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What is dark radiation? · Daniel and Kelly’s Extraordinary Universe

0:08
Speaker 1: Hey, Daniel, how do you like your coffee? Oh? I
0:10
Speaker 1: like it very dark, basically black. What about your chocolate?
0:15
Speaker 1: Also pretty dark? Maybe? Like? What about your wine? How
0:20
Speaker 1: do you drink your wine? Well? I like a pretty
0:22
Speaker 1: dark cabernet. Actually, now, are you optimistic about the fate
0:26
Speaker 1: of humanity? You know, I'll be honest until we start
0:28
Speaker 1: dismantling more nuclear weapons. I have a pretty dark view
0:31
Speaker 1: of our future. You kind of a dark physicist. Maybe
0:36
Speaker 1: you should lighten up a little, you know, try some dessert, wine,
0:38
Speaker 1: some rose, maybe maybe even some white chocolate. No, no, no, man,
0:42
Speaker 1: we live in a dark universe where dominated by dark matter,
0:45
Speaker 1: dark energy, and dark chocolate. You know what Yoda says,
0:50
Speaker 1: once you go into the dark side, forever your destiny
0:54
Speaker 1: well dominate. Do you think Yoda like dark chocolate? I
0:59
Speaker 1: always knew you were a dark fisicist. Daniel. Hi am
1:18
Speaker 1: poor handmade cartoonists and the creator of PhD comics. Hi,
1:21
Speaker 1: I'm Daniel. I'm a particle physicist and a professor UC Irvine.
1:25
Speaker 1: And white chocolate is not chocolate. It is chocolate. Then
1:28
Speaker 1: it's made from chocolate, made from chocolate, not the same
1:31
Speaker 1: as chocolate. You just don't like it. You still want
1:35
Speaker 1: to categorize this chocolate, But scientifically, I think if you
1:38
Speaker 1: asked a you know, chemist, they would say it's a
1:41
Speaker 1: it's chocolate. I don't know. I think it doesn't have
1:43
Speaker 1: any cocoa in it. It can't be chocolate. Doesn't taste
1:47
Speaker 1: like chocolate. You know, white chocolate is chocolate the same
1:49
Speaker 1: way deep dish pizza is pizza. But you do know
1:52
Speaker 1: it's made from chocolate, right, Like I think it uses
1:54
Speaker 1: like the cocoa butter from chocolate beans. Yeah, it's sort
1:57
Speaker 1: of like hangs around when chocolate is made, sort calls
2:00
Speaker 1: itself chocolate nearby it's chocolate and I'll give it that much.
2:05
Speaker 1: Oh man, how can it be a jacent if it
2:07
Speaker 1: comes from chocolated Daniel, I think you're stretching things a
2:10
Speaker 1: little bit here. My kids are coming from chocolate, but
2:13
Speaker 1: they're not chocolate, right. You should be more candy inclusive, Tenny,
2:17
Speaker 1: white chocolate is delicious. It's just not chocolate. But welcome
2:20
Speaker 1: to our podcast. Daniel and jorhead the Bait Chocolate apparently
2:23
Speaker 1: for an hour instead of talking about physics and explain
2:26
Speaker 1: the universe, in which we explore all the questions out there,
2:29
Speaker 1: the dark ones, the white ones, the milky ones, all
2:32
Speaker 1: the questions of the universe that are rattling around in
2:34
Speaker 1: your brain and in hours, the questions that make us human,
2:38
Speaker 1: the questions that make us wonder why the universe is
2:42
Speaker 1: this way and not some other way? Could it have
2:44
Speaker 1: been this way? Did it have to turn out in
2:46
Speaker 1: this particular manner? What are the rules of this universe?
2:49
Speaker 1: And is it possible for them to make sense to us?
2:51
Speaker 1: And is it possible for Daniel and Jorge to explain
2:54
Speaker 1: them to you in less than an hour while eating chocolates? Apparently,
2:57
Speaker 1: but only dark or milk? What about chocolate? Are you
3:00
Speaker 1: a fan of milk chocolate? Milk chocolate is chocolate. But
3:03
Speaker 1: I'm not a fan, I see, And there are different
3:07
Speaker 1: categories here of exclusion for you. Oh yeah, I got
3:09
Speaker 1: a whole matrix going here. But it is an amazing
3:12
Speaker 1: and beautiful and sometimes even delicious universe, full of amazing
3:15
Speaker 1: mysteries and tantalizing questions to answer and discover out there,
3:19
Speaker 1: and fortunately humans are here for all of it, to
3:21
Speaker 1: answer these questions and to wonder about the amazing things
3:25
Speaker 1: that are out there. That's right, and one of the
3:27
Speaker 1: most basic questions we ask about the universe is just
3:30
Speaker 1: what's in it? What's out there in the universe sharing
3:33
Speaker 1: this cosmos with us. There's this sense that if you
3:36
Speaker 1: could like make an accounting of all the stuff, all
3:38
Speaker 1: the forces in the matter, and all the particles in
3:41
Speaker 1: the universe, you'd get a sense for why the universe
3:44
Speaker 1: is the way that it is the way. For example,
3:47
Speaker 1: if you'd like looked at the ingredients of a pizza,
3:49
Speaker 1: you can get a sense for, like what makes a
3:51
Speaker 1: pizza a pizza. Yeah, because for thousands of years, we
3:54
Speaker 1: thought that, you know, the stuff that we were made
3:56
Speaker 1: out of was all there was too stuff, you know,
3:59
Speaker 1: the electron and corks and protons and neutrons that we're
4:02
Speaker 1: made out of. We thought that was the whole thing
4:04
Speaker 1: that was in the universe. But actually it turns out
4:06
Speaker 1: that most of the universe is made out of something else,
4:09
Speaker 1: something dark and mysterious. Yes, And the history of physics
4:13
Speaker 1: is these waves of realization, discovering that we are not
4:16
Speaker 1: at the center of the universe, we are not at
4:18
Speaker 1: the center of the Solar system, we are not really
4:20
Speaker 1: at the center of anything, and then discovering that our
4:23
Speaker 1: kind of matter is not even that special that we
4:25
Speaker 1: make up a tiny little fraction of this incredible universe pizza.
4:29
Speaker 1: Oh boy, Daniel, are you saying we are universe at Jason.
4:32
Speaker 1: We're not really part of the universe. We're not really
4:34
Speaker 1: universe material. We're sort of dark matter adjacent, right, We're
4:39
Speaker 1: around when the dark matter formed all this structure. We
4:42
Speaker 1: sort of like we're followers, but we're not dark matter. Yeah.
4:46
Speaker 1: Do you think there's some snob courmet I don't know,
4:48
Speaker 1: universe eater out there judging us talking down about the
4:52
Speaker 1: humanity and all the stars and planets and galaxies in
4:55
Speaker 1: the universe, saying that's not really universe. Yeah, I hope. So,
4:58
Speaker 1: I hope that there are some dark a adans out
5:00
Speaker 1: there made of dark matter, with their incredibly dark dark
5:03
Speaker 1: chocolate made of dark matter, and they're looking at our
5:05
Speaker 1: dark chocolate. They're like, that's ridiculous. Well, I guess the
5:09
Speaker 1: good news is they they're not gonna eat us, because
5:12
Speaker 1: if they're there's nobby about it, like you are white chocolate.
5:16
Speaker 1: That's good news for the white chocolate. Yeah. Here ago
5:18
Speaker 1: you can turn anything into positive news. I appreciate that. Yeah,
5:21
Speaker 1: but there is a lot of dark matter in the universe.
5:23
Speaker 1: In fact, it's most of the stuff in the universe
5:25
Speaker 1: is dark matter. Of the stuff in the universe. I mean,
5:27
Speaker 1: that's right. Even though we can't see it directly, we
5:30
Speaker 1: can tell that dark matter is there, that it's a
5:32
Speaker 1: thing that is affecting the whole shape of the universe.
5:35
Speaker 1: It affected their universe early on and its little wiggles
5:38
Speaker 1: and jiggles. It affected the formation of structure in the universe.
