# Listener questions #53

An episode of [Daniel and Kelly’s Extraordinary Universe](https://invisiblenetwork.ai/podcast/1436616330), 15 Oct 2026, 41 min.

Audio: https://podtrac.com/pts/redirect.mp3/traffic.omny.fm/d/clips/e73c998e-6e60-432f-8610-ae210140c5b1/f5d5fac6-77be-47e6-9aee-ae32006cd8c3/229ed583-b97a-415e-8a91-b4e40058aa28/audio.mp3?utm_source=Podcast&in_playlist=b26cbbeb-86eb-4b97-9b34-ae32006cd8d6

Daniel and Kelly talk about how particles are detected, the heavy proton discovery, and de Sitter space. See omnystudio.com/listener for privacy information.

## Transcript

[0:07] Speaker 1: I heard the LHC made a heavy proton out of
[0:10] Speaker 1: thin air. But what does it mean and why should
[0:13] Speaker 1: I care?
[0:14] Speaker 2: You smash particles together and they go boom. But how
[0:18] Speaker 2: does their data get to the computer room?
[0:21] Speaker 1: I really want to understand desider space. Can you explain
[0:25] Speaker 1: it so I get a big smile on my face?
[0:27] Speaker 2: Whatever questions keep you up at night, Daniel and Kelly's
[0:30] Speaker 2: answers will make it right.
[0:32] Speaker 1: Welcome to Daniel and Kelly's Extraordinary Universe, Listener Questions, All
[0:37] Speaker 1: Physics Edition.
[0:38] Speaker 3: 53! Hello, I'm Kelly Wiedersmith.
[0:54] Speaker 2: I study parasites and space, and we're talking about a
[0:58] Speaker 2: lot of particles today. And I'm pretty excited because we've got,
[1:00] Speaker 2: you know, Daniel, the particle physicist. And so, Daniel, what
[1:03] Speaker 2: I want to know is, and I'll go ahead and
[1:05] Speaker 2: introduce you. My co-host is Daniel Weitz, and he thinks
[1:07] Speaker 2: about aliens all the time, but sometimes he also thinks
[1:09] Speaker 2: about particles.
[1:10] Speaker 3: And so, Daniel.
[1:12] Speaker 1: That's my day job.
[1:14] Speaker 3: What is your favorite particle?
[1:16] Speaker 1: Oh man, I don't have a favorite particle. What I
[1:18] Speaker 1: love is the variety of particles, the diversity, the weirdness,
[1:23] Speaker 1: the patterns. Because it's in those patterns that are the
[1:27] Speaker 1: clues to understanding the next layer of reality. The way
[1:31] Speaker 1: that you need all the elements in the periodic table
[1:34] Speaker 1: to help you understand that all the weird chemistry comes
[1:37] Speaker 1: from the structure of the atom, how the protons and
[1:40] Speaker 1: neutrons and electrons all click together. In the same way,
[1:43] Speaker 1: the weirdness of the current set of particles is a
[1:47] Speaker 1: clue as to what's going on underneath. We just don't
[1:50] Speaker 1: know it yet. And so I love looking at it
[1:52] Speaker 1: and imagining some physicist in 100 years who knows that
[1:55] Speaker 1: answer and is saying like, wow, all the clues were
[1:58] Speaker 1: right there. Anybody in 2026 could have won a Nobel
[2:02] Speaker 1: Prize if only they were smart enough.
[2:04] Speaker 4: Nope.
[2:04] Speaker 3: What's your favorite particle?
[2:05] Speaker 2: That was uplifting or whatever, but that wasn't the answer
[2:10] Speaker 2: to the question.
[2:13] Speaker 1: All right. Well, I got my PhD on the top cork,
[2:15] Speaker 1: so then I got.
[2:16] Speaker 3: To go for the top cork.
[2:17] Speaker 1: Yeah, that's the one.
[2:18] Speaker 3: Thank you.
[2:18] Speaker 1: I spent a lot of time with the top cork.
[2:21] Speaker 1: It was back when we had a small amount of data.
[2:24] Speaker 1: And so I had like seven collisions on which I
[2:26] Speaker 1: wrote my PhD and I knew all of them by name. So, yeah.
[2:32] Speaker 3: Amazing. OK, there you go.
[2:34] Speaker 2: Because, you know, I was wondering, like, is Daniel going
[2:35] Speaker 2: to go into politics next? I can't let him get
[2:38] Speaker 2: away with evading my questions.
[2:40] Speaker 3: So anyway.
[2:41] Speaker 1: All right.
[2:41] Speaker 3: Now we're good.
[2:42] Speaker 2: But now let's get to some more heavy hitting questions.
[2:45] Speaker 2: The questions from our listeners.
[2:47] Speaker 4: All right.
[2:47] Speaker 2: So let's start with our first particle question of the
[2:50] Speaker 2: day from Catherine.
[2:51] Speaker 4: Hi, Daniel and Kelly. I just heard about a new
[2:55] Speaker 4: particle that was discovered at the Large Hadron Collider. They're
[3:00] Speaker 4: calling it a heavy proton. I'd like you to comment
[3:04] Speaker 4: about the importance of this discovery. And also, if it
[3:08] Speaker 4: only lasts for a billionth, trillionth of a second, does
[3:13] Speaker 4: it really have any value? All right.
[3:16] Speaker 1: I love how she starts out with the science and
[3:19] Speaker 1: then she's like, What's it worth, man?
[3:22] Speaker 2: I mean, I think that's a totally great question. And actually,
[3:25] Speaker 2: I got to say, I must be living in Mars
[3:28] Speaker 2: in a cave or something. I didn't hear that we
[3:30] Speaker 2: just discovered a new particle at the LHC. I mean,
[3:33] Speaker 2: is that Nobel Prize level discovery here?
[3:37] Speaker 1: It's not really. And the particle physicists who work on
[3:40] Speaker 1: this kind of stuff are going to hate me for
[3:42] Speaker 1: saying this, but this is like the chemistry side of
[3:45] Speaker 1: particle physics. And it's not really that earth shattering of
[3:50] Speaker 1: a discovery. I mean, it's cool. And I'm glad they
[3:53] Speaker 1: did it. And we definitely learned something. But for people
[3:56] Speaker 1: who were like, hey, they got a Nobel Prize for
[3:57] Speaker 1: the Higgs. Why isn't this making the same kind of
[4:00] Speaker 1: earthquake in particle land? There's a reason for that.
[4:04] Speaker 3: I like how you threw shade on two communities at once.
[4:06] Speaker 2: You're like a bunch of physicists aren't going to like me,
[4:08] Speaker 2: but it's boring because it's the chemistry version.
[4:10] Speaker 3: And I was like, whoa, Daniel's hitting out at everyone today.
[4:13] Speaker 4: Yeah.
[4:15] Speaker 1: Well, the difference is fundamental versus composite particles. So fundamental
[4:20] Speaker 1: particles are things that we don't know that they're made
[4:23] Speaker 1: of anything smaller. They might just be made of themselves,
[4:26] Speaker 1: like the electron. We don't know that there's anything inside
[4:29] Speaker 1: the electron. There might be. It might be that a
[4:31] Speaker 1: future collider tells us what the electron is made out of.
