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Could dark matter be a superfluid? · Daniel and Kelly’s Extraordinary Universe

0:08
Speaker 1: Jorge, I have an idea for our Daniel and Jorge
0:12
Speaker 1: explain the universe food truck. Oh nice, wait, are reactually
0:15
Speaker 1: doing that? I thought it was a joke. Well, it
0:17
Speaker 1: was a joke, but then our listener Tim Lazarov road
0:19
Speaker 1: in to ask when our food truck is going to
0:21
Speaker 1: be in his neighborhood. May should be more like a
0:24
Speaker 1: food spaceship it would be more appropriate. Well, that goes
0:27
Speaker 1: perfectly well with my idea. You see, normal food trucks
0:31
Speaker 1: sort of drinks right fluids to wash down their taste treats.
0:34
Speaker 1: But our food spaceship should serve super fluids like zero
0:39
Speaker 1: viscosity beverages nice, so they go down easier. Or do
0:43
Speaker 1: they have Bose Einstein condensation on the outside. I'm thinking
0:47
Speaker 1: we should test it on some undergrads, you know, make
0:49
Speaker 1: sure it's safe before we sell it to the public.
0:51
Speaker 1: I'm sure the FDA is all over that. I don't
0:53
Speaker 1: think they have a physics food division yet. That's the
0:55
Speaker 1: p d A Physics and Drugs Administration. Hi, I'm or
1:14
Speaker 1: hand me a a cartoonists and the co author of Frequently
1:16
Speaker 1: Asked Questions about the Universe. Hi I'm Daniel. I'm a
1:20
Speaker 1: physics professor and a particle physicist who does research at CERN.
1:24
Speaker 1: And every time I'm in a lab, I'm always tempted
1:26
Speaker 1: to taste everything that sounds like a terrible Daniel, especially
1:31
Speaker 1: if you visit a virology lab. Yeah, but you know
1:34
Speaker 1: they got like weird glowing goo. You're like, m I
1:37
Speaker 1: wonder what flavor that is. I'm never gonna do it,
1:40
Speaker 1: of course, I hope, but you know, the curious mind wonders, right,
1:44
Speaker 1: Remind me never to invite you to my lab, otherwise
1:46
Speaker 1: you'll be licking everything like a dog or a two
1:50
Speaker 1: year old, like that kid in the movie that licks
1:52
Speaker 1: the flagpole and wonders if his tongue is really going
1:55
Speaker 1: to stick to it. We should get into the physics
1:57
Speaker 1: of a Christmas story will shoot your eyes out. But
2:01
Speaker 1: welcome to our podcast Daniel and Jorge Explain the Universe,
2:04
Speaker 1: a production of I Heart Radio in which we invite
2:07
Speaker 1: you to taste the entire universe to enjoy the flavor
2:10
Speaker 1: of knowledge as well as ignorance, to take a bite
2:14
Speaker 1: out of everything that we do and do not know
2:16
Speaker 1: about the universe. We don't shy away from the big mysteries.
2:20
Speaker 1: On this podcast. We talk about the smallest things, the
2:22
Speaker 1: medium sized things, and even the biggest things, and we
2:26
Speaker 1: attack all of them and try to explain them to you. Yeah,
2:29
Speaker 1: it is a delicious looking universe, like a giant cosmic
2:32
Speaker 1: bouffet of amazing ideas and incredible phenomena that are there
2:36
Speaker 1: for us to dig into and fill our bellies with
2:40
Speaker 1: amazing knowledge. Yeah. And if you're not a curious person,
2:43
Speaker 1: then you wouldn't take a bite to these weird things.
2:45
Speaker 1: And I think that's why when I'm in some kind
2:47
Speaker 1: of laboratory and I see something weird bubbling in a
2:49
Speaker 1: flask and I wonder, I wonder if that would make
2:52
Speaker 1: a good soda for our food truck, It's that same
2:55
Speaker 1: curiosity that inspires me to try to take a bite
2:57
Speaker 1: out of the whole universe because I want to know.
3:00
Speaker 1: I want to understand. It's not enough to just say
3:02
Speaker 1: I bet that green bubbling thing tastes something like lemon
3:05
Speaker 1: lime soda. I want to actually know the truth. I
3:08
Speaker 1: think there are easier ways to find out what something is, Daniel,
3:11
Speaker 1: rather than bringing it in your mouth and in your body,
3:14
Speaker 1: Have you tried asking what it is? It seems like
3:16
Speaker 1: the polite thing to do. But then how would they know,
3:18
Speaker 1: right if they haven't tasted it. Maybe some questions are
3:21
Speaker 1: not meant to be answered, What like, are you curious
3:23
Speaker 1: about how sanide tastes? I am curious? Actually, you know,
3:27
Speaker 1: I like almond pastries and so hey, maybe you know
3:29
Speaker 1: a nice cyanide after flavor is not the worst thing
3:32
Speaker 1: in the world. But yeah, I'm curious about all this stuff,
3:34
Speaker 1: even the stuff that might kill you to find out
3:36
Speaker 1: the answer. It's just this deep desire to know these truths. Well,
3:40
Speaker 1: speaking of dark matters like tasting poison, there are amazing
3:44
Speaker 1: mysteries out there, including one that is maybe one of
3:47
Speaker 1: the biggest mysteries in the universe. At least it's the
3:49
Speaker 1: second biggest mystery in the universe by percentage. Boys, right,
3:52
Speaker 1: that's right. If the universe was laid out as a buffet,
3:54
Speaker 1: most of it would be dark energy, but a huge,
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Speaker 1: heaping pile of it would be dark arc matter. Most
4:01
Speaker 1: of the actual stuff in the universe, the matter, the things,
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Speaker 1: the bits and pieces that move around in our universe,
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Speaker 1: are not the things that make up me and you
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Speaker 1: and weird beakers of bubbling green goo in chemistry laboratories,
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Speaker 1: it's something else, something different, something we do not yet understand,
4:20
Speaker 1: but we have a cool name for it. That's right,
4:21
Speaker 1: we have a cool name for it. It's dark matter.
4:23
Speaker 1: And that is an interesting analogy, Daniel. I guess the
4:26
Speaker 1: universe is like a giant buffet, and five percent of
4:29
Speaker 1: it is like regular food, right, chicken and bread and
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Speaker 1: pasta slad, And about twenty seven percent of that buffet
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Speaker 1: is a big giant mystery, some kind of weird dark stuff.
4:41
Speaker 1: And I guess you would be right in there tiling
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Speaker 1: it on on your plate. Yeah, I don't know if
4:46
Speaker 1: I'll go back for seconds. You know, I got to
4:47
Speaker 1: try the first serving, but yes, serve me up some
4:50
Speaker 1: dark matter. I want to know what it is. Does
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Speaker 1: it in the end just taste like chicken? Would it taste?
4:55
Speaker 1: I guess it would just go through your tongue, wouldn't it.
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Speaker 1: That's right. Dark matter sounds like something black and heavy,
5:02
Speaker 1: but actually it's invisible and intangible. Dark matter would pass
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Speaker 1: right through you like a cloud of neutrinos, because we
5:10
Speaker 1: don't think that it interacts with normal matter in any
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Speaker 1: way other than with gravity, and gravity is a very
5:16
Speaker 1: very weak force, so you couldn't even like pick up
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Speaker 1: a spoon of dark matter. You had like a blob
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Speaker 1: of dark matter, and you dropped it, it would fall
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Speaker 1: to the center of the Earth, right, And we don't
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Speaker 1: even know if it is matter. We don't even know
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Speaker 1: if it is stuff. All we know about it is
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Speaker 1: its effect on the rest of the universe and the
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Speaker 1: rest of the stars and galaxies out there that we
5:35
Speaker 1: can see. That's right. We have never confirmed the particle
5:38
Speaker 1: nature of dark matter. We don't even really know a
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Speaker 1: hundred percent that it's stuff. And we've talked about it
5:43
Speaker 1: on the podcast a lot of times and we've said
5:44
Speaker 1: that we are pretty sure it's matter, but there are
5:47
Speaker 1: some questions that remain. There are some things that we
5:49
Speaker 1: see out there in the universe that the idea that
5:52
Speaker 1: dark matter is stuff is some kind of invisible new
5:55
Speaker 1: matter in the universe doesn't quite explain. And there are
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Speaker 1: a few other our ideas, different hypotheses to try to
6:02
Speaker 1: explain it. And I know that it's one of the
6:03
Speaker 1: favorite pastime of our listeners because they're always writing the
6:06
Speaker 1: emails about maybe dark matter is actually this other thing,
6:09
Speaker 1: or what if dark matter it could be something else
6:11
Speaker 1: totally different. It is one of the biggest most accessible
6:14
Speaker 1: mysteries in the universe. That's right. Maybe it is a
6:18
Speaker 1: giant tree of some kind of cosmic buffet for some
6:21
Speaker 1: giant beings. Perhaps. Yeah, maybe it's just like weird pasta
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Speaker 1: instead of squidding, because they put something else into it
6:28
Speaker 1: to make it like really dark or invisible. But I
6:31
Speaker 1: guess what you mean, right, Yeah, if there's some kind
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Speaker 1: of animal, let's bray something that makes it invisible, maybe
6:36
Speaker 1: they've just inserted that into the dark matter pasta. Well,
6:38
Speaker 1: hopefully it's more like the dessert of the universe, because
6:40
Speaker 1: that would be pretty neat, right. A third of the
6:42
Speaker 1: universe is just desserts. Does that tell us about your diet?
