 Who has a beer in their hands? Where did it come from? Joining us today to answer that question is you dumb graduate student Trevor Donaldson, join me in welcoming Trevor. How's it going? Awesome, awesome, awesome. So I'm here to tell you all a very strange story, an unbelievable tale of how beer gets made from scratch. So, let's talk about it. You tell me, what ingredients go into a beer? Water. Yeah, water, malt, something like yeast and grain. Hot, awesome. I heard yeast. I want to make a glass to put it all in once it's all done. Now of course, all of you are completely wrong. I said let's make a beer from scratch. We have to go a little bit further back. So, what's in water? Well, water is actually pretty simple, right? Water is just H2O, two hydrogens, one oxygen. What about the wheat or the hops? What goes into that? Well, they're plants, so they're all made up of DNA, right? It is a complicated molecule, but it's not that complicated. It's just hydrogen, oxygen, nitrogen, carbon, phosphorus. Really simple. There's something important that's in both of these. That's sugar, right? The yeast needs something to act on to ferment, to make the alcohol that goes into a beer. So, sugar is not too complicated either. Carbon, hydrogen, oxygen. And there's one more thing that's especially in hops that gives us the flavor that we love in a beer. It's called cumulose. Cumulose is a bit of a complicated molecule, again, but it's not that complicated. Hydrogen, carbon, oxygen. You might be noticing a trend mode. What's next? Yeast. Yeast, again, while it's living, so it's got DNA, hydrogen, carbon, oxygen, nitrogen, phosphorus. Not that complicated. As part of the chemical reactions that yeast does to make us beer, it produces carbon dioxide, so carbon, oxygen. It also produces ethanol, the alcohol that lines up in our beer, carbon, hydrogen, oxygen. And it does this through the use of all of its biological reactions. They're all very complicated, but all of them involve, if you guess yet, hydrogen, carbon, oxygen, plus a bit of phosphorus, say, nitrogen. All very complicated, but all of them involve, if you guess yet, hydrogen, carbon, oxygen, plus a bit of phosphorus, say, nitrogen. That's it. So if you can keep and track the ingredients so far, hydrogen, carbon, oxygen, nitrogen, phosphorus. Turns out the most complicated thing that goes into a beer is the glass itself. The glass is mostly made out of silicon dioxide with a little bit of sodium oxide, calcium oxide, aluminum oxide, and really trace amounts of these elements. We got some potassium, some magnesium, some iron, some titanium, some sulfur, and that's it. So if you're keeping track, we got 13 elements. Hydrogen, carbon, oxygen, nitrogen, phosphorus, all the things that go into glass. So if we're going to talk about how to make a beer from scratch, we need to figure out how to make those things into things. I wish I could tell you that this is a simple story. I wish I could say, all we do is just find a beer star, pull the tap on it, all 13 of these come out. Boom, we can make beer. But, like I said, it's a bit more complicated. It's a bit more of a beautiful story, actually. It's a bit of a hot beer with a little tail. And to tell that tail, we need to go back to the beginning. All the way back to the beginning. Well, only sort of. See, there's a problem when we start going back in time into the very early universe, how we can describe what's going on, all the physics of what's happening in the early universe, and it's the fact that we're not exactly sure. In fact, before about 10 to the minus 43 seconds after the Big Bang, we have no idea what's going on. We have a couple ideas, so-called theories of everything. But they're just that. We don't really have any observational proof to tell us one theory from the next, which one's good. It's not until about maybe 10 to the minus 43 seconds after the Big Bang that we start getting into theories that we can actually validate, we can actually improve. So-called grand unified theories. Now, these theories are grand and unified in the sense that the stuff that's in a blender is grand and unified. As in it takes all the things that we might recognize, like strawberries, bananas, berries, whatever, and it blends them all up until we can't tell one from the next. It blends all of the physics that we're used to thinking of, electromagnetism and the strong and weak nuclear forces. It just blends them together until we can't tell them apart. It's not until a billionth of a second after the Big Bang that we start getting things to recognize, quarks, blue-ons, electrons, photons, all the bosons that we love to talk about. And this is the stage of the universe that we like to call quark, blue-on, plasma. This isn't an actual picture of quark, blue-on, plasma. It's a picture of one of those things. We can find it at the