Daniel and Jorge Explain the UniverseDaniel and Jorge talk about 3-armed galaxies, the color of the Universe and its phases.
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Terms apply. Hey, Orgey, do you ever wish you had more than two arms?
That would be weird, but sometimes it would be useful. You know, if you're a parent, you're carrying around a couple of kids'd be great to have extra arms.
Well, is it more arms that you want or more hands?
I think what I want is maybe more brains. That would be handy. Then I can have twice a number of thoughts, or one of them could think while the other one naps, and then they can take turns.
I think I already have more ideas than my arms and hands can handle.
Sounds like you less brains than.
Or more arms, Like a whole army of arms.
That would be pretty handy. It would be quite a handful. I am poor hand cartoonists and the creator of PhD comics.
Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I'm pretty sure I could make use of a third arm if it had a hand attached to it.
Where would you put it though? In your body, Like at the top of your head. That would be useful.
I was just gonna say it top of my head, yeah, exactly. You could like scratch your nose or scratch your back even that would be pretty handy.
Yeah, But how would you scratch your arm?
I'd have two other arms for that job, but would they reach I think the more interesting question is how you would call them, Like is it your right arm, you left arm, and your top arm, or you're like your dominant arm, subdominant arm, and your sub subdominant arm.
Maybe you could call it like your color arm or your weak art.
What if it's extra strong though on the top of my head anyway, lots of fun things to think.
About, Yeah, because it is a fun universe with a lot to think about. There are a lot of stars and galaxies and amazing objects and invisible matter and invisible energy out there for us to wonder about and to have questions about.
No matter which arm you like to use to scratch your head.
Welcome to our podcast Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which we dig into all of the heads scratching mysteries about the universe, why it looks the way it does, what color it is, if we can even possibly understand it, Why everything out there seems to be spinning, and why they spin in such beautiful, worly patterns. We dig into all of the mysteries of the universe, from the tiny quantum particles to the inside of black holes, to the edge of the universe, to its very beginning and its very end, because we love these mysteries, and we love marinating in our understanding and our ignorance.
Yeah, because there are beautiful patterns out there in the universe. Patterns in color, patterns, in shape patterns, also in mysteries. It seems like the universe has sort of a recurring pattern of always having things that are difficult to explain or that don't reveal how they work right away.
It is interesting that the universe is mysterious, but not so mysterious that we can't make progress. It's like we are just smart enough to understand like the next chunk of physics, but not so smart that we figure it all out right away, but also not so dumb that it's totally a mystery to us. We seem to be sort of like fine tuned to be entertained by the mysteries of this universe.
You're seeing we're like the goldilocks of all species in the universe. But how do you know this, Daniel, How do you know we're not behind? How do you know we're not actually like at the back of the class roster.
Yeah, we could be. There might be aliens out there that like figured out the physics of the universe and about ten seconds. But what I'm saying is that maybe this is more fun. Maybe it's more fun to like be a little confused for a while and then figure something out, rather than just have the entire theory of everything come to you in a single flash of insight.
That sounds like something a student who's not doing well in school might say, like, Hey, I got an F because it's F is for fun.
It's more like somebody who wants to keep the mysteries alive because it's part of my job. I mean, if we like solid physics tomorrow, then what would I do the rest of my life?
Is that what you tell the funding agencies, like, Hey, you paid me all this money and I haven't figured anything out, but I'm having a lot of fun. And really what's more important than that.
It's the friends you make along the way to figuring out the universe.
That's right. I got an F on my research paper, but F stands for friends and fun, not funding.
And it's not just people like me you were wondering about the nature of the universe and enjoying thinking about it. It's everybody sciences of the people, by the people, and for the people, and that includes me and you. It includes anybody who thinks about the universe, wonders why it works the way that does, and tries to figure it out.
That's right. Everybody has questions, and sometimes we even answer those questions on this podcast, although sometimes the answer is we don't know.
All too often the answer is we don't know, so give us some money to figure it out. Stay tuned, But we encourage everybody out there to engage with their curiosity, to look out the universe and connect with their personal questions. You know, something that I think maybe people don't appreciate is how science is driven by individual people's curiosity. The reason we study this and not that, the reason people investigate the mating patterns of South American bats is because somebody has decided that that's the most important question, the one to dedicate their life to. So I like to encourage people to think about what is your most important question. If you could ask a single question of the universe and get an answer, what would it be. And so we encourage our listener to think about the universe and to write to au us with their questions.
Yeah, we get questions all the time, and sometimes we even answer them on the podcast. We will pull up a question that we get and we'll try to give you our best answer on the air.
That's Right. We answer all of our questions that listeners send us to questions at Danielanjorge dot com. But sometimes there's one that I think is especially intriguing or requires a little bit of background research, and so we answer it here on the podcast.
And so today on the program, we'll be tackling listener questions episode number thirty six of our listener question series.
That's Right, which puts us well above one hundred in terms of questions answered on air.
And do we have a theme for this set of questions?
This one's sort of like big questions about the big universe.
I see the usual, then.
Everything exactly.
Today we have questions about questions exactly.
