Daniel and Kelly’s Extraordinary Universe - If the Universe is infinite, why is the night sky dark?

Episode Date: August 30, 2022

Daniel and Kelly wrestle with competing infinities to understand why the night sky is not catastrophically ablaze with light. See omnystudio.com/listener for privacy information.

This is an I-Heart podcast. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, everything changed. There's been a bombing at the TWA terminal. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism. Listen to the new season of Law and Order criminal justice system on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts.

I'm Dr. Scott Barry Kaufman, host of the Psychology Podcast. Here's a clip from an upcoming conversation about how to be a better you. When you think about emotion regulation, you're not going to choose an adaptive strategy which is more effortful to use unless you think there's a good outcome. Avoidance is easier. Ignoring is easier. Denials easier. Complex problem solving takes effort. Listen to the psychology podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Hi, it's Honey German and I'm back with season two of my podcast. Grasias, come again. We got you when it comes to the latest in music and entertainment with interviews with some of your favorite Latin artists and celebrities. You didn't have to audition? No, I didn't audition. I haven't auditioned in like over 25 years.

Oh, wow. That's a real G-talk right there. Oh, yeah. We'll talk about all that's viral and trending with a little bit of cheesement and a whole lot of laughs. And, of course, the great bevdas you've come to expect.

Listen to the new season of Dresses Come Again on the Aheart Radio app, Apple Podcast, or wherever you get your podcast. Every case that is a cold case that has DNA. Right now in a backlog will be identified in our lifetime. On the new podcast, America's Crime Lab, Every case has a story to tell, and the DNA holds the truth.

He never thought he was going to get caught, and I just looked at my computer screen. I was just like, ah, gotcha. This technology's already solving so many cases. Listen to America's Crime Lab on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Is it getting warm where you guys are? Oh my gosh, yeah. It's Virginia, and the Virginia summer is definitely here. So does that mean sunscreen for the kids every single day?

Yeah, they hate it, but I'm a pretty big believer in that. And what about at nighttime? Do you guys put sunscreen on at night? Why would we put sunscreen on at night? What do you know, physicist, that I don't know? Well, you know, stars are actually just other suns, right? So it's still sunlight, even at night? So you're trying to tell me that the stars are going to give us skin cancer?

Look, I'm not trying to make astronomy scary. I'm just looking out for your kids. Uh-huh. Well, I guess I got to order a gallon of Star Screen. Somebody out there is going to get Star Cancer. Oh, boy. Or someone's going to make a lot of money off of Star Screen. Hi, I'm Daniel.

I'm a particle physicist and a professor at UC Irvine, and it was the night sky that got me into science. I'm Kelly Wienersmith. I'm an adjunct assistant professor at Rice University, and while I prefer parasites, I do love looking at the night sky. What about parasites at night? I mean, you know, the parasites are always out there, and they're just as good at night as they are during the day. They're always fascinating. And then the super meta question, do parasites look at the stars? Can you enjoy the stars with your parasites? Oh, you know, ectoparasites can probably look at the stars, but the endoparasites, the ones like in your guts, they probably don't have as good of you. Wait, exo parasites? Are those like exoplanets and exo moons? Are you talking about astro parasites, parasites on other planets?

I said, ecto, E-C-T-O. But, you know, there could be exo parasites. It wouldn't surprise me to find out that, you know, the second organism on another planet was a parasite of the first. That would not be too surprising to me. Well, welcome to the podcast, Daniel and Jorge Explain the Universe, where we have just invented the field of exoparasatology. Yes, job security. On this podcast, we do delve deep into the mysteries of the universe. What is out there? How does it work?

What squirmy little beings are living on the backs of other squirmy little beings on weird planets around other stars? We don't shy away from the biggest, deepest, squishest questions in the universe and sometimes we like to ask really basic fundamental questions about the nature of the universe we find ourselves in because we think that our tiny little squishy human brains are weirdly somehow capable of understanding the deepest cosmic mysteries of looking out into the night sky and from that information gleaning something big and deep and true about the nature of the cosmos my friend and co-host Jorge can't be with us today but we are very happy to

have our regular guest host, Kelly Weiner-Smith. Kelly, thanks again for joining us today. Thanks for having me. I'm excited to be here again. And today's topic is super interesting. I can't wait to talk about it. Awesome. Well, one reason I love thinking about today's topic is because it really was the night sky that got me into science. That wasn't just a sound bite. When I was a kid, I was just like all those other undergrads who write cheesy essays about staring up in the night sky and wondering about the universe. You know, it really is a very attractive and easy way to get into asking questions about the universe. Were you also a star watcher as a kid? Uh, you know, I was more looking down at the ground and, you know, as an ecologist, all of our essays start off with, I always liked playing in the

woods. So I mostly was looking down, but I did like looking up when it got too dark to find salamanders and stuff. And as an adult, I really like looking at the night sky. Well, the funny thing about the night sky in terms of science is that it's very attractive. It's like easy for people to hear about and astronomy seems like a very accessible topic. But when it gets down to, to it, you know, like doing science of the stars is mostly like standing around in the cold, looking through a telescope. And so while I was very excited about astronomy as a young kid, when I got older and tried to get into it a little bit, I found that it wasn't really actually for me. You know, I didn't really like staying up late at night or staring through a telescope

or dealing with optics. So sometimes the day-to-day grind of science doesn't quite match with your like fantastical aspirations. Yeah. And you know, I think one thing that draws astronomy students, Ecology students together is that both of those groups of students think that it's going to be one thing, like playing outside a lot. And then it ends up being a lot of math, for example. And that is where we lose a bunch of the outside enthusiasts. Is there a lot of math in ecology? You're like putting down squares and counting how many slugs or something? Well, I mean, yeah, there's counting. But then there's also trying to like, you know, write mathematical models to describe host predator dynamics or whatever. And actually, I took ecology because I thought it was going to be an easy A because it's like hippies playing in the woods. But then when I found the equations I fell in love. So for me, that's what hooked me, which I'm sure is what hooks some students on astronomy as well. Yeah, absolutely. It is amazing to think that we can describe what's going on over there. And it's fascinating to me that we can learn about the rest of the universe just from looking at our local neighborhood, you know, that we have an example star right here in our solar system. We can study it and think about and understand it. And then we can

apply that knowledge to the stars to saying, oh, those are just other sons. And you know, I have to embarrass my daughter because it was only six months ago or so I was talking to her and I said something like, you know, the stars, they're just other sons, right? And she was like, what? Are you serious? And then I was like, what? Are you serious? You didn't know that already? She was like, no, I had no idea. And I was so embarrassed. Like, here I am, you know, a physicist, a science communicator. And my own daughter doesn't know this very basic thing about the universe. Yeah, I was going to ask if you're a little embarrassed admitting that. And I, yeah, I guess you are. But, you know, we all have gaps, things that we just assume our kids intuitive, but they didn't. And it's, you know, surprising sometimes.

