Latest / Daniel and Kelly’s Extraordinary Universe / Could dark matter be making flashes of light?

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Could dark matter be making flashes of light? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey, Dannie, I'm curious how does a physicist make mental
• 0:12
  Speaker 1: images of some of the tricky things you do research on.
• 0:14
  Speaker 2: You know, I'm not sure you really want to see
• 0:16
  Speaker 2: inside the brain of physicists. It's a bit of a mess.
• 0:20
  Speaker 1: Well, let's find out what's your mental image of dark matter?
• 0:23
  Speaker 2: Okay, that's a really tough one because it's invisible. I
• 0:27
  Speaker 2: guess I sort of imagine it like water, which is,
• 0:29
  Speaker 2: you know, mostly transparent, but you can definitely tell it's there.
• 0:33
  Speaker 1: So we're all swimming in a bath of dark matter.
• 0:36
  Speaker 2: I hope there's some dark matter rubber duckies out.
• 0:38
  Speaker 1: There, some dark duckies. I wonder if they have a
• 0:41
  Speaker 1: cute song for that on Sesame Street.
• 0:42
  Speaker 2: That would make dark matter bath time lots of fun.
• 0:45
  Speaker 1: It's a special episode on the Letter D for dark Matter.
• 1:04
  Speaker 3: Hi.
• 1:04
  Speaker 1: I am Horam mccartoonist and the author of Oliver's Great
• 1:07
  Speaker 1: Big Universe. Hi.
• 1:08
  Speaker 2: I'm Daniel. I'm a particle physicist and a professor you
• 1:11
  Speaker 2: see Irvine. And this episode is brought to you by
• 1:14
  Speaker 2: the taxpayers of California.
• 1:15
  Speaker 1: Is it They're not paying me?
• 1:18
  Speaker 2: This professor is brought to you by the taxpayers of California.
• 1:21
  Speaker 1: I should say I thought our heart worth paying you.
• 1:25
  Speaker 1: Are you double dipping here, Daniel? Sounds like it. I
• 1:28
  Speaker 1: am multifaceted, your multi paid? Is that what you're saying
• 1:33
  Speaker 1: by multiple people? Sounds like a good setup there.
• 1:37
  Speaker 2: I got no complaints, but.
• 1:38
  Speaker 1: Anyways, welcome to our podcast, Daniel and Jorge Explain the Universe,
• 1:41
  Speaker 1: a production of iHeartRadio.
• 1:43
  Speaker 2: In which we try to bring multiple streams of understanding
• 1:46
  Speaker 2: together into your brain. There's so many ways to understand
• 1:50
  Speaker 2: the universe, so many questions to ask about it, so
• 1:53
  Speaker 2: many things to understand, and the challenge of physics is
• 1:56
  Speaker 2: to weave all those together into one coherent, comprehend of
• 2:00
  Speaker 2: story that explains the universe to us and to you
• 2:04
  Speaker 2: and to our kids. And that is the goal of
• 2:06
  Speaker 2: this podcast.
• 2:07
  Speaker 1: That's right, because it is a vast universe full of
• 2:10
  Speaker 1: all kinds of things that start with all kinds of letters,
• 2:12
  Speaker 1: the letter A, the letter B, the letter C, all
• 2:14
  Speaker 1: of the letters in the universe, even the ones we
• 2:17
  Speaker 1: haven't discovered.
• 2:17
  Speaker 2: Yet, even letters in other alphabets. In particle physics, we
• 2:21
  Speaker 2: often reach to the Greek alphabet to name our particles.
• 2:24
  Speaker 1: Is that why it's all Greek? To me.
• 2:27
  Speaker 2: That's exactly right. And sometimes when we run out of
• 2:29
  Speaker 2: Greek letters, we dip into the Hebrew alphabet.
• 2:32
  Speaker 1: Mmm. I thought you were going to say, we're gonna
• 2:33
  Speaker 1: you're gonna dip into alien alphabets, or one day we
• 2:36
  Speaker 1: might have variables that are only defined in an alien language.
• 2:40
  Speaker 2: That sounds wonderful. I look forward to figuring out how
• 2:43
  Speaker 2: to write alien letters in word.
• 2:45
  Speaker 1: You're going to need like another app like trio Linguo
• 2:48
  Speaker 1: or something.
• 2:50
  Speaker 2: I'm sure this's gonna be a Unicode symbol for alien languages.
• 2:53
  Speaker 1: Oh so, I mean they'll be alien emojis.
• 2:57
  Speaker 2: What if the first message we get from aliens is
• 2:59
  Speaker 2: just in emojis that we need our kids to help.
• 3:02
  Speaker 1: Us interpret it. Yeah, let's hope it's not like food
• 3:05
  Speaker 1: icons like hey, hey dinner, Hey hot dog, hamburger, pizza.
• 3:11
  Speaker 2: I think the food emojis have other meanings sometimes, you know,
• 3:14
  Speaker 2: the eggplant for example.
• 3:15
  Speaker 1: I don't know what you're talking about, Daniel. What kinds
• 3:18
  Speaker 1: of websites have you been surfing?
• 3:19
  Speaker 2: Ask your kids about it later.
• 3:24
  Speaker 1: I doubt it. But anyways, it is a big universe
• 3:28
  Speaker 1: full of amazing things to study and observe. If we
• 3:31
  Speaker 1: can actually see them.
• 3:33
  Speaker 2: One of the challenges of understanding the universe is first
• 3:36
  Speaker 2: figuring out what's out there. We begin by using the
• 3:39
  Speaker 2: natural senses. We're all familiar with our eyes, our ears,
• 3:42
  Speaker 2: our noses, et cetera. But there's so much more out
• 3:45
  Speaker 2: there that we can detect with more subtle methods.
• 3:48
  Speaker 1: Yeah, because there's a lot of stuff out there that
• 3:50
  Speaker 1: we can see, but also a lot of stuff we
• 3:51
  Speaker 1: can't see. The most amazing discoveries in recent decades has
• 3:56
  Speaker 1: been the idea that most of the universe is out there,
• 3:59
  Speaker 1: but we can't see it, or touch it or feel it.
• 4:02
  Speaker 2: As we progress scientifically and technologically, we build new kinds
• 4:06
  Speaker 2: of eyeballs, new kinds of sensors, new kinds of ears
• 4:09
  Speaker 2: that let us detect things happening in the universe that
• 4:12
  Speaker 2: were otherwise invisible and impossible for us to notice. Sometimes
• 4:16
  Speaker 2: that means seeing entirely new signals like photons of very
• 4:19
  Speaker 2: high energy or low energy. Sometimes that means noticing patterns
• 4:23
  Speaker 2: in other signals, like the rotations of galaxies and gravitational
• 4:26
  Speaker 2: hints in the motions of other objects that tell us
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  Speaker 2: there's so much more going on out there than we
• 4:32
  Speaker 2: could immediately see.
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  Speaker 1: Yep, and one of the biggest pieces of stuff out
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  Speaker 1: there that we can see is called dark matter. It
• 4:39
  Speaker 1: accounts for about twenty seven percent of the universe, right, Daniel.
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  Speaker 2: That's right. In any given chunk of the universe, just
• 4:44
  Speaker 2: over a quarridor of the energy is devoted to dark matter,
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  Speaker 2: and only five percent of it is made of the
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  Speaker 2: kind of stuff that you and I are made out of, baryons, quarks, leptons,
• 4:54
  Speaker 2: this kind of stuff, which means that there's a lot
• 4:56
  Speaker 2: more of the invisible stuff out there than the visible stuf.
• 5:00
  Speaker 1: Yeah, which can I make you wonder if maybe we're
• 5:02
  Speaker 1: the ones that are invisible.
• 5:03
  Speaker 2: Maybe we needs learn those dark matter emojis pretty quickly,
• 5:07
  Speaker 2: but could.
• 5:07
  Speaker 1: We see them? Maybe you are receiving dark matter emojis,
• 5:10
  Speaker 1: you just don't know it.
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  Speaker 2: I've kind of an outdated operating system, so a lot
• 5:12
  Speaker 2: of the emojis I get are question marks anyway. Maybe
• 5:15
  Speaker 2: those are the aliens trying to talk to me.
• 5:17
  Speaker 1: Mmm, maybe they're actually sending you question marks. They're like, Daniel,
• 5:21
  Speaker 1: why are you getting paid so many ways for the
• 5:23
  Speaker 1: same thing?
• 5:25
  Speaker 2: You know, I do get lots of questions from listeners,
• 5:27
  Speaker 2: so maybe some of those are actually coming from the aliens.
• 5:30
  Speaker 1: Interesting, are you calling our listeners aliens?
• 5:33
  Speaker 2: I'm saying we're inclusive, right, everybody is welcome. We try
• 5:36
  Speaker 2: to reach everybody, not just humans.
• 5:38
  Speaker 1: Well, there you go. If you want to stump a physicists,
• 5:40
  Speaker 1: just send them a question in the form of emojis.