These fall into the big questions category.
All right, big questions Here today we have three awesome questions about the shape of our galaxy, about the color of the universe, and also about whether the universe is maybe tearing itself apart. You mean emotionally or like, physically.
I think first physically and then emotionally.
If you tear yourself apart physically, then if you want to really be able to tear yourself apart emotionally.
Yeah, that's true. Depending on how the universe collapses, you might not have time for an emotional response.
Well, let's dig into these questions because they're pretty interesting. The first one comes from Matt from Indiana.
Hey, Daniel and Hore, this is Matt from Indiana. I was just reading an article which has some of the most recent Hubble pictures now that it's successfully returned to prime time. The question I have is about the galaxy arp m ador zero zero zero two dash five oh three. NASA is saying it's noteworthy as it only has three arms to it, and most spiral galaxies have even numbers. Why wouldn't we find an equal amount of even an odd armed disc galaxies symmetry. I'm perplexed on this. Thanks for your time, Matt.
All right, awesome question for Matt. He's asking not about the milk away, but a different galaxy than the Hubble telescope has found.
Yeah, we have imaged so many galaxies. You know, when you look up at the night sky, you mostly see stars, but behind those are tiny little smudges which are galaxies. And as we saw from the recent James Webs based telescope images, every tiny little dot of sky is filled with galaxies and they have lots of really interesting shapes and characteristics. And so now we have lots and lots of examples of what other galaxies look like. And Matt is asking about one particular one that NASA said was a little weird.
Yeah, and he spelled out the name of it. Maybe we should spell it out again in case anyone wants to look it up.
Yeah, that's galaxy ARP Dash M A. D ore Than. The number is two one one five Dash two seven three. And we'll put a link to NASA's page about this in the show notes.
They just got a catchy name.
My daughter. It sounds like I Love you or something.
Well, if you look up the image and the link in our website, you'll see basically a picture of our galaxy. But it looks kind of interesting because it's got two short arms, but then one long arm on the bottom.
Yeah, lots of these spiral galaxies have the same basic features you have, like a central bar and then some arms swirling around them. And this one is a little weird because ye as you say, it has two sort of shorter arms and one longer arm. And that's the thing that Matt picked up on. That the fact that this has three arms, and according to this press release, having an odd number of arms, like not two or four or six is a little weird.
You mean, it's a little odd you have an odd number of arms, because I think we're kind of used to arms coming in pairs, right.
I certainly have two arms, though i'd like a third. But if we're talking about galaxies, then it sort of makes conceptual sense to imagine them being even numbers, like or basically there's just two arms because you have the central bar and then the arms swirling off around it. But it turns out that galaxy arms are a lot more complicated than you might imagine.
Hmmm, well, let's dig into it. First of all, why do galaxies even have arms? And I guess maybe we should define what we mean by arms. It's kind of like a you look at a picture of a galaxy, you see a cluster of stars, but then you see these kind of like tendrils, these rows of stars kind of swirling from the center of it. That's what an arm is.
Yeah, and so we tend to call these things spiral arms. And there's really two things going on there, the spiral nature of them and the arms. Right, So let's first talk about like why are these things spiraling at all? Why is there a spiral pattern in the galaxy? And that just comes from the fact that the galaxy is spinning. So everything in space is spinning, and as it collapses, it spins faster and faster. But things at different distance from the center of the galaxy don't always rotate at the same number of angles per second. Instead, they tend to move through space at the same linear speed. So galaxies don't rotate like a DVD or a compact disc, where like every point along some line rotates with the same angular speed. It's more like they rotate like runners going around a track, where people on the outside tend to fall behind even if they're running at the same speed.
Well, maybe let's take it a step back. Because you mentioned everything is always spinning. What does that mean? Why are things in space necessarily spinning? Or do you mean, like everything's moving but relative to like the center of gravity or the center of a cluster of stuff, you're sort of spinning around that.
So everything in space is sort of whizzing around. And remember that spinning is relative to an axis. You like, draw a line through space and say, are things moving around this point? And so you can pick any axis you like. You know, pick like the center of the sun. That makes sense to think about the motion of the Solar system, or you know, the north south axis of the Earth. But you really could pick anything, But it makes most sense to pick like the center of mass of a big blob of stuff and ask are things moving around this center of mass? And because everything is sort of flying around through space, it's not stationary with respect to like the center, then all that stuff tends to add up to some spinning. Like it's possible for a huge blocks of stuff to not be spinning, but that would require everything inside of it to like exactly balance all of its motion, it's sort of unlikely, like flipping a million coins and having exactly fifty percent of them land up heads. So any big blob of stuff tends to have some spin around its center.
Yeah, so I guess you know, things tend to fly in a straight line in space. But once you get a bunch of it sort of in the same area, it's going to have some gravity and it's going to start pulling stuff inwards towards the center of massive that blob, and that's where the kind of the spinning happens, right, That's where the circular emotion happens. And so that's why everything's kind of spinning around a galaxy cluster.