Yeah, she thought that they were sort of like other stars, but they were much closer and much dimmer. We were surrounded by like an ocean of not very bright suns or something. I don't think she had actually thought about it very much. And so you're right. It's just something we never actually came to the point of talking about. But now we have a fun running joke, which is at any time something obvious comes up about the universe. I'm like, you are aware, of course, that the Earth is round, right? She's like, dad.

It's important you never let kids forget if they got something wrong, you know. You need to remind them of that all the time. No, I try not to make her feel bad. Now it's just my opportunity to get to like insert a little bit of science into any random conversation because now I have an excuse because maybe this is another thing we just never got around to talking about. That's right. And I'm sure she doesn't find it frustrating that you do that at all. Oh, she teases me back.

She is quite capable of that. I'm glad. But this question of the stars and the night sky really has lots of fascinating layers to it. A lot of people are surprised when they learn, for example, that the stars are there during the daytime. Like, you could see them in principle. They are shooting starlight at you, and it's hitting the earth. It's just sort of like overwhelmed by the sun. I feel like that's probably something I didn't figure out until I was much older.

Like, that's another one of those obvious things that you should have known. But I feel like I remember maybe as a senior in high school having a like, oh, they're still there moment, which I should be particularly embarrassed about. But as I said, I wasn't looking up that much. I was mostly looking down. Yeah. And there's no shame in coming to understanding of the universe at any age. We should just be rewarding people for their curiosity and their enthusiasm. And one of the things for me that I love about the night sky and just staring at it is trying to get a mental image or conception or grappling with the idea of how ridiculously far away they are. You know, I like standing on the top of a mountain.

and seeing 80 miles, 100 miles, or on a clear day even further. But looking up in the night sky is like standing on the top of a mountain the size of the earth and staring across billions of light years, right? Those photons left those stars millions or billions of years ago just now arriving on Earth. It's like it's the most spectacular view in the universe. My brain has so much trouble wrapping its head around distances in space. Like even just knowing that it takes like, what, six months to get to Mars? That seems crazy because, you know, it's like two days of driving to get across the U.S.

So it feels to me like anything should be accessible within 48 hours. I should be able to drive to Mars in two days, right? Stopping at gas stations and getting like spaced snacks. I mean, I understand you're going to need a different vehicle. But it seems like it should be reachable pretty quickly. And one of the real challenges with understanding these distances in particular is that you have two things you have to grapple with. Not just are the stars super far away, but they're even. enormous. Like the size of a star is just flabbergastingly huge. Like the sun, for example, right,

so much bigger than the Earth. Jupiter is like a thousand times the volume of the Earth and the sun is like a million times the volume of the Earth, right? That's flabbergasting. It's hard to hold that many Earths in your head. And there are stars out there that are much, much bigger. And yet you look up at the night sky and they are these tiny little pinpricks, right? And so you have to have both of these things in your head that these objects are enormous fireballs really just like bigger than you can even imagine and yet so distant that these enormous fireballs now look super duper tiny right so two things in your head that you have to sort of like divide by each other both huge numbers how big is our son relative to some of the others you said some of the others were much much bigger is our

sun sort of a tiny sun or is ours like about average our son is not unusual but there are many stars out there that are much bigger. For example, Beetlejuice, if you put it in our solar system, each radius would extend out into the asteroid belt. Like Mars would be inside Beetlejuice. We did an episode about the biggest stars in the universe. Some of them are even larger. Some of their radii would extend out, you know, into the outer solar system, you know. So there are monsters out there, absolute gargantuan, monstrous balls of burning plasma. That's crazy. Really hard for me to imagine. That's right. They're huge, they're enormous, and yet they only appear as pinpricks in our sky.

And the reason, of course, is math, because as those photons shoot out from that star, they go in all directions. And we only see a tiny fraction of those photons, right? If you're standing like a meter away from a light bulb and you have a solar panel gathering some of that light, you're not gathering all of the light, right? You're gathering some fraction of the photons that come off of that light bulb, right? It's shooting in all directions, and the fraction that you get is like the area of your solar panel divided by the area of that sphere that's at your distance, right? So that's the fraction of

the photons you're getting. If you take two steps away, for example, now you're twice as far, then the area of that sphere that the photons are getting spread over is now four times as big because the surface of a sphere with twice the radius is four times as big. So the same solar panel is now capturing one-fourth of what it did before. So the luminosity of a star, the brightness of its appearance goes like one over the distance squared. And these distances we're talking about are huge, right? Other stars are not just super bright. They're really, really far away. So one over their distance squared becomes a really big number. But if you do that over and over and over and over again, like billions or trillions of times, shouldn't it be much brighter out there? Yeah, it's a really good

question. So we're balancing lots of big numbers here. We have huge stars. So they should be emitting a lot of light. But they're really far away. So that cuts down their life. a lot but then there's a lot of them right so we have like three almost infinite numbers and we're wondering like how do those get fit together you know if the universe is in fact infinite wouldn't all those numbers add up to be like a crazy amount of light wouldn't Kelly's kids get like star burns if they go out at night looking at the stars right this is a question that people have asked sort of since antiquity like why isn't the night sky like catastrophically blazing full of starlight thank goodness for star screen and so today on the podcast

we'll be answering why is the night sky dark and I love this kind of question because it's such a simple basic question and it's the kind of thing that people can think about and have been thinking about for a long time right you don't need special tools or apparatuses just to sit here on the surface of this rock and to ask this question like if I have an understanding of how the universe works my mental model is that there are stars everywhere then what should I expect to see in my night sky, right? And this is a perfect example of what physics really is at its core. You build a model of the universe in your head. You make a prediction for what you should see, and then you ask, like, does that agree with how the universe actually works? And if it doesn't,

