Latest / Daniel and Kelly’s Extraordinary Universe / Where is all the missing matter?

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Where is all the missing matter? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey, Daniel, I think we've been using too much toilet humor.
• 0:11
  Speaker 2: You mean, all those obvious dark matter jokes we make.
• 0:14
  Speaker 1: Yeah, you know, I'm sure it makes all the nine
• 0:16
  Speaker 1: year old to google in the audience. But I don't
• 0:17
  Speaker 1: think we want to undercut our educational message.
• 0:20
  Speaker 2: All right, that's a good point. Let's try that. All right.
• 0:23
  Speaker 1: Well, so what are we talking about today today?
• 0:24
  Speaker 2: We're talking about hot gas.
• 0:26
  Speaker 1: Well, that didn't last very long. Hi. I am joeham Mack,
• 0:44
  Speaker 1: cartoonists and the author of Oliver's Great Big Universe. Hi.
• 0:48
  Speaker 2: I'm Daniel. I'm a particle physicist and a professor at
• 0:51
  Speaker 2: UC Irvine, and I'm often full of hot air.
• 0:55
  Speaker 1: Are an all physicists full of hot air?
• 0:57
  Speaker 2: I'm just talking about the weather here in southern California.
• 0:59
  Speaker 2: I don't know what you mean.
• 1:00
  Speaker 1: What do you mean the weather is inside of you.
• 1:02
  Speaker 2: I'm breathing in the atmosphere literally.
• 1:05
  Speaker 1: I guess if you were breathing out cold there, that
• 1:07
  Speaker 1: would be bad news, because we all know physicists aren't
• 1:10
  Speaker 1: very cool.
• 1:11
  Speaker 2: I'm trying to make physics hot, is what I'm doing.
• 1:13
  Speaker 1: But anyways, welcome to our podcast. Daniel and Jorge explain
• 1:16
  Speaker 1: the Universe, a production of iHeartRadio.
• 1:18
  Speaker 2: In which we try to marinate in all of the
• 1:20
  Speaker 2: wonders and mysteries of the universe. We think that everything
• 1:25
  Speaker 2: that's out there should make sense to you, can make
• 1:27
  Speaker 2: sense to you, will make sense to you if you
• 1:30
  Speaker 2: just think about it, ask enough questions and listen to
• 1:33
  Speaker 2: this podcast long enough.
• 1:34
  Speaker 1: That's why we try to breathe in the universe and
• 1:37
  Speaker 1: breathe it out and think about all of the hot
• 1:40
  Speaker 1: and cold stuff out there in the universe, even the
• 1:42
  Speaker 1: things in toilets.
• 1:44
  Speaker 2: I thought we're avoiding the toilet jokes.
• 1:46
  Speaker 1: Well that was in the joke. I mean, there is
• 1:48
  Speaker 1: physics in toilets, isn't there.
• 1:50
  Speaker 2: That's true. You once challenged our listeners to record their
• 1:53
  Speaker 2: toilet spinning to see if they flush differently in Australia.
• 1:56
  Speaker 1: Oh did they do it.
• 1:57
  Speaker 2: I haven't gotten any didy yet, so we're still waiting
• 1:59
  Speaker 2: for the rest to those experiments. But that is serious
• 2:02
  Speaker 2: toilet science.
• 2:03
  Speaker 1: Yeah, there you go.
• 2:04
  Speaker 2: But in the non toilet realm of the universe, we
• 2:06
  Speaker 2: are very curious about how everything works out there, and
• 2:09
  Speaker 2: more specifically, what's out there and where is it all?
• 2:14
  Speaker 2: Can we figure out what in the end the universe
• 2:16
  Speaker 2: is made out of and where it's all distributed.
• 2:18
  Speaker 1: Yeah, because that is a fundamental human quest to figure
• 2:21
  Speaker 1: out what's going on out there. What is this universe
• 2:23
  Speaker 1: we're in, what's in it? Who else is in it?
• 2:26
  Speaker 1: And what is it made out of?
• 2:27
  Speaker 2: And where have they been dropping all their trash?
• 2:30
  Speaker 1: Wait?
• 2:30
  Speaker 2: What well you mentioned who else is in it? Makes
• 2:33
  Speaker 2: it sound like, you know, we're trying to figure out
• 2:34
  Speaker 2: where all their stuff is, Like did they lose their keys?
• 2:37
  Speaker 2: Where did that box go? This kind of stuff?
• 2:40
  Speaker 1: I was just wondering, you know, so we could say, hi,
• 2:42
  Speaker 1: not find their keys.
• 2:44
  Speaker 2: The first thing we want to do when we talk
• 2:46
  Speaker 2: to the aliens is ask them where they left their stuff.
• 2:48
  Speaker 2: Is this your trash? Did you leave this over here?
• 2:50
  Speaker 2: Please pick that up?
• 2:51
  Speaker 1: Although if they leave their keys to their spaceship line around,
• 2:54
  Speaker 1: I'm not really going to return that one. No one's
• 2:56
  Speaker 1: staying with me.
• 2:58
  Speaker 2: Well. On this podcast, we are often talking about one
• 3:01
  Speaker 2: of the deepest mysteries in modern physics, which is where
• 3:05
  Speaker 2: the dark matter is. We know that most of the
• 3:08
  Speaker 2: stuff in the universe is an invisible kind of matter
• 3:11
  Speaker 2: We've only recently discovered and have very little concrete information
• 3:15
  Speaker 2: about what it is. So we're used to the concept
• 3:18
  Speaker 2: of not understanding everything that's out there in the universe.
• 3:21
  Speaker 2: But it might surprise you to learn that even the
• 3:23
  Speaker 2: kind of stuff that we're used to, the hydrogen, the helium,
• 3:26
  Speaker 2: the kind of matter where made out of, is still
• 3:28
  Speaker 2: something of a mystery.
• 3:30
  Speaker 1: Wait what so then, how do we know how much
• 3:31
  Speaker 1: of it there is out there?
• 3:32
  Speaker 2: We have a bunch of really clever ways of figuring
• 3:35
  Speaker 2: out how much normal matter there should be out there
• 3:37
  Speaker 2: in the universe, but it's tricky to actually find all
• 3:41
  Speaker 2: of it.
• 3:41
  Speaker 1: I see, we know how much of there should be,
• 3:43
  Speaker 1: but we just haven't found it.
• 3:45
  Speaker 2: Is that what you're saying, that's basically it episode done?
• 3:47
  Speaker 1: All right, Well, thank you for joining us. I can
• 3:50
  Speaker 1: go do something else now.
• 3:53
  Speaker 2: Well, maybe the aliens have stolen all that missing matter.
• 3:56
  Speaker 1: WHOA, that's a pretty serious allegation or just you know,
• 4:00
  Speaker 1: impugning the goodwill of the aliens and their legality.
• 4:05
  Speaker 2: Well maybe instead of making a big mess, they've been
• 4:07
  Speaker 2: a little bit too aggressive about cleaning up after themselves.
• 4:11
  Speaker 1: Maybe it's the physicist mmm who stole all the matter
• 4:14
  Speaker 1: on the planet Earth with the wrench.
• 4:17
  Speaker 2: In the end, it's not about understanding the universe. It's
• 4:19
  Speaker 2: about figuring out who to blame for it.
• 4:21
  Speaker 1: Or who do thank for it? Right? Also, right, maybe
• 4:24
  Speaker 1: it's good that we live in this universe. I would
• 4:27
  Speaker 1: think so. But anyways, it is a big question about
• 4:30
  Speaker 1: where all the matter in the universe is that we
• 4:33
  Speaker 1: think should be there, and where it all went. So
• 4:36
  Speaker 1: today end the podcast, we'll be asking the question where
• 4:43
  Speaker 1: is all the missing matter? I guess this is kind
• 4:46
  Speaker 1: of a surprising question because because I didn't know there
• 4:48
  Speaker 1: was missing matter? Did this happen recently or a long
• 4:53
  Speaker 1: time ago?
• 4:53
  Speaker 2: I mean, you're making it sound like an Agatha Christie novel,
• 4:56
  Speaker 2: like the Case of the Missing Matter, Like we put
• 4:58
  Speaker 2: all this hydrogen over here and we came back and
• 5:01
  Speaker 2: it was gone.
• 5:01
  Speaker 1: Yeah. Yeah, there was a blackout, the lights went out,
• 5:04
  Speaker 1: there were some screens, and suddenly there was a missing
• 5:06
  Speaker 1: matter and we're all trapped on an island with a
• 5:08
  Speaker 1: limited number of suspects.
• 5:10
  Speaker 2: That's right. No, it's been a long standing mystery. It's
• 5:13
  Speaker 2: gotten a little bit less play and a less attention
• 5:16
  Speaker 2: than the grander mystery of dark matter, but it's still
• 5:19
  Speaker 2: a very important question in understanding how galaxies form and
• 5:22
  Speaker 2: how the universe looks the way that it does, and
• 5:24
  Speaker 2: where all this stuff is.
• 5:26
  Speaker 1: Now you're saying that this is actually called, or it's
• 5:28
  Speaker 1: called physics, the missing baryon problem.
