Speaker 1: Hey, Daniel, if you were dark Matter, where would you hide?
Speaker 2: I wouldn't hide. If I was dark matter, I would
Speaker 2: totally parade myself in front of all the scientists in
Speaker 2: the galaxy.
Speaker 1: Ooh, a parade. You mean like a pageant.
Speaker 2: Queen, Yeah, something like that. You know, just don't be
Speaker 2: so shy.
Speaker 1: Well, if it turns out you are dark matter, we'll
Speaker 1: definitely throw you a parade. But so far, it seems
Speaker 1: like dark matter is kind of reclusive, right, It's kind
Speaker 1: of shy, So maybe it is hiding. What would be
Speaker 1: some good spots for it to hide it?
Speaker 2: Well, if dark matter doesn't want a tiara and it's
Speaker 2: hiding somewhere, then I don't know where it would hide.
Speaker 2: I mean, if I knew, I would go and look
Speaker 2: for it there.
Speaker 1: What if it's somewhere kind of.
Speaker 2: Obvious, like what like right behind me?
Speaker 1: Yeah, or right in front of you, or right on
Speaker 1: TV and the Matter universe contest, that.
Speaker 2: Would be a great twist ending for the m Knight
Speaker 2: Shamanlan version of this story.
Speaker 1: Well, man, do you think he knows I see dark Matter?
Speaker 3: Hi?
Speaker 1: I'm Jorge Mack, cartoonists and the author of Ollor's Great
Speaker 1: Big Universe.
Speaker 4: Hi.
Speaker 2: I'm Daniel. I'm a particle physicist, and I wish I
Speaker 2: had a dark matter Tiara.
Speaker 1: Oh, but it wouldn't be very shiny or bright. It
Speaker 1: would be dark, So what's the point. Also, when it
Speaker 1: had just fall through your head, it.
Speaker 2: Would be hard to wear, but it'd be like the greatest,
Speaker 2: most amazing piece of jewelry.
Speaker 1: Ever, how would you even keep it in your house?
Speaker 2: These are just like engineering details, you know. Once I've
Speaker 2: solved the physics of a dark matter Tiara, I'll just
Speaker 2: pass that off to the engineers.
Speaker 1: This is just all part of your dream to be
Speaker 1: the universe's doctor Universe.
Speaker 2: I would like a little bit of bling. Yeah, you know,
Speaker 2: physics blining would be nice. I'm not going to win
Speaker 2: a Nobel Prize anytime soon, So dark matter Tira sounds good.
Speaker 1: I see. I see. You could just say you have
Speaker 1: a dark matter Tierra, and they nobody would be able
Speaker 1: to see it, or feel it or detect it. They
Speaker 1: would just have to believe you.
Speaker 2: I need evidence, man, That's what science is all about.
Speaker 2: You got to have data.
Speaker 1: I don't think those beauty contests depend on data very much.
Speaker 2: But I'm trying to win a science contest.
Speaker 1: But anyway's welcome. Dark podcast Daniel and Jorge Explain the Universe,
Speaker 1: a production of iHeartRadio in which.
Speaker 2: We enter you in the greatest science contest of all time,
Speaker 2: the quest to understand the nature of the universe. What
Speaker 2: is it, what's in it, what's it made out of?
Speaker 2: How does it all work. We think these questions are
Speaker 2: deep and fundamental parts of being a human being in
Speaker 2: this cosmos, and unraveling these questions is a joy that
Speaker 2: everybody should share. So on this podcast we take those
Speaker 2: questions apart and try to share our answers and our
Speaker 2: ignorance with you.
Speaker 1: That's right, because science is the greatest beauty contest in
Speaker 1: the universe, where the goal is to discover the beauty
Speaker 1: of how this universe is put together, how it works,
Speaker 1: and what is our place in it.