• 5:43
  Speaker 1: You know how they summarize movies sometimes with just emojis.
• 5:46
  Speaker 1: I wonder if you could do that with physics theory.
• 5:48
  Speaker 2: What they summarize movies with just emojis?
• 5:52
  Speaker 1: Yeah? Or books or stories or news items.
• 5:55
  Speaker 2: Oh, I feel really out of touch.
• 5:57
  Speaker 1: Speaking of out of touch, that's what dark matter is.
• 6:00
  Speaker 1: Stuff that's out there that you can't see and you
• 6:02
  Speaker 1: can't even touch, right, because it doesn't feel the electromagnetic force,
• 6:06
  Speaker 1: so you can feel it with your fingers.
• 6:08
  Speaker 2: That's right. It doesn't emit light, give off light, reflect light,
• 6:11
  Speaker 2: or interact with light at all, which makes it pretty dark.
• 6:15
  Speaker 2: And if a huge chunk of the universe is so
• 6:17
  Speaker 2: dark but so important, then scientists really have to figure
• 6:21
  Speaker 2: out how to study, how to understand what it is.
• 6:24
  Speaker 2: So we're doing our best to be creative to find
• 6:27
  Speaker 2: new ways.
• 6:28
  Speaker 1: To look for it so that we can study it
• 6:30
  Speaker 1: and kind of figure out what it's made out of.
• 6:33
  Speaker 1: So there are maybe new ideas out there about how
• 6:36
  Speaker 1: to do this. So today on the podcast, we'll be
• 6:38
  Speaker 1: tackling the question good dark matter be making flashes of light?
• 6:48
  Speaker 1: I always figured dark matter was pretty flashy.
• 6:52
  Speaker 2: Well, I don't know. The name dark matter is more
• 6:54
  Speaker 2: mysterious than flashy, isn't it.
• 6:56
  Speaker 1: Well, that's just what we'll call it. Maybe it's something
• 6:59
  Speaker 1: we can but really inside it's fancy and flashy.
• 7:03
  Speaker 2: Maybe when we finally meet the beings made of dark matter,
• 7:05
  Speaker 2: they'll be like annoyed or offended or disappointed that we
• 7:08
  Speaker 2: call them dark matter.
• 7:10
  Speaker 1: Hopefully they won't flash us.
• 7:12
  Speaker 2: You mean like zap us with a laser being from
• 7:14
  Speaker 2: orbit or open the trench code.
• 7:15
  Speaker 1: I mean like send this fruit emojis. So, as usually,
• 7:20
  Speaker 1: we were wondering how many people out there had thought
• 7:22
  Speaker 1: about the idea of seeing dark matter through flashes of light.
• 7:26
  Speaker 2: Thank you very much to our group of volunteers who
• 7:28
  Speaker 2: answers these questions. We'd love hearing your thoughts on the
• 7:31
  Speaker 2: topic of the day. If you would like to contribute,
• 7:34
  Speaker 2: please don't be shy. Everybody is welcome, whether you've been
• 7:37
  Speaker 2: listening for years or weeks or days or this is
• 7:39
  Speaker 2: your first episode, just write to me too, questions at
• 7:42
  Speaker 2: Danielandjorge dot com.
• 7:44
  Speaker 1: So think about it for a second. Do you think
• 7:46
  Speaker 1: dark matter could be making flashes of light that we
• 7:49
  Speaker 1: could see? Here's what people had to say.
• 7:51
  Speaker 2: I don't know, but that'd be cool.
• 7:53
  Speaker 3: The concept of dark matter making flashes of light is
• 7:58
  Speaker 3: quite interesting since dark matter seems to make up a
• 8:01
  Speaker 3: large part of the universe. I don't see why it
• 8:04
  Speaker 3: could be giving off light pulses given the right circumstances.
• 8:09
  Speaker 3: I think that only directly by making stuff made of
• 8:13
  Speaker 3: regular matter to behave in a certain way due to
• 8:16
  Speaker 3: gravitational effects, since it doesn't interact with the electra week force, I.
• 8:21
  Speaker 1: Think not all right. I think that pretty much summarizes
• 8:23
  Speaker 1: the episode here. I don't know, but that would be cool.
• 8:26
  Speaker 1: I feel like that's al those every episode.
• 8:29
  Speaker 2: That's the emoji version of the episode. Yeah, if you
• 8:31
  Speaker 2: have to summarize it, so that would be what shrug
• 8:34
  Speaker 2: question mark check mark is how you summarize the emojis.
• 8:37
  Speaker 1: Yeah, or like a black square for dark matter question
• 8:41
  Speaker 1: mark trump, and then the emoji with the sunglasses.
• 8:44
  Speaker 2: For cool yeah or sparkles. Isn't there a sparkles emoji.
• 8:47
  Speaker 1: Well, depends how flashy you want to get.
• 8:49
  Speaker 2: Daniel, let's go all out. We got multiple funding sources here.
• 8:52
  Speaker 1: There you go. Let's go out with a flash of
• 8:54
  Speaker 1: jail time. But anyways, let's get down to it, Daniel,
• 8:59
  Speaker 1: let's recap for listeners. What is dark matter in the
• 9:02
  Speaker 1: first place.
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  Speaker 2: It's important that we explain what we mean when we
• 9:04
  Speaker 2: say dark matter, because I noticed there's lots of different
• 9:07
  Speaker 2: ideas out there about what dark matter is. Online you
• 9:10
  Speaker 2: see a lot of people saying dark matter is just
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  Speaker 2: a placeholder. Is just a way to say we don't know.
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  Speaker 2: Other people talk about dark matter as if it was
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  Speaker 2: a very specific theory of a very specific particle. There's
• 9:21
  Speaker 2: a whole bunch of people in the middle to talk
• 9:22
  Speaker 2: about dark matter as a sort of general catalog of ideas.
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  Speaker 2: But all of these things are there to explain something
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  Speaker 2: that we don't understand, which is that there's a lot
• 9:32
  Speaker 2: of gravity happening in the universe that we cannot explain,
• 9:36
  Speaker 2: Like when you look at how galaxies spin, and when
• 9:38
  Speaker 2: you look at how the universe formed, and all the
• 9:40
  Speaker 2: gravity necessary to pull the stars together into galaxies. We
• 9:45
  Speaker 2: just cannot explain all that galaxy using the stuff that
• 9:48
  Speaker 2: lights up, using the stuff made of quarks. It either
• 9:51
  Speaker 2: glows or reflects light or gives off light. We just
• 9:54
  Speaker 2: cannot tell the story of the universe and have it
• 9:57
  Speaker 2: make sense without something else out there provid a bunch
• 10:00
  Speaker 2: of gravity. So much gravity is missing that you need
• 10:03
  Speaker 2: five times as much of this mysterious stuff we call
• 10:06
  Speaker 2: dark matter as there is normal matter. So very briefly,
• 10:09
  Speaker 2: dark matter is just an idea to explain all this
• 10:11
  Speaker 2: unexplained gravity in the universe.
• 10:14
  Speaker 1: Yeah, and there are different ways that scientists have sort
• 10:16
  Speaker 1: of found or think that dark matter is there and there.
• 10:19
  Speaker 1: As you said, they all relate to gravity. But I
• 10:21
  Speaker 1: think basically the main idea is that what we see
• 10:24
  Speaker 1: of the universe tells us that there's more matter out
• 10:26
  Speaker 1: there than the stuff that glows or that we can
• 10:28
  Speaker 1: see and feel right exactly.
• 10:29
  Speaker 2: And the story started with the galaxy rotation curves. We
• 10:32
  Speaker 2: looked at galaxies and measured how fast they spin, and
• 10:35
  Speaker 2: we notice that they spin really really fast, and that
• 10:38
  Speaker 2: if you add up all of the stars and the
• 10:40
  Speaker 2: gas and the dust in those galaxies, they don't provide
• 10:43
  Speaker 2: enough gravity to hold that galaxy together as it spins.
• 10:47
  Speaker 2: So that was evidence number one, and for decades we
• 10:49
  Speaker 2: knew about that, but it was sort of hard to
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  Speaker 2: accept the idea that there could be so much more
• 10:54
  Speaker 2: missing matter out there. It was just one piece of evidence.
• 10:58
  Speaker 2: But slowly, over the decades we've pieced together lots of
• 11:01
  Speaker 2: totally independent measurements that tell us that there is missing
• 11:05
  Speaker 2: stuff out there, that there's matter out there providing gravity
• 11:08
  Speaker 2: that we cannot see.
• 11:10
  Speaker 1: Like initially, for example, it could have just been that
• 11:12
  Speaker 1: galaxies out there had a lot of like dark rocks,
• 11:14
  Speaker 1: right or gas that you couldn't see through the telescope exactly.
