Daniel and Jorge Explain the UniverseBefore the stars and galaxies formed, the Universe was dark and foggy for hundreds of millions of years!
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Hey Daniel, what do you think about when you look at the night scout?
Well, it's just staggeringly gorgeous, of course, But what I'm most amazed at is the depth of the view. What do you mean, Well, it's just incredible, Like how far we can see from the Moon that's kind of close by, all the way to the Sun. Two stars that are like billions of light years away. Yeah, that is pretty deep. That's like the deepest view ever. Yeah, it makes you feel lucky, right.
What do you mean lucky? Are you imagining that space could have been foggy?
Yeah? In fact, the universe didn't always offer such crystal clear views of crystals. The Yelp reviews from the early universe had fewer stars.
I am Poor Hamm, a cartoonist and the creator of PhD Comics.
Hi. I'm Daniel. I'm a particle physicist, and on Yelp, I give our universe five stars.
Yeah. Do physicists have Yelp reviews?
No?
I wish we did, though. I wish we could just review parts of physics and be like, Wow, this part is awesome. This part's kind of sticky and gooy. I don't like it that much.
I got terrible service when I try to order a black hole.
This collider works great, but this one is usually down. My collider accidents have destroyed the universe. Thumps down, zero star.
Welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which we explore all the amazing and wonderful star filled universe, all the things that are incredible and visible that are out there that we can see from Earth, all the things that we can't see that we have to use our imagination, All the things that are happening right now and things that happened in the deep dark past.
Yeah, because it is a huge universe and we can see a lot of it out there. There's a billions and tunings of stars that we can see in galaxies, and there's a lot that we can't see as well.
That's right. It's amazing to me. It sort of feels like you're standing at the top of a mountain and you're looking out and you can see things that are like billions of light years away. It's like looking across a vast, vast ocean of space. And those photons, you know, they had to travel so far and for so long just to get to your eyeball. It's amazing that nothing stopped them along the way.
Yeah, it seems like we just happen to be looking at the universe on a clear day. You know, it could have been an overcast day, or a foggy day, or a hazy day, or you know, there could have been small from all those aliens. But somehow it's a pretty clear view of really far away stuff.
And imagine what life would be like if we didn't have such a clear view. If the universe was foggy, if you looked out into space and it was just sort of like a gray blob, if you couldn't see the stars and the galaxies, we couldn't learn about the shape of the universe and its structure and its history. We would be so clueless if we couldn't see as far as we do.
Yeah, we would probably still think that we are like the center of the universe and that just the things we see around us is all there is to it.
Yeah. Absolutely, And we can see pretty far in the universe in the wavelengths we're familiar with, you know, in the wavelengths of visible light, but there are lots of different wavelengths of light, and in some wavelengths of the universe is more or less transparent. And so these days we've opened up lots of new kinds of eyeballs onto the universe, infra red light and UV light and X ray telescopes to be able to see different parts of the universe at different depths.
Yeah, it's a clear day in the universe. But it sort of makes you wonder if it was always this clear, we always able in the universe to look so far away and to see so many stars and galaxies.
Yeah, and there's actually a really fascinating period at the beginning of the universe. You know, people think about the universe starting the big bang boom, huge explosion, lots of stuff rushing out, dot dot dot. Galaxies are formed, and we have stars and stuff, but there's a lot of interesting stuff happening in that dot dot dot period, whereas stars get formed, before we actually have the structure of the universe that we're familiar with today, before we can see as far as we can out into the deep reaches of the universe.
Well, a lot of YadA YadA happened, I imagine in those dot dot dot moments. But yeah, the Big Bank does get a lot of attention, and you sort of assume that it's really bright the Big Bang, I guess because it's a big expansion and a big explosion, But uh, there happens to be a period right after it in which you couldn't see a lot of stuff.
Yeah, it's fascinating to imagine why the universe is bright at all. You know, we only have light in the universe because it's created by these pin pricks of stars. If we didn't have those, the universe would be super dark. And so there was this period after the Big Bang and before the first stars when we didn't have light in the universe, and another really fascinating period after we had stars, before the universe cleared up. And so it doesn't usually get as much attention as I think it should. But it's a really interesting period of the universe and helps us understand like how stars and galaxies actually came together.
Yeah, So to the podcast, we'll be asking the question what happened during the dark ages of the universe before the Renaissance, before the Cosmic Renaissance.
I guess, yeah, and there actually is something of a cosmic Renaissance. It's a fascinating parallel to sort of a human intellectual history.
Was a universe full of like feudals, societies, and everyone were armor and you swords.
Yeah, it makes for really great like television epic dramas.