Mm hmm exactly. And as that's been happens, it very naturally forms a spiral pattern, right, because things that the outside get left behind. They're not spinning as fast as things closer in. Like if you're really close to the center, it doesn't take you as long to go all the way around the galaxy. For example, if you're really far out and you're moving at the same speed, takes you a lot longer to go all the way around the gall So things in the outside tend to get left behind, and that's why you end up with spiral patterns in the galaxy. But that doesn't explain why you get arms. Right, if you just have like a big blob of stuff and it was spinning and collapsing, it would tend to sort of like wind itself up. You wouldn't necessarily get blobs like arms. So the spinning explains the spiral nature, but not the arms.
Right, Like, if you had a big blob of stuff out there in space that was evenly distributed, like a hazy cloud, and then you just got it going, you would think it would just kind of like swirl towards the center, kind of like a toilet, right, There'd be no clustering. It's just like a tornado, like an even swirl down to the center.
Yeah, Like if you put a fork in spaghetti and spin it, you're gonna end up with lots and lots and lots of strands, not like a few big clumps. But what we see in galaxies is if we got like really big chunks, we got like two or four or three in this case chunks of stuff flying out in this spiral pattern.
Or more like the three giant or three or four giant spaghetti noodles, right, instead of like a bunch of little spaghetti noodles. Somehow the spaghetti's kind of cluster into giant strands of spaghetti.
Yeah, exactly like metapasta or something megapasta formations. And so a lot of people think that when you're looking at a galaxy and you're looking at these spiral arms, that you're looking at structures of matter, that like, the arms are a blob of stars like a blob of spaghetti, and that whole arm is sort of rotating, that the stars are moving with the arm. But that's actually not the case. The arms are not structures of matter. They're just density waves. They're more like traffic patterns in cars, you know, like a traffic wave can move along the highway, making some cars slow down and some cars speed up or clump together. But the cars don't necessarily move with those waves in the same way the arms in the galaxy are rotating. But stars don't necessarily rotate with the arms. They can be left behind by the arm, the arm can catch up with them. The stars don't move with the arms.
Well, first of all, what do you mean, because it aren't the arms made of stars, Like if we can see them in the night sky in space. That means it's bright, and so that means we're seeing the stars in them.
Yeah, they are made of stars, for sure, the same with the like traffic patterns are made of cars. But the things that make the arm the arm is that there's a denser spot of stars. There's more stars there than somewhere else. But as the arm moves, it sort of moves through the stars the same way that like waves move through water, but the individual particles of water don't necessarily move with the wave. Right, the wave is motion of the water.
Oh, I see what you're saying. You're saying, like if I looked at a sped up or fast forwarded movie of a galaxy, I would see it looking like it's a squirrel, like it's spinning. But it's not actually spinning, you're saying. It just has these waves running through it that go around.
The waves are spinning. But if you tracked a wave and you also tracked an individual star, you would not necessarily see them move together. Like a star can be part of an arm and then later not part of an arm, and then part of another arm.
WHOA, and so how do we know this because we haven't been looking long enough for us to see that.
Yeah, it's a really interesting idea. It's only been around for a few decades, and it's not one hundred percent certain. Though in the last few years we've got some evidence that this is true because we've looked at the color of light in these stars. Because the galactic arms tend to be aligned with star formation, these galactic arms are places of greater density, which means you get more stars being made because you're compressing the gas. So you tend to have younger stars in the arms as they are forming, and younger stars tend to be bluer because bluer stars don't live as long. So anyway, that long story is short. You can look at the pattern of color in these arms and you can see sort of how old they are and the age of stars within the arms, and so you can sort of confirm this hypothesis. So I should say it's not one hundred percent totally established.
So you're saying that arms of a galaxy are actually kind of like waves that are going through the huge cloud of stars in a galaxy. Watch costing these waves.
So these are density waves, so they're just caused by things not being totally smooth the same way like all gravitational effects are. If you have a little perturbation things aren't totally smooth, then gravity tends to pull on that and exaggerate it. So gravity will take a little perturbation in like a totally smooth clump and turn it into larger and larger perturbations. So it's not again totally understood where these come from and why they last so long. But they think they come from original density perturbations and like the central clump of the galaxy.
So they are structures. Then you said earlier that they weren't structures. So it is there because the stuff in it is kind of holding together gravitationally.
Yeah, but it's a density structure. It's not like a matter structure. It's not like the same stars are sweeping around and staying in the arm. There is a structure there. It's the density.
Structure, right, And then you're saying the density is caused by the gravity between them. So like, let's say I'm a planet or I'm a star around a galaxy. What's going to make me want to join one of these waves?
Well, it's sort of sweeping through the galaxy and it creates regions with higher gravity and regions with lesser gravity. And so some stars are like getting pulled towards these things, and some stars are getting left behind, right, And so that's how a density wave propagates, right, It creates regions of greater and lesser force, which tends to apply differential forces on the stars.
Right. But unlike a wave and water, you have forces that pull and push, right, Like something behind you pushes you forward, but then something in front of you pushes you back. And that's kind of how the wave occurs. But in gravity, gravity only attracts. So what moves the wave forward?