dentist's office to keep an eye on the fact that you're at the dentist's office. But I do my best. It's not until about a billionth of a second after the Big Bang that we get things that we really start recognizing, nucleons, like protons and neutrons. In fact, we just did our very first step in making beer. We made hydrogen. These protons up here, these are just little atoms of hydrogen. Hydrogen just has one proton. We made hydrogen. Yes. Awesome. All right. So, out of a millionth of a second after the Big Bang, the universe is hot and dense. It is the ideal environment for making new things from the things that we already have. But there's one problem with the fact that the universe is super hot and super dense. That's the fact that it is bathed in this bath of hydrogen. Why is that a problem? Let's say that we have a proton and a neutron and we want them to be friends and become what we call deuterium, an isotope of hydrogen with one proton and one neutron. Well, deuterium really hates gamma radiation. And so that gamma radiation hits the deuterium and splits it apart. It's not until about 10 seconds after the Big Bang that we can smoosh a proton and a neutron together and have deuterium, have that deuterium last. Once we have that deuterium, though, we can add a proton and we've made a whole new element. We've made helium-3. We can instead have a neutron and make another isotope of hydrogen. This is called tritium. We can take either one of those and add the nucleon that's missing. We can add a proton to tritium or a neutron to helium-3. We've made helium-4. Now, our helium's not getting bigger. We're really going to need that helium later. So this is a really important step. I don't know if I close my mouth. Is that better? Cool. All right. So now that we have our helium... Oops. So we've made our helium, right? We're about 1,000 seconds after the Big Bang. But there's a problem now. The universe was hot and it was dense, but it is no longer as hot and dense and so we can't do anything with that helium. It just stays there and does nothing. And so for the next 1.5 million years, we've entered the cosmic dark ages. Nothing is happening. And of course, the cosmologists know we're getting 80% of this. There is so much interesting stuff that's happening, but for me, a stellar astrophysicist, nothing interesting is happening. Until 1.5 million years later, the first stars are being invaded. So, clouds of gas, clouds of that primordial hydrogen and helium that we've already made, bits of leftover deuterium, a little bit of lithium gas produced in the process, clouds of gas start collapsing in on themselves. And as they collapse, they get denser and denser and hotter and hotter and they start fusing elements. They're stars, right? They're exactly what we think of stars, except they're a little bit different. The first stars in the universe are these behemoths. They're hundreds of times the mass of our sun. They live and die in just a few million years, a very short lifetime to a star. It's gotten to a little while later that we start making things like these. This is the sun, can't you tell? Look, it's the sun. Let's take a look inside. All right, so stars like our sun like to spend most of their 10 billion or so year lifetime fusing hydrogen into helium, just like what happened during the Big Bang. I'm going to skip over all that and get to the next thing that stars do right towards the end of their lifetimes. Stars at the end of their lifetimes do what's called the triple-alpha reaction, so-called because there are three things that go into it, and all of them are called alpha particles. What's an alpha particle? It's helium-4. We made it already. Awesome, we can get triple-alpha right off the bat. Here's how it works. I take three helium atoms, I smash them together, I have carbon. It's super easy. We're all doing nuclear physics, and it's so easy. Good. So, now that we've made our carbon, let's say if the star is a little bit more massive than our sun, maybe about two times the mass of our sun. In addition to carbon, this star can also make oxygen by adding one more alpha particle, one more helium nucleus onto the nucleus. And now we have oxygen. Unfortunately, this is about as far as a low-mass star can get. They can make carbon, they can make oxygen. That's about it. Low-mass stars are boring, by the way. Alright, how do we get all of that helium and carbon and oxygen that we just made out of the star? It does us no good if you want to make beer if all these elements are locked up in the star. Well, at the end of this star's 10 billion inch year lifetime, it becomes called a red giant. It expands and it cools down. It becomes so cool that it starts to boil. That's right, stars, when they get cold, boil. How weird is that? Just like a pot of boiling water, these stars take the hot stuff that's at their