Speaker 1: Hey, Daniel, do you ever wonder if physics might be
Speaker 1: like really wrong? Are you talking about me or like
Speaker 1: the entire community? Well, I know you're never wrong, Daniel,
Speaker 1: that's unthinkable, but you know, like, has physics ever gotten
Speaker 1: something about the very nature of the universe? Kind of? Uh?
Speaker 1: Not right? You mean, like what's the best snack food?
Speaker 1: Or what colored lab coat should we wear? Hey? Yeah,
Speaker 1: you know, like can I eat antimatter or not? Maybe
Speaker 1: it's delicious. Physics could definitely be wrong about snacks for you. Well,
Speaker 1: I mean think bigger, like, is it possible that maybe
Speaker 1: things are not quite what they seem? Well, it wouldn't
Speaker 1: be the first time physics is wrong, and I hope
Speaker 1: it's not the last time. I am organ made cartoonists
Speaker 1: and the creator of PhD comments, Hi, I'm Daniel. I'm
Speaker 1: a particle physicist, and I've never been wrong about snack foods,
Speaker 1: and I've never been wrong about being wrong. So I
Speaker 1: think that means that I'm always wrong. I don't know,
Speaker 1: but welcome to our podcast. I'm definitely right about that.
Speaker 1: This is our podcast, Daniel and Jorge Explain the Universe,
Speaker 1: a production of I Heart Radio. That's right. Our podcast
Speaker 1: in which we take a mental tour of all the
Speaker 1: crazy stuff that's out there in the universe and try
Speaker 1: to bring it into your head. We try to wrap
Speaker 1: up the entire universe, all those trillions and trillions of
Speaker 1: stars and weird blobs of gas and dust and invisible stuff,
Speaker 1: and inserted through a little hole in your ear into
Speaker 1: your brain. Yeah, all of the amazing and incredible stuff
Speaker 1: out there in the universe, and also all of the
Speaker 1: stuff that's normal. You know, And sometimes I think when
Speaker 1: you examine what's spears to be normal in your everyday lives,
Speaker 1: it turns out to have all kinds of wonders and
Speaker 1: all kinds of small miracles in it. Are there small
Speaker 1: miracles in your snack foods? Is that what you're talking about? Like, Oh,
Speaker 1: look this chocolate chips in this trail mix. Every snack
Speaker 1: is a miracle, Daniel, especially banana's net. But in this podcast,
Speaker 1: we go beyond the miracles of banana based snack foods
Speaker 1: and talk about the incredible things that scientists are trying
Speaker 1: to figure out, Because, contrary to popular perception, scientists don't
Speaker 1: have it all figured out. There are lots of really
Speaker 1: big mysteries out there and wondering about the universe is
Speaker 1: something that belongs to everybody, including you. Yeah, so they're
Speaker 1: one of the biggest mysteries out there in the universe,
Speaker 1: and literally sort of like not just like because we
Speaker 1: don't know it, but also because it's a huge part
Speaker 1: of the universe. Is dark matter? Dark matter is a
Speaker 1: little bit crazy, right, It's like twenty of the universe,
Speaker 1: but we have no idea what it is. That's right
Speaker 1: of the energy budget of the universe. It's a pretty
Speaker 1: big slice. It's like a little bit more than a
Speaker 1: quarter of all the energy in the universe. Is this
Speaker 1: weird stuff and we've never seen it directly. We're pretty
Speaker 1: sure it's there, but we don't really know what is it.
Speaker 1: Is it made out of particles? Isn't made out of
Speaker 1: black holes? Isn't made out of lost socks? Two really
Speaker 1: huge mystery in modern physics. In fact, I would say
Speaker 1: it's one of the biggest open questions in science. I
Speaker 1: think it's just dark socks actually, but didn't that makes sense?
Speaker 1: I always lose those. How many dark socks have you
Speaker 1: lost for her? I mean we're talking a lot of songs. Well,
Speaker 1: to be out of time a cartoonists I don't have
Speaker 1: to wear dark socks very often or socks at all,
Speaker 1: because I also lived in California. But yeah, dark matter,
Speaker 1: I mean, it's a big deal. There's five times more
Speaker 1: dark matter than there is regular matter, like planets and
Speaker 1: stars and gas and dust and black holes, there's all
Speaker 1: that stuff. There's actually it's only of the stuff in
Speaker 1: the universe, which means the normal matter, the regular matter,
Speaker 1: the stuff that you're familiar with, is not actually regular
Speaker 1: or normal. It's the unusual stuff. If you just took
Speaker 1: like a survey of stuff in the universe, most of
Speaker 1: the stuff is dark matter. The things that make up
Speaker 1: stars and planets and galaxies and hamsters and me and
Speaker 1: you and bananas and snack foods. That's unusual in the universe.
Speaker 1: It's a minority of what's out there in the universe.
Speaker 1: And yet we still don't know what this dark matter is.
Speaker 1: It's a big mystery and a lot of times, you know,
Speaker 1: whenever people talk about dark matter, I feel like a
Speaker 1: common question we get, at least and in talks and
Speaker 1: appearances is that people ask us like what if dark
Speaker 1: matter doesn't exist? Like what if it's just an error
Speaker 1: in the equations that you have about physics and the universe,
Speaker 1: Like what if we just maybe like misunderstood gravity, or
Speaker 1: haven't counted all the stars in the galaxy, or you
Speaker 1: know what if there's something else that is maybe normal
Speaker 1: but we just haven't thought about. And it's a great
Speaker 1: question because most of the evidence we have for dark
Speaker 1: matter is a little bit indirect, like because dark matter
Speaker 1: is so dark and hard to interact with, we don't
Speaker 1: have clear pictures of it, right, we haven't seen what
Speaker 1: it's made out of. We've only sort of seen its
Speaker 1: effects and sometimes second hand, and so it's tempting to
Speaker 1: wonder if it's really there. You know. It's like if
Speaker 1: you've only seen the footprints of an animal, are you
Speaker 1: really sure it exists? Or could it be something else
Speaker 1: spoofing you Until you really capture one or see one
Speaker 1: in the wild, you don't really believe it exists. And
Speaker 1: dark matter has been eluding our searches for decades and
Speaker 1: makes people wonder like, well, maybe you people have it wrong. Yeah,
Speaker 1: I mean it's kind of a crazy idea, right to
Speaker 1: think that there's that much stuff out there, and conveniently
Speaker 1: it's invisible and you can't see it. You know what,
Speaker 1: I mean like I would be like, maybe you should
Speaker 1: take your math or you know, maybe you should have
Speaker 1: another grad student do the calculation. So, which do you
Speaker 1: think is the conspiracy theory dark matter like there's so
Speaker 1: much of it and you can't see it because it's
Speaker 1: so dark and that proves that it exists, or the
Speaker 1: anti dark matter conspiracy theory. Wait, anti dark matter? That's
Speaker 1: another episode right there? Can you have anti dark matter Danny? Yeah,
Speaker 1: that's another great question. We think probably not because then
Speaker 1: they would annihilate a dark matter and turn into photons,
Speaker 1: which we would see, what if it turns into dark photons? Yeah,
Speaker 1: that's actually a thing, dark photon. Really? Yeah, there goes
Speaker 1: my double price. You don't get credit for that one.