• 11:19
  Speaker 2: Or it could have been that gravity work differently over
• 11:22
  Speaker 2: really really long distances, like we've measured gravity in the
• 11:25
  Speaker 2: Solar System and on Earth, but maybe over hundreds of
• 11:28
  Speaker 2: thousands of light years gravity operates differently than Newton and
• 11:32
  Speaker 2: even Einstein suggested that could have been the explanation when
• 11:36
  Speaker 2: you were just looking at, one example, just at galaxy
• 11:39
  Speaker 2: rotation curves. But now we have lots of other ways
• 11:42
  Speaker 2: to probe this, you know, we look for example, at
• 11:44
  Speaker 2: the structure of the universe. How did it come together?
• 11:46
  Speaker 2: How did you go from blobs of gas mostly dispersed
• 11:50
  Speaker 2: through the universe clumping together into stars and galaxies, and
• 11:53
  Speaker 2: that requires gravity. And if you run the universe without
• 11:57
  Speaker 2: any dark matter, just with the kind of matter we
• 11:59
  Speaker 2: can see, you don't get stars and galaxies after fourteen
• 12:02
  Speaker 2: billion years. There isn't enough gravity to do it. You've
• 12:05
  Speaker 2: got to add in the dark matter and boom, then
• 12:07
  Speaker 2: you get a universe that looks just like ours. So
• 12:11
  Speaker 2: it's another very convincing piece of evidence that there is
• 12:13
  Speaker 2: matter out there. It's not just like gravity operates differently
• 12:16
  Speaker 2: that those distance scales. There really is missing matter.
• 12:19
  Speaker 1: But could you ask the same question about these large
• 12:21
  Speaker 1: scale structure theories. Could it be just that gravity works
• 12:24
  Speaker 1: differently though we thought at different scales, and that might
• 12:27
  Speaker 1: explain why galaxies form the way they are.
• 12:29
  Speaker 2: It is possible, and people who work on these theories
• 12:32
  Speaker 2: they're called like mond modified Newtonian dynamics, have tried to
• 12:36
  Speaker 2: tweak them. I've not seen one that can successfully explain
• 12:39
  Speaker 2: both the galaxy rotation curves and the large scale structure
• 12:43
  Speaker 2: of the universe. Mostly these theories are tuned to explain
• 12:47
  Speaker 2: the galaxy rotations, and they don't even try to explain
• 12:50
  Speaker 2: the other evidence for dark matter.
• 12:52
  Speaker 1: What's this other evidence.
• 12:53
  Speaker 2: Maybe one of the most compelling and precise piece of
• 12:56
  Speaker 2: evidence for dark matter is seeing its effect on the
• 12:59
  Speaker 2: very very early universe plasma. Before stars were formed, we
• 13:02
  Speaker 2: really had any structure in the universe at all. It
• 13:05
  Speaker 2: was just huge blobs of hot gas everywhere in the universe.
• 13:08
  Speaker 2: And we see the glow from that gas in the
• 13:10
  Speaker 2: cosmic microwave background radiation. When that gas cooled enough to
• 13:14
  Speaker 2: become transparent, when it formed neutral atoms, so photons mostly
• 13:17
  Speaker 2: could fly through it. Those photons are still around and
• 13:20
  Speaker 2: we see them, so they're like the last glow of
• 13:22
  Speaker 2: this plasma from the very early universe, and we see
• 13:25
  Speaker 2: ripples in that plasma, ripples that show us how the
• 13:28
  Speaker 2: normal matter and the dark matter and the photons were
• 13:31
  Speaker 2: all sloshing around. And it's a very very precise measurement,
• 13:35
  Speaker 2: and it tells us how much normal matter there is
• 13:37
  Speaker 2: in the universe, how much radiation there was in the universe,
• 13:39
  Speaker 2: how much dark matter there was in the universe back then.
• 13:42
  Speaker 2: It's very very precise because we've taken these very very
• 13:45
  Speaker 2: detailed maps of this early universe plasma, and that tells
• 13:48
  Speaker 2: us that there is a component of that plasma that
• 13:51
  Speaker 2: doesn't interact with photons, it's not buryonic, it's not our
• 13:55
  Speaker 2: kind of matter at all. So it's another completely independent
• 13:58
  Speaker 2: measurement that tells us there's a dark but gravitationally active
• 14:02
  Speaker 2: component to the universe.
• 14:03
  Speaker 1: Now, is that also due to gravity? Does that evidence
• 14:07
  Speaker 1: also depend on our current model of gravity?
• 14:10
  Speaker 2: It does, but those are much shorter distances. Those oscillations
• 14:13
  Speaker 2: ended up seeding the larger scale structure of the universe,
• 14:16
  Speaker 2: but it was before a lot of the expansion. So
• 14:18
  Speaker 2: we're talking about things that happened over short distance scales.
• 14:21
  Speaker 1: There were a short distance but there are large distance now.
• 14:23
  Speaker 2: That's right, But the CMB comes from when it was
• 14:26
  Speaker 2: short distance. Earlier, you were asking if this could all
• 14:29
  Speaker 2: just be due to like long distance gravitational effects, and
• 14:32
  Speaker 2: the CMB proves shorter distance scales gravity because the picture
• 14:36
  Speaker 2: we have of it comes from back when things were
• 14:38
  Speaker 2: much more cozy and compact.
• 14:39
  Speaker 1: All right, So then the prevailing picture is that there's
• 14:42
  Speaker 1: a lot of stuff out there, stuff that creates gravity
• 14:45
  Speaker 1: and feels gravity, but we just can't see it. So
• 14:48
  Speaker 1: let's get into what it could be, how we might
• 14:50
  Speaker 1: see it, and what might be new ways to figure
• 14:53
  Speaker 1: out where it is and what it's doing. So we'll
• 14:56
  Speaker 1: dig into that, but first let's take a quick break.
• 15:11
  Speaker 1: All right, we're talking about dark matter now, Daniel. How
• 15:13
  Speaker 1: many episodes now have we talked about dark matter?
• 15:15
  Speaker 2: Oh? Man, so many episodes. But it's still a thing
• 15:19
  Speaker 2: people are most confused and most interested about. In the
• 15:22
  Speaker 2: emails we get from people, people are still in the
• 15:25
  Speaker 2: dark about it. Yeah, And it's a really active area
• 15:27
  Speaker 2: of research, obviously, because it's one of the biggest open
• 15:30
  Speaker 2: questions in modern physics. So people are constantly trying to
• 15:34
  Speaker 2: come up with new theories for what dark matter might be.
• 15:36
  Speaker 2: Is it this particle, is it that particle, Is it
• 15:39
  Speaker 2: not a particle at all? Is it something else entirely?
• 15:42
  Speaker 2: And new ways to spot dark matter. If it's this
• 15:45
  Speaker 2: kind of particle, how could we see it? Could we
• 15:46
  Speaker 2: build a detector to observe it. So it's a huge
• 15:50
  Speaker 2: area of active research.
• 15:51
  Speaker 3: Mm.
• 15:51
  Speaker 1: Yeah, I guess we can't just wait for the Sesame
• 15:53
  Speaker 1: Street episode on it.
• 15:55
  Speaker 2: We could just sit back and wait for the aliens
• 15:57
  Speaker 2: to show up and tell us the answers to the universe,
• 15:59
  Speaker 2: But that kind of embarrassing if they showed up and
• 16:01
  Speaker 2: we had nothing to contribute.
• 16:03
  Speaker 1: Yeah, it'd be more embassing if they have to do
• 16:04
  Speaker 1: it over dinner while they eat us. I wonder if
• 16:07
  Speaker 1: they would feel less bad about eating us if they
• 16:10
  Speaker 1: knew we weren't. You know, dark matter intelligence, All right, Well,
• 16:14
  Speaker 1: we just kind of define what dark matter is. It's
• 16:17
  Speaker 1: the stuff we think that's out there to explain a
• 16:19
  Speaker 1: lot of the gravitational effects we see in how the
• 16:22
  Speaker 1: universe form and also in the microwave background radiation. Now
• 16:25
  Speaker 1: there are candidates where what we think this stuff might.
• 16:28
  Speaker 2: Be, right Daniel, There are lots of ideas for what
• 16:30
  Speaker 2: dark matter might be, and people initially thought, well, maybe
• 16:33
  Speaker 2: dark matter isn't some new, weird kind of stuff. It's
• 16:37
  Speaker 2: just more of the kind of stuff we already know about.
• 16:39
  Speaker 2: But you know, it's just hiding or something. People thought,
• 16:42
  Speaker 2: maybe dark matter is like neutrinos, because neutrinos are tiny
• 16:46
  Speaker 2: little particles that don't interact with photons, they don't give
• 16:49
  Speaker 2: off light, they don't reflect light, they pass right through
• 16:52
  Speaker 2: a lot of stuff. So they seemed initially like a
• 16:55
  Speaker 2: really good candidate maybe for dark matter, Like maybe the
• 16:58
  Speaker 2: universe is just filled with accountable numbers of neutrinos that
• 17:03
  Speaker 2: would have been amazing. But neutrinos don't have a lot
• 17:05
  Speaker 2: of mass. They're very very low mass particles, which means
• 17:09
  Speaker 2: they almost always move nearly the speed of light. And
• 17:11
  Speaker 2: one thing we do know about dark matter is that
• 17:14
  Speaker 2: it's kind of slow moving. It's not a fast particle.