6:46
Speaker 1: Or Hey, are you like desserts? Sure? Why not? I
6:50
Speaker 1: guess it all depends on your perspective. Vegetables can't be dessert, right, sure, yeah,
6:55
Speaker 1: I guess so I like a nice zucchini bread. Yeah, which,
6:58
Speaker 1: it's that's technically what whread you eat at the end? Right,
7:01
Speaker 1: sounds good. Well, I'm hoping that we can gobble of
7:03
Speaker 1: the mystery of dark matter one day, but until then,
7:06
Speaker 1: we have to think carefully about what we have seen,
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Speaker 1: what we know, what we can explain, what we can't
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Speaker 1: explain and what new ideas we might need to tell
7:15
Speaker 1: a complete and true story about everything that's happening out
7:18
Speaker 1: there in the universe. Yeah, it is an ongoing debate
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Speaker 1: about what dark matter is, and it's an ongoing exploration
7:23
Speaker 1: of what it could be. So today we'll be talking
7:25
Speaker 1: about one possible idea for dark matter. So today on
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Speaker 1: the program, we'll be tackling the question could dark matter
7:37
Speaker 1: be a super fluid? And if so, is it's sparkling?
7:41
Speaker 1: And will it kill you? I guess if you drink
7:43
Speaker 1: it question number two? Right, First, I want to know
7:46
Speaker 1: if it's carbonated, and then question number two is can
7:49
Speaker 1: I survive drinking it? Well, it dissolve all the carbon
7:51
Speaker 1: in your body is the second question. I guess you
7:54
Speaker 1: would want to know before you drink anything, unless you're
7:57
Speaker 1: Daniel whites It. Yeah, and it's a really interesting question.
8:00
Speaker 1: Other dark matter is a super fluid, and you might
8:02
Speaker 1: wonder like, why do we care? Why do we think
8:04
Speaker 1: it might be a super fluid. And for all the
8:06
Speaker 1: successes that dark matter has had in explaining the large
8:10
Speaker 1: scale structure of the universe and gravitational lensing and the
8:13
Speaker 1: wiggles we see in the cosmic microwave background radiation. We'll
8:16
Speaker 1: talk about it in a minute, But there are some
8:18
Speaker 1: things that dark matter as a theory of some weird
8:21
Speaker 1: invisible particle really struggles to explain in our universe. It
8:25
Speaker 1: needs a little bit of help. Yeah, and I feel
8:27
Speaker 1: like we maye skipped the question here, Like I feel
8:28
Speaker 1: like we never even tackled the question could dark matter
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Speaker 1: be a fluid? Like do we even know if it
8:33
Speaker 1: could be a fluid or a solid or gas? You will, Actually,
8:36
Speaker 1: dark matter already we think is kind of a collisionless fluid,
8:40
Speaker 1: sort of like an ideal gas. You know, we think
8:42
Speaker 1: about it as these particles flying around in the universe,
8:44
Speaker 1: not interacting with each other at all, because again, the
8:48
Speaker 1: only interactions we think it has is gravity, and gravity
8:51
Speaker 1: between particles is basically zero. So already we think of
8:54
Speaker 1: dark matter sort of like a collisionless fluid or an
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Speaker 1: ideal gas. So here we're talking about it having like
8:59
Speaker 1: special produced from being a super fluid like a superhero.
9:03
Speaker 1: But shouldn't be like a super gas then? Yeah, exactly,
9:07
Speaker 1: Maybe it gets bitten by a radioactive spider and then
9:09
Speaker 1: turns into a super fluid or super gas. Yea radioactive
9:12
Speaker 1: fluid spider, I guess it would have to be the
9:14
Speaker 1: marvel theory of the universe. Well, as usually, we were
9:17
Speaker 1: wondering how many people out there had considered this question
9:19
Speaker 1: whether dark matter could be a super fluid. So Daniel
9:23
Speaker 1: went out there into the wilds of the internet, or
9:25
Speaker 1: maybe the campus of UC Irvine, which one this time? Daniel,
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Speaker 1: these are Internet answers, So thanks very much to everybody
9:32
Speaker 1: who participates in these and waits patiently for us to
9:35
Speaker 1: get to the episode. If you'd like to participate for
9:37
Speaker 1: future episodes, please don't be shy right to us. Two
9:40
Speaker 1: questions at Daniel and Jorge dot com. So think about
9:43
Speaker 1: it for a second. Do you think dark matter could
9:46
Speaker 1: be a super fluid? Here's what people had to say. Well,
9:50
Speaker 1: I wish I knew what a super fluid was, because
9:52
Speaker 1: that sounds like a really awesome thing to get to know.
9:54
Speaker 1: The dark matter could be a lot of different things
9:57
Speaker 1: still at this point, um, so sure it could be
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Speaker 1: a super fluid. It could be a great soft drink
10:03
Speaker 1: that sadly just passes right through your body. I don't
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Speaker 1: really think that's true because the other superfluids that we've
10:10
Speaker 1: created are all made out of hawks, they're just in
10:12
Speaker 1: a different arrangement, and I don't think quarks can, you know,
10:16
Speaker 1: display the behaviors that dark matter does. So no, I
10:19
Speaker 1: don't think that dark matter is a super fluid, but
10:22
Speaker 1: who knows, well, what's a super fluid. I believe that's
10:25
Speaker 1: material that doesn't lose energy when it's moving, So it
10:29
Speaker 1: sounds like document that would really hit that point because
10:31
Speaker 1: it doesn't even inter fear with itself. On the other hand,
10:34
Speaker 1: we know that doc meto is impacted by gravity, so
10:36
Speaker 1: that would speak against it. So I'm not really sure.
10:39
Speaker 1: But if I would have to make a bed, I
10:40
Speaker 1: would say, yeah, it's a super fluid. I don't see
10:43
Speaker 1: how can anything out in space be considered a fluid
10:48
Speaker 1: given how low density it is, and if it isn't
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Speaker 1: a fluid, it could be a super fluid. No idea.
10:55
Speaker 1: That's fascinating. I would not have thought dark matter was
10:58
Speaker 1: dense enough to be a fluid in the sense that
11:00
Speaker 1: we understand it. Um my understanding that dart matter is
11:03
Speaker 1: going to be as diffuse as regular matter and its
11:07
Speaker 1: distribution through a nearly infinite universe, so that it's going
11:12
Speaker 1: to behave like a guess. I would think if I
11:14
Speaker 1: remember correctly, a super fluid doesn't as a fluid fluid
11:17
Speaker 1: without viscosity. I think it was viscosity. And well, we
11:22
Speaker 1: know dark matter as supposed to interact with matter only
11:25
Speaker 1: through gravity. But I suppose if it interacts any through gravity,
11:29
Speaker 1: that implies some form of attraction, which means, if we
11:32
Speaker 1: regarded as a fluid, it must have some sort of viscosity, which,
11:35
Speaker 1: if I remember the definition of a superfluid currictly means
11:38
Speaker 1: that can't be a super fluid. Sure, I guess it
11:41
Speaker 1: could be anything. We really don't know much about dark
11:44
Speaker 1: matter other than it exists and it has gravity. Um,
11:49
Speaker 1: so why not? Could be, could be super fluid, could be,
11:53
Speaker 1: could be anything? Really m M interesting answers some skepticism.
11:58
Speaker 1: Some people were like, I don't know, don't think so
12:01
Speaker 1: this one sounds weird to people. I think the idea
12:04
Speaker 1: of having like a fluid out in space sounds weird.
12:08
Speaker 1: People think of spaces like cold and mostly empty, maybe
12:12
Speaker 1: filled with tiny little crystals or particles flying around, But
12:15
Speaker 1: like a fluid is a weird thing to think about
12:17
Speaker 1: having in space, right, And it seems like a lot
12:19
Speaker 1: of people are like, maybe it could be a fluid,
12:21
Speaker 1: but a super fluid, I don't know if I would
12:23
Speaker 1: give it, you know, supernatural powers. Yeah, well, at least
12:26
Speaker 1: one guy is ready to taste it, though, you know
12:27
Speaker 1: he's thinking about super soft drinks. Hmm, interesting, super soda,
12:32
Speaker 1: super dark soda. Exactly. It's very massive. It's like Coca
12:35
Speaker 1: cola dark coke. Give us a call. We got ideas,
12:39
Speaker 1: special dark recipe. But a lot of people didn't seem
12:43
Speaker 1: to know what even a super fluid is. I guess
12:46
Speaker 1: that's not a common word even I'm not sure what
12:49
Speaker 1: it quite means. Yeah, super fluids are not the kind
12:51
Speaker 1: of thing you have experience with that you don't see
12:54
Speaker 1: them in your everyday life. The river that runs through
12:56
Speaker 1: the park in the middle of your town doesn't ever
12:58
Speaker 1: become a super fluid. You don't make super fluids in
13:01
Speaker 1: your kitchen. They're like a weird quantum state of matter
13:05
Speaker 1: that we only recently even we're sure could exist. And
13:09
Speaker 1: so it's a sort of a new theoretical idea, and
13:12
Speaker 1: whenever that happens, people have fun applying into like, oh,
13:15
Speaker 1: this is new and cool. Maybe this works also over
13:17
Speaker 1: here in this different part of physics where there's something
13:20
Speaker 1: we don't understand we have a new hammer. So let's
13:23
Speaker 1: see what else could be a nail. Yeah, it seems
13:25
Speaker 1: like maybe dark matter being a super fluid could maybe
13:27
Speaker 1: explain some of the things we can't quite figure out
13:29
Speaker 1: about it. And so Dania, let's step people through this.