then you get an important clue about how the universe might be different from your mental model. Well, you forgot about the part where you spend like a decade writing the grant so that you can get the money to try to test the model. But yes, essentially, that's how physics works. We're trying to make science sound glamorous here, Callie, we're not talking about all the emails and the meetings. I'm sorry. I'm sorry. I didn't mean to take away all the beauty of physics. All right. Well, let's tap into the apparent beauty of physics by asking our listeners if they know why the night sky is dark. So I wrote to all of them and I asked them, if the universe is infinite, why is the night sky dark? If this sounds like a lot of fun to you and you would be

willing to participate for future episodes, please don't be shy. Write to us. to Danielanhorpe.com, and we'll send you our recent questions. So think about it for a minute. Do you know why in an infinite universe the night sky is not blazingly bright? Here's what our listeners had to say. Well, I guess that's because from the electromagnetic spectrum, that's the light emitting of all stars and everything in the universe, we are only able to see just this tiny fraction that's the visible, the visible spectrum.

So I guess that there are photons all around the universe, but they are in different wavelength, so we are not able to see them. That's why the night sky looks dark for us because we cannot perceive it. Okay, so first of all, the universe is not infinite. It's just insanely huge, and it's expanding faster than the speed of light. So it may seem infinite, but it's not infinite. As for the question itself, I can come up with two different explanations. One is that the light coming from really distant stars and galaxies,

eventually they get really spread out. They're not concentrated enough for Aster spot. So we're not able to see them in the night sky. The other reason that I could come up with was that although the speed of light is fast, it's not fast enough compared to the size of the universe. So I imagine this bubble of visibility around Earth that keeps growing every second as new light reaches us from further places, but there is still a lot of the universe out there

from which the light has simply not had enough time to reach us. It's because all those stars are just too spread out and they're too far away so that they can really make a strong light. And I also believe that inflation plays a role, right? Because I think that in a few million or billion years, there will be rarely any stars to be seen in the night sky. So maybe that's the point. Well, first of all, prove to me that we live in an infinite universe,

But supposing we do, it's not just jam-packed with stars all the way out. And the intensity of light varies with the square of your distance from it. So the really far away stuff is extremely dim. And I'm sure there's some kind of math you can do that shows a curve that approaches an asymptote or one of the axes and the zero pans out there. It's kind of like if you keep going, you go one foot and then you go half a foot and then you go a quarter of a foot, you never quite get there two feet away. And I'm glad it's not infinitely light because it's nice to have some darkness every once in a while. It is not dark at all frequencies.

If we shift to the right frequency, there's usually something coming from every point in the sky we look at. However, for the visual range of humans, even though at any given, even point in the sky, if we look deep enough in, there probably is a source of light. There are dust clouds and gas clouds and lots of other things that obstruct the light before it gets to us. So within the human visual range, it can look very dark. But if we shift to a different frequency, there's usually some form of light coming in. I know this one. The answer is dust. The interstellar gases are just thick enough to absorb enough. of the radiation sent by the more distant stars that we can't with our naked eyes see things

all the way back to the dawn of time. It's what we need things like Hubble for. So those more distant and fainter lights do get filtered out by the dust. And so the night sky appears dark to us instead of appearing light. Light from different stars takes time to travel from wherever the star is to where we are. So depending on how far the stars, the light from it might not have reached us yet. And so the space in the interim for the duration for which the light hasn't gotten here yet will be dark. Well, that is debatable, if that's even true, that we live in an infinite universe. But I guess the question is, why wouldn't there be a star in every direction we look? And this would be due to, there would be still a couple of photons arriving from any direction.

I guess, but the brightness dissipates over long distances in a sphere. So we are not getting a lot of photons. So I guess if our eyes would be good enough, we would be able to see a totally lit-up universe at night. You know, for this set of answers, I was particularly impressed with your audience. Now, of course, your audience is brilliant, and they always give good answers.

But for this set in particular, they really had some clever answers. And so first of all, like, when you ask this question to the listeners, do they have to answer like immediately or do they get the question, think about it for a day and then call in? That's a good question. Well, the rules are no preparation, no Googling, and you're supposed to give immediate off-the-cuff answers. Now, I can't police them. So I don't know if they've Googled or they've gone and looked up their astronomy professor from college and then tried to give an intelligent answer. But I'm trusting them that these are what they immediately think, that these are their off-the-cuff responses. Yeah, yeah.

I think they're not just smart, but they're trustworthy. And good-looking. And good-looking. That's right. Many, many good features. You know, you'd have to be a great person to be listening to this podcast. I think that's called the Halo effect. Anyway, getting off topic.

But, yeah, there were like some good skeptical answers. You know, we don't know if the universe is infinite. You've clearly taught them about what we do and don't know. and dust came up. To be honest, dust I hadn't thought of as a potential explanation until reading the answers. And so I was pretty impressed with this set of answers. What did you think? Yeah, they really run the gamut. There's a lot of different things to think about. And that's why this is a great question, because it forces you to sort of clarify your understanding for what really is going on. What is interfering with the light that's coming to Earth? How much should be arriving? There's a lot of good stuff here. There is a lot of good stuff there. And so one of the listeners said, we don't know if the universe is infinite. Is that right? What do we know about the size of the universe? That is 100% correct.

We do not know if the universe is infinite. We know that our patch of the universe, what we can see, what we call the observable universe, no part of it seems to be different from any other part of it. That is the universe seems to be sort of homogenous. And so that suggests that no part of the universe should be special. And it implies that perhaps the universe is infinite. We don't know that. We've tried to measure things like we can measure the curvature of sense.

space, how much space itself is bent. Though we talked about in a recent episode about whether the universe is shaped like a donut or a sphere or an infinitely flat plane, we can't actually tell. We've measured the universe's curvature to be consistent with zero curvature, like as if it was flat. But the universe could be flat and also not be infinite. It could like tie together at the edges, sort of like the screen in Pac-Man or asteroids. So there's lots of things we don't know. but so far, it's consistent with us seeing a finite patch of an infinite universe, but absolutely we don't know. What do you mean by homogenous?