Speaker 1: But you know which idea sounds more bonkers, right, that
Speaker 1: the universe has filled with an incredible amount of invisible
Speaker 1: matter nobody had detected until recently, or that it's not. Yeah.
Speaker 1: So today on the podcast, we'll be asking the question
Speaker 1: does the universe need dark matter? Is it an essential
Speaker 1: part of the unit, Like could you have a universe
Speaker 1: without dark manner? Does that make sense? Or is it
Speaker 1: maybe that the universe doesn't need it? And maybe it
Speaker 1: is kind of an error that we have in our
Speaker 1: calculations and observations about the universe. And this kind of
Speaker 1: skepticism is very healthy. When you have a crazy idea
Speaker 1: you're trying to accommodate when you see results in your
Speaker 1: experiments you don't understand. You need to be flexible about
Speaker 1: this sort of theoretical framework with which you come at
Speaker 1: the problem. You need to be open to crazy new ideas,
Speaker 1: but you also need to be open to the fact
Speaker 1: that maybe you got your measurements wrong. There always can
Speaker 1: be an alternative explanation. So before you go big and say, wow,
Speaker 1: we're going to revolutionize our understanding of the universe, you've
Speaker 1: got to rule out all the more prosaic, basic, simpler explanations.
Speaker 1: And so it's always a good idea to keep those
Speaker 1: ideas in mind. YEA, So how sure are we that
Speaker 1: dark matter exists in the universe? And could it be
Speaker 1: something else? So I went out there into the internet
Speaker 1: and I asked people, can we explain what we see
Speaker 1: in the universe without dark matter? Are there good alternative
Speaker 1: theories that don't require a new particle or a new
Speaker 1: blob of stuff. Before you listen to these answers from
Speaker 1: the internet. Think about it for a second. Do you
Speaker 1: think dark matter is necessary in the universe or do
Speaker 1: you think the universe could ignore it or live without it.
Speaker 1: Here's what people had to say. I would think we
Speaker 1: would be much more baffled if we didn't have dark
Speaker 1: matter to explain the expansion of the universe. Oh man,
Speaker 1: And this is tough because I still don't have a
Speaker 1: good handle on what dark matter really is. But I
Speaker 1: think I think we really don't know what dark matter is,
Speaker 1: So I'm going to say, yeah, we could definitely explain
Speaker 1: what we see without it, because we're kind of just
Speaker 1: making up what it is. Yes, dark matter is just
Speaker 1: a made a term for the stuff that's there that
Speaker 1: we can't explain. So truly, any theory is under the
Speaker 1: umbrella of dark matter. I have a strong suspicion that
Speaker 1: the thing could be explained without dark matter, recalled Daniel,
Speaker 1: saying that dark matter is just the name that we've
Speaker 1: come up with for the phenomenon that we can't explain.
Speaker 1: I don't know what we would see without dark matter.
Speaker 1: My understanding is that we do know that there's dark
Speaker 1: matter because the math doesn't work out. At some point,
Speaker 1: we will have to explain the universe without dark matter,
Speaker 1: because like the dark in the matter sort of implies
Speaker 1: that we don't know what it is. I believe that
Speaker 1: dark matter is a theory that we came up with
Speaker 1: to help explain why we couldn't account for all of
Speaker 1: the gravity that we see in the universe. I think
Speaker 1: it's a fairly recent discovery. I don't believe Einstein knew
Speaker 1: about it, so he must have had some other way
Speaker 1: to account for all of the gravity. All Right, some
Speaker 1: pretty good answers there, Yeah. I like the people who
Speaker 1: treat dark matters just sort of like as an umbrella
Speaker 1: idea for all the things we don't understand. And so
Speaker 1: whatever we find out there, we just call that dark matter.
Speaker 1: And I think that really touches on the sense people
Speaker 1: have that we don't really have a clue what's out there.
Speaker 1: We just sort of labeled it dark matter, and we're
Speaker 1: talking about it as if it's a thing, but it's
Speaker 1: really just a name we applied to our cluelessness. Interesting,
Speaker 1: like if you put an S at d end, it
Speaker 1: becomes dark matters, and then then it's sort of like
Speaker 1: an umbrella term for things that are dark. That's true,
Speaker 1: and you know, that is definitely true of dark energy.
Speaker 1: Dark energy is another piece of the universe pie. Right,
Speaker 1: the universe pie is five percent normal matter, twenty dark matter,
Speaker 1: dark energy. Dark energy definitely in the category of just
Speaker 1: stuff we don't understand. We gave a fancy sounding name
Speaker 1: dark energy, this stuff that's making the universe expand right.
Speaker 1: Dark matter, on the other hand, is much better understood,
Speaker 1: is much more concrete and idea much more detailed observation.
Speaker 1: So they're both called dark both things we don't understand.
Speaker 1: But dark energy definitely a label for our cluelessness, while
Speaker 1: dark matter is a much better founded, well described theory.
Speaker 1: It's less dark. I guess we're less in the dark
Speaker 1: about exactly. We are less in the dark. Our minds
Speaker 1: are not quite so filled with dark shadows. All right.
Speaker 1: Well that's the question for today, And that's the question is,
Speaker 1: you know, do we need dark matter, like is it
Speaker 1: a concept that is totally necessary for the universe to
Speaker 1: make sense or is it just something weird that exists
Speaker 1: out there and that maybe we could have a totally
Speaker 1: wrong idea about, you know, And are there other theories
Speaker 1: that are being worked on in the scientific community that
Speaker 1: might explain it without needing to add some new kind
Speaker 1: of stuff to the universe, darker matter, the darkest matter.
Speaker 1: And you'll find that in science there are always competing voices.
Speaker 1: You know, there's often like a mainstream most people think
Speaker 1: the answer is X, but there's always somebody out there
Speaker 1: who thinks it's why, somebody who thinks it's Z. And
Speaker 1: you've got to give these people room because sometimes they're right,
Speaker 1: and sometimes their ideas of the ones that turn into
Speaker 1: the mainstream. That's how the mainstream became mainstream. It used
Speaker 1: to once be lunatic fringe or their alternative physicists, you know,
Speaker 1: French physicists. There definitely are there are people out there,
Speaker 1: once they get tenure, start working on crazy Bonker's theories
Speaker 1: and sometimes for decades that nobody pays attention, nobody really
Speaker 1: reads their papers, that people even laugh behind their hands.
Speaker 1: But sometimes they're right, you know. Literally, the history of
Speaker 1: physics is filled with revolutions that start as crazy ideas,
Speaker 1: and so we definitely got to pour water on some
Speaker 1: of those seedlings because they could sprout into huge new
Speaker 1: intellectual trees, awesome dark physics trees. I'm picturing all right, Well,
Speaker 1: step us through um like what's the main argument for
Speaker 1: dark matter, Like, what's the main evidence about it, and
Speaker 1: what makes this think that, you know, it's something new
Speaker 1: and different as opposed to maybe it's just more stuff
Speaker 1: out there that we can't see. Yes, So if you're
Speaker 1: going to come up with another theory of the universe,
Speaker 1: another way to explain the way the universe works, you
Speaker 1: have to explain what we do see, right, I mean
Speaker 1: that's the whole idea behind making a theory of physics.