13:32
Speaker 1: First of all, I guess let's recap what dark matter
13:34
Speaker 1: is and what is it that we don't understand about
13:36
Speaker 1: it that is making us consider this idea. So we
13:39
Speaker 1: think that the universe has a bunch of invisible matter
13:43
Speaker 1: in it because we see a lot of gravity out
13:46
Speaker 1: there in the universe that we can't explain from visible matter.
13:49
Speaker 1: You know, we know that stars are huge balls of
13:52
Speaker 1: hydrogen and they have a lot of mass, and so
13:54
Speaker 1: they have a lot of gravity, and the Earth spins
13:56
Speaker 1: around the Sun, for example, because of the mass of
13:59
Speaker 1: all that grab But if you look at a galaxy
14:01
Speaker 1: and you add up all of the mass from all
14:03
Speaker 1: the stars that you can see, you can't explain all
14:06
Speaker 1: the gravity that's happening in the galaxy. Like the galaxy
14:10
Speaker 1: is spinning like all galaxies do, and that spinning would
14:12
Speaker 1: tend to toss stars into outer space the way like
14:15
Speaker 1: ping pong balls on a Merry Go Round. If you spin,
14:17
Speaker 1: it would toss those ping pong balls out past the
14:20
Speaker 1: Merry Go Round, But the gravity of the galaxy keeps
14:23
Speaker 1: those stars in place. That's why this Milky Way is
14:26
Speaker 1: not just like throwing all of our stars away. But
14:28
Speaker 1: the galaxies are spinning really really fast, and in order
14:31
Speaker 1: to hold them in place, they need more gravity than
14:34
Speaker 1: we can account for. The gravity from the stars we
14:36
Speaker 1: can see doesn't give us enough gravity to hold the
14:39
Speaker 1: galaxy together. And on a bigger scale, we also need
14:43
Speaker 1: to hold galaxy clusters together. Galaxy clusters are big groups
14:47
Speaker 1: of galaxies, and we don't think those galaxies seem to
14:50
Speaker 1: have enough mass to hold themselves together. Galaxy clusters are
14:53
Speaker 1: also spinning. But if you add a bunch of invisible
14:57
Speaker 1: mass to the galaxies, then it all works because it's invisible,
15:01
Speaker 1: explains why you can't see it, and it's new matter,
15:04
Speaker 1: so it adds more gravity, and so it solves those
15:08
Speaker 1: problems if you add this weird new invisible stuff to
15:11
Speaker 1: the universe. The weirdest thing about it, though, is that
15:14
Speaker 1: you need much more dark matter than visible stuff. It's
15:17
Speaker 1: not like you just add a little sprinkling of dark matter.
15:19
Speaker 1: You need to take every star and add five stars
15:22
Speaker 1: worth of dark matter to explain all the missing gravity. Yeah,
15:25
Speaker 1: it's it's almost like dark matter is kind of like
15:28
Speaker 1: the missing piece. And what we see of the universe, right,
15:31
Speaker 1: and the way the galaxies stick together and the galaxy
15:34
Speaker 1: clusters stick together, they stick together more than they should
15:37
Speaker 1: given what we can see in them. And so one
15:40
Speaker 1: solution is that maybe there's invisible stuff out there that's
15:43
Speaker 1: holding it together. Yeah, and this is the kind of
15:45
Speaker 1: thing we're always trying to do, is reconcile everything we see.
15:49
Speaker 1: We think we understand how gravity works. Let's check it.
15:51
Speaker 1: Let's make sure that our explanation makes sense, that it
15:55
Speaker 1: works for this scenario. And that's how we discovered oh
15:57
Speaker 1: my gosh, it doesn't. And that was the clue that
15:59
Speaker 1: maybe it was something else going on, or there was
16:02
Speaker 1: something else new out there. But before you believe that,
16:06
Speaker 1: just like crazy new idea that the universe is filled
16:08
Speaker 1: with a huge amount of invisible stuff you just happened
16:11
Speaker 1: and never noticed before, you want other pieces of evidence.
16:14
Speaker 1: And so we have other clues that dark matter might
16:17
Speaker 1: be real. We see it affecting the way light moves
16:19
Speaker 1: through the universe because if it has mass, it changes
16:22
Speaker 1: the curvature of space, and so it can lends light.
16:25
Speaker 1: We see that it existed in the very early universe
16:28
Speaker 1: because it affected the wiggles in the cosmic microwave background radiation,
16:33
Speaker 1: these photons from the plasma that filled the universe very
16:36
Speaker 1: very early on. And we also know that affected the
16:38
Speaker 1: whole way that the universe form, the large scale structure
16:42
Speaker 1: of the universe. Galaxies we think wouldn't even exist if
16:45
Speaker 1: dark matter hadn't created little gravitational wells to pull stars
16:49
Speaker 1: into mostly all hangs together into a very nice story, right,
16:52
Speaker 1: But it's kind of interesting. I guess that it's a
16:54
Speaker 1: story we made up assuming that what we know of
16:57
Speaker 1: the rest of the universe is true. Right, Like, if
17:00
Speaker 1: we assume that the laws of fixed work the way
17:02
Speaker 1: we think they do, then you sort of need this
17:04
Speaker 1: invisible matter to just make what we see make sense.
17:07
Speaker 1: But that's only assuming that we're right about the laws
17:09
Speaker 1: of physics. Yeah, that's saying gravity works a certain way,
17:13
Speaker 1: and so in order to explain this missing gravity, we
17:15
Speaker 1: need more mass. But you're right, there are other ideas.
17:18
Speaker 1: People have also thought, well, maybe gravity doesn't work the
17:21
Speaker 1: way that we thought maybe there isn't any missing gravity.
17:24
Speaker 1: It's just signs that our theory of gravity is wrong.
17:28
Speaker 1: And people have tried to modify the theory of gravity
17:31
Speaker 1: to explain what we see, and this is called Mond
17:34
Speaker 1: modified Newtonian dynamics. The theory says that instead of gravity
17:38
Speaker 1: going like one over distance square the way Newton said,
17:42
Speaker 1: there's another factor there that when things have very low accelerations,
17:45
Speaker 1: gravity is a little bit different. It gets a little stronger.
17:48
Speaker 1: So if you tweak gravity in just this way, you
17:51
Speaker 1: can also explain how galaxies rotate without using dark matter.
17:55
Speaker 1: That's really interesting. So it could be that dark matter
17:58
Speaker 1: is not dark matter at all, Like maybe we just
18:01
Speaker 1: have the laws of physics a little bit wrong. But
18:03
Speaker 1: does that explain everything about the way the galaxies stick
18:06
Speaker 1: together and even the gravitational lensing. No, So Mond, this
18:09
Speaker 1: alternative theory gravity does in fact a better job at
18:13
Speaker 1: explaining how galaxies rotate than dark matter does. There's some
18:16
Speaker 1: things about galaxy rotations that dark matter just can't seem
18:19
Speaker 1: to get right, but it doesn't explain everything else that
18:22
Speaker 1: dark matter does. Like Mond does not do a good
18:25
Speaker 1: job of describing how galaxy clusters rotate and spin. Around themselves,
18:29
Speaker 1: and it's much more difficult for it to explain, like
18:31
Speaker 1: the cosmic microwave background and lensing and all sorts of
18:35
Speaker 1: other very strong evidence for dark matter. So mond is
18:38
Speaker 1: sort of a nice idea you can explain one thing
18:40
Speaker 1: actually better than dark matter can. But dark matter is
18:43
Speaker 1: sort of like a stronger idea across the board. But
18:46
Speaker 1: neither of them, I guess, is perfect. And let's maybe
18:48
Speaker 1: dig into that a little bit, like what is it
18:50
Speaker 1: about the idea that dark matter is invisible stuff that
18:53
Speaker 1: doesn't explain what we see out there? So by now
18:55
Speaker 1: we've seen a lot of galaxies, and what we try
18:58
Speaker 1: to do is understand like how am my dark matter
19:00
Speaker 1: is in a galaxy versus how much normal matter? And
19:03
Speaker 1: is that common across galaxies? Like do all galaxies have
19:06
Speaker 1: the same amount of dark matter and the same amount
19:08
Speaker 1: of normal matter? And we also try to understand how
19:11
Speaker 1: that could have happened. You know, if dark matter is
19:13
Speaker 1: this weird particle, this new heavy, invisible thing, then it
19:16
Speaker 1: would have clustered together and we can make models for
19:19
Speaker 1: how that would have happened informed galaxies. We look out
19:21
Speaker 1: into the universe, the galaxies we see don't really line
19:24
Speaker 1: up with what we expect for dark matter. So one
19:26
Speaker 1: thing specifically we look at is a relationship between how
19:29
Speaker 1: bright the galaxies are and how fast they are spinning.