• 5:31
  Speaker 2: Yeah, that's right, because the kind of matter that we
• 5:33
  Speaker 2: are made out of is made of protons and neutrons,
• 5:36
  Speaker 2: and those are things called baryons. A baryon is anything
• 5:39
  Speaker 2: made out of three quarks, and protons and neutrons are
• 5:42
  Speaker 2: made out of three quarks. So the kind of matter
• 5:44
  Speaker 2: that we are made out of, me and you, and
• 5:46
  Speaker 2: stars and galaxies and all the dust, all the visible
• 5:49
  Speaker 2: matter that's out there, we call that baryonic matter. And
• 5:52
  Speaker 2: so scientists have been trying to understand, like, where are
• 5:54
  Speaker 2: all the baryons in the universe? Are there as many
• 5:57
  Speaker 2: as we think there should be, And when they couldn't
• 5:59
  Speaker 2: find them, they call it the missing baryon problem.
• 6:02
  Speaker 1: M sounds very mysterious, and you also kind of make
• 6:05
  Speaker 1: it sound like it's somebody else's problem.
• 6:07
  Speaker 2: Hey, it's all about pre assignment to blame, right.
• 6:10
  Speaker 1: Right, Yeah, Like if you say like, yeah, it's a problem,
• 6:13
  Speaker 1: I think you're basically saying it's somebody else's problem.
• 6:15
  Speaker 2: Mistakes were made, right.
• 6:17
  Speaker 1: That's right, Yeah, things went missing.
• 6:21
  Speaker 2: Grand funding misallocated, I don't know.
• 6:24
  Speaker 1: So as usual, we were wondering how many people out
• 6:26
  Speaker 1: there knew or know that there is missing baryonic matter
• 6:30
  Speaker 1: out there in the universe.
• 6:31
  Speaker 2: So thanks very much to everybody who participates in this
• 6:34
  Speaker 2: segment of the podcast. We would love to hear your
• 6:37
  Speaker 2: voice among the coorse of listeners, so please don't be
• 6:40
  Speaker 2: shy write to me to questions at Danielandjorge dot com.
• 6:43
  Speaker 1: So think about it for a second. Do you know
• 6:46
  Speaker 1: where the missing baryonic matter in the universe could be?
• 6:49
  Speaker 1: What is the missing baryon problem?
• 6:52
  Speaker 3: I have never heard of the missing baryon problem, but
• 6:54
  Speaker 3: it might be something like the way that we had
• 6:57
  Speaker 3: predicted that the Higgs boson exists and we hadn't experimentally
• 7:01
  Speaker 3: verified it. So maybe there is a baryon, some form
• 7:04
  Speaker 3: of Bearyon particle that we mathematically know must exist, but
• 7:09
  Speaker 3: have it found.
• 7:09
  Speaker 1: I don't know what the missing baryon is, but I
• 7:12
  Speaker 1: hope someone finds it.
• 7:13
  Speaker 4: This is the term I've actually heard of before, if
• 7:15
  Speaker 4: I remember correctly. It has to do with the fact
• 7:19
  Speaker 4: that there is unexplained difference between the matter that existed
• 7:24
  Speaker 4: right after the Big Bang and the matter that exists today.
• 7:27
  Speaker 5: The baryon sounds like some sort of barrier to a atom,
• 7:33
  Speaker 5: So I suppose if it's missing, then it would be
• 7:37
  Speaker 5: some sort of other force that we cannot explain, that
• 7:43
  Speaker 5: it is holding something like an atom together.
• 7:46
  Speaker 1: All right, or interviews here didn't give us a lot
• 7:49
  Speaker 1: of clues.
• 7:51
  Speaker 2: This has not gotten a lot of press compared to
• 7:53
  Speaker 2: dark matter, out of which they've been like dozens and
• 7:56
  Speaker 2: dozens of books written, and it's all sorts of podcasts.
• 7:59
  Speaker 2: Whatever it's name is problem in physics, but the missing
• 8:02
  Speaker 2: baryon problem is sort of like its second cousin that
• 8:05
  Speaker 2: doesn't get top building.
• 8:06
  Speaker 1: It sounds like maybe it's a branding problem, you know,
• 8:09
  Speaker 1: like dark matter. Where's the dark matter in the universe?
• 8:11
  Speaker 1: That sounds mysterious and intriguing. Where's the baryonic matter in
• 8:15
  Speaker 1: the universe. It's like, I'm not a fan of Barry.
• 8:19
  Speaker 2: What they should have called it the dark baryons or something.
• 8:22
  Speaker 1: M yeah, or some other name, right, shining matter, super matter.
• 8:28
  Speaker 2: Well, you know, dark means a lot of different things.
• 8:30
  Speaker 2: As you know, dark can mean mysterious, unknown, not yet understood.
• 8:33
  Speaker 2: It can mean literally dark light does not emit light.
• 8:37
  Speaker 2: And it's confusing because there are things out there that
• 8:39
  Speaker 2: are dark and are made of matter, but are not
• 8:42
  Speaker 2: dark matter, right, Like a lump of charcoal is pretty dark,
• 8:46
  Speaker 2: but it's not dark matter.
• 8:47
  Speaker 1: You might think that physicists name thinks, very confusingly.
• 8:51
  Speaker 2: The missing Physics name committee.
• 8:53
  Speaker 1: So there's a bunch of matter that's missing that we
• 8:55
  Speaker 1: think should be there, but it's missing. That's what we'll
• 8:57
  Speaker 1: be talking about here today. And so let's break it down, Daniel.
• 9:00
  Speaker 1: What is baryonic matter?
• 9:02
  Speaker 2: So baryonic matter is our kind of matter, hydrogen, helium,
• 9:06
  Speaker 2: all of the elements are built out of baryons, because again,
• 9:10
  Speaker 2: a baryon is a particle made of three quarks. Number.
• 9:13
  Speaker 2: Quarks are these little particles that we think are probably fundamental,
• 9:16
  Speaker 2: maybe fundamental, but they interact with the strong nuclear force.
• 9:20
  Speaker 2: And the way they form stable objects is either you
• 9:23
  Speaker 2: get a pair of quarks like quark antiquark that can
• 9:26
  Speaker 2: make a pion, or you can get three of them
• 9:28
  Speaker 2: together to cancel out a red quark, a green cork,
• 9:31
  Speaker 2: and a blue quark, and that gives you a color
• 9:33
  Speaker 2: neutral object like a proton or a neutron that has
• 9:36
  Speaker 2: no overall strong force.
• 9:38
  Speaker 1: Okay, So a baryotic matter is matter made out of
• 9:41
  Speaker 1: quarks basically, right, that's the basic definition of it, like
• 9:43
  Speaker 1: the things that we're made out of, which are protons
• 9:46
  Speaker 1: and neutrons. But it sounds like there are other things
• 9:48
  Speaker 1: besides protons and neutrons you can make out of quarks.
• 9:51
  Speaker 2: Yeah, you can make all kinds of things out of quarks.
• 9:54
  Speaker 2: You can make other hadrons. There's other combinations of quarks
• 9:58
  Speaker 2: that you can use to make other hadrons, like you
• 10:00
  Speaker 2: put three strange quarks together, or you can make an
• 10:03
  Speaker 2: up and down and a strange etc. There's lots of
• 10:05
  Speaker 2: different baryons you can make out of three quarks. You
• 10:08
  Speaker 2: can also make combinations out of pairs of quarks. It's
• 10:11
  Speaker 2: a huge zoo of particles made out of quark pairs.
• 10:14
  Speaker 2: The only stable one is the proton. The proton by
• 10:16
  Speaker 2: itself we think will last for a long long time,
• 10:19
  Speaker 2: and the neutron is stable when combined with the proton
• 10:22
  Speaker 2: inside of nucleus. So that's why protons and neutrons are
• 10:26
  Speaker 2: the most common kind of baryon out there.
• 10:28
  Speaker 1: So today we're talking about which kind specifically all of
• 10:32
  Speaker 1: them or mostly protons and neutrons.
• 10:34
  Speaker 2: Mostly protons and neutrons, because that's what we expect the
• 10:37
  Speaker 2: baryons out there to be made out of. If you
• 10:39
  Speaker 2: have other baryons out there, they typically decay down to
• 10:42
  Speaker 2: protons and neutrons. Really, though, we're trying to account for
• 10:45
  Speaker 2: all the quarks. In the end, we don't really care
• 10:47
  Speaker 2: if they're in protons or in neutrons, or in helium
• 10:49
  Speaker 2: or in hydrogen. We just want to know how much
• 10:51
  Speaker 2: of our kind of matter, quark based matter, is there,
• 10:54
  Speaker 2: and how much of the other stuff is there, and
• 10:56
  Speaker 2: can we figure out where all the quarks.
• 10:58
  Speaker 1: Went saying baryon matter, barry on which kind of matter
• 11:03
  Speaker 1: it settles in.
• 11:06
  Speaker 2: Yeah, that's right, And it's a fascinating situation to be
• 11:08
  Speaker 2: in because we have all these really clever ways of
• 11:11
  Speaker 2: knowing how many quarks there should be in the universe.