Speaker 1: So if you're gonna come up with your theory, you
Speaker 1: have to understand what are the observations, what are the
Speaker 1: experiments reveal that need to be explained that you know,
Speaker 1: what's the motivation for creating this idea of dark matter?
Speaker 1: And the short version is it's all gravity. Like everything
Speaker 1: we see out there in the universe that we need
Speaker 1: dark matter to explain our weird gravitational effects that we
Speaker 1: can't explain with all the other stuff, just the gas
Speaker 1: and the dust and the stars right with the universe
Speaker 1: feels dark matter in terms of gravity, like it's they're
Speaker 1: affecting the gravity of other things, but you can't see it.
Speaker 1: That's the main evidence for it. Yeah, basically there's unexplained gravity,
Speaker 1: like we thought we knew where all the stuff was
Speaker 1: in the universe from the stars and the gas and
Speaker 1: the dust, and from that you can calculate how much
Speaker 1: gravity there should be, and we can see the effects
Speaker 1: of gravity, and will go through in a list of
Speaker 1: how we see the effects of gravity. But there's more
Speaker 1: gravity than we expected. So either there's more stuff e
Speaker 1: dark matter, or gravity is weird and different, and so
Speaker 1: it's all about the gravity then, right, because that's kind
Speaker 1: of at the basis of the theory about dark matter,
Speaker 1: is that it feels gravity but not anything else exactly,
Speaker 1: and that's why it's dark. Because if it felt electromagnetism,
Speaker 1: it would reflect light, or it would give off light
Speaker 1: like everything else does than the universe, it glows, or
Speaker 1: if it felt the strong force, it would bind with
Speaker 1: corks and form nucleons and interact with us. So it
Speaker 1: doesn't interact with us in any way that we know
Speaker 1: of other than gravitational And that's why we call it
Speaker 1: matter because we think it's something that has new gravity.
Speaker 1: But you know, it could also just be a tweak
Speaker 1: to the way we understand gravity. But at its core,
Speaker 1: it's really an observation that our theory of gravity doesn't
Speaker 1: work either because there's missing mass or the theory is wrong. Right,
Speaker 1: So those are two sides of the coin, right, Like,
Speaker 1: according to what we know about how gravity works, there's
Speaker 1: a lot of gravity missing, or there's too much gravity
Speaker 1: in the universe. Almost. Yeah, there's gravity out there and
Speaker 1: we don't have mass to explain it, and so we
Speaker 1: have to sort of fill in those gaps. And that's
Speaker 1: an uncomfortable feeling, right, You're like, well, you can't just
Speaker 1: like fill in the gaps and assume that your theory
Speaker 1: is right and add extra stuff to make it work out.
Speaker 1: You know, that feels uncomfortable, Like there's snack food missing
Speaker 1: from my fridge. Surely it was my son who cut
Speaker 1: up in the middle of the night to eat it.
Speaker 1: But you can't you can't just assume that. You can't
Speaker 1: just assume that could have been your daughter. Maybe you
Speaker 1: sleepwalked and aided or or And that's when you install
Speaker 1: a camera in front of your fridge and you get
Speaker 1: those weird videos of yourself at four am stuffing cake
Speaker 1: in your face. Experience the hypothetically hypothetically hypathetically right, Alright,
Speaker 1: So we think dark matter is there because of gravity.
Speaker 1: And there are several ways that we have seen this
Speaker 1: kind of missing gravity, right, that's in the galaxy and rotations.
Speaker 1: The way galaxies rotade is kind of one of the
Speaker 1: first one, maybe even Yeah, one of the most dramatic
Speaker 1: and earliest pieces of evidence that there was more gravity
Speaker 1: in the universe than we expected was looking at how
Speaker 1: galaxies rotate. And we can add up all the mass
Speaker 1: of the stars and the stuff in the galaxy and say, okay,
Speaker 1: we know how much gravity there should be, and then
Speaker 1: we can calculate how fast those galaxies are rotating. And
Speaker 1: you know, for a galaxy, when it's rotating, it's trying
Speaker 1: to push stuff off. It's trying to throw stuff off
Speaker 1: the edge. Like if you put ping pong balls on
Speaker 1: a merry go round and spin it, the ping pong
Speaker 1: balls fly out. The thing that keeps the galaxy from
Speaker 1: tearing itself apart from throwing those ping pong balls out
Speaker 1: into inter galactic space, is the gravity. So you can
Speaker 1: ask how fast is the galaxy spinning and is there
Speaker 1: enough gravity to hold it together, because the faster spins,
Speaker 1: the more gravity unied. Right. Yeah, It's kind of like
Speaker 1: our solar system, right, like you know, the mass of
Speaker 1: the Sun is what keeps all the planets kind of
Speaker 1: spinning around it. But what if, like the planets for
Speaker 1: spinning faster than what you could explain by the mass
Speaker 1: of the Sun. You would need some other explanations, that's right,
Speaker 1: You need more force to hold them into their orbits.
Speaker 1: And so you say, well, maybe there's extra gravity or
Speaker 1: some other force or something. And so we know there's
Speaker 1: something else holding the galaxy together. And so the first explanations,
Speaker 1: oh well, what if there's more invisible mass. It's just
Speaker 1: some stuff in the galaxy that's providing gravity and we
Speaker 1: just can't see it. And you can explain these rotation
Speaker 1: curves the way the stars move around centers of galaxies.
Speaker 1: If you distribute a bunch of mass sort of smoothly,
Speaker 1: it's like a big clump in the middle, and then
Speaker 1: sort of smoothly outpass the edge of the galaxy into
Speaker 1: a big halo that's even actually bigger than the galaxy.
Speaker 1: That explains to this as that would give you the
Speaker 1: kind of gravity that we are seeing, right, because if
Speaker 1: you look at a galaxy doesn't have that enough mass, right,
Speaker 1: like there aren't enough stars or planets in it that
Speaker 1: you can see. That's right. We count up all the
Speaker 1: visible stuff and we say how much mass does it have?
Speaker 1: And that just doesn't give us enough gravity to explain
Speaker 1: how those galaxies are holding themselves together. And that was
Speaker 1: the sort of genesis of it. I mean, for a
Speaker 1: long time people were like, well, wow, that's must be
Speaker 1: a mistake, you know, because coming to the idea that
Speaker 1: there's five times as much mass as you can see
Speaker 1: is a really big idea. It's not something people just
Speaker 1: came to an afternoon and then accepted, Yeah, it doesn't
Speaker 1: seem likely. It does not seem likely. It seems more
Speaker 1: likely that you mismeasured something that you got the velocity
Speaker 1: is wrong, or you know your grad student is pranking
Speaker 1: you or something. It's a big idea, right, It's like
Speaker 1: jumping to the conclusion right away that maybe there are
Speaker 1: five ghosts in my house eating my snacks. You know,
Speaker 1: that's like a big that's a big leap from like, hey,
Speaker 1: maybe it's just your u. And so it took other
Speaker 1: pieces of evidence before dark matter became mainstream. Right, all right,
Speaker 1: let's get into those other ways that we know dark
Speaker 1: matter is there, and let's get into whether or not
Speaker 1: it is there, or me we just have gravity wrong.