Speaker 2: Over the last fifty one hundred years, we've developed a
Speaker 2: pretty good sense for what's in the universe. We know
Speaker 2: about stars and galaxies and all the bright and shiny
Speaker 2: stuff that's out there in the universe, and we've also
Speaker 2: figured out that there's a lot of the universe that
Speaker 2: we can't see directly using our senses or any of
Speaker 2: the forces that we've discovered except for gravity. We know
Speaker 2: that a huge chunk of the stuff that's out there
Speaker 2: in the universe is invisible. It's intangible, which makes it
Speaker 2: very hard to discover and to figure out how to
Speaker 2: make it into a tiara.
Speaker 1: Yeah, because it turns out that a pretty good understanding
Speaker 1: of the universe only covers about uh five percent of
Speaker 1: what we know is out there. The rest, the ninety
Speaker 1: five percent of the universe that we know is there,
Speaker 1: we have no idea what it is or how it works.
Speaker 2: That sounds like a good title for a book.
Speaker 1: Yeah, I think we rode One Daniel, which is available
Speaker 1: for a sale everywhere.
Speaker 2: That's right. The kind of stuff that you and I
Speaker 2: are made out of, atoms specifically, or what physicists called baryons,
Speaker 2: only makes up five percent of the energy budget in
Speaker 2: the universe. There's another twenty five twenty seven percent that's
Speaker 2: dark matter, some kind of stuff that we know is matter.
Speaker 2: We know it's out there, but we don't know what
Speaker 2: it is, and we only have a very rough sense
Speaker 2: of even where it is around us. The rest of
Speaker 2: the universe is something we call dark energy, which is
Speaker 2: contributing to the accelerating expansion of the universe and we
Speaker 2: have even less clue about what makes that up.
Speaker 1: Yeah, there's a lot we don't know, and it seems
Speaker 1: like these are maybe the defining mysteries of our times
Speaker 1: is to figure out what the universe is actually made
Speaker 1: out of, given that what we're made out of counts
Speaker 1: is so little of it.
Speaker 2: Yeah, you're right. And in the last few decades there's
Speaker 2: been a huge program of people looking for dark matter.
Speaker 2: We've talked on the podcast about trying to make dark
Speaker 2: matter in the laboratory by smashing particles together. We're searching
Speaker 2: for the dark matter wind. We might be floating through
Speaker 2: with very sensitive underground facilities looking for an individual piece
Speaker 2: of dark matter to bump into liquid xenon, for example,
Speaker 2: or maybe evidence of dark matter annihilating itself in the
Speaker 2: center of the galaxy. But so far, none of these
Speaker 2: experiments have found dark matter, which means we've got to
Speaker 2: get creative about other ways to maybe detect this most
Speaker 2: important or at least most common kind of matter in
Speaker 2: the universe.
Speaker 1: So to be on the podcast, we'll be tackling the
Speaker 1: question could quantum clocks detect dark matter and how many
Speaker 1: jargon words can we fit into one podcast title.
Speaker 2: I know it does sound like buzzword sound, you know, like,
Speaker 2: could we use AI generated crypto bitcoin to detect dark matter?
Speaker 1: You mean quantum nanomtter Yes, exactly, quantum nanomtter tierras.
Speaker 2: Wow, I like quantum nano matter. I go use that
Speaker 2: in a proposal.
Speaker 1: That's good, I said it first, I said at first, Daniel. Also,
Speaker 1: it's probably already on sale on Amazon. There's probably some
Speaker 1: product out there with that name.
Speaker 2: So yeah, but you didn't say ching tm after it,
Speaker 2: so I can use it.
Speaker 1: No, you don't have to.
Speaker 2: What I gotta brush up on my podcast property law.
Speaker 1: Yeah, you better or else I'm gonna see you for
Speaker 1: nano dollars for nano bitcoins, you know what?
Speaker 2: Or hey, you can have all of my nano bitcoins.
Speaker 1: What's the price of bitcoins these days?
Speaker 2: Nano bitcoins zero? Yeah, doesn't exist.
Speaker 1: But anyways, it's kind of an intriguing title. Could quantum
Speaker 1: clocks detect dark matter? And quantum clocks sounds like it
Speaker 1: does sound like something you could buy an off of Amazon.
Speaker 1: Did you check to see if it's something you can
Speaker 1: just get next day?
Speaker 3: Oh?