• 11:15
  Speaker 2: That seems sort of crazy, like, how could you possibly
• 11:18
  Speaker 2: have an idea of how many quarks they're on the universe.
• 11:20
  Speaker 2: They're here, they're there, they're everywhere. How could you possibly
• 11:23
  Speaker 2: count them?
• 11:24
  Speaker 1: Well, I mean that's kind of basically what you're asking, right,
• 11:26
  Speaker 1: is you're asking where are all the quarks in the universe?
• 11:29
  Speaker 2: Right, exactly. We are asking that, but we're asking in
• 11:31
  Speaker 2: two ways. One way is using information from the very
• 11:35
  Speaker 2: early universe, which tells us how many quarks there should be,
• 11:38
  Speaker 2: and then another way is more direct, is going out
• 11:40
  Speaker 2: there and actually looking for them and saying, can we
• 11:43
  Speaker 2: find all the quarks that our early universe theories predict
• 11:47
  Speaker 2: are out there? And that's where the discrepancy comes from.
• 11:50
  Speaker 1: Hmmm, So I think you're saying that we could have
• 11:52
  Speaker 1: just titled the episode where are all the Missing quarks?
• 11:55
  Speaker 2: Yeah, where are all the missing quarks? Exactly? But in
• 11:57
  Speaker 2: physics it's called the missing barrier problem, and it makes
• 12:01
  Speaker 2: up the kind of matter that we're familiar with. Right,
• 12:04
  Speaker 2: we think that dark matter is not made of quarks,
• 12:06
  Speaker 2: that's made of something else entirely. So this little sliver
• 12:10
  Speaker 2: of the universe that we think is about five percent
• 12:12
  Speaker 2: of all the energy density of the universe, baryonic matter
• 12:15
  Speaker 2: stuff made out of quarks. That's the thing we're still
• 12:18
  Speaker 2: trying to understand after all these years.
• 12:21
  Speaker 1: Is there an important distinction between asking where all the
• 12:23
  Speaker 1: baryonic matter is and asking where all the quarks are? Like,
• 12:27
  Speaker 1: are there quarks that are not in baryonic matter? Or
• 12:30
  Speaker 1: is it all the same term.
• 12:32
  Speaker 2: There are no quarks that are not in some kind
• 12:33
  Speaker 2: of particle because quarks can't be by themselves, so they
• 12:36
  Speaker 2: always form either masons, which are quark quark pairs, or baryons,
• 12:40
  Speaker 2: which are triplets of quarks. Baryonic matter technically probably also
• 12:44
  Speaker 2: includes the electrons. So if you have, for example, a
• 12:47
  Speaker 2: hydrogen atom that's a proton and an electron that you
• 12:50
  Speaker 2: could call baryonic matter because it's based on the baryon
• 12:53
  Speaker 2: the proton, that technically includes the electron. So baryonic matter
• 12:57
  Speaker 2: is probably more accurate description because it includes the electrons.
• 13:00
  Speaker 2: Also they bind with the protons.
• 13:02
  Speaker 1: Wait, so what there's electrons missing too?
• 13:05
  Speaker 2: Well, electrons are part of the five percent of the
• 13:06
  Speaker 2: universe made out of normal matter, basically quarks and leptons.
• 13:11
  Speaker 1: Okay, so then there's a certain amount of quarks and
• 13:13
  Speaker 1: electrons in the universe that we think should be there.
• 13:16
  Speaker 1: And you're saying, we have an idea of how much
• 13:18
  Speaker 1: there should be there based on our measurements of the
• 13:21
  Speaker 1: origin of the universe.
• 13:22
  Speaker 2: Yeah, we have all these really clever ways of looking
• 13:25
  Speaker 2: at details from their early universe and using that to
• 13:28
  Speaker 2: figure out essentially how many quarks there should be today.
• 13:32
  Speaker 2: In order to build stuff up, we should be able
• 13:34
  Speaker 2: to predict how much hydrogen and how much helium and
• 13:36
  Speaker 2: all sorts of stuff there are from our pictures of
• 13:38
  Speaker 2: the early universe. And there's two totally separate ways to
• 13:42
  Speaker 2: predict how much baryonic matter there should be left over today.
• 13:46
  Speaker 2: One of them comes from the cosmic microwave background radiation,
• 13:49
  Speaker 2: this very early light from about three hundred and eighty
• 13:52
  Speaker 2: thousand years after the Big Bang, and another comes from
• 13:55
  Speaker 2: the ratio of the elements, how much hydrogen, how much helium,
• 13:59
  Speaker 2: how much detery there is in the universe. Both of
• 14:02
  Speaker 2: those are very sensitive to the quark density in the
• 14:05
  Speaker 2: early universe and so can tell us how many quarks
• 14:08
  Speaker 2: there should be.
• 14:09
  Speaker 1: Meaning like, we maybe start with a guess and see
• 14:13
  Speaker 1: if that makes the universe make sense as we see
• 14:15
  Speaker 1: it today, and then you adjust that until you get
• 14:17
  Speaker 1: an amount that do you think makes what we see
• 14:20
  Speaker 1: in the cosmic microwave background and in the amount of
• 14:24
  Speaker 1: stuff we see makes sense.
• 14:26
  Speaker 2: Yeah, I don't know that we have to start with
• 14:27
  Speaker 2: a guess. It's more like there's information in the cosmic
• 14:30
  Speaker 2: microwave background radiation that tells us exactly how many baryons
• 14:34
  Speaker 2: there should be. And also by measuring the ratios of
• 14:37
  Speaker 2: the elements how much hydrogen, how much helium, we can
• 14:40
  Speaker 2: use that to make a calculation of how many baryons
• 14:42
  Speaker 2: there should be, so we don't have to guess. We
• 14:44
  Speaker 2: can just like extract it directly from these measurements.
• 14:48
  Speaker 1: Well, maybe break it down for people. How does the
• 14:50
  Speaker 1: ratio of hydrogen and helium tells how many quarts the
• 14:54
  Speaker 1: universe started with?
• 14:55
  Speaker 2: So in the very early universe, things were super duper
• 14:57
  Speaker 2: dense and hot, right, the basic story of the universe,
• 15:00
  Speaker 2: things were very very hot and dense. We don't know
• 15:02
  Speaker 2: how we got to that state, that's sort of a
• 15:04
  Speaker 2: big question mark, but we're very certain that things were
• 15:07
  Speaker 2: very hot and dense and very compressed. And then the
• 15:09
  Speaker 2: universe expanded, and as it expands, it cools. So you
• 15:12
  Speaker 2: start out with like crazy high energy, and then things
• 15:15
  Speaker 2: cool further and those quarks form protons and neutrons, et cetera.
• 15:19
  Speaker 2: And then as things cool even further, those protons and
• 15:22
  Speaker 2: neutrons start to form bonds, so you make for example, deuterium,
• 15:25
  Speaker 2: which is a combination of protons and neutrons the deuterium
• 15:29
  Speaker 2: can then fuse into helium. So what's happening is the
• 15:32
  Speaker 2: universe is cooling and things are sort of like settling
• 15:34
  Speaker 2: into place. You're like baking bits and pieces of the universe.
• 15:37
  Speaker 2: After about twenty minutes, things are then too cold to
• 15:41
  Speaker 2: make any more helium or make any more deuterium, so
• 15:44
  Speaker 2: you sort of ran out of time to make deterium.
• 15:46
  Speaker 2: So in the very early universe you had this little
• 15:48
  Speaker 2: window to make deterium and to make helium, and the
• 15:51
  Speaker 2: rest of everything is just hydrogen. And the amount of
• 15:53
  Speaker 2: deuterium and helium you get depends very very sensitively on
• 15:57
  Speaker 2: the density of quarks, Like you have more we're exploding
• 16:00
  Speaker 2: around in that window, you get more deterium, you have
• 16:03
  Speaker 2: fewer quarks, you get less deterium. So if you measure
• 16:06
  Speaker 2: the hydrogen deterium helium ratios, now you can tell the
• 16:11
  Speaker 2: quark density back in that first little window in the
• 16:13
  Speaker 2: first twenty minutes of the universe.
• 16:16
  Speaker 1: And how do you measure that ratio right now? Like
• 16:19
  Speaker 1: we can we go out there into space and gather
• 16:22
  Speaker 1: hydrogen and helium. How do we determine it?
• 16:24
  Speaker 2: Yeah, you can actually just fill up a glass of
• 16:26
  Speaker 2: water from your tap, because one out of like every
• 16:29
  Speaker 2: six thousand atoms of hydrogen is actually an isotope of
• 16:32
  Speaker 2: hydrogen called deuterium, has a little neutron stuck to it,
• 16:35
  Speaker 2: and that deuterium is pretty stable. So the amount we
• 16:38
  Speaker 2: made back then is still the amount we make now.
• 16:40
  Speaker 2: There's like basically no other natural, significant sources of deuterium,
• 16:44
  Speaker 2: So the universe is kind of like locked into this
• 16:46
  Speaker 2: deterium ratio. When you fill a glass of water at
• 16:49
  Speaker 2: the tap, one out of six thousand atoms of those
• 16:52
  Speaker 2: waters has a hydrogen in it that's actually deuterium. How
• 16:56
  Speaker 2: do you measure that? You can just put it through
• 16:57
  Speaker 2: like a mass spectrometer to measure the weight of the
• 16:59
  Speaker 2: at and you'll see this little peak of some water
• 17:02
  Speaker 2: that's a little heavier.