Speaker 1: But first, let's take a quick break, all right, Daniel,
Speaker 1: we're talking about whether dark matter is necessary in the
Speaker 1: universe or you know, maybe it's just the hanger on
Speaker 1: and the universe could care less about dark matter. But
Speaker 1: we we know it's definitely there because we see it
Speaker 1: from the rotation of galaxies and also we've set off
Speaker 1: kind of can see it, right, We can see it
Speaker 1: in the way that distorts the light from other far
Speaker 1: away stars. That's right. These days, we have a good
Speaker 1: handful of ways to indirectly detect dark matter, and one
Speaker 1: of the coolest is seeing it act like a lens
Speaker 1: in the sky because dark matter only has gravitational forces,
Speaker 1: but gravity can bend space, right, It's a bending of
Speaker 1: space and time. So if you have a big blob
Speaker 1: of invisible stuff in the sky, it will curve the
Speaker 1: space it's in, so that photon is traveling through it
Speaker 1: will get bent as if they're moving through a huge lens. Right,
Speaker 1: So if there's a big blob of dark matter between
Speaker 1: you and some really far away galaxy, it will distort
Speaker 1: that galaxy, creating duplicates of it, stretching it just as
Speaker 1: if there was a huge lens in the sky, right,
Speaker 1: and then we can see that, like if you look
Speaker 1: at pictures as a sky, you see these kind of distortions,
Speaker 1: these ripples, these lensing effects. You can sort of see
Speaker 1: dark matter almost, you can definitely see it. And there's
Speaker 1: sort of two categories. There's strong lensing, like there's a
Speaker 1: big dense blob and it's distorting the galaxies and it's
Speaker 1: pretty hard to explain that kind of lensing in any
Speaker 1: other way. And then there's weak lensing. We just sort
Speaker 1: of like look at all the galaxies out there to see, like,
Speaker 1: are any of them sort of just a little distorted?
Speaker 1: They're just looking a little tweaked. And from that we
Speaker 1: can get sort of like a map of where in
Speaker 1: the sky we think the dark matter is just by
Speaker 1: looking at small distortions. And that's how we've gotten a
Speaker 1: pretty good map for where we think this missing mass is.
Speaker 1: How we know that it's mostly in the center of
Speaker 1: the galaxy and how far out past the edge of
Speaker 1: the visible galaxy the dark matter halo might go. So
Speaker 1: it's a really powerful technique, right, And so that's kind
Speaker 1: of how dark matter entered in kind of our view
Speaker 1: of the universe was these first initial ways. But since
Speaker 1: then and we sort of have put more nails into
Speaker 1: sort of the coffin of whether or not dark matter
Speaker 1: is out there, right, I mean, it's now sort of
Speaker 1: shows up in pictures of the universe, the early universe,
Speaker 1: it kind of shows up in our calculations about all
Speaker 1: of the energy in the universe. Right, It's gotten more
Speaker 1: and more convincing that there's something there that's right, it
Speaker 1: becomes very difficult to explain the universe you see without
Speaker 1: dark matter. For example, we see the influence of dark
Speaker 1: matter on the formation of structures in the universe. Like
Speaker 1: the universe be in as a sort of diffuse cloud,
Speaker 1: you know, just of gas, mostly hydrogen, and then it
Speaker 1: started clumping together, and that clumping comes from gravity. Right,
Speaker 1: So gravity is the thing that draws these things together
Speaker 1: and eventually gives you stars and galaxies and planets and
Speaker 1: all that cool stuff. If you run a stimulation of
Speaker 1: the universe without any dark matter, then you don't get
Speaker 1: galaxies in the first ten billion years. It takes like
Speaker 1: another ten or twenty billion years. So it's dark matter
Speaker 1: that's that's created these like gravitational wells for stuff to
Speaker 1: fall into to make the stars in the galaxies and us.
Speaker 1: So just like the whole structure of the universe would
Speaker 1: look very different without some kind of gravitational stuff out there,
Speaker 1: and we should have just called them dark clumps or
Speaker 1: dark do it. And even earlier in the universe, like
Speaker 1: we've talked on this program about the cosmic microwave background radiation.
Speaker 1: Those are photons from the very very early universe, three
Speaker 1: hundred thousand years after the universe was created, the first
Speaker 1: moment when the universe became Rand's parent to light. Before
Speaker 1: that it was thick and soupy and light got reabsorbed,
Speaker 1: and after that it was cool enough that light could
Speaker 1: travel through the universe without being absorbed. And the shape
Speaker 1: of that plasma that gave off that light was affected
Speaker 1: by dark matter and how much dark matter there was
Speaker 1: and much normal matter there was, and that stuff like
Speaker 1: bounced off each other and oscillated and like squeezed and
Speaker 1: squished that plasma. So the amount of dark matter in
Speaker 1: that moment of the universe affects the shape of that light,
Speaker 1: the currents, the sort of patterns we see in that
Speaker 1: light in a very very precise way that's hard to
Speaker 1: describe in any other way other than there's some other
Speaker 1: kind of stuff out there. So that's giving us this graphic. Yeah,
Speaker 1: you can see like it's imprint in the light from
Speaker 1: the early universe, Like it's visually and like tangibly and like,
Speaker 1: you know, you can calculate it the storts that light.
Speaker 1: That's right. And so if you just take the universe
Speaker 1: and you add to it a new particle, a particle
Speaker 1: that doesn't move really fast, we call it cold and
Speaker 1: doesn't feel anything but gravity, it explains all of this stuff.
Speaker 1: It explains why galaxies rotate the way they do, why
Speaker 1: the cosmic microwave background rediation looks the way it does,
Speaker 1: why the structure of the universe has this structure at
Speaker 1: this time in the universe. And also there are very specific,
Speaker 1: awesome experiments that the universe has done to sort of
Speaker 1: demonstrate dark matter to us. Yeah, I guess, you know,
Speaker 1: I think maybe a question that a lot of people have,
Speaker 1: and I'm sure if physicists had at the beginning, was,
Speaker 1: you know, why does it need to be something special?
Speaker 1: Like why does it need to be a new kind
Speaker 1: of particle or matter? Couldn't it also just be something regular?
Speaker 1: But that you just can't see, Like, you know, what
Speaker 1: if there's a whole bunch of black asteroids out there
Speaker 1: that are hard to see, or you know, a lot
Speaker 1: of small dust that we can see, or maybe even
Speaker 1: like a whole bunch of little black holes kind of
Speaker 1: spread around the universe. Yeah, that's a great question, like
Speaker 1: why do we know it's a new kind of thing.
Speaker 1: Why can't it just be more of the same but
Speaker 1: just kind of dark, right? Yeah, yeah, Well we don't
Speaker 1: really know anything in our current set of particles that
Speaker 1: is that dark. I mean, other than neutrinos. Everything else
Speaker 1: has some kind of interaction, like if it's a black
Speaker 1: rock or something, well that does reflect light, it does
Speaker 1: give off light. So if it's made out of the
Speaker 1: normal kind of matter, it's going to have the kind
Speaker 1: of interactions we have, and therefore we would be able
Speaker 1: to see it, except of course, neutrinos. Neutrinos were candidate
Speaker 1: for dark matter for a long time. The problem is
Speaker 1: neutrinos move away too fast, they zoom around the universe
Speaker 1: because they're so light, so they don't give the same
Speaker 1: sort of structure to the universe that dark matter does.