Because, you know, when I think about galaxies, they sort of seem like clumps. But I guess just like in general, it's everything's somewhat evenly distributed. Is that what that means by homogenous? We don't mean literally exactly homogenous because there are parts of the universe where there are galaxies and parts where there are not. We mean that if you zoom out far enough, like sort of on the biggest scales, everything seems basically smooth. There's, you know, clusters and super clusters, but there's no real structure beyond that. And the rules of the universe seem to be the same everywhere. There don't seem to be

any special locations. There's no center to the universe as far as we can tell. Everyone in the universe seems to be similar to everywhere else in the universe. That's what we mean. And so I thought that everything was moving away from a central point. But is that not true? There's no like point that we know that everything's moving away from, like expanding out? Everything is moving away from everything else. So the expansion is also homogenous. Like every point in the universe is expanding just like every other point. No matter where you are in the universe, it will look like everything is moving away from you.

So either you are at the center of the universe and there's just expansion away from that one point or everywhere in the universe is expanding, which is much more likely. I am probably the center of the universe, but maybe I'm not. I can accept that. Okay. You're the center of your kid's universe, I'm sure. But this question about why the night sky is dark is actually a really old question and really predates any modern understanding of sort of like the size and shape of the universe. And it helped spark some of these questions like, is the universe infinite? Could we possibly tell?

And a long time ago, people thought it was obvious that the universe was infinite. One of my favorite things about the history of astronomy is seeing how like conceptions of what is obvious or natural change with time, right? Like a long time ago, people thought the universe was obviously infinite. It should just go on forever. And it was just sort of sprinkled with stars. There were no galaxies at all. They just thought, here's a star, there's a star. The whole universe is just like a vast sea of stars.

So when did we start learning enough to start having a good answer to these questions? Well, it was like 100 years ago with Hubble and lots of others who discovered that there are galaxies and that those galaxies are moving away from us and the universe is expanding. And then it became later much more natural to imagine that the universe might be finite in age. It seemed like obvious that the universe should have a beginning. Whereas before that, people thought it was obvious that the universe had existed forever and had no beginning and went on forever. Right. So what seems to be like obvious and natural changes with time, which I think is really fascinating and an important lesson, you know, for like making assumptions about the universe.

Anyway, take yourself back to like 150 years ago when people thought, okay, the universe is infinite. There are stars everywhere that sort of like dotted in this vast ocean. So pretend you're an astronomer 250 years ago. and that's the sort of understanding. People were asking themselves a question like, how much starlight should we expect to fall on the earth in that situation, in an infinite universe filled with equally spaced stars?

And so, I mean, of course, you look out at the night sky and you sort of know what you get. What did they think that the answer was? Right. So obviously they knew that the night sky was dark, right? That wasn't the mystery. The question was like, why is the night sky dark? Because when they sat down to do the calculation,

they were quite surprised, they couldn't explain it, right? Their calculations suggested that the night sky should be infinitely bright if there are infinite number of stars out there. Okay, well, I am dying to know what explanation they came up with to explain the discrepancy between

what they thought they should see and what they were seeing, but first, I think we need to take a break. December 29th, 1975, LaGuardia. Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal.

Apparently, the explosion actually impelled metal glass. The injured were being loaded into ambulances. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged. And it was here to stay. Terrorism. Law and order criminal justice system is back. In season two, we're turning our focus to a threat that hides in plain sight.

That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is one. way too friendly, and now I'm seriously suspicious. Well, wait a minute, Sam, maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her.

Now, he's insisting we get to know each other, but I just want her gone. Now, hold up, isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor, and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him

because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. I'm Dr. Joy Harden Bradford. And in session 421 of Therapy for Black Girls, I sit down with Dr. Othia and Billy Shaka to explore how our hair connects to our identity. identity, mental health, and the ways we heal.

Because I think hair is a complex language system, right? In terms of it can tell how old you are, your marital status, where you're from, you're a spiritual belief. But I think with social media, there's like a hyper fixation and observation of our hair, right? That this is sometimes the first thing someone sees when we make a post or a reel is how our hair is styled. You talk about the important role hairstyles play in our community.

the pressure to always look put together and how breaking up with perfection can actually free us. Plus, if you're someone who gets anxious about flying, don't miss session 418 with Dr. Angela Neal-Barnett where we dive into managing flight anxiety. Listen to therapy for black girls on the iHeart Radio app, Apple Podcasts,

or wherever you get your podcast. Get fired up, y'all. Season two of Good Game with Sarah Spain is underway. We just welcomed one of my favorite people and an incomparable soccer icon Megan Rapino to the show and we had a blast. We talked about her recent 40th birthday celebrations

co-hosting a podcast with her fiance Sue Bird, watching former teammates retire and more. Never a dull moment with Pino. Take a listen. What do you miss the most about being a pro athlete? The final. The final. And the locker room. I really, really like you just, you can't replicate,

you can't get back. Showing up to the locker room every morning, just to shit talk. We've got more incredible guests like the legendary Candice Parker and college superstar AZ Fudd. I mean, seriously, y'all. The guest list is absolutely stacked for season two.

And, you know, we're always going to keep you up to speed on all the news and happenings around the women's sports world as well. So make sure you listen to Good Game with Sarah Spain on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Presented by Capital One, founding partner of IHeart Women's Sports. All right, and we're back. So before we left, you were telling us that in the past, there was this big question about, like, well, how much light should we be seeing and why aren't we seeing a lot more of it?

And what sort of answers did they come up with? Hopefully, hopefully the answers we have now are better. Well, the interesting thing is they were trying to figure out whether the nice guy should be dark or not. They knew something about how light was transmitted, so they didn't really understand it on a microscopic scale. But they knew, for example, that as you got further away from something, it's light dimmed by a power of one over the distance squared. So you apply that math to, for example, like Proxima Centauri, that's the nearest start

to Earth, but it's really still very, very far away. It's only a few light years, but in terms of like distances in our solar system, an AU, for example, is the distance between the Earth and the Sun. Proxima Centauri is 270,000 AU, right? So it's 270,000 times further from the Earth than the sun is. So that means that Proxima Centauri's light gets reduced by 1 over 10 to the 11 relative to the sun. So our distance to the sun means the light from the sun is reduced by a certain amount, but Proxima Centauri is 1 over 10 to the 11 times dimmer than the light from the sun because the distance between here and there is so large.