5:41
Speaker 1: It even shapes how galaxies spin today. So we know
5:45
Speaker 1: that it's there, we know that it's out there, and
5:46
Speaker 1: we know that it dominates the universe in terms of
5:49
Speaker 1: like the budget of the universe is mostly dark matter,
5:52
Speaker 1: not what we used to call normal matter. I e us. Yeah,
5:56
Speaker 1: it's something like, what's the exact budget percentage of dark
5:58
Speaker 1: matter in the universe compared to the regular stuff we're
6:00
Speaker 1: made out of. It's about five to one dark matter
6:03
Speaker 1: to normal matter, all right, So then that's like eight
6:06
Speaker 1: percent of the universe is sort of dark matter. Yeah,
6:09
Speaker 1: eighty percent of the universe. So you could almost neglect
6:12
Speaker 1: our part of the universe and you still got to
6:14
Speaker 1: be on your exam Befo, bueno, that's right, bueno. Barry
6:20
Speaker 1: on is exactly. Yeah, you could ignore all the atoms
6:23
Speaker 1: in the universe and that would only be five percent
6:26
Speaker 1: of the energy in the universe or twenty percent of
6:28
Speaker 1: the matter in the universe. So in some sense, the
6:30
Speaker 1: question what is the universe made out of? What is
6:33
Speaker 1: all this crazy stuff? Tells you that what we're made
6:36
Speaker 1: out of is not a big part of it is
6:38
Speaker 1: not a central element in the structure of the universe. Right,
6:41
Speaker 1: And just to clarify, most of this stuff and energy
6:44
Speaker 1: in the universe is dark energy, which is something totally different.
6:48
Speaker 1: But if we're just talking about stuff like matter, things
6:50
Speaker 1: that feel gravity, then most of it is dark matter.
6:54
Speaker 1: That's right. The matter portion of the universe is about
6:57
Speaker 1: and of that thirty percent, eight percent that is dark matter.
7:03
Speaker 1: So if the matter portion of the universe it is
7:06
Speaker 1: dark matter, well that's pretty amazing. It's almost like most
7:08
Speaker 1: of the stuff in the universe is this other stuff
7:10
Speaker 1: called dark matter, but we don't know actually what it is, right,
7:13
Speaker 1: It's pretty mysterious. We've only know it's there, we haven't
7:16
Speaker 1: actually seen it directly because it's dark. Yeah, but it's
7:19
Speaker 1: a great story. You know. I got into physics for
7:22
Speaker 1: exactly these kinds of realizations, discovering that the universe out
7:26
Speaker 1: there is not the one that you thought it was,
7:28
Speaker 1: or that scientists and deep thinkers for thousands of years
7:31
Speaker 1: hadn't known the true picture of the universe. You know.
7:34
Speaker 1: Physics is this incredible technique to like reveal the truth
7:38
Speaker 1: about the universe, to methodically build up knowledge and tell
7:42
Speaker 1: us what's actually out there. So for it to discover
7:45
Speaker 1: something shocking, like an enormous plot twist, like wow, it
7:48
Speaker 1: turns out most of the stuff in the universe out
7:50
Speaker 1: there is something you never heard about or thought about
7:53
Speaker 1: or felt before. That's fantastic and it's exactly the kind
7:56
Speaker 1: of thing that I hope happens, you know, again and again,
7:58
Speaker 1: overturning everything we thought we knew about the universe. Yeah,
8:01
Speaker 1: we know you went into physics for dark reasons. Daniels
8:06
Speaker 1: that it's pretty close to home, given that a group
8:09
Speaker 1: in Los Almos where they invented nuclear weapons which are
8:11
Speaker 1: now being used to threaten genocide against civilian populations. So yeah,
8:15
Speaker 1: that one stings a little bit, but it might say
8:17
Speaker 1: humanity even if the media ever comes towards Earth and
8:20
Speaker 1: we you know, break it up with nuclear weapons, then
8:23
Speaker 1: then your parents would be heroes. There you go. All right,
8:25
Speaker 1: So in some scenario we are saving the Earth instead
8:28
Speaker 1: of destroying it. You know, you apply the quantum physics principle.
8:31
Speaker 1: You know, it's all true. It's just the different probabilities.
8:35
Speaker 1: There's a little white chocolate lining to that dark chocolate cloud.
8:38
Speaker 1: Oh no, that ruins it for you though. It doesn't
8:42
Speaker 1: taste as good, but it goes down easier. Yeah. Yeah,
8:44
Speaker 1: So most of the stuff in the universe is made
8:46
Speaker 1: out of dark matter, and so it kind of makes
8:48
Speaker 1: you wonder if that's all that's dark in the universe.
8:51
Speaker 1: Could there be other things in the universe that we're
8:54
Speaker 1: not seeing or that we can't see. And it's certainly
8:57
Speaker 1: true that most of the universe are things that you
9:00
Speaker 1: cannot see directly. If you look out in front of you,
9:02
Speaker 1: the information that's coming to you is just from photons,
9:05
Speaker 1: and photons can only interact with things that have electric charges.
9:09
Speaker 1: For example, there are particles flying right in front of
9:12
Speaker 1: you right now that you cannot see. Billions of neutrinos
9:15
Speaker 1: coming from the Sun raining down constantly in every square
9:19
Speaker 1: centimeter per second, but they are invisible to you. So
9:22
Speaker 1: the true universe out there. The actual reality of the
9:25
Speaker 1: universe outside your skull is vastly different from the tiny
9:29
Speaker 1: slice of it that you can see. Yeah, because if
9:31
Speaker 1: we can't see of the stuff in the universe, it
9:35
Speaker 1: kind of makes me wonder what else it's doing or
9:37
Speaker 1: what else it can do, like is it maybe radiating
9:40
Speaker 1: dark forces or dark light? Exactly? Because our kind of
9:44
Speaker 1: matter does all sorts of complicated things. It doesn't just
9:47
Speaker 1: sit there right. It shoots off photons at each other.
9:50
Speaker 1: It has electromagnetic forces and strong forces and weak forces,
9:53
Speaker 1: and forms complicated things like ice cream and pizza and chocolate,
9:56
Speaker 1: and so a natural question is what's going on with
9:59
Speaker 1: the dark matter? What else can it do? Can it
10:02
Speaker 1: interact with itself in some way? So today on the podcast,
10:05
Speaker 1: we'll be asking the question what is dark radiation? Now, Daniel,
10:14
Speaker 1: this sort of sounds like an oxy moron, you know,
10:16
Speaker 1: you're almost asking like, what is not light light? Exactly?
10:19
Speaker 1: But this is the kind of game we play in
10:21
Speaker 1: physics all the time. We don't really know how to
10:23
Speaker 1: grapple with the unknown, so we tend to explore it
10:26
Speaker 1: in terms of the known. Like when we think about photons,
10:30
Speaker 1: we don't really know how to deal with the quantum objects.
10:32
Speaker 1: We say, is it a particle? Is it a wave?
10:34
Speaker 1: It's kind of both. That's kind of the same. It's
10:36
Speaker 1: a contradiction there, right, and so here that's what we're doing.
10:39
Speaker 1: We're saying, well, we know about photons, is there like
10:41
Speaker 1: another kind of like dark matter version of the photon.
10:46
Speaker 1: Were extrapolating from what we know into what we don't know. Interesting, well,
10:50
Speaker 1: it sounds like the plot device for a great science
10:52
Speaker 1: fic to novel or the next Marvel movie. You know,
10:56
Speaker 1: dark radiation. That's how you know Stephen Strange gets his
10:59
Speaker 1: powers or something. That's right. And if they are like
11:01
Speaker 1: what ten avengers made of normal matter, there should be like,
11:05
Speaker 1: you know, forty avengers made of dark matter, the dark avengers,
11:09
Speaker 1: Oh many, they can make another gazillion dark billions of dollars.
11:13
Speaker 1: That's right, and my one percent cut of that is
11:15
Speaker 1: going to be pretty sweet. Hopefully not you don't like
11:19
Speaker 1: sweet things exactly, it'll be pretty dark. Pile up those
11:23
Speaker 1: dark dollars in my dark bank account. Only pay Daniel
11:25
Speaker 1: with bitter dollars. We should start some sort of dark
11:29
Speaker 1: matter currency, that's right, dark chocolate coin. But it is
11:35
Speaker 1: a real question in physics, what is going on with
11:38
Speaker 1: the dark matter? Is it interacting with itself? Are dark
11:41
Speaker 1: matter particles shooting dark photons at each other? We just
11:46
Speaker 1: don't know. It is a dark question. And so as usual,
11:49
Speaker 1: we were wondering how many people out there had thought
11:51
Speaker 1: about this question or even know what these two words
11:55
Speaker 1: put together could mean. So, as usual, Daniel went out
11:57
Speaker 1: there into the Internet to ask people what is dark radiation?
12:01
Speaker 1: And I'm very grateful to those of you who volunteered
12:04
Speaker 1: to try to answer this question without having the opportunity
12:06
Speaker 1: to look it up or Google or get a PhD
12:09
Speaker 1: in physics first, And so thank you to all of
12:11
Speaker 1: those of you who volunteered. And if you would like
12:13
Speaker 1: to hear your voice speculating baselessly on the podcast, please
12:17
Speaker 1: don't be shy right to me. Two questions at Daniel
12:20
Speaker 1: and Jorge dot com. Has anyone tried that? They're like, oh,
12:23
Speaker 1: that's a great question, give me a seven years, I'll
12:25
Speaker 1: come back with a PhD and answer. Or is that
12:27
Speaker 1: what you do to your grad students every day? Yeah?
