Daniel and Jorge Explain the UniverseDaniel and Jorge answer listener questions about the solar system and the early Universe.
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Hey Daniel, I have a deep philosophical question for you.
Ooh awesome, let me just get some banana peels ready over here?
Hey, it is a slippery question, so watch out all right, So which came first? Physics or math?
Ooh, tough one. I'm inclined to say math because people have been doing that since there was like money. I think there are cuneiform tablets they have found with receipts for like cows that somebody bought in two thousand BC.
So economics came first.
Well, you know, economics is doing math to describe the physical world like cows. So in a way they're secretly physicists, aren't they.
I see you're just trying to point it all back to physics. So even if I buy a hamburger, I'm being a physicist.
Well, you know, if you spend money doing it, then I guess you're like a mathetarian.
Wait, are you saying that I eat math or I eat mathematicians?
That depends on your ethical framework. Man, what came first or physics?
Maybe philosophy came first? Would you get a dog crit in those?
I think podcasts definitely didn't come first.
Hi am Jorge May, cartoonist and the creator of PhD Comics.
Hi.
I'm Daniel. I'm a particle physicist and a professor at U c Irvine, and I definitely liked math before I liked physics.
Really, math is your first love or just your first experience with the academics.
Well, you know, you learn math in elementary school, but they don't really teach you a lot of physics in elementary school. I mean, maybe you do a little bit of like this is what it's inside a rock, but you definitely don't talk a lot about astrophysics in elementary school.
I see, so Daniel Whitson was a mathematician before he was a physicist.
Yeah, my dad was really into math, and so I'd learned a lot of math at home, and I enjoyed math in elementary school. I was definitely a math nerd before I was a physics nerd.
WHOA. That kind of makes me a little sad. I feel like that's like learning that Michael Jordan really wanted to be a baseball player and not a basketball player.
I think that's true, actually, isn't it.
It is true? Yeah, his first love was baseball.
But I'm pleased with any analogy that puts me in the same phrase as Michael Jordan. I'd like to be the Michael Jordan of anything.
You are full of air, hot air sometimes, but you know, don't they say that all babies are kind of physicists when they're born. You know, they're trying to explore the physical world around them, and they're trying to, you know, learn the loss of physics in a way.
Yeah, it sounds to me like you're saying everybody who's curious about the world is a physicist.
No, just curious about the physics of the world, you know, like how do I stand up? Or what happens if I dropped this ball?
Or how do I get more food?
Although babies come from biology, so made biology came first? Now I'm confused.
It's all philosophy in the end.
But anyways, welcome to our podcast Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which the entire universe as one grand physics question. We ask, how does it work? Why does it work this way and not some other way? And how will it work in the future? And most of all, we ask is it possible for our tiny little mathematical, biology, economics, philosophy loving brains to understand it?
Yeah? It is an amazing universe and it makes you wonder if we are still just kind of babies in it trying to figure out the basics of how it works, or are we PhD holders who pretty much are going to understand everything there is to know about the universe right now.
It is fun to look back at that sort of history of physics and how it developed, people stumbling forward, having silly ideas, having to backtrack, having new ideas, and then bursts of progress. It really is similar to the way kids develop.
I mean, physics are just like banging blocks together in a way. That's kind of what you're doing, just banging particles together seeing what happens.
Yeah, well, there definitely are false leads and stumbling blocks, you know. I was reading some history of physics yesterday, and even after like the Michaelson Morley experiment that light travels at the same speed no matter who measures it, most physicists still believed in the ether for years and years afterwards. It takes physics a long time sometimes to change direction and figure out a new course, the same way it takes kids time to break old habits.
Yeah, tell me about it. We tried telling a kid what to do, or try to instill the habit of cleaning up the room.
Impossible, impossible, And so I hope that we are still babies when it comes to the physics of the universe, because that suggests we're going to grow up into some new, deeper understanding of the way the cosmos works. That in our future are some revelations.
Yeah, we're going to get PhDs in PhDs or something metaphd.
But there is still plenty to understand about the universe and all the mysteries of the cosmos, how it works, how things swirl around each other, how things form, how they burn, how they die, generate questions, not just in the minds of academic physicists, but in children and in everybody out there.
Yeah, maybe in a way before math or before physics or biology or philosophy came just asking questions, Like that's kind of how everything starts by a human asking a question about how something works.
Yeah, proto humans asking questions like how fast do I have to throw my spear to get that mammoth?
Yeah, that sounds like more of an engineering problem, Daniel. We're all proto engineers, is that what you're saying? Before asking questions, we're engineers.
We ask questions and the answers lead to engineering problems, Like all right, I need a spear, this lon somebody build me one.
Yeah, Well, regardless of who came first, what's important is that we ask questions. That seems to be a very common human trait that everyone does it, no matter how old you are or where you come from, because we all look at the universe and we wonder like, what's going on, how does it all fit together? And what's going to happen next?
And if you're listening to this podcast, probably you're the kind of person who desperately wants to know the answer to these questions. Feels like there is a truth out there about how the universe works and how began and what its future holds, and we want to know it because we believe that if we apply our minds, we can understand the universe.
Yeah, it's not just physicists asking these questions. It's people like you asking these questions, and sometimes listeners like you send their questions to us.
And we invite you to send your questions as well. If there's something about the universe you don't understand, or you'd like to hear us talk about and make silly jokes about, please write to us to questions at Danielandjorge dot com Yeah.
Daniel answers every physics questions he gets, even if they are crazy out there, right.
That's right, And not just physics questions. I answer every message I get from our listener.