Okay, so the equation where they were trying to figure out that, like, light dims at one over the distance squared, that must have been done on Earth. When they were looking out at space, were they assuming that, like, space sort of had the same atmosphere and the same sort of dynamics or, like, how did they deal with that sort of uncertainty? Yeah, yeah, great question. It wasn't always obvious to people that the rules here on Earth also applied to space, that you could say, like, things were fundamental and physics was universal. Newton was one of the first people to do that, to say, gravity here on Earth also applies in space and can describe the motions of the planets. So you're right, that is kind of a big leap. Plus, they're assuming that light can travel through those distances, that there isn't like dust or gas blocking it. We'll get into the details of whether or not gas and dust can explain it in just a minute.

But first, let's start with sort of the simpler vision. Like, let's just imagine that light is not blocked by anything. It's just a question of distance and the number of stars. And that's sort of like simpler model, how much light do we expect to fall on Earth? Okay, so they had an understanding then about how light should fall off with distance. Did they have like an estimate for how many stars were out there? So they didn't know how many stars were out there, but they were assuming that the stars were uniform, right? That like every chunk of space had on average the same number of stars.

And so you can take the fact that stars get dimmer as they get further by one over distance squared. and the fact that there are an infinite number of stars, and you can do the math, and you can ask, like, which one wins out? Does the infinity of the number of stars win out, or does the growing distance to those stars suppress the light faster than, like, more stars get added? And so then because the night sky is dark, that means the distance must win? Is that the conclusion they came to? That's not the conclusion they came to. Actually, they did the math, and they discovered that the number of stars should win. It's actually not that hard to do the math yourself. brightness of a star goes like one over distance squared. And at a given distance, the area of a sphere around the earth also goes like distance squared.

So that means that like any shell of universe at an arbitrary distance from the earth, the stars from that shell get suppressed by one over distance squared, but the number of stars in that shell goes like distance squared. So those two numbers both cancel. So that means that like any shell of universe, an arbitrary distance away from you, should have a constant brightness. Like, every shell should have the same amount of brightness. If you have, like, a shell of universe further and further away,

each star in it gets dimmer, but the number of stars grows perfectly to match that. So that means that every shell of universe around us should be equally bright. Further ones have many, many more stars, each of which are dimmed, and the closer ones have fewer stars, but they're not dimmed as much. Okay, but, and this is why I find physics so frustrating, But the night sky is dark. So what were they missing? What was not in the equation that should have been there?

You're absolutely right. The night sky is dark. And so something is wrong with this calculation. But just to underline it for the listeners, that means that every shell of the universe is a fixed brightness, but there's an infinite number of shells, right? So all those shells should add up to be an infinite amount of light. And so this is like Heinrich Olbers is a guy in the 1700s.

He's doing this calculation. And, you know, he gets this number. he's like, hold on a second, something must be wrong, as you say, because if there's an infinite number of stars, even if distance dims them like one over distance squared, the night sky should be infinitely bright, you know? His calculations suggest that if you go out at night, it should be brighter than the daytime. You should get like infinitely crisped up, you know, by all of these stars, right? So did he start like the Olbers Prize to be like trying to try to solve this famous problem or like how many people cared about about this problem at the time a lot of people

were thinking about this and olbers thought that this was proof that the universe wasn't infinite right obers thought oh well something must be wrong one of the assumptions that go into this calculation right that stars go like one over distance squared and that the universe is infinite and uniformly filled with stars one of those assumptions must be wrong and he thought it was clear that the universe couldn't be infinite because that would solve the problem you can't get infinite light on Earth if there aren't infinite stars out there. So he was convinced that that means that the universe is not infinite. Okay, that makes sense.

But apparently, well, you've told us that that is a question that we're still trying to figure out the answer to. So it must be more complicated yet? It is, in fact, more complicated. It's possible to live in an infinite universe without an infinitely bright night sky, right? There are other solutions out there to this problem. But first, let's tackle one of the ones that the listeners brought. up and that you mentioned earlier, which is gas and dust. Another suggestion people had,

not just our listeners, but people over the centuries, was imagining that not all the light is getting to the earth. That maybe some of it is getting absorbed by gas and dust. Basically, it's being blocked before it gets here. And so, I mean, I guess when I think about space, I don't think about there being a lot of gas and dust, but of course, the International Space Station needs to have, what is it called, a whiffle barrier? Because it gets hit by all of this space dust that you want to make sure it doesn't get into the international. National Space Station. So there must be dust up there, but is there enough dust up there when you get out past like low Earth orbit to be blocking the light? Absolutely. Most of the

mass of the galaxies in terms of gas and dust, right? Stars do not make up most of the stuff in the galaxy. Even if we're just talking about baryonic matter, we're not even talking about dark matter. There are vast clouds of gas out there, which might in the future become stars. And there huge expanses of dust from old solar systems that blew up. And so there's a lot of gas and dust out there. And people who study the universe have to map that gas and dust. If they're looking at a star and they're trying to figure out how bright it should be, they have to know how much stuff is between us and that star. There are people whose entire theses are like maps of dust in the galaxy because it's so important. And it's one reason, for example, that we can't see

through the galaxy. One of the big mysteries in astronomy these days is the great attraction. tractor, this weird source of gravitational attraction that seems to be on the other side of the Milky Way. And we can't see what's there because the Milky Way is so gassy and dusty that is basically blocking our view. It's definitely something that people have to take into account when they're figuring out how bright an individual star should be when seen from Earth. Are the people who study that, like not invited to the parties of people who are excited about space stuff? Because to me, when I think about space dust, I think you can't travel to another galaxy because that space dust is going to be like bullets going through your capsule or whatever

on the way to another galaxy. So are these like not popular people because they kill dreams? No, they're super popular because they enable the rest of astronomy. You know, there's so many people who need to know how much gas and dust is there between this object I'm studying for my thesis. So I think people are very grateful that somebody has gone out there in like devoted five years of their life to mapping dust in the galaxy. And, you know, they also get zillions of citations. I see these thesees sometimes have like 5,000 citations because it's such vital work just to understand like what's out there between us and other stuff. Well, I'm happy for them. But unfortunately, this idea that gas and dust is dimming the otherwise infinite light from stars, that can't explain why the night sky is dark.

