The Hunt for Dark Energy with Jason Rhodes

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2:18StarTalk listeners can get 20 % off their Rosetta Stone Sapphire subscription when they sign up today. This gets you access to Rosetta Stone Sapphire in 25 languages. Visit RosettaStone.com slash StarTalk to redeem your 20 % off. That's RosettaStone.com slash StarTalk. Just la hora, amigos. Paul, we're on the trail of dark energy for this episode. Yeah. And we're hoping to find something, but if we don't find something, that means we found something, so everything's fine, and it's all going to work out in the end. Okay. Not exactly how science works, but we'll catch up on the latest of NASA's effort to decode this most mysterious thing in the universe coming right up.

3:06Welcome to StarTalk, your place in the universe where science and pop culture collide. star talk begins right now this is star talk neil degrasse tyson here your personal astrophysicist my co-host today paul mccurio how you doing paul i'm great neil good to see you again all right professional comedian you got a broadway show uh is it on broadway or off broadway it was off broadway and broadway but now we're touring around the country with it we're touring We love that. Yeah. We love that. We don't want to keep you just for new. No, people want a lot of me. Plus, my wife wants me out of the house and the late show's over.

3:52Oh, that's right. That's right. You worked with the late show. I forgot about that. Yeah. Well, now it's. Everybody's on the street looking for gigs. Yeah, exactly. I'm selling lemon ice in an hour. So can we get this moving along? I got a cart that's not going to sell itself. So, subject of today is dark energy. Ooh. Is that what you are, Paul, you think? I am. Yes. I'd say dark, low energy. There's a telescope en route to its destination at one of the Lagrangian points called the Nancy Grace Roman Space Telescope. Another generation of space telescopes taking the universe by storm. And we have one of the world's experts on that, a friend and colleague, Jason Rhodes.

4:42Jason, welcome to StarTalk. Thanks for having me on. I'm super excited to talk about Roman and dark energy and all the science it's going to do. Yeah, very cool. Let me get your proper CV here. Senior research scientist at NASA's Jet Propulsion Lab. We all love JPL out there in Pasadena, California. It's one of the jewels in the crown of all that California gives the world. So thanks for being a part of that. And it's not your first rodeo with us, so thanks for returning. Thanks for having me back. Which is weird because Jason said he'd never come on again. That's how he told you. He called me.

5:18He said, what's up with the thing? I'm like, I don't know. I can't. I got my own problems. So the envelope of cash changed his mind. Is that what that was? Exactly. Jason, the last time we had you on, you talked about the Euclid mission. We'll get an update on that later in this conversation. so so just tell us all about the nancy grace roman telescope first who was nancy grace roman and how can this telescope see something that is called dark like what's up with that yeah so nancy grace roman was nasa's first chief astronomer back in the 1950s and one of the things she did is she championed the idea of space telescopes you know before that all the telescopes were on the ground.

6:01And she was in fact called the mother of the Hubble Space Telescope because that was NASA's first big flagship space telescope. And we decided to give her her due by naming NASA's next flagship space telescope, the Nancy Grace Roman Space Telescope, after her because of all the incredible work she did in convincing NASA and the world that putting telescopes above the atmosphere was a great way to study the universe. At the risk of saying something completely obvious, but I just want to make sure we're on the same page, remind people of the value of putting a telescope into space rather than on Earth's surface.

6:43Well, there's a few. The biggest one is being above the atmosphere. And so when we're kids, we learn this song, Twinkle, Twinkle, Little Star. And stars don't naturally twinkle. It's actually the atmosphere that's causing what we see as the twinkling. And so if you go above the atmosphere, you get a much clearer picture of stars and galaxies. The other big thing that we're allowed to do when we go above the atmosphere is we can go to somewhere called the Lagrange point, which is beyond the moon, and it's dark there all the time. So we don't have to only use the telescope at night. So this is a more efficient place to have a telescope in terms of how often we can make observations.

7:29Well, we have a special explainer on Lagrangian points, which was fun to deliver, and I think it's actually done quite well on one of our YouTube channels. But that Lagrange point, that's not the only telescope at that Lagrange point. Isn't the James Webb telescope at that same Lagrange point? That's right. The James Webb Space Telescope is there. The Euclid Space Telescope, which I talked to you about last time, is there. And there's telescopes there like the Planck Space Telescope. This is a telescope that European Space Agency launched quite a while ago to study the earliest light in the universe.