Even funding requests. He takes the funding request. I guess you can always answer no.
I'd always answer no. Sometimes people write in with life advice questions like I'm forty years old and I'm a computer programmer, but I always wanted to be a physicist, and is there a way for me to get there?
Mmmm? Cool? Life advice, that's right. Career advice from a physicist.
Life advice from somebody who doesn't really know how the real world works.
Yeah. So sometimes we get these questions and sometimes are so interesting Daniel puts them up to answer on the podcast live in front of us studio audience.
Who's the studio audience exactly by the laugh track, Now.
It's a studio in my head. We have a live audience in my head.
In front of a studio audience of nobody. Sometimes I get a question that I think will be fun to talk about, or I suspect other people will want to hear the answer to, and so then we get audio from that listener, so we can talk about it here on the podcast.
Yeah, So to the other program, we'll be tackling listener questions Number twenty six. That's the twenty six episode in which we answer questions from listeners.
That's right. And last time we did this, Orge, you had so much fun, you said we should do this more often, and so here we are again, just a couple weeks later, doing it more often.
Oh man, I didn't I had that kind of infl wents in the universe. Should I wish for more things? Oh? Man, Daniel, I wish I had a bazillion dollars.
You can submit a request to the Daniel Science Foundation, but they usually say no.
Do they ever say yes? What's your track record? Zero percent?
We responded to all requests one hundred percent.
I see you have one hundred percent response rate, zero percent affirmative response.
We have issued one hundred percent of our Foundation of Bank account.
Have issued one hundred percent. Knows in your operation.
That's right.
But anyways, were so we're answering questions from listeners today, and we have some awesome questions here today, some from kids about the solar system and the planets in the sun and the moons around us, and also some interesting questions about asteroids that may or may not kill us, and also about matter and energy at the big Dang, we're going all the way back to the beginning.
That's right. We want to understand everything about the universe from the way it is today to the way it started.
Yeah. So we have awesome questions here, and the first few are from a couple of kids who listen to the podcast, and they have questions about kind of our immediate neighborhood. So the first one is from Kendall, who is seven years old. Hi, my name is Kendall. I'm seven years old. I would like to know why our stars so hot?
Or hey, you're a star, why are you so hot?
I don't know. You know, I work out, I eat well, I'm I'm a cartoonists. I think that adds to that air of attractiveness.
Yeah, so great, another piece of life advice from somebody who doesn't live a typical life.
That's right, So one who doesn't leave their house very much. But thank you Kendall for sending in this question. That's awesome that you're curious about the sun, about stars, about what's out there in space.
That's amazing, And it's a great question because it sounds like a simple question on the surface but actually gets into a lot of really interesting physics. And it's not that simple a question to answer.
Whoa see, Kendall, you just dumped a footy seven year old physicist. So Kendall's question is why are stars so hot? I guess stars are pret hot, right, They're not cold.
Stars are pretty hot. The reason we can see them is because they're so hot. Remember, everything in the universe glows, and the frequency at which it glows depends on its temperature. So the sun is hot enough to glow in the visible spectrum, which is pretty cool or pretty hot.
Well, it's interesting because I guess you know, maybe people your age and mind associated light and something bright is something being hot, right, because light bulbs are hot. You don't want to touch a light bulb from when we came from, but nowadays, you know, with LED lights you can have like cool lights, right, you can have a cold light bulb.
Yeah, because the light generated by an LED is not like black body radiation the way light from like a tungsten filament is. It comes from a quantum mechanical process, which is pretty super cool. But one of the interesting things about stars is that they are hot, but in order for them to even get formed, they have to actually start out very very cold. So they have a really interesting sort of thermal history.
To them, right, right, because I guess all stars there in space in the universe start off as cold clouds of gas, right, That's how they all start. Like, the gas isn't hot, it's like a it's just floating out there in space, and space is really cold, so really it comes from cold gas.
It comes from cold gas. And if you have a big cloud of gas, if it starts out too hot, it can't form stars. Because remember stars are formed by gravity pulling together all these little bits of stuff. But gravity is super duper weak. So for gravity to succeed pulling together a big cloud of gas, it can't be too hot. If it's too hot, it'll just ignore the gravity. So a cloud has to cool down enough for gravity to be able to take over and compress it. And so if a cloud is more than like ten or twenty degrees kelvin, it just can't form stars.
So a star starts off as cold gas and then gravity makes it all sort of clump together into one kind of smaller ball of super hot.
Gas exactly, and it's that gravitational pressure that provides the heat. A lot of people think that stars are hot because they have fusion going on, because they are burning, but it's the other way around. Stars get hot from gravity and that temperature allows fusion to happen, and then the fusion sustains them. But the reason that they're hot is that gravity takes the gas and squeezes it into a smaller space and that heats up the gas.
Hmm.
Maybe step us through a little bit on because that's kind of a tricky step. Like when you start off with a big cold cloud of gas, well, why does crunching it together make it hotter?
Yeah, it's an interesting bit of chemistry, right, If you compress something, you make it hotter. And that feels weird because you're like, hold on a second, it's the same amount of stuff. I'm not doing anything. I'm just squeezing it down.
You're just like storing it closer together.
Yeah, it feels counterintuitive to think about it getting hotter, and it's helpful to think about the temperature of that gas as like the speed of the molecules of gas flying around in it. Temperatures are really complicated topping. We have a whole podcast about just that. But a simple way to think about it is that temperature is like a speedometer of the particles in the gas. So a hotter gas means particles moving faster, and a colder gas means particles moving more slowly.