The problem is that gas and dust also absorbs energy, right? So if the universe was filled with effectively infinite light from infinite stars had infinite time to get here, then that gas and dust would be super duper hot, right? If it's blocking infinite light, then it's absorbing infinite light and basically gets to be the same temperature as the stars and it should also be glowing. So you can't explain the non-infinitely bright night sky with gas and dust. And that would make those thesees much easier if mapping it just meant you had to look for the glowing patches. Exactly. And yet we know that the night sky is not dark.

And so we have to think more deeply about what those assumptions are. which one might be wrong. And one of my favorite bits of history is that an early thinker on this question is somebody you might not imagine. Somebody you all know very well, but probably don't think of in terms of astronomy. And that's Edgar Allan Poe. What? No way. He was at UVA for a little while. You can go to the dorm room that he was in briefly before he left. But I don't know if I'd highlight the fact that he was only here briefly so much during the tour. But anyway, so did he generally think about astronomy questions? Or is this like the one area of astronomy me that really drew him in.

No, he was really prolific and he wrote about all sorts of stuff. But, you know, guy who writes horror movies spends a lot of time up late at night. So I think he spent a lot of time thinking about the stars and going for long, crisp walks, you know, in the evening. So let me read you this quote from Edgar Allan Poe. He says, were the succession of stars endless, then the background of the sky would present us a uniform luminosity, like that displayed by the galaxy, since there could be absolutely no point in all that background at which would not exist a star. So he's saying basically in any

direction you look, you should be able to see a star. If the universe is infinite, then every line you make, you should hit a star. And so every point in the sky should basically look like a star. Then he goes on to say, the only mode, therefore, in which under such a state affairs, we could comprehend the voids which our telescopes find in innumerable directions would be by supposing the distance of the invisible background so immense that no ray from it has yet been able to reach us at all. Oh, so he's saying everything is so far away that the light hasn't gotten here yet? Gotten here yet, exactly. And that's a really vital point. He's thinking about the time it takes light to get here from those stars. And he's assuming that it hasn't had an infinite amount of time

because in Ulbur's calculation, he not only assumes that the universe is infinite in size, but also infinite in age. And that's necessary because if a star is super duper far away from us, its light will take a long time to get here. If the universe is infinite in age, then it will get here and it will already be here because that stars existed infinitely in the past and it's had plenty of time to get here. But if the universe is not infinitely old, if it started a certain number of years ago, that means that there are some stars who are so far away that the light from them has never reached us, that not a single photon from that star has arrived here on Earth. It's always surprising to me how quick physics goes from math to like existential questions.

So was Poe sort of on track with what other physicists at the time were thinking? Or was he the first one to sort of think about it this way? Or should we wait until after a break and then find out if Poe was right? Let's leave our listeners in deep dark Edgar Allan Poe's suspense and come back after the break. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal.

Apparently, the explosion. actually impelled metal glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order, criminal justice system is back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop.

Listen to the new season of Lerner, law and order criminal justice system on the iHeart radio app apple podcasts or wherever you get your podcasts my boyfriend's professor is way too friendly and now i'm seriously suspicious oh wait a minute sam maybe her boyfriend's just looking for extra credit well dakota it's back to school week on the okay story time podcast so we'll find out soon this person writes my boyfriend has been hanging out with his young professor a lot he doesn't think it's a problem but i don't trust her now he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy? That sounds totally inappropriate.

Well, according to this person, this is her boyfriend's former professor and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcast, or wherever you get your podcast. I'm Dr. Joy Harden-Brandford, and in session 421 of therapy for black girls,

I sit down with Dr. Othia and Billy Shaka to explore how our hair connects to our identity, mental health, and the ways we heal. Because I think hair is a complex language system, right? In terms of it can tell how old you are, your marital status, where you're from, you're a spiritual belief. But I think with social media,

there's like a hyperfixation and observation of our hair. right, that this is sometimes the first thing someone sees when we make a post or a reel is how our hair is styled. We talk about the important role hairstylists play in our community, the pressure to always look put together, and how breaking up with perfection can actually free us. Plus, if you're someone who gets anxious about flying, don't miss Session 418 with Dr. Angela Neil Barnett, where we dive into managing flight anxiety. Listen to therapy for black girls on the IHeart Radio app, Apple Podcast. or wherever you get your podcast.

Get fired up, y'all. Season two of Good Game with Sarah Spain is underway. We just welcomed one of my favorite people and an incomparable soccer icon, Megan Rapino, to the show, and we had a blast. We talked about her recent 40th birthday celebrations, co-hosting a podcast with her fiancé Sue Bird, watching former teammates retire and more.

Never a dull moment with Pino. Take a listen. What do you miss the most about being a pro athlete? The final. the final, and the locker room. I really, really, like, you just, you can't replicate, you can't get back. Showing up to locker room every morning just to shit talk. We've got more incredible guests like the legendary Candace Parker and college superstar AZ Fudd.

I mean, seriously, y'all. The guest list is absolutely stacked for season two. And, you know, we're always going to keep you up to speed on all the news and happenings around the women's sports world as well. So make sure you listen to Good Game with Sarah Spain on the I IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Presented by Capital One, founding partner of IHeart Women's Sports. All right. I've been dying to know, was Edgar Allan Poe right?

Edgar Allan Poe was totally correct, and he was also sort of a vanguard of thinking at the time. Remember that until Hubble saw that the universe was expanding, this is the beginning of the 1900s. People thought it was very likely that the universe was infinitely old, that it didn't have a beginning. The natural concept was that everything is just hanging in space. Nothing is changing. I mean, you don't see stars blinking out or new ones appearing. They thought the universe was eternal and static. And so it wasn't until we saw that the universe was expanding and that we could sort of wind that history backwards to some time when the universe was infinitely dense before which it didn't even make any sense to talk about time. So,

this whole idea of the age of the universe being finite, being about 14 billion years old, that's only about 100 years old. Before that, people mostly thought the universe was static and infinitely old. So Poe was sort of ahead of his time here, imagining this as an explanation for why the night sky was dark. He's so great. He has a story, the title of which I forget, where essentially one guy locks or says like, oh, let's go find this wine, which is in this basement. Cast of a matiato, yeah.