12:29
Speaker 1: I take the answers people give me. I'm like, oh,
12:31
Speaker 1: that's a good idea for a project, and then I
12:33
Speaker 1: go write a grand proposal based on it nice, and
12:36
Speaker 1: then you get dark bitter money for it, and my
12:39
Speaker 1: grad students spend dark bitter years working on it. Yeah.
12:41
Speaker 1: So here's what people had to say. When I figure
12:44
Speaker 1: of radiation, I think of waves being admitted from something,
12:48
Speaker 1: so that could be heat radiation, or it could be
12:50
Speaker 1: light radiation. And even when something is invisible light to
12:56
Speaker 1: humans radiation, UM, it's still quote unquote light. So dark
13:01
Speaker 1: radiation I imagine. I think it has something to do
13:05
Speaker 1: with dark energy. Probably I have to give all credit
13:09
Speaker 1: to no Degress Tyson for why I know this. But
13:12
Speaker 1: dark radiation is the mediator of dark matter particle interaction.
13:17
Speaker 1: Say that five times fast. The best analogy for it is, um,
13:21
Speaker 1: it's the dark matter equivalent of a photon. I think
13:24
Speaker 1: dark radiation is radiation coming from dark matter right away.
13:28
Speaker 1: It makes me think of dark matter and dark energy,
13:31
Speaker 1: and I know they both interact with regular matter only
13:34
Speaker 1: through gravity. So I would guess that it has something
13:39
Speaker 1: to do with how dark matter radiates away or evaporates
13:45
Speaker 1: in the same manner regular mass does with like a
13:48
Speaker 1: black hole. All right, some pretty good answers here, mostly questions.
13:53
Speaker 1: I feel like people answered back with some questions too. Yeah,
13:55
Speaker 1: and people get the sense that it has something to
13:57
Speaker 1: do with dark matter or dark inner g right, because
14:00
Speaker 1: people have this concept that radiation energy, and so maybe
14:03
Speaker 1: it falls into the like energy category rather than the
14:06
Speaker 1: dark matter category. So yeah, some great answers. Yeah, I
14:10
Speaker 1: feel like you've really sort of branded that word dark,
14:13
Speaker 1: Like people automatically anything you associated with the word dark,
14:15
Speaker 1: people know it's oh dark matter or dark energy. Yeah.
14:18
Speaker 1: The funny thing is that the word dark and physics
14:21
Speaker 1: just means we don't know anything about it. It's like
14:24
Speaker 1: hidden from us, something we can't see, and so like
14:27
Speaker 1: the only relationship between dark matter and dark energy really
14:30
Speaker 1: is that we're pretty clueless about both of them. Well,
14:33
Speaker 1: my question is, what's gonna happen when you do discover
14:35
Speaker 1: what it is and when you can see it. Do
14:36
Speaker 1: you need to change the name. Oh, that's a great question.
14:39
Speaker 1: It depends, I suppose, on whether it remains dark or not.
14:43
Speaker 1: You know, if we find some way to communicate with
14:45
Speaker 1: the dark sector with these dark particles, then they won't
14:48
Speaker 1: any longer be totally dark. So yeah, because it depends
14:52
Speaker 1: specifically on what we figure out about it. Well, you
14:54
Speaker 1: just said that it's you call it dark when you
14:56
Speaker 1: don't know anything about it. So if you do know
14:58
Speaker 1: something about it and can't see it, maybe think about
15:00
Speaker 1: changing the name to like, you know, Horhi matter or
15:03
Speaker 1: cam matter, just saying, you know, some suggestions. We'll put
15:06
Speaker 1: that on the list, right next to white chocolate matter. Yeah,
15:08
Speaker 1: I just realized its kind of running for a guy
15:10
Speaker 1: named white sun. It sounds like you have some father issues. Yeah,
15:13
Speaker 1: self loathing matter, that's what it is. That's that's pretty dark.
15:18
Speaker 1: That's pretty dark. I'm gonna go in some more dark
15:21
Speaker 1: chocolate and now feel better. Alright, So Daniel, we're going
15:23
Speaker 1: to answer this question. What is dark radiation? Which is
15:26
Speaker 1: sounds very tantalizing, it sounds cool. It sounds maybe dangerous
15:30
Speaker 1: dark radiation, or maybe dark radiation is good for you
15:32
Speaker 1: because it's the opposite of regular radiation. It's not like
15:36
Speaker 1: entire radiation like that. What you need is a dose
15:39
Speaker 1: of dark radiation that'll cure Peter Parker, right, he'll no
15:41
Speaker 1: longer be Spider Man. The you know, damage right out
15:44
Speaker 1: of you. No, dark radiation is an analog to radiation,
15:50
Speaker 1: but in dark matter. So in our kind of matter,
15:52
Speaker 1: we have you know, electrons and quarks, and they can
15:55
Speaker 1: radiate things like photons because there are forces between these particles,
15:59
Speaker 1: and so dark radiation would imagine that between dark matter
16:04
Speaker 1: particles there might be some new dark force, and that
16:07
Speaker 1: new dark force would be capable of generating dark radiation.
16:12
Speaker 1: But you know, I think technically in physics you use
16:15
Speaker 1: the word radiation for basically any particle, any quantum particle
16:19
Speaker 1: moving in a quantum field, right, I think that's isn't
16:21
Speaker 1: that the technical definition? Unfortunately, we're not totally consistent that
16:24
Speaker 1: when we talk about radiation. When we talk about radiation
16:27
Speaker 1: sort of chemically like what is producing radiation, that can
16:30
Speaker 1: include things like photons, but also, as you say, high
16:33
Speaker 1: energy particles. Here, when we talk about radiation and we
16:36
Speaker 1: distinguish it from matter, we're talking about the particles that
16:39
Speaker 1: are associated with forces rather than the particles that are
16:43
Speaker 1: associated with matter. So for example, a photon would be radiation,
16:47
Speaker 1: whereas a cork would be matter. Even if a cork
16:49
Speaker 1: moving at high speed, a chemist would call it radiation.
16:52
Speaker 1: Oh I see, So if we're going with the chemist definition,
16:55
Speaker 1: then radiation is just any particle moving kind of what
16:58
Speaker 1: if you're going, if you're going with the day annual interpretation. Here,
17:01
Speaker 1: radiation just means a force particle or like a particle
17:04
Speaker 1: associated with a force moving through space. The idea is
17:07
Speaker 1: that maybe dark matter also produces dark radiation. That's the idea,
17:11
Speaker 1: and it's a really interesting area to study because you know,
17:15
Speaker 1: we don't know what's going on with dark matter. We
17:18
Speaker 1: just know that there's a lot of it in the universe.
17:20
Speaker 1: But it's tempting to extrapolate from the kind of matter
17:23
Speaker 1: that we have, right, the kind of matter we have
17:25
Speaker 1: does all sorts of interesting crazy stuff. It feels forces,
17:28
Speaker 1: it forms complex objects like ice cream and chocolate and pizza.
17:32
Speaker 1: So we don't know what's going on with the dark matter.
17:35
Speaker 1: There's various possibilities all the way from like it's totally
17:37
Speaker 1: inert it feels no forces. It just sort of sits
17:39
Speaker 1: there and feels gravity too. It has like seventy five
17:43
Speaker 1: new forces we haven't even imagined. They're capable of forming intricate,
17:47
Speaker 1: complex things that would blow our minds. And in that scenario,
17:52
Speaker 1: those forces would be mediated by dark particles, and so
17:55
Speaker 1: those would be dark radiation, right, Because I think all
17:58
Speaker 1: we know about dark matter is that it it sort
18:00
Speaker 1: of looks like it's a big giant, fuzzy clump. But
18:03
Speaker 1: that's just what we can see of it. You know,
18:04
Speaker 1: it could be something really detailed and organized. We just
18:08
Speaker 1: have a very unfocused view of it. That's right, And
18:11
Speaker 1: that's because so far, our only way to learn things
18:13
Speaker 1: about dark matter, to interact with dark matter so as
18:16
Speaker 1: to figure out like where it is and what it's doing,
18:19
Speaker 1: is through gravity, and gravity is the weakest force in
18:23
Speaker 1: the universe we've discovered, and not by a little bit,
18:26
Speaker 1: but by like ten to the thirty six. It's like
18:28
Speaker 1: super duper crazy week. So it's like trying to look
18:31
Speaker 1: at dark matter, but you're looking through very very dark glasses,
18:35
Speaker 1: so you can just barely see it. You can only
18:37
Speaker 1: see huge clumps of it, and that gives us a
18:39
Speaker 1: very fuzzy view of what's going on. The glasses are
18:42
Speaker 1: made out of dark matter. I'm a little confused here.