• 17:17
  Speaker 1: Well, I guess that's Those are two questions. First of all,
• 17:20
  Speaker 1: why can't theatrinos go slow? Even if they're light? Can't
• 17:22
  Speaker 1: you still stop them from moving?
• 17:24
  Speaker 2: You can stop a neutrino because they have very low mass,
• 17:27
  Speaker 2: but their mass is so low it's like thousands of
• 17:29
  Speaker 2: times lower than even an electron. That essentially any energy
• 17:33
  Speaker 2: in putrino has means it's moving at almost the speed
• 17:36
  Speaker 2: of light. So it's almost impossible to have a natural
• 17:38
  Speaker 2: process that produces a huge number of neutrinos and have
• 17:41
  Speaker 2: them be slow moving.
• 17:42
  Speaker 1: And you also say dark matter is cold. How do
• 17:44
  Speaker 1: we know it is cold if we can't feel it.
• 17:45
  Speaker 2: Yeah, we know that dark matter can be moving very
• 17:48
  Speaker 2: fast because of the way it's influenced the structure of
• 17:51
  Speaker 2: the universe, like, dark matter is mostly responsible for what
• 17:54
  Speaker 2: we see out there. The reason you have a galaxy
• 17:56
  Speaker 2: here or a galaxy there is because there's a huge
• 17:58
  Speaker 2: blob of dark matter that created gravitational attraction that pulled
• 18:02
  Speaker 2: all that gas in to form the stars and the galaxy. Now,
• 18:05
  Speaker 2: if dark matter was moving really really fast, if it
• 18:08
  Speaker 2: was hot, then it wouldn't clump the same way. It
• 18:10
  Speaker 2: would spread itself out much more. So, we know that
• 18:13
  Speaker 2: dark matter has to be below a certain speed basically,
• 18:16
  Speaker 2: or it wouldn't have clumped into these blobs, which then
• 18:19
  Speaker 2: formed the structure of the universe. Like you run simulations
• 18:22
  Speaker 2: where dark matter is a fast moving particle, you don't
• 18:25
  Speaker 2: get the same kind of structure that we see in
• 18:27
  Speaker 2: our universe. That means dark matter has to be slow
• 18:29
  Speaker 2: moving or cold, as physicists say, and that means that
• 18:32
  Speaker 2: it can't be neutrinos.
• 18:33
  Speaker 1: Couldn't it be like super massive but hot too?
• 18:36
  Speaker 2: Well, hot essentially refers to its velocity regardless of its mass.
• 18:40
  Speaker 2: The issue is the velocity, and the problem is neutrinos
• 18:42
  Speaker 2: basically can't have low velocity. We know that dark matter
• 18:45
  Speaker 2: can't be moving very fast, otherwise it would spread itself
• 18:48
  Speaker 2: out and wash out the structure of the universe.
• 18:50
  Speaker 1: All right, well, then how is it that we can
• 18:52
  Speaker 1: see it? How can we hope to see it and
• 18:54
  Speaker 1: study it.
• 18:54
  Speaker 2: Then yeah, it's tricky. You know. The one thing that
• 18:57
  Speaker 2: we do know is that dark matter feels gravity. Vitational
• 19:00
  Speaker 2: studies are surefire way to detect dark matter. The problem
• 19:04
  Speaker 2: is that gravity is super duper weak. It's like the
• 19:06
  Speaker 2: weakest of the fundamental forces. If it even is a
• 19:09
  Speaker 2: fundamental force, it's weaker than the weak force by like
• 19:12
  Speaker 2: ten to the thirty, which means that it's basically impossible
• 19:16
  Speaker 2: to use gravity to detect tiny bits of dark matter,
• 19:20
  Speaker 2: like we can see like Solar System sized chunks of
• 19:23
  Speaker 2: dark matter maybe, but anything smaller than that, the gravity
• 19:26
  Speaker 2: from it is too weak for us to even detect it.
• 19:28
  Speaker 2: And that means that you couldn't really use gravity to
• 19:31
  Speaker 2: detect the particle nature of dark matter. Like one of
• 19:34
  Speaker 2: the deepest questions is what is dark matter made out of?
• 19:37
  Speaker 2: Is that this kind of particle? Is that kind of particle?
• 19:39
  Speaker 2: But gravity is really too weak to tell us anything
• 19:42
  Speaker 2: about the particle nature of dark.
• 19:44
  Speaker 1: Matter, and we don't even know if it is a particle, right,
• 19:46
  Speaker 1: it could be that dark matter is something that doesn't
• 19:49
  Speaker 1: form into particles. Is that possible.
• 19:51
  Speaker 2: It's totally possible. It's not a mainstream idea, like most
• 19:55
  Speaker 2: of modern physics right now, is focused on the idea
• 19:57
  Speaker 2: of particle dark matter, because the kind of matter we
• 20:00
  Speaker 2: know is all made of particles, and so we extrapolate
• 20:02
  Speaker 2: and we say, well, probably this other kind of matter
• 20:04
  Speaker 2: is made out of particles. And you might think that
• 20:07
  Speaker 2: sounds reasonable. It's a pretty basic assumption, but it's also
• 20:10
  Speaker 2: extrapolating from five percent of the universe to like twenty
• 20:13
  Speaker 2: five percent of the universe. It's entirely possible that the
• 20:16
  Speaker 2: physics of this other huge section of the universe is
• 20:19
  Speaker 2: very different from anything we've imagined. We've talked in the
• 20:22
  Speaker 2: podcast before about unparticles or other weird kind of theories
• 20:26
  Speaker 2: that describe it as not made of particles. So like
• 20:28
  Speaker 2: as you zoom in, it doesn't ever change. It's not
• 20:31
  Speaker 2: like there's a basic unit of it. You can just
• 20:33
  Speaker 2: keep zooming in forever and it always looks the same.
• 20:36
  Speaker 2: That would be really weird but super awesome. But the
• 20:39
  Speaker 2: mainstream theories are mostly particle dark matter because that's what
• 20:42
  Speaker 2: we know how to.
• 20:43
  Speaker 1: Think about, because that's kind of the only way to
• 20:46
  Speaker 1: think about things right.
• 20:47
  Speaker 2: Well, you know, there are people trying to think outside
• 20:49
  Speaker 2: the box. That requires a lot more creativity and flashes
• 20:52
  Speaker 2: of insight. But there definitely are people out there working
• 20:54
  Speaker 2: on sort of crazier theories of what dark matter is.
• 20:57
  Speaker 2: But I think most people are working on article dark
• 21:00
  Speaker 2: matter because yeah, that's what we're good at thinking about.
• 21:03
  Speaker 2: I mean, you talk to a particle physicist, you're going
• 21:05
  Speaker 2: to get a particle explanation for everything.
• 21:07
  Speaker 1: I guess. I mean, like, we haven't seen anything that
• 21:10
  Speaker 1: isn't explained by particle theory, right, and we wouldn't even
• 21:14
  Speaker 1: know what that math would look like.
• 21:16
  Speaker 2: Yes and no, we've never seen anything that we've been
• 21:19
  Speaker 2: able to explain with a non particle based theory. But
• 21:22
  Speaker 2: remember there's ninety five percent of the universe dark matter
• 21:25
  Speaker 2: and dark energy that we still can't really explain. So
• 21:28
  Speaker 2: particle based theories are the only ones that have ever
• 21:30
  Speaker 2: been successful, but they've only been successful in five percent
• 21:32
  Speaker 2: of the universe.
• 21:34
  Speaker 1: So yes and no, I guess there's a lot out
• 21:36
  Speaker 1: there that we can't still explain. So maybe our current
• 21:39
  Speaker 1: theory only covers five percent of the universe.
• 21:42
  Speaker 2: Yeah, that's exactly right. So we should definitely keep an
• 21:44
  Speaker 2: open mind to other crazy theories of what dark matter
• 21:47
  Speaker 2: might be. But currently we're mostly working on. Is dark
• 21:51
  Speaker 2: matter a particle? Is it a new kind of particle?
• 21:54
  Speaker 2: What does it do? How could we possibly spot it
• 21:56
  Speaker 2: if it is a particle?
• 21:57
  Speaker 1: All right, So if it is a particle, how do
• 21:59
  Speaker 1: we see it? How do we study it? We know
• 22:01
  Speaker 1: that it feels gravity, what else does it feel or
• 22:04
  Speaker 1: not feel?