Yeah, so there was a long period in where the universe wasn't as bright as it is now. In fact that it was hundreds of millions of years of darkness and fog, right.
Yeah, exactly before the universe looked the way that it did today. There was a lot of work that had to happen between the Big Bang and molecule's form and you get this hot, dense gas and then for stars to actually pull together and to light up.
Yeah. It's kind of interesting to think because you know, you don't usually assume that there was a dark age. You just assume that, you know, the real dark age happened before the Big Bang. But I guess we don't know what happened before the Big Bang really.
Yeah, we have no idea if that was dark, or if it was crazy bright, or if it was part of the meta universe or space didn't even exist. Those are the kind of questions we can't even really ask. We don't even know how to probe those questions. But this is a part of the universe when things actually had formed, when the rules of physics as we know them were in charge, and so we could ask these questions. But it's a period that's also very difficult to study because it was so dark.
Yeah, and so this happened right after the Big Bang, and maybe a lot of people don't know that we had a dark age at all in the universe. I imagine most people just assumed that there was a big Bang and then thanks got brighter from there. And so, as usual, Daniel went out there into the wild of the Internet to ask listeners what they thought happened during the dark ages of the universe.
Thank you to everybody who participated in this exercise, and if you would like to send answers to questions for which you are totally unprepared to give responses to please write to us two questions at Danielandhorge dot com.
Think about it for a second. Have you heard or know what are the Dark Ages of the universe. Here's what people had to say.
Something to do with the point in time where the universe was so hot and tense that no light could escape.
My guess is that the dark ages of the universe was when you know, there was no light so you couldn't see what else is in the unit. I would put these dark ages before being big bang. That's it.
I think it is the time before the universe cooled down enough to be transparent to photons.
That's the photons emitted in that time are stuck in that time and not detectable by us.
The universe is fourteen billion years old, give or take a few, so maybe it was at a time when the universe had had had time to cool off and not be so intensely hot. So maybe five six billion years ago.
I think that was after the universe was cool enough such that the guest was not emitting light anymore, at least not an invisible spectrum. But before the first stars formed.
All right, A lot of interesting answers here. Some of them sort of band your brain a little bit, like the universe is so bright that you couldn't see light or something like that, or there was no light so you couldn't see anything.
Yeah, or somebody else suggesting that it was pre Big Bang, like you were.
That's a fun idea, yeah, And so it's pretty tricky, I guess, because you know, the Big Band was such a chaotic mess, and it's hard to tell when light could go around and when it could not go around, or when it was created, or when even light was created itself because light didn't always exist, right.
Yeah, exactly. And there are a lot of these answers that thought that the Dark Ages were somehow before the cosmic microwave background, and so I think there's a bit of confusion out there about the order of events. So it's a good idea, I think, for us to clear it up and walk through what happened before, during, and after in the Dark Ages of the universe.
And I guess nobody guess that it involved armor and castles and shields and feudal societies.
And epic love poems, probably with loot.
All right, So step us through here. Daniel let's go all the way back. I guess, so before there was even a dark age in the universe. What happened step us through from the moment of birth of the universe to for a dark age.
Yeah, so it's pretty fascinating, and it always amazes me that we know as much as we do about these first few moments of the universe. You know, the Big Bang happens. We don't really understand that at all, but we think that it happened. There's some moment of singularity there and then the universe is filled with this very high density of energy and very rapidly things start to stretch in the superiod we call inflation, when the universe grew very very quickly in a very short amount of time. So you have a universe that's really hot and dense and filled with stuff gets stretched out to a much cooler, more dilute universe by a factor of ten to the thirty in about ten to the minus thirty seconds. So that's the very beginning of the universe. And after, you know, like ten to the minus five microseconds, you have things happening like quarks are forming, particles are coming into existence. Before that, you have this really dense soup of energy, but you can't really think of it as part. It's more like thinking about an ocean of droplets rather than thinking about an individual drop on its own.
Yeah, and you can even think about forces like it. There was a point right after the Big Bang or during inflation, in which you couldn't even say, hey there's gravity, Hey there's electrominietism. It was all just part of the same soup.
Yeah, that fits a bit more speculative. But we think that when you have really high energy and really high density of stuff, that all the forces are the same. They have the same strength, and as you cool down, that sort of break out into different strengths, which is why we have the strong force is the strongest force, and gravity is the weakest one, and they all have sort of different characteristics. We think that only happens when things sort of get cold and separate, But when things were hot and dense in the early universe, we think they unified into one force. And so as you go forwards in time and the universe cools, we think of those things that's sort of breaking out. So the force is separated into the forces we know now, and then particles formed and you get like quarks and gluons are still super duper hot, and so those quarks and gluons they don't like break off and make little particles like we know now like protons and neutrons. They were in this state called a cork gluon plasma, which is sort of like the way we think about a plasma like hydrogen gas, where the electrons have so much energy that they just fly around. You don't get little bound states. Here for cork gluon plasma, there's so much energy that you don't get like bound states of quarks like protons and masons and other kinds of stuff. It's just a big sea of quarks and gluons all mixing around together.