18:44
Speaker 1: They filter dark radiation. I think you mean like fuzzy glasses. Yeah, yeah,
18:50
Speaker 1: all right, Well maybe for the people who are not
18:52
Speaker 1: familiar with dark matter, maybe give us a quick refresher
18:55
Speaker 1: of what it is and how we know it's there.
18:57
Speaker 1: So we don't know that much about dark matter, but
18:59
Speaker 1: we do know that it makes up most of the
19:01
Speaker 1: stuff in the universe, and it's some kind of matter
19:04
Speaker 1: by which we mean that it provides gravity. And you know,
19:07
Speaker 1: we invented the idea of dark matter to explain why
19:11
Speaker 1: there was gravity in the universe that we couldn't otherwise explain. So,
19:15
Speaker 1: for example, we see that galaxies are rotating really really fast,
19:18
Speaker 1: and there's apparently enough gravity to hold them together to
19:22
Speaker 1: keep the stars from going out into interstellar space being
19:24
Speaker 1: tossed out. But we can't explain where that gravity is
19:27
Speaker 1: coming from, so we say probably dark matter. And if
19:30
Speaker 1: we want to understand the structure of the universe, how
19:33
Speaker 1: it got to have these galaxies and these superclusters and
19:36
Speaker 1: all of this stuff. If you run a simulation of
19:38
Speaker 1: the universe without dark matter, then it just doesn't form
19:42
Speaker 1: galaxies and stars this quickly. You need more gravity to
19:45
Speaker 1: pull that stuff together. So we need dark matter not
19:48
Speaker 1: just to explain how galaxies are spinning, but also the
19:51
Speaker 1: whole structure of the universe. And if we look in
19:54
Speaker 1: the very early ever beginnings of the universe and we
19:57
Speaker 1: see like how wiggles in the first plasma of the
20:00
Speaker 1: universe formed, and how those wiggles propagated, they don't really
20:03
Speaker 1: make sense unless you add dark matter to our calculations.
20:07
Speaker 1: So we have a lot of evidence that dark matter
20:09
Speaker 1: is a thing, that it's out there, that it clumps
20:11
Speaker 1: together in these big structures that shaped our whole universe.
20:15
Speaker 1: We just don't really know what it's made out of
20:18
Speaker 1: other than something that gives gravity. Yeah, we we know
20:20
Speaker 1: it's there and it has to be there to explain
20:22
Speaker 1: what we see. But I think that's the crazy things
20:25
Speaker 1: that we don't know what it is, Like, we really
20:27
Speaker 1: have no idea, Like it could be a totally new
20:29
Speaker 1: kind of thing that's not even a particle, or even
20:32
Speaker 1: something sort of like cohesive. It could be anything, right, Yeah,
20:35
Speaker 1: And we've done a lot of podcast episodes diving into
20:37
Speaker 1: some of those examples. Sort Of the mainstream idea is
20:40
Speaker 1: a whim weakly interacting massive particle that's sort of like,
20:44
Speaker 1: you know, a generic idea like what's the simplest possible
20:47
Speaker 1: explanation for dark matter? But there's lots of other more
20:50
Speaker 1: exotic and fascinating ideas, from things like axions, these weird
20:54
Speaker 1: heavy photons, to things like primordial black holes formed very
20:59
Speaker 1: very early in the universe to things like super duper
21:02
Speaker 1: long wave photons generated by dark stars. So we just
21:07
Speaker 1: don't really know what it is. And as you say,
21:08
Speaker 1: it might not even be a particle. It might be
21:12
Speaker 1: that this whole idea of particles and fields and quantum
21:15
Speaker 1: forces only applies to the little bit of the universe
21:18
Speaker 1: that we've been studying for the last few hundred years,
21:20
Speaker 1: and that you can't extrapolate to the rest of the
21:22
Speaker 1: universe the same way you can't, like look at an
21:24
Speaker 1: elephant's tail and assume the rest of the elephant is
21:27
Speaker 1: like the tail. So it might be that we have
21:29
Speaker 1: dramatic mind blowing lessons to be learned about dark matter,
21:33
Speaker 1: or it could be super boring and just be one
21:35
Speaker 1: particle that doesn't do anything. Some pretty extreme possibilities there.
21:39
Speaker 1: But but are you saying that maybe, like maybe even
21:41
Speaker 1: quantum mechanics only applies to a small part of the universe.
21:44
Speaker 1: I think that's true. Yeah, All of the tests that
21:46
Speaker 1: we've done of quantum mechanics use our kind of matter
21:50
Speaker 1: and our kind of forces, and so we have a
21:52
Speaker 1: pretty good quantum description of quantum particles, but we don't
21:56
Speaker 1: really have a quantum description of gravity and gravity is
21:59
Speaker 1: our poor to dark matter. The only thing we know
22:01
Speaker 1: about dark matter is that it does feel gravity, and
22:04
Speaker 1: so it could be some other new, weird kind of
22:06
Speaker 1: thing that generates gravity but doesn't otherwise follow the rules
22:11
Speaker 1: of quantum mechanics. Well, all right, so that's a dark matter. Now,
22:15
Speaker 1: what would you say is a dark force? Besides the
22:18
Speaker 1: obvious Star Wars reference, a dark force would be anybody
22:22
Speaker 1: who tries to force me to eat white chocolate, the
22:26
Speaker 1: dark force in my life. Now, a dark force would
22:29
Speaker 1: be in the assumption that dark matter is made of
22:32
Speaker 1: particles that follow the rules of quantum mechanics like our particles,
22:36
Speaker 1: then you might imagine that they also feel some dark
22:39
Speaker 1: forces between them. You know that too. Dark matter particles
22:43
Speaker 1: can exchange some like dark photon or dark z boson
22:47
Speaker 1: or dark higgs boson that they can like push or
22:50
Speaker 1: pull on each other. They can do more than just
22:52
Speaker 1: feel each other's gravity. Maybe there's some additional dark forces
22:55
Speaker 1: and they're passing particles back and forth as a way
22:58
Speaker 1: to mediate those forces. Rights. Even the matter in our
23:01
Speaker 1: universe is sort of selective about which forces it feels
23:04
Speaker 1: or which forces they give out, right, Like some particles
23:07
Speaker 1: in our type of matter only feel like the magnetic forces,
23:11
Speaker 1: or they don't feel the strong force and things like that. Right,
23:14
Speaker 1: that's exactly right. Neutrinos, for example, only feel the weak force.
23:17
Speaker 1: They ignore the strong force, they ignore electromagnetism. Electrons they
23:22
Speaker 1: do feel electromagnetism and the weak force, but they ignore
23:25
Speaker 1: the strong force. Only the corks feel all of the forces,
23:28
Speaker 1: including the strong force. And so for an individual particle,
23:32
Speaker 1: you can ask, like whether it has a charge for
23:34
Speaker 1: that force. So electromagnetism only interact with particles that have
23:38
Speaker 1: electric charges. For example, we know that dark matter doesn't
23:41
Speaker 1: have electric charges, and it doesn't have weak charges, or
23:44
Speaker 1: it doesn't have strong charges, but it might have charges
23:47
Speaker 1: for other forces we haven't yet discovered. Wow, like there
23:51
Speaker 1: could be a whole different category of forces that we
23:54
Speaker 1: just don't happen to feel in our kind of matter,
23:57
Speaker 1: but that maybe dark matter it does feel exactly So
23:59
Speaker 1: there could be like one or forty new forces that
24:02
Speaker 1: we haven't yet discovered because our particles don't feel those,
24:05
Speaker 1: or maybe more, not just forty, maybe four thousand exactly.
24:11
Speaker 1: All right, Well, let's dig into what this new kind
24:13
Speaker 1: of force might be, this dark force and what it
24:16
Speaker 1: could all mean and whether or not we can never
24:18
Speaker 1: hope to see it or feel it. But first let's
24:20
Speaker 1: take a quick break. All right, we're talking about dark radiation,
24:36
Speaker 1: and in this case, the word radiation sort of is
24:37
Speaker 1: associated with the word force. So really we're asking does
24:41
Speaker 1: dark matter feel dark forces that maybe are out there,
24:45
Speaker 1: but that we in our kind of matter can feel
24:47
Speaker 1: or touch or detect. But then maybe it is maybe
24:50
Speaker 1: organizing dark matter into structures or maybe you know, even
24:53
Speaker 1: making dark matter particles and Adams exactly. And it's part
24:57
Speaker 1: of this imagination game we play, you know, we wonder
25:00
Speaker 1: what's going on out there in the dark universe. Is
25:03
Speaker 1: it simple, is it fascinating, is it complex? What is
25:06
Speaker 1: going on? What is they're out there to learn? And
25:09
Speaker 1: usually when we go out and explore the universe, we
25:11
Speaker 1: find that things are crazier and more fascinating and richer
25:16
Speaker 1: than we ever imagined. And so we're at this point
25:19
Speaker 1: where we really don't know about most of the universe.