8:06It's no longer active, but it was at L2, the Lagrange point two as well. This sounds very crowded. I'm just wondering. I was thinking the same thing. But one goes on the other, right? Hubble uses mostly visible light, James Webb's infrared light, and Roman is near-infrared light with some visible light capability, right? So there's sort of a stepped process here. Paul, you're showing off now. Paul, you're showing off. I'm done for the day. You know this. That's all the science you have to put back in the convo? I have a very small brain, and I just gave myself a headache. So, Jason, I was out under the stars a few nights ago pointing out constellations for random passersby.

8:47And I couldn't help notice how many artificial satellites were crossing my field of view. Not 10 or 15 years ago, I would go the entire evening spotting maybe one or two of them, at most three. And that evening, I counted 40. Many of them are probably Starlink from SpaceX. But what has that done to ground-based observing that may require that everything have to be put in space in the future? Can you just comment on that? Yes. So these multiple, you know, small satellites that are being put into low Earth orbit. Thousands. Don't say multiple. Say thousands. Thank you. Thank you. They create streaks in the image from a ground-based telescope, but they also create streaks in the images from some telescopes that are also in low Earth orbit.

9:46So NASA's got a telescope called SPHEREX, which is doing a survey of the whole sky in the mid-infrared, and that sees streaks from these thousands of telescopes. And that's another reason we want to send a telescope like Roman out to the Lagrange point, because then we're very far away from Earth. We're also very far away from these thousands of low Earth orbit satellites. So we can add that to the list of reasons we're sending Roman to the Lagrange point. So you agree it's pollution. It's another form of pollution, in a sense. That you have to work around and factor in, right? Yeah. In terms of developing this technology.

10:27You could say it's a data processing challenge. How's that?

10:41I'm Brian Futterman, and I support StarTalk on Patreon. This is StarTalk with Neil deGrasse Tyson.

10:55What is the Nancy Grace Roman Telescope going to be looking at that enables it to track dark energy? Because last I checked, you can't see dark energy. So what's up with that? The Nancy Grace Roman Telescope is going to have three different ways of measuring dark energy. And dark energy is the name we give to whatever is causing the accelerating expansion of the universe. And we don't know what that is. And we don't know what that is. It's really the name we give to our ignorance of what that is. That's why we call it dark. Yeah. Well, I think, I mean, dark is a little more elegant than we have no effing idea energy.

11:32You know what I mean? Oh, gotcha. It feels a little more elegant on some level. A little more mysterious. Okay. Yeah. So we have to study this dark energy very indirectly because we can't see it. And so one of the ways that we study it is with supernova. And a supernova explodes, and it's what we call a standard candle. So we know how bright it was and how far away it was. And by looking at those over cosmic time, we can see how the universe has expanded over cosmic time. There's another way that we're going to use with Roman, and that's look at the clustering of galaxies. Yeah. So the expansion rate over time, the extent to which that doesn't match what matter would have it do, you then ascribe the rest of that to the influence of dark energy.

12:25Is that a fair way to say what you just described there? That's exactly right. In a universe with just matter and gravity, we would expect the expansion to be slowing down due to gravity. And in the 1990s, two teams simultaneously were trying to find out how much the universe was slowing down due to gravity. And they were using supernova. And they both came up with the same answer, which was it wasn't slowing down. That expansion was speeding up. And it was great that there were two teams because both teams thought this can't be right. And in terms of what they thought was happening, they were correct.

13:02There was more to the universe than just matter and gravity. There was the dark energy. And one of the great lessons there, of course, is a singular scientific result, especially if it's either unexpected or weird, is not really a scientific result until it's verified. And so I wonder what would have happened if it was just one group that came up with that result. That would have been a little weird, right? That's exactly right. And that's why we're using multiple techniques with Roman to study this dark energy. And in fact, there's multiple telescopes out there with a primary goal of studying dark energy because we want more than one telescope to understand this really mysterious aspect of the universe.

13:44And so we've all heard about this Hubble tension that came about from the observation of galaxies, misbehaved galaxies in the early universe with the James Webb telescope. Would the Nancy Grace Roman help address this Hubble tension, this cosmology and crisis that headlines are talking about? Absolutely. Roman is coming at just the right time to address this Hubble tension. And this tension arises from us having very good measurements of the early universe and thinking we understand the physics that gets us from the early universe to the universe we see today. But the universe we see today not quite matching what we would expect given that early universe and the physics.

14:31So something we think might be wrong. It might be our understanding of the early universe, but we've got really good measurements of that. It might be we don't know the physics that gets us to the later time universe that we see now, or maybe it's imperfect measurements of the late time universe. And what Roman is going to do is it's going to give us really, really excellent measurements of the late time universe. And so while scientists were supposed to be sort of agnostic about what we're studying, most of my colleagues are hopeful that the answer is new physics because that's what's exciting.