Thank you. Yes. And he locks the other guy in the basement. And then he leaves. And a collaborator and I were talking about how that's sort of the way, sort of like how parasitoids lock their hosts inside the goals that they make. Anyway, you know, we love connecting literature to our wasps whenever we can. And that was one of our connections. But anyway, I digress. No, but that Edgar Allen Poe is sort of like our two degrees of separation, right? He wrote about parasitology and he wrote about cosmology. So he connects us. Well, except he didn't think he was writing about parasitology, whereas he did think he was writing about cosmology. But sure, yes. Let's go with it. He was just so far ahead of his time, he didn't realize he was breaking new ground in every field. Okay, so we are back to an area where my brain sort of has trouble keeping up with the distances and the speeds and the sizes.

So, okay, so the universe is expanding, and we're looking at, like, the speed of expansion relative to the speed of light. So does this mean that, like, at some point in the future, the life? light is going to catch up to us and the night sky is going to be bright, or am I missing something fundamental? I think I'm missing something fundamental. No, you're absolutely not. That's a great question. So let's take it one step at a time. So first we say the universe is not infinitely old, which means that light from some places hasn't reached us yet. So you can imagine maybe the universe is infinite. Maybe it goes on forever, but we can only see a part of it. The part of it that we can see is determined by the speed of light and the age of the universe. So there are things

out there that have sent us photons that are on their way screaming at the speed of light across billions of light years, but have not yet arrived. But will in the future arrive, right? We'll get here at some point. While that explains why the night sky is not infinitely bright right now, it makes you wonder like, does that mean it will be much brighter in the future, right? In that sort of scenario, you can imagine the night sky getting brighter and brighter every year is sort of like more stars appear in the night sky so that eventually it sort of like fills in all the gaps, right? And then you really need star screen.

I feel like we've got to start this company before this episode goes out because otherwise somebody else is going to pick up on this idea and we're going to be really grumpy that they make a billion dollars off a star screen. I agree. I think this is going to be the thing that makes us rich. Forget our books and everything else. Star screen. Star screen, exactly.

Endorsed by astronomers. We need like seven out of eight astronomers agree or something. Yeah, that's right. That's right. Let's convince people that don't have to worry about medical doctors. They should listen to any old specialist in anything. And so you might worry about that, the future of the infinitely bright night sky. And while I might want you to believe in that so you buy a big tub of star screen and smear on your kids,

it's not actually something we think is going to happen. We actually think the opposite is happening. That as time goes on, the night sky gets darker and darker. And that's for the reason that you mentioned earlier. that the universe is expanding, right? So even in a universe that wasn't expanding, where the stars are just sort of like hanging there, but the universe is not infinitely old.

You wouldn't expect the night sky to be infinitely bright, but it would be getting brighter and brighter. If time goes on and the size of the observable universe, the fraction of it that we can see, got larger and larger. But what's happening is that the universe is expanding. And so things are rushing away from us, and they're rushing away from us faster and faster every year. So there's this sort of weird effect where,

We can see a larger portion of space, but things are sort of moving out of that space faster than light itself. So imagine like a sphere that's growing, that's our observable universe. We can see anything in that sphere, but things are rushing out of that sphere faster than the sphere itself is growing.

So the expansion of the universe, the creation of new space between us and other galaxies, is decreasing the number of things in the observable universe, increasing the darkness of the night sky. So is it that as it moves away super fast that our square distance is increasing so much that it dissipates before it gets to us or the light never gets to us, period, because it's moving away so quickly? Both effects actually are happening. There are some things that we can see now, so their photons have reached Earth, and some of the photons they have sent in the meantime will reach Earth.

But there are some photons that are traveling through space, and that space is expanding faster than the speed of light. So those photons will never reach us. It's like if Usain Bolt is running at you, but somebody's laying new track between you and him faster than he's running, he's never going to get at you no matter how fast he is, right? You have to be laying track pretty fast. And so there are some things out there that we will eventually see that we have not seen yet, things that are about 62 billion light years away. There are some photons they emitted that we'll get here and we will be able to see them. But anything past 62 billion light years, we will never see it because the space between us and it is expanding so fast that all of its photons are basically moving away from us. So they're moving locally through space of the speed of light, but globally, because that space is expanding between us and them, they're actually moving away from us, which is really weird because like photons pointing towards us are actually getting further away from us every year.

Nothing about physics is intuitive, or plenty of it is, I guess, but plenty of it's not. Okay, and so then that is the final answer. Like, is that an answer that we definitely know to be true, or is this sort of on the, like, we revisit this in a couple years and people will be talking about how cute it was that Daniel and Kelly thought this was the answer. Like, how confident are we that this is the truth? Ooh, you're definitely trying to trap me here. You want to sound by so in five years you can go like, man, Daniel, you were so overconfident.

We should definitely always be taking these things with a grain of solved because our understanding of them is fairly recent. Our measurement of the expansion of the universe and its acceleration is only 20 years old. And that's a blink of an eye in terms of cosmology and science. Right. And so while we're fairly certain that the universe is expanding and that that expansion is accelerating, we have no idea what's causing that. We call this dark energy. That's just like a name we give it because we have no concept of what could be causing it. There's nothing in our equations that can't explain it. You can put a number into Einstein's theory of general relativity to describe this happening, but that doesn't explain why it's

happening, like what part of the universe is doing this? Why does it have to happen? Could it stop and turn around and do something else in the future? We just don't know. So there's a heavy dose of like, oh, that should be added to this. But it's sort of like our current understanding of what might be going on with the universe. And so does this answer help us answer the question about the universe being infinite or no, because it can be infinite, well, expanding because infinity is also complicated. Exactly. Infinity is so complicated.

Unfortunately, what this tells us is that the question of whether the night sky is dark can't tell us whether the universe is infinite. Because an infinite universe and a non-infant universe, both can give you dark night skies. So you can't tell the difference. Sorry, Ober's. But that's not even the full answer. There's another reason why the night sky is dark in an expanding universe. And I think you might have mentioned earlier, which is while space is expanding, it doesn't just affect the space between us and other galaxies.

It also stretches that light. So if space is expanding, if it's getting larger, that means like new space is being created. And so photons that are flying through that space, they get stretched. Their wavelengths get longer. They get redshifted. So your photon, for example, that was emitted from the cosmic microwave background, this super hot plasma that existed just. after the Big Bang, that plasma was really, really hot, and the light that it generated was very, very high frequency, short wavelengths. But it's been flying through the universe ever since,

and it's been getting stretched out to very long wavelengths. So does that mean that the night sky could be bright, but just at a wavelength that we don't see? So, yeah, what does that mean? It means the night sky actually is kind of bright, but just in wavelengths we cannot see. So some of the starlight that's been emitted has been red shifted outside of the visible spectrum. Like there are stars out there that are shining, that are bright, but your eyeballs cannot see them. And optical telescopes cannot see them because their wavelengths have been shifted into the infrared. So the night sky is actually brighter than you see, right? Because there are all these invisible stars out there that are shining at us in the infrared that our eyeballs cannot see.