• 17:03
  Speaker 1: But how do I know that's just not the water
• 17:05
  Speaker 1: in my town that has that level of deuterium, or
• 17:10
  Speaker 1: even like in our solar system or even galactic neighborhood.
• 17:12
  Speaker 1: How do you do you extrapolate my tap water to
• 17:15
  Speaker 1: the entire universe?
• 17:17
  Speaker 2: You're right, You've unraveled this entire science. No, we obviously
• 17:20
  Speaker 2: don't just base it on the top water in your
• 17:22
  Speaker 2: house or in anybody else's house. We make measurements all
• 17:24
  Speaker 2: over the place. We can make measurements in the rest
• 17:26
  Speaker 2: of the Solar system by looking at like vibrational modes,
• 17:29
  Speaker 2: because deuterium has slightly different energy levels than normal hydrogen,
• 17:33
  Speaker 2: so you can see evidence for this all over the universe.
• 17:36
  Speaker 2: And so we see a pretty well known mixture of
• 17:38
  Speaker 2: deuterium inside hydrogen.
• 17:40
  Speaker 1: All right, So then that tell us how much quark
• 17:42
  Speaker 1: matter there should be in the universe, and how much
• 17:45
  Speaker 1: is that amount?
• 17:46
  Speaker 2: That's about five percent of the energy density of the universe.
• 17:50
  Speaker 2: And this is a number that's easy to misunderstand. What
• 17:52
  Speaker 2: we mean by that is like, take a big chunk
• 17:54
  Speaker 2: of the universe, like a cubic light year, and out
• 17:56
  Speaker 2: of all the energy inside of it, all the photons,
• 17:59
  Speaker 2: all the dark matter, all the normal matter, all the
• 18:02
  Speaker 2: dark energy, all of that stuff, and the normal matter
• 18:05
  Speaker 2: should account for five percent of the energy density of
• 18:08
  Speaker 2: that chunk. So we're not saying anything about the size
• 18:10
  Speaker 2: of the universe or the total number. We're just saying, like,
• 18:13
  Speaker 2: what's the ratio five percent of all the energy in
• 18:15
  Speaker 2: any given chunk of space should be due to buryonic matter.
• 18:19
  Speaker 1: According to what we know of the Big Bang and
• 18:23
  Speaker 1: the cosmic microwave background. But it seems that some of
• 18:26
  Speaker 1: that matter is missing. Somebody took it or destroyed it,
• 18:30
  Speaker 1: or I don't know, hate it. And so let's get
• 18:33
  Speaker 1: into that mystery and who we can blame for that
• 18:37
  Speaker 1: in more detail. But first let's take a quick break.
• 18:52
  Speaker 1: All right, we're talking about some missing matter in the universe.
• 18:55
  Speaker 1: There's a certain amount of quark matter in the universe
• 18:58
  Speaker 1: that we think should be there. Five percent of the
• 19:01
  Speaker 1: energy and matter in the universe should be quark matter.
• 19:03
  Speaker 1: But Daniel, it sounds like that's not what we're seeing.
• 19:06
  Speaker 2: Yeah, that's right. We have not yet figured out where
• 19:08
  Speaker 2: that five percent of matter is. And if you're skeptical
• 19:11
  Speaker 2: about that five percent calculation, know that we have other
• 19:14
  Speaker 2: ways to calculate this number that are totally independent. Right.
• 19:17
  Speaker 2: The description we gave you about the deterium fraction of
• 19:19
  Speaker 2: the universe, that's called Big Bang nucleosynthesis. It's understanding how
• 19:23
  Speaker 2: much of various elements were made in the very early universe.
• 19:26
  Speaker 2: We have other measurements from the cosmic microwave background radiation
• 19:30
  Speaker 2: which come from much later in the universe, like three
• 19:32
  Speaker 2: hundred and eighty thousand years that are completely independent, totally
• 19:36
  Speaker 2: separate measurements. There, we see the early universe plasma sloshing
• 19:39
  Speaker 2: around in a way that's sensitive to the number of
• 19:42
  Speaker 2: baryons and the amount of dark matter and the number
• 19:45
  Speaker 2: of photons. And that's a very very precise measurement, much
• 19:48
  Speaker 2: more precise even than the Big Bang nucleosynthesis, and it degrees.
• 19:51
  Speaker 2: It's about five percent of the energy density should be baryons.
• 19:56
  Speaker 1: But I wonder are they really that independent? I mean,
• 19:59
  Speaker 1: don't they both depend on our model of the universe
• 20:02
  Speaker 1: and or at least our model of the Big Bang.
• 20:04
  Speaker 2: Absolutely, yeah, there are a lot of assumptions in common,
• 20:06
  Speaker 2: but there are independent measurements. Like they have different sources.
• 20:09
  Speaker 2: You know, one is measuring the fraction of deterium in
• 20:12
  Speaker 2: the universe. The other one is like looking at these
• 20:14
  Speaker 2: very cold photons in the night sky. They also come
• 20:18
  Speaker 2: from a different age in the universe. So they're absolutely
• 20:20
  Speaker 2: they're not completely independent, but they're very useful cross checks. Right,
• 20:24
  Speaker 2: we would be surprised and confused if those two numbers
• 20:27
  Speaker 2: didn't agree with each other.
• 20:28
  Speaker 1: Right, all right, So then those measurements are telling us
• 20:31
  Speaker 1: there's missing matter, how much quark matter in the universe
• 20:33
  Speaker 1: is missing, so like most of it, five percent of
• 20:37
  Speaker 1: the universe is missing.
• 20:39
  Speaker 2: More like eighty percent of the universe. If you look
• 20:42
  Speaker 2: around for quark matter, you can find loss of it. Right,
• 20:44
  Speaker 2: Like I'm made a cork matter, You're made of cork matter, right,
• 20:47
  Speaker 2: your lunch is made of cork matter. The Earth, the
• 20:50
  Speaker 2: Sun is made out of quark matter. All this stuff
• 20:52
  Speaker 2: is pretty easy out of all the galaxies and the
• 20:55
  Speaker 2: stars and the gas that glows in the universe, and
• 20:58
  Speaker 2: then add the harder bits. Right, Some of the stuff
• 21:00
  Speaker 2: that's out there in the universe, like we were talking
• 21:02
  Speaker 2: about earlier, is matter that is dark, but it's not
• 21:05
  Speaker 2: dark matter. You know, things like black holes or things
• 21:09
  Speaker 2: like big massive planets that are not glowing. These things
• 21:12
  Speaker 2: are harder to spot and harder to account for. But
• 21:16
  Speaker 2: people have done a sort of census of all of
• 21:18
  Speaker 2: this stuff. Where is all the stuff that we know about,
• 21:21
  Speaker 2: how much is there, and how does it add up?
• 21:23
  Speaker 2: And together it comes to, you know, about fifteen twenty
• 21:26
  Speaker 2: percent of what we.
• 21:27
  Speaker 1: Expect, fifteen to twenty percent of the five percent that
• 21:30
  Speaker 1: we think should be there.
• 21:31
  Speaker 2: Mm hmm exactly. So most of the buryonic matter in
• 21:34
  Speaker 2: the universe is not in the stars and in the
• 21:36
  Speaker 2: galaxies and in the gas, or in black holes, or
• 21:39
  Speaker 2: in planets, or we think in big chunks of rock
• 21:42
  Speaker 2: floating out there in the universe. And again we're not
• 21:44
  Speaker 2: talking about dark matter, right. We know dark matter is
• 21:46
  Speaker 2: out there and it's another mysterious thing. We're just talking
• 21:49
  Speaker 2: about the missing quarks. We just can't find as many
• 21:52
  Speaker 2: quarks as we expect.
• 21:54
  Speaker 1: I wonder if then you just need to lure your
• 21:56
  Speaker 1: expectations anyway, like mactation is wrong. Maybe that's the real problem.
• 22:03
  Speaker 2: Yeah, but we have these two fairly independent measurements that
• 22:06
  Speaker 2: tell us that the universe should be five percent. And
• 22:09
  Speaker 2: this all fits in very nicely with our model of
• 22:12
  Speaker 2: the universe, how it expands and how structure has formed.
• 22:15
  Speaker 2: We have all these ideas for how the universe comes
• 22:18
  Speaker 2: together from the hot gas to forming these very cold
• 22:21
  Speaker 2: galaxies later on, and all these things are very sensitive
• 22:24
  Speaker 2: to the dark energy, dark matter, and normal matter fraction
• 22:28
  Speaker 2: of the universe. So it's the number we feel pretty
• 22:30
  Speaker 2: confident in five percent, and it gives us enough confidence
• 22:34
  Speaker 2: that we want to go out there and look for
• 22:35
  Speaker 2: these missing burials. We're pretty sure they exist, we just
• 22:38
  Speaker 2: hadn't seen them yet.