25:21
Speaker 1: But at some point in the future, I hope a
25:22
Speaker 1: hundred years, five hundred years from now, we will know
25:25
Speaker 1: what's going on in the dark sector and those people
25:27
Speaker 1: will look back at our ideas as ridiculous. Probably you
25:31
Speaker 1: might think of us as the Dark Ages physics. They
25:34
Speaker 1: like the really dark ages, not that the trial run
25:36
Speaker 1: in the Middle Ages, but more serious. Yes, back when
25:40
Speaker 1: people ate white chocolate, that's right. Maybe we're looking forward
25:45
Speaker 1: to an age of dark enlightenment, in the age of oxymorons.
25:50
Speaker 1: But yeah, So in our kind of matter, we feel
25:52
Speaker 1: the electromagnetic force, which is what basically holds our atoms together.
25:57
Speaker 1: And what you know when you touch something, when you
25:58
Speaker 1: touch the table or you hold the banana, that's the
26:01
Speaker 1: force you're feeling. And that force is transmitted by a
26:04
Speaker 1: particle called the photon. So the photon is not just
26:07
Speaker 1: lighted Tosso what transmits the electromagnetic force? And so the
26:11
Speaker 1: question daniel I guess is does dark matter have the
26:13
Speaker 1: equivalent of a photon or at least an electromagnetic force field.
26:17
Speaker 1: We just don't know, and so we're playing this game
26:20
Speaker 1: of trying to extrapolate from what we do know. And
26:22
Speaker 1: in the same way that we imagine maybe dark matter
26:25
Speaker 1: is made of a particle, because we're made of particles,
26:28
Speaker 1: we wonder if there are dark forces that look like
26:31
Speaker 1: our forces. And so one of the simplest forces to
26:34
Speaker 1: understand is electromagnetism because it just has like one particle
26:38
Speaker 1: and it interacts with lots of stuff, and so a
26:41
Speaker 1: simple proposals to say, well, what if dark matter has
26:44
Speaker 1: a dark electromagnetism, meaning a dark photon. This would be
26:48
Speaker 1: a particle that has a lot of properties similar to
26:51
Speaker 1: our photon, but it would be different. You know, those
26:54
Speaker 1: dark matter particles would have like a dark electric charge
26:58
Speaker 1: and the dark photon, but only interact with particles with
27:01
Speaker 1: a dark electric charge, not ones with our electric charge
27:05
Speaker 1: and our normal vanilla photons wouldn't interact with dark matter
27:09
Speaker 1: because they don't have an electric charge, only a dark
27:12
Speaker 1: electric charge. But it wouldn't necessarily be the same or
27:16
Speaker 1: the sort of the analog of light. Right you're just
27:19
Speaker 1: saying like, maybe it's a force, and let's why not
27:21
Speaker 1: let's qual it the dark electromagnetic force. It doesn't have
27:24
Speaker 1: to be, and it could be the dark matter fields
27:26
Speaker 1: forces that are more similar to like our weak force,
27:28
Speaker 1: or forces that are more similar to our strong force,
27:31
Speaker 1: or forces that are totally different from these forces and
27:34
Speaker 1: have other new weird capacities. Right before we discovered the
27:37
Speaker 1: strong force, who could have imagined this crazy force, you know,
27:41
Speaker 1: where it gets stronger as things get further apart, and
27:43
Speaker 1: it has like eight different kinds of gluons pulling it together.
27:46
Speaker 1: It's bonkers. Nobody would have written that into the script.
27:49
Speaker 1: So it's possible that there are other kinds of forces.
27:52
Speaker 1: But if there is a dark force that's very similar
27:55
Speaker 1: to electromagnetism, then that dark photon would have properties very
27:58
Speaker 1: similar to our photon, because those properties come from the
28:01
Speaker 1: structure of the force, all right. And also it makes
28:04
Speaker 1: for a cool name, dark photon, because it kind of
28:07
Speaker 1: it trips up your brain, right, Like, how can a
28:09
Speaker 1: photon which transmits light be dark? That's right, because it
28:13
Speaker 1: transmits dark light into dark eyeballs. Oh yeah, I feel
28:18
Speaker 1: like you should maybe just call it something different. What
28:20
Speaker 1: would you call it the dark on the invisible photon?
28:23
Speaker 1: I don't know, dark on is good, But then what
28:25
Speaker 1: do you find another force? Yeah, we'll have to be
28:27
Speaker 1: even more creative with our names. We'll just have, you know,
28:30
Speaker 1: a brainstorming session with lots of chocolate, and we'll come
28:32
Speaker 1: up with something good and then and then who knows
28:35
Speaker 1: what you'll get out of it? Maybe a heart attack,
28:37
Speaker 1: all right? So dark matter might feel this new kind
28:39
Speaker 1: of or strange new kind of force, a dark force.
28:42
Speaker 1: So how would we ever detected Daniel, would we ever
28:45
Speaker 1: hope to feel it or you know, know it's there
28:47
Speaker 1: if we can't touch it or see it. So in
28:49
Speaker 1: the end, this question is really asking what dark matter
28:53
Speaker 1: does to itself? You know, can we speculate about what's
28:56
Speaker 1: going on in the dark sector beyond these particles existing
28:59
Speaker 1: can like touch each other and become sticky and do stuff,
29:03
Speaker 1: And so we have sort of two ways to probe this.
29:05
Speaker 1: The first category is sort of like indirect ways to
29:07
Speaker 1: look at it, and broadly speaking, we can tell that
29:10
Speaker 1: dark matter is doing things because of its gravity. And
29:13
Speaker 1: even though it's not a great way to study dark matter,
29:16
Speaker 1: we can use its gravitational effects to ask questions like
29:19
Speaker 1: is it clumping? Is it interacting with itself? Because if
29:22
Speaker 1: it interacts with itself, it forms sort of different structures
29:25
Speaker 1: that have different gravity. So we can sort of ask
29:27
Speaker 1: questions about whether dark matter is feeling itself by trying
29:30
Speaker 1: to look to see how it organizes itself in the universe.
29:34
Speaker 1: I see, we can't maybe see it directly or touch
29:37
Speaker 1: dark matter, but if we can somehow kind of know
29:40
Speaker 1: what it's doing, And if we see it doing stuff
29:42
Speaker 1: to itself, then we know that it's there must be
29:44
Speaker 1: some kind of force that it does interact with exactly.
29:47
Speaker 1: For example, if dark matter felt a version of the
29:50
Speaker 1: strong force, if it interacted with itself very very strongly
29:53
Speaker 1: and could like clump together very very very sticky ways,
29:56
Speaker 1: then it would form much denser objects than we see
29:59
Speaker 1: currently in the universe. Currently, dark matter looks really big
30:03
Speaker 1: and fluffy, like the dark matter in our galaxy isn't
30:06
Speaker 1: nearly as compact as the normal matter in our galaxy.
30:09
Speaker 1: It spreads out much further out. It's a big, fluffy
30:12
Speaker 1: cloud hasn't collapsed nearly as much, and we think that's
30:16
Speaker 1: because it's not as sticky as our matter. We think
30:19
Speaker 1: that it doesn't feel like a super powerful force that
30:22
Speaker 1: sticks it together, because that would help it like form
30:25
Speaker 1: denser objects like dark planets and dark stars. So we
30:28
Speaker 1: already know very broadly something about how dark matter can't
30:32
Speaker 1: feel itself because it stays sort of fluffy and doesn't
30:35
Speaker 1: seem to clump as much as normal matter. Right, But
30:38
Speaker 1: I wonder you know it sort of looks fluffy to
30:40
Speaker 1: us because we don't have a good way of seeing it.