center and physically bubbles it up to the surface. That means that we can take all the atoms that we've produced with our nucleosynthesis and drag them up to the surface where we can see them, where this star can now lose them via stellar wind, just like our sun's stellar wind. Cool, so now we've produced, or rather we polluted the interstellar medium with helium, with carbon, with oxygen. We have three of the things that we need to make beer. All right, like I said, low mass stars are boring. What about high mass stars? What about a star like this, that started about 10 times the mass of our sun? Well, let's take a look inside and see what it does. Now, just like our sun, it spends most of its very short time fusing hydrogen into helium. It also fuses helium into carbon. It can also make oxygen, like that low mass star. But it can go even further. It can go even further. It can go even further. It can make neon. It can make titanium and silicon and sulfur and calcium and magnesium and aluminum and all of these fun things. Just because it's a very massive star it's incredibly hot in its core so it can unlock all of these additional stages of nuclear fusion. How cool is that? Really cool. So, at the end of this process, here's what it's made. It's made this nucleus called nickel-56. It's called nickel-56 because it has 56 neutrons plus protons. There's a problem with nickel-56 though. It's really unstable. Two of those protons decay by shooting off a positron. It's a plenty of metal particles. And this turns now into iron-56. There's another problem with iron-56. Iron-56 is the end of the line for a star. There is no physical way to get energy out of an iron-56 nucleus. You can't fuse it with something else. You can't fission it and turn it into two more things. You get nothing out of this nucleus. That's a problem for a star. So, here we are. We're looking at the core of a high-match star that's about to have its worst day ever. It just ran out of iron to fuse. Rather, it just ran out of stuff to fuse into iron. This core is made out of iron. And so, because it's run out of its energy source, there is nothing preventing it from collapsing under its own weight. It collapses into a small, tiny, hard, dense nugget of matter. The outer envelope of this star collapses onto that inner core and rebounds into a supernova explosion. That's how stars, that's how massive stars, explode. This explosion, though, is so energetic. All of the stuff that this star is made is released into the interstellar medium. All of that carbon, oxygen, agnese, potassium, silicon, sulfur, all the things that go into our beer are released in this explosion. Now, I'd be sad if I didn't mention some other stuff that happens in this explosion. It's not very relevant to beer, but it turns out the environment around this supernova explosion, it is so energetic that you can make pretty much anything you want. Think any element in the periodic table that's heavier than iron. It's probably made in a supernova. European, supernova. Uranium, supernova. Thorium, supernova. Seriously, pick an element, it's made in a supernova. That's awesome. So, if you remain in tension, you may have noticed I missed one crucial ingredient in beer. That's nitrogen. The nitrogen that goes into DNA, nitrogen that at least uses to produce ethanol in our beer, it's really hard to make nitrogen. It's really, really hard to make nitrogen. You can sort of make some of it in supernova explosions. You can make some of it at the very end of a low mass star's lifetime, which you don't make enough. The only way to produce nitrogen that you need is via this thing called the Carbon Nitrogen Oxygen, or CNO, cycle. Turns out this is the way that low mass stars and high mass stars use to produce helium out of hydrogen. So here's how it works. I have some hydrogen. It uses these three nuclei, carbon, nitrogen, oxygen. It bounces around and uses them as catalysts to produce helium. It's super cool. No carbon, nitrogen, or oxygen is made in this process. It just uses these as a cycle to produce helium. It's super neat, right? So, the carbon, nitrogen, and oxygen cycle kind of works like a NASCAR race where all the cars are going around the track listening, carbon, nitrogen, oxygen, carbon, nitrogen, and oxygen. And they like to take a pit stop here and there. Turns out that the worst pit stop that they take is at nitrogen. It takes them a really long time to get through the stop that involves nitrogen. And just like a racer on a track, if I have something that's stopping the race at one point, all the cars are going to build up at that one point on the track. Same thing happens with nitrogen. Because it takes so long for this step that involves nitrogen to happen, the star starts building up nitrogen. Here's what I mean. Here is the abundance, the cosmic abundance, of nitrogen compared to