[4:34] Speaker 1: And it's all made of squiglions underneath. And that explains
[4:37] Speaker 1: all the amazing patterns. But so far, we can't see that.
[4:41] Speaker 1: And so we treat the electron as if it's fundamental.
[4:44] Speaker 1: Same for the top quark and the other quarks and
[4:46] Speaker 1: the force particles like the photon. So we have this
[4:49] Speaker 1: set of fundamental particles that we include in our table
[4:52] Speaker 1: of fundamental particles. And so you can think of those
[4:55] Speaker 1: sort of like atoms of particle physics, right? The indivisible
[4:59] Speaker 1: building blocks out of which everything is built. The other
[5:02] Speaker 1: kind of particle is a composite particle. It means it's
[5:04] Speaker 1: made of other stuff. So for example, the proton, it's
[5:08] Speaker 1: made out of three quarks, two up quarks and a down.
[5:11] Speaker 1: Or the neutron is one up and two downs. And
[5:14] Speaker 1: there's a zillion different kinds of these composite particles because
[5:18] Speaker 1: there's a zillion different ways to click together quarks to
[5:20] Speaker 1: make them. You can do pairs of quarks like a pion,
[5:23] Speaker 1: different pairs of quarks, different triplets of quarks. So you
[5:26] Speaker 1: can combine these basic building blocks of fundamental particles to
[5:30] Speaker 1: make lots of different composite particles. So in the particle
[5:33] Speaker 1: physics land, these are more like molecules than atoms. They're
[5:36] Speaker 1: made of fundamental bits, but they're just rearrangements of those bits.
[5:41] Speaker 2: And so it sounds like you're saying that's what happened
[5:43] Speaker 2: at the LHC recently, is we clicked together bits in
[5:45] Speaker 2: a new combination? Yeah.
[5:47] Speaker 1: And so if you discover something like the Higgs boson
[5:51] Speaker 1: or the top quark, or the charm quirk, or the Tao,
[5:54] Speaker 1: or something that's new and fundamental, that's a big deal
[5:57] Speaker 1: because it's like discovering a new atom. And it tells
[6:00] Speaker 1: you about what the universe itself can do. It gives
[6:03] Speaker 1: you a clue as to either the fundamental nature of
[6:06] Speaker 1: the universe, if these really are fundamental, or the next
[6:10] Speaker 1: layer down, the squiglions that make up what we think
[6:14] Speaker 1: is fundamental. So that's really cool. That's really insightful. That's
[6:17] Speaker 1: an earthquake in physics when it happens, right? But it
[6:20] Speaker 1: doesn't happen very often. You know, we found the Higgs
[6:23] Speaker 1: in 2012. We found the top quark in 95, right?
[6:27] Speaker 1: Before that, it was the bottom quark in 77 and
[6:29] Speaker 1: a few neutrinos here and there. And so it's a
[6:32] Speaker 1: rare thing. It happens every couple of decades. It's almost
[6:34] Speaker 1: always a Nobel Prize because it gives you really deep
[6:37] Speaker 1: insight either into the nature of space-time itself or into
[6:41] Speaker 1: the next layer of reality. So really a big deal.
[6:44] Speaker 1: But when you discover a new composite particle, it's just
[6:47] Speaker 1: like you say, you're clicking together the stuff you already
[6:50] Speaker 1: know in a new way. And that's not without value, right?
[6:53] Speaker 1: In the same way that like when you build a
[6:55] Speaker 1: new kind of structure in chemistry, you're learning about the
[6:58] Speaker 1: kind of structures you can make in chemistry. Oh, it
[7:00] Speaker 1: turns out you can make this kind of molecule and
[7:02] Speaker 1: this is stable and whatever. And so that's what's happened
[7:05] Speaker 1: here is it tells you what the fundamental particles can do.
[7:09] Speaker 1: So this is like doing chemistry with the atoms of
[7:12] Speaker 1: fundamental physics, right? Which are now the fundamental particles. What
[7:16] Speaker 1: they did was they found a particle that was made
[7:18] Speaker 1: of two charm quarks and a down quark. So remember,
[7:21] Speaker 1: the proton is two up quarks and a down quark.
[7:25] Speaker 1: And it's stable. It lasts forever. You have a proton.
[7:28] Speaker 1: You leave it in space. You come back a billion
[7:30] Speaker 1: years later. It'll still be there. We've never seen a
[7:33] Speaker 1: proton decay because it's made of the lightest quarks. It
[7:37] Speaker 1: just sits there. And neutrons are not stable because there
[7:40] Speaker 1: are a little bit more energy stored in them And
[7:43] Speaker 1: so they can decay into a proton, but a proton
[7:45] Speaker 1: is stable. But you can click together other stuff, right?
[7:48] Speaker 1: You can replace those up quarks with a charm quark,
[7:51] Speaker 1: because remember, the charm quark is just like the up quark,
[7:54] Speaker 1: but it has more mass. So two charms and a down,
[7:58] Speaker 1: which is this new particle they found, is very similar
[8:01] Speaker 1: to ups and a down, which is the proton. So
[8:04] Speaker 1: you can call this in popular science language, a heavy proton.
[8:08] Speaker 1: But in physics language, it has its own name, which
[8:11] Speaker 1: we don't need to get into because I didn't tell
[8:12] Speaker 1: you anything, but it's some new particle.
[8:16] Speaker 2: And so does the heavy proton, is this less stable
[8:21] Speaker 2: because it has more mass than the normal proton? And
[8:24] Speaker 2: then what else do we learn by knowing that this exists?
[8:26] Speaker 1: Yeah, you're exactly right. It's very unstable. It doesn't last
[8:29] Speaker 1: for very long. It doesn't like to stick around. It
[8:32] Speaker 1: decays very quickly. And so what do we learn? We
[8:35] Speaker 1: learn about how these particles click together, which is very
[8:37] Speaker 1: interesting because the thing that determines what particles can click
[8:41] Speaker 1: together and how long they live is the strong nuclear force. Remember,
[8:45] Speaker 1: quarks have an extra kind of charge. Electrons have an
[8:48] Speaker 1: electric charge, but quarks have an electric charge and a
[8:51] Speaker 1: color charge, which means that they participate in the strong
[8:55] Speaker 1: nuclear force and they pass gluons around. And that force
[8:59] Speaker 1: is very, very strong, which makes it very hard to
[9:01] Speaker 1: calculate What will happen? And so it's difficult to know
[9:05] Speaker 1: what particles can form. How long do they live? Which
[9:08] Speaker 1: ones are more stable? Which ones are less stable? These
[9:11] Speaker 1: calculations are very difficult because our calculational tools work best
[9:16] Speaker 1: for weaker forces because we can't do any of these
[9:19] Speaker 1: calculations straight up exactly. We have to do approximations where
[9:22] Speaker 1: we break up the calculation into pieces and ignore a
[9:25] Speaker 1: bunch of the ones that we can't do. And when
[9:28] Speaker 1: you're dealing with a strong force, there are fewer that
[9:30] Speaker 1: you can ignore because the force is so strong. So
[9:33] Speaker 1: there's a huge community of folks calculating these things and
[9:36] Speaker 1: trying to predict it. It's big. It's complicated. The sort
[9:39] Speaker 1: of the way chemistry is complicated, like it's hard to
[9:42] Speaker 1: know in advance what molecules you can make and what
[9:45] Speaker 1: they're going to do. And so in the same way,
[9:48] Speaker 1: when you make a new particle, a new composite particle,
[9:51] Speaker 1: you learn something about what the strong force can do
[9:54] Speaker 1: and whether your calculations are correct. And that's really valuable.