30:42
Speaker 1: You know, we talked earlier about having we kind of
30:44
Speaker 1: have a fuzzy lens when we look at dark matter
30:47
Speaker 1: because we can only see it through gravity. You know,
30:50
Speaker 1: is it maybe even possible that there are dark matter
30:52
Speaker 1: stars out there, which is don't have the resolution to
30:55
Speaker 1: see them. You know, absolutely, there's a very big loophole
30:58
Speaker 1: in this argument that you allude to, which is that
31:00
Speaker 1: you can see sort of the bulk of dark matter,
31:02
Speaker 1: but we can't tell what it's doing in detail. In
31:04
Speaker 1: an episode recently about where is the dark matter, and
31:08
Speaker 1: we talked about how we can tell sort of the
31:10
Speaker 1: dark matters in these big fluffy clouds, but we also
31:12
Speaker 1: can't really tell if it is forming clumps. So you
31:15
Speaker 1: could imagine that dark matter maybe it's made out of
31:17
Speaker 1: a few different kinds of things. So most of it,
31:20
Speaker 1: maybe like you know, half of the dark matter or
31:22
Speaker 1: three fourths of the dark matter, is some big, fluffy
31:24
Speaker 1: stuff that hardly interacts with itself. But there could be
31:26
Speaker 1: a component of the dark matter that does do interesting,
31:30
Speaker 1: complicated things and has crazy interactions and forms dark stars
31:34
Speaker 1: and dark planets and dark life, and that would not
31:36
Speaker 1: mess up the distribution of dark matter, because remember, there's
31:40
Speaker 1: like so much dark matter out there that even like
31:43
Speaker 1: if a quarter of it does more interesting stuff, that's
31:46
Speaker 1: still more than all of our kind of matter. So
31:49
Speaker 1: there's plenty of room to have like a component that
31:51
Speaker 1: has complex interactions without missing up these constraints about the
31:55
Speaker 1: big picture of dark matter. So I feel like dark
31:58
Speaker 1: matter could be in the shape of I don't know,
32:00
Speaker 1: like rubber duckies. It's just that they're sort of distributed
32:03
Speaker 1: out in space, these rubber duckies, and to us it
32:06
Speaker 1: just seems like a big fluffy cloud. Yeah, most of
32:08
Speaker 1: it has to be pretty big and fluffy to form
32:10
Speaker 1: that big fluffy cloud. It can't stick to itself. But
32:13
Speaker 1: it could be that inside that big fluffy cloud there
32:16
Speaker 1: are like rubber duckies made out of like a special
32:19
Speaker 1: kind of dark matter, you know, the way they like
32:21
Speaker 1: our matter. There's lots of different kinds is electrons, is
32:23
Speaker 1: different kinds of quarks. Right, we have twelve different matter particles.
32:27
Speaker 1: Dark matter could have like fifty different kinds of particles,
32:30
Speaker 1: and maybe most of them don't interact and make a
32:32
Speaker 1: big fluffy cloud, but one or two of them form
32:35
Speaker 1: dark rubber duckies that are floating out there in the universe,
32:37
Speaker 1: and we couldn't tell the difference because the only way
32:40
Speaker 1: we can see them is through their overall gravitational interaction.
32:43
Speaker 1: I'm pretty sure that's what dark Vader uses in his bathtuff.
32:46
Speaker 1: But I guess the question is, you know, isn't the
32:48
Speaker 1: fact that dark matter does seem to be sort of
32:51
Speaker 1: fluffy and doesn't seem to stick to itself. Is that
32:53
Speaker 1: evidence that maybe it doesn't interact with itself other than
32:57
Speaker 1: with gravity. It's evidence that it doesn't interact with itself
33:00
Speaker 1: very very strongly. But again, the loophole is that some
33:03
Speaker 1: component of it might be able to Now. The way
33:05
Speaker 1: to probe that a little bit more deeply is to
33:08
Speaker 1: do experiments. Is to take like two big clouds of
33:11
Speaker 1: dark matter and throw them against each other and see
33:14
Speaker 1: if they pass right through each other, or if maybe
33:16
Speaker 1: they stick together and make them like dark explosions. That
33:19
Speaker 1: kind of experiment is pretty tough to do, but we
33:22
Speaker 1: were lucky and the universe did it for us. It
33:24
Speaker 1: collided two huge clusters of galaxies, each of which have
33:28
Speaker 1: their own dark matter associated with them, smashed them together
33:32
Speaker 1: millions of years ago, and we got to see what
33:34
Speaker 1: happened and what did happen, and so this is called
33:36
Speaker 1: the bullet cluster. You can go ahead and look at
33:38
Speaker 1: these pictures online if you're interested. It's really beautiful. What
33:41
Speaker 1: happened is that the stars in these galaxy clusters mostly
33:44
Speaker 1: passed through themselves because stars are pretty sparse, so it's
33:47
Speaker 1: like two clouds of sand passing through each other. The
33:50
Speaker 1: gas and the dust that were in these galaxies smashed
33:53
Speaker 1: together and admitted a lot of light and radiation. But
33:55
Speaker 1: the dark matter looks like it basically passed right through itself.
33:59
Speaker 1: You might ask school like, how could we know where
34:01
Speaker 1: the dark matter is? We can see the dark matter
34:03
Speaker 1: because it distorts the stuff behind it. From the dark
34:06
Speaker 1: matter is matter, it feels gravity, so it bends space
34:09
Speaker 1: a little bit, which creates like gravitational distortions in the
34:12
Speaker 1: light that passes through it. So from this bullet cluster,
34:16
Speaker 1: it looks like these two clouds mostly passed right through
34:18
Speaker 1: each other. So not it doesn't have any strong interactions
34:21
Speaker 1: with itself, but it could still have some interactions with itself,
34:24
Speaker 1: which would maybe give rise to something like a dark photon.
34:27
Speaker 1: That's right, and so people often cite the bullet cluster
34:30
Speaker 1: is evidence that dark matter can't feel anything with itself,
34:32
Speaker 1: and that's not exactly true, because, as you say, there's
34:35
Speaker 1: still room in there for some kind of interaction. Because
34:38
Speaker 1: remember that the stars, which do definitely feel each other,
34:41
Speaker 1: also passed right through themselves. Right. The star is hardly collided,
34:45
Speaker 1: and that's just because it's pretty sparse, and so could
34:48
Speaker 1: be that dark matter forms the structures, but they didn't
34:50
Speaker 1: collide with each other because just like the stars, they're
34:53
Speaker 1: pretty sparse and space is pretty big. And it could
34:56
Speaker 1: also be that some components of the dark matter did
34:58
Speaker 1: collide with itself, did get stuck sort of in the
35:01
Speaker 1: middle there. But we don't really have the resolution to tell.
35:04
Speaker 1: We can't very precisely measure how much dark matter passed
35:07
Speaker 1: through and how much stuck. We can just tell that
35:09
Speaker 1: a lot of it passed through, but some component could
35:12
Speaker 1: have gotten stuck and could be doing like crazy stuff
35:14
Speaker 1: there in the middle. I see, like maybe the Rubert
35:17
Speaker 1: duckies didn't all crash into each other, but some just
35:19
Speaker 1: kept going. I think the key point to understand is
35:22
Speaker 1: that there's so much dark matter out there that even
35:25
Speaker 1: if a tiny fraction of it is doing interesting things
35:28
Speaker 1: we couldn't tell, and that tiny fraction would still be
35:30
Speaker 1: more stuff than all of the stars and gas and
35:33
Speaker 1: dust in the universe that we know. All right, well,
35:35
Speaker 1: let's get into other ways that we might be able
35:36
Speaker 1: to detect this dark radiation and maybe even see these
35:39
Speaker 1: dark or not see these dark photons. I'm a little
35:42
Speaker 1: confused about how he might see are not photon But
35:45
Speaker 1: first let's take another quick break. All right, we're talking
35:59
Speaker 1: abot dark gradiation and dark photons, which it might be
36:03
Speaker 1: what dark matter sees and feels with itself when dark
36:06
Speaker 1: matter looks in the mirror. That's what they would see
36:08
Speaker 1: dark photons. Yeah, exactly. I hope they haven't eating too
36:12
Speaker 1: much dark chocolate. But to us it's pretty elusive because
36:15
Speaker 1: we can see or feel the dark matter or maybe
36:18
Speaker 1: even these forces. So, Daniel, what are some of the
36:20
Speaker 1: other ways that we might hope to detect whether or
36:23
Speaker 1: not dark matter has these dark interactions. There are a
36:26
Speaker 1: couple other indirect ways, basically again using gravity. One of
36:30
Speaker 1: them is looking at neutron stars. Neutron stars are these
36:34
Speaker 1: crazy dense objects that are the remnants of stars that
36:37
Speaker 1: have blown up and left this very very compact core,
36:41
Speaker 1: and sometimes neutron stars come in pairs and then those
36:44
Speaker 1: pairs spin around each other in this sort of like
36:47
Speaker 1: death spiral before they collide, and when they do that,
36:50
Speaker 1: they create gravitational waves that we can see here from Earth.