Speaker 2: Yeah, it turns out Amazon will sell you something. It
Speaker 2: calls a quantum clock, like a quantum entanglement led wall clock,
Speaker 2: but none of these things are actually quantum clocks the
Speaker 2: way that we understand them.
Speaker 1: Well, technically, isn't everything a quantum something? Well, I mean
Speaker 1: not everything, but you know, the five percent that we
Speaker 1: know about in the universe is in it all quantum technically,
Speaker 1: like this is a quantum podcast.
Speaker 2: I mean, that's a really interesting philosophical question and not
Speaker 2: one that we really have an answer to, because on
Speaker 2: one hand, you're right that everything is made out of
Speaker 2: quantum particle, so isn't the whole universe quantum? On the
Speaker 2: other hand, we know that when you zoom out things
Speaker 2: behave by different rules. We call that classical. We don't
Speaker 2: really understand why there is that transition, but there definitely
Speaker 2: is a transition. So to call everything quantum is either
Speaker 2: to say that look classical is just big zoomed out quantum,
Speaker 2: or is to say that clackical doesn't really matter, which
Speaker 2: doesn't really sit well with me. Or what if I
Speaker 2: have no class, then you probably have a lot of
Speaker 2: big coin.
Speaker 1: Then I'm not going to win any beauty contest. I
Speaker 1: have poise, but just no class.
Speaker 2: Yeah, exactly, But you know, for example, a clock that
Speaker 2: just works on mechanical parts would also work in the
Speaker 2: universe where quantum mechanics didn't rule the microscopic because it's
Speaker 2: not sensitive to those microscopic details, and so that wouldn't
Speaker 2: be a quantum clock, for example, like a pendulum clock
Speaker 2: or an old fashioned Swiss gear based clock.
Speaker 1: A discussion about new mankla Sure that's my favorite.
Speaker 2: Hey, you brought it up, But.
Speaker 1: Anyways, it's a kind of an interesting question and so
Speaker 1: we'll dig into it. But as usually, we were wondering
Speaker 1: how many people out there had thought about putting the
Speaker 1: concepts of dark matter and quantum and clocks all together
Speaker 1: in one sentence.
Speaker 2: So thanks very much to everybody who participates in this
Speaker 2: segment of the podcast. We love that you volunteer, We
Speaker 2: love hearing your thoughts, and we love sharing your voice
Speaker 2: with all of the other listeners. Please chime in if
Speaker 2: you'd like, writeing me two questions at Danielanjorge dot com
Speaker 2: and you can't participate.
Speaker 1: So think about it for a second. Do you think
Speaker 1: quantum clocks can use to detect dark matter? Here's what
Speaker 1: people had to say.
Speaker 4: I've heard of a quantum clock, but I'm not sure
Speaker 4: how it would be able to detect dark matter anymore
Speaker 4: than a regular clock could. I guess maybe even with
Speaker 4: a regular clock, you could send it out into space,
Speaker 4: and if it hits a huge clump of dark matter
Speaker 4: and therefore gravity, maybe we could learn that there's a
Speaker 4: big well of gravity out in some location that we
Speaker 4: otherwise couldn't detect.
Speaker 1: So sure, I suppose it's possible, but I have no
Speaker 1: clue how it would Maybe something to do with entanglement.
Speaker 3: Since you're asking, the answer is probably yes, but maybe
Speaker 3: still theoretical. I would think you'd have to use the
Speaker 3: idea of measuring light passing through an area of more
Speaker 3: density that's possibly dark matter that causes curvature of space
Speaker 3: and also time dilation. How to do that, I'm not sure.
Speaker 2: Since we don't possess a quantum clock, it doesn't seem
Speaker 2: unreasonable to suggest that a non existent clock cannot detect
Speaker 2: dark matter.
Speaker 1: All right, it's pretty uh intense answers here. I feel
Speaker 1: like it's something that some of the listeners have I
Speaker 1: heard about before. Did you pull your professor colleagues this time?
Speaker 2: No, these are our listeners online. You know there's some
Speaker 2: good answers here about entanglement and light passing through areas
Speaker 2: with dark matter density in them, and just in general
Speaker 2: sense that this is a hard problem.