• 22:40
  Speaker 1: We Well, just so you know, that is an option
• 22:42
  Speaker 1: in life. You can just lower your expectations and then
• 22:45
  Speaker 1: you can take a vacationion.
• 22:46
  Speaker 2: Well, I want to encourage all of our listeners in
• 22:48
  Speaker 2: the opposite direction to keep pushing forward until your questions
• 22:51
  Speaker 2: are answered. Don't give up.
• 22:52
  Speaker 1: All right, Well, let's keep going then. So, there is
• 22:55
  Speaker 1: a certain amount of cork matter in universe we think
• 22:57
  Speaker 1: should be there, but we can't seem to for it.
• 23:00
  Speaker 1: Like we do some accounting of what we can see
• 23:02
  Speaker 1: and what we think is there, and it's not enough
• 23:04
  Speaker 1: to where could it be and how are we going
• 23:06
  Speaker 1: to find it?
• 23:07
  Speaker 2: So one obvious place to look is between the galaxies.
• 23:11
  Speaker 2: Like we know there's a lot of quark matter in galaxies.
• 23:13
  Speaker 2: We can see it. There's gas, this dust, is stars,
• 23:16
  Speaker 2: is all that stuff. But we also know that there
• 23:17
  Speaker 2: should be a lot of matter between the galaxies, that
• 23:20
  Speaker 2: there should be these huge filaments of gas and dark
• 23:24
  Speaker 2: matter as well between the galaxies. Because remember, the universe
• 23:27
  Speaker 2: is not just like all these little dots of stars
• 23:29
  Speaker 2: and dots of galaxies. It's more like a big cosmic web.
• 23:34
  Speaker 2: Because as the universe cooled down. It was this hot,
• 23:36
  Speaker 2: dense plasma. You have these little dense spots that gather
• 23:40
  Speaker 2: together more stuff. The universe is expanding, and then those
• 23:43
  Speaker 2: dense spots see the formation of structure, right, they see
• 23:47
  Speaker 2: those galaxies, but they don't become isolated. You still have
• 23:50
  Speaker 2: these strands between them. And so the place to look,
• 23:53
  Speaker 2: the place that our simulations predict there should be a
• 23:56
  Speaker 2: lot of quark matter that's sort of hard to spot
• 23:59
  Speaker 2: is between the gas.
• 24:00
  Speaker 1: Galaxies because they can't be in the galaxies. Because you
• 24:04
  Speaker 1: think you can see everything in a galaxy.
• 24:06
  Speaker 2: We think we know how much matter there is in
• 24:08
  Speaker 2: a galaxy. Yeah, we can see all the luminous stuff
• 24:11
  Speaker 2: that's there, all the gas, and all the stars and
• 24:14
  Speaker 2: the dark matter, and the motion of those stars tells
• 24:17
  Speaker 2: us a lot about the gravitational profile of the galaxy. Remember,
• 24:21
  Speaker 2: as the galaxy spins, we can tell how much gravitational
• 24:24
  Speaker 2: force there is on those stars by looking at the
• 24:27
  Speaker 2: rotation velocity of the stars. That's how we deduce the
• 24:30
  Speaker 2: existence of dark matter in the first place. We're pretty
• 24:33
  Speaker 2: sure we understand the density profiles of galaxies, which is
• 24:36
  Speaker 2: why outside of galaxies is a good target.
• 24:39
  Speaker 1: So you're saying that maybe eighty to eighty five percent
• 24:41
  Speaker 1: of the missing quark matter in the universe might be
• 24:44
  Speaker 1: in between galaxies where we can't see them or what.
• 24:48
  Speaker 2: Yeah, that's exactly right. Most of the quarks in the
• 24:50
  Speaker 2: universe are not in galaxies. Like you might imagine that.
• 24:54
  Speaker 2: You know, matter forms in the Big Bang and then
• 24:56
  Speaker 2: things cool and clump together and form galaxies, and that's
• 24:59
  Speaker 2: part of the story. But it turns out it's not
• 25:01
  Speaker 2: most of the story, that this galaxy formation process is
• 25:05
  Speaker 2: kind of inefficient, that most of the normal matter in
• 25:07
  Speaker 2: the universe didn't participate it or hasn't.
• 25:10
  Speaker 1: Yet, because I guess the stuff that does come together
• 25:15
  Speaker 1: is kind of the fancy stuff that everyone pays attention to,
• 25:18
  Speaker 1: right the stars and the planets.
• 25:19
  Speaker 2: Yeah, it's got the most glitter and glam.
• 25:22
  Speaker 1: Okay, So then now is that confirmed? Like if you
• 25:25
  Speaker 1: look for things in between galaxies, do you find all
• 25:27
  Speaker 1: of this missing quark matter?
• 25:29
  Speaker 2: So there's several steps here. The first thing is to
• 25:31
  Speaker 2: look for hydrogen, so like, are there huge amounts of
• 25:35
  Speaker 2: hydrogen between the galaxies? And you can imagine the galaxies
• 25:38
  Speaker 2: is sort of like in these gravitational wells you have
• 25:40
  Speaker 2: a blob of dark matter which has gathered together the
• 25:43
  Speaker 2: normal matter to form stars and galaxies. And you can
• 25:46
  Speaker 2: think about like gravitational filaments like feeding into these wells,
• 25:49
  Speaker 2: sort of the way rivers feed into a lake, and
• 25:52
  Speaker 2: gas flowing into these galaxies. And we know that gas
• 25:56
  Speaker 2: is flowing into these galaxies, we can see like the
• 25:58
  Speaker 2: impact of gas flowing to these galaxies. Sometimes it even
• 26:01
  Speaker 2: affects star formation in those galaxies. But this gas can
• 26:04
  Speaker 2: be tricky to see because it's very, very dilute. Remember,
• 26:07
  Speaker 2: there huge space between galaxies, millions and millions of light years,
• 26:12
  Speaker 2: and so seeing these things is tricky. One way that
• 26:15
  Speaker 2: we have seen them though, is using quasars.
• 26:17
  Speaker 1: What do you mean? How do those help us see
• 26:20
  Speaker 1: the hydrogen between galaxies?
• 26:22
  Speaker 2: They basically light it up for us in this really
• 26:24
  Speaker 2: cool way. Remember, a quasar is like a black hole
• 26:27
  Speaker 2: at the center of a galaxy that's actively feeding. It's
• 26:30
  Speaker 2: like gobbling up a lot of stuff and emitting a
• 26:32
  Speaker 2: huge amount of radiation. Now it's confusing for people sometimes
• 26:36
  Speaker 2: when you say a black hole is emitting a lot
• 26:37
  Speaker 2: of radiation, the black hole itself is not emitting the radiation.
• 26:41
  Speaker 2: But if there's a very intense disk of matter near
• 26:44
  Speaker 2: the black hole. It's going to be very hot because
• 26:46
  Speaker 2: of all the gravitational tidal forces glowing, and a lot
• 26:49
  Speaker 2: of that radiation gets funneled up because of the magnetic
• 26:51
  Speaker 2: field of the black hole, and you get these extraordinarily
• 26:54
  Speaker 2: powerful beams of light that sort of like pencil raised
• 26:57
  Speaker 2: through the universe. Some of them hit the Earth. So
• 27:00
  Speaker 2: if there's this very powerful beam of light that passes
• 27:03
  Speaker 2: all the way through the universe, it's also going to
• 27:05
  Speaker 2: pass through some of these filaments of gas. And when
• 27:07
  Speaker 2: it does so, it changes the spectrum of light because
• 27:10
  Speaker 2: that gas likes to absorb some light. So if this
• 27:13
  Speaker 2: hydrogen there, it's going to absorb the light that likes
• 27:15
  Speaker 2: to interact with hydrogen, it's sort of deleted from the spectrum.
• 27:19
  Speaker 2: So by looking at the spectrum of light from these quasars,
• 27:22
  Speaker 2: we can tell how much hydrogen there is between us
• 27:25
  Speaker 2: and the source of the light.
• 27:27
  Speaker 1: You mean, like all of this quark matter that's floating
• 27:29
  Speaker 1: out there between galaxies X kind of like a filter.
• 27:32
  Speaker 1: So you have something bright like a quasar is shining
• 27:35
  Speaker 1: just directly at us and it filters through this gas.
• 27:38
  Speaker 1: You can sort of tell how much of the gas there.
• 27:40
  Speaker 2: Is exactly, and it's even more detailed and powerful than that,
• 27:44
  Speaker 2: because the hydrogen between us and this distant quasar is
• 27:48
  Speaker 2: all going to be moving at different velocities relative to us,
• 27:51
  Speaker 2: Like the further away it is, the faster it's going
• 27:53
  Speaker 2: to be moving away from us, it's going to be
• 27:54
  Speaker 2: red shifted, and that actually changes the frequency of light
• 27:58
  Speaker 2: that it interacts with. So if you look at the
• 28:01
  Speaker 2: spectrum of life from a quasar, you don't just see
• 28:03
  Speaker 2: one dip that tells you how much hydrogen there is.