15:08You know, what's exciting for a scientist is when they look at something, they go, huh, I didn't see that coming. So you feel confident that that's 100 times the span that the Hubble telescope can cover. Right. So you're all feeling confident that some answers will come regarding dark energy. But what would surprise you more what dark energy is or maybe that our understanding of gravity or physics is incomplete. We have to come up with a new science. Do you all have a gut as to what you think you might be getting through, Roman? Well, I really hope it's this new physics. And I don't know exactly what that new physics might be.

15:47And the reason I hope that is all scientists hope to live through a revolution in the understanding of their field. That's the most exciting time to be a scientist. And I was in graduate school in the 1990s when we had this revolution of learning that there was dark energy. And so I'm really fortunate to now be, you know, in the midst of my career working on something that might have another revolution, which tells us what dark energy is. You know, I just hit on something. I just hit on something real quick. You scientists are brilliant because even if something fails, you will say it didn't fail.

16:24we just found something incredibly informative that we didn't know you i want to be you i you guys have figured this out man because neil will always say like a failure isn't a failure in science it's just opening up another avenue that we haven't thought of right but so jason wouldn't wouldn't changing dark energy because in in general relativity dark energy is just a constant term in that equation. So with a changing dark energy term, that is, dark energy is a function of time or size of the universe, that kind of means new physics, right? Because you're not getting that for free out of general relativity, because general relativity requires that it just be a constant number.

17:11Are you still thinking of yet some other physics nobody has even conjured yet? No, certainly some of the models of dark energy have evolving dark energy, a changing dark energy. Those aren't the simplest models, which is the constant dark energy or a so-called cosmological constant. But what we're seeing is tantalizing data from other telescopes that tell us that maybe that simplest model isn't the right model. And we do have perhaps an evolving dark energy. We have an incomplete, rather than wrong, incomplete understanding of how gravity works. Of course. See how we do that, Paul? You got that, Paul?

17:53Wow. Hang on. I got to make sure I still have my wallet on me. You guys are slippery. That's right. You are a slippery group of people. So Roman's like doing the job of like the USS Enterprise, right? It's exploring the universe. The difference is when Roman Link finds a new planet, nobody immediately falls in love with a green alien, right? I mean, is that the difference here? We hope not. So is time-dependent dark energy what you're calling new physics? Or is there some other physics undreamt of that you're considering in this scenario? There are many, many different theorists with many, many different ideas for what this might be.

18:37and time evolving dark energy is one of them. But as I said, modified gravity, that's what we call the fact that Einstein's theory may have been incomplete. You could have modifications to our theory of gravity that would explain some of the observations as well. And one of the reasons we're going to study this phenomenon with multiple different ways with Roman is we want to be able to distinguish between time-evolving dark energy and a modification to gravity and all these other theories. And any one way of probing dark energy might not get at it, but multiple ways will allow us to study the whole gamut of theories.

19:18So Jason, like the James Webb Space Telescope, which was tuned for the infrared and conceived, because I remember when we were specking that telescope in the decadal survey, now three decades ago, we wanted it to be able to specially get access to the early universe where galaxies were being born. It just so happens that same design telescope can probe nearby gas clouds and observe stars and planets being born, which is a fun sort of duality of that telescope. You're telling me that you're going to see supernova across the universe, across time. does that capacity give you other utility in questions we might have about the universe that might have nothing to do with dark energy?

20:09Oh, certainly. So the supernova survey is only going to look at a small area of the sky and wait for these supernova to happen. But the other surveys that we're going to do to study dark energy are going to look at big swaths of the sky. And one of the ways we do that is the camera, the wide field instrument in Roman is about a hundred times as big as the comparable camera in Hubble. So we'll look at hundreds or thousands of times more area of the sky and we'll look at things that allow us to study dark energy, but we'll put that data in an archive and that archive data is going to be useful for a huge range of astrophysical questions literally for decades to come from planets in our solar system to, you know, planets throughout our galaxy to studying galaxies throughout the universe.

21:05There's going to be a huge range of science questions that we can address with this same data that we're taking to study dark energy. I just have a quick question. So can we talk about the telescope for one moment? So you talk about multiple ways that it's going to do this. So, and Neil's going to yell at me for knowing this, but it's a total spectrum range spans wavelengths from 0.48 to 2.3 micrometers, right? So the telescope can break down light coverage through two core instruments, which is a wide field instrument and a coronagraph instrument. Are those the, those are the two main vehicles through which this information will get taken?