So when when you take a big cloud of gas and you squeeze it together, somehow that makes the molecules, the little gas particles inside in the cloud move faster.
Exactly because what you're doing when you squeeze it is that you're pushing in on it. You're providing energy. You're actually putting energy into that gas by squeezing it down. Think about, for example, throwing a tennis ball against the wall. It comes back at the same speed as you threw it. Cool, But what if you throw a tennis ball against the front of a train, Then when it comes back it would be going faster. So if you're a tennis ball inside a box and that box is shrinking, then every time you hit the wall, you're going to bounce off with more energy, and so very gradually, as the box gets compressed, the balls start moving faster and faster and they have a higher temperature.
Hmm. Interesting. Now, just to be clear, Kendle seven year old should not be throwing balls in front of moving trains, right.
That's a parenting question. I'm not going to step in because I don't have realistic life advice.
That's right as your parents first, always for all things. But that's interesting, and that's an interesting analogy. Like if the walls are closing in on you, they're going to be imparting some energy on the walls, hitting the walls. But I guess in space there are no walls. It's just gravity moving things together. So where does that extra energy come from?
Right, Well, gravity is pulling stuff together, and the way it creates more pressure is that it's like pulling gas on the outside of you in. So the wall is like the next layer of gas, which is less and less pressure, but effectively it acts like a wall. So gravity is pulling everything in. It creates this gravitational well which makes it harder for the particles to leave. So each shell of gas is sort of compressing the next shell of gas.
Interesting, all right, So then you have a big cold cloud of gas that gets compressed, then that gets hot, and at some point it gets so hot it starts to explode in the middle.
Yeah, when it reaches like twelve million degrees calvin internally, it can start to fuse hydrogen into helium and that releases a bunch of energy, and that helps the start stay hot, and it actually also keeps a star from collapsing further. If you just let gravity do its thing, it would turn those particles into a black hole. But fusion pushes back, and then you get this balance between the energy released from fusion, the outward pressure and the inward pressure of gravity, and the star burns for a few million, billion or trillion years, depending on its size. I see.
So then I guess the answer to Kendall's question is that stars are hot because they can't have to be Otherwise you won't have a star, Like you can't have a cold star.
Right, You can't have a cold star unless you call it black dwarf, a star which is a remnant from a white dwarf that has cooled off. But yeah, you can't have a cold star. So I guess by definition, right, a star is something that is hot. But I think the most direct answer to his question is that gravity is what makes a star hot. To begin with, it ignites the star and then fusion keeps it hot.
Yeah, because I guess you know, once gravity crunches everything together, it'll stay hot even if there's no fusion, right.
True, But if there was no fusion, it would compress into a black hole, and then you get into questions of like what's the temperature of a black hole?
Subject of another podcast that's a whole rabbit hole. All right, Well, thank you Kendall. Hope that answered the question. And so we have another question from Meghan who's ten years old. Who is a question about the Moon.
How many names, Meghan, and I'm wondering why they are on the moon.
Yeah, why are there craters on the moon? Like if you look at the moon? Great question, Meghan. By the way, if you look at the moon, it's not like a perfect little sophia or perfect circle, it's not just all one color or one one mooth surfer that. It has a bunch of holes and pop marks in it. Right.
Yeah, there are a lot of craters on the Moon. By last count, there were thirty seven recognized.
Craters with names nine thousand. That's a lot. I have a friend who did her PhD in like moon craters.
Like she was in a moon crater when she did her PhD.
That sounds yeah, Suddenly she became a lot cooler. You're right.
Yeah, yeah, there are a lot of these craters, and it's fascinating because you look up at the Moon you're like, Wow, the Moon is filled with craters, but the Earth is not. And so that's an interesting question.
Mmmm.
Yeah. We don't have like giant holes here on Earth, at least not that are visible.
And it's not a question we actually knew the answer to. Until we went to the Moon. This was an open question about the source of these craters. Some people thought maybe there was like volcanic activity on the Moon and each crater was like a little mini volcano, and other people thought they were impact from rocks from space, and there were even crazier ideas. And until we went to the Moon and got samples and studied the age of the surface, we didn't know the answer to Megan's question.
Interesting, Yeah, they could have been like holes on a piece of cheese.
Was that your friend's thesis topic?
Yeah, on the lore of the Moon cheese hypothesis.
Well, now we know that the surface of the Moon is about as old as the surface of the Earth about four and a half billion years old. But the Moon, unlike the Earth, doesn't have an atmosphere, right, it doesn't have like a cloud of gas surrounding it. And so the short answer to Megan's question is that it's rocks from space. Space is filled with rocks that are constantly hitting everything in the Solar System, and if you have a shield, like the Earth does, then most of those don't hit the ground. But the Moon doesn't have a shield, and so it gets smacked by every rock that comes its way.
Yeah, it's kind of interesting to think like that happened or is happening all over the Solar System, right, Like there are planets who also don't have an atmosphere who are filled with craters too.
Yeah, Basically every surface on the Solar System will get impacted with craters, and so you need some kind of protection if you're going to live there, either an atmosphere or like a really strong umbrella.
All right, So, to answer Megan's question, the Moon has craters because it gets hit by a lot of rocks from space and it doesn't have a coating of air to kind of protect it.
Yeah, and some of these craters are like more than two billion years old. No wind or water on the Moon, so if you form a crater, it will last a very very long time. There's one crater on the Moon that might even be four billion years old, and scientists think that an asteroid more than one hundred and fifty miles across smashed into it about four million years ago, such a big explosion. It probably rained a debris down on the surface of the Earth.