• 22:04
  Speaker 2: So the short answer is we have no idea. Like,
• 22:06
  Speaker 2: it could be that dark matter feels some new kind
• 22:08
  Speaker 2: of force with itself. It could be the dark matter
• 22:11
  Speaker 2: feels no forces other than gravity, and like that could
• 22:14
  Speaker 2: totally be our universe, in which case it's almost impossible
• 22:18
  Speaker 2: to ever discover the particle nature of dark matter. It
• 22:21
  Speaker 2: could just be a mystery forever because gravity is just
• 22:24
  Speaker 2: so weak. There's another possibility that dark matter is kind
• 22:27
  Speaker 2: of misnamed, that dark matter does actually interact with our
• 22:31
  Speaker 2: kind of matter through some mechanism we haven't discovered yet
• 22:35
  Speaker 2: that's not really truly one hundred percent.
• 22:37
  Speaker 1: Dark, But I guess you mean using electromagnetic forces or
• 22:41
  Speaker 1: other kinds of forces, like it dark in terms of
• 22:44
  Speaker 1: light or dark in terms of all the forces in nature.
• 22:47
  Speaker 2: We're imagining maybe there's a new force out there also,
• 22:50
  Speaker 2: So we're suggesting maybe dark matter is some new kind
• 22:52
  Speaker 2: of particle, right, And in addition, maybe there's a new
• 22:55
  Speaker 2: force out there, a force that helps dark matter particles
• 22:59
  Speaker 2: interact with our kind of particles. So call this a
• 23:02
  Speaker 2: new dark force or a portal to the dark sector
• 23:04
  Speaker 2: or whatever. If there is this new kind of force,
• 23:08
  Speaker 2: then maybe it helps dark matter particles bump into our
• 23:11
  Speaker 2: kind of particles, or turn into our kind of particles,
• 23:14
  Speaker 2: or somehow interact with our kind of particles, which would
• 23:17
  Speaker 2: make them effectively visible.
• 23:20
  Speaker 1: But would you need to come up with a new
• 23:22
  Speaker 1: kind of force. Couldn't interact with us through the weak
• 23:25
  Speaker 1: force or the strong force somehow?
• 23:27
  Speaker 2: It's totally possible that dark matter could have interacted with
• 23:29
  Speaker 2: us via one of the forces we know already, but
• 23:32
  Speaker 2: we've basically ruled that out with our experiments.
• 23:35
  Speaker 1: Have we really is that official?
• 23:36
  Speaker 2: If dark matter interacted with a strong force, it would
• 23:39
  Speaker 2: be a very powerful interaction because the strong force is
• 23:41
  Speaker 2: super duper strong, and that would actually be pretty easy
• 23:45
  Speaker 2: to find. We look for dark matter giving off photons.
• 23:47
  Speaker 2: We've never seen that, so we don't think that dark
• 23:49
  Speaker 2: matter actually directly interacts with photons. We've also looked for
• 23:54
  Speaker 2: dark matter interacting via the weak force. And this is
• 23:56
  Speaker 2: probably the biggest area of experimental dark matter particle physics
• 23:59
  Speaker 2: right now, with these huge tanks underground very quiet liquid
• 24:04
  Speaker 2: like xenon, and we wait for dark matter to pass
• 24:07
  Speaker 2: through the Earth and interact with one of these xenon
• 24:10
  Speaker 2: molecules and give it a little kick. So these huge
• 24:13
  Speaker 2: tanks of underground liquid xenon are just waiting for a
• 24:16
  Speaker 2: dark matter particle to bump into it via the weak force.
• 24:19
  Speaker 2: And if it does interact via the weak force, we
• 24:20
  Speaker 2: can calculate how often that should happen. And we've been
• 24:23
  Speaker 2: running these experiments for years and years and years, and
• 24:26
  Speaker 2: we've never seen a blip that looks like dark matter
• 24:29
  Speaker 2: kicking one of these xenon molecules via the weak force.
• 24:33
  Speaker 2: So now we can pretty definitely rule it out.
• 24:36
  Speaker 1: I see, we've been putting stuff out there to hopefully
• 24:39
  Speaker 1: interact with dark matter through the weak force, but so
• 24:41
  Speaker 1: far nothing has been bumped that way. So now you're
• 24:44
  Speaker 1: saying the dark matter probably doesn't interact with the weak force.
• 24:48
  Speaker 2: As time goes on and we don't see any of
• 24:50
  Speaker 2: those interactions, we more confidently say that they never happen.
• 24:53
  Speaker 2: If you only listen for a day. It might be
• 24:55
  Speaker 2: that they only happen once a year and you just
• 24:56
  Speaker 2: haven't seen one yet. But after you've listened for five years,
• 24:59
  Speaker 2: ten years, twenty years, either you're getting very very unlucky
• 25:03
  Speaker 2: or it just doesn't happen. And so now we've had
• 25:05
  Speaker 2: big enough detectors running for enough years that were pretty
• 25:08
  Speaker 2: confident in ruling that out. But it doesn't mean that
• 25:11
  Speaker 2: there isn't a new kind of force, like an even
• 25:14
  Speaker 2: weaker force, that would allow dark matter to interact with
• 25:17
  Speaker 2: our detectors. So that's what they're looking for now. Like
• 25:19
  Speaker 2: they call it the feeble force.
• 25:21
  Speaker 1: It's weaker than weak. That's the idea, exactly weaker than weak.
• 25:25
  Speaker 1: We only we have seen that already with our detectors,
• 25:28
  Speaker 1: with the tanks of Xenon they're sitting there waiting.
• 25:31
  Speaker 2: Depends on how weak it is. If it's super duper
• 25:33
  Speaker 2: extra week, if it's the feeblest force, you can imagine
• 25:36
  Speaker 2: it might take a very very long time. It might
• 25:38
  Speaker 2: be so unlikely they have to run for ten years
• 25:41
  Speaker 2: or one hundred years in order to see it. And
• 25:44
  Speaker 2: that's why we're also at the same time using other
• 25:46
  Speaker 2: methods to try to look for these kinds of interactions,
• 25:49
  Speaker 2: like we're hoping to use this new feeble force to
• 25:51
  Speaker 2: create dark matter at particle colliders.
• 25:54
  Speaker 1: What do you mean, like when you collide protons or
• 25:57
  Speaker 1: quarks like that, it might make dark matter.
• 25:59
  Speaker 2: Yeah, if this feeble force exists that allows dark matter
• 26:04
  Speaker 2: to bump into protons and neutrons inside a xenon atom,
• 26:07
  Speaker 2: then in principle you can reverse that. You can say, well,
• 26:11
  Speaker 2: what if we smash protons together, maybe sometimes they can
• 26:14
  Speaker 2: use the feeble force to create dark matter. Because that's
• 26:16
  Speaker 2: what we do with the particle collider. We annihilate protons
• 26:19
  Speaker 2: together and create new kinds of stuff. And the cool
• 26:22
  Speaker 2: thing about a collider is that anything that's out there,
• 26:24
  Speaker 2: you can make it as long as your protons can
• 26:27
  Speaker 2: interact with it. So anything that protons interact with we
• 26:30
  Speaker 2: produce at the collider eventually. Things that interact with protons
• 26:32
  Speaker 2: a lot, we produce them all the time. Things that
• 26:35
  Speaker 2: don't interact with protons very often, we produce them more rarely,
• 26:38
  Speaker 2: So higgs bosons are pretty rare, for example. But we
• 26:40
  Speaker 2: comb through all of those collisions looking for evidence of
• 26:43
  Speaker 2: the production of dark matter.
• 26:44
  Speaker 1: Wouldn't we have seen evidence of that already? I mean,
• 26:47
  Speaker 1: you've been running the LHC for a long time and
• 26:49
  Speaker 1: particle colliders for decades. You know, if there was some
• 26:53
  Speaker 1: sort of unaccounted for force, wouldn't we have seen it
• 26:56
  Speaker 1: by now?
• 26:56
  Speaker 2: We haven't seen anything. You're right, And again it's a
• 26:59
  Speaker 2: question to the of that force. If that force was
• 27:02
  Speaker 2: as strong as the weak force, yeah, we probably would
• 27:04
  Speaker 2: have seen it. And the longer we run our colliders
• 27:06
  Speaker 2: and don't see it, the weaker that force has to
• 27:09
  Speaker 2: be to still be consistent with our data, to still
• 27:11
  Speaker 2: be hiding from all of these experiments. But we don't
• 27:14
  Speaker 2: know how weak that force is. Maybe it's really ridiculously weak,
• 27:18
  Speaker 2: so weak that we haven't seen it underground and we
• 27:20
  Speaker 2: haven't seen it in our colliders. So we actually turn
• 27:22
  Speaker 2: to another mechanism to try to see this super duper
• 27:25
  Speaker 2: weak force in action, which is to look at the
• 27:28
  Speaker 2: center of the galaxy to see if dark matter is
• 27:30
  Speaker 2: smashing into itself.