[9:58] Speaker 1: And we've done a bunch of it at the LHC.
[10:00] Speaker 1: Like we haven't found a new fundamental particle since 2012,
[10:03] Speaker 1: the Higgs boson, but we found literally dozens of these
[10:07] Speaker 1: composite particles. Last time I checked the count, it was
[10:10] Speaker 1: more than 50. Wow. And so that's why they're not
[10:13] Speaker 1: awarding a new Nobel prize for each one, but they
[10:16] Speaker 1: do tell you something about the strong force and how
[10:18] Speaker 1: it clicks together and how our universe works. And so
[10:21] Speaker 1: it is very valuable. And I'm probably biased because it's
[10:24] Speaker 1: not the kind of thing that I study. So it's
[10:26] Speaker 1: not the kind of thing that I'm particularly excited about,
[10:28] Speaker 1: which is discovering a new fundamental particle. That doesn't mean,
[10:31] Speaker 1: of course, it's without value. It just means it's, you know,
[10:35] Speaker 1: a value to a different community and for different reasons.
[10:38] Speaker 3: All right. Well, that was illuminating. Let's see what Catherine
[10:41] Speaker 3: has to say.
[10:42] Speaker 4: Thank you, Daniel and Kelly. I appreciate your clear explanation
[10:47] Speaker 4: of a heavy proton. If I could use a cooking analogy,
[10:52] Speaker 4: it's rather like taking an old dish and tweaking the
[10:56] Speaker 4: ingredients rather than coming up with a completely new dish.
[11:01] Speaker 4: As a retired art teacher and a non-science major, I
[11:06] Speaker 4: appreciate your making science accessible to me. Keep up the
[11:11] Speaker 4: good work.
[11:32] Speaker 3: And we're back. And the next question is a CERN
[11:34] Speaker 3: question from Chris.
[11:36] Speaker 5: Hi, Daniel and Kelly. I feel like I have a
[11:39] Speaker 5: decent grasp of how particle colliders get the particles up
[11:42] Speaker 5: to high velocities and smash them into each other. I
[11:45] Speaker 5: think that can be fairly summarized as magnets. You've discussed
[11:50] Speaker 5: that a few times on the show, but something I'm
[11:52] Speaker 5: in the dark about is how CERN and other projects
[11:55] Speaker 5: collect so much data about these infinitesimal little particles that
[11:58] Speaker 5: come out of the collisions. How do we determine the
[12:01] Speaker 5: mass and the velocity and the direction of all these particles?
[12:04] Speaker 5: What sort of materials do we use to collect the
[12:06] Speaker 5: particles and How do we get that information into computers?
[12:10] Speaker 5: How can we tell a proton from a muon from
[12:12] Speaker 5: a Higgs? How do we know if they all came
[12:14] Speaker 5: from the same collision? I would love to hear you
[12:16] Speaker 5: talk about that in some detail. That'd be great.
[12:19] Speaker 1: Thank you so much.
[12:20] Speaker 3: All right, Daniel, how do we make these measurements?
[12:22] Speaker 1: Yeah, thanks for this question, Chris. I love talking about
[12:25] Speaker 1: this stuff. People have asked a version of this a
[12:27] Speaker 1: few times, but there's always more to say about how
[12:30] Speaker 1: to see particles. And so the basic version of the
[12:34] Speaker 1: story is that you're right. We have the collider. And
[12:37] Speaker 1: we use magnets and little linear accelerators to make things
[12:40] Speaker 1: go fast. So the way the accelerator works is you
[12:43] Speaker 1: have a little linear accelerator, which is just like a
[12:45] Speaker 1: big voltage difference. Like you put an electric field and
[12:48] Speaker 1: it pulls particles with the charge and makes them go faster.
[12:52] Speaker 1: And then you bend them with a magnet. And then
[12:54] Speaker 1: you push them with a field. And then you bend
[12:56] Speaker 1: them with a magnet. So it's push and bend, push
[12:58] Speaker 1: and bend, push and bend all the way around the ring.
[13:00] Speaker 1: Now you have your particles going really, really fast. But
[13:03] Speaker 1: you actually have two colliders. And two colliders are going
[13:06] Speaker 1: in different directions around the ring. So you have these
[13:08] Speaker 1: two beams circling at insane speeds around the ring opposite
[13:13] Speaker 1: each other. And then you cross them. So you collide
[13:16] Speaker 1: the beams. And the beams are not just like a
[13:19] Speaker 1: big stream of particles. They're organized in bunches. That's the
[13:23] Speaker 1: technical term. See, we don't use some ridiculous Latin phrase.
[13:27] Speaker 1: And each bunch is like 10 to the 12 or
[13:30] Speaker 1: 10 to the 13 protons. And they pass through another
[13:34] Speaker 1: bunch going the other direction. So you have these bunches
[13:37] Speaker 1: and they cross at this collision point. And then the
[13:40] Speaker 1: next bunch crosses and the next bunch crosses.
[13:43] Speaker 2: When you cross the beams, do you then use them
[13:45] Speaker 2: to like send ghosts back to the portal that they
[13:47] Speaker 2: came from?
[13:47] Speaker 1: You're propagating misinformation.
[13:52] Speaker 2: Oh, no, I was thinking about the Ghostbusters where they say,
[13:56] Speaker 2: don't cross the beams. I watched the original Ghostbusters movie
[14:00] Speaker 2: with my daughter recently and A, was surprised by how
[14:02] Speaker 2: much sexism I had forgot about was in that. But
[14:05] Speaker 2: the don't cross the beams is in my head right now.
[14:08] Speaker 2: So anyway, no ghosts being sent back to another portal
[14:11] Speaker 2: at CERN.
[14:11] Speaker 1: We are not opening portals at CERN. It's not happening. No,
[14:16] Speaker 1: what happens when you cross the beam is sometimes the
[14:18] Speaker 1: particles collide. And sometimes you get no protons colliding because
[14:23] Speaker 1: it's really hard to get tiny protons to hit each other.
[14:25] Speaker 1: Mostly they just pass through, which is why you have
[14:27] Speaker 1: like 10 to the 12 in a bunch. Because sometimes
[14:30] Speaker 1: you get zero collisions, sometimes you get 10, sometimes you
[14:33] Speaker 1: get 200 collisions. And the job of the LHC engineers
[14:36] Speaker 1: is to make more collisions happen so we can see
[14:39] Speaker 1: more stuff and we can see rarer and rarer stuff.
[14:42] Speaker 4: Okay.
[14:43] Speaker 2: And so once they collide, how do you know that
[14:47] Speaker 2: that has happened?
[14:48] Speaker 3: You can't see it.
[14:49] Speaker 1: You can't see the collision itself. You're absolutely right. What
[14:53] Speaker 1: we can see is the debris from the collision. So
[14:56] Speaker 1: it's like a car crash happened and we're coming in
[14:58] Speaker 1: afterwards and And we're picking up the pieces that were
[15:00] Speaker 1: like thrown onto the sidewalk.