36:53
Speaker 1: This is like the shaking of space itself. If you're
36:57
Speaker 1: interested in learning more about that, we have a couple
36:59
Speaker 1: of episodes about gravitational waves. It's really cool because the
37:02
Speaker 1: gravitational waves reveal in detail how these stars are spiraling
37:06
Speaker 1: towards the center, how they're losing energy, and we can
37:09
Speaker 1: calculate with great precision how fast they should be going
37:12
Speaker 1: and how much energy they're losing. And so this is
37:14
Speaker 1: a really nice test of sort of like what's going
37:17
Speaker 1: on with this kind of matter, Because if these neutron
37:19
Speaker 1: stars were capable, for example, of feeling this dark radiation
37:24
Speaker 1: at some level, if the particles in there could feel
37:27
Speaker 1: this force at all, then they would radiate a little
37:29
Speaker 1: bit of those dark photons and it would change the
37:32
Speaker 1: way this inspiral happens, and we would be able to
37:34
Speaker 1: see that by looking at the gravitational waves. Wait, so
37:38
Speaker 1: these neutron stars would be made out of regular matter,
37:40
Speaker 1: the kind we're made out of. But you're saying that
37:42
Speaker 1: even though the regular matter it might admit this dark radiation,
37:45
Speaker 1: how is that possible. It might be that our matter
37:48
Speaker 1: can feel these sort of like new forces, just at
37:50
Speaker 1: a very very low level. We don't know, and so
37:53
Speaker 1: this is like, you know, one way to look for
37:55
Speaker 1: it under the assumption that our kind of matter could
37:57
Speaker 1: feel these dark forces, which is not something we know.
38:00
Speaker 1: It's just sort of like a guess. We do this
38:02
Speaker 1: in physics a lot. We're like, we don't know if
38:04
Speaker 1: it's possible to see it this way, but let's check,
38:06
Speaker 1: because if it does feel this force, if neutron stars
38:09
Speaker 1: can make these dark photons, we would be able to
38:12
Speaker 1: see that. I see neutron stars are so it's such
38:15
Speaker 1: an extreme event when they crash into each other that
38:17
Speaker 1: that's one possible, you know, crazy scenario where it might
38:21
Speaker 1: make dark gradiations exactly. And it's a place where we
38:23
Speaker 1: can make very very precise calculations about the gravitational waves
38:26
Speaker 1: and compare them to very very detailed data. So it's
38:29
Speaker 1: an opportunity to look for like very small deviations, you know,
38:33
Speaker 1: things that the neutron stars are doing that we can't
38:35
Speaker 1: otherwise explain that might be explainable through dark photons. I see,
38:40
Speaker 1: all right, what are some other ways we could maybe
38:42
Speaker 1: feel this dark force? All the most generic ways you
38:45
Speaker 1: just use gravity the kind of tests that we did before,
38:47
Speaker 1: But there are some other approaches to look for these
38:49
Speaker 1: dark photons, hoping that there's some connection between our kind
38:53
Speaker 1: of matter and the dark matter, Like hoping that somehow
38:56
Speaker 1: maybe these dark photons can turn into normal photon very
39:00
Speaker 1: very rarely, and then we could detect that what how
39:04
Speaker 1: can a dark photon turn into a regular photon. It
39:06
Speaker 1: turns out that if you have another kind of force
39:09
Speaker 1: that's very similar to the photon, has sort of like
39:11
Speaker 1: a similar mathematical structure, that these forces like to talk
39:15
Speaker 1: to each other, that there's like it's very easy to
39:18
Speaker 1: build a physics model in which another kind of photon
39:21
Speaker 1: can turn into our photon wha like spontaneously or only
39:25
Speaker 1: in like high energy completions or you know, moments where
39:29
Speaker 1: you have kind of this a state of pure energy.
39:32
Speaker 1: It would be spontaneous, and in order for that to happen,
39:34
Speaker 1: they would have to be some kind of particle in
39:37
Speaker 1: the universe that has both kinds of charges. So imagine
39:41
Speaker 1: some new kind, very very rare dark matter that does
39:44
Speaker 1: have electric charges and also has some new kind of
39:48
Speaker 1: dark electric charge. That particle could effectively be like a
39:51
Speaker 1: portal that connects our photons to these other photons, and
39:56
Speaker 1: it might be that these particles never really exist in
39:58
Speaker 1: the universe, the way like top corks almost never exist
40:02
Speaker 1: in the universe on their own, but they're sort of
40:04
Speaker 1: like on the list of possibilities. As long as it's
40:07
Speaker 1: on the list of possibilities, then dark photons can use
40:10
Speaker 1: that as a portal to become normal photons and vice versa.
40:14
Speaker 1: This allows them to spontaneously turn from one into the other. Whoa,
40:18
Speaker 1: So that wouldn't make dark matter not dark, right, It
40:21
Speaker 1: would mean that you can sort of see them. It would,
40:23
Speaker 1: but these particles again wouldn't actually have to exist in
40:25
Speaker 1: the universe. So imagine now the dark sector is some
40:29
Speaker 1: kind of particle that's actually out there, that most of
40:31
Speaker 1: the dark matter is made out of this particle. And
40:33
Speaker 1: then there's the possibility for this other particle that has
40:37
Speaker 1: electric charges and dark charges, even though it's never really
40:40
Speaker 1: out there in the universe, as long as the possibility
40:43
Speaker 1: for it to exist is part of sort of nature's menu.
40:47
Speaker 1: That possibility allows dark photons to turn into photons. It's
40:50
Speaker 1: called kinetic mixing because we see it happening with regular matter, right,
40:54
Speaker 1: Like our photons turned into other kinds of stuff all
40:57
Speaker 1: the time, yes, exactly, Like photons turned into pairs of
41:00
Speaker 1: particles electrons and positrons, and then those can turn into
41:04
Speaker 1: z bosons, right because z's also interact with electrons impositron.
41:08
Speaker 1: So even if there weren't a single electron or positron
41:11
Speaker 1: in the universe, a photon could still turn into a
41:14
Speaker 1: z boson. And in the same way, as long as
41:17
Speaker 1: there's the possibility for some virtual particle that connects these
41:20
Speaker 1: two forces to exist, then photons could turn into dark
41:23
Speaker 1: photons and vice versa. And that's kind of our only
41:26
Speaker 1: hope of seeing this dark force directly. That's the best
41:29
Speaker 1: way to see these dark forces directly, exactly, And so
41:33
Speaker 1: people have built really cool experiments to try to like
41:35
Speaker 1: make this happen more often, try to like create the
41:38
Speaker 1: scenarios that would help induce dark photons to spontaneously turn
41:43
Speaker 1: into photons. They have these resonant cavities at Fermilab, for example,
41:47
Speaker 1: that should enhance the rate of this happening. If you
41:50
Speaker 1: like build something with the right shape and size, it
41:52
Speaker 1: creates a situation where this kind of spontaneous transformation is
41:56
Speaker 1: more likely to happen. And so they look for this
41:58
Speaker 1: kind of signature. Wait, that's being built right now, Like
42:02
Speaker 1: there are people building basically dark forest boxes. These things
42:06
Speaker 1: exist already and they are being run and they're just
42:09
Speaker 1: building them bigger and bigger. It's sort of like the
42:11
Speaker 1: way people are looking for a dark matter. They look
42:13
Speaker 1: in these containers underground, and they started with small ones,
42:15
Speaker 1: and then they're making bigger and bigger and bigger ones.
42:17
Speaker 1: Nobody's seeing a dark photon yet, but they're hoping as
42:20
Speaker 1: they make these cavities more precise and larger to induce
42:23
Speaker 1: a dark photon to turn into a normal photon. Cool,
42:27
Speaker 1: and how else can you look for these? Another way
42:29
Speaker 1: to look for these is to look for particles appearing
42:32
Speaker 1: where they shouldn't be. So one of my favorite kind
42:34
Speaker 1: of experiments, it's called a beam dump experiment, where you
42:37
Speaker 1: take a particle beam you were using for something else
42:39
Speaker 1: and you dump it, meaning you just like shoot it
42:41
Speaker 1: into a huge block of concrete or into a mountain side,
42:45
Speaker 1: just because you know, it's got to go somewhere. You
42:47
Speaker 1: don't want to like sprayed over the neighborhood because it's dangerous, right,
42:50
Speaker 1: just shoot it through the earth at people on the
42:51
Speaker 1: other side of the earth. Is that what you're saying, Yeah, exactly.
42:54
Speaker 1: And so Sho didn't do a mountain. It was on
42:56
Speaker 1: the other side of Daniel. It's not California, is I'm
43:00
Speaker 1: to have to look that up. But if you shoot
43:02
Speaker 1: this particle beam into a mountain, for example, and then
43:05
Speaker 1: you put a particle detector on the other side of
43:08
Speaker 1: the mountain, none of the particles should make it through
43:10
Speaker 1: the mountain, but you might see particles appearing in your
43:14
Speaker 1: detector on the other side of the mountain, because dark
43:17
Speaker 1: photons might make it through the mountain because they basically
43:20
Speaker 1: see the mountain is invisible as transparent. The ideas if
43:22
Speaker 1: your beam sometimes occasionally produces dark photons, those dark photons
43:27
Speaker 1: would make it through the mountain. And so essentially it's
43:30
Speaker 1: like looking for light shining through walls or I see
43:33
Speaker 1: so many the ideas that you send this beam out
43:35
Speaker 1: into the mountain, some of it turns into dark photons,
43:38
Speaker 1: and then somehow it turns back into regular photons before
43:42
Speaker 1: it hits your detector. Yeah, that's exactly right. And so
43:44
Speaker 1: you're hoping that sometimes those dark photons turned back into
43:48
Speaker 1: normal photons. So you're assuming a lot of things here.