• 27:32
  Speaker 1: I see use the center of the galaxy as a
• 27:34
  Speaker 1: particle collider.
• 27:36
  Speaker 2: Exactly because one problem with the particle collider is that
• 27:39
  Speaker 2: it's not very dense. Right. We have protons smashing into protons,
• 27:42
  Speaker 2: but it's like very few protons and we try to
• 27:45
  Speaker 2: run it as often as we can, and it adds
• 27:48
  Speaker 2: up to zillions of collisions, but it just might not
• 27:51
  Speaker 2: be enough. But we think that the center of the
• 27:53
  Speaker 2: galaxy is very very dense with dark matter. We can
• 27:56
  Speaker 2: map out where the dark matter is in the galaxy
• 27:58
  Speaker 2: by looking at how things rouse and how fast things
• 28:01
  Speaker 2: are moving, and we suspect that the center of the
• 28:03
  Speaker 2: galaxy is very dense with dark matter. And so if
• 28:07
  Speaker 2: dark matter has this feeble force, this super weak force,
• 28:10
  Speaker 2: then occasionally two dark matter particles should bump into each
• 28:13
  Speaker 2: other and produce normal matter particles, like the opposite of
• 28:17
  Speaker 2: what we think might happen in the collider, which two
• 28:19
  Speaker 2: protons smash together to make dark matter run that backwards
• 28:22
  Speaker 2: in time. We hope that's the operation happening in the
• 28:25
  Speaker 2: center of the galaxy. So we turn these special telescopes
• 28:28
  Speaker 2: to the wards the center of the galaxy and look
• 28:30
  Speaker 2: for these characteristic flashes of light that might come from
• 28:34
  Speaker 2: those collisions.
• 28:35
  Speaker 1: Interesting, that sounds a little cheaper than building a thirty
• 28:37
  Speaker 1: billion dollar collider here.
• 28:40
  Speaker 2: Well, it was only ten billion dollars, right, so we
• 28:42
  Speaker 2: can save you twenty billion off the top right there,
• 28:45
  Speaker 2: and it wasn't that cheap because you're building a particle
• 28:47
  Speaker 2: detector and launching it into space, which is never simple.
• 28:51
  Speaker 1: All right, Well, let's get into the details of how
• 28:53
  Speaker 1: we're using the center of the galaxy as a collider
• 28:55
  Speaker 1: to look for dark matter. Let's dig into that, but
• 28:57
  Speaker 1: first let's take another quick break. All right, we're looking
• 29:13
  Speaker 1: for dark matter. I had some right here, Daniel. You
• 29:15
  Speaker 1: don't know where I put it.
• 29:16
  Speaker 2: I can give you emoji based directions to it, Derry,
• 29:19
  Speaker 2: I'll send you some arrows.
• 29:21
  Speaker 1: That might not be helpful there. But yeah, there's a
• 29:24
  Speaker 1: lot of matter missing in the universe. All twenty seven
• 29:27
  Speaker 1: percent of the universe is out there, but it's invisible.
• 29:30
  Speaker 1: We can't see it or touch it called dark matter,
• 29:32
  Speaker 1: and our only hope for ever studying its particle nature
• 29:36
  Speaker 1: is that there's some sort of new force that we
• 29:39
  Speaker 1: haven't discovered yet, some super weak force that you're calling
• 29:42
  Speaker 1: the feeble force. Although Daniel, I'm kind of disappointing you
• 29:45
  Speaker 1: didn't call it the dark force.
• 29:48
  Speaker 2: Because then forever it would dominate my destiny exactly right.
• 29:52
  Speaker 1: Then you get the cool red lightsabers or the cool
• 29:55
  Speaker 1: laser pointers when you give your lectures.
• 29:57
  Speaker 2: Yeah, that's true, but I didn't want to have to
• 29:58
  Speaker 2: grow those horns.
• 30:00
  Speaker 1: Sith have horns.
• 30:01
  Speaker 2: That's relief.
• 30:03
  Speaker 1: You need to brush up on your Star Wars there apparently. Yeah,
• 30:05
  Speaker 1: but yeah. Our only hope forever studying the particle nature
• 30:08
  Speaker 1: of dark matter is that it feels a new kind
• 30:10
  Speaker 1: of force we haven't seen before, and we can't generate
• 30:13
  Speaker 1: that force apparently here in our colliders. But there's hope
• 30:16
  Speaker 1: that maybe you can use the center of the galaxy
• 30:18
  Speaker 1: as a collider to maybe study this part of this
• 30:23
  Speaker 1: aspect of dark matter we think we're hoping is there.
• 30:26
  Speaker 2: Exactly, And the idea is dark matter smashes into itself
• 30:29
  Speaker 2: and then via this new feeble force, turns into standard
• 30:33
  Speaker 2: model particles, maybe tau leptons or be quarks or something,
• 30:38
  Speaker 2: and those particles can then give you flashes of light
• 30:40
  Speaker 2: because those particles do interact with light. So what we
• 30:44
  Speaker 2: do is we turn this telescope to the center of
• 30:46
  Speaker 2: the galaxy and we look for these flashes of light
• 30:48
  Speaker 2: that we can't otherwise explain. If you see flashes of
• 30:52
  Speaker 2: light that look like they come from dark matter turning
• 30:54
  Speaker 2: into particles, we know, then you can say, oh, there's
• 30:57
  Speaker 2: evidence for dark matter. There.
• 30:58
  Speaker 1: Wait, the idea is that dark matter smashes into itself.
• 31:02
  Speaker 1: Why does it have to smash into itself.
• 31:05
  Speaker 2: It doesn't have to. It's possible for dark matter also
• 31:07
  Speaker 2: interact with normal matter particles in the sension of the galaxy,
• 31:10
  Speaker 2: the way it might interact, for example, with our tanks
• 31:12
  Speaker 2: of Xenon underground. But the signature we're looking for would
• 31:16
  Speaker 2: come from two dark matter particles smashing into itself, producing
• 31:20
  Speaker 2: like a pair of bottom quarks or a pair of
• 31:21
  Speaker 2: tau leptons, which then give off some photons which travel
• 31:25
  Speaker 2: to our telescope and we observe them.
• 31:27
  Speaker 1: Wait, so two dark matter particles can interact with each
• 31:31
  Speaker 1: other and generate regular kind of matter? Yeah, exactly does
• 31:35
  Speaker 1: that work the other way too? Like, can regular matter
• 31:37
  Speaker 1: interact and come up with dark matter?
• 31:39
  Speaker 2: That's what we're trying to do with the Large Hadron
• 31:40
  Speaker 2: collider is smash regular matter together two protons and turn
• 31:44
  Speaker 2: it into dark matter. We haven't seen that yet, so
• 31:46
  Speaker 2: we're trying to do the opposite, smash dark matter together
• 31:49
  Speaker 2: and turn it into regular matter. It's like the inverse collider.
• 31:52
  Speaker 1: What's the inverse of a collider? An expander as a separator.
• 31:56
  Speaker 2: It just runs it the other direction, you know, instead
• 31:58
  Speaker 2: of colliding normal matter to make dark matter, and we
• 32:00
  Speaker 2: collide dark matter to make normal matter.
• 32:02
  Speaker 1: So the picture is that in the center of the galaxy,
• 32:05
  Speaker 1: you're saying, there's a high density of dark matter, and
• 32:08
  Speaker 1: some dark matter particle just happens to smash head on
• 32:11
  Speaker 1: with another dark matter particle. Hopefully they're going fast enough
• 32:14
  Speaker 1: to actually sort of interact and create a lot of energy.
• 32:18
  Speaker 1: And then out of that comes a regular matter particle
• 32:22
  Speaker 1: from the center of the galaxy that then we see
• 32:24
  Speaker 1: here on Earth and go, yep, that came from two
• 32:27
  Speaker 1: dark matter particles.
• 32:28
  Speaker 2: Yeah, And if you want the microparticle physics explanation, two
• 32:31
  Speaker 2: dark matter particles smashed together form some new kind of
• 32:34
  Speaker 2: particle that mediates this feeble force, call it a dark
• 32:38
  Speaker 2: photon or something. And then that dark photon turns into
• 32:42
  Speaker 2: a pair of normal particles like two bottom corks or
• 32:45
  Speaker 2: two tau leptons or two muons or something, and then
• 32:49
  Speaker 2: those produce photons which then we see here.
• 32:51
  Speaker 1: But then how can we hope to like discern that
• 32:54
  Speaker 1: from all the way here the center of the galaxy is,
• 32:57
  Speaker 1: you know, fifty thousand light years away.