19:33
Speaker 1: How bright they are is really interesting because it tells
19:35
Speaker 1: us like how much normal matter is there, how many stars,
19:38
Speaker 1: how fast they're spinning should tell us something about how
19:41
Speaker 1: much dark matter there is in the galaxy. And if
19:43
Speaker 1: you do a bunch of simulations, then you expect like
19:46
Speaker 1: a loose relationship there. You expect, like some galaxies to
19:49
Speaker 1: have a lot of dark matter and something to have
19:50
Speaker 1: a little bit, but there to be a lot of variation.
19:53
Speaker 1: What we see when we look at these galaxies, though,
19:55
Speaker 1: is that there's a very very tight relationship. It's like
19:58
Speaker 1: almost no variation, like the amount of stars in a
20:01
Speaker 1: galaxy and amount of dark matter and the galaxy has
20:03
Speaker 1: a very very close relationship, which we think is weird
20:06
Speaker 1: and we can't explain with our models. You mean, like
20:09
Speaker 1: when you look at the galaxies out there in the universe,
20:11
Speaker 1: they almost have the same proportion of regular matter and
20:14
Speaker 1: dark matter. I think that's what you're saying, right, Like,
20:16
Speaker 1: there aren't galaxies out there with a lot of dark matter,
20:18
Speaker 1: and there aren't a lot of galaxies with a little
20:20
Speaker 1: bit of dark matter, which is weird. But I guess
20:23
Speaker 1: to me, it's weird that you would think it's weird.
20:25
Speaker 1: Why wouldn't they all it's sort of the same. But
20:27
Speaker 1: they were all made in the Big Bang, you know,
20:28
Speaker 1: because there's a random element here, right, Like, how do
20:32
Speaker 1: galaxies form? Anyway? It comes from a quantum fluctuation in
20:36
Speaker 1: the initial seeds of the universe that gave you a
20:38
Speaker 1: slight over density in the dark matter that pulled together
20:42
Speaker 1: a little well and then grab some stuff. And you know,
20:45
Speaker 1: we do expect some relationship. We expect there to be
20:48
Speaker 1: a relationship between the amount of matter and the amount
20:50
Speaker 1: of dark matter, because in the beginning we think this
20:52
Speaker 1: stuff is mostly evenly spread out. But we also expect
20:56
Speaker 1: some variation. And when they do simulations to try to
20:58
Speaker 1: predict what kind of variation we see and we run
21:01
Speaker 1: all of our laws of physics, we see a much
21:03
Speaker 1: wider variation in our simulations than we see out there
21:06
Speaker 1: in the actual universe. That tells us like, maybe there's
21:09
Speaker 1: something wrong with this theory. That's something that we're putting
21:11
Speaker 1: into our simulations that isn't doing a good job of
21:14
Speaker 1: describing what we're actually seeing. I think you're saying that
21:17
Speaker 1: the ratio between dark matter and regular matter is too constant,
21:21
Speaker 1: like it's too consistent across the board of the universe,
21:25
Speaker 1: which means that maybe the problem is that what we
21:27
Speaker 1: expect to see in the universe is wrong or something. Yeah,
21:30
Speaker 1: because for that to happen, you might expect some sort
21:32
Speaker 1: of interaction between them, for them to like turn back
21:35
Speaker 1: and forth into each other, or interact with each other,
21:37
Speaker 1: some process that's keeping them so tightly coupled. But we
21:40
Speaker 1: think that dark matter and atomic matter don't interact except
21:43
Speaker 1: through gravity, so we don't have a process for making
21:46
Speaker 1: this happen. The alternative theory MOND actually predicts this perfectly,
21:51
Speaker 1: like Mon says, there is no dark matter, there's just
21:54
Speaker 1: normal matter, and gravity changes how things spin, and the
21:57
Speaker 1: apparent rotation of velocity of these galaxies should be very
22:01
Speaker 1: tightly connected to their brightness because the rotation velocity just
22:05
Speaker 1: comes from stars. So the Mond prediction is like bang
22:09
Speaker 1: on exactly what we see, whereas the dark matter prediction
22:12
Speaker 1: is sort of like scattered all over the place and
22:14
Speaker 1: doesn't do a good job of describing what we see.
22:17
Speaker 1: For astronomy nerds out there. This is called the Tully
22:19
Speaker 1: Fisher relation. M I think you're saying that maybe this
22:22
Speaker 1: idea of Mond, that maybe our laws of physics are wrong,
22:25
Speaker 1: does a better job of explaining the consistency of what
22:29
Speaker 1: we see out there in the galaxies. Like, it makes
22:32
Speaker 1: more sense that gravity works differently than we think it does,
22:35
Speaker 1: and then it would be for other to be a
22:37
Speaker 1: bunch of invisible mass. Yeah, it does a better job
22:39
Speaker 1: of explaining the relationship between galaxy brightness and rotation that
22:43
Speaker 1: we see in the universe. We see them much more
22:46
Speaker 1: tightly coupled and connected in the universe than we would
22:49
Speaker 1: expect if it was due to dark matter. If you've
22:50
Speaker 1: got like a random sampling of how much dark matter
22:52
Speaker 1: and how much normal matter, you expect there to be
22:54
Speaker 1: more of a spread. But Mond predicts a very tight
22:57
Speaker 1: relationship because there is no dark matter, So it does
23:00
Speaker 1: a better job of predicting what we actually see out
23:03
Speaker 1: there in the universe. This is like kind of a
23:04
Speaker 1: headache for dark matter as a theory. Interesting, like it
23:08
Speaker 1: has its failings. The idea that it's invisible matter, and
23:11
Speaker 1: this idea that maybe the laws of physics are wrong
23:13
Speaker 1: comes in and says, hey, I can fix that, but
23:15
Speaker 1: maybe it doesn't fix everything, which is why it's still
23:18
Speaker 1: not the prevailing theory. Yeah, exactly, But it's been like
23:21
Speaker 1: a real thorn in the side of dark matter for
23:23
Speaker 1: a long time and keeps a lot of people, I think,
23:25
Speaker 1: from accepting this idea that dark matter might be real. Well,
23:28
Speaker 1: there is a new theory, a new idea that maybe
23:31
Speaker 1: would make dark matter make more sense, and that's the
23:33
Speaker 1: idea that it maybe it's a super fluid. So let's
23:36
Speaker 1: get into what a super fluid is and whether dark
23:39
Speaker 1: matter could be one of these superpowered fluids. But first
23:42
Speaker 1: let's take a quick break. All right, we're asking the question,
23:57
Speaker 1: could dark matter be a super fluid? It? And we're
24:00
Speaker 1: asking the question because there are some things about dark
24:02
Speaker 1: matter that we can't quite explain out there. Even if
24:05
Speaker 1: we assume it's some kind of stuff, some kind of particles,
24:07
Speaker 1: some kind of fluid, it doesn't quite explain the ratio
24:11
Speaker 1: of regular matter and dark matter we see out there
24:13
Speaker 1: in the universe. Yeah, that's right, And so people are
24:15
Speaker 1: trying to be creative. They're saying, like, dark matter by
24:17
Speaker 1: itself doesn't quite work as a theory. Mond by itself
24:21
Speaker 1: has lots more problems than dark matter by itself, like,
24:23
Speaker 1: neither of them are perfect. Is there some way we
24:25
Speaker 1: could take dark matter and make it a little Mond
24:28
Speaker 1: dear right, to try to capture some of the things
24:31
Speaker 1: that Mond has. Remember, the key feature of minds that
24:34
Speaker 1: it changes the effect of gravity over some distances. So
24:38
Speaker 1: people were like, well, is there any way we could
24:40
Speaker 1: change dark matter or tweak dark matter so that it
24:44
Speaker 1: basically has the same effect as Mond, but only in
24:46
Speaker 1: these scenarios the hearts of galaxies where dark matter seems
24:49
Speaker 1: to be having a problem all right, And so the
24:52
Speaker 1: idea is that maybe dark matter is a super fluid,
24:54
Speaker 1: which is like a superpowered fluid that was I don't know,
24:57
Speaker 1: born in krypton or something inherited power ring from an am.