Speaker 1: Maybe you should ask a bunch of beauty queens next
Speaker 1: time we're making one of the standard questions in a
Speaker 1: beauty pageant. Forget howdy, how would you save the world
Speaker 1: or how would you know make things better? What do
Speaker 1: you think about quantum plock?
Speaker 2: Well, where is the dark matter? Yeah, I'd love to
Speaker 2: hear that answer in the beauty pageant.
Speaker 1: Not that it couldn't happen, of course, no, absolutely. All right, Well,
Speaker 1: let's dig into this intriguing question of whether dark matter
Speaker 1: can be detected by quantum clocks, and let's start with
Speaker 1: the basics, Daniel, what do we know about dark matter?
Speaker 2: So there's a lot that we do and do not
Speaker 2: know about dark matter. So let's start with what we
Speaker 2: do know. We know that it's out there, and we
Speaker 2: know that it's here as well. We know that dark
Speaker 2: matter is something that exists in the universe. And then
Speaker 2: it's matter. We know that because we see its gravity.
Speaker 2: We see it holding galaxies together as they spin. There
Speaker 2: isn't enough gravity from the stars and the gas and
Speaker 2: dust that make up those galaxies to keep the stars
Speaker 2: in place as they swirl around the center of the
Speaker 2: galaxy at very high speeds, and yet they do stay
Speaker 2: in place. Galaxies are mostly not throwing stars out into
Speaker 2: intergalactic space, and so we infer that there must be
Speaker 2: some matter there to hold that galaxy together. But it's
Speaker 2: more than just that one inference, that one fudge factor
Speaker 2: to make that particular equation work. We see evidence for
Speaker 2: dark matter all over the history of the universe, from
Speaker 2: the very first few moments when the early universe plasma
Speaker 2: is slashing around and you have dark matter and normal
Speaker 2: matter and photons all acting very differently and creating different
Speaker 2: slashing patterns. From looking at that slashing in the cosmic
Speaker 2: microwave background radiation, we can figure out that there was
Speaker 2: dark matter, even measure how much of it there is,
Speaker 2: and we can trace the history of dark matter's gravity
Speaker 2: as it shapes the structure formation of the whole universe.
Speaker 2: Why we have galaxies at all this early in the
Speaker 2: history of the universe, and so dark matter is definitely
Speaker 2: out there as a kind of matter, but we don't
Speaker 2: know really what it is or very specifically where it
Speaker 2: is because it's so hard to see since it only
Speaker 2: feels gravity. It doesn't feel any of the other forces
Speaker 2: that we've discovered.
Speaker 1: And we can also sort of see dark matter right like,
Speaker 1: we can see it in the same way that you
Speaker 1: can see a lens or glass lens or example. You
Speaker 1: can see how it distorts the light behind it.
Speaker 2: Right, Yeah, exactly, we can see dark matter through gravity,
Speaker 2: and so that means we can see stuff bending around
Speaker 2: dark matter. We can see it holding galaxies together, and
Speaker 2: that even impacts how light moves in the vicinity of
Speaker 2: dark matter. If you have a big blob of dark
Speaker 2: matter between you and some distant galaxy, for example, the
Speaker 2: photons from that distant galaxy will bend as they move
Speaker 2: through that dark matter, creating apparent distortions in your image.
Speaker 2: You can even sometimes see the same galaxy twice in
Speaker 2: the sky because of this gravitational lensing, and so we
Speaker 2: know that it's out there, and we can use some
Speaker 2: techniques like that to sometimes tell roughly where it is.
Speaker 2: But because dark matter is so weak it's particles only
Speaker 2: feel gravity, we think it's very difficult to figure out
Speaker 2: what exactly is made out of To isolate one piece
Speaker 2: of dark matter, because gravity is so weak that essentially
Speaker 2: a particle's gravity is almost impossible to measure.
Speaker 1: Yeah, and dark matter is also something that's not just
Speaker 1: out there in space. It's sort of like all around us,
Speaker 1: right like it's floating through us right now, sort of
Speaker 1: like the fourth you know, it flows through us, binds
Speaker 1: us all together. It's made out of meti chlorians.