Well, what's moving the wave forward? Like at the forefront of the wave, it's dense, so it's pulling those stars towards it, right, So the density of the arm creates a denser region in front of it.
Oh I see, So the wave in front of it eats up more stars, which moves the center of gravity of the arm forward, which then leaves behind the stars behind it.
Mm hmm exactly. And so that's how a density wave propagates. And what's really interesting to me is that the velocity of the arms is not the same as the velocity of the stars. That means where your star is in the galaxy determines whether these density waves are passing you or whether you're passing them right, Like, for example, our sun moves around the center of the galaxy at a certain speed, which is basically determined by where it is a distance from the center, and so it's actually moving around the galaxy about twice as fast as the arms. So we are catching up to arms and passing them by. But if we were further out, then the density waves would be passing us by, and.
So that's where arms come from. Now. Matt's question was, why is it weird that this one galaxy that we saw has three arms? Why is it weird to have an odd number of arms?
So they make this comment on the page describing this galaxy. So I chatted with a couple of experts about galaxy formation, and they quibbled a little bit with this cl that it is unusual. First of all, they say, it's not even really easy to define like how many arms a galaxy has, you know, because it's basically just visual inspection. You're just sort of like looking at it and seeing sirels. But you know, galaxies have more complex structure than just like here's an arm, there's an arm. Like if you look at the Milky Way our galaxy, it has sort of two major arms, but lots of like little spurs off of it. For example, we live in the Orion spur, which is like a little offshoot from the major Sagittarius arm. So is that really another arm or not. It's not like a well defined way to count these arms. It's just sort of like by looking at.
It, I see, So it's hard to define what makes an arm.
It's hard to define what makes an arm exactly. And so you look at this particular galaxy and you're like, yeah, I could call that three or I could call that four maybe. And so the short answer is that I don't think there's broad agreement on how to define arms or how many arms it makes sense for galaxies to have.
I guess my question would be, if you look at all the galaxies that we can see out there in space, what is more common? Is it more common to have an even ish number of arms or an odd ish number of arms.
Yeah, it's a great question, and it's a hard question to answer without like a systematic way to analyze these things. Basically, a human has to look at it and say, I think it has three, but another human might look at the same galaxy and say, no, I think this one has four. So to get like enough statistics to do some analysis of that, you need some like really rigorous way to analyze these things. And people have done like furry analysis or the distribution of density waves through galaxies, but that's really just a way of counting like the strength of these things. Again, you have the problem of like deciding when to call it another arm. So right now, it's really just mostly anecdotal. People have seen a bunch of galaxies and haven't seen ones that look like this to them, And there are ways to explain it. Like if you look at a galaxy like this and you say, how did this galaxy get this way? Well, one possible explanation is that it recently had a strong gravitational interaction with another galaxy that sort of messed it up. Because this one also seems sort of asymmetric, right It's got like one long arm on one side and two shorter arms on the other side, So it may just be that like a passing galaxy sort of pulled on it in a way that separated those density waves.
But I mean, I guess, is it easy to pull up pictures of galaxies that look like they have three arms? Is it maybe harder or easier or the same as pulling up pictures that looked like they have four arms or two?
I think it's probably true that most of the galaxies you look at, if you've just counted them, you would probably get an even number of arms. A lot of them just look like they have two, though they're sort of like tightly wrapped around. But look at the Milky Way, for example, it's not easy to say, like how many are there? Like I count one, two big ones and at least two maybe four little ones.
Although we don't really have a picture of the Milky Way, do we?
We certainly don't have an actual image of the Milky Way from the outside, so we can reconstruct the density of stars in the Milky Way using a lot of our observations.
Right, well, could there be maybe some effect? Is we are talking about waves right around sort of a fixed medium. Is it possible that, you know, given the typical size of a galaxy with the typical number of stars, maybe like a standing wave of four arms is more likely than a standing wave of three arms, you know, like waves around the spiral of the galaxy.
I read some papers about these things, and there are some arguments for why you might get two or four if these things really do come from the density perturbations in the center of the galaxy, because you would expect that to be somewhat symmetric, right, that it would cause similar effects in one direction and in the other. And so it makes some sort of sense for this thing that collapse into a bar that then generates two arms, and that those might split, but that splitting would always give you an even number. So there are some papers suggesting that you would expect, on average to get an even number of arms, and I think that makes some sense, but it's not very well established.
Well, so then the picture that Matt saw, he sawed an article that said that NASA think it is weird to have an odd number of arms. What was NASA saying there?
So the quote the article says, while most disc galaxies have an even number of spiral arms, this one has three. But you know, the astronomers I talked to quibbled with that a little bit. They didn't think it was so weird. They've seen galaxies with three arms before.
M I guess we'll have to ask NASA. I mean, what do they.
Know, Let's have them on the podcast.
All right, Well, I think that answers Matt's question, which is like, maybe it's maybe it's not that weird, right. It seems like some astronomers don't think it's as weird to have three arms. It seems like it's kind of a fuzzy thing. Anyways, it is.