• 28:05
  Speaker 2: You see a lot of dips. You see a forest
• 28:08
  Speaker 2: of these dips, each one corresponding to absorption of hydrogen
• 28:12
  Speaker 2: at a different red shift. And so not only does
• 28:15
  Speaker 2: it tell you how much hydrogen there is between you
• 28:17
  Speaker 2: and the quasar, it's like a one d map that
• 28:19
  Speaker 2: tells you where that hydrogen was between you and the quasar.
• 28:23
  Speaker 2: You can use these quasars to sort of like X
• 28:25
  Speaker 2: ray the universe and tell you where the hydrogen is.
• 28:28
  Speaker 1: WHOA, but how often do we get signals like this?
• 28:31
  Speaker 1: How many quasars are pointing directly at us?
• 28:33
  Speaker 2: Yeah, not as many as we'd like, of course, lots
• 28:35
  Speaker 2: of them, because there's lots of galaxies out there, and
• 28:38
  Speaker 2: in the early universe, quasars were very active. It's a
• 28:41
  Speaker 2: whole other mystery like why the quasars mostly get formed
• 28:44
  Speaker 2: in the early universe and not so much now. But
• 28:46
  Speaker 2: there are a lot of very distant, very bright quasars
• 28:49
  Speaker 2: that sort of like shine these lights through the universe,
• 28:51
  Speaker 2: and we'd like to see more of them. It's tricky,
• 28:53
  Speaker 2: but there's enough that we could have an estimate for
• 28:55
  Speaker 2: how much hydrogen gas there is in these filaments between galaxies.
• 28:59
  Speaker 1: And these quasars basically like illuminate the hidden matter between galaxies.
• 29:04
  Speaker 2: They do. They illuminate the hydrogen. Right. That's when you
• 29:06
  Speaker 2: have a proton and an electron together, because that's what's
• 29:09
  Speaker 2: going to interact with these photons. The neutral hydrogen will
• 29:13
  Speaker 2: do this. So when you look at this information from
• 29:15
  Speaker 2: the quasars, you can add it all up and you
• 29:16
  Speaker 2: can guess how much neutral hydrogen gas there is between galaxies,
• 29:21
  Speaker 2: and that brings you to about half of the five
• 29:23
  Speaker 2: percent that we expected. So just stars and galaxies and
• 29:26
  Speaker 2: all that stuff gives you like fifteen percent. Adding the
• 29:29
  Speaker 2: neutral hydrogen between galaxies and you're up to about fifty percent.
• 29:33
  Speaker 1: That we can account for.
• 29:34
  Speaker 2: That, we can account for exactly Well.
• 29:36
  Speaker 1: You're saying it's not missing, then that we know where
• 29:38
  Speaker 1: it is.
• 29:38
  Speaker 2: Well, even this very clever technique only brings us to
• 29:41
  Speaker 2: fifty percent. The other half is still not explained.
• 29:44
  Speaker 1: Mm so only half of that five percent is missing.
• 29:47
  Speaker 2: Then, Yeah, so like fifteen percent of it is stars
• 29:50
  Speaker 2: and galaxies and black holes and the obvious easy stuff.
• 29:53
  Speaker 2: Another like thirty five percent turns out to be this
• 29:56
  Speaker 2: neutral hydrogen between galaxies. Until very re we've had no
• 30:01
  Speaker 2: explanation for the other fifty percent that part was still missing.
• 30:05
  Speaker 1: Could it be some other kinds of gases in between galaxies?
• 30:08
  Speaker 2: So the crucial thing is that this quasar method will
• 30:11
  Speaker 2: tell us about neutral hydrogen, because you know, the photons
• 30:14
  Speaker 2: passing through these filaments will excite. Neutral hygrogen has these
• 30:18
  Speaker 2: very particular energy levels. The rest of a popular theory
• 30:21
  Speaker 2: is that it's a low density plasma that it's ionized.
• 30:25
  Speaker 2: It's not like a proton or electron hanging out in
• 30:27
  Speaker 2: a hydrogen atom. It might just be like a bunch
• 30:29
  Speaker 2: of protons and a bunch of electrons that are too
• 30:32
  Speaker 2: hot to settle down into a hygrogen atom. They're like
• 30:34
  Speaker 2: flying around free and they wouldn't interact with equasars in
• 30:37
  Speaker 2: the same way. And people argue about whether it's warm
• 30:40
  Speaker 2: or whether it's hot, and so they give this stuff
• 30:43
  Speaker 2: the name warm hot Intergalactic medium WHIM or.
• 30:48
  Speaker 1: WHIM interesting acronym there. So you're saying that light doesn't
• 30:54
  Speaker 1: interact with cork matter unless there's an electron attached to it,
• 30:58
  Speaker 1: and that's because light only interacts with electrons.
• 31:02
  Speaker 2: Light will interact with any charged particle. But this particular
• 31:05
  Speaker 2: signature that we can see relies on a feature of
• 31:08
  Speaker 2: neutral hydrogen. So photons will interact with protons when electrons
• 31:12
  Speaker 2: and scatter and do all sorts of stuff. But this
• 31:15
  Speaker 2: particular method only lets us see the neutral hydrogen.
• 31:17
  Speaker 1: Why doesn't it let us see the protons.
• 31:20
  Speaker 2: Well, what happens when the life from the quasar hits
• 31:22
  Speaker 2: a proton or hits an electron is it just basically
• 31:24
  Speaker 2: gives it a boost. It makes it glow a little bit.
• 31:26
  Speaker 2: But it's hard to know how to interpret that. We
• 31:28
  Speaker 2: can't see very well the glow from these protons and
• 31:30
  Speaker 2: these electrons because they're very very hot, so we think
• 31:34
  Speaker 2: they might emit some X rays or some UV rays
• 31:37
  Speaker 2: but it's very hard to detect those here on Earth.
• 31:40
  Speaker 1: So we wouldn't see it in the signature from the quasars.
• 31:42
  Speaker 2: Exactly, because these free protons and these free electrons can
• 31:45
  Speaker 2: interact with any kind of photon, so they generally would
• 31:48
  Speaker 2: just like overall, reduce the signature from the quasars neutral
• 31:51
  Speaker 2: hydrogen because it's a bound state of the proton, and
• 31:53
  Speaker 2: the electron is very rigid about which photons it will
• 31:56
  Speaker 2: interact with, and so it makes this very particular measurable
• 31:59
  Speaker 2: signature on the quasars. A free proton or free electron
• 32:02
  Speaker 2: can interact with any kind of photon, and so it
• 32:04
  Speaker 2: doesn't create this like obvious signature in the quasar beam.
• 32:08
  Speaker 2: We need another method to see these protons and electrons.
• 32:11
  Speaker 1: I see the light from the quasar is maybe getting
• 32:14
  Speaker 1: absorbed by these free quarks floating out there, but it
• 32:18
  Speaker 1: would just look like it's a little dimmer to us,
• 32:20
  Speaker 1: which we can tell if it's because of that or
• 32:22
  Speaker 1: maybe because the quasar is not as bright as we
• 32:24
  Speaker 1: thought it is. All right, well, let's get into some
• 32:26
  Speaker 1: of the ways that we maybe could measure this missing
• 32:29
  Speaker 1: quark matter and what it all means about our understanding
• 32:32
  Speaker 1: of the universe. But first, let's take another quick break.
• 32:48
  Speaker 1: All right, we are slowly piecing together this problem, this
• 32:52
  Speaker 1: missing matter in the universe. Apparently there's a lot of
• 32:55
  Speaker 1: quark matter that we think should be there, but it's not.
• 32:57
  Speaker 1: Although I feel like we've already a kount of for
• 32:59
  Speaker 1: fifty percent of it. We started with only being able
• 33:01
  Speaker 1: to count fifteen percent of it, but now we're up
• 33:04
  Speaker 1: to fifty percent of it.
• 33:05
  Speaker 2: Yeah, and you know, I guess fifty percent is like
• 33:07
  Speaker 2: on the edge of a passing grade. So you might
• 33:10
  Speaker 2: be tempted to call it a day move on, But
• 33:12
  Speaker 2: you know, some of us are curious. We want to
• 33:14
  Speaker 2: know where is the other half of all the matter in.
• 33:16
  Speaker 1: The universe, don't Some of these measurements have like a
• 33:19
  Speaker 1: plus or minus fifty percent uncertainty or error bar on them.
• 33:23
  Speaker 2: Anyway, I guess that's one way to resolve the mystery.
• 33:25
  Speaker 2: Just be like, well, let's just inflate the aerror and
• 33:28
  Speaker 2: it's no longer a mystery.
• 33:29
  Speaker 1: There you go.
• 33:31
  Speaker 2: Yeah, there are big uncertainties on some of these measurements,
• 33:34
  Speaker 2: but they're smaller than the discrepancy. And that's how you
• 33:36
  Speaker 2: know when you have an interesting scientific puzzle that you
• 33:39
  Speaker 2: think you have measured things well and yet you still
• 33:41
  Speaker 2: can't explain it. Things are not adding up. The error
• 33:44
  Speaker 2: is smaller than the size of the effect you're looking for.
• 33:47
  Speaker 1: All right. So now we've accounted for fifty percent of
• 33:49
  Speaker 1: the quark matter in the universe. There's still fifty percent missing.