Interesting also, I think another part of the answer is that there's no lava on the Moon, right like we have lava here on Earth, and that's kind of making the surface move a lot, which kind of gets rid of all of the craters that we used to have. But in the Moon there's no lava, so it does nothing ever.
Moves and the surface of the Moon really interestingly is covered in this like really fine grain soil. If you look at the astronaut's footsteps, for example, you notice that they were walking through like several centimeters of what looks like dust, and this lunar dust. It's basically the shattered surface. There's been so many impacts on the Moon that its surface is basically covered with shattered little pieces of rock.
I guess the question is like, are there still new craters being formed on the Moon, Like does the Solar System now have fewer asteroids flying around? Or are there still is the Moon still getting bombarded by meteors.
It's still getting bombarded. We actually all one happened in twenty thirteen, which was visible to the naked eye, a ninety pound meteoroid strike the surface at like ninety thousand kilometers per hour and left a new crater. So it's still happening.
Wow, But is it happening faster or at the same rate as before, or it has the Solar system sort of calmed down a little bit?
The Solar system definitely has calmed down. In the very early part of the history of the Solar System, that was the heavy bombardment period when the Solar System was a huge mess. Since then, things have calmed down and larger objects have pulled together to make fewer objects. Since you have fewer rocks out there than you used to.
I see, Yeah, we've made it past purity, right. The skin is not going to clear up a little bit more. All right, Well, thank you Kendall and Meghan for these awesome questions. We hope you keep asking questions, and so now let's get to our other questions about asteroids that might kill us here on Earth, and also about the nature of matter and energy. But first let's take a quick break.
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All right, we are answering questions from listeners, and we've just answered some awesome questions about the stars in the moon, and so now let's get into some cheerier topics like the possible extension of humankind.
Hi, Danian and Jorge, This is Sean calling from Ottawa, Ontario, Canada. We always hear about asteroids and comets hitting the air at thousands of kilometers per second and wiping out life as we know it.
But I was wondering, is.
It possible for a comet or an asteroid to come in and slowly hit the Earth where it won't kill us all? Maybe if we're both on the same trajectory and it can come in and just gently land somewhere on Earth and not destroy everything. Anyways, Thanks for the great podcast.
Bye all right. Awesome question, Thank you, Sean. It's an interesting question, yeah, because I guess when you think of asteroids hitting the Earth, you usually think of them as coming in fast and crashing on Earth. But he's asking, you know, could one somehow sort of like creep up on us and kind of sheet me onto our planet and gently you know, land in the middle of the ocean or something.
Yeah, it's very Canadian. He's looking for life, a friendly asteroid that just comes and sets down gently.
Yeah, maybe a land in Canada and apologize for causing a disturbance.
It is an awesome question. Why do we always think about asteroids as basically like bullets aimed at the Earth. Can't we think about them like moving in parallel to the Earth and very gently coming into the surface. It's a really cool question.
I guess it maybe seems unlikely that something would just come out of the blue and then just happen to like fly right next to us slowly.
And that's the answer. It is possible, but it's much less likely if you just picked like random trajectories for rocks in space that are going to come in contact with the Earth. It's just much easier for those rocks to be going the opposite direction of the Earth, or to be going opposite direction of the Earth. At least at some level. It's possible for a rock from the asteroid belt or the Kuiper Belt or even the Orc Cloud to end up in like the Earth's orbit, but it would take a very special circumstance.
You mean, like it is possible maybe for one of the asteroids around us to like suddenly kind of jump into our orbit.
It is possible. But everything right now in the system hasn't orbit. The reason it's still around is that it hasn't fallen into the Sun. It's in some orbit. So even to come into contact with the Earth would require it most likely to change its orbit, and a collision happens when the trajectory of one of those objects intersects with the Earth, right which is very unlikely to happen in parallel. In order for one of those things to like jump into the Earth's orbit, it would needs to change its trajectory, which means like hitting something else and bouncing off. So you need like two things to come into contact and change each other's orbit so that one of them happens to end up in Earth's orbit.
And kind of going at the same speed. But I guess couldn't it also happened that the Earth, you know, maybe passes by close enough to a cloud of asteroids that maybe like pulls one long with our gravity.
Yeah, that is possible. And in fact, there are some things out there that have been sort of like captured by the Earth. They haven't landed on the Earth, but they came close enough to the Earth that there sort of now in orbit around the Earth or sharing the Earth's orbit around the Sun. At least one of these things is called the space being because it traces out this weird path relative to the Earth. It's this five kilometer diameter rock.
Wait, there is a rock like that that has somehow fallen into our orbit and is kind of going along with us.
Yeah, officially, it's like a quasi satellite of the Earth. It's got a fancy name which I can't pronounce, and it has its own elliptical orbit around the Sun that's sort of in resonance with the Earth's, and so from our perspective, it has this like weird bean shaped orbit around the Earth. But effectively it's been captured and in a very similar orbit to the Earth. But of course it's not landing on our.
Surface, right, right, But it's interesting that it's possible, right, Like, what maybe can happen again and we could pick up another bean?
Well, this one, the closest it ever comes is like seven and a half million miles from the surface of the Earth, which is like thirty times further than the Moon.
I see, I see. But maybe it eventually, could it somehow, you know, creep into the Earth, Like maybe not now, maybe, but maybe in a million years, could it somehow, you know, start creeping in and maybe go into orbit around the Earth at some point?
It certainly possible, right if it impacts something or something else comes along and tugs on it, it could change its orbit. And it is possible for something to get even closer to the Earth and eventually even come into the atmosphere and in theory, it could come in slowly, it could like gently approach the Earth's atmosphere.
