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John Green: There will be no season two of the universe, but there will be an Episode 2 of this podcast. Today, Dr. Mack and I discuss the fundamental forces of nature, the tiny ovens we know as particle colliders, and why the Higgs field matters so much. Also, Dr. Mack makes me extremely anxious by introducing me to the wild complexity of protons. It wouldn't be cosmology if it didn't make me nervous. All right, here's our conversation. 

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John Green, Very Curious: So the last time we talked, we got about two minutes in to the universe's existence. I learned that there are some hydrogen atoms that were created then that are in me now. And that provided me with a lot of comfort

Dr. Katie Mack, Astrophysicist: [chuckles]

John: after you gave me a lot of early universe anxiety. So thank you. 

Dr. Mack: I'm glad that it's helpful? You know, I feel like it's... It's nice to be star stuff, but it's even better to be big bang debris, right? Like, I think that that's just really cool. 

John: Yeah, I absolutely agree. But in trying to resolve that anxiety for me, which I deeply appreciate, we did skip past some stuff.

Dr. Mack: Yes. 

John: Some fundamental stuff. 

Dr. Mack: Yeah. Yeah. 

John: The fundamental forces. 

Dr. Mack: Yeah. There's some really interesting... cosmic evolution that happened in the very, very first few, like, microseconds of the universe that are essential to how the universe works now and

Dr. Katie Mack: could have implications in the future for how the universe will ultimately end, which, 

John Green: Hmmm.

Dr. Mack: we'll get into that later on. But it's important to know that, like the laws of physics, as we understand them now, things like how electricity works, how nuclear physics works, how, you know, the forces that hold the nucleons inside the nucleus of an atom, the forces that allow radioactive decay to happen, the forces that govern electricity and, and magnetism... Those are essentially universal insofar as they act through most of what we experience in the world, in the universe. But there's an important sense in which they're not universal, which is that they are energy dependent. 

John: Hmmm.

Dr. Mack: What I mean by that is that they are different when the ambient energy, the ambient temperature, is really, really high. It's kind of as if, you know, gravity works differently when you walked into a hot room. 

John: Oh. 

Dr. Mack: Gravity is not part of this. Gravity is a different thing and, and acts totally differently and is not part of this conversation, but with the other forces of nature, it is different in a really, really, really hot room. [chuckles] So this is why we use particle colliders. 

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John: Okay, we're about to get way more into this. But particle colliders are scientific instruments that speed up particles or tiny bits of matter and collide them together onto a target. We're going to talk about why they do that in a second. 

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Dr. Mack: We talk about particle colliders, you know, as like smashing protons togther, that kind of thing, as though there's something interesting inside the proton that we're trying to crack into. And there are interesting things inside the proton. I'm not, I'm not going to say that they're not. But the main purpose of particle colliders is to just create a really high energy environment, because we know that the laws of physics are different at really high energy environments. 

John: Ohhhh. So when we think of, like, the fundamental laws of the universe...

John Green: Those are only the fundamental laws for the universe at its current temperature, which it's been approximately at for a long time, but not for the whole time.  

Dr. Katie Mack: Yeah, exactly. And so, one of the things that people talk about with like CERN, the Large Hadron Collider, stuff like that, they talk about these instruments as "recreating the conditions of the Big Bang" - that's one of the sort of taglines - That is really what they're trying to do. They're trying to recreate the conditions of the very, very early universe when the universe was hot and dense, because the laws of physics were different. 

John: Uh - I - I don't want to criticize physicists on this one, but it seems like maybe y'all shouldn't have called them "Particle Colliders" if it's not primarily about the Particle Colliding...

Dr. Mack: Well, I mean, you have to. 

John: Couldn't you have called them... Hot...

Dr. Mack: Yeah.

John: Dense... Recreators?

Dr. Mack: Just like tiny ovens? [chuckles]

John: Tiny ovens!

Dr. Mack: [chuckles some more]

John: Tiny ovens!!

Dr. Mack: Yeah, yeah.

John: Super hot... super small...

Dr. Mack: Mhm.

John: The world's smallest, hottest oven. 

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Dr. Mack: The particles themselves are also interesting, like some of the early particle colliders really were trying to like, figure out what the particles are made of... by firing electrons, protons, you can kind of probe the interior of the proton, which is fantastically complicated, like it is upsetting how complicated a proton is. 