• 33:52
  Speaker 1: How are we looking for it?
• 33:53
  Speaker 2: So we're using all sorts of clever techniques to look
• 33:55
  Speaker 2: for this stuff the whim. And this stuff is hard
• 33:58
  Speaker 2: to see because even though it could be pretty hot,
• 34:00
  Speaker 2: we're talking about like a million calvin right ten to six,
• 34:04
  Speaker 2: ten to seven calvin, it's also very very dilute, you know,
• 34:08
  Speaker 2: it's like one atom per cubic meter. It's like a
• 34:11
  Speaker 2: billionth of a billionth of the density of our atmosphere.
• 34:15
  Speaker 2: So this stuff is not very easy to see, especially
• 34:17
  Speaker 2: if it's very far away. And so we're looking for
• 34:20
  Speaker 2: a way to excite it. We're looking for something that's
• 34:22
  Speaker 2: going to pass through it and get interacted with it
• 34:25
  Speaker 2: in a characteristic way that can tell us about the
• 34:27
  Speaker 2: density of this plasma. And one really cool way is
• 34:30
  Speaker 2: to use another cosmic mystery, these things called fast radio bursts.
• 34:35
  Speaker 2: Something out there in the universe is generating these very
• 34:38
  Speaker 2: intense pulses of radio waves. Remember, radio waves are just
• 34:42
  Speaker 2: photons with very very long frequency. We call it radio waves.
• 34:46
  Speaker 2: If it's in a certain frequency regime, we call them
• 34:48
  Speaker 2: X rays, and another frequency regime, and visible light in another.
• 34:51
  Speaker 2: It's all just photons of different energies. But these very
• 34:54
  Speaker 2: very bright pulses of radio waves are created somewhere out
• 34:58
  Speaker 2: there in the universe, passing through all the matter between
• 35:01
  Speaker 2: us and them, And as we study them here on Earth,
• 35:03
  Speaker 2: we can look at the details of those radio waves
• 35:06
  Speaker 2: as a way to sort of like X ray, this whim,
• 35:08
  Speaker 2: this warm, hot intergalactic medium.
• 35:10
  Speaker 1: So how do these bursts of radio waves tell us
• 35:14
  Speaker 1: about this plasma that might be hiding all of the
• 35:17
  Speaker 1: missing cord matter.
• 35:18
  Speaker 2: Yeah, so you had the basic idea earlier when you're saying, like,
• 35:21
  Speaker 2: wooden photons interact with this whim. The protons, they're electrons,
• 35:25
  Speaker 2: they're charged particles, and you're absolutely right they do. But
• 35:27
  Speaker 2: you need the right kind of photon in order to
• 35:30
  Speaker 2: tell you what you need to know. As light passes
• 35:32
  Speaker 2: through matter, it slows down like the speed of light
• 35:35
  Speaker 2: through a vacuum. Is the famous speed that we all know,
• 35:37
  Speaker 2: but light passing through glass or through air will move
• 35:40
  Speaker 2: slower than light through a vacuum, and that effect actually
• 35:43
  Speaker 2: depends on the energy of the photon. So longer wavelengths
• 35:47
  Speaker 2: of light are slowed more than shorter wavelengths of light.
• 35:51
  Speaker 2: So if you start with the pulsive light of several
• 35:53
  Speaker 2: frequencies and then you measure the arrival time of that
• 35:56
  Speaker 2: light here on Earth, you can actually measure the density
• 35:59
  Speaker 2: of stuff between you and the pulse, because the higher
• 36:03
  Speaker 2: the density, the more the difference in the arrival times
• 36:05
  Speaker 2: between the long wavelengths and the short wavelengths.
• 36:08
  Speaker 1: I see, But don't you need to know what that
• 36:10
  Speaker 1: bursts looked like before it went through the filter of
• 36:13
  Speaker 1: this plasma between galaxies? How do we know that if
• 36:16
  Speaker 1: these are of unknown origin?
• 36:18
  Speaker 2: You're right, we do need to know something, But essentially
• 36:20
  Speaker 2: all we need to know is that they're all produced
• 36:23
  Speaker 2: at the same moment, or very very close to the
• 36:25
  Speaker 2: same time. We don't need to know something about the
• 36:28
  Speaker 2: spectrum because we're looking for it's just the difference in
• 36:30
  Speaker 2: arrival times. If you shoot a long wavelength and a
• 36:33
  Speaker 2: short wavelength photon at me at the same time, then
• 36:36
  Speaker 2: I can tell you the density of matter between us
• 36:38
  Speaker 2: by looking at the difference in the arrival times between
• 36:41
  Speaker 2: the short and the long wavelength photon, because the long
• 36:44
  Speaker 2: wave looking photon will be slowed down more by higher
• 36:47
  Speaker 2: density material. So I don't need to know anything else.
• 36:49
  Speaker 2: I just need to know that there's like a pulse
• 36:51
  Speaker 2: created and these two photons were made of basically the
• 36:54
  Speaker 2: same moment. And that's what these fast radio bursts do.
• 36:57
  Speaker 2: We don't know what's actually making them. That's a big mystery,
• 37:00
  Speaker 2: but we suspect that they're being made in a very
• 37:02
  Speaker 2: short amount of time, like a one millisecond pulse.
• 37:05
  Speaker 1: But how do you know they weren't made at different times.
• 37:07
  Speaker 2: Yeah, we're not exactly sure. That's an assumption. When they
• 37:09
  Speaker 2: arrive here on Earth, they're spread out over a few
• 37:11
  Speaker 2: seconds or sometimes tens of seconds. But because of the
• 37:14
  Speaker 2: enormous amount of energy overall, we suspect that it was
• 37:17
  Speaker 2: a very fast event, though we still don't understand it.
• 37:20
  Speaker 1: I think I know what you're saying. You're saying like
• 37:21
  Speaker 1: there's a burst of radio waves, like a bright flash
• 37:24
  Speaker 1: of light that we see that was made out there
• 37:27
  Speaker 1: in the universe, and we measure that burst of light
• 37:30
  Speaker 1: when it gets here on Earth at different frequencies. You're saying, like,
• 37:33
  Speaker 1: the bursts at one frequency is going to arrive earlier
• 37:37
  Speaker 1: than the burst from another frequency, and that difference in
• 37:40
  Speaker 1: the arrival time tells you like, oh, there must have
• 37:42
  Speaker 1: been some quark matter in plasma form between us and
• 37:47
  Speaker 1: that burst that absorb or slowed down some of that
• 37:51
  Speaker 1: second frequency exactly.
• 37:53
  Speaker 2: This effect is called dispersion, you know, wavelength dependent effect
• 37:57
  Speaker 2: on the speed of light essentially, and by measuring this
• 37:59
  Speaker 2: dip you can infer the density of the plasma between
• 38:03
  Speaker 2: you and the source. But you're right, we're making some
• 38:05
  Speaker 2: assumptions about the nature of the source. We're assuming, essentially
• 38:08
  Speaker 2: that the length of time over which those radio waves
• 38:11
  Speaker 2: were produced is negligible compared to the length of time
• 38:14
  Speaker 2: over which they arrive.
• 38:15
  Speaker 1: You also have to know where that burst came from,
• 38:17
  Speaker 1: don't you.
• 38:18
  Speaker 2: Yeah, you do. You have to know the direction. And
• 38:20
  Speaker 2: so we've been seeing these fast radio bursts over the
• 38:23
  Speaker 2: last few decades. They were discovered sort of accidentally. We
• 38:26
  Speaker 2: have a whole fun podcast episode about that, but only
• 38:29
  Speaker 2: recently have we been able to locate them, to tell
• 38:32
  Speaker 2: where in the sky they come from, and to do
• 38:34
  Speaker 2: that you need like larger instruments, or you need coordination
• 38:37
  Speaker 2: between various instruments so you can tell about their arrival
• 38:40
  Speaker 2: time at various parts on Earth. But in the last
• 38:42
  Speaker 2: couple of decades they've been able to do that and
• 38:44
  Speaker 2: gather enough information to estimate the mass of the WHIM
• 38:48
  Speaker 2: from these fast radio.
• 38:49
  Speaker 1: Bursts, at least the part of that quark plasma that's
• 38:53
  Speaker 1: hiding that we can tell using this method.
• 38:56
  Speaker 2: Yeah, exactly. And you always want to have like multiple
• 38:59
  Speaker 2: ways to measure things, especially if it's very uncertain, and
• 39:02
  Speaker 2: if you're talking about half of all the stuff in
• 39:04
  Speaker 2: the universe or the normal matter. So there actually is
• 39:07
  Speaker 2: a second, completely independent way to measure this WIM to
• 39:12
  Speaker 2: see where it is and how much stuff there is.
• 39:15
  Speaker 2: And this one is more sensitive to the electrons in
• 39:17
  Speaker 2: the wim. Remember we think the WIM is a plasma.
• 39:19
  Speaker 2: It's protons and its electrons, and those are separated, and
• 39:22
  Speaker 2: the electrons themselves can get like jazzed up by interacting
• 39:26
  Speaker 2: with the old cosmic microwave background light in a way
• 39:29
  Speaker 2: that some people can see and can use that to
• 39:32
  Speaker 2: estimate where the WIM is and how much there is.