Really, they don't snap together. I thought you couldn't have quarks by themselves.
Yeah, you can't have them by themselves, but you can have them in a super dense ocean of quarks and gluons. So they're not on their own. They're just sort of like enmeshed in this soup. Or you can think about like the whole universe is one big quark particle, you know, filled with quarks and gluons all mixing around, sort of like the interior of a proton, right, is a bunch of quarks and gluons flying around together. Think about like the whole universe in that state.
Wow, so the universe is like a giant.
Proton exactly, It's like a giant proton.
The proto universe was a proton.
But then it continued to expand and to cool, and then it sort of broke up. Right, instead of being one massive quark low and plasma, we have these hegrons forming, so you get things like chons and pions and protons and neutrons, things that are combination of quarks to sort of like snap out into their own little lego pieces. And that happened about a second after the Big Bang, we think. So we're a second into the universe and we already have particles made out of quarks.
Okay, so now it's starting to look more familiar to what we know, like protons and neutrons, and so the universe is like a sea of them, like still a hot soup and not as hot.
Yeah, still a hot soup. And you also had particles like electrons flying around. And then in the next twenty minutes or so, the universe spend some time building atoms, and so you got protons and electrons that come together and make hydrogen.
For example, Wait, how did the electrons form? They just form that of the energy in the hanging around. They just popped into existence.
The same way the quarks did. You have this sort of raw energy that was in all of these matterfields, sloshing around between them, using the forces to interact, and then it's sort of crystallized out into the various matterfields. You get quarks, you got electrons, You got heavier stuff probably also, which then decayed.
All right, so now we're starting to form nuclei and atoms, and that's where the most of the I guess hydrogen came from.
Yeah, And so then it crystallizes out and you get hydrogen. You get some helium also, but mostly hydrogen. You get very small amounts of lithium. But things are still very very hot and dense, like you would want to be in this situation. The temperature is very very high. It's sort of like the interior of the sun. You know, it's still a hot soup. I mean, we spent twenty minutes already expanding and cooling the universe from the much hotter initial state. But it's still very hot. It's still emitting photons, it's still sort of glow and absorbing that light.
It's still a hot mess.
It's still hot.
Don't you want no part of that?
Yeah, exactly, And at this point we still have about fifteen percent of the matter in the universe. Is the kind of matter we're familiar with. It's made at of baryons. You know, it's going to be atomic matter eventually, but dark matter is also formed, right, You don't just make quarks and electrons. We don't know the particle nature of dark matter, but we think it was created. We're pretty sure it was created back in those same moments when you made your quarks and electrons. So whatever dark matter is made out of, it was already present back then in the early universe.
It was created just out of thin air, just like the quarks and electrons too.
Yeah, it was just the energy in those fields collapsed into the matterfields, and that's what making particles is. And so yeah, all that stuff was made. And then you know, that soup sort of sat around, you know, oscillating and glowing at itself for like one hundred thousand years or so until you get to the moment when it cools enough that the electrons like to hang out around the nuclei that the nuclei can sort of grab their own electrons and become neutral.
Oh so before, I mean before you had hydrogen and maybe helium, but maybe the electrons weren't sticking around to the nuclear to form like a regular hydrogen atom.
Yeah, it was more like a plasma. Right. You have electrons and they're flying around. You have protons and they're flying around, but they haven't like cooled off together where they're going to pair off and become neutral. And so you have helium nuclei and hydrogen nuclei and electrons all flying around in this big, messy plasma. But sort of an analogy to the way we were talking about cork luon plasma before. Here we have a nuclei electron plasma. So it's very hot and it's emitting a lot of light, but it's also absorbing that light, and so it's opaque. It glows giving off light, but it also absorbs that same light, so it's kind of like the sun. It's hot and it's glowy, but it's not see through yet. And then there's this moment when it cools enough that the protons and electrons come together to make neutral hydrogen and it doesn't absorb that light anymore, and so it becomes transparent.
Right, But at this stage they say that still the universe was transparent because like a light could still move around almost unimpeded, right, Like nothing really absorbed light. That's why they say it was transparent.
Yeah.