Interesting, Well, you said it's not very likely because I guess we have most asteroids out there kind of catalog. So I imagine if any two sort of surprises is they're going to be coming in pretty fast. But maybe, just for fun, let's assume that sean scenario here comes through in which is like, make an asteroid appear right next to Earth. Would it kill us or would it just kind of gently bump us?
Yeah, I just want to make one more common and the likelihood of it. Another way to think about why it's unlikely is that these objects are moving typically faster than the Earth. You know, the Earth moves at like thirty kilometers per second around the Sun, and these asteroids move like forty to fifty or even faster. If there are commets from the outer Solar System. And if you think about like two velocity vectors, in order for the one of these to catch the Earth, they basically have to be perfectly aligned with the Earth, otherwise to impact they could have at any angle. So it's just unlikely for these things to be perfectly aligned with the Earth's direction. But you ask a great question, like, what would happen if this thing like gently came up to the Earth's atmosphere? Would that actually hurt us? And I like Sean's fantasy that this thing would like gently sink down to the surface of the Earth so we could like you know, touch it and build a monument to it or whatever. But actually I don't think that's likely either.
I guess maybe let's paint the picture a little bit better. So the Earth is moving through space, We're spinning, and somehow, like another and aster it kind of like shimmys up to us, going at the same speed, in the same direction, maybe in the same orbit, and then just little by little, just kind of bumps into the Earth. Is that possible.
It's possible for it to get close to the Earth and like join our orbit, but then it's going to be captured by the Earth and it's going to fall into the Earth's gravitational Well, remember the Earth itself has a lot of gravity. So if you just like dropped a big rock at zero velocity at the top of the atmosphere, what would happen, Well, the Earth would pull on it. By the time it reached the surface, it would have a lot of kinetic energy. You imagine what would happen if you drop like a penny from the top of the atmosphere. It would be going super duper fast by the time it hit the ground.
Oh, I see, you're seeing, Like, even if I park this asteroid close to us, just the Earth, gravity's going to pull it in and make it go faster towards us.
Yeah. The escape velocity of the Earth is like eleven kilometers per second, and so that means if you're going at like zero kilometers per second at the top of the atmosphere, then by the time you get to the bottom, you're going to be going in eleven kilometers per second. So it's a lot of kinetic energy, right.
But I guess maybe Sean's point was that, you know, even if it's going at eleven kilometers per second, that's still not as fast as most asteroids that hit Earth are going. And so maybe it would He's saying it it might survive the atmosphere, right, not get burned up by all the friction from the air, and maybe it will crash onto Earth.
Yeah, And I think that's likely that it would make it to the surface the Earth. You know, it wouldn't actually get to eleven kilometers per second by the time it hits the Earth because of the resistance from the air. It would heat up and parts of it would blow off, But probably it would survive, but it might make a crater when it lands because it would be going pretty fast. But even asteroids that do hit the Earth at high speed, some of them make it to the surface if they're big enough to survive the trip through the atmosphere.
Interesting, I guess maybe then the real answer to Seann's question of could an asteroid hits slowly without killing us, The answer is no, because an aster it can hit it slowly. I think any asterid that hits is going to be coming in pretty fast because the Earth's gravity pulls it in and it's going to pick up speed.
You might imagine another scenario where a rock comes near the Earth and has like negative velocity, like the Earth is catching up to it, but it's running away and the atmosphere gradually slows it down so it lands on Earth. But that's even more unlikely. The Earth would have to like sneak up on this rock.
Right, It's less likely, but much cooler to think about. So you're saying, there could be an asters flying through space sort of in our orbit, and so Earth sort of sneaks like we sneak up behind it, and we're in such a trajectory, and it's in such a trajectory that it really just kind of slowly touches us.
Is that what you're saying, Yeah, I think that's probably possible. I haven't run the simulation, but you'd have to have a lot of factors exactly aligned to make that work.
Like what's the slow as it could hit Earth? You know what I mean? Like would it still pick up eleven kilomers per second? Or is there a scenario in which it literally like just slowly kind of touches the Earth.
Well, there's some things you have to balance there, because in order for it to be going slower when it hits the Earth, you want to start with like negative velocity velocity away from the Earth at the top of the atmosphere. But then you know, how is it getting to the top of the atmosphere if it has velocity away from the Earth, So it can't be going too fast away from the Earth. The Earth has like sneak up behind it while it's moving fast away from the Earth. And then the atmosphere somehow slows it down and pulls it in a pretty tricky set of circumstances, but I bet it's technically possible. And you know, if the solar systems around for long enough, maybe it'll happen.
Right right, just got to the mask, right, Anything's possible with that. But are you envisioning that this could like literally just like touch down like a spaceship or would it crash land anyways, just because you know the sky is big and it's going to fall.
Well, the slower you wanted to hit the Earth's surface, the less likely this scenario is because the faster it have to be going away from us at the top of the atmosphere. I think technically it might be possible for it to like gradually sink into the Earth's atmosphere if it has enough initial velocity away from us, and the atmosphere just sort of like slurps it in gradually.
M interesting. That was pretty cool just to see a giant rock slowly land on Earth.
I don't expect that to happen. And after this, I'm gonna have to go write some code to simulate this to siege it would actually work. But that's my instinct.
All right, I'll stay tuned. Well that Daniel writes in a scientific paper about it, and when it comes out, well we'll let you know.
That's right, Sean will make you a co author.
Oh wow, nice. See what can happen when you write questions to us? You might become a physicist for real. All right, well, let's get into our last question about the nature of matter and energy at the Big Bang. But first, let's take another quick break.