21:45So the coronagraph is a whole different instrument that's not useful for studying dark energy. So what a coronagraph is, is it's an instrument that allows us to take direct images of exoplanets, planets outside of our solar system. And what it does is it creates an artificial eclipse. And it eclipses the star so that we can see the much fainter planet that's orbiting the star. And if you think of, if you've ever seen a solar eclipse, it's an amazing thing to see. The moon eclipses the sun, and you can see the light from around the sun. That's called the corona, you know, Latin for crown, around the sun.

22:28And that's the only way you can see that light directly around the sun, because you have to block out the very bright sun. So the Roman coronagraph is a technology demonstration instrument that uses a bunch of new technologies to give us about 100 to 1 ,000 times better ability to block starlight and see very faint planets orbiting those stars. Can I ask a layperson's question for a moment? It seems to me, Rome, it's counterintuitive in a way. If we want to really try to drill down on dark energy, does it exist? What is it? A wider swath. It seems to me that a more narrow focused telescope analysis would get us to that answer more so than a wide angle.

23:12I know that sounds probably rudimentary, but. Well, he said he's doing both. He's got the narrow field of view that'll look and wait for supernovae. Because if you've taken enough of the universe, you're pretty much guaranteed to get a supernova going off practically on schedule. So he's got that. And that's the sort of the pencil beam view through the greatest depths of the universe. And that's one way. And then another way. So are you looking for, in your wide field view, what are you looking for that could reveal the presence of dark energy in that field of view? So in the very wide surveys, we're going to have two different ways of studying dark energy.

23:52One is looking at the clustering of galaxies and how that clustering of galaxies changes over cosmic time. And how close galaxies are to each other is sort of an interplay between gravity pulling them together and the dark energy pushing them apart. And so to do that, we need a huge statistical sample of galaxies. And that's why we want to look very, very wide. But you have to disentangle the effects of dark matter on top of that. That's right. That's the other big component of the universe. But how do you disentangle something that you don't even know exists? That was my next question, Paul. It was not.

24:34Don't lie. We don't know what dark energy is. We don't know what dark matter is. And there they are intermingled in the clustering of these galaxies. And what hope do you have of disentangling those two effects? Roman is going to be amazing at mapping where this invisible dark matter is. and how we do that with Roman or any telescope, but Roman is going to be just amazing at this, is we look at a distant galaxy and the light from that distant galaxy comes to us and the path of the light is bent by that intervening dark matter that we can't see, but we know that dark matter is there because it has gravity and gravity bends space and the light travels through space.

25:17So those distant galaxies will have slightly deformed and warped shapes. and by looking for coherent distortions in galaxy shapes across many thousands or millions, or in the case of Roman, hundreds of millions of galaxies out there in the universe, we're going to be able to create very intricate maps of where that dark matter is. And that's the third technique we're going to use to study dark energy by mapping the dark matter using this technique called weak gravitational lensing. And the gravitational lensing is the bending of light, and the weak just means that we're seeing very small distortions in the shapes of these background galaxies.

25:59If you map in detail the dark matter, and we can trust what those maps are and the distribution is, then any effects beyond that, you get to credit or blame dark energy. Is that a fair way to characterize that exercise? That's exactly right. if we believe that our knowledge of gravity is 100 % complete and accurate. Right. So this becomes the problem. And this is why I want my taxpayer dollars back. But this is why we're using three techniques. Right. And so, I mean, look, we're going to map billions of galaxies. Is there a more efficient way to do this? I mean, if Men in Black taught us anything, it's just go to a locker in Grand Central Station and it's there.

26:47Right. It's C-18. That's the that's the place to find your galaxies right there. Right. Yeah. Yeah. That's a missed the memo on that one. Yeah. We're still doing it the old fashioned way. Thank you. Yeah. We still use telescopes. Yeah. Let me get back to the chronograph for a minute. So with the chronograph, you're just piggybacking on a telescope that had other priorities. What did you find some extra sort of square footage on its outer surface and slap on and the whole other. I mean, what was the planning for this? Did you just have exoplanet people looking outside over the fence? Can you let us in?

27:26Can we join this launch? Yeah, I mean, how did exoplanets show up in the portfolio here? Well, first I'll say that the Wide Field Instrument is also going to do a survey. Maybe we'll talk about that later to find a bunch of exoplanets. But when you talk about, that was always a plan for Roman since the very beginning. But when you talk about how the coronagraph came to be part of this telescope, the original plan for Roman was a smaller telescope than what we have now, about a meter and a half across instead of the 2.4 meters we have now. But when it came time to start building Roman, there was another government agency that had a surplus telescope already built that said to NASA, hey, do you have a use for this?