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