Speaker 1: You need this thing to be sort of slow moving
Speaker 1: and cold in order to stick around long enough to
Speaker 1: give the structure of galaxies. Could you have cold neutrinos
Speaker 1: like slow moving neutrinos. Then we talk about that the
Speaker 1: other in another episode. Could you have cold neutrinos, Yes,
Speaker 1: but we don't think that neutrinos are that cold. We
Speaker 1: haven't seen cold neutrinos. Neutrinos are so light they have
Speaker 1: almost no mass that they essentially almost always travel near
Speaker 1: the speed of light. They're always in a rush, They're
Speaker 1: always in a hurry. Yes, neutrinos are hot, as we
Speaker 1: call them in particle physics. And it literally and figuratively
Speaker 1: is it's it's a pretty big trend right now, that's right,
Speaker 1: all right? Well, I guess if it's not maybe something
Speaker 1: we know about, could it be that just maybe we
Speaker 1: have our theories wrong about how things work, Like, you know,
Speaker 1: maybe it's not a new particle or a new kind
Speaker 1: of matter, but maybe we just have gravity wrong. Like
Speaker 1: maybe gravity doesn't work the way we think it is.
Speaker 1: And maybe these larger universe size scales could gravity, you know,
Speaker 1: could there be a different theory of gravity that would
Speaker 1: maybe account for what we think is dark matter. It's
Speaker 1: definitely something to consider, right, because all these observations are
Speaker 1: just observations of gravity. And what we're doing is we're saying,
Speaker 1: we assume there's a certain amount of mass out there,
Speaker 1: we assume we know how gravity works. We estimate how
Speaker 1: much gravity there should be based on that mass. Right,
Speaker 1: But there are two steps in there. There's figure out
Speaker 1: where the mass is and in calculate how much gravity
Speaker 1: there is from that mass. If that second step is wrong, right,
Speaker 1: if the theory of gravity works differently from what we expected,
Speaker 1: then yeah, that could possibly explain it. Because remember, gravity
Speaker 1: is very very weak, which makes it very very hard
Speaker 1: to test, Like it's difficult to measure the force of
Speaker 1: gravity at the scale of one centimeter between two pebbles
Speaker 1: because there's force there's almost zero, Like you need to
Speaker 1: build a very sensitive instrument to measure the gravitational force
Speaker 1: between anything that's smaller than you know, planets and moons. Yeah,
Speaker 1: because you know, like our current theory of gravity says that,
Speaker 1: you know, gravity changes by one of our squared, Like
Speaker 1: the force of gravity kind of depends on the distance
Speaker 1: between two things squared. And then you put down in
Speaker 1: the denominator and that always seems kind of almost too
Speaker 1: simple to me, Like, what are the chances at the
Speaker 1: universe would pick such a simple little formula to calculate gravity.
Speaker 1: You know, why isn't it like one over our squared
Speaker 1: times are to the zero point seven five? You know,
Speaker 1: I mean, like it seems so simple. Maybe what if
Speaker 1: it's wrong, Like what if gravity isn't one of our
Speaker 1: our square but maybe changes over distances in a way
Speaker 1: that could maybe explain dark matter. Yeah, that's a totally
Speaker 1: realistic thing to think. Although you know, there's a lot
Speaker 1: of these patterns, these one of our our squared patterns
Speaker 1: in physics and enforces and there is a good reason
Speaker 1: for it and a fairly simple way to understand it.
Speaker 1: If you imagine like the surface of a sphere surrounding
Speaker 1: a point. Think about like all the gravitational energy coming
Speaker 1: out of a point, the surface of a sphere surrounding it,
Speaker 1: all the gravitational energy passes through that sphere, and then
Speaker 1: as the radius of that sphere gets larger, what's the
Speaker 1: surface of that sphere? Will it goes like are squared,
Speaker 1: and so the power at any point should go like
Speaker 1: one over our squared. It sort of makes sense geometrically
Speaker 1: but what if geometry is wrong. What if geometry is wrong? Right?
Speaker 1: What is wrong? What if podcasting is wrong? What if
Speaker 1: one plus one is wrong? Well, it kind of, I mean,
Speaker 1: you know, we talk about sometimes about how space is
Speaker 1: not you know, this nice and neat, orderly thing, and
Speaker 1: that sometimes you can even like measure triangles in real
Speaker 1: space that have angles that are bigger than a hundred
Speaker 1: and eighty degrees, could maybe, like space be weird in
Speaker 1: such a way that it's not really one over our squares? Yeah? Absolutely,
Speaker 1: And there are forces that don't go like one of
Speaker 1: our our squared, Like the strong force doesn't go like
Speaker 1: one of our squared at small distances. It gets even
Speaker 1: stronger as you get further away. So you definitely got
Speaker 1: to be open to weirdness. And so around the time
Speaker 1: when dark matter was sort of coming up in the
Speaker 1: world as an idea, when it was based mostly on
Speaker 1: galaxy rotations, people thought, well, how can I tweak gravity
Speaker 1: to explain what I'm seeing without dark matter? What would
Speaker 1: I need to change? How what would you have to
Speaker 1: be like one over our to the third or one
Speaker 1: of our at one point five or whatever in order
Speaker 1: to explain these galaxy rotations without dark matter, and so
Speaker 1: they came up with a different theory. It's called mond
Speaker 1: m O n D for modified Newtonian dynamics. Know, I
Speaker 1: would have just called the dark bath. I wish you
Speaker 1: could get in a time machine and go back and
Speaker 1: tell them because I hate moms. Would that be a
Speaker 1: lot catch here and fun? Dark bath? Well, mon, I
Speaker 1: guess if you're French, then it's like, oh, yeah, it
Speaker 1: means the world. I suppose it's missing the E and
Speaker 1: it commits the terrible acronym crime of taking two letters
Speaker 1: from one of the words, you know, modified. Yeah, all right,
Speaker 1: so there is a kind of a theory in physics.
Speaker 1: It says like maybe we do have gravity wrong, right,
Speaker 1: is like an idea you guys take seriously, like maybe
Speaker 1: there is no dark matter, it's just dark bath. It's
Speaker 1: definitely an idea that physics should take seriously in the
Speaker 1: sense that we should think about alternatives. This one theory
Speaker 1: in particular doesn't have a lot of supporters, and we'll
Speaker 1: get into exactly why, but you know, it's an interesting
Speaker 1: idea and it says like maybe gravity works differently at
Speaker 1: very very large distances, like you know, we've tested gravity
Speaker 1: here on Earth. We know how it works. We've tested
Speaker 1: gravity in the Solar System pretty well. But you know,
Speaker 1: maybe the first time we're looking at gravity on galaxy scales,
Speaker 1: maybe gravity just works differently over like, you know, fifty
Speaker 1: thou light years, right, we haven't done that experiment before.
Speaker 1: Maybe it gets going, like, maybe it gets stronger in
Speaker 1: galaxy size scales. Yeah, And so the idea is actually
Speaker 1: even weirder than that. It says, maybe gravity works differently
Speaker 1: when you have a very very small acceleration, things are
Speaker 1: not being pulled very hard. Maybe gravity works a little
Speaker 1: bit different. Oh my god, you just blew my mind.