But what is weird is that arms exist at all. It's really fascinating in the dynamics of galaxies. They have these things slashing and swirling around, and it just reminds you that galaxies are dynast chemical objects. They're not fixed things that have been formed millions of years ago and unchanged. Right. They are swirling, they are crashing into each other, they are constantly changing, just on these vast, vast time scales that we can hardly even imagine.
Yeah, and they're not just dynamic, they're like wavy, right, They're rippling. That's what these arms are. They're ripples in their structure. All right, Well, let's get into some of our other questions. One is about the color of the universe, and the other is about the fate of the universe. So let's get into those, But first let's take a quick break.
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All right, we're answering listener questions here about everything as usual, the whole she bang, the whole universe, and our second question comes from Genie, Hi, Daniel and Hage. The question I would really like to ask is did the universe have a color after the Big Bang? If there was no color, when was their first color and what was it?
Thank you. Of all the questions we've gotten, this is the one that really threw me for a loop, Like Wow, a question I've never even thought of before, never heard of before what a super fun question.
Yeah, it's a very colorful question. Genie asked, did the universe have a color? After the Big Bang? So I guess the Big Bang happened, and I guess her Maybe her question is like, if there was a human present there, what would it look like? Would it look red, purple, green, pulka dot? Or would it just fry your eyes?
Yeah? Really one question? What would you see if you were there?
Right?
Really love this question, and I think it's really fun because it makes us think about, like what is color? Anyway?
Yeah, let's dig into that. What is color? How would you define it? I know it's related to the wavelength of the light.
It is related to the wavelength of light. But I think it's important to distinguish, right, Like, photons have a wavelength, which means like how long it takes for them to go up and down. It's related to their frequency, right, how many times they wiggle per second. But the color is not a property of the photon, like photons themselves don't have color. Color is something inside your head. It's like how your brain responds to a signal of a photon of a specific color. So it's not part of the photon itself. It's like the taste of salt. Salt itself doesn't have a taste. Your tongue has a response to sensing salt.
Right, I guess you're sort of quivaling about the definition of things. But I mean light does have of different wavelengths, right.
It does. But there are lots of wavelengths of light that we can't see and our brain doesn't respond to. So photons above the visible spectrum like have no color to them.
Early, they have no colors. So far we could they innically start naming other colors, right.
Yeah, absolutely, you could even imagine creating a new internal response that's a different color than anybody has ever imagined before. Right, If colors are really just part of your mind, if there are a response to signals from your optic nerve, then in principle there's no limitation on experiencing new colors, not just combinations of existing colors, but like brand new colors. And so in principle that's possible, and you could assign those to very high frequency light. You can imagine like building a technological eyeball that sends messages to your brain. Your brain would learn to interpret those responses by giving you some new experience that would be like a new color.
Yeah. I think what you're talking about is that you know, light has a certain frequency that can come in certain frequencies, and let's say like seven gigaherds or something, or like seven hurts might be a frequency. And when I see that frequency of light, I think the color green, for example. And you and I agree that if we see light at this frequency, we're going to call it green. But I think what you're saying is like, maybe what I experienced is green is different than what you experience is green.
That's certainly true. And there's only also a narrow band of photon frequencies that we even have colors assigned to. And sort of the long history of the universe is that it started out really really hot and dense, and photons created in the very very beginning of the universe after the Big Bang had very very high energies, very high frequencies. Then the universe is cooling down, so the photons created get longer and longer, right lower frequencies, and so the universe sort of starts out invisible and then passes through the visible spectrum. And so, like Genie's asking, what color was the universe when it started, right, And the problem is that the energy of the photons that very beginning of the universe don't really have a color. They're too high frequency for us to see.
Right, Because the energy of a photon is related directly related to its frequency, right, Like the higher the energy, the higher the frequency.
Exactly, and hot stuff tends to make higher energy photons. We've talked about this on the podcast a few times. Everything generates photons. Everything that has charged particles inside of it generates photons, and it generates photons based on its temperature. So the Sun generates photons at some temperature because of its thousands of degrees Calvin, the Earth glows and generates photons at some temperature because it's much cooler. You generate photons at some wavelength. Your eyes can't see the photons generated by yourself or by the Earth. They can see the ones from the sun. So some of these photons are visible and some of them are invisible. But the hotter something is the higher energy the photons it generates.
Right. So you're saying, maybe at the Big Bang, everything all the photons that were there were super high frequency or low wavelength. What are you saying that initially at the Big Bank, thinks were so crazy. All the photons were super duper high energy.
They were super high energy, which means very short wavelength, which means very high frequency. Right, And so these photons were zipping around the universe. And if your eyeball was there just after this moment, when the universe was like at the Plank temperature, then not only would it be cooked instantly, but the photons that hit it it wouldn't know how to interpret. Your eye wouldn't see them, So the universe would just be black, even though it'd be super duper hot and filled with photons.
Yeah, Like if your eye could somehow survive being in a big bang, it wouldn't. You would see total darkness, right, because all the light would be sort of like X rays, they just passed through your eyeball.
One question is would they interact with your eyeball or they passed through like X rays?
Right.