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All right, we are answering listener questions and we've answered questions from kids about the sun and the moon and also a question about an asteroid slowly killing us slowly with its song? Is that with its a space song?
I guess it's telling our whole life with its trajectory.
I guess that's that's I know a philosophical question. If an asteroid is going to come and kills do you want it to be fast or do you do you want it to be slow? And do you want to see it coming?
M I definitely want to see it coming so we can potentially divert it so it doesn't come and kill us.
Well, what if, like you do see it coming, but there's nothing we can do about it?
We always have Bruce willis Man, did.
You see that latest movie with the Leonardo DiCaprio and the asteroid don't look up? Yeah?
Yeah I did. That was a lot of fun. I heard that he couldn't write the equations himself on the board, so they had to have a hand double doing the math close ups for those shots.
WHOA, that could have been you, Daniel.
Now I have a new life.
The real Leonardo DiCaprio's hand physics hand model.
It's like being a stuntman basically.
It's just that dangerous, right right, Yeah, you could get carpal tunnel from doing it.
Or I could become a movie star and then I could brag and say I do my own math.
Well let's see what happens first, It's.
More likely that a huge rock will slowly touch down in the atmosphere than that any of that happens.
Yeah, I guess if you become a movie star that that would be the end of the world. You go, is that what you're saying?
That's one of the signs of the apocalypse.
Right there? Frogs falling from the guy Daniel co starring in a movie with Leonardo DiCaprio.
Yeah, although Neil de grass Tyson has been in big movies, right, so it's possible there are physicists out there that have broken into Hollywood.
Oh man, it is the end of the world then. But anyways, we're answering listener questions and our last question of the day comes from Jills, who has a question about which came first in the universe.
Hello, Daniel and Jorge, how are you guys. My name is Chill, and I was curious about the following. I know that matter and energy are intimately connected, but I was wondering what came first, matter or energy. I would appreciate if you guys can address these in your podcast. Thanks a lot, Bye bye.
All right, awesome question. I feel like this is getting back to like elementary school philosophy, you know, like which came first, the chicken or the egg.
It's a deep question about the early history of the universe. I love this stuff.
Yeah, so Geo's kind of acknologies. First of all, that matter and energy are really closely related, and I always thought that matter is energy, right, isn't that what EMC squarre says? That they're the same.
Thing sort of, But it's not entirely symmetric. The way I would explain it is that mass is a form of energy. Right. The reason things have mass is because they have internal stored energy. So you can think about mass as like a form of energy, or you can think about mass as like a little dial that tells you how much stored energy is inside this thing. But you can turn mass into other kinds of energy, like velocity, or you can turn velocity into mass, and so you can think about mass it's like a form of energy. But energy is not a form of mass. So they're not entirely symmetric.
Oh I see, it's not really an equivalence equals EMPC square. It just says that mass is energy, but it doesn't say that energy is mass.
Yeah, equals mc squared tells you how much energy is stored in an object at rest with mass.
M I see, so I guess you're saying that matter is a subset of energy, and therefore therefore it can be first, can it.
Yeah, that's right. Matter is a kind of energy, so it can't really predate energy. You can't imagine a scenario where you have matter in the universe without energy because matter is a kind of energy.
It's like saying an egg is really a baby chicken, so therefore the chicken came first.
Not a biologist knocking to weigh in on that one. But it sounded good.
It sounded good, the mass found it right. We'll go with that.
I'll have to do a simulation later, but yeah, it sounded another paper.
Oh man, we are cracking out the assigns here.
So I think it's pretty clear that energy came first, because you can't have matter with energy. But it's interesting to think about sort of what forms of energy were created in the universe at what time? When did matter come about, When did we get radiation, what came first? How did that all happen? Because the history is quite complicated and really nuanced.
Oh interesting, because you're saying that you know in the Big Bang, maybe there was sort of an opportunity for matter to be more dominant.
Yeah, the way we think about it in the very early universe is that you have very high energy density. Right, the universe used to be much more dense, It used to be much more compact, it used to be higher temperature. So things were flying around, they were crazy, and there was such high energy that all the quantum fields were buzzing with so much energy that doesn't even really make sense to talk about particles in the way we think about it. There was a moment very early on in the universe when there's a lot of energy, but there weren't even really particles flying around in the universe. I had to like cool down a little bit before you can even start to talk about the quantum fields buzzing in the way that we think about it today as like these little discrete pockets of energy flying around the universe. It was just more like a huge ocean of energy.
Whoa like pure Like everything was just pure energy. I guess the question now I have is which came first, energy or quantum fields.
Yeah, that's a great question, and we don't know the answer. We have a description of the universe in terms of quantum fields. For certain energies, like for the energies that exist today in the universe, which are very very cold, we know that we can describe the universe in terms of quantum fields. And for higher energies like what happens inside the large Hadron Collider, and going back to the early moments of the universe, we can describe that in terms of quantum fields. Beyond that, we don't know, like we have quantum fields, and we suspect that those theories and the description of the universe in terms of quantum fields probably works at very very high temperatures very early on in the universe. But the truth is that we just don't know. One of the reasons we don't know is that we don't understand how gravity works in a quantum sense. So what you're really asking about is like, can you give a quantum field description of the universe when gravity was just as important as all these other forces? And we don't know because we don't have a theory of quantum gravity. So we're really pretty clueless about sort of a quantum picture of the universe when gravity was very important early on.
Well, interesting, I guess you're saying, you know that in the beginning of the universe, at the Big Bang, things were so crazy, so crunched together and so high energy density. Did we really don't know what was going on at that moment.