John: [chuckles]

Dr. Mack: Like so... So okay, so I'm just going to go off on a tangent about protons because [chuckles] I've been

John: Great. 

Dr. Mack: I've been doing some reading about protons. Because there has been some interesting results coming out recently. And my goodness, like we are... okay - We are lied to about atoms in so many ways.

Dr. Katie Mack: So first you get the picture that an atom is a little ball, right? Like the smallest indivisible piece of matter. That's like the ancient Greek version of an atom, right? And then you find out, okay, no, it's not actually a little ball... It's like a bunch of little balls in the middle and then other little balls orbiting around them. Right? So you got the protons and neutrons in the middle, and then you got the electrons orbiting around in these little loops. And you know, you have, you've got that... those famous drawings of like the little balls in the center in these little loops of the electrons orbiting. Okay. 

John Green: That is my understanding of an atom. 

Dr. Mack: Right, right. And that's like the picture that, that, that takes you into, into like high school. Right?

John: That got me through high school, Katie. 

Dr. Mack: Yeah. Sure. Sure. Yeah. But then when you get into quantum mechanics in like college, you learn that electrons are actually in a cloud of probability of electron-ness that sort of engulfs the atom in various ways and the electron is not actually localized as a specific point, but it's kind of in this nebulous state. But you, you still kind of don't hear anymore about the protons and neutrons. Those are still just kind of inside the nucleus. Right? And you sort of ignore them. And then at some point you learn that a proton and neutron, each of those are actually composed of quarks, which are a fundamental constituent of matter. So a quark is a kind of tiny particle. And you put three quarks together and you get a proton, [and] you put three different quarks together and you get a neutron. And the quarks are, are fundamental. The protons and neutrons are made of three quarks each. 

John: Okay.

Dr. Mack: This is like the final thing that usually people are told about protons - if they get that far. 

John: You cannot get smaller than a quark. 

Dr. Mack: Right. You can't because quarks are fundamental. So electrons are fundamental partices. Quarks are fundamental particles. They're not divisible. There's nothing inside a quark. 

John: No sub-quark. 

Dr. Mack: There's no sub-quark, right? However, [chuckles] what you're told about these quarks... So the quarks come in different flavors. And this is where it gets really, really cute, right?

John: Uh huh. Up, down, strange, charm, top, bottom. 

Dr. Mack: Exactly. Yes. Up, down, strange, charm, top, bottom.

John: My brother wrote a song about this. 

Dr. Katie Mack: The strong nuclear force carrier is called a gluon. So there's gluons inside the protons, there's quarks and there's gluons. And you're like, okay, so how much does a gluon weigh? Turns out they're massless. 

John Green: Oh. Oh well that's... That's a surprise to me.

Dr. Mack: Yeah.

John: I did not - That's like the twist at the end of Usual Suspects. I did not see it coming. 

Dr. Mack: So a proton is made of three quarks, whose masses add up to about 10 MeV, and a whole bunch of massless gluons, and somehow it still has 938 MeV as its mass. 

John: Do we know why?

Dr. Mack: [chuckles before continuing] Yeah, yeah. So it turns out that the mass is, is essentially due to the energy of the confinement of the quarks. There's some kind of energy associated with the, the way that the quarks are hold together by the strong nuclear force. And also, depending on how you look at the proton, by like firing particles at it... you actually find that there's a whole sea of quarks. There's like a whole bunch of like quarks and antiquarks kind of popping in and out of existence all the time. And there's other quarks in there too. It's not even just the up and down quarks. You can do experiments and you can find, I think, charms quarks in protons? Which is ridiculous because those weigh more than protons do.

John: Oh God.

Dr. Mack: [chuckles before continuing] So sometimes when you [chuckles some more before continuing] So sometimes when you do these experiments, you find quarks in there that are more massive than, than the proton. 

John: Oh God.

Dr. Mack: So like none of this, none of this makes any sense at all. And the way that they do some of these experiments is by firing electrons through the proton and those, they can, like, go into the proton and, like, penetrate into the proton. And so we're trying to figure out even how big the proton is. And there have been a bunch of new results about the size of the proton. And you do that by firing like electrons or neutrinos or something into the proton. Because you can just do that. You can just punch right through it with other particles, and then you find all these weird things like charm quarks just existing inside a proton, even though they're too massive to possibly be there. And so it's a whole thing about like, everything's