25:01
Speaker 1: The superfluid is not from cartoons and not just from
25:04
Speaker 1: science fiction. It's a real thing. A couple of Nobel
25:07
Speaker 1: Prizes have been won already because of superfluids, and they're
25:10
Speaker 1: called superfluids sort of analogy to superconductors, right. A superconductor
25:15
Speaker 1: is something that conducts electricity, so you can send energy
25:18
Speaker 1: down a wire if it's superconducting and lose none of
25:21
Speaker 1: it right, you don't turn any of it into heat,
25:23
Speaker 1: and so super fluid is similar. It's a liquid that flows,
25:27
Speaker 1: but without any internal resistance, so the bits just sort
25:30
Speaker 1: of slide by each other. It doesn't heat up at
25:33
Speaker 1: all as it flows, doesn't lose energy. Like if you
25:35
Speaker 1: take a bucket of water and you put your finger
25:37
Speaker 1: in it and spin it, you get a little vortex
25:39
Speaker 1: that's forming. But eventually that vortex will sort of peter
25:42
Speaker 1: out right, the energy will diffuse and the water will
25:45
Speaker 1: stop moving. In a superfluid, that doesn't happen. You start
25:48
Speaker 1: a vortex and it just spins forever. Wow, it's super interesting.
25:52
Speaker 1: I guess that's the idea of zero viscosity, which means
25:55
Speaker 1: no friction between the molecules of the fluid. But I
25:58
Speaker 1: guess maybe let's dig in a little. This might be interesting.
26:01
Speaker 1: What exactly is viscosity or what exactly is friction? Like?
26:04
Speaker 1: Where does that come from? So it comes from the
26:06
Speaker 1: interaction of the bits inside of it. Right, when we
26:09
Speaker 1: talk about like an ideal gas, we're talking about particles
26:12
Speaker 1: flying through space, but we ignore the possibility that they
26:15
Speaker 1: can bump off each other and exchange energy. In real life,
26:18
Speaker 1: the particles inside of gas can bump off each other,
26:21
Speaker 1: can exchange energy, and the same thing with a liquid.
26:23
Speaker 1: In the case of a zero viscosity liquid a super fluid,
26:27
Speaker 1: then the particles don't really bump off each other and
26:29
Speaker 1: they can like change places without losing any of their energy.
26:33
Speaker 1: What do you mean they don't bump into each other.
26:35
Speaker 1: They do bump, but they don't lose energy, or they
26:37
Speaker 1: don't bump at all, Like the things inside of the
26:40
Speaker 1: liquid don't interact with it with the self. When you're
26:42
Speaker 1: thinking about a liquid, it's sort of like an emergent object,
26:45
Speaker 1: and it's easiest to think about it like layers of liquid.
26:47
Speaker 1: Imagine like two layers of a liquid passing by each other,
26:51
Speaker 1: and think about whether there's like friction between those layers. Say,
26:54
Speaker 1: for example, say for example, you have a tube and
26:56
Speaker 1: you're pushing some liquid through it, right, then if it's
26:59
Speaker 1: a very vis gets liquid, it's going to flow more
27:01
Speaker 1: rapidly near the center than near the walls, because I
27:05
Speaker 1: get the fluid particles near the walls of the tube
27:08
Speaker 1: are hitting the particles of the tube, right, and so
27:11
Speaker 1: they lose energy. They're like bumping against the wall, and
27:14
Speaker 1: it's not just that they're bumping against the wall. Think
27:16
Speaker 1: about like, as the layers are passing by each other,
27:18
Speaker 1: are the particles grabbing at each other? Like what is
27:21
Speaker 1: friction anyway? Like if you run your finger along the surface,
27:24
Speaker 1: why is kinetic energy getting turned into heat? Because the
27:27
Speaker 1: particles in your finger are grabbing at the particles on
27:30
Speaker 1: the table. There's little deformities and there's bonds between them
27:33
Speaker 1: that are getting broken and reformed. And the same thing
27:36
Speaker 1: happens inside liquid. When you have like layers of liquid
27:39
Speaker 1: passing by each other, they have an interaction, then they
27:42
Speaker 1: can grab at each other and sort of like slow
27:44
Speaker 1: the next layer down and it's super fluid, that doesn't happen,
27:48
Speaker 1: and the layers can sort of like pass by each
27:49
Speaker 1: other without any friction at all. And why is it?
27:53
Speaker 1: I guess it just depends on the interaction between the particles. Right.
27:56
Speaker 1: It's not something you can do with the normal liquid
27:57
Speaker 1: very easily. It's a quantum property, right, It's not something
28:00
Speaker 1: you can really understand at an intuitive level just thinking
28:02
Speaker 1: about little balls. Instead, you need to think about these
28:05
Speaker 1: objects as quantum objects, which means you think about their
28:08
Speaker 1: wave functions and when these things get really really cold,
28:11
Speaker 1: then you have very little uncertainty on their temperature that
28:14
Speaker 1: their wave functions grow really really wide, because the Heisenberg
28:18
Speaker 1: and certainty principle tells you can't know something's momentum and
28:21
Speaker 1: its location very very well. So when you cool something down,
28:24
Speaker 1: its wave function grows very very large. So now instead
28:27
Speaker 1: of having just like a bunch of little particles bouncing
28:29
Speaker 1: around that you can sort of think of a particles,
28:31
Speaker 1: you have these overlapping wave functions between these objects, and
28:34
Speaker 1: they form like one big quantum state, and they tend
28:37
Speaker 1: to move like all together instead of interacting with each other,
28:41
Speaker 1: so they're like more tightly coupled to each other weirdly,
28:44
Speaker 1: which gives this super fluid state. I see, I guess
28:47
Speaker 1: that you're saying. I think the cold or something gets
28:49
Speaker 1: the bigger the wave function of the particles gets, which
28:52
Speaker 1: means that their things get fuzzier almost in a way,
28:55
Speaker 1: right like instead of a little tiny ball, suddenly it's
28:57
Speaker 1: more like a hazy blob. And it's kind of hard
29:00
Speaker 1: maybe for too hazy blobs to really drag on each other.
29:03
Speaker 1: Is that kind of what you're saying. Yeah, And it
29:04
Speaker 1: acts more coherently instead of individual particles which you can
29:07
Speaker 1: grab at each other. Now it's like a huge train
29:10
Speaker 1: of particles that tend to move together rather than bumping
29:13
Speaker 1: against each other. So it's like it's all much more coordinated. Now.
29:17
Speaker 1: It's not like a random crowd of people bumping into
29:18
Speaker 1: each other. Now it's like a tightly packed formation of
29:21
Speaker 1: a marching band walking down the street. But they don't
29:24
Speaker 1: bump into each other at all. They just sort of
29:25
Speaker 1: like flu and so this happens. For example, here on Earth,
29:28
Speaker 1: of you cool helium a lot, you get a Bose
29:30
Speaker 1: Einstein concert which is super fluid. The first demonstration of
29:34
Speaker 1: this was in super fluid helium. We get the Nobel
29:38
Speaker 1: Prize and Physics at Stanford for that. That wasn't actually
29:41
Speaker 1: a Bose Einstein condensate, but it is. A super fluid
29:44
Speaker 1: can flow without losing any energy. Another example of a
29:47
Speaker 1: super fluid is a Bose Einstein condensate. Another special state
29:50
Speaker 1: of matter rape a whole podcast about that again, where
29:53
Speaker 1: you're cooling atoms down in a trap to make them
29:56
Speaker 1: very very cold and overlapping. So they have other weird
29:58
Speaker 1: quantum properties as well, which include being a super fluid.
30:02
Speaker 1: We also think we have seen super fluid sort of
30:05
Speaker 1: indirectly inside the large Hadron collider. When we smash big
30:09
Speaker 1: atoms together, like lead nuclei and gold nuclei, we can
30:13
Speaker 1: make this state of matter called a cork gluon plasma.
30:16
Speaker 1: And one of the features of it, we think, is
30:18
Speaker 1: that there's a little bit of super fluidity, very very
30:20
Speaker 1: briefly at the heart of that thing while it exists.
30:23
Speaker 1: I mean, when you smash particles together, you get so
30:25
Speaker 1: much density of energy, and these particles really packed together
30:29
Speaker 1: that they behave like a super fluid for a tiny
30:32
Speaker 1: little bit. Yeah, for a tiny little bit, even though
30:34
Speaker 1: it's super duper hot. It's also so dense that these
30:37
Speaker 1: particles undergo this new phase change into a cork gluon plasma,
30:41
Speaker 1: which can also be a super fluid. So a super
30:43
Speaker 1: fluid isn't like one unique state of matter. It's like
30:45
Speaker 1: a description of a phase of matter, the way like
30:47
Speaker 1: some phases of matter conduct electricity and some don't. Some
30:51
Speaker 1: phases of matter are fluid and some are super fluid
30:54
Speaker 1: and others aren't. So these are just examples of places
30:56
Speaker 1: where we have seen super fluidity happening, Like really is
31:00
Speaker 1: a thing in the universe. We're sure about that. That's
31:02
Speaker 1: not a hypothetical thing, and we think it might even
31:05
Speaker 1: be what's happening inside of neutron stars, right, Yeah, the
31:08
Speaker 1: inside of neutron stars is a lot like a cork
31:10
Speaker 1: glow on plasma. It's very very dense, and the particles
31:13
Speaker 1: get squeezed together and their wave functions start to overlap.
31:16
Speaker 1: And we don't really know what happens inside a neutron
31:19
Speaker 1: star because it's some state of matter that we can't
31:21
Speaker 1: really access anywhere else, and all the forces come into play,
31:25
Speaker 1: including gravity and the strong force, and it really tests
31:28
Speaker 1: our ability to even do calculations or predicular what might happen.