Don't some species see in the infrared? So, like, are there some species out there for which the night sky is bright? That's a great question. I should ask my biology friend about that because I don't know. Not this one. But we did an episode recently about eyeballs and how they work. And we do know that different species are sensitive to different wavelengths of light. But, you know, we are very ingenious as a species and we're capable of building other kinds of eyeballs.

And so we can build telescopes that can see in the end. infrared and can look up at the night sky in the very, very long wavelengths. And something that's really fun to realize as we think about this question is that if you look deep enough into long enough wavelengths, the sky actually is very, very bright. Cosmic microwave background radiation, that's everywhere. That's in every direction. No matter what direction you look at in the sky, you will see some of it. So if your eyeballs could see the cosmic microwave background radiation, this light from the very, very early universe plasma plasma that filled the whole universe, then the night sky would be bright.

All right. So we've got to find a star screen angle to like, we got to make sure everybody knows this and then explain to them that the star screen protects against these other parts of the spectrum. And that's where the millions are going to come from. Right. And not to confuse the listeners, the night sky is not infinitely bright in the cosmic microwave background radiation, right?

Ober's paradox, this question of why we weren't seeing light in every direction really suggested that the night sky should be infinitely bright. The cosmic microwave background is almost uniformly bright because it comes not from like little dots of stars the way optical visible light does, but because it came from this plasma which filled the whole universe back before the universe was itself transparent. And so we can still see those photons and we see them in every direction because that plasma used to be filling all of space in every direction. So if you were a little creature like a parasite that looked up at the night sky and could only see the microwave, then at night the sky would be uniformly bright.

It wouldn't be infinitely bright, but it would be uniform. It would look very different from our night sky. It's important to know how the parasites see things. So I've had like three, four, maybe five existential crises during the span of our talk here. So what does this all mean then? So what it means is that while we can think about the size of the universe and what it might be made out of, and we can play these games. trying to figure out how the universe actually looks, we can't actually tell what's out there

past our observable universe. You know, this felt like maybe a trick, like maybe a way to figure out what was in the deep, dark, ancient depths of the universe because it should be contributing to our night sky. Really what this tells us is that we're forever in a bubble. We can't ever see what's past that bubble, so we'll never really know what's out past the observable universe. And even worse than that, our bubble was sort of shrinking. Well, like, physically, in terms of, terms of length, it's getting larger and larger. Space is expanding faster than that bubble is expanding. So it's sort of like our bubble of the universe is shrinking and shrinking. And as time goes on, it gets smaller and smaller. It's like a fraction of the universe. So our children in the

far, far future, will see an even smaller fraction of the universe than we are seeing today. So if we want to answer those questions, we better get on it like stat. Well, I'm feeling slightly depressed now, but I guess I'm going to go ahead and hope that this is one of those like 100 years from now. they'll be like, Daniel didn't think we could ever study everything, but now we know how to study everything. So I suppose in this particular area, I'm hoping that you're wrong, but you're probably not. And I agree. We should be, we should be studying as much of this stuff as we can now. Well, our great-grandchildren will be sitting in their mansions paid for by the Star-Screen Empire, and they'll be laughing all the way to the bank. That's great. And they'll be thanking us, and it'll be

great. So we still don't know if the full universe is infinite or if it's, It's finite and wraps around on itself forever. It's a question people are still thinking about. People will still be thinking about. Maybe someday in the future, people will find a way to probe this question to sort of like extend our minds past the edge of the observable universe. Currently, it feels like that's impossible, according to the current laws of physics. But, hey, let's hope future Daniel proves today, Daniel, wrong.

And that's how you'll get your Nobel Prize. That's my plan. A good plan. I wish you luck. In case the star screen doesn't work out, you can, you know, make all the money that the Nobel Prize winners make. But I think the larger lesson aside from this particular question of why isn't the night sky dark is that the larger strategy, physics is employing of building a model in your head, thinking about the consequences of it, and then asking yourself like, well, why doesn't that work? What does that mean that the ideas I have don't describe the universe I'm seeing? That's generally the best way to win a Nobel Prize is to try to find some discrepancy there, to discover some.

some thread to pull on to unravel some deep mystery of the universe. It definitely is beautiful the way these models that you create in physics can have these amazing existential implications, the more you think about them. And that in our minds, we can imagine what would happen in an infinitely old universe with an infinite number of stars, beaming an infinite number of photons to us. Somehow the math all hangs together. It's incredible. Well, thanks everyone for going on that journey with us to answer the question, why is the night sky dark after all? all, why don't you need to buy a big tub of Star Scream to protect your children from Star Cancer? Don't tell them that.

In the end, we believe in honesty and advertising. So thanks, everyone, for joining us. And thanks again, Kelly, for coming along, asking great questions and contributing a lot of laughs. Thank you for having me. I had fun as always. Thanks, everybody. Until next time. All right, tune in next time.

Thanks for listening and remember that Daniel and Jorge Explain the Universe is a production of IHeartRadio. For more podcasts from IHeartRadio, visit the IHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, everything changed. There's been a bombing at the TWA terminal. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism.

Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. I'm Dr. Scott Barry Kaufman, host of the psychology podcast. Here's a clip from an upcoming conversation about how to be a better you. When you think about emotion regulation, you're not going to choose an adaptive strategy which is more effortful to use unless you think there's a good outcome. Avoidance is easier, ignoring is easier, denials easier, complex problem solving, takes effort. Listen to the psychology podcast on the iHeart radio app, Apple Podcasts,

or wherever you get your podcast. Yes. Every case that is a cold case that has DNA. Right now in a backlog will be identified in our lifetime. On the new podcast, America's Crime Lab, every case has a story to tell. And the DNA holds the truth. He never thought he was going to get caught. And I just looked at my computer screen. I was just like, ah, gotcha. This technology is already solving so many cases. Listen to America's Crime Lab on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. This is an IHeart podcast.