[15:02] Speaker 3: That's dark.
[15:02] Speaker 1: And so the protons collide. And then something happens because
[15:08] Speaker 1: the quarks inside them interact. So the protons don't actually collide.
[15:12] Speaker 1: At those energies, the bonds between the quarks have low
[15:16] Speaker 1: energy compared to the velocity of the quarks. And so
[15:19] Speaker 1: the fact that they're in a proton together becomes kind
[15:21] Speaker 1: of irrelevant. And you just have like a pile of
[15:23] Speaker 1: quarks hitting another pile of quarks. And then maybe those
[15:26] Speaker 1: quarks will interact. So you have like a quark from
[15:29] Speaker 1: one proton interacting with a quark from the other proton,
[15:32] Speaker 1: and then they do something. Last episode, we talked about
[15:34] Speaker 1: annihilation or interaction. So the quarks can annihilate with each
[15:38] Speaker 1: other or they can just turn into something else. So
[15:41] Speaker 1: all sorts of stuff can happen. And the most common
[15:44] Speaker 1: thing is that it's just like a quark bounces off
[15:46] Speaker 1: quark and they go off their separate ways and everybody
[15:48] Speaker 1: reforms into particles and it's very boring. And most of
[15:51] Speaker 1: it just goes down the bean pipe. That's the most
[15:53] Speaker 1: common thing to happen. Basically nothing interesting. But sometimes they
[15:57] Speaker 1: make like a weird heavy particle, maybe a Z or
[16:00] Speaker 1: a top or a Higgs or something. And then that
[16:03] Speaker 1: doesn't last for very long, like 10 to the minus
[16:05] Speaker 1: 20 seconds. So you're right, you can't see it. But
[16:08] Speaker 1: it decays and it sprays into a huge stream of
[16:11] Speaker 1: other particles. And those are the ones that we can see.
[16:14] Speaker 1: So it throws muons or electrons or neutrons or protons
[16:18] Speaker 1: or something, a bunch of stuff out the sides. And
[16:21] Speaker 1: then we build detectors around the collision point, basically like
[16:24] Speaker 1: camera's to capture those and to then infer from the
[16:28] Speaker 1: patterns of those particles what's going on. And that's basically
[16:32] Speaker 1: my job. That's the piece I work on. You know,
[16:35] Speaker 1: it's a huge complex, people who built the accelerator, people
[16:37] Speaker 1: who make it work, people who built the detectors, people
[16:40] Speaker 1: who work on like keeping the detectors working and checking
[16:43] Speaker 1: that they're working and maintaining it and replacing bits, all
[16:46] Speaker 1: sorts of stuff. The bit that I'm most interested in
[16:49] Speaker 1: is the bit where you do the statistical analysis to
[16:51] Speaker 1: try to figure out like what happened there. And how
[16:54] Speaker 1: do we develop new statistical tools to get the most
[16:56] Speaker 1: information out of that? Because it's a complicated statistical problem
[17:00] Speaker 1: because you have really high dimensional information. We take 100
[17:04] Speaker 1: million measurements of every particle collision in various ways. And
[17:08] Speaker 1: we have to use that information to figure out, was
[17:10] Speaker 1: this dark matter? Was it just two protons bouncing off
[17:13] Speaker 1: each other? What was going on? And so the detector
[17:16] Speaker 1: is built out of several layers to help us do that.
[17:19] Speaker 3: So every time.
[17:21] Speaker 2: a new particle is made, you get a hundred million
[17:23] Speaker 2: measurements of it?
[17:25] Speaker 1: Every single time we collide protons, we get a hundred
[17:28] Speaker 1: million measurements of the collision.
[17:30] Speaker 4: Yeah.
[17:31] Speaker 3: Got it.
[17:31] Speaker 4: Okay.
[17:31] Speaker 2: I was like, how do you measure one thing a
[17:34] Speaker 2: hundred million times? And is that overkill?
[17:37] Speaker 3: But anyway, okay.
[17:38] Speaker 1: It's sort of just like having a big camera, you know,
[17:40] Speaker 1: it's like a hundred megapixel camera, right? And it has
[17:43] Speaker 1: a bunch of possibilities. Often a lot of those are
[17:45] Speaker 1: just blank, right? Because no particle hit it. but we
[17:48] Speaker 1: have 100 million channels in which to see particles. And
[17:51] Speaker 1: we have it staggered in these various layers that surround
[17:54] Speaker 1: the collisions so that we can figure out, just to
[17:57] Speaker 1: answer Chris's question, what particle was there and how do
[18:00] Speaker 1: we get the information about it?
[18:02] Speaker 2: Okay, and so the data that's collected is essentially which
[18:05] Speaker 2: one of the sensors got hit. And then that's the
[18:08] Speaker 2: information that goes to you.
[18:10] Speaker 1: Yeah, exactly. And we have several different kinds of sensors.
[18:13] Speaker 1: Just closest around the beam itself We have these silicon-based trackers.
[18:18] Speaker 1: These are just wafers of silicon. And when a particle
[18:22] Speaker 1: goes through them, it knocks off an electron and the
[18:25] Speaker 1: wafer is kept under voltage so that when you knock
[18:27] Speaker 1: off that electron, it gets pulled towards one side and
[18:30] Speaker 1: you can read it out as a current. And so
[18:32] Speaker 1: that's how you know, oh, a particle went through this
[18:34] Speaker 1: wafer of silicon.
[18:35] Speaker 3: Clever.
[18:35] Speaker 1: And silicon wafers are great because you can print them
[18:38] Speaker 1: using silicon lithography techniques that we borrow from consumer industries
[18:43] Speaker 1: to be really, really small little pieces of the wafer.
[18:45] Speaker 1: So you can tell exactly where in the wafer it
[18:48] Speaker 1: hit because you've subdivided it into all these little bits.
[18:51] Speaker 1: So it's really high precision and we can make them
[18:54] Speaker 1: really thin. And so we surround the beam pipe with
[18:56] Speaker 1: these to get really precise measurements of where the particles went.
[18:59] Speaker 1: That gives you like a visual picture of like, oh,
[19:01] Speaker 1: a particle went through this layer and then this layer
[19:03] Speaker 1: and then this layer. So you can reconstruct its trajectory, right?
[19:07] Speaker 1: You can say, oh, it went this way. Another one
[19:08] Speaker 1: went to that way. So you have as many layers
[19:11] Speaker 1: of the silicon as you can. The downside with silicon
[19:14] Speaker 1: is that it's expensive and it's very fragile. Like it
[19:17] Speaker 1: can't take radiation for very long. It's electronics. Electronics don't
[19:21] Speaker 1: like radiation. So every couple of years we got to
[19:24] Speaker 1: rip it out and put in new ones because it
[19:25] Speaker 1: gets used up basically.
[19:27] Speaker 2: And each one of these levels that you're telling us about,
[19:30] Speaker 2: do they interact with particles in different ways? Or do they,
[19:34] Speaker 2: like for the silicon chips, no matter what hits it,
[19:37] Speaker 2: does it give off a signal?
[19:39] Speaker 1: Yeah, great question. So silicon only interacts with charged particles.
[19:43] Speaker 1: So a neutrino goes to the silicon, does nothing. But
[19:46] Speaker 1: anything that carries a charge, so like an electron, a muon,
[19:48] Speaker 1: a proton, these will leave a trace in your silicon.