Well, there's this threshold here about three hundred and eighty thousand years after the Big Bang, when the universe becomes transparent. And so before that, it was like a big, hot, glowing mess, and photons were being created, but they were also being absorbed because any particle that's making photons can also absorb those photons, so the photons can always go very far.
Oh I see.
But there's this moment when the universe cooled sort of the crystallized literally around three hundred and eighty thousand years after the Big Bang. That's the moment when things became neutral. And so now the photons that had been created at that moment, there was no longer anything around that could absorb them as well, so those started just flying through the universe.
Because neutral atoms don't absorb light.
They do absorb light, but not at the same wavelengths. Right, Free electrons and free protons can absorb stuff at lots of different wavelengths, but neutral atoms they're much more constrained into what wavelengths of light they can create and they can absorb because of the quantization effects. Like electrons have layers of energies that they can be in, they can't just be at any energy. That's different. For a free electron that's just wandering around the universe, it can emit a huge spectrum of light and it can absorb a huge spectrum.
All right, So then the universe went from transparent to non transparent, and that's ironically sort of like when things went dark.
Yeah, Actually the universe went from opaque to transparent, and that light emitted at that moment was sort of the last light emitted before the universe went dark. Right. It was hot and glowing but opaque, and then it's switched to being transparent but not really creating any more.
Light like any light that was there, it just flew away.
Yes, And that light, of course is famously still flying around the cosmic microwave background like those created at that moment is the stuff we see in the sky. You know, people write it in and they ask questions like, how come we can still see the cosmic microwave background radiation? It was just created at one moment, right, hasn't it washed over us already? Why can we still see it in the sky, Which is a cool question, And the answer is because remember that has sort of happened everywhere, Like the universe was a big, hot, glowing plasma. It was emitting this cosmic microwave background radiation everywhere at the same moment, and so we're still seeing it because it's coming to us from different parts of the universe, from further and further away, all.
Right, And so that's when the Dark Ages of the universe started. And so let's get into what actually happened during those dark ages and how we know about what happened then. But first let's take a quick break.
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All right, we're talking about the dark ages of the universe, so that there was a point in the universe's childhood teenage years. Yeah, exactly when you couldn't see anything. I mean, it was really bright the universe. It was dance and bright, and then suddenly it became transparent and not bright. And that's kind of when things went dark.
Yeah, because two things happen at once, Right, The universe goes from being opaque to being transparent, and everything that was creating light sort of switched off. The ionized particles are no longer glowing because they became mostly neutral hydrogen. So now you are the universe is just filled with neutral hydrogen but not creating any light, and so light can pass through that universe, but there's not anything really glowing. The only thing that's left is the light from the cosmic markerwave background radiation, which is gradually getting redder and redder as the universe expands.
It's kind of like the party ended, or you know, like the club suddenly turn off the music and so everyone's like, oh, all right, I'll conserve my energy, I'll stop dancing.
Yeah exactly. And so the stuff is still there, right, the stuff that made the hot plasma of the CMB is still around. It's just a little cooler, which is why I sort of fell into these neutral atoms. And it's not glowing as much anymore. It's a little bit of glow because neutral hydrogen, which is still pretty hot, can glow at one wavelength, right, twenty one centimeter wavelength and give this broad spectrum of light that you get from the hot plasma. So the only light you have in the universe at this point is this gentle cosmic microwave background radiation left over from the hot plasma that was there, and then the very very light glow of neutral hydrogen. So it's basically just all black in the universe.
Interesting, So I guess the universe is just full of hot hydrogen and that glows a little bit, but not like a regular light.
Yeah. And also it glows at a certain frequency, and it also absorbs at that frequency, so that light doesn't really go very far. So if you're in the universe. At that point, you basically really don't see anything except for the CMB if you can detect it. And so, you know, if you're transported in your time machine back to the dark age of the universe and you unroll the window or whatever, you look out, it's just black. There are no stars, there's no galaxies, there's no nebula. There's really nothing to see in that view.
And also you get a lot of hot hydrogen hitting you in the face if you roll down the window.
Yeah, exactly, make sure to put your space suit on before your roll down the window.
Just crack it open a little bit first, just to check. Because the universe was pretty hot. I mean it's not it's not like warm hydrogen. It's like four thousand degrees hydrogen.
Yeah, exactly. It's cool relative to the early universe, but it's still pretty hot relative to where we are today. And so the early universe is like four thousand degrees and then it gradually cools down to you know, like sixty degrees.
Calvin, and it's cooling just because the universe is expanding or you know, things are bumping into each other. Where is that all that energy going?