Speaker 1: All right, let's let's get into this crazy idea that
Speaker 1: gravity depends on how you're moving maybe, and whether or
Speaker 1: not that could work. But first let's take another quick break, right, Daniel,
Speaker 1: we're talking about dark math to maybe explain dark matter.
Speaker 1: And so there's an idea that maybe our formulation of
Speaker 1: gravity or how we think gravity works could be wrong.
Speaker 1: Maybe and it could maybe act very differently over larger scales,
Speaker 1: like maybe it gets stronger the galaxy scale or when
Speaker 1: you're telling me it's actually when there's lower accelerations. And
Speaker 1: this is just an idea again, right, this is just
Speaker 1: an idea. But hey, everything is just an idea, right,
Speaker 1: even lunch lunch is just an idea. Remember, Oh no, Daniel,
Speaker 1: lunch is very real to me. Well, the idea is,
Speaker 1: you know, somehow you have to get gravity to be
Speaker 1: stronger without breaking things we already know. So what if
Speaker 1: you know affecting things on the edge of the galaxy,
Speaker 1: you could have gravity instead of going like one over
Speaker 1: our squared, which you make it very very weak as
Speaker 1: our gets large, you can make it go like one
Speaker 1: over R. It doesn't fall off as quickly, doesn't get
Speaker 1: weak as quickly with large distances. Interesting, So like the
Speaker 1: gravity I feel with another planet on the other side
Speaker 1: of the Milky Way, maybe it's stronger than I think. Yeah,
Speaker 1: maybe it's not like one over our squares, more like
Speaker 1: one over R and R is still really really large.
Speaker 1: So you know, those planets don't affect you because the
Speaker 1: gravity from them is still really tiny. But if you're
Speaker 1: adding up lots of planets and you're trying to calculate,
Speaker 1: like how a whole galaxy spins, then it really does
Speaker 1: make a big difference to go like one of our
Speaker 1: are instead of one of are squared. But it seems
Speaker 1: a bit hacky as opposed to dark matter. Dark matter
Speaker 1: doesn't seem hacky. Well, dark matter, you know, you can
Speaker 1: explain a lot of really different things adding just one
Speaker 1: simple idea, like hey, what if there's a new particle
Speaker 1: that's not hacky, Like we don't know why there's a
Speaker 1: certain number of particles in the universe and not more,
Speaker 1: or if there are more, so adding one new particle
Speaker 1: doesn't feel as hacky. Is like let's have gravity have
Speaker 1: a knob on it, or like a distance above which
Speaker 1: it starts behaving different rules, or you know, small accelerations
Speaker 1: below which it starts behaving differently. Really, what why does
Speaker 1: it need to be low accelerations? How does that work? In?
Speaker 1: It doesn't really work as I think I heard you
Speaker 1: react because like the acceleration with respect to what right,
Speaker 1: all of a sudden, that gravity you feel depends on
Speaker 1: your reference frame, and it brings all sorts of symmetries.
Speaker 1: But there is that one idea that accelerations like one
Speaker 1: ten trillions of the gravity on Earth. If you feel
Speaker 1: an acceleration less than that, then the gravity on you
Speaker 1: behaves differently than it does for larger accelerations. Oh, I see.
Speaker 1: It's not you're not saying when you're going at a
Speaker 1: low acceleration, it's just you mean the when the effects
Speaker 1: of gravity are small, maybe it doesn't behave as one
Speaker 1: over our square. Yeah, and the effects of gravity at
Speaker 1: very very far distances are really small. Like what is
Speaker 1: the acceleration on some star at the edge of the
Speaker 1: galaxy due to the black hole the center of the galaxy. Well,
Speaker 1: the distance is fifty thou light years, so the acceleration
Speaker 1: is very small, also because the masses are large, and
Speaker 1: so it's just a way to say, let's have it
Speaker 1: have an effect where we see this weirdness and not
Speaker 1: have an effect anywhere else. Let's try not to break
Speaker 1: what we already know and understand and only have this
Speaker 1: theory turn on in special cases. All right, so that's
Speaker 1: a possibility. But where did this idea come from? Like
Speaker 1: why would we think that maybe gravity is wrong? So
Speaker 1: for a long time there wasn't really a good idea
Speaker 1: that was just like, well, I don't know, but if
Speaker 1: I put in this other formula, I can explain the
Speaker 1: galaxy rotation curves without dark matter. Without dark matter. Yeah,
Speaker 1: So like all right, so either there's missing masks or
Speaker 1: gravity works this other weird way, and then people started thinking, well,
Speaker 1: why would gravity work that way? Is there any reason
Speaker 1: for it? And that's a totally valid line of inquiry, right,
Speaker 1: like what theory do we have to have to explain
Speaker 1: the data? And does that theory make sense? Can we
Speaker 1: come up with a reason why? Maybe that theory is right?
Speaker 1: A theory about a theory underpinnings of the theory, right.
Speaker 1: We always in physics want to have a microscopic understanding.
Speaker 1: We don't want to just say gravity just has this
Speaker 1: number on it. We want to know why does it?
Speaker 1: Where does that come from? Why isn't it something else?
Speaker 1: Just like you were saying earlier, why is it one
Speaker 1: of our square not one over our two point one
Speaker 1: or whatever? That's the next version upgraded gravity. And so
Speaker 1: recently there is an idea from a guy in Holland
Speaker 1: to Eric Verlinda, and he has this crazy idea of
Speaker 1: gravity called entropic gravity that i'd be able to explain
Speaker 1: why gravity works differently at these distance scales. I feel
Speaker 1: like maybe he just grabbed two cool sounding things and
Speaker 1: put them together. Tropic answer like dynamic gravity or something.
Speaker 1: But it comes from a cool place. You know, it
Speaker 1: was Stephen Hawking who first connected sort of thermodynamics and gravity.
Speaker 1: He started thinking about the temperature of black holes and thinking,
Speaker 1: you know, if black holes have temperatures, that means they
Speaker 1: should radiate. Oh wait, and that's Hawking radiation. So in
Speaker 1: the last sort of forty years, people have been thinking
Speaker 1: about gravity and through our dynamics as a connection. They're
Speaker 1: trying to understand like, you know, actually, maybe gravity isn't
Speaker 1: a fundamental force, and maybe, you know Einstein's idea that
Speaker 1: gravity is just a curvature spacetime, maybe that's also wrong.
Speaker 1: Maybe instead, gravity is just like an emergent phenomena of thermodynamics.
Speaker 1: Maybe it's just like comes out of the manipulation and
Speaker 1: interaction of some tiny little bits of space in a
Speaker 1: way that feels like gravity to us. That's a little
Speaker 1: bit mind blowing. Yeah, it's a little bit mind blowing.
Speaker 1: This whole idea of emergent phenomena can be hard to
Speaker 1: get your mind around, but it's actually very familiar. You know,
Speaker 1: Like we can talk about wind, right, Wind is an
Speaker 1: emergent phenomena. It's not a fundamental force in the universe.
