look into and why we need it.

And Becky, I know that that was something that you wanted to talk about as well. Yeah, we've had some news this month. Me and Robert will probably just, you let us will grumble about it for a long time. So we won't take too long time. but there's been some news that there are proposed cuts coming to essentially the body that gives out the money to astronomy and astrophysics research in the UK. Yeah. And they've essentially said there's been a proposed cut of 30% in the budget, but that team should prepare for scenarios of 20, 40 or even 60% cuts. Wow.

Yeah. And it's very frustrating because it all comes from sort of the, so we've got the, UK research institution at the top, UKRI, and then that sort of like divvies up funding two different bodies. And the one that astronomy falls under is called the STFC, the science technology and facilities council. And basically, the reason the funding cuts seem to be coming is because facilities costs are going up. So like the big facilities, the big, you know, sort of like experiments, that kind of thing, who like the rest of us are just dealing with absolutely huge energy bills. Right. And so weirdly because of the way the SDFC is set up, that's not coming from a

different pot of money. It's all coming from the same. And so basically, like, astronomy and nuclear and atomic physics are seeing a cut to their research budget because of rising energy and whatever other costs for running big facilities that aren't just used, even by astronomy and nuclear and atomic. It's also used by, like, medicine as well. So we seem to be, like, paying the brunt of the cost for this. And I think that's why people are so frustrated here. Yeah. Is there anything that can be done in terms of listeners and support and anything that can help kind of voice that and voice concerns. I'll jump in, yeah. I'll jump in.

The answer is I think yes. And the other aspect of this is that UKRI, the body that Becky was referring to, is supposed to work things out for the whole of science. So it's sort of like no science should be left behind, if you like. And it's just this unfortunate structural issue that's meaning that SDFC and astronomy, which is what we're talking about, but also particle physics and nuclear is being here hard as a result. And I think that's a huge shame. It's incredibly inspiring science.

So we've actually got an open letter. If you're a physics teacher in the UK and listening to this, we've got an open letter that you can sign saying how good it is for your students. And I think we've got, we've pretty sure we've got a bit of getting on for 100 signatures on that already. So it's doing pretty well already. Big on the knowledge. Yeah, exactly. Big up the physics teachers because they're people that the government wants to get on board.

They want people to be doing physics. They want people to be doing science in general. And astronomy is a great vehicle for that. So at the very least. It's a gateway science, as I like to call it. Exactly. Yeah. People are addicted and lose them in with pretty pictures.

So you can sign that if you're a visitor teacher. We might do a more general open. This is we, the RAs, might do a more general open letter soon as well. But we also have a model letter mainly for our fellows, but anybody's welcome to use it where you can, it's on our website. You can basically take the text on that, adapt it for your local MP and write to them and say why this stuff matters to you. And that would be really, really helpful.

Because I think it just seems to me that, you know, why would you even inadvertently single out sciences like astronomy, particle physics and nuclear physics. It's like it just seems absolutely ridiculous when we know our inspiring there are. And it's almost simply a structural issue, simply the way the research councils was set up, which was what 17, 18 years ago in their current form, there's no reason to my mind where that can't be fixed. Now, I may be widely optimistic. Somebody can probably turn on me and say, oh, it's impossible for whatever reasons. But I don't believe that. I think this can be fixed. It's a very small part of the science budget. And let's not trash UK astronomy,

not given that we're so good at it, Frankie. It would be an enormous shame to see that happen. Yeah, we really punch above our way, you know. And just as a reminder when people are thinking budgets, money, like, you know, it's not like we just fire this money into space. People are like, whatever. This is money funding people on the ground, right? This is, you know, actually like contributing to UK economy and things like that. For example, my PhD was funded by STFC. I have applied for a funding to actually stay in a job from UKRI. You know, there's things like that. It's funding PhD students. It's funding early career researchers, you know, that aren't like fully academics, hired. by universities yet like myself. So it's just, it's like it's the people that you end up missing out on. So if there are people out there who are like, I want to be an astrophysicist in the future or have people in their family that are like, you know, aspiring to be that. There's not going to be the jobs for those people in the future if this kind of cut comes through because this stupid, just bureaucratic way of things being structured.

This is why we're like all up in arms. So yeah, I've written to my MP. I agree. I hope everyone else does it too. Okay. And actually I can put a link to how people can get involved, email their MP, anything like that in the episode description. So take a look at that. So as usual, shall we finish with some stargazing? What should we look out for in March, Robert? Yeah, well, we're moving back to those longer days now. And on the 20th of March, we've got the Equinox.

I know, I know, you shouldn't say this as an astronomer, but I actually quite like the summer too. It's a warm stargazing. Exactly. Exactly. Exactly. And that's when the equinox is when the sun appears to be on the equator of the sky, the celestial equator. So if you lived on the equator, it would be directly overhead. But as it happens, that's not actually the day of equal day and night, because when the sun is rising or setting, there's a noticeable lift in the position of the sun due to the bending of light that's caused by the atmospheric refraction.