X rays do interact with some parts of your body, but not others. And as a frequency of photons change, there are chances of interacting with you changes. But you're right, a lot of these photons might just fly right through you like X rays. Which are higher energy photons than our eyeballs can see. But then the universe temperature change.
But then eventually after the Big Bang, the universe started cooling down, right, and so you started seeing photons with lower.
Energy, Yes, exactly. So as the universe cools and it's really dense, plasma gets more more dilute, it cools down, and so it starts generating photons with longer wavelengths. So as time goes on, the temperature of the universe is dropping and the energy those photons is dropping, and so the wavelength is increasing.
So they're like the general light of the universe started off way too high for our eyes, but then it gradually as it cools, starts to approach the visible spectrum.
Yeah, and there's a really fascinating moment around three hundred and eighty thousand years after the Big Bang, when the universe cooled so much that atoms could now form. So you have protons and electrons whizzing around with so much energy that they couldn't be bothered to bond together. But after a certain time things cool down, those electrons that no longer had enough energy to escape the pull of those protons, which have a positive charge and pull on the electrons, and so you get neutral hydrogen forms. And in this moment, the universe goes from being opaque like a really hot plasma like the center of the Sun, to being transparent, just like clouds of gas in space. That light could mostly pass through, So all the light generated before this moment was just reabsorbed by the hot plasma. Light generated after this moment can fly through the universe, and like, hit your eyeball, and this light is still flying through the universe. It's the cosmic microwave background light. We can see it with our telescopes. When it was generated, at that moment in time, the universe was still filled with a pretty hot plasma. It was like several thousand degrees. So that was the moment when the universe first became transparent and the light that were created sort of becomes persistent.
Right, But still that light is too high energy for eyeballs to capture. Right Like when I look up at the night sky, I can't see the cosmic microwave background with my eyes, can I.
You cannot see the cosmic microwave background with your eyes currently. When it was created, it actually was in the visible spectrum because Remember that the wavelength depends on the energy on the temperature, and when that light was created, the universe was still pretty hot. It was several thousand degrees calvin, which is about the same temperature as the surface of the sun, which produces visible light. So when the CMB light was created, it was in the visible spectrum. You could have seen it if Genie had her eyeballs back in the early universe. Back then, she could have seen the CMB with her eyeballs. Now, you're right, when you look up at the night sky, you don't see it. That's because it's no longer at that frequency. It's been stretched by the expansion of the universe down to much much longer wavelengths.
Right, And that's why you need like infrared telescopes.
Right exactly. But it's too low frequency for us to see.
Right.
It started out in the visible spectrum and it got stretched out below the visible spectrum to very very long wavelengths infrared. And so that's why we need really sensitive telescopes in order to see it, because it's now super duper infrared. And people say the temperature of the universe is two point seventy three degrees calvin. What they're talking about is the temperature a plasma would have to be to generate the photons that we see in the CMB. The plasma that actually generated those photons much much earlier, was much hotter, but then it's light got stretched out, so now it looks like a plasma that's much cooler generated this light.
Right, So that's a cosmic microwave background radiation which comes from the moment when the universe became transparent and not hazy. But that's I wonder if that's really what would fit into her definition of the first light, Like, you know that the light still existed when the universe was hazy and opaque.
Right, yeah, exactly. So backing up again, the universe started out really really hot, and then as it cools, it passes into the visible spectrum that happened before this moment when the universe became transparent, but just about the same time. It's like an interesting overlap here that the universe became transparent around the same time as it became visible. The temperature for hydrogen become neutral is about the same as the temperature of the surface of the Sun where visible light is generated.
Right, So then as the universe moved into the visible spectrum. What would have been the first color that you would have seen if you were there and was able to survive, Like, what's the highest frequency color that we can see with our eyes?
Yeah, it'd be like the most violet violet. It'd be like super duper purply blue is the highest frequency light that we can see.
So then the first color was blue. I was right.
I don't know if purple and blue are the same, but yeah, it was definitely very very bluey, very purply blue ultraviolet.
You said, violet blue. All right, we'll go with purple. The first color in the universe was purple, basically, is.
What you said.
Yeah, I think that's true. It was purple.
All right, Well, Genie, thank you for that question. I hope purple is your favorite color as well, because it is apparently the universe first color.
But you know, if there are aliens out there and they have eyeballs and their brains interpret things differently, if they brains give them like a red experience for that same frequency and a purple experience for very low frequencies, then aliens would say a different color was the first color. And that's just because, again, color is not part of the universe. It's part of our brains. So it's a very human thing to say that violet was the first color in the universe. It was the first human color in the universe.
I suppose, Well, it's the first name that the human would give it. But the frequency was still the same, so we would all agree. I mean, the experience I have a violet might not do the same experience you have a violet, but we can all agree that about that frequency.
That's true. Though Aliens might be able to see much higher frequencies, and they might say an even higher frequency was visible before our violet.
I see, they might have a different first color, assuming they call it color. Yeah, maybe they spell it with a K or something, but they put a U after the second. O Oh my god, that's just that's crazy.
I mean I think you went too far there.