• 32:59
  Speaker 2: It's very very tricky, and that's exactly the difficulty of
• 33:02
  Speaker 2: this method. Number one. It's far away. We think that
• 33:05
  Speaker 2: these photons would be very high energy, so we think
• 33:08
  Speaker 2: that gamma rays would survive travel from the center of
• 33:11
  Speaker 2: the galaxy. But the real problem is that we don't
• 33:14
  Speaker 2: understand the center of the galaxy. So a lot of
• 33:16
  Speaker 2: stuff going on there, making flashes of light anyway that
• 33:19
  Speaker 2: we can't really understand. And so actually we have seen
• 33:23
  Speaker 2: flashes of light from the center of the galaxy that
• 33:25
  Speaker 2: we cannot explain that No astrophysical explanation has been provided
• 33:29
  Speaker 2: to explain these flashes of light, and so some people
• 33:31
  Speaker 2: are actually pretty excited about that. They say, whoa, maybe
• 33:34
  Speaker 2: this is dark matter. But you know, the problem is,
• 33:36
  Speaker 2: we don't really know what's in there in the center
• 33:39
  Speaker 2: of the galaxy. It's a very weird, dense region. We
• 33:41
  Speaker 2: just did a whole episode about how weird it is
• 33:44
  Speaker 2: and how little we understand about what's there. So it
• 33:46
  Speaker 2: could just be new, weird stuff made of normal matter
• 33:49
  Speaker 2: in the center of the galaxy flashing lights and ways
• 33:52
  Speaker 2: we don't understand, or it could be dark matter creating
• 33:55
  Speaker 2: these flashes of light.
• 33:56
  Speaker 1: Wait, wait, wait, what do these flashes look like? Like
• 33:59
  Speaker 1: You're just looking at at the galaxy center of the
• 34:01
  Speaker 1: galaxy and suddenly there's like a spike or a pulse
• 34:05
  Speaker 1: or a train of pulses. What do these flashes look like?
• 34:08
  Speaker 2: So these flashes come as individual photons. So this telescope,
• 34:12
  Speaker 2: a Fermila telescope, can see gamma ray photons, which are
• 34:15
  Speaker 2: just photons in a certain energy range in this case
• 34:18
  Speaker 2: from fifty million electron volts up to a trillion electron volts.
• 34:22
  Speaker 2: And they see a bunch of these gamma ray photons
• 34:25
  Speaker 2: from the center of the galaxy, and we cannot explain.
• 34:27
  Speaker 1: Them otherwise, like one at a time, Well, the.
• 34:29
  Speaker 2: Detector can only see one photon at a time.
• 34:32
  Speaker 1: Yeah, I guess. I mean, like you see one and
• 34:33
  Speaker 1: then you don't see one for another year. Or is
• 34:36
  Speaker 1: it do you see like a whole bunch of them
• 34:37
  Speaker 1: in a cluster or something.
• 34:38
  Speaker 2: So the higher energies are definitely more rare than they
• 34:40
  Speaker 2: are at the lower energies, but there's a lot of them.
• 34:42
  Speaker 2: It's not just like one or two or seven photons.
• 34:45
  Speaker 2: You know, we're talking about thousands of photons here, accumulated
• 34:48
  Speaker 2: over many, many years and so people are trying to
• 34:51
  Speaker 2: understand where are these photons coming from. Is there something
• 34:54
  Speaker 2: going on with normal matter at the center of the
• 34:55
  Speaker 2: galaxy or is this actually dark matter?
• 34:58
  Speaker 1: But I guess, why are they eplainable or why are
• 35:00
  Speaker 1: they so mysterious. Isn't it just like, oh, here's a
• 35:03
  Speaker 1: photo with a lot of energy.
• 35:05
  Speaker 2: Well, we have an idea for what's in the center
• 35:07
  Speaker 2: of the galaxy. We think that there's a black hole there,
• 35:10
  Speaker 2: and we think there's a swirl of stuff around the
• 35:11
  Speaker 2: black hole, and we think there's a certain density of stars.
• 35:14
  Speaker 2: We think there's gas and dust and all sorts of stuff,
• 35:17
  Speaker 2: and we use that model to predict what we should
• 35:19
  Speaker 2: see from the center of the galaxy, and we see
• 35:21
  Speaker 2: all that stuff, plus we see more. We see another
• 35:24
  Speaker 2: spectrum of photons that have sort of like a different shape,
• 35:27
  Speaker 2: like they emit light in different patterns. They're distributed around
• 35:31
  Speaker 2: the center of the galaxy, and their brightness and their
• 35:33
  Speaker 2: wavelengths can't be explained by any of the components that
• 35:36
  Speaker 2: we do know about in the center of the galaxy.
• 35:38
  Speaker 2: So it's definitely something new happening in the center of
• 35:41
  Speaker 2: the galaxy emitting photons in a way that we can't
• 35:43
  Speaker 2: otherwise explain, and it's consistent with some theories of dark matter.
• 35:48
  Speaker 1: All right, so well, let's dig into that part of it. Then,
• 35:51
  Speaker 1: what's the connection between gravity and or what might be
• 35:54
  Speaker 1: the connection between gravity and these flashes of light.
• 35:56
  Speaker 2: Yes, so we've been seeing these flashes for a while,
• 35:58
  Speaker 2: and there's been theories of dark matter for decades from
• 36:01
  Speaker 2: the center of the galaxy, but people have been unsure
• 36:04
  Speaker 2: about what it means because we don't understand what's going
• 36:06
  Speaker 2: on at the center of the galaxy very well. So
• 36:08
  Speaker 2: recently people came up with a really cool clever idea
• 36:12
  Speaker 2: to combine gravitational information with these flashes of light. They say, look,
• 36:17
  Speaker 2: if there is dark matter creating these flashes of light,
• 36:20
  Speaker 2: we should be able to zero in on where these
• 36:22
  Speaker 2: flashes come from and see if there's dark matter there.
• 36:25
  Speaker 2: By seeing if there's a gravitational effect from that dark matter,
• 36:28
  Speaker 2: Like if there's a blob of dark matter there that's
• 36:30
  Speaker 2: extra dense and making these flashes, we should be able
• 36:33
  Speaker 2: to see gravitational lensing from that dark matter blob to
• 36:37
  Speaker 2: tell us, oh, that really is dark matter and not
• 36:39
  Speaker 2: just some star going crazy.
• 36:41
  Speaker 1: Couldn't it just be a star going crazy or maybe
• 36:43
  Speaker 1: like a quasar or something like that. Doesn't that seem
• 36:46
  Speaker 1: more likely? But like, how do you know which is
• 36:48
  Speaker 1: more likely?
• 36:49
  Speaker 2: Exactly? We don't really understand what's there, so it is tricky.
• 36:52
  Speaker 2: But the first thing they did is they tried to
• 36:54
  Speaker 2: map all the gravitational lensing near the center of the
• 36:57
  Speaker 2: galaxy and measure that by seeing like how that does
• 37:00
  Speaker 2: or it's light from behind the galaxy, Like galaxies in
• 37:02
  Speaker 2: the background far away, how is their light being distorted
• 37:05
  Speaker 2: as it passes through the center of the galaxy. So
• 37:08
  Speaker 2: that's the gravitational lensing measurement. They use that as a
• 37:11
  Speaker 2: way to just see like are there pockets of extra
• 37:13
  Speaker 2: gravity in the center of the galaxy. So they make
• 37:16
  Speaker 2: a map of all this gravitational lensing and then they
• 37:19
  Speaker 2: line that up with the map of these extra flashes
• 37:22
  Speaker 2: from the center of the galaxy, and boom, boom, boom,
• 37:24
  Speaker 2: they do line up. They line up very nicely. So
• 37:28
  Speaker 2: there seems to be this correlation between where there's extra
• 37:32
  Speaker 2: gravitational lensing and where there's more gamma ray flashes.
• 37:36
  Speaker 1: That's pretty interesting, although it could just be something else.
• 37:39
  Speaker 1: I wonder, like, you know where maybe where there's a
• 37:41
  Speaker 1: lot of dark matter. There are also a lot of
• 37:44
  Speaker 1: black holes.
• 37:45
  Speaker 2: Exactly, and everybody's very skeptical at first, right, you don't
• 37:47
  Speaker 2: want to just like jump up and down and claim
• 37:49
  Speaker 2: you discover dark matter. So then they try to explain
• 37:52
  Speaker 2: this with other sources, you know, And one idea they
• 37:54
  Speaker 2: have in this paper is that maybe it's blazars. Blazars
• 37:58
  Speaker 2: are these super awesome galaxies that are generating a really
• 38:01
  Speaker 2: powerful beam of light from the center of the galaxy.
• 38:03
  Speaker 2: If you have a super massive black hole the core
• 38:06
  Speaker 2: of a galaxy, then its magnetic field can funnel radiation
• 38:10
  Speaker 2: up and down the north and south pole of that
• 38:13
  Speaker 2: galaxy and produce a very powerful beam of light. And
• 38:16
  Speaker 2: if that beam of light is pointed right at the Earth,
• 38:19
  Speaker 2: the relativistic effects effectively make the Earth a little shorter
• 38:22
  Speaker 2: and pile up the light beams a little bit to
• 38:24
  Speaker 2: make it extra bright. So these things are called blazars,
• 38:27
  Speaker 2: and blazars could also explain these effects that we're seeing.