31:31
Speaker 1: We think that weird states of matter like nuclear pasta
31:35
Speaker 1: might occur, and there might also be super fluid states
31:38
Speaker 1: inside the heart of a neutron star. But is there
31:40
Speaker 1: generally like a recipe for making super fluids? Like, what's
31:44
Speaker 1: the thing that makes all of these different examples? What
31:46
Speaker 1: do they have in common? They all have in common
31:48
Speaker 1: high density. So you squeeze these particles together basically so
31:52
Speaker 1: that their wave functions are overlapping, and that's how you
31:55
Speaker 1: achieve it. It's easier to do that if they're very
31:58
Speaker 1: very low temperature because they're way from are larger. But
32:01
Speaker 1: if you get high enough density, you can also achieve
32:03
Speaker 1: it even at high temperatures, like the inside of a
32:05
Speaker 1: neutron star. But the crucial thing is density. Wonever. It's like,
32:09
Speaker 1: you know, taking a bunch of water balloons. When you
32:12
Speaker 1: squeeze them together, they almost become super fluid. Haven't you
32:16
Speaker 1: been to a birthday party recently? He saw this happen. Well, like,
32:19
Speaker 1: if you have a bunch of water balloons out and
32:21
Speaker 1: they're really far spread, far apart, they sort of behaved
32:24
Speaker 1: like maybe like little particles, but if you sort of
32:26
Speaker 1: packed them together in a bucket, they kind of act
32:29
Speaker 1: like a fluid. Right, Yeah, that's true. I never thought
32:31
Speaker 1: about what it's like for a bunch of water balloons
32:34
Speaker 1: to slide out of a bucket. Have you like dumped
32:36
Speaker 1: a bucket of water balloons on somebody's head before? Yeah? Yeah,
32:39
Speaker 1: super super flat water balloons. Actually that sounds like super fun.
32:43
Speaker 1: But you're exactly right. When simple things come together, they
32:46
Speaker 1: can do new, weird things. And that's the whole amazing
32:49
Speaker 1: size of chemistry. Right. We have these phases of matter
32:52
Speaker 1: that come out of the way, these particles interact with
32:55
Speaker 1: each other or don't interact with each other, and generate
32:57
Speaker 1: these emergent properties electrical activity or shiny nous or liquid
33:02
Speaker 1: phases or other weird phases of matter. It's incredible what
33:05
Speaker 1: matter in the universe can do. The variety of things
33:07
Speaker 1: that come out just of the basic laws from the
33:09
Speaker 1: interactions at the microphysical level. It always amazes me. M Okay,
33:13
Speaker 1: So that's what a super fluid is. And now the
33:15
Speaker 1: idea is that maybe dark matter could be a super fluid.
33:19
Speaker 1: So it's the idea that dark matter is made out
33:21
Speaker 1: of little particles and then when you somehow get them
33:23
Speaker 1: really close to each other, they behave like a super fluid. Yeah.
33:26
Speaker 1: The idea is that dark matter is still dark matter.
33:29
Speaker 1: It's still some particle that's invisible and intangible and doesn't
33:33
Speaker 1: interact with us except through gravity. But you get enough
33:37
Speaker 1: dark matter together under the densest conditions, maybe it's forming
33:42
Speaker 1: a super fluid. And now we give it new properties
33:45
Speaker 1: like those water balloons in the bucket. It can do
33:48
Speaker 1: things when it's all together in those conditions that it
33:50
Speaker 1: couldn't do otherwise. And the idea is that this new
33:53
Speaker 1: super fluid state of dark matter might explain what's happening
33:57
Speaker 1: inside galaxies that currently dark matter as a theory can't explain.
34:02
Speaker 1: Interesting But I thought maybe dark matter didn't interact with itself.
34:05
Speaker 1: So isn't it already a super fluid that doesn't have
34:08
Speaker 1: any internal friction. Yeah, so currently we think that dark
34:11
Speaker 1: matter doesn't have any any interactions. So you might think, oh, yeah,
34:14
Speaker 1: dark matter out there in space is a collisionless fluid.
34:16
Speaker 1: Isn't that also a super fluid, right, Not technically, because
34:19
Speaker 1: they don't have overlapping wave functions. Like if you just
34:22
Speaker 1: have a really dilute gas of dark matter, like we
34:24
Speaker 1: think exists out there at the edge of the galaxy
34:27
Speaker 1: and beyond, that's not really a super fluid because the
34:29
Speaker 1: particles are just really far away from each other. To
34:32
Speaker 1: have a super fluid have these new phenomena emerge, you
34:34
Speaker 1: really have to have them close enough to each other,
34:37
Speaker 1: so the wave functions overlap. So it's more about the
34:40
Speaker 1: quantum overlap of the individual particles and less about the
34:44
Speaker 1: kind of frictionless flow of the fluid for dark matter. Yeah,
34:48
Speaker 1: And in this case, it's the overlap of those particles
34:51
Speaker 1: that generates new phenomena like frictionless flow, and in the
34:54
Speaker 1: case of dark matter super fluid, they think it can
34:57
Speaker 1: effectively create a new force. What emerges from a dark
35:01
Speaker 1: matter super fluid. It's sort of like a new force
35:03
Speaker 1: which effectively can change the way that gravity works to
35:07
Speaker 1: give you exactly the same behavior that we see in
35:10
Speaker 1: the mond theory of dark matter. To me, the question
35:13
Speaker 1: should be is dark matter a super duper fluid? All right, Well,
35:16
Speaker 1: let's get into how dark matter being a super duper
35:19
Speaker 1: fluid at the heart of galaxies could explain some of
35:21
Speaker 1: the things we can understand or explain about the current
35:25
Speaker 1: model of dark matter. But first let's take another quick break.
35:41
Speaker 1: All right, we're asking the question could dark matter be
35:43
Speaker 1: a super fluid? And we're asking the question because there
35:46
Speaker 1: are things about dark matter that we can't quite explain.
35:49
Speaker 1: I mean, we don't know what it is or what
35:51
Speaker 1: it could be. But even our idea of it as
35:54
Speaker 1: a particle, as a bit of matter, as bits of matter,
35:56
Speaker 1: doesn't quite explain some of the things we see out
35:58
Speaker 1: there in the universe. And so the idea is that
36:00
Speaker 1: maybe dark matter is a super fluid, which might explain
36:03
Speaker 1: these things. Yeah, and I think the kernel of the idea.
36:05
Speaker 1: What generated it is noticing that dark matter as a
36:08
Speaker 1: theory seems to have trouble in the densest situations. It
36:12
Speaker 1: works really well between galaxy clusters, it works out there
36:16
Speaker 1: in space for gravitational lensing of lots of galaxies. It
36:20
Speaker 1: works in the early universe, but inside galaxy is currently
36:23
Speaker 1: the densest places in the universe is where it struggles.
36:26
Speaker 1: So people thought, well, maybe when dark matter gets denser,
36:30
Speaker 1: it forms this new state, this super fluid, and then
36:32
Speaker 1: we can figure out how to give this superfluid new properties.
36:35
Speaker 1: Maybe you can solve the problems of dark matter inside
36:38
Speaker 1: galaxies without breaking with dark matter is already so good
36:41
Speaker 1: at explaining everywhere else, right, So the idea is that
36:44
Speaker 1: it only forms a super fluid inside the dense environment
36:47
Speaker 1: of a galaxy. Everywhere else it's just this normal, boring,
36:50
Speaker 1: old dark matter, normal boring, but it's still quite mysterious
36:54
Speaker 1: and elusive. They're saying that at the center of galaxies,
36:57
Speaker 1: where things are pretty dense anyways, right, there are sometimes
37:00
Speaker 1: black holes in the middle of galaxies. There are a
37:02
Speaker 1: lot of stars clustered together. The ideas that maybe dark
37:05
Speaker 1: matter is super duper compact at the center of galaxies
37:08
Speaker 1: more so than like at the edges of galaxies, and
37:11
Speaker 1: not just at the center, but yes, definitely denser at
37:13
Speaker 1: the center. But essentially we're thinking about galaxies as like
37:16
Speaker 1: a dense place in the universe. And as we talked
37:19
Speaker 1: about earlier, how do you make a super fluid. You
37:21
Speaker 1: need to get the particles close enough so their wave
37:23
Speaker 1: functions overlapped and make the super fluid thing happen. And
37:27
Speaker 1: so that can happen in a galaxy because there's a
37:29
Speaker 1: lot of gravity there, it gathers together a lot of
37:32
Speaker 1: dark matter. Another trick they pull is to make dark
37:34
Speaker 1: matter very very very very low mass. We know like
37:38
Speaker 1: how much mass the dark matter we need, but we
37:41
Speaker 1: don't know how much mass each particle has. So if
37:44
Speaker 1: you make dark matter out of really massive particles, you
37:47
Speaker 1: have fewer of them. If you make dark matter out
37:49
Speaker 1: of really low mass particles, you need more of them.