And so that means the date for the UK when day and night appear to be equal, which is called the Equilux at our latitude is actually around the 17th of March. just something to be aware of. It only makes a difference of a few minutes. But either way, we're definitely moving into spring. So that means more spring stars. So Ryan's still around and keep looking at that. When is that not good to look at?

But then further round, you've got constellations like Cancer and Leo and Virgo are more obvious and the plow on us a major higher up in the sky. It's also a really good time to look for galaxies, actually. So connecting with our episode a bit in a slightly 10-year-s way, looking at galaxies with binoculars or a telescope is a good thing to do in the spring. They're not visible to the naked eye, definitely, but you know, a good bit of oculars will pick out the brighter ones. You can sort of see the list, Messy 87, for example, is reasonably bright. And if you're lucky enough to have a

sea star, which, of course, I always tend to forget these days, there's so many of those out there, it must be a really, really good time to take pictures of those galaxies as well, because there's simply so many of them. It's simply so good at imaging them. So do that, and please, you know, tag us in your pictures as usual. And for planets, Venus is back in the evening sky, and that's always dazzlingly bright, and it'll be visible now until the autumn. So, the western sky and then getting higher over the next few months. And if you look at it through a telescope, it looks like a tiny moon, a gibbous moon, and it'll be shrinking in phase, so becoming, first of all, more like a half moon and then a crescent shape and so on, and getting bigger

as the weeks pass. Saturn is just about visible in March, and then too close to the sun to be seen, and Mars is out of view this month. Jupiter, though, is still easily really visible in Gemini, so, you know, do have a look at that with binoculars or a telescope, and you can see the weather systems and all those kind of things. At the time I'm recording this, I actually got a rare clear night because the weather's been absolutely terrible and saw it last night. Neptune's really close to the moon on the 7th of March, so that's one of those things where it'll look like not much. It'll look like a tiny dot with a decent telescope or a star with a pair of binoculars. But on the 7th March, if you become Stelarium or one of the apps, you can find that

one if you've never seen that ice giant. And then on the 29th March, the moon moves in front of the brightest star in Leo, regulus. That's something we call an occultation, which just means, well, one object moving in front of another. And in the UK, we don't see it go into, we don't see the moon covering up regulars because it's happening in daylight, but 8.20 that evening it will come out and you can just see it poking out. It's always quite a fun thing to see. You really need a telescope for it.

I think it's hard with binoculars. But you get that sense that the moon is actually moving just as you do during a solar eclipse and then this star just suddenly pokes its way out. And then finally, we're still, you know, not that far off solar maximum. and there's still lots and lots of sunspots. There's a really fantastic group visible just the other day. If you've got a safe solar filter, it's a really good time to look at that. And there's still a good chance of displays in the northern lights as well.

Which also means that you can see the aurora if you're flying anywhere, don't forget. So even if you're not going to be anywhere, like, you know, if you're not going to be in Iceland or Norway, but you happen to be flying transatlantic, you might be able to see the aurora on a night flight. I have seen it before. So you have to make sure that you book your seat on the correct side of the plane. Fine. Noted. So yeah, usually if it's a night flight, it's coming back from the US to the UK.

So if you're flying that way around, then make sure you're on the left side, the north side of the plane. Yeah, yeah. Every time I'm on the right, well, the right side of a plane, I'm like... The correct side. Exactly. It's like, don't confuse people. I always just have that feeling of like, maybe I'll be lucky. and it doesn't happen.

But hey, we can always hope. Yeah. Because you can also, you can speak to the flight attendants, right? And say, look, I would like to see the Aurora if they're visible tonight. If you hear, if you see anything or you hear from the captain, because sometimes the captain will make an announcement, but they're often conscious that if it's like the middle of the night and people are sleeping, they won't do.

Which I'm like, no, wake me up. Like, I want to be woken up. So, like, you can speak to the flight attendants beforehand and say, if they're visible, could you please come and wake me up if I'm asleep? Or just let me know. That's such good. Good tip. So, I mean, I obviously, I leave my window blind open.

And if I'm watching a film, I'm like every five minutes, I'm like glancing. I'm like twitching to look out of the window. Double screen, like, oh. Yeah. And obviously I know people will want to sleep on flights, but that's one way to do it. It's just to sort of say to your flight attendant, if they are very strong and obvious with the naked eye, then please wake me up. Oh, so good. Okay. Well, I think that's what I do.

Yeah. And I will now also do that too. I think that's us done for today. All the flight attendants listening going, no. No. Hi, I want to breathe. I'm so sorry, fly a dog. You can't sleep because I need to not sleep to see the auroras.

Got it. Thank you. But I think that's it for this episode. We'll be back with a Q&A in a few weeks' time. And our next main episode is going to be about rogue objects in space. Oh, sounds fun. Very intriguing. I like it, Izzy.

Contact us if you try some astronomy at home. It's at Supermassive pod on Instagram or email your questions to podcast at r. RAS.ac.ac. and we'll try and cover them in a future episode. But until next time, everybody, happy stargazing.