It's just cooling because the universe is expanding. As you expand the volume of a gas, its temperature goes down, right, And so here we're expanding space. Space is getting bigger and bigger, but we're not creating any more matter, and so it's getting more dilute, and so the temperature is just dropping. And you know that's still happening today.
M I guess this is a little technical, but I thought temperature was related to like the kinetic energy. Not really. The density.
Temperature is a really tricky quantity, as we've dug into on the podcast before. But you know, it's connected not just to the energy of the particles, but it's a statistical quantity that you can only really talk about for a large number of particles. And so the temperature of a gas, for example, depends also on the pressure. You know, there's the ideal gas formula that tells you that as you lower the pressure, the temperature will drop.
All right, So the gas got more diluted, so that cooled it down, and that's pretty much the dark ages of the universe, right. It's all you know, no light out there when you look out, it's just pitch black and it lasts for hundreds of millions of years, right, Like, it wasn't just a short period, Like there were hundreds of millions of years where there was nothing going on. You couldn't see anything.
Yeah, and if you'd been around in the universe at this point, you might think, well, I guess this is it. You know, we had a moment of creation. Things were hot and dense for a while and exciting and glowy, and I guess we're just going to sort of settle in comfortably to this boring, dark universe. And yeah, it lasted for a long long time. But you know, things eventually happen, and there's this transition between when the really powerful forces are in charge, you know, like electromagnetism, which is what gives you the neutralization of the hydrogenera, pulls those protons and those electrons together, and it's happy. Now. It's like, all right, I've done my job. I've made a bunch of neutral stuff. And then finally the weakest force in the universe, gravity, it wakes up and it's time for gravity to be in charge.
Right. But it's not like it just suddenly wakes up and turns on. It's just said, as things cool down, gravity sort of becomes more significant, right, Like it's always been there, it's always been acting. But you know, the party was too crazy at the beginning for it to really be able to control anything.
Yeah, exactly, it was basically irrelevant. I mean the very early universe. Gravity played a little bit of a role in how these things come together and the over densities in the very very early universe. But then it's electricity and magnetism and the strong force that really dominate the formation of these particles and then their neutralization into hydrogen gas and helium gas. And you're right, gravity was around. It was doing its thing. It was tugging on stuff. But remember that gravity is like ten to the forty times weaker than the other forces, and so until the other forces get neutralized, gravity really can't do its thing.
Right, And so then that's what it was doing. During all those hundreds of millions of years of the dark Ages, gravity was getting to work making stuff.
Yeah, and so you have these huge clouds of hydrogen, and just like we still have happening in our universe, something can sde them, like a small spot of over density where dark matter has clumped stuff together, or for some random quantum fluctuation. In the early universe, you have more stuff there than you know, one meter over, and that can see sort of a gravitational runaway effect where it has more stuff to it, so it has more gravity, so it pulls other stuff nearby, which then gives it more mass, which means it has more gravity. So gravity pulls stuff together, and then eventually it can do things like make a star.
Right, And a lot of it had to do with dark matter, right, Like I guess dark matter was important in the dark ages.
Yeah, the reason this happened at the speed that it did was because of dark matter. Remember that most of the matter in the universe is dark matter, eighty five percent of the matter, right. All the stuff that's out there that has gravity is dark matter, and so it dominates this early universe. It dominates the structure, like where are you're going to get a star. You're going to get a star in a little gravity well determined by the dark matter. So it doesn't really matter in the early universe how the hydrogen is distributed. It's much more important how the dark matter is distributed. And that's kind of cool because it means that the normal matter which turned into stars and galaxies. It's sort of like a tracer for the dark matter. It tells you where the dark matter was because this sort of follows it because it has to because it's gravity pulls it in.
It's not a pioneer in making stuff. It was just following what dark matter was doing, which was clumped for some reason in the early universe.
Yeah, quantum fluctuations in dark matter led to small amounts of clumping and dark matter and gravity did his job, and then the normal matter sort of follows along in that process. But you know, it doesn't dictate what happens because it's only a small bit of it. And you would still get even without dark matter. You would still get formation of structure and stars and stuff even if you just had normal matter, but it would take a lot longer. Like the dark ages were only as short as they were a brief few hundred million years because of dark matter. Without dark matter, they could have lasted billions of years, right.
And so then that's how the first stars were born. And these were huge, right, These weren't like the stars we know today, Like the first stars were much bigger than the ones we have, for example in our Solar system.
Yeah, Weirdly, these are called population three stars, even though they're the first population of stars.
Why would you name something confusing.
Because they're not as smart as particle physicists astronomers. They have no idea what they're doing when it comes.
To me, we just lost a couple of astronomy listeners there.