Speaker 1: You know, two particles interacting don't feel wind. Wind is
Speaker 1: a combination of lots of other things we do understand
Speaker 1: on a microscopical level that has a macroscopic effect, or
Speaker 1: like economics. You know, there are laws of economics that
Speaker 1: come from you know, supply and demand or whatever. It's
Speaker 1: not a fundamental force in the universe, but still you
Speaker 1: could have an understanding of it. And so they think
Speaker 1: maybe gravity is just like a macroscopic effect of something microscopic,
Speaker 1: maybe the thermodynamics of space time. Like there there is
Speaker 1: no gravity, it's just kind of like how space itself
Speaker 1: kind of arranges itself. Yeah, because we know that space
Speaker 1: likes to increase entropy, likes to increase disorder, and so
Speaker 1: we think entropy always increases in the universe, and so
Speaker 1: maybe gravity is just an effect of that. You know.
Speaker 1: The argument goes something like when things fall into a
Speaker 1: black hole, for example, that increases the entropy of the
Speaker 1: black hole, because otherwise it would violate the second law
Speaker 1: of thermodynamics. Things can't just disappear into the black hole.
Speaker 1: But maybe it's the opposite. Maybe it's not that gravity
Speaker 1: pulls things into the black hole and then increases the entropy.
Speaker 1: Maybe it's entropy that's pushing things into black holes, and
Speaker 1: that's actually what gravity is. That's just like you know,
Speaker 1: the way gas diffuses in a box. You put a
Speaker 1: blob of gas in the corner of a box and
Speaker 1: it spreads out into the box. That's entropy the same way.
Speaker 1: Maybe entropy is stuff falling into itself, like you know,
Speaker 1: having more stuff near itself dense blobs of mass increases
Speaker 1: the temperature, which changes the entropy of the situation. I mean,
Speaker 1: it's a complicated argument involving like quantum entangled space time,
Speaker 1: but I think that's the gist of it, and all
Speaker 1: of that kind of crazy idea is just explain how
Speaker 1: maybe gravity could not be one over our square. Yeah,
Speaker 1: if you have in tropic gravity, so maybe if gravity
Speaker 1: is not a fundamental force in the universe but just
Speaker 1: like an emergent property of quantum space time, and you
Speaker 1: have dark energy, then Virlindis theory predicts that space curs
Speaker 1: in this way, that gravity, the effective force of gravity,
Speaker 1: goes the way mind needs it to explain the galactic
Speaker 1: rotation curves. So that's kind of cool thing. That's an
Speaker 1: alternative to dark matter. Is one alternative to dark matter
Speaker 1: to say we have this weird gravitational thermodynamics idea that
Speaker 1: changes the way gravity works. That explains why we thought
Speaker 1: that was missing stuff. Instead, it's just the gravity works
Speaker 1: differently than we expect it. Interesting alright, So then I
Speaker 1: guess the big question is could that work? Is that
Speaker 1: a valid or plausible theory that maybe explains gravity in
Speaker 1: a different way that then explains dark matter and and
Speaker 1: so that it's not just another particle or kind of stuff.
Speaker 1: Could that war? Well, it's a cool idea, and it
Speaker 1: does explain galaxy rotation curves, and it actually explains galaxy
Speaker 1: rotation curves better than dark matter. There's some galaxies out
Speaker 1: there that we still can't explain using dark matter, Like
Speaker 1: they rotate in weird ways and we don't understand it.
Speaker 1: And you know, but hey, galaxies are weird. They they
Speaker 1: have their own history. No prize, sir. My theory, that's right,
Speaker 1: My theory that the universe is just weird explains everything,
Speaker 1: oh man, the whites and theory of everything, the whites
Speaker 1: and theory of weirdness. But it explains the gaxy rotation
Speaker 1: curves really nicely. But there's a big caveat there, which
Speaker 1: is it was sort of invented to explain those curves,
Speaker 1: like you came up with a theory to fit that data. Really,
Speaker 1: a good test of a theory is does it explain
Speaker 1: other data? Is that a real general principle about the universe,
Speaker 1: something which is really deeply true? Or is it just
Speaker 1: a mathematical tweak to this one plot, this one fig
Speaker 1: or to make. Because if it only works to explain
Speaker 1: one thing, it's it's kind of suspicious, right exactly, And
Speaker 1: if it only works to explain the one thing that
Speaker 1: motivated it, and then probably it's not a deep truth
Speaker 1: of the universe, right a right, So maybe it doesn't work.
Speaker 1: Can it explain some of the other things that we
Speaker 1: know about dark matter, like the lensing and the cosmic
Speaker 1: microwave background and the structure of the universe? A tweak
Speaker 1: to our theory of gravity also explain all of these things?
Speaker 1: In a word, No, it just doesn't work. No, galax
Speaker 1: is are just weird. No galax is just weird. No,
Speaker 1: it does not explain the cosmic microwave background, Like, it's
Speaker 1: very difficult to explain that using anything else other than
Speaker 1: some new kind of particle or promodial black hole or
Speaker 1: something some new kind of stuff. You just can't explain
Speaker 1: it using deviation and gravity because it was on a
Speaker 1: really small scale. This is like, you know, things were
Speaker 1: near by each other. This wasn't galactic distances interesting, And
Speaker 1: it's very difficult to explain the structure of the universe.
Speaker 1: And then there is one really awesome example of dark
Speaker 1: matter that's sort of like a smoking gun that makes
Speaker 1: it almost impossible to explain using anything but some new
Speaker 1: kind of matter stuff, some new kind of stuff. Yeah,
Speaker 1: and that's this Bullet cluster. There was this collision millions
Speaker 1: and millions of years ago, far far away between two
Speaker 1: clusters of galaxy that passed through each other. And we
Speaker 1: thought that those clusters of galaxies they had normal matter
Speaker 1: like stars and planets, etcetera, and then also clumps of
Speaker 1: dark matter. So what happened is they passed through each other,
Speaker 1: and the gas and the dust it all collided amid
Speaker 1: big collisions and slowed down and all that stuff. But
Speaker 1: the dark matter, it doesn't interact with the normal matter,
Speaker 1: and it doesn't interact with itself very much at all
Speaker 1: either because gravity is so weak, so the dark matter
Speaker 1: is sort of passed through. So what we see when
Speaker 1: we look up in the skies, we see like a
Speaker 1: big blob in the center while the gas and dust interacted,
Speaker 1: and then on either side we see the dark matter
Speaker 1: that passed through, and we can see that because of
Speaker 1: the gravitational lensing. Right, But doesn't it all I know,
Speaker 1: we talked about the bullet cluster it before, but doesn't
Speaker 1: it still just come down to gravitational lensing, Like what
Speaker 1: if gravity can explain gravitational lensing, could that also explain
Speaker 1: the bullet cluster that we see. It's very difficult to
Speaker 1: explain the bullet cluster in any other way because you
Speaker 1: need to have gravitational lensing in exactly those right spots
Speaker 1: on opposite sides of this very obvious collision. So it's
Speaker 1: a very nice explanation to think, oh, there's some invisible
Speaker 1: matter that passed through and it's now sitting there distorting
Speaker 1: the background galaxy. See, the bullet cluster is like proved
Speaker 1: that whatever it's causing these gravitational things is mobile, like
Speaker 1: it can move like stuff. But if it was just
Speaker 1: a gravitational theory tweak, that wouldn't like keep going or
Speaker 1: move or change from here to there exactly, and it
Speaker 1: can be separated from the normal matter. It's not just
Speaker 1: a gravitational tweak from the normal matter, right, the normal
Speaker 1: matter was left behind in the middle. It's its own
Speaker 1: kind of stuff. It has its own gravity. And so
Speaker 1: that's sort of like a bullet in the brain of
Speaker 1: the you know, non dark matter theories. The bullet cluster
Speaker 1: is a bullet suspicious. People really took Moms sort of
Speaker 1: seriously until then. And then when the bullet cluster was discovered,
Speaker 1: people are like, oh, well, that's it. Dark matter is real,
Speaker 1: and Mond is dead and never Mond. And at that
Speaker 1: point people really didn't take months seriously. So since then,
Speaker 1: Mond has been much more of a fringe theory. I mean,
Speaker 1: Virlin's idea is more recent, and it's quote of cool,
Speaker 1: but it sort of explains something that nobody really takes
Speaker 1: seriously anymore. So it's very fringe in a way. The
Speaker 1: bullet cluster shows you that dark matter or whatever it's
Speaker 1: causing these gravitational distortions and footprints, is mobile like it's
Speaker 1: it can move like stuff. It moves like a stuff
Speaker 1: can move. Yeah, And so again it's unsatisfying because we
Speaker 1: don't know what it is and and we've been looking
Speaker 1: for for a while it's not like we're just like, oh,
Speaker 1: it's some invisible stuff, let's move on. We've built dedicated
Speaker 1: experiments to look for it. We thought several times that
Speaker 1: we would definitely find it and then haven't seen it.