Speaker 2: Perhaps, perhaps, yeah, exactly, you'll only really understand it after
Speaker 2: nine hundred years of study. That's a really good question,
Speaker 2: and that's sort of the central question of this episode
Speaker 2: is exactly where is the dark matter and can we
Speaker 2: find like concentrations of it? Can we map it out?
Speaker 2: Because dark matter is so weakly interacting like only gravity,
Speaker 2: it takes huge amounts of it to feel anything, and
Speaker 2: so that makes it very hard to tell exactly where
Speaker 2: the dark matter is. It might be that it's mostly
Speaker 2: spread out evenly through the galaxy. It might be more
Speaker 2: clumpy than that depends a lot on your particular theory
Speaker 2: of dark matter. Where it exactly is. So it could
Speaker 2: be that we are in a dark matter wind as
Speaker 2: the Earth orbits the Sun and the Sun moves through
Speaker 2: the galaxy. We could also be in a dark matter
Speaker 2: Liss bubble, a bubble of space in which there's comparatively
Speaker 2: little dark matter, or it could be that dark matter
Speaker 2: is fairly dense in our area.
Speaker 1: You know, I have to say every time you say
Speaker 1: dark matter wind, it makes me think of dark.
Speaker 2: Part elevating the discourse every week.
Speaker 1: That's my job. That's why I'm here. Smells all grounded
Speaker 1: or grounded or you know, flat as in fletch winds.
Speaker 1: But anyways, so it's sort of all around this, and
Speaker 1: I guess I'm wondering, like, if it is all around us,
Speaker 1: would we be able to tell, Like, you know, if
Speaker 1: let's say dark matter is floating through the Earth right now,
Speaker 1: or let's say it wasn't, would you be able to
Speaker 1: tell the difference.
Speaker 2: That's exactly what these experiments are trying to measure. And
Speaker 2: to give you a sense of the difficulty the challenge
Speaker 2: of this, think about like why we didn't discover dark
Speaker 2: matter earlier. Just in studying how our Solar system moves.
Speaker 2: We have now very precise measurements of the orbit of
Speaker 2: Jupiter and Mars and all the planets and all the
Speaker 2: little pieces of the Solar System as they orbit the Sun.
Speaker 2: You might think, hey, if dark matter is here in
Speaker 2: our Solar system and it has gravity, wouldn't it change
Speaker 2: the way those things orbit? Shouldn't we be able to
Speaker 2: detect it? But because we think dark matter might be
Speaker 2: spread very thin, probably there isn't that much dark matter
Speaker 2: in the vicinity of our solar system. So even those
Speaker 2: very very precise measurements, you know, like knowing the motion
Speaker 2: of Jupiter to meters or centimeters, can't detect dark matter
Speaker 2: because it would be very thin and very spread out,
Speaker 2: and mostly we think homogeneous, which in the end doesn't
Speaker 2: give much much gravitational pull on the objects in the
Speaker 2: solar system. So it takes a very specialized, highly sensitive
Speaker 2: device to be able to detect this dark matter.
Speaker 1: Yeah, and then don't we say once like, if you
Speaker 1: take all the dark matter that is potentially floating through
Speaker 1: the Earth right now, it would only weigh about as
Speaker 1: much as a squirrel or something like that.
Speaker 2: Yeah, exactly, though that's very speculative, right. That assumes that
Speaker 2: dark matter is essentially equally spread out in our galaxy,
Speaker 2: which we don't believe is true. But if you assume
Speaker 2: that there is, then we know our galaxy, for example,
Speaker 2: is ninety five percent dark matter. That means for every
Speaker 2: kilogram of matter made out of atoms like hydrogen and
Speaker 2: helium or whatever, there's nineteen kilograms of matter made out
Speaker 2: of whatever dark matter is made out of, And so
Speaker 2: it's like nineteen to one in our galaxy.
Speaker 1: Which sounds like a lot, but I guess also galaxies
Speaker 1: kind of very empty mostly, right, Like it's probably like
Speaker 1: ninety nine percent empty.