Obviously I'm making fun of particle physics there, but I think they count backwards. The stars we have the most recently created called population one, and the stars in the previous generation are called population two, and then the previous generation, which happens to be the first one ever made, are called population three stars.
That is kind of smart, actually, because you don't know, maybe there are more populations than the initially thought, so it makes sense to go, you know, in the negative direction.
Yeah, maybe they should have called the population minus three or something. Anyway, we don't actually know about population three stars. They're still theoretical. We've never observed one on its own because they existed for such a brief period in the very early universe. They were brief because they were so big. Remember that a star burns faster and hotter if it's much bigger, And you're right, these stars were much bigger than the stars we have in our universe. They're like thirty to three hundred times the mass of our sun and they're just hydrogen and they burned really quickly after a few million years and spewed out their light.
And so these are starting to form in the Dark Ages. So that is this kind of when the Dark Ages end when you first have these stars, Like, how long did it take for them to start forming?
Well, it didn't take that long for them to start forming, but the Dark Ages didn't end as soon as you got stars because these stars were burning, but they were still surrounded by these shrouds of hydrogen. Like you didn't get all the hydrogen clumped together into stars. You got these like little pockets that collapsed into a star, But then they're still surrounded by huge cloud of hydrogen gas. And the light that's created by these stars is mostly the light that hydrogen makes when it glows, and that light is also absorbed by hydrogen. So you have this universe filled with hydrogen clouds and then pinpricks of it start to glow, but that light can't really penetrate the hydrogen cloud.
Oh, I see there is light. Light is being created in these Dark Ages. But it's also really foggy. So this is more like the foggy Ages. I mean, you couldn't really call it the dark Ages. It's more like the dark Ages became the foggy Ages.
Yeah, but if you were anywhere far away from any of these stars, you couldn't see any of them. It wouldn't look any different to you. You couldn't tell that these stars had started to burn. It's like it's nighttime and you're in deep, deep fog, and yet somebody turns on a light a mile away, but the light is totally absorbed by the fog, so you can't see it.
But wouldn't there be likely somebody turning on light near you? Because you know the stars are forming everywhere.
Yeah, well, in a random spot in the universe, you're probably not that close to a star. Remember, space is much much bigger than we can even possibly grasp in our minds, even in our current space. Like, if you picked a random cubic meter of space, you would be far away from any supercluster, not to mention any galaxy, you not to mention any star. Space is really vast, and these stars are few and far between in comparison.
I see, so things were that foggy, like, I guess we're thinks as separate as they are now. Like, were there big patches of empty universe like there are now or was it pretty, you know, foggy throughout.
Oh that's a great question. Well, we think structure form sort of bottom up. So what happens first is that these stars form, and then later they gather together into galaxies. So things are more spread out in the early universe than they are today. Like today we have these dense clusters of stars that we call galaxies and superclusters and stuff, and then these huge voids where there's basically nothing. Back in the early universe, things were more evenly spread out, sort of sprinkled through the universe because the stars hadn't pulled together to form galaxies.
All right, Well, let's get into what else happens in these foggy dark ages, and let's talk about how we know any of this because it happened so long ago and it was dark, so how do we know anything about it? But first, let's take another quick break.
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All right, Daniel, I have my folk lights on now. As we're in the foggy part of the Dark Ages. Everything's a giant cloud of hydrogen. There are stars they're burning bride, but yeah, everything's so foggy you can't really see anything, and so that is part of the Dark Ages. There is light, but it's foggy.
There is light, but it's foggy. And what happens next is that that fog clears. Now, remember what happened to make the universe go dark was that we went from ions nuclei that didn't have electrons around them, to neutral atoms like hydrogen mostly and then a little bit of helium. So what happens next is called reionization, is when we break that neutral hydrogen back up into the proton and the electron so that it's transparent to light. So the next thing that happens is that these stars or maybe black holes or maybe we don't know what broke up this fog.
Yeah, it broke apart all of those hydrogen atoms and that made it transparent.
Again eventually, So you have this picture of, like, you know, a foggy universe with these little dots of light in it. And then we don't exactly understand how this happened. One theory is that the light from these stars eventually started to ionize that hydrogen because the stars emit light that's absorbed by that hydrogen, but they also emit higher energy light, these ultra violet waves that the hydrogen can't absorb. Instead, it breaks up those nuclei, It knocks off those electrons sometimes, and so you break them up and you reionize, and then you've broken that up, it's become transparent and so eventually it sort of pushes through that cloud the way it sort of like the sun can burn the fog off on a really sunny day.
Mmmm.
So you get to these kind of like bubbles of visibility forming in a giant, foggy universe.