Yeah, in the same way that we don't know today what's going on inside a black hole for the same reasons, Like you send a particle inside a black hole, we think of it like a little wiggle in a quantum field. What happens when it goes inside a black hole? Well, now it's under very strong gravitational pressure. Is it still a quantum wiggle? Does it turned into something else, a new kind of matter? Are there gravitational quantum fields? We just don't know. In the same way we don't know what was the state of the universe when gravity was really strong and very important early on. So it might be that we can describe it in terms of wiggles and quantum fields. But it might be that we can. But we do have a pretty nice picture of what happens like after the universe drops in temperature to a point where it turns into particles, and we can then think about, like how much of the energy in the universe is in terms of these particles or in terms of the photon, so that go between them and that kind of stuff.
Oh, I see, but I guess before that it starts to cool off. Does it even make sense to talk about energy as we know it? Like inside of a black hole? Does it make sense to talk about energy or can you still, you know, define energy in such a scenario.
We can define energy, but you're right, we don't know if it's the most important quantity. Like people think about energy, it's fundamental to the universe and a really insightful way to think about the state of the universe. Or remember that we've discovered recently that energy is not even conserved in the universe. Right, It turns out it's something we can measure, and it seems to be conserved in most of our experiments. But we know that in an expanding space, if the universe is growing, if space itself is changing, then the amount of energy in the universe is also changing. So energy might not be the right way to think about the nature of the universe. We talked a few weeks ago about what happened in those first few moments of the universe, this inflation theory, and you know, we have some like pictures of what that means. Maybe there was this infloton field with these infloton particles which decayed into normal matter, So you can possibly think about it in terms of like weird new quantum fields. But we just don't know if any of those theories are at all accurate. They're just more like sketches of ideas that we're using to try to think about it in terms of stuff we already know, but there's no guarantee that the kinds of ideas we have are the right ideas.
Well. I feel like you're saying like we almost don't even know if math worked at the beginning of the universe, you know, like maybe one thus one was three back then, you know, because energy things were just popping out of nothingness.
There's definitely a very weird situation, and I'm pretty sure there's going to be mind blowing surprises when we figure out how that worked and how to even think about it and how to talk about it. And that's one reason why we do crazy collisions as super high energy, because we want to probe the most extreme situations to see when do our our theories break down? When do we need a new kind of structure you know, quantum field theories themselves are only a few decades old, and they came into play to explain collisions at high energy that we couldn't otherwise understand. And so maybe that at crazier high energies we need a whole new kind of idea about what's going on in the universe. Or maybe quantum fields will describe everything up to the Plank scale. We just don't know.
Yeah, I think that's how I would describe my childhood as well. It's a lot of weird things happen and I'm still trying to understand it.
Did you break mathematics?
I probably thought I could. Yeah, that broke a lot of things when I was a kid. But I think your main point, though, is that we maybe don't know what happened during the Big Bang or before the Big Bang, but right after the Big Bang we do have kind of a clear picture of how much of the universe was matter and how much of it was kind of like flying energy, which you call radiation.
Yeah, so some mysterious thing happens the universe exists, and then some other mysterious things what happens The universe inflates and expands and cools, down rapidly, and just after that we can start to talk more concretely about quantum fields. And in that situation when the universe is still very very hot, but we can talk about it in terms of quantum fields. It's a really interesting situation because every particle back then was massless. This is before the Higgs boson even came into play, and so every particle, the electron that w the Z, all these particles had zero mass.
Whoa, whoa, Yeah, that's wild. Yeah, at some point the universe had nothing had mass because the Higgs field hadn't come into being.
Yeah, none of these initial particles had mass. You could still have mass by combining particles into some like object, the same way like if you put a bunch of photons into a mirrored box, it actually gains mass because any stored energy turns into mass. But the particles themselves, none of them had mass in the very early universe until the Higgs boson sort of settled into this weird state that it's in today that gives them that mass.
So if if nothing had mass, that means nothing what nothing mattered kind of in a way, like you didn't have matter.
Particle physicists talk about the difference between matter and radiation, and it's sort of a fuzzy line because you know, when we talk about radiation chemically, we say like, oh, electrons are alpha particles, that's radiation, even though they have mass. So we have all sorts of totally inconsistent definitions of radiation. But in terms of like early universe physics, we divide things into matter and radiation. Things that are radiation are things that are traveling at light speed, and things that are matter are things that are traveling not at light speed. But in the very early universe everything was massless, so everything was moving at light speed, so it was just one hundred percent radiation. Oh.
Interesting, So we don't know which came first, matter or energy, but we know which game second. Yes, which is radiation, which is really energy?
Right, Yes, So in the first moments of the universe that we can really talk about, we have all these buzzing quantum fields with massless particles flying everywhere. The whole universe was radiation. Then the Higgs field broke that symmetry between electromagnetism and the made the W in the Z massive and also made a bunch of other particles massive, and then you have matter, and then the electron has mass, you know, the quarks have mass, and so that happened very early on in the universe. But still most of the energy in the universe was in terms of radiation otons and other massless particles.
Meaning like it was in particles, but it was it was in particles moving at the speed of light.
And so the first like fifty thousand years of the universe was a radiation dominated era. Most of the energy in the universe was in terms of massless speed of light particles for the first fifty thousand years.
Whoa, which sounds like a lot in human years, but in the terms of the age of the universe, it's it's like just the first blink.
Yeah, exactly, it's just like a blip. Like if you ruled for fifty thousand years, that sounds pretty impressive, but if the universe is fourteen billion years, then it's almost forgettable, m all right.