[19:53] Speaker 1: But sometimes a non-trace is useful because if you see
[19:56] Speaker 1: like a trace downstream in a different kind of detector
[19:59] Speaker 1: that like can see neutrons and then no trace in
[20:02] Speaker 1: your silicon, That's a confirmation. Oh, that probably was a
[20:05] Speaker 1: neutron because it didn't leave a trace here in the silicon.
[20:09] Speaker 1: And that's the kind of thing we put together later.
[20:10] Speaker 1: We say like, okay, you have information from this layer
[20:13] Speaker 1: and then that layer and the other layer. And all together,
[20:15] Speaker 1: it'll tell you what kind of particle it was. So
[20:18] Speaker 1: the inner detector mostly responds to charge particles. Then the
[20:22] Speaker 1: whole thing is immersed in a magnetic field. So the
[20:25] Speaker 1: particles bend. And that lets us know the charge of
[20:28] Speaker 1: the particle and its momentum. Because only charged particles bend
[20:32] Speaker 1: in magnetic fields. And if they're charged positive, they bend
[20:35] Speaker 1: one way. If they're charged negative, they bend the other way.
[20:38] Speaker 1: So we can tell if it's a positive or negative charge.
[20:41] Speaker 1: And if it's going really fast, it hardly bends at all.
[20:44] Speaker 1: If it's going really slow, it bends a lot. So
[20:47] Speaker 1: by measuring that curvature, we can tell how fast was
[20:50] Speaker 1: it going.
[20:51] Speaker 2: This does sound like a pretty difficult experiment. Like statistical
[20:54] Speaker 2: analysis that needs to happen afterwards. There's like a lot
[20:56] Speaker 2: of pieces of information that need to get integrated to
[20:58] Speaker 2: figure out what went through there.
[21:00] Speaker 1: Exactly. And historically, what we've done is simplify the problem
[21:03] Speaker 1: by doing each of those separately. Like let's first figure
[21:06] Speaker 1: out the angle of the particle, then let's combine it
[21:08] Speaker 1: with this. And along the way, we would lose information.
[21:11] Speaker 1: So the trend these days is to try to do
[21:13] Speaker 1: end-to-end analysis of the lowest level information to slurp up
[21:17] Speaker 1: as much information as possible. And that used to be
[21:20] Speaker 1: computationally intractable, but now thanks to AI and machine learning,
[21:24] Speaker 1: we're starting to do that. And that's kind of my expertise.
[21:27] Speaker 4: Cool.
[21:28] Speaker 3: And so is that all of the layers then?
[21:30] Speaker 1: No, then the outer layer measures the energy of the particles.
[21:33] Speaker 1: So the inner layer tries to figure out where the
[21:35] Speaker 1: particles went to give you like a visual picture of
[21:37] Speaker 1: the trajectories without affecting their angles, because you want to
[21:41] Speaker 1: measure their momentum. You don't want to change their direction.
[21:43] Speaker 1: So it's very lightweight. The outer layer of the detector
[21:46] Speaker 1: is the opposite. It tries to stop the particles. So
[21:49] Speaker 1: it forces them to interact and just dump their energy.
[21:53] Speaker 1: So we call that a calorimeter because it just measures
[21:55] Speaker 1: their energy and its layers of thick material that have
[21:59] Speaker 1: lots of protons in them and lots of neutrons in
[22:01] Speaker 1: them so that they'll slam into them. And even neutrons
[22:04] Speaker 1: will lose their energy there. They create a little shower
[22:06] Speaker 1: by hitting one particle, which hits another particle, which hits
[22:09] Speaker 1: another particle. And so all their energy gets dumped into
[22:12] Speaker 1: these layers and we can measure how much energy was deposited.
[22:16] Speaker 1: And so that creates like a little splash of energy
[22:18] Speaker 1: and we can tell this particle had this much energy.
[22:21] Speaker 1: So those are the two basic layers of the detector.
[22:24] Speaker 1: And that lets us figure out what was what. For example,
[22:27] Speaker 1: if you have an electron, It'll leave a trace through
[22:30] Speaker 1: your inner detector because it's charged, and then a splash
[22:33] Speaker 1: in the outer detector that looks like a little charged particle.
[22:36] Speaker 1: A photon will fly through your inner detector and leave
[22:39] Speaker 1: no trace because it doesn't have a charge. But then
[22:42] Speaker 1: it will make a splash in the outer detector that
[22:44] Speaker 1: looks just like an electron. So the difference between an
[22:47] Speaker 1: electron and a photon in our detector is, does it
[22:50] Speaker 1: have a trace in the inner detector or not? And
[22:53] Speaker 1: muons look different because they interact with the outer layer
[22:56] Speaker 1: a little bit differently, so they leave a smaller trace.
[22:59] Speaker 1: So with all these clues, we can figure out what
[23:01] Speaker 1: was there, what was going on. Some particles are really
[23:04] Speaker 1: challenging because they leave no information at all. Like a
[23:07] Speaker 1: neutrino does not interact with our detector. It's just gone.
[23:12] Speaker 1: So we have to deduce the presence of invisible particles
[23:15] Speaker 1: by looking at the balance. Like the beams come in
[23:18] Speaker 1: along the beam pipe. And so anything that shoots out
[23:20] Speaker 1: the side needs something shooting out the other side to
[23:23] Speaker 1: balance its momentum. So if you only see stuff on
[23:26] Speaker 1: one side, you know there was something invisible on the
[23:28] Speaker 1: other side. So we can deduce the existence of invisible
[23:32] Speaker 1: particles that way. And that's, for example, how we look
[23:35] Speaker 1: for dark matter. And so it's big, it's complicated, it's really,
[23:39] Speaker 1: really fun. And it's extra complicated by the fact that
[23:41] Speaker 1: these bunches come every 25 nanoseconds. <HAL> <HAL> <HAL> <HAL> <HAL> <HAL> <HAL> <HAL> <HAL> <HAL> <HAL> <HAL>
[23:47] Speaker 1: Oh my gosh. And every bunch has multiple collisions. So
[23:51] Speaker 1: sometimes you get like 200 collisions all on top of
[23:54] Speaker 1: each other, filling your detector up. with these signals and
[23:57] Speaker 1: it's really hard to disentangle them. It's good to get
[24:00] Speaker 1: lots of bunches because you have a higher chance to
[24:02] Speaker 1: see rare stuff and weird stuff you're looking for, but
[24:05] Speaker 1: it's harder to analyze because they're all on top of
[24:07] Speaker 1: each other. And sometimes something will take a while to
[24:11] Speaker 1: drift to the detector and will leave energy that deposits
[24:14] Speaker 1: across several bunches. And that's extra complicated because it's out
[24:18] Speaker 1: of time. And so, you know, everything is happening as
[24:21] Speaker 1: fast as possible. to get as many collisions as possible,
[24:25] Speaker 1: to look for the weirdest, rarest stuff, but that makes
[24:28] Speaker 1: it harder to understand the data.
[24:30] Speaker 2: So this system is like absolutely amazing and incredibly impressive,
[24:34] Speaker 2: like human ingenuity, wow. But if you were magic and
[24:38] Speaker 2: you could have one extra layer in there, is there
[24:41] Speaker 2: something else you would measure if we knew how to
[24:44] Speaker 2: do it or could afford to do it? Or is
[24:45] Speaker 2: this everything you could possibly want?