Speaker 1: So there's definitely some tension there. It's not like dark
Speaker 1: matter is a beautiful theory that's all wrapped up, like
Speaker 1: we don't understand why we haven't been able to find
Speaker 1: the dark matter yet. There's definitely something weird going on there,
Speaker 1: and it's very healthy to think about new ideas, but
Speaker 1: mond doesn't quite work. There is no other idea out
Speaker 1: there that explains what we see nearly as well as
Speaker 1: some new cold particles. I have an idea is it's
Speaker 1: snack based. It's called Hey, maybe dark matter is weird.
Speaker 1: It's weird, yeah, And that's why people are sort of
Speaker 1: digging further and further into the barrel of ideas for
Speaker 1: dark matter. People thought for a long time, Okay, dark
Speaker 1: matter must just be some weakly interacting massive particle, some
Speaker 1: new lava stuff, but we haven't seen it, and so
Speaker 1: then people are well, maybe it's axions, or maybe it's
Speaker 1: primordial black holes, or and there are some other even
Speaker 1: crazier ideas like squirmyons, what like they're uncomfortable and social situations.
Speaker 1: What do you mean introvertons? Yeah, no, squirmy on are
Speaker 1: this crazy idea that you know how particles are like
Speaker 1: excitations of quantum fields are like little bundles of energy
Speaker 1: in a quantum field. People think, well, maybe not all
Speaker 1: energy and quantum fields are particles. Maybe some of them
Speaker 1: are like more distributed or spread out in weird ways.
Speaker 1: And they found that you can like tangle up quantum
Speaker 1: fields in these weird ways, like make nots of them,
Speaker 1: and that's what they call squirmyons. And it's not could
Speaker 1: like it could create gravity. Yeah, because any energy density
Speaker 1: creates gravity. Well, we'll have to dig into that for
Speaker 1: another episode. Sounds pretty for sure. So there's lots of
Speaker 1: ideas the whole spectrum, right, dark matter is not just
Speaker 1: one idea, the sort of spectrum of ideas all satisfied
Speaker 1: the condition that it's some new kind of cold object.
Speaker 1: But what that object is. It could be one particle,
Speaker 1: could be many kinds of particles. It could be black holes,
Speaker 1: it could be squirmyons, it could be something else we
Speaker 1: haven't even thought of yet. Whatever, it is. We're pretty
Speaker 1: sure it's stuff. It's something that has gravity stuff when
Speaker 1: it's there, that's right. But I mean it's really interesting
Speaker 1: because I feel like we've known dark matters is there
Speaker 1: for a while now, and we just can't seem to
Speaker 1: crack it. We can't seem to find it keeps um
Speaker 1: eluding us, you know, like it just keeps on hiding
Speaker 1: there and not letting us know what it is. That's right,
Speaker 1: But we don't know how long the story is. You know,
Speaker 1: we were looking for the Higgs boson for fifty years
Speaker 1: and then we found it. We were looking for the
Speaker 1: top cork for twenty years before we found it. A
Speaker 1: lot of those things. People thought, oh, we'll find this
Speaker 1: in the next year two and then they were confused
Speaker 1: and disappointed to not discover it soon. But you know,
Speaker 1: eventually we got there and we we figured it out.
Speaker 1: So maybe we're just five years away from discovering dark matter,
Speaker 1: or maybe it's going to be another hundred. Maybe we
Speaker 1: need a new crazy idea for what dark matter is.
Speaker 1: But dark matter, I'm pretty sure is so all those
Speaker 1: physicists squirming around relax. Maybe dark matter is in our future.
Speaker 1: That's right. I certainly hope it is. It would be fascinating.
Speaker 1: And remember that it's most of the stuff out there
Speaker 1: in the universe. Like, what a crazy opportunity to learn
Speaker 1: about the way the universe works, you know, to know
Speaker 1: that of the stuff out there in the universe has
Speaker 1: been hidden from us. The day we crack that open
Speaker 1: and get to learn about it, like, it could have
Speaker 1: incredibly complex structure, it could have interactions and biology and
Speaker 1: chemistry and all sorts of crazy stuff. Movest of the
Speaker 1: stuff out there in the universe we haven't yet gotten
Speaker 1: to play with, and so we're eager, we're desperate to
Speaker 1: figure out what this stuff is. Yeah, because if you're
Speaker 1: the scientist that discovers what dark matter is, I mean,
Speaker 1: that's like a lot of three cred you know. It's
Speaker 1: like you could say that you discovered eight eight percent
Speaker 1: of everything in the universe. I think they would have
Speaker 1: to give you five Nobel Prizes, you know, just for
Speaker 1: that one discovery. They have to give you eighty percent
Speaker 1: of all the Nobel prizes. I think, Yeah, yeah, there
Speaker 1: you go. You get all the Nobel Prizes for the
Speaker 1: next four hundred years, just to balance it out. Yeah,
Speaker 1: So it's a big question, and who knows, maybe one
Speaker 1: of our listeners will be the one who discovers it.
Speaker 1: That's right, It could be you out there, it could
Speaker 1: be your kids out there. What we definitely need to
Speaker 1: do or keep our minds open and come up with
Speaker 1: new ideas for what dark matter is really cool? All right, Well,
Speaker 1: we hope you enjoyed that view into this story is
Speaker 1: dark matter and how we know it's there and how
Speaker 1: we know it's not just a weird fluke of gravitational equations.
Speaker 1: Thanks for tuning in, See you next time. Thanks for listening,
Speaker 1: and remember that Daniel and Jorge Explain the Universe is
Speaker 1: a production of I Heart Radio. For more podcast For
Speaker 1: my heart Radio, visit the i heart Radio app, Apple Podcasts,
Speaker 1: or wherever you listen to your favorite shows.