So then at first it was all radiation. And then what happened when did have changed?
Things are expanding, things are cooling down, and that expansion affects matter and radiation differently, because as the universe expands, matter gets dilute, right, the same amount of matter exists, we have more volume, so the density of matter drops. That makes sense, But radiation is effected in another way. As space expands, radiation gets dilute. It also gets red shifted. Like if you have a photon in space and that space expands, it doesn't just make the photon have fewer neighbors, It makes the photon have a longer wavelength, which means less energy. So this red shifting of radiation means that radiation loses energy faster than matter does as the universe expands.
Whoa interesting, It's like it slows down light. But you can't slow down light, but it it makes it kind of less energetic.
Yeah, it steals away energy from light. And we know that happens. We see it all the time. Like the cosmic background radiation with generated actually really high energies like three thousand degrees Calvin. We see it now like three degrees calvin, really long wavelengths because the universe has expanded and red shifted all of that, and so radiation sort of lost out after about fifty thousand years, and then for a long time the universe was matter dominated. Most of the energy in the universe was in the form of.
Matter, and a lot of that came because matter kind of transformed from that early energy, right, like things kind of clumped together and then they became matter.
Yeah, the Higgs boson gave mass to a lot of those particles and shifted them from the radiation category into the matter category because now they had mass. And so then there was this huge universe filled with particles, you know, electrons and protons, and stars were formed and galaxies were formed, and that was the most of the energy budget of the universe for billions of years was in terms of stuff, mostly dark matter actually, but in terms of like things we would think of today as stuff. It was the stuff dominated era of the universe.
WHOA, well, you just blew my mind a little bit here through in the dark matter here as a surprise twist. So, like we know where dark matter came from, is that what you're saying, Like we trace the history of dark matter.
We know that dark matter was made at the same time as all those other particles. When the energy in the early universe coalesced into the different fields electrons and quarks. That happened equally across all of the fields. And so if dark matter is a particle and it's described by a quantum field. Then it was also made in the early universe, and it's been around since then. We're pretty sure about that because it's changed the way the universe has evolved. Like the reason we have stars and galaxies is because of the gravity of dark matter early on in the universe. So it had to have been around for a long time.
So when you say that the universe became mad or dominated, really you mean dark matter dominated, because there's like, even since the beginning of time and those early moments, there's been you know, five times more dark matter than regular matter.
Yeah, although the ratio between dark matter and regular matter does change through the history of the universe, we think there was even more dark matter early on, and some of it converted into normal That's a whole other podcast episode. We talked about the Wimp miracle ones about how we think dark matter converted into normal matter. But yes, there's been dark matter since the very beginning.
Wow.
And so when really in this period of matter domination, really you're saying it's dark matter domination.
Yeah, dark matter ruled for about nine billion years.
Long lived dark matter, but then something happened, the dark energy Revolution.
Yes, dark energy took over. Remember that the universe is expanding, and so as the universe gets bigger and bigger, every new chunk of space that's created comes with its own dark energy. So unlike matter and radiation, which get more and more dilute as space expands, dark energy doesn't get diluted because a new chunk of space comes with its own fresh dark matter. So as the universe expands, dark energy starts to climb and eventually at some point it crosses over and is more dark energy in the universe than there is energy in the dark matter. That happened about four or five billion years ago.
Yeah, and we're still in that period, right, We're still in the dark energy dynasty.
We're still in that period, and this period's going to last for a long long time, maybe forever, because once dark energy is dominant, it accelerates the expansion of the universe, which makes more dark energy more rapidly. And so now dark energy is like completely dominated seventy percent of the energy of the universe, and the future suggests it's going to get higher and higher.
And it might even expand the universe to almost nothingness right into my expanded So that there's nothing left.
Yeah, although remember, dark energy is something we observe, we see it happening, we have these ideas about how it works, but we're really not very confident in it, which makes it very difficult to make solid predictions for the future of dark energy. It could turn out the dark energy is much more complicated than we imagine, and it has some weird oscillations in it, for example, and maybe it's going to turn around and cause a big crunch. We really just can't say for sure because we don't understand it like at all.
But I guess we go back to Jew's question. He kind of just wanted to know which came first, matter or energy. I think what you're saying is theture is kind of complicated. It's not just kind of about the sequence of things. It's you know, to physicists, it's kind of like which is more dominant, And that question has changed over the Big Bang and the history of the universe.
Yeah, it's a really fascinating history and nuanced and one that we've only really picked a part in the last couple of decades. So we're just at the very beginning of understanding the whole history of the universe in terms of its energy budget, how it formed, and how that evolved.
I see, But I guess to answer the question the question, the answer is that energy came first, that's kind of for sure, you sort of have high confidence in. But in terms of what came second and third and four, that's been changing and it's a more complex picture.
And can we described the early moments of the universe in terms of energy? That is an open question.
Yeah, Methatherians, I think people who ate men.
That's a question for people to chew on.
I'm sure we'll have a very feeling answer. All right, Well, thank you Jils for that great question, and thank you to everyone who sent in their questions. We really enjoy answering them on the podcast.
We absolutely do we of your messages with or with out questions, So please don't be shy if it's something you've been thinking about, don't hesitate right to us. Do questions at Danielandhorge dot com.
Yeah, we look forward to your awesome questions. Until then, keep being curious about the universe. Come up with questions and look at the things around you and think about what might have come first, or a second or third, or whether or not. You can get a PhD of a.
PhD because science is just people asking questions and that includes you.
We hope you enjoyed that. Thanks for joining us, 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. How is 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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