[24:48] Speaker 1: There's always more angles you can use by getting more information. Like,
[24:53] Speaker 1: for example, sometimes you can add timing information to these detectors. Like,
[24:58] Speaker 1: you can tell exactly when it was hit. So you
[25:01] Speaker 1: can deduce, like, how long it took the particle to
[25:04] Speaker 1: fly from here to there. And you can tell, like,
[25:06] Speaker 1: is it out of time? Is it from another bunch?
[25:09] Speaker 1: Or in the tracking detectors, sometimes you can do more
[25:12] Speaker 1: than just say, was there a particle here? You can measure, like,
[25:16] Speaker 1: how much energy deposited, like, per millimeter. And that can
[25:20] Speaker 1: help you discriminate between different kinds of particles. some of
[25:23] Speaker 1: which are ionized more strongly and some of which ionize
[25:26] Speaker 1: less strongly, or new weird models of particles with strange interactions.
[25:31] Speaker 1: And so there's always more depth that you could add
[25:34] Speaker 1: to these things if you have the money to build
[25:36] Speaker 1: more instrumentation. But I think the most powerful thing is
[25:39] Speaker 1: just more layers. If we had more money, we could
[25:43] Speaker 1: have more layers in these detectors, it would give us
[25:45] Speaker 1: a clearer picture of what's going on and helping us disentangle.
[25:49] Speaker 1: Like if you have a hundred layers, you do a
[25:51] Speaker 1: better job than if you have 10 layers of figuring
[25:53] Speaker 1: out like which particle was going where. So that's where
[25:57] Speaker 1: I would put the money.
[25:57] Speaker 2: So Okay, our third question of the day is from Mark,
[26:21] Speaker 2: and Mark is asking about something I have never heard
[26:24] Speaker 2: of before.
[26:26] Speaker 1: Hi, Dr.
[26:27] Speaker 4: Dan. I'm just a little perplexed about the sitter space.
[26:31] Speaker 3: I don't kind of get it. Would you be able
[26:33] Speaker 3: to explain it to me as though I'm a five-year-old?
[26:35] Speaker 4: Thank you.
[26:37] Speaker 2: Okay, Daniel, is De Sitter Space the place where the
[26:39] Speaker 2: babysitter tends to sit when they come to watch your kids?
[26:44] Speaker 1: De Sitter Space is named after a very smart dude,
[26:47] Speaker 1: Willem De Sitter, who died in 1934. He was a
[26:51] Speaker 1: professor in Leiden. And he worked closely with Albert Einstein
[26:55] Speaker 1: and thought a lot about the universe and the shape
[26:57] Speaker 1: of the universe and the nature of space itself. And
[27:00] Speaker 1: he came up with sort of a really useful thought
[27:02] Speaker 1: experiment for how to think about the universe in a
[27:05] Speaker 1: clear way. And that's called de-sitter space. And so we
[27:10] Speaker 1: have this tradition in physics of naming things after the
[27:13] Speaker 1: people who came up with them. And I think it's
[27:16] Speaker 1: a little awkward when that person's name starts with one
[27:20] Speaker 1: of these like prepositions, you know, like de or of, or,
[27:23] Speaker 1: you know, there's a guy in the Netherlands, his name
[27:26] Speaker 1: is tehoeft, you know, T apostrophe. But, you know, that's
[27:30] Speaker 1: what happened. So we call it de-sitter space.
[27:33] Speaker 2: So when you come up with something, do you just
[27:34] Speaker 2: have to hope that people will go ahead and name
[27:37] Speaker 2: it after you and they won't, like, miss that opportunity?
[27:39] Speaker 2: Or do you go ahead in your paper and say,
[27:41] Speaker 2: let's go ahead and call it DeSitter Space. Don't miss
[27:43] Speaker 2: that I came up with this.
[27:44] Speaker 1: You don't call it that yourself. You hope that people
[27:46] Speaker 1: refer to it. If it's a really useful idea, they'll
[27:49] Speaker 1: refer to it later as, you know, the Wienersmith model or,
[27:54] Speaker 1: you know, the Goldstone boson or whatever it is. Yang-Mills theory.
[27:58] Speaker 1: This is coined by other people who refer to it.
[28:01] Speaker 1: And this is sort of controversial. You know, like the
[28:04] Speaker 1: reason the Higgs boson is called the Higgs boson is
[28:07] Speaker 1: because Steven Weinberg started referring to it that way in
[28:10] Speaker 1: his papers because he just looked at the papers and
[28:13] Speaker 1: which ones arrived first at the journal first. And he thought, well,
[28:17] Speaker 1: that's the end of the story. Higgs paper arrived first
[28:19] Speaker 1: at the journal. But actually, he was reading the order
[28:22] Speaker 1: of the dates of publication and other papers arrived first.
[28:26] Speaker 1: And there was a team of young postdocs whose paper
[28:29] Speaker 1: arrived later, but was done independently. And they were nice
[28:32] Speaker 1: and they cited Higgs just like to be kind, even
[28:35] Speaker 1: though their work was totally independent. And so folks like
[28:38] Speaker 1: Weinberg thought that their work must be derivative because they
[28:42] Speaker 1: cited Higgs and didn't give them any credit. And they
[28:44] Speaker 1: were actually cut out of the Nobel prize 50 years
[28:46] Speaker 1: later because of that. I'm not blaming Weinberg. It's like
[28:50] Speaker 1: an innocent mistake, but this stuff is important. Yeah.
[28:53] Speaker 4: Okay.
[28:54] Speaker 1: Down the road.
[28:56] Speaker 4: All right.
[28:56] Speaker 3: So we've got a thing called de Sitter space. What
[28:58] Speaker 3: is de Sitter space?
[29:00] Speaker 4: All right.
[29:00] Speaker 1: So we live in a complicated universe because we have
[29:03] Speaker 1: matter and we have radiation and And matter and radiation,
[29:07] Speaker 1: what does it do to the universe? It tends to
[29:09] Speaker 1: collapse it, right? Like it pulls things together. And if
[29:13] Speaker 1: we had more matter in the universe, it would collapse
[29:15] Speaker 1: the universe more. We also have things like dark energy.
[29:19] Speaker 1: Dark energy is accelerating the expansion of the universe. It's
[29:22] Speaker 1: pushing stuff apart. So these two things are working against
[29:25] Speaker 1: each other. Dark energy is expanding space. Matter is collapsing space.
[29:30] Speaker 1: So that's complicated. And De Sider thought, well, let's think
[29:33] Speaker 1: of a simpler universe. What would happen if you had
[29:36] Speaker 1: a universe with no matter in it at all? No photons,
[29:39] Speaker 1: no electrons. nothing except for dark energy. So at the time,
[29:44] Speaker 1: they called that a positive cosmological constant, something to expand
[29:48] Speaker 1: the universe. And the interesting thing about that, even though
[29:52] Speaker 1: it sounds kind of boring because you've got like no
[29:54] Speaker 1: cats and no lava and nothing, is that in that universe,
[29:58] Speaker 1: space still expands.
[30:00] Speaker 3: Okay.
[30:00] Speaker 1: And so the point is empty space is not really empty.