• 39:35
  Speaker 1: And so using these measurements what is our estimate of
• 39:38
  Speaker 1: orre all this missing quark matter up to.
• 39:41
  Speaker 2: So it comes out pretty close to one hundred percent.
• 39:44
  Speaker 2: So the current idea is that this WIM fills in
• 39:47
  Speaker 2: the gap that when you add in the WHIM and
• 39:50
  Speaker 2: the neutral hydrogen between galaxies and then all the stuff
• 39:53
  Speaker 2: inside the galaxies, it all adds up to explain the
• 39:56
  Speaker 2: amount of baryonic matter we predicted from the CMB and
• 40:00
  Speaker 2: from Big Bang nucleosynthesis. So it all sort of like
• 40:03
  Speaker 2: clicks into place amazingly.
• 40:04
  Speaker 1: So then we think we found all the missing matter.
• 40:07
  Speaker 2: Then we have cracked the case of the missing matter
• 40:09
  Speaker 2: in the universe, which is like sort of exciting and
• 40:12
  Speaker 2: also sort of disappointing.
• 40:14
  Speaker 1: So wait, using these radio burss, we think we've seen
• 40:17
  Speaker 1: all of the missing matter.
• 40:18
  Speaker 2: Yeah, the current thinking is that this WHIM is that
• 40:20
  Speaker 2: missing piece, that fifty percent that we couldn't account for
• 40:23
  Speaker 2: after we figured out the neutral hydrogen component is probably
• 40:26
  Speaker 2: all the WHIM, which means that like half of all
• 40:29
  Speaker 2: the quarks in the universe are in the WHIM.
• 40:31
  Speaker 1: Are in hot gas in between in the middle of nowhere.
• 40:34
  Speaker 2: Basically, yeah, the universe is half hot gas.
• 40:38
  Speaker 1: It's incredible sort of like the US. I guess, so
• 40:42
  Speaker 1: the population lives in the middle of nowhere.
• 40:44
  Speaker 2: Yeah, exactly. And so if you want to like make
• 40:46
  Speaker 2: a ranked list of all the stuff that's out there
• 40:48
  Speaker 2: in the universe, it's mostly, you know, stuff that's very
• 40:50
  Speaker 2: susceptible to toilet humor. It's dark matter is a lot
• 40:54
  Speaker 2: of the universe, and then of the five percent that
• 40:56
  Speaker 2: makes up our kind of stuff, half of it is
• 40:59
  Speaker 2: hot gas floating out there in the universe between galaxies.
• 41:02
  Speaker 1: Well, it's only toilet humor if you like, if your
• 41:05
  Speaker 1: head is in the toilet.
• 41:08
  Speaker 2: Maybe it's good or humor then. But you know, it's
• 41:10
  Speaker 2: exciting to have these confirmation to be like, wow, we
• 41:13
  Speaker 2: do really understand what's going on out there in the universe.
• 41:15
  Speaker 2: These incredible calculations from the early universe that make these
• 41:18
  Speaker 2: predictions about how many baryons should be floating out there
• 41:21
  Speaker 2: billions of years later are kind of accurate. And we've
• 41:25
  Speaker 2: been able to like X ray and pinpoint the universe
• 41:28
  Speaker 2: using all these clever techniques to figure out where the
• 41:30
  Speaker 2: stuff actually is. And it tells us this amazing story
• 41:33
  Speaker 2: that galaxies are not the most important thing in the universe.
• 41:36
  Speaker 2: They're not even the most important part of the normal matter.
• 41:39
  Speaker 2: There are these massive halos of gas surrounding the galaxies
• 41:43
  Speaker 2: and then between the galaxies, So that's super exciting, but
• 41:47
  Speaker 2: it's also kind of a letdown because when you do
• 41:49
  Speaker 2: these kind of calculations, which you're hoping for is some
• 41:52
  Speaker 2: great new discovery. Right the way we discover dark matter
• 41:55
  Speaker 2: by finding a discrepancy in our calculations, this could have
• 41:58
  Speaker 2: been the discovery of something else, totally weird and new.
• 42:02
  Speaker 1: Well, you're disappointed that you solve the problem. You wanted
• 42:05
  Speaker 1: more problems.
• 42:05
  Speaker 2: Yes, I wanted more problems exactly.
• 42:07
  Speaker 1: You want it more, more of a job.
• 42:11
  Speaker 2: It would be fascinating, right, Like finding out that it's
• 42:13
  Speaker 2: the whim is cool, it makes sense, But it would
• 42:16
  Speaker 2: have been more exciting if it was some new kind
• 42:18
  Speaker 2: of matter, something else that we didn't expect, quarks forming
• 42:21
  Speaker 2: some new kind of stuff that we hadn't anticipated, or
• 42:24
  Speaker 2: maybe discovering something was wrong in our early universe calculations.
• 42:28
  Speaker 2: That would have been I think a bigger discovery because
• 42:30
  Speaker 2: we would have learned more about the universe.
• 42:33
  Speaker 1: Well, maybe that's why this problem didn't get a lot
• 42:35
  Speaker 1: of press, because you guys sold it as like, Eh,
• 42:37
  Speaker 1: we found it. Whatever, it's not that exciting. Now you're
• 42:41
  Speaker 1: complaining that it doesn't get any uh.
• 42:43
  Speaker 2: Press, Well, here we are trying to get it some
• 42:45
  Speaker 2: more attention. Right, So I'm out here trumpeting the case
• 42:48
  Speaker 2: of the missing matter and its whimsical solution.
• 42:50
  Speaker 1: Well, I think maybe the other reason is that it's
• 42:52
  Speaker 1: not really a problem anymore, exactly.
• 42:55
  Speaker 2: Yeah, Unfortunately we've mostly figured it out. I unfortunately or
• 42:58
  Speaker 2: unfortunately fortunately because it means our theories of physics are
• 43:01
  Speaker 2: mostly working and our techniques are clever and effective. Unfortunately,
• 43:04
  Speaker 2: because it means now we've got to move on to
• 43:06
  Speaker 2: something else.
• 43:07
  Speaker 1: So maybe you just need to rename it. Right, It's
• 43:10
  Speaker 1: no longer the missing baryon problem is just the found
• 43:12
  Speaker 1: barian flat.
• 43:16
  Speaker 2: Yeah, the once missing baryon. The Baryon's formerly known as
• 43:19
  Speaker 2: missing all right.
• 43:20
  Speaker 1: Well, another interesting reminder that the universe keeps surprising us,
• 43:24
  Speaker 1: even in I guess not so surprising ways. It's surprising
• 43:28
  Speaker 1: that you can sort of make these models and figure
• 43:31
  Speaker 1: out where everything should be and where it needs to be.
• 43:34
  Speaker 2: Yeah, asking questions in several different ways, trying to do
• 43:37
  Speaker 2: calculations from this and from that, piecing it all together
• 43:40
  Speaker 2: is a great way to figure out what's actually out
• 43:42
  Speaker 2: there in the universe, and sometimes actually leads you to
• 43:45
  Speaker 2: an answer.
• 43:46
  Speaker 1: Well, I kind of wish we had read the last
• 43:47
  Speaker 1: chapter of this mystery. I had to save this a
• 43:49
  Speaker 1: lot of time here.
• 43:50
  Speaker 2: This was decades of work and lots of careful energy,
• 43:54
  Speaker 2: and like lots of people's peachdtcs. You know, we're like
• 43:57
  Speaker 2: taking tiny steps in this direction. So you can summarize
• 44:00
  Speaker 2: it all in about five seconds, but you know, it
• 44:03
  Speaker 2: was a.
• 44:03
  Speaker 1: Journey, and also it's kind of a still a work
• 44:06
  Speaker 1: in progress, I imagine. I mean, you have some measurements,
• 44:08
  Speaker 1: but you can always refine those or somebody might find
• 44:12
  Speaker 1: something that disproved those measurements.
• 44:13
  Speaker 2: Right, yeah, precisely. Now we fold these things into our
• 44:16
  Speaker 2: models of galaxy formation. Because we have a better understanding
• 44:19
  Speaker 2: of the density and the temperature of this whim. We
• 44:22
  Speaker 2: can make sure that it describes the kinds of galaxies
• 44:25
  Speaker 2: that we see, the sizes of galaxies, the rate of
• 44:27
  Speaker 2: galaxy formation, how often galaxies merge. It all gets folded
• 44:31
  Speaker 2: into a more precise description of our universe, which we
• 44:34
  Speaker 2: hope will reveal more discrepancies and more surprises in the future.
• 44:39
  Speaker 1: And more toilet humor inevitable. All right, well it's time
• 44:43
  Speaker 1: to flush. I guess we hope you enjoyed that. Thanks
• 44:46
  Speaker 1: for joining us, see you next time.
• 44:57
  Speaker 2: Thanks for listening, and remember that. Daniel and Jorge Explaining
• 44:59
  Speaker 2: You Universe is a production of iHeartRadio. For more podcasts
• 45:03
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• 45:08
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