43:51
Speaker 1: You're assuming that maybe sometimes dark photons are created in
43:54
Speaker 1: your beam, and that sometimes they turn back into normal photons. Right,
43:57
Speaker 1: But if they turn back into regular photons, how would
43:59
Speaker 1: you know they turned into dark photons in the middle. Yeah,
44:02
Speaker 1: you wouldn't know for sure. You would just know that
44:04
Speaker 1: something passed through the mountain that typically shouldn't be able to.
44:07
Speaker 1: So you calculate, like how often should particles be able
44:10
Speaker 1: to pass through the mountain and turn into photons? And
44:14
Speaker 1: if that happens more often than you expect, then you
44:17
Speaker 1: know there's something else and new there, maybe a dark photon,
44:20
Speaker 1: maybe something else. But you know, that's often the case
44:22
Speaker 1: with particle physics. We find something new, we're not exactly
44:25
Speaker 1: sure what it is, and then we study it in detail,
44:28
Speaker 1: we try to characterize exactly what it is, just like
44:31
Speaker 1: with the Higgs boson. First thing, we saw some new
44:33
Speaker 1: particle decaying into two photons, and we weren't sure is
44:37
Speaker 1: this the Higgs boson or is it something else? We
44:38
Speaker 1: didn't expect, and over decades of study we sort of
44:41
Speaker 1: pinned down what it must be because of all of
44:43
Speaker 1: its behaviors. I see, it's like, the only way it
44:45
Speaker 1: could have made it through the mountain to and out
44:48
Speaker 1: into California to hit us it was if it turned
44:51
Speaker 1: into something invisible like dark photons somewhere in the middle.
44:56
Speaker 1: Otherwise it wouldn't have made it through. Exactly, I have
44:58
Speaker 1: to phase through the mountain by turning into something that
45:01
Speaker 1: doesn't interact with mountains. All right, cool, Well, what are
45:04
Speaker 1: some other ways we might be able to see these
45:05
Speaker 1: dark forces? A lot of the other experiments are very similar.
45:08
Speaker 1: There's one at CERN called Phaser Forward Search Experiment. It's
45:13
Speaker 1: a pretty tortured acronym, but a really cool idea for
45:17
Speaker 1: I don't even know what is there an A actually
45:19
Speaker 1: in the name, there's an A and forward and an
45:23
Speaker 1: R experiment. Oh man, it's a really cool idea because
45:27
Speaker 1: they're taking an already existing experiment Atlas where we collide
45:31
Speaker 1: protons together and they're wondering like maybe dark photons are
45:35
Speaker 1: created and shoot down the beam. So they built a
45:37
Speaker 1: detector like really far down along the beam past where
45:41
Speaker 1: the collisions happen to see if maybe dark photons are
45:44
Speaker 1: created in those collisions and then fly along the beam
45:47
Speaker 1: and then turn into something that they can see sort
45:49
Speaker 1: of downstream. So they added this little bit to the
45:53
Speaker 1: detector that can do something totally novel and new. It's
45:55
Speaker 1: actually led by a team here at you see Irvine,
45:58
Speaker 1: m M, I see. But we don't actually know if
46:00
Speaker 1: dark matter can switch back and forth that easily, right,
46:03
Speaker 1: We don't know. And again, it could be that dark
46:05
Speaker 1: matter is only some inert particle that feels gravity and
46:09
Speaker 1: nothing else and there are no dark forces and no
46:11
Speaker 1: way to interact. It could also be that dark matter
46:14
Speaker 1: does feel some new dark force, but can only interact
46:17
Speaker 1: with itself, and none of those dark forces can ever
46:20
Speaker 1: turn into normal matter or normal photons. Here, we're just guessing.
46:24
Speaker 1: We're trying to like study the various possibilities in the
46:27
Speaker 1: various ways that those possibilities might manifesto well, And so
46:32
Speaker 1: what does it all mean? Do you think we will
46:34
Speaker 1: find it has interactions with itself or do you think
46:37
Speaker 1: it just represents this whole part of the universe that
46:40
Speaker 1: we will never be able to see or touch or
46:42
Speaker 1: even confirm that it's there. You know, like we could
46:45
Speaker 1: be swimming in dark rubber duckies and never ever ever, Yeah,
46:50
Speaker 1: part of it comes down to what you think is
46:52
Speaker 1: more natural. Does it make sense to you to have
46:54
Speaker 1: a huge component of the universe be sort of simple
46:58
Speaker 1: and inert and not really doing any being interesting, or
47:01
Speaker 1: does this seem more natural for it to be complex
47:03
Speaker 1: and interactive the way that our matter is. Now, what
47:06
Speaker 1: I know is that the universe doesn't follow what we
47:09
Speaker 1: think is natural. Our conceptions of how the universe should
47:12
Speaker 1: work don't seem to be very well aligned with how
47:14
Speaker 1: it usually does work, and so I suspect there are
47:17
Speaker 1: some surprises out there. The other side of that question
47:19
Speaker 1: is what you asked, is might we ever be able
47:22
Speaker 1: to tell? And it could be that dark matter doesn't
47:24
Speaker 1: feel any of our forces, and none of these forces
47:26
Speaker 1: can talk to our forces, and we can never find
47:28
Speaker 1: these dark rubber duckies. But I have faith in physicists
47:31
Speaker 1: and engineers to come up with clever ways to probe
47:34
Speaker 1: these things, ways that we can't even today. Imagine kinds
47:37
Speaker 1: of experiments that people might think of in ten years
47:40
Speaker 1: or twenty years, experiments thought up by you know, clever
47:43
Speaker 1: Listeners to this podcast who aren't constrained by the kind
47:46
Speaker 1: of thinking that academic physicists have been trained to do.
47:49
Speaker 1: I think I know how you can do it, Daniel,
47:51
Speaker 1: Dark Chocolate collisions. You just gotta want it enough. You know,
47:55
Speaker 1: you have to really want it, because, as Yoda says,
47:58
Speaker 1: you know, wanting these to pain and pain needs to suffering,
48:02
Speaker 1: and suffering leads to the dark side, and so that's
48:05
Speaker 1: that's how you can get there faster. Maybe, Yeah, there
48:07
Speaker 1: is no try. I should just do it, that's right,
48:09
Speaker 1: Just I mean, do it? You should, yes, all right.
48:15
Speaker 1: I don't know why I didn't think of that before.
48:16
Speaker 1: I'm just gonna go do it right after we're done
48:18
Speaker 1: with this podcast, or not do it. I guess we're
48:20
Speaker 1: doing in the dark. Gosh, I'm so confused. But to me,
48:23
Speaker 1: it really touches on these deep mysteries of physics that
48:25
Speaker 1: we know the universe out there is telling stories that
48:28
Speaker 1: we haven't heard yet. We're desperate to hear those stories.
48:31
Speaker 1: We have hints that we know the shape of those stories,
48:33
Speaker 1: but we don't know any of the details yet, and
48:35
Speaker 1: I just hope that one day we'll be able to
48:37
Speaker 1: fill those in. Yeah, it's almost like there's a whole
48:39
Speaker 1: universe out there, sitting right in front of us that
48:42
Speaker 1: we have yet to discover, and that anyone listening to
48:45
Speaker 1: this could become part of that search. That's right. So
48:47
Speaker 1: there's plenty more of the universe to find out, and
48:50
Speaker 1: we desperately need new ideas. And whether the universe counts
48:54
Speaker 1: as dark chocolate or not, that's for other people to debate.
48:57
Speaker 1: That's right. And if you love white chocolate, take my apologies.
49:00
Speaker 1: I love all of them. You love listeners more than
49:03
Speaker 1: you love your chocolate, exactly, And if you eat white
49:07
Speaker 1: chocolate while listen to this podcast, I forgive you because
49:11
Speaker 1: he can't see your or feel you, so it doesn't
49:13
Speaker 1: matter to exactly. Please accept my dark apologies. All right, Well,
49:17
Speaker 1: we hope you enjoyed that. Thanks for joining us, See
49:20
Speaker 1: you next time. Thanks for listening, and remember that Daniel
49:30
Speaker 1: and Jorge Explain the Universe is a production of I
49:33
Speaker 1: Heart Radio. For more podcast for my heart Radio, visit
49:36
Speaker 1: the I heart Radio app, Apple Podcasts, or wherever you
49:40
Speaker 1: listen to your favorite shows. Yeah,