[30:05] Speaker 1: It has this cosmological constant, has dark energy. And so
[30:08] Speaker 1: it can still do stuff. Empty space can still expand,
[30:13] Speaker 1: which is like, it's weird enough to think about the
[30:15] Speaker 1: universe expanding by like making new space between galaxies and
[30:20] Speaker 1: Now we're talking about the universe expanding and there's nothing
[30:23] Speaker 1: in it. And still it's getting bigger, which is like, okay,
[30:28] Speaker 1: the space between what are you talking about? Because we
[30:31] Speaker 1: say on the show a lot, and I think it's true,
[30:33] Speaker 1: that space is just the distances between stuff, right? You
[30:36] Speaker 1: have pairs of objects and you measure the distance between
[30:39] Speaker 1: the stuff. That's what space is. It's just a list
[30:42] Speaker 1: of distances between objects. So in a universe with nothing
[30:46] Speaker 1: in it, what does it mean to have distances? And
[30:49] Speaker 1: so There's a bit of a technical distinction here. We
[30:52] Speaker 1: say the universe has nothing in it, but when we
[30:53] Speaker 1: talk about distances, we imagine two observers in the universe
[30:58] Speaker 1: and measuring the distance between them. So when we talk
[31:01] Speaker 1: about disorder space, we don't literally mean a totally empty universe.
[31:04] Speaker 1: We mean a universe with nothing in it except for
[31:07] Speaker 1: two observers who are measuring the distance between them in
[31:11] Speaker 1: free fall. And if they just sit in the universe
[31:14] Speaker 1: and it has nothing in it but dark energy, they
[31:16] Speaker 1: will notice space expanding between them.
[31:20] Speaker 4: Okay.
[31:20] Speaker 3: So dark energy is all you need for expansion.
[31:23] Speaker 1: Dark energy is all you need for expansion. Exactly. And
[31:26] Speaker 1: that's the point of De Sitter Space. You strip it
[31:28] Speaker 1: all down, remove the matter, remove the radiation, and what
[31:32] Speaker 1: you get is De Sitter Space. So this is named
[31:35] Speaker 1: after William De Sitter, who thought about this solution in
[31:37] Speaker 1: the early 20th century. And they were trying to understand
[31:42] Speaker 1: what is the vacuum? What is space? What is the universe?
[31:44] Speaker 1: How does it work? What do you need? And a
[31:47] Speaker 1: common trick in physics is think about the extreme version
[31:50] Speaker 1: because often that's easier to calculate and it tells you something.
[31:54] Speaker 1: It tells you about the direction of the solutions, right?
[31:57] Speaker 1: Like that's what a black hole is. It's an extreme
[31:59] Speaker 1: version of gravity. This is the opposite of that. It's
[32:02] Speaker 1: like take away all the matter. What happens? Oh, interesting.
[32:05] Speaker 1: It still expands, right? And the expansion still accelerates. And
[32:11] Speaker 1: so it's sort of like your classic raisins and a bread,
[32:15] Speaker 1: except there's no raisins and there's no bread, but it's
[32:19] Speaker 1: still expanding and expansion still continues indefinitely.
[32:23] Speaker 2: And was this something that we would not have realized
[32:26] Speaker 2: without this thought exercise? I mean, I guess that must
[32:29] Speaker 2: be why it got a name is because this was
[32:31] Speaker 2: not something we had realized until he set out this
[32:33] Speaker 2: thought experiment.
[32:34] Speaker 1: Yeah, this is very early in general relativity, right? We
[32:38] Speaker 1: are sort of familiar with this. We're comfortable with the idea.
[32:40] Speaker 1: We've even observed this expansion. This is many decades before
[32:45] Speaker 1: we observed the accelerating expansion of the universe. This is
[32:48] Speaker 1: back when people were still playing around with general relativity
[32:50] Speaker 1: and trying to understand why. what does it predict? And thinking,
[32:53] Speaker 1: does that make any sense? Remember earlier, Einstein, when he
[32:57] Speaker 1: was developing his theory of general relativity, he thought the
[32:59] Speaker 1: universe was static. And so his solution suggested, oh, if
[33:03] Speaker 1: you just have a bunch of mass in the universe,
[33:05] Speaker 1: it'll just collapse. And our universe hasn't collapsed. So he
[33:08] Speaker 1: was like, hmm, that's weird. So he added in basically
[33:11] Speaker 1: dark energy to balance that, to make the universe static.
[33:15] Speaker 1: Then later we discovered, oh, the universe is not static.
[33:18] Speaker 1: It's expanding. So he got rid of dark energy and
[33:20] Speaker 1: just thought, while the universe is shooting out in every
[33:23] Speaker 1: direction and it is collapsing, it just hasn't collapsed yet.
[33:27] Speaker 1: And then later we discovered, oh no, it's not collapsing
[33:30] Speaker 1: at all. It's accelerating. And so to put the dark
[33:32] Speaker 1: energy back in and say, okay, it's expanding and there's
[33:37] Speaker 1: this force increasing the expansion.
[33:39] Speaker 3: Okay. Got it.
[33:40] Speaker 1: So this is very early on. People are trying to
[33:42] Speaker 1: understand what this means. And when you create a universe
[33:45] Speaker 1: like this, that's filled with nothing except for dark energy,
[33:48] Speaker 1: there's still weird stuff that happens and that's insightful. Like
[33:52] Speaker 1: there's still a horizon. Like because of the accelerated expansion
[33:56] Speaker 1: of the universe, there are parts of space where the
[33:58] Speaker 1: expansion means we will never see them. Like a photon
[34:02] Speaker 1: that's shot out from far enough away will never get
[34:05] Speaker 1: here because the expansion of space between us and the
[34:09] Speaker 1: thing that shot out the photon is happening faster than
[34:11] Speaker 1: the speed of light. Basically space is being created Faster
[34:15] Speaker 1: than the photon is going through it.
[34:16] Speaker 4: Whoa.
[34:16] Speaker 1: So it'll just never get here, right? It's like somebody's
[34:19] Speaker 1: creating new track in front of it constantly. And so
[34:22] Speaker 1: it's never going to get to where it's going.
[34:24] Speaker 4: Wow.
[34:24] Speaker 1: And that happens even in an empty universe. And so
[34:28] Speaker 1: you have this cosmic horizon in desider space, which is
[34:32] Speaker 1: weird to think about because the universe is empty. But
[34:36] Speaker 1: it does lead to fascinating consequences, right? Like later on,
[34:39] Speaker 1: people were thinking about desider space and they were like, huh,
[34:43] Speaker 1: you have a horizon. How does that interact with quantum mechanics?
[34:47] Speaker 1: Because we know that if you have a black hole
[34:49] Speaker 1: event horizon, that that generates radiation. Because quantum mechanical fields
[34:55] Speaker 1: near an event horizon will generate radiation. That's Hawking radiation.
[34:59] Speaker 1: And so people have done calculations and realized that this
[35:03] Speaker 1: kind of horizon, the cosmic horizon in the center space,
[35:07] Speaker 1: also interacts with quantum fields in the same way and
[35:09] Speaker 1: also generates radiation. So if you are an observer in
[35:14] Speaker 1: an expanding universe in desider space, you will see radiation
[35:20] Speaker 1: from the cosmic horizon. So they call this a thermal bath.