Yeah, it's sort of like the universe is a huge Swiss cheese with these bubbles in it, and the bubbles are growing and growing and growing, and eventually they meet and then the universe essentially is more clear than it is foggy.
Mm.
That is a pretty good analogy. A little teesy, but pretty clear.
Yeah, And it's sort of incredible to imagine, like what it could have been light to be alive. Then, you know, imagine that you are around one of these stars and you're living there and you see this fog sort of like blocking your view of the universe, and then one day it's just sort of like it breaks and you can see another star or two other stars, or you know, sometimes when the fog lifts, you can see like enormous views and you can see lots and lots of other stars, and then you finally understand the context you're living in. What an exciting moment that must have been.
Yeah, but was it a moment? It probably took you know again, millions of years, didn't it.
Yeah?
Absolutely, But you know, from the cosmic time scales, it's basically a moment. And of course there was nobody around then. There were no galaxies and that probably weren't even really planets, maybe not even life and any of these early objects. And so it's just sort of like a mental exercise to imagine what that might have looked like if you had been around, or if we could send a time machine back in time to visualize it. To me, that's pretty cool to think about.
It and press the fast forward one because you don't want to wait around a few hundred million years.
It's like that video on YouTube of watching paint dry, like ten million views. People do like watching stuff happen gradually, all.
Right, And so is that the end of the dark ages when now you have the fog kind of burning.
Away, Yeah, that's it. And we have this one theory that maybe it was starlight, that the ultraviolet light from these stars eventually burned these holes in the fog and cleared things up, but we're not one hundred percent sure because population three stars are still sort of theoretical. We don't really understand it. Another idea is that you get super massive black holes created early on, maybe from primordial black holes from the Big Bang, that then grow as they eat a lot of gas and they can emit a lot of radiation which might have helped clear this fog. And so it's not something we totally understand. It's like a few ideas for how the fog lifted, but again not something we totally understand because it's very difficult to study, right.
All right, So then we get the universe as we know it. Then you get galaxies and galaxies, clusters and superstructures, and everything's clear the way it is now.
Yeah, And it's about after like a billion years that the universe starts to look familiar things that you would recognize, as you say, stars and galaxies and structures of galaxies and black holes at the center of those galaxies and all that familiar stuff. But it took about a billion years, you know, between three hundred and eighty thousand years after the Big Bang, when the universe went transparent, to a billion years later when structure formed and the stars were created and the fog lifted. So that's a long period between the Big Bang and when the universe started to look familiar.
It's kind of like the adolescence of the universe. You know, you're in a bad mood, you're feeding dark, you can't feel foggy the whole time. But then suddenly, yeah, things clear up and you sort of come into your own.
Maybe you're not happy with your complexion, so you prefer to spend some time in the dark rather than go out into the sunlight. So yeah, exactly the awkward teenage moments of the universe, and then finally it grows up into the beautiful, gorgeous views that we know and love today.
Yeah. All right, Well, maybe a big question that a lot of people might have is how do we know any of the information about the Dark Ages or that even that there was a dark age in the universe. I mean, it happened so long ago, fourteen billion years ago. How can we look back and know with so much detail what happened.
Well, a lot of this is speculation because we don't have data about this stuff. You know, we can see the consic microwave background radiation. That's the last light created before the universe became transparent and neutral, and we can still see that, and then we can see things start to form later, you know, hundreds of millions of years or billions of years later, and we see this gap, right, we know when the knstic microwave background radiation happened. We can look back further and further in time and try to see these early galaxies and these early stars, but we just sort of don't see anything further. There's just nothing there to.
See I see. So you're saying you're just guessing. Well, also you're saying there's a gap in what we can see, like there's a missing spot in the our picture of the universe.
Yeah, but we don't see stars and galaxies from before that time because we think that there weren't there. And so it's sort of like, how do you see the dark ages? You're seeing the lack of something, right, The dark ages are the lack of stars and light and all sorts of fancy emissions that we could study, and so we don't see them because we don't think that information was being created there because there weren't stars and galaxies and stuff to create pictures for us to see.
But I guess you're not just guessing. I mean you're piecing together what makes sense from what we know now, Like if you run a simulation of the universe backwards, this is kind of what makes sense for things to be the way they are now exactly.