37:53
Speaker 1: So the folks who are working on this theory say
37:55
Speaker 1: that dark matter is really really low mass, then there's
37:57
Speaker 1: a huge number of them, right, And so they're imagining
38:00
Speaker 1: the centers of galaxies being swarmed with zillions and zillions
38:04
Speaker 1: of very very low mass dark matter particles. That come
38:07
Speaker 1: together into a super fluid, and when they do that,
38:10
Speaker 1: they get all sorts of new weird behaviors. Cool, well,
38:13
Speaker 1: it's getting too a little bit of what those behaviors are, Like,
38:15
Speaker 1: what do you think happens when dark matter is that
38:17
Speaker 1: close together that the wave funtionings overlap. So it's really
38:20
Speaker 1: hard to do these calculations because you're talking about like
38:23
Speaker 1: overlapping wave functions of lots and lots and lots and
38:26
Speaker 1: lots of particles. So when physics needs to do that,
38:28
Speaker 1: they try to describe these new behaviors in terms of
38:30
Speaker 1: something they're already familiar with. So the way they usually
38:33
Speaker 1: talk about it is in terms of sound waves propagating
38:37
Speaker 1: through this super fluid. I think about like shock waves
38:40
Speaker 1: moving through it. How if you pull on one part
38:43
Speaker 1: of it that would affect the other parts of it.
38:45
Speaker 1: And dark matter is this super fluid, so it's like
38:47
Speaker 1: weirdly tightly couple that acts like a big coherent blob
38:50
Speaker 1: instead of individual pieces. And so they talk about phonons,
38:53
Speaker 1: which are like sound waves moving through this super fluid,
38:56
Speaker 1: and they build up this whole theory which comes out
38:59
Speaker 1: looking a new force sort of like this dark matter
39:02
Speaker 1: when it enters this super fluid as a new way
39:04
Speaker 1: to interact with itself that it didn't have before. Well,
39:07
Speaker 1: I guess maybe one thing that's confusing me is that
39:09
Speaker 1: I thought dark matter didn't interact with itself, right like
39:12
Speaker 1: it The particles of dark matter don't usually or can't
39:15
Speaker 1: bump into themselves. That's what was part of the idea
39:18
Speaker 1: of dark matter. So why would bring them together really
39:21
Speaker 1: close together make them interact in a different way. But
39:24
Speaker 1: if they can't interact with each other, you're right, at
39:26
Speaker 1: a particle level, they don't have that kind of interaction.
39:28
Speaker 1: We're only talking about gravity, but now we're adding other
39:31
Speaker 1: weird quantum effects, and quantum effects when they all work together,
39:35
Speaker 1: can make it feel like there's a force. Another example
39:37
Speaker 1: is the poly exclusion principle. As someone that tells you that,
39:40
Speaker 1: like two fermions can't be in the same location. That's
39:43
Speaker 1: the thing that keeps some kinds of stars from collapsing.
39:47
Speaker 1: It allows you to resist the force of gravity is
39:50
Speaker 1: trying to push it in. It's not technically a force
39:52
Speaker 1: at the particle level, there's no force there, but this
39:55
Speaker 1: quantum behavior of the objects basically acts as a block
39:59
Speaker 1: to g so in the same way, this weird quantum
40:03
Speaker 1: behavior of dark matter when it's a super fluid acts
40:06
Speaker 1: sort of in a way to change gravity. It's sort
40:09
Speaker 1: of like there's a new force. It's not an individual
40:11
Speaker 1: new force on the particles. It's a way to describe
40:15
Speaker 1: what happens to all these particles when they do this
40:17
Speaker 1: new quantum thing. You can tell a story about it
40:20
Speaker 1: as if it was a new force. Okay, I think
40:23
Speaker 1: maybe I'm starting to get it. Like if I have
40:25
Speaker 1: two particles of dark matter, and I have them really
40:28
Speaker 1: far apart, then they do interact with each other, and
40:30
Speaker 1: not like they can't bump into each other, but they
40:33
Speaker 1: can attract each other gravitationally, like there's a gravitational force
40:36
Speaker 1: between the two particles of dark matter. I think what
40:39
Speaker 1: you're saying is when you bring them really really close
40:41
Speaker 1: to each other, so that wave function of these two
40:43
Speaker 1: dark matter particles starts overlap, then there are other effects
40:46
Speaker 1: that start to kick in, other quantum effects then maybe
40:50
Speaker 1: affect the gravity between them. Yeah, that's precisely it. And
40:53
Speaker 1: you can talk about those new quantum effects as a
40:55
Speaker 1: new force and introduce even like new particles for that force.
41:00
Speaker 1: Call these things phone ons, or you could just say,
41:03
Speaker 1: maybe that changes the overall effective gravity, right, it changes
41:07
Speaker 1: the impact of gravity because now you have to factor
41:10
Speaker 1: in this new, weird quantum effect. And the amazing thing
41:12
Speaker 1: that comes out of the math is that the change
41:14
Speaker 1: it makes to gravity is to make it look exactly
41:17
Speaker 1: like Mond predicts. Remember, Mind, is this change in Newtonian
41:21
Speaker 1: gravity that would beautifully describe everything we see at the
41:25
Speaker 1: hearts of galaxies, but fails everywhere else. It turns out
41:28
Speaker 1: if you make dark matter of super fluid, it changes
41:30
Speaker 1: the gravity within this dark matter to make it look
41:33
Speaker 1: just like Mind. But wait, I thought that you know
41:35
Speaker 1: the gravity The gravity is just between the two particles, right,
41:39
Speaker 1: Like the gravity between these two dark matter particles maybe
41:42
Speaker 1: changes when you bring them closer together, so that maybe
41:44
Speaker 1: they feel or not feel more or less gravity. But
41:47
Speaker 1: to someone standing far away from these two particles, why
41:51
Speaker 1: would they why would the gravity change for them? No,
41:53
Speaker 1: it doesn't. You're absolutely right. And so if you're outside
41:55
Speaker 1: of a galaxy, it doesn't matter whether the dark matter
41:58
Speaker 1: is fluid or not. But we're talking about inside of galaxy.
42:01
Speaker 1: We're talking about what's happening internally, how fast things are
42:04
Speaker 1: spinning the gravity that like one blob of dark matter
42:08
Speaker 1: is feeling on another blob of dark matter inside the
42:10
Speaker 1: same galaxy. So this affects how dark matter inside the
42:14
Speaker 1: Milky Way, for example, is pulling on other dark matter
42:17
Speaker 1: inside the Milky Way, which is exactly what keeps the
42:19
Speaker 1: whole galaxy together as it spins. So these quantum effects
42:24
Speaker 1: make the gravity stronger of the superfluid or weaker. It
42:27
Speaker 1: makes the gravity stronger, right, enhances their gravity. What do
42:31
Speaker 1: you mean, like, do you know what the quantum effect
42:33
Speaker 1: is or are just kind of postulating that there's maybe
42:35
Speaker 1: some quantum effect that would make the gravity stronger. The
42:38
Speaker 1: quantum effect comes from these overlapping wave functions, and when
42:41
Speaker 1: you put it together and you do the math, and
42:43
Speaker 1: you squeeze it theoretically sort of into the box of
42:46
Speaker 1: a force and say, how do I interpret this as
42:49
Speaker 1: a force. Then the calculations come out to predict a
42:52
Speaker 1: change in the force of gravity that looks just like
42:55
Speaker 1: the math you get from Mond. It's not just speculation.
42:58
Speaker 1: You can go directly from these quantum effects to calculating
43:01
Speaker 1: the new effective force of gravity, and it looks just
43:04
Speaker 1: like Mon's prediction, which is as we know something that
43:07
Speaker 1: works very very well well. But I think what you're
43:09
Speaker 1: saying is that the super compact dark matter forms a
43:12
Speaker 1: super fluid which has stronger gravity between the dark matter
43:17
Speaker 1: particles that are in the super fluid. But with something
43:20
Speaker 1: outside of the super fluid, would it feel this extra
43:23
Speaker 1: gravity or not? Well, something inside the galaxy would, but
43:25
Speaker 1: something outside the galaxy wouldn't. Right, So something outside far
43:30
Speaker 1: far away other galaxies in the cluster wouldn't feel any
43:33
Speaker 1: change in the effective gravity. And that's key because we
43:35
Speaker 1: don't want to change the predictions for dark matter in
43:37
Speaker 1: the cluster that already works really really well. The way
43:40
Speaker 1: we see the galaxies rotate around each other, and big
43:43
Speaker 1: clusters of galaxies rotate around other clusters of galaxies. That's
43:47
Speaker 1: very well described by the dark matter theory. So we
43:49
Speaker 1: don't want to change that. So the super fluid thing
43:52
Speaker 1: only changes what happens inside galaxies, not between galaxies. And
43:55
Speaker 1: so how would that explain what we talked about earlier
43:58
Speaker 1: was one of the shortcomings of dark matter, which is
44:00
Speaker 1: that the proportion of dark matter and regular matter is
44:03
Speaker 1: too consistent between galaxies. How would this explain it? Well? Conceptually,
44:07
Speaker 1: you can imagine that it gives us away for like
44:09
Speaker 1: dark matter and normal matters sort of talk to each
44:11
Speaker 1: other more intimately, so effectively it solves a problem by saying,
44:15
Speaker 1: you do still have some variation in how much dark
44:17
Speaker 1: matter and normal matter you have, but dark matter itself
44:20
Speaker 1: acts a little bit differently, so it changes how galaxies rotated,
44:23
Speaker 1: changes the effective gravity of that dark matter, and that's
44:27
Speaker 1: what determines how fast a galaxy can rotate without tearing
44:30
Speaker 1: itself apart. And remember the discrepancy we saw it was
44:33
Speaker 1: not actually directly in the dark matter density of these galaxies,
44:36
Speaker 1: but the rotation speed of the galaxies versus their brightness.