carbon. Now, ever in the universe before the CNO cycle happens, there's about maybe five, four or five carbon atoms for every nitrogen atom. Inside stars that are doing the CNO cycle, here's what happens. There's more than 100 times the amount of nitrogen in a star that's doing the CNO cycle than there is the carbon in that star. So via this process of converting hydrogen in the helium, we actually make the nitrogen to five carbon atoms. All right, cool. So we've made all 13 ingredients of our beer. We've made our hydrogen, carbon, oxygen, nitrogen, and phosphorus that we need to make beer itself. And we've made all the other atoms that we need to make F-racks. So there was a bit of milk from this beer star, right? It wasn't just one star, but it was the whole conglomerated effort of massive stars and low-mass stars that produce all these other elements. With a little bit of help from some big, big beer nucleus synthesis which made our hydrogen in the first place. All right, let's get the beer from the stars into our glasses. So this right here is an interstellar cloud of gas and dust. This has all the things we need to make beer. Turns out this cloud is really cold. In fact, it's so cold it's a great place to do some chemistry. One of the easiest things to make in these clouds is water. We look at interstellar states and find water. If we look at these clouds a little bit further, we can actually start seeing the very beginnings of stars. We see proto stars. And if we look at some of these proto stars, and these are all real images, we can see what looks like disks of dark gas and dust that are orbiting these stars. These disks are also the perfect place for chemistry. In fact, a disk, much like these ones that formed around our sun as it was moving, formed minerals like silicates, carbonates, things that we need to make glass. This right here, ooh, now that this is totally this is totally a protective cloud. So this is a picture of an actual disk around a star taken by the Alma telescope. These gaps in the disk here are real. Parts of this disk are a little bit more massive than others. They were gravitationally unstable. They collapsed down to become planets. Or rather, they collapsed down to become small little chunks of things that started creating more and more matter. I already gave away the ending. They are becoming planets. Right here in this gap of stuff are planets that are carving out material from this disk of gas and dust. One of these planets might actually grow, or might actually manage to hold on to an atmosphere. It might have active volcanism going on on the surface. This really harsh environment sounds terrible to me and I, but it's actually a really good place for very, very, very early life. Early life that might one day evolve to become something that we see as yeast. Wait a couple billion years, right? Not that option. Maybe this planet has oceans, forests, deserts, jungle, tundra, an atmosphere, weather, volcanism, all the things we need for complicated life and not so complicated life too. Maybe this person sees these ingredients and decides, oh, you know what would be an awesome idea? Let's take that leaf, let's mash it up and soak it in water for a little bit. Let's put some hops in, let's expose it to yeast. Let all this sit in a barrel for a little while. Let the yeast do its magic. Look at that. We've made beer. Don't applaud me. Really what we should be doing is raising our glass. So please, everyone join me in a toast. I don't have beer. You're done. I don't have beer. So, what? All right. So, please join me in thanking the universe for this lovely stuff that's in your glass. Thanks for listening. I'll take your questions and you take this beer too. Give it back. Sorry, I can't do it. Also, if you still have trivia, please bring those and turn those in. Cool. So, the question was, can I repeat the mass range of stars that participate in the carbon nitrogen-oxygen cycle? So, it turns out there's another way to make helium out of hydrogen. You might think a good way to make helium out of hydrogen is just to smash the two together, or smash a bunch of hydrogen together to make helium. That's actually an okay way to do it. Very low-mass stars do do that. But as stars get more and more massive, the efficiency of the CNO cycle ends up going up and up and up. The point of the transition between where the CNO cycle is more efficient than the so-called heat chain which is smashing protons together to make helium. That's right around our sun. It turns out our sun does about 10% of its fusion via the PPP chain and about 90% of its fusion via the CNO cycle. So, our sun is the transition. Everything more massive than our sun does the CNO cycle. All right. Any other questions? All right. Thank you all so much. Don't forget to review trivia and thank the universe for the stuff in your glass.