[35:24] Speaker 1: They will just be like photons and other particles created
[35:27] Speaker 1: from this horizon. And we've dug into like, what is
[35:31] Speaker 1: Hawking radiation? What is it not? How does it work
[35:33] Speaker 1: another time? For now, just remember that having a horizon
[35:37] Speaker 1: and having quantum mechanics means radiation. And so that happens
[35:41] Speaker 1: even in an empty universe.
[35:43] Speaker 4: Wow.
[35:43] Speaker 1: De Sitter space, you see this radiation, which is kind
[35:47] Speaker 1: of cool.
[35:48] Speaker 3: That is kind of cool.
[35:49] Speaker 1: Yeah. So basically it provides like, you know, a laboratory
[35:52] Speaker 1: for thinking about horizons and quantum fields and gravity and
[35:55] Speaker 1: what is empty space anyway. And the cool thing is
[35:59] Speaker 1: that our universe is becoming more De Sitter like every day.
[36:03] Speaker 3: What does that mean?
[36:04] Speaker 1: Well, De Sitter space is a universe that's just dark energy.
[36:08] Speaker 1: Everything else is gone. And our universe is heading that
[36:11] Speaker 1: way because as the universe expands, dark energy does not dilute.
[36:17] Speaker 1: You make new space, it comes with more dark energy.
[36:20] Speaker 1: But matter does get diluted. You make new space, you
[36:22] Speaker 1: don't make new protons and electrons. Proton energy density goes down.
[36:27] Speaker 1: And new space means more dark energy, which means more space,
[36:31] Speaker 1: which means more dark energy. So the dark energy fraction
[36:33] Speaker 1: of the universe is going up. Around 6 billion years ago,
[36:37] Speaker 1: it began to dominate. And now it's even more dominant.
[36:41] Speaker 1: And in another 10 billion years, it'll be even more dominant.
[36:44] Speaker 1: And in a trillion years, the universe will be 99.99
[36:47] Speaker 1: whatever percent dark energy. And the sitter space is a
[36:52] Speaker 1: universe that's 100% dark energy. So we're moving towards the
[36:55] Speaker 1: sitter space, basically, as the universe gets more and more
[36:58] Speaker 1: spread out. And we transition to like a bunch of
[37:01] Speaker 1: huge black holes separated by vast expanding distances. That's like
[37:07] Speaker 1: almost De Sitter space. It's De Sitter space with a
[37:09] Speaker 1: bunch of big black holes scattered through it. They can't
[37:13] Speaker 1: really do anything.
[37:14] Speaker 4: Wow.
[37:14] Speaker 3: So, okay.
[37:15] Speaker 2: So if dark energy is all you need to create
[37:17] Speaker 2: an expanding universe, when we get more dark energy, does
[37:20] Speaker 2: that mean we should predict that the universe will keep
[37:23] Speaker 2: accelerating and maybe it'll keep speeding up and we'll get
[37:27] Speaker 2: more radiation at the horizon over time?
[37:31] Speaker 1: Yes, but that radiation is really, really tiny, like absurdly
[37:34] Speaker 1: tiny because dark energy is not that dense, right? It's
[37:38] Speaker 1: a very small amount of dark energy per unit of space.
[37:41] Speaker 1: So I don't know that we'll ever be able to
[37:42] Speaker 1: see that. The other interesting thing about De Sitter space
[37:45] Speaker 1: is that there's the opposite thought experiment as well. So
[37:49] Speaker 1: dark energy creates positive curvature. It's expanding the universe. You
[37:54] Speaker 1: can also imagine a universe where you have nothing but
[37:57] Speaker 1: negative curvature. So the universe is collapsing. And so that's called.
[38:01] Speaker 3: Is this going to be... De-stander space?
[38:03] Speaker 1: I'm going to take a nap space. Yeah, exactly. Nice, nice. No,
[38:11] Speaker 1: they're not that clever. They call it anti-de-sitter space.
[38:13] Speaker 3: Oh, okay.
[38:14] Speaker 1: It's the opposite. And if you hear about holography and
[38:18] Speaker 1: something called ADS-CFT, which is a big deal in string
[38:23] Speaker 1: theory and fundamental physics and a huge step forward by
[38:26] Speaker 1: Juan Maldicena, something like 20 years ago, because it connects
[38:30] Speaker 1: quantum mechanics and gravity. It shows you that some theories
[38:34] Speaker 1: of gravity which live in anti-de Sitter space are the
[38:38] Speaker 1: same as theories of quantum mechanics in conformal field theories. ADS,
[38:44] Speaker 1: anti-de Sitter space, CFT, conformal field theories. A big result
[38:48] Speaker 1: in quantum gravity because it showed for the first time
[38:51] Speaker 1: that there are some gravitational theories that are very similar
[38:53] Speaker 1: to quantum theories. That's cool. But that's what ADS stands
[38:57] Speaker 1: for in ADS CFT. And The big fly in the
[39:01] Speaker 1: ointment is that it only works for anti-de-sitter space, right?
[39:05] Speaker 1: Whereas we live in a de-sitter universe. So the whole
[39:09] Speaker 1: quantum gravity step forward of ADS-CFT is relevant to the
[39:13] Speaker 1: opposite kind of universe than the one that we live in. Which,
[39:17] Speaker 1: you know, doesn't mean one day somebody won't figure out
[39:19] Speaker 1: how to do it in de-sitter space instead of anti-de-sitter space. But,
[39:24] Speaker 1: you know, it means it's further from being relevant.
[39:27] Speaker 3: All right. All right, Mark. Find de-space. to sit down
[39:31] Speaker 3: and let us know what you think of this answer.
[39:34] Speaker 2: Wow.
[39:35] Speaker 3: Thanks, Dan and Kelly. What a concept.
[39:39] Speaker 4: I think I've got a bit more of a handle
[39:42] Speaker 4: on it now. Thanks very much. All right.
[39:45] Speaker 1: Thank you very much, everybody, for sending in those questions.
[39:48] Speaker 1: I love hearing from you. I love your questions. Please
[39:51] Speaker 1: write to us, questions at danielandkelly.org. It literally makes our day.
[39:56] Speaker 3: It does. Until next time.
[40:04] Speaker 1: Thanks, everybody, for listening. Please go and do us a
[40:06] Speaker 1: favor and rate the show on whatever podcast app you're using.
[40:10] Speaker 1: It really helps people find us.
[40:12] Speaker 2: Daniel and Kelly's Extraordinary Universe is edited by the amazing
[40:16] Speaker 2: Matt Kesselman.
[40:17] Speaker 1: He really is a wizard. You can also find us
[40:20] Speaker 1: online on Blue Sky, Instagram, and X, D & K Universe.
[40:25] Speaker 1: Come engage with us.
[40:27] Speaker 2: You can email us at questions at danielandkelly.org. We really
[40:31] Speaker 2: do want to hear from you.
[40:32] Speaker 1: And you can find our website, www.danielandkelly.org, where you'll also
[40:38] Speaker 1: find an invitation to join our Discord, where everybody comes
[40:41] Speaker 1: and talks about the amazing universe.
[40:43] Speaker 2: And we also have the most amazing moderators. This is
[40:47] Speaker 2: an iHeart podcast. Thanks for joining us.

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