44:40
Speaker 1: So now we have a new way for dark matter
44:42
Speaker 1: and normal matter to side interact a little bit more
44:44
Speaker 1: strongly because this new force that's inside the dark matter
44:48
Speaker 1: super fluid, because we think that's sort of like couples
44:50
Speaker 1: the stars and the dark matter a little bit more tightly,
44:53
Speaker 1: makes it possible for them to have like more feedback
44:56
Speaker 1: mechanisms to potentially explain what we're seeing out there in
44:59
Speaker 1: the universe. I think what you're saying is that maybe
45:01
Speaker 1: there's like an extra effect here that comes from the
45:04
Speaker 1: super fluidity of dark matter that maybe makes it not random, right,
45:09
Speaker 1: because before the problem was that we expected the ratio
45:12
Speaker 1: of dark matter and normal matter to be is a
45:14
Speaker 1: little bit more random, more variation. But maybe this special
45:17
Speaker 1: effects kind of acts in a way that gives you
45:19
Speaker 1: less variation. Like if you have more dark matter, it
45:22
Speaker 1: acts in a way so that you have more regular
45:24
Speaker 1: matter as well. And if you have less dark matter,
45:26
Speaker 1: then maybe acts in a way to give you less
45:28
Speaker 1: regular matter. That's the kind of feedback effect we're looking for.
45:32
Speaker 1: We see out there in the universe, this is strangely
45:34
Speaker 1: tight relationship between the dark matter and the normal matter.
45:37
Speaker 1: We didn't understand that if the only relationship between the
45:40
Speaker 1: two was this fairly weak gravity. But if gravity gets
45:43
Speaker 1: a little bit stronger, it helps solve those problems. And
45:46
Speaker 1: more specifically, we see that the effective gravity inside these
45:50
Speaker 1: galaxies now follows exactly the prediction of mind, which, as
45:54
Speaker 1: we said before, predicts very precisely the ratio of these
45:57
Speaker 1: dark matter to normal matter inside the galaxy. So it
46:00
Speaker 1: all clicks very nicely into place. M M. It seems
46:04
Speaker 1: like a pretty super idea. This is a super fluid,
46:08
Speaker 1: but it also sort of constrains dark matter in a
46:10
Speaker 1: bit right like it it depends also, like it can
46:14
Speaker 1: only be a super fluid if dark matter is made
46:16
Speaker 1: out of really light small particles, right, And there are
46:19
Speaker 1: ideas out there for dark matter to be very very
46:22
Speaker 1: light particles. The most common idea is a whimp, a
46:24
Speaker 1: weekly interacting massive particle where the mass of the particle
46:28
Speaker 1: would be like a hundred times the mass of the proton.
46:31
Speaker 1: But there are other ideas where dark matter could be
46:33
Speaker 1: very very light. We've talked about it before on the podcast,
46:36
Speaker 1: the idea of an axion sort of like a photon
46:39
Speaker 1: with a little bit of mass to it, And so
46:41
Speaker 1: this idea is a little bit more like an axion
46:43
Speaker 1: than a whimp, which would also maybe make dark matter
46:46
Speaker 1: harder to eventually detect and study right directly, Yeah, a
46:51
Speaker 1: lot of our searches for dark batters, these big underground
46:54
Speaker 1: tanks that are looking for a dark matter particle to
46:56
Speaker 1: come and bounce off a zenon atom for example, are
46:59
Speaker 1: not will of sensing dark matter and very very low mass.
47:03
Speaker 1: But we have other experiments that are looking for very
47:05
Speaker 1: very low mass dark matter particles. But there are also
47:08
Speaker 1: other ways to test this theory. People think that if
47:11
Speaker 1: this is true, it will also affect like how galaxies merge.
47:15
Speaker 1: I mean, if you have two merging galaxies and they
47:17
Speaker 1: each have their own halo of dark matter, then what
47:21
Speaker 1: happens when they emerge. You will see the super fluidity
47:24
Speaker 1: effect because the halos won't merge as fast as they
47:27
Speaker 1: would otherwise. Like two halos made of a normal fluid,
47:30
Speaker 1: you'll expect a little bit of friction. Two halos made
47:33
Speaker 1: of a super fluid, they'll basically pass through each other
47:36
Speaker 1: and it'll be gravity that pulls them back, so they
47:38
Speaker 1: would like oscillate more times as they merge. If it's
47:42
Speaker 1: a super fluid, then if it's just a fluid, So
47:45
Speaker 1: if we can like study merging galaxies as a chance,
47:48
Speaker 1: we can see whether dark matter is a super fluid
47:51
Speaker 1: or a normal fluid. I think we're saying is that
47:54
Speaker 1: the dark matter at the outsides and the edges of
47:57
Speaker 1: the galaxy, which is not as compact or super fluid,
48:00
Speaker 1: would sort of become a superfluid once it crashes into
48:03
Speaker 1: another galaxy. I'm saying that we can test the super
48:06
Speaker 1: fluidity of dark matter by slamming into another blob of
48:09
Speaker 1: super fluid. Dark matter, if it really is super fluid,
48:12
Speaker 1: should basically pass right through. If it isn't super fluid,
48:15
Speaker 1: then we should see some friction between the two blobs
48:18
Speaker 1: of dark matter. And we can't do this very easily,
48:20
Speaker 1: but sometimes galaxies collide, right, huge galaxies slam into other galaxies,
48:25
Speaker 1: basically testing this hypothesis, doing this experiment of slamming one
48:29
Speaker 1: blob of dark matter into another. So if we can
48:32
Speaker 1: study those collisions, we might be able to tell the
48:34
Speaker 1: difference between super fluid collisions and normal fluid collisions because
48:38
Speaker 1: they should look a little bit different. Pretty interesting to
48:40
Speaker 1: think that dark matter, which we can see or touch,
48:44
Speaker 1: could be doing things that we can maybe imagine and
48:47
Speaker 1: even the dunk right and figure out, yeah, because we
48:50
Speaker 1: can't see the dark matter directly, but we can see
48:52
Speaker 1: it indirectly because of gravitational lensing and because of its
48:55
Speaker 1: impact on the other stars. So doing a lot of
48:58
Speaker 1: statistics and very careful measurements, we can get a sense
49:01
Speaker 1: for where the dark matter is and what's happened to it.
49:03
Speaker 1: And then we can check that against our calculations and
49:05
Speaker 1: see does it look like it's being a superfluid or
49:07
Speaker 1: a normal fluid? Right, And if you see that it
49:10
Speaker 1: has a cape on it, then you know, like Hey,
49:12
Speaker 1: it definitely has superpowers, right, that's right, And then it
49:14
Speaker 1: needs to stop by our food truck so we can
49:16
Speaker 1: promote our super fluid beverages, which we has not quite
49:20
Speaker 1: passed the p d A approval. Right, that's right. Don't
49:24
Speaker 1: go at drinking any super fluid yet, please people. Yeah,
49:27
Speaker 1: and don't invite Daniel to your lab because he will
49:29
Speaker 1: definitely put his own super fluids on everything. Hey, I'm
49:34
Speaker 1: a curious person. What can I say? All right, Well,
49:37
Speaker 1: another interesting idea about dark matter, the one that could
49:39
Speaker 1: explain what is going on out there, and another example
49:43
Speaker 1: of how this is still work in progress. We don't
49:45
Speaker 1: know what this thing is. We're trying to figure it out,
49:47
Speaker 1: and there are still new ideas coming up that could
49:50
Speaker 1: explain what's going on. Yeah, there are whole categories of ideas.
49:53
Speaker 1: Some of them even try to combine dark matter with
49:56
Speaker 1: mond and say, maybe dark matter is real but also
49:59
Speaker 1: gravity and used to be modified. Lots of people out
50:02
Speaker 1: there trying to make the best of both worlds, and
50:04
Speaker 1: this is like a cool alternative to try to capture
50:07
Speaker 1: all of the best bits of all of those theories.
50:09
Speaker 1: You could make a dark Mond to the theory, right, Yeah,
50:12
Speaker 1: and we could have a dark mond flavored coke. There
50:14
Speaker 1: you go, and you can make a dark Mont Sunday
50:17
Speaker 1: ice cream Sunday as well. All right, well, we hope
50:20
Speaker 1: you enjoyed that. Thanks for joining us, see you next time.
50:31
Speaker 1: Thanks for listening, and remember that Daniel and Jorge explained.
50:34
Speaker 1: The Universe is a production of I heart Radio. For
50:37
Speaker 1: more podcast from my heart Radio, visit the i heart
50:40
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50:44
Speaker 1: favorite shows. Ye