Yeah, who would do that? All right, Well, I think that answers Genie's question. Thank you, Genie, And so we'll get to our last question. This one is about the universe tearing itself apart. So let's take that apart. But first let's take another quick break. When you pop a piece of cheese into your mouth or enjoy a rich spoonful of Greek yogurt. You're probably not thinking about the environmental impact of each and every bite, but the people in the dairy industry are. US Dairy has set themselves some ambitious sustainability goals, including being greenhouse gas neutral by twenty to fifty. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. Take water, for example, most dairy farms reuse water up to four times the same water cools the milk, cleans equipment, washes the barn, and irrigates the crops. How is US Dairy tackling greenhouse gases. Many farms use anaerobic digestors that turn the methane from maneure into renew uble energy that can power farms, towns, and electric cars. So the next time you grab a slice of pizza or lick an ice cream cone, know that dairy farmers and processors around the country are using the latest practices and innovations to provide the nutrient dense dairy products we love with less of an impact. Visit US dairy dot com slash sustainability to learn more.
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All right, we're answering questions about the universe and our last question. It's a bit uh dramatic, bit drastic.
It certainly is, which is why we saved it from last.
All right, our last question comes from Courtney, and she has a question about the universe.
Hey, Daniel and Jorge, I have a question for y'all. Is our universe tearing itself apart? Is physics as we know and measure it stable enough to be relied upon?
If so?
For how long? If at the beginning of the universe the electroweek force broke and one moment everything was whizzing around at the speed of light, then suddenly the next some particles experienced mass, fundamentally altering the trajectory of our universe. Could we be looking forward to another dramatic change in how our physical forces manifest themselves. Could we measure that looking forward to hearing back?
Thanks?
All right? Awesome question for Corney. I think really what she's asking is does she have to do her homework for tomorrow or do that errand she needs to do or is the universe just totally going to flip on itself and that maybe she could be doing other things today.
Yeah. I did get the sense that she was trying to make plans and she wanted to know how far in the future she needed to think, Like, if I buy this house, is it going to be for sale in twenty years or is the whole universe going to get shredded before that.
Yeah, do I still have to pay my mortgage? Or can I just buy the biggest mansion I can now because the universe is going to end.
That's right, real estate investment advice from people you shouldn't be listening to about real estate.
Well, she's going to ask the multi part question. She asked whether the universe is tearing itself apart, which I guess maybe is related to her second question, which is like how stable do we think the universe is?
Like?
Is it going to stay like this forever? Can we invest in real estate? Or is it possible for the universe to suddenly change tomorrow or today or right now and make it a whole different universe? And maybe that happened? Would we notice?
Even I really love this question because it touches on one of the most interesting ideas in physics that I think is not very widely appreciated, And it's actually connected to Genie's question about like the temperature of the universe. You know, we think about the universe and how it works, but we're really just describing the universe in one phase. When I say phase, I don't mean like, you know, a toddler throwing a tantrum more like a phase is in the state of matter. Like if you're a scientist and you're trying to understand water, then you might have one understanding of how it works when it's a vapor, and another understanding of how it works when it's a liquid, and another understanding of how it works when it's a solid. Right, we notice these phase transitions when water changes its behavior pretty dramatically as it heats up or as it cools down, and we can have a law that describes each of those phases. And in principle, if you had like the ultimate theory of physics, you could have a single law that describes all of them. But typically what we do is we have effective laws that describe like one phase at a time. And so the universe, the whole universe is cooling down, as we talked about it a minute ago, and so we think it's passing through different phases. And so our current understanding of physics, the standard model of quarks, the photons, the weak force, the Higgs boson, all that stuff just describes the current phase of the universe in the sense of like having an effective theory that describes how things work, right, now.
Right, because, as we kind of talked about a minute ago with Genie's question, the universe kind of went through a pretty significant phase change early after soon after the Big Bang, Like before this event, everything all the matter had so much energy, so much velocity, so much going on that like not even protons and electrons could hold together or come together and stick into atoms and matter. Things were just kind of like giant plasma. And then when things cool, when space expanded, things cool suddenly, like things clicked into atoms and the stuff we see today, which is I think what you're trying to say is similar to what happens to vapor or ice. It's like the molecules are flying around, but at some point they lose so much energy that some of the other forces in play start to click them together or to bring them together as a liquid exactly.
And what Cordy's bringing up is another kind of phase transition, even deeper phase transition than just like how do protons and electrons click together? She was talking about the moment when things got mass. Right, we've described the nature of the universe as we understand it in terms of all these quantum fields that are slashing around and we talk about how the Higgs field is there and it's giving mass to particles by interacting with them and changing how they move through the universe and all of this stuff. But if you go back to one of our podcasts where we talk about the very early history of the universe, you know that there is a moment before this happened, before the Higgs field was giving mass to particles, when we still had this description of everything in terms of quantum fields, but effectively the universe was very different. Everything was basically mass lists, electrons and quarks and all this stuff were flying through the universe all at the speed of light before the Higgs boson sort of kicked in and gave everything mass. So that was another big phase transition in our universe.