We're trying to put together a holistic, coherent explanation for how the universe came to be, and it makes sense for it to have a dark age, like the physics suggests that it should. You shouldn't get stars immediately after the universe gets filled with nutril hydrogen. Should take a while for gravity to pull it together, and our simulations, which now include dark matter, explained pretty well how long that should happen and what it should look like, even the nature of the structure. You know, if you didn't have dark matter, or if dark matter had a different temperature even or a different distribution, you would get a whole different shape of the universe. We talked about that on a podcast once, about the temperature of dark matter and how the speed of those dark matter particles changes how things clump together. So we actually have a really detailed picture of that period. Well, we're lacking a sort of direct evidence, but we can do something pretty cool, which is we make this whole coherent view of how the universe should have worked the history of the universe, and then we try to identify things we can do to test that. We're like, well, if this picture is true, what could we see And there's a few opportunities there to maybe get some hints about what was going on in those dark ages, right, And.
I guess if we're looking out into the universe and we're looking backwards in time, you can maybe literally see this dark age, right, you could see the fog almost or at least the first few stars that form the brook through the fog, right, because I mean at some point and when you look out space you would see those, right, yeah, exactly, the ones that were happening really far away.
Yeah. And so those are the two primary areas of investigation where it's like, let's see the oldest things we can and see when they formed and what was going on. And you know, the oldest things we see are like three hundred seventy to four hundred million years after the Big Bang, and we see, for example, clumps of stars that were all created at the same time we think, we don't really understand why. And you know, we can't study these stars individually. These things are so far away that they're just like blobs of many, many, many stars that we can study all together. We don't have the resolving power to identify one individual population three star. But people are looking for that. And then the second area of investigation is, as you say, to look for that fog like we should be able to see it. It did emit some light. It was neutral hydrogen, and neutral hydrogen when it's hot does emit light at one particular wavelength, this twenty one centimeter wavelength, and so we can look for that. But that's a radio signal, which means it's really hard to listen to because frankly, our society makes a lot of radio noise, and so it's very difficult to listen for this very faint signal of the early universe hydrogen.
Well, maybe in the future will be making less freea waste, right, I mean, nobody watches broadcast TV now it's all Netflix.
Yeah, that's true. We still use a lot of wireless communication, however, which makes a lot of noise. All of your Wi Fi out there and your cell phone signals and all that contributes to noise roughly in this spectrum. But we do have some fun ideas for how to find quiet spots that we can use to listen for this radio signal from the early universe, and one of them involves building something on the far side of the moon.
Hmmm, cool because it's quiet there.
Yeah, because it's quiet there. It's like the quietest spot in the Solar system if you don't want to listen to all of humanity's noise. And so the idea is to build something which actually orbits the Moon and it goes around the Moon. It's called the Dark Ages Radio Explore Dare, and it goes around the Moon and when it's on the quiet side, the far side, it listens for this hydrogen signal, and then when it's on the fore side, the side that we can see, it sends back us information. And so that's a pretty cool idea.
I like that it goes to the dark side of the Moon to study the dark ages that had dark matter in.
Them exactly, and hopefully it will brighten our day with some illuminations about the nature of the universe.
There you go lift the fog in our understanding of the universe. All right, Well that's the dark ages of the universe. It sort of makes you think, what a roller coaster, right, this whole universe is. You know, first it was really bright and explosive, and then it was dark and quiet and foggy, and now it's pretty bright and pretty. But maybe someday it will go back to being dark and quiet again, right.
Yeah, I think that's the lesson. You know that one period of the universe can seem sort of final, like it's sort of settled into its final form, and it can last for hundreds of millions of years, and then it can change to something totally different. Right, And so even though the universe is now fourteen billion years old and it seems like to have mostly settled into this whole structure of stars and galaxies and whatever, who knows, in another one hundred billion years, if something else will happen, if we could be in a totally new form, and people will look back at this as like the bright period of the universe, or the light ages.
Of the universe, like the prime of the universe, the middle age of the universe, that's right, or going into the not so active part of the universe.
Yeah, or maybe the universe will continue like this forever, or you know, it's one possibility is that things will keep getting pulled apart and the universe will get dark, not because things will turn off, but because things will just be so distant that we can't see each other, that all the other galaxies will get yanked away from us due to dark energy, and so the night sky will get darker and darker again, not because stuff is disappearing, but because it becomes invisible. It goes beyond our event horizon, because it's just so far away.
Yeah, so guess people should go out there at night and hopefully somewhere where you can see stars and appreciate the view because it's not gonna last forever.
You got a few billion years, but still make some plans.
I guess appreciate it on a cosmic skit All right, Well, we hope you enjoyed that little trip down memory lane for the universe and enjoyed spending some time in the dark and quiet period of the universe awkward teenage years, but also nice and quiet. Thanks for joining us, See you next time.
Thanks for listening, and remember that Daniel and Jorge explain the universe is a production of iHeart Radio. 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 digestors 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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This is Malcolm Gladwell from Revisionist History.
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