• 38:31
  Speaker 2: And so in the paper they analyze like, well, is
• 38:33
  Speaker 2: this just more blazars than we anticipated, or is it
• 38:36
  Speaker 2: dark matter? And they can explain part of this effect
• 38:39
  Speaker 2: with blazars, but there's a part of it that blazars
• 38:42
  Speaker 2: cannot explain, and that is very nicely explained by dark matter.
• 38:46
  Speaker 2: And so this is the challenge with studying dark matter.
• 38:49
  Speaker 2: It's like, is what we're seeing dark matter or is
• 38:51
  Speaker 2: it something else we don't understand because dark matter is
• 38:54
  Speaker 2: still kind of a fuzzy idea.
• 38:56
  Speaker 1: M yeah, I mean we don't really know or have
• 39:00
  Speaker 1: a clear idea what it's nature is. I feel like
• 39:02
  Speaker 1: we're sort of like putting assumptions on top of assumptions
• 39:05
  Speaker 1: on top of assumptions and then checking that.
• 39:07
  Speaker 2: That is what we're doing. We're making hypotheses and we're
• 39:10
  Speaker 2: checking them, and we're coming up with alternatives, like is
• 39:12
  Speaker 2: this dark matter? Is this something else? What we know
• 39:15
  Speaker 2: is that there is something new happening at the center
• 39:17
  Speaker 2: of the galaxy. Something is generating these flashes of light
• 39:20
  Speaker 2: that we do not understand. Maybe it's dark matter, maybe
• 39:22
  Speaker 2: it's some other new astrophysical source. Maybe it's some new
• 39:26
  Speaker 2: process that's distorting light from behind the galaxy. We don't know.
• 39:29
  Speaker 2: There's something new to be discovered there. We don't know
• 39:31
  Speaker 2: if that lines up with these other mysteries we're seeing,
• 39:33
  Speaker 2: like galactic rotation, curves and the structure of the galaxy.
• 39:36
  Speaker 2: So maybe this reveals something about dark matter, but maybe
• 39:39
  Speaker 2: it reveals something about something else. Right, we're so clueless
• 39:41
  Speaker 2: about the nature of the universe that we're trying to
• 39:44
  Speaker 2: put these puzzle pieces together. But maybe they don't click.
• 39:46
  Speaker 2: Maybe they're parts of different puzzles. It's just because we're
• 39:49
  Speaker 2: at the beginning of understanding the universe that we're so
• 39:52
  Speaker 2: clueless about how to put this all together.
• 39:54
  Speaker 1: Yeah, I guess it could be anything. Could be alien
• 39:57
  Speaker 1: sending us emojis. Maybe those high speed photons are there
• 40:00
  Speaker 1: version of.
• 40:01
  Speaker 2: Emojis exactly, Maybe there are express emojis, hopefully they're safer work.
• 40:07
  Speaker 2: This is a very difficult kind of science because the
• 40:09
  Speaker 2: data is sparse. You just have like these flashes of
• 40:12
  Speaker 2: life from the center of the galaxy, and we're very
• 40:14
  Speaker 2: far away from the center, as you said. So I've
• 40:16
  Speaker 2: been to like whole conferences dedicated just to this signal
• 40:19
  Speaker 2: and understanding it, and people show completely different interpretations. They say, oh,
• 40:23
  Speaker 2: I can explain all of it using some astrophysical source,
• 40:27
  Speaker 2: and other people say, no, that's impossible, it can't describe it.
• 40:29
  Speaker 2: And other people say, well, you forgot to account for
• 40:32
  Speaker 2: all these uncertainties in that and if you let these
• 40:34
  Speaker 2: things float and consider other possible ways that these things
• 40:37
  Speaker 2: get interact, then maybe it explains it. So we really
• 40:39
  Speaker 2: are at the beginning days of understanding what it is
• 40:41
  Speaker 2: we're seeing. But it's cool to see people try to
• 40:43
  Speaker 2: line these things up, you know, gravity and flashes of
• 40:45
  Speaker 2: light and other ways to try to get ideas for
• 40:48
  Speaker 2: what dark matter might be.
• 40:49
  Speaker 1: All right, well, it sounds like it's still kind of
• 40:52
  Speaker 1: an open question and a big mystery, but it is
• 40:54
  Speaker 1: a pretty exciting idea to kind of like use one
• 40:56
  Speaker 1: mystery to try to explain another mystery. It's like you're
• 40:59
  Speaker 1: piling on the mysteries.
• 41:00
  Speaker 2: We are piling on the mysteries, and we're trying to
• 41:02
  Speaker 2: line things up. You know, we're trying to come up
• 41:05
  Speaker 2: with a coherent explanation for everything we see out there
• 41:07
  Speaker 2: in the universe. It's not fair to have one story
• 41:09
  Speaker 2: you tell in one case and a completely different story
• 41:12
  Speaker 2: you tell in another case. Right, you need a single
• 41:14
  Speaker 2: theory that explains everything we see. And that's really a challenge,
• 41:18
  Speaker 2: especially because the data is not as good as we'd
• 41:20
  Speaker 2: like it to be. You know, we'd like to have
• 41:22
  Speaker 2: these sensors at the center of the galaxy probing these
• 41:24
  Speaker 2: things in detail with very fine spatial resolution. But instead
• 41:28
  Speaker 2: we're limited to these like tiny cameras orbiting very far
• 41:31
  Speaker 2: from the center of the galaxy trying to get a glimpse.
• 41:34
  Speaker 2: Like imagine you were trying to understand what was happening
• 41:36
  Speaker 2: in Manhattan and all you had was like a camera
• 41:38
  Speaker 2: in Indiana. It'd be pretty tricky.
• 41:40
  Speaker 1: Yeah, especially with all those buildings, be hard to kind
• 41:42
  Speaker 1: of see what's going on between there. So it sounds
• 41:45
  Speaker 1: like maybe we just need to send a pro to
• 41:47
  Speaker 1: the center of the galaxy right figure out what's there,
• 41:50
  Speaker 1: you know, and just wait fifty thousand years or so.
• 41:53
  Speaker 2: Yeah, some poor graduate student is going to wait fifty
• 41:56
  Speaker 2: thousand years to defend their thesis.
• 41:58
  Speaker 1: I'll get paid for that. I could get paid for
• 41:59
  Speaker 1: that while I'm doing this podcast.
• 42:02
  Speaker 2: Sounds good.
• 42:02
  Speaker 1: I mean, as long as we're double dipping.
• 42:04
  Speaker 2: Are your checks going to come from the sense of
• 42:06
  Speaker 2: the galaxy because you might be waiting a while?
• 42:08
  Speaker 1: Yeah, no, no, no, they're going to come in a dollar bill.
• 42:11
  Speaker 1: Emojis the magically transform into cash into my Venmo or the.
• 42:16
  Speaker 2: New x app quantum Cash entanglement.
• 42:18
  Speaker 1: There you go. I'll be rich and not rich at
• 42:20
  Speaker 1: the same time.
• 42:22
  Speaker 2: I hope your finances don't collapse.
• 42:24
  Speaker 1: All right, Well, another reminder that there are still humongous
• 42:28
  Speaker 1: mysteries out there in the universe, and that there are
• 42:30
  Speaker 1: scientists out there actively searching for the answers and searching
• 42:33
  Speaker 1: for it, trying to find ways to study it and
• 42:36
  Speaker 1: reveal to the rest of us what its true nature is.
• 42:39
  Speaker 2: So remember that dark matter is really a whole suite
• 42:42
  Speaker 2: of ideas. It's not just like a blank check placeholder
• 42:46
  Speaker 2: for things we don't understand. It's an empty chalkboard for
• 42:48
  Speaker 2: us to fill in with details, and scientists are constantly
• 42:51
  Speaker 2: coming up with ideas for what dark matter might be
• 42:54
  Speaker 2: and then being creative about how we might discover it
• 42:57
  Speaker 2: because we hope one day to fill that chalkboard in
• 42:59
  Speaker 2: with some thing we really do understand.
• 43:01
  Speaker 1: Does that mean you have to call it dark matters
• 43:03
  Speaker 1: or dark's matter? These are the types of questions that
• 43:07
  Speaker 1: I get paid to the thing about from multiple people.
• 43:11
  Speaker 2: That sounds good. Sounds like you are qualified to answer.
• 43:13
  Speaker 1: That question, as are we all all right, well, we
• 43:16
  Speaker 1: hope you enjoyed that. Thanks for joining us. See you
• 43:19
  Speaker 1: next time.
• 43:28
  Speaker 2: Thanks for listening, and remember that Daniel and Jorge Explain
• 43:30
  Speaker 2: the Universe is a production of iHeartRadio. For more podcasts
• 43:34
  Speaker 2: from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever
• 43:39
  Speaker 2: you listen to your favorite shows.