Now that one's pretty fundamental, like the universe went from not having mass to having mass. Things having mass, and you said, something clicked, but like the laws of physics change, or within our laws just some sort of like potential change, or we reached the threshold where suddenly the laws preferred to be this way rather than having no mass.
So we think that the laws we have now described the universe now and also before this transition, so same laws of physics, but you have different temperature, and so as the Higgs field was cooling down, it got stuck in sort of a local minimum, and that's what you referred to as electroweak symmetry breaking. It got stuck in this sort of weird spot where it treats w's and z's differently from how it treats photons, and it gave those particles mass, and it gives mass to the other particles sort of because where it got stuck as the universe was cooling. So it's the same basic laws of physics, but as the universe cools down, the effect of those laws changes, and one of the effects is that the Higgs field got stuck in this weird spot and that's why these particles have mass. And so really, I think her question is like, do we expect further similar phase transitions in the future of the universe that could fundamentally change what we experience.
Yeah, I guess she's not asking like can the laws change? She's more asking like, is the universe, like you said, is the universe stable? Are we like in a spot where the basic configuration of the universe is going to be the same, or can it change like it did once before.
Though, you know, it is possible that the laws could change, because even though we can describe the history of the universe pretty far back using our laws and quantum fields, there's a moment beyond which we can't. Right at the very very beginning of the universe, just after inflation, with things 're at the plank temperature. We think our laws break down there, and before that we need something else, some theory of quantum gravity that's deeper. We think that even our laws of physics that do a great job of describing the universe today and very very far back in time, they are just effective laws. They're like understanding water when it's a liquid and how it flows, but not deeply understanding the true theory of water that would explain all of its phases. So there is a sense in which the actual effective laws of physics do change over time, though we don't know what's going to happen in the future. We think the universe is just going to keep cooling and probably this current effective set of laws are going to hold fast. But even if these laws hold fast, there might be phase transitions still in our future.
Right.
We talked in the podcast once about how the Higgs field is sort of stuck in this one spot, but it's not that stable. We don't know if it's going to stay stuck in that spot or if it's going to collapse and change the masses of everything, And that would be like another effective face transition. So it might be that sometime in the future, you know, maybe spurred on by particle collisions, that some super collider could spark a change in the Higgs field which creates an effective phase transition in the basic laws of physics.
Yeah, I think we talked about this in our book. Frequently asked questions about the universe. But you know, is the universe going to end at some point or how is the universe going to end? And one possibility is for this Higgs field to collapse, because it can collapse right like, it's sitting at a place where it can still fall down in terms of energy.
Yeah, the reason the Higgs field does what it does is because it has a lot of energy still stored in it. It's like the whole universe is cooling down, but the Higgs field got stuck and it's sort of staying hot. But it's kind of like a ball that's stuck on a shelf, and it could roll off that shelf and fall further down in temperature. We don't really understand very well how stable the spot it's stuck in is and what it would take to sort of nudget out of that, and so there's a possibility that it could collapse even further and that would mean a change in the math aids of all the particles, which would mean like chemistry out the window, need totally new chemistry, and you know, everything that relies on chemistry, like life and podcasts also out the window.
And I guess buying a house also along with that. But I think you describe it as sort of like a spark and a spark propagating. I know we've covered this in the book, but it's it's almost like if something happens and does cause a Higgs boson to kind of fall over or give up its energy in one spot, it would basically cause the entire universe to do the same, Like it would spread out like a wave, right mm hmm.
If it happened anywhere, it would spread out like a wave propagating at the speed of light. So it may have already happened somewhere else in the universe and that wavefront of phase transitions is heading for us or maybe not, and maybe it'll be stable forever.
Right, And you're saying that one thing that could trigger it maybe is building a large particle collider, maybe under Geneva or something.
Yeah, or around the surface of the Moon or around the edge of the galaxy.
It sounds like we need to shut those things down right away.
It sounds like we need to build one and find out.
No, that sounds like exactly the opposite thing. You want to find out if you can destroy the universe.
I don't know. I'm pro curiosity. I don't know how you feel.
I am pro not destroying the universe, because once you find out that you can destroy the universe, you've destroyed the universe, Daniel.
But you've learned something along the way.
No, because you won't be here.
Look what I'm saying, is nobody ever regretted destroying the universe.
Well, I think the answer here for Corney is that go ahead and buy that house you're thinking of buying. And maybe you should write to Daniel, tell him not to destroy the universe.
Send us your questions, your ideas, your requests to not destroy the Universe two questions at Danielanjorge dot com.
All right, thank you everyone for sending us their question. A lot of interesting things we've learned about here. I think we can give ourselves a pat on the back. Daniel, maybe with that third army having at the top of your head.
Yeah, exactly, it's busy. Scratch my head right now.
You can give yourself three handshakes.
Triple high five. It'd be the highest of fives.
It be a triple five. Yeah, it'd be a fifteen. All right, Well, thanks for joining us. We hope you enjoyed that. See you 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. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. House US dairy tackling greenhouse gases many farms use anaerobic digesters to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as Dairy dot COM's Last Sustainability to learn more.
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