Speaker 2: Yeah, exactly. Now, normal matter clumps up a lot, right
Speaker 2: like the Sun is an extraord ordinarily dense collection of
Speaker 2: normal matter. Normal matter is not spread evenly through the galaxy.
Speaker 2: But if you take dark matter and spread it evenly
Speaker 2: through the galaxy, you get a pretty small density. It's
Speaker 2: like ten to the twenty six kilograms per cubic light year,
Speaker 2: which is a huge volume, which means it's like ten
Speaker 2: to the negative twenty two kilograms per cubic meter. So
Speaker 2: then if you add up all the cubic meters in
Speaker 2: the Earth, that adds up to about two thirds of
Speaker 2: a kilogram of dark matter inside the volume of the Earth. Again,
Speaker 2: assuming that dark matter is evenly spread throughout the galaxy,
Speaker 2: which it probably isn't, but it might be.
Speaker 1: Roughly, which is about the size or mass of a squirrel.
Speaker 2: Yeah, exactly, so one squirrel of dark matter inside the
Speaker 2: volume of the Earth compared to you know, the many,
Speaker 2: many millions and billions of kilograms of normal matter inside
Speaker 2: the volume of the Earth. That sounds the importance of clumping, right,
Speaker 2: Because normal matter clumps together, its gravity is much more
Speaker 2: powerful in our local neighborhood than dark matter. Even though
Speaker 2: dark matter outweighs normal matter by nineteen to one, if
Speaker 2: it's much more thinly spread out, the local effects of
Speaker 2: its gravity are much harder to detect.
Speaker 1: I think maybe what you're saying is that dark matter,
Speaker 1: in terms of the universe scale, it mostly hangs out
Speaker 1: in galaxies. Like you don't see a lot of dark
Speaker 1: matter floating out there on its own between galaxies.
Speaker 2: Yeah, we can do really precise measurements of where dark
Speaker 2: matter is on the galaxy scale, because galaxies are really
Speaker 2: really big. If you can tell how galaxies are orbiting
Speaker 2: around each other, just the way we can tell how
Speaker 2: stars are moving through the galaxy, so enormous clumps of
Speaker 2: dark matter, absolutely we can measure their gravity. But when
Speaker 2: you zoom in in a really fine grained way and
Speaker 2: want to say, hey, is there a moon sized blob
Speaker 2: of dark matter anywhere in our solar system. That's a
Speaker 2: tough question to answer.
Speaker 1: So then within the galaxy, you're saying, like, there's a
Speaker 1: lot of dark matter within our galaxy. Ninety five percent
Speaker 1: of the mass of our galaxy is dark matter. And
Speaker 1: what does it look like. Does it look like, you know,
Speaker 1: an intense, dense ball of dark matter in the middle.
Speaker 1: Is it evenly distributed? And also like our galaxy looks
Speaker 1: like a disc, sort of like a flat disk. Is
Speaker 1: dark matter also shaped like a flat disk?
Speaker 2: So we have the best answers the more we zoom out,
Speaker 2: and then as we zoom in, things get literally fuzzy.
Speaker 2: But on the scale of the galaxy, we have some ideas.
Speaker 2: We think that dark matter is like a big halo.
Speaker 2: So imagine the visible galaxy right at the edge of
Speaker 2: the stars. Dark matter is a big halo that goes
Speaker 2: out beyond the visible stars, and it's bigger and fuzzier.
Speaker 2: It hasn't collapsed the way normal matter has because it
Speaker 2: just doesn't clump right. In order to clump, things need
Speaker 2: other kinds of interaction other than gravity. Like if you
Speaker 2: have two dark matter particles, they attract each other gravitationally
Speaker 2: and then just pass right through each other. They're just
Speaker 2: gonna zig and zag back and forth, oscillate forever. They're
Speaker 2: not going to clump together. To do that. You need
Speaker 2: like electromagnetism or the strong force or something that wants
Speaker 2: to grab onto each other. So dark matter stays a
Speaker 2: big puffy halo, and the galaxy is sort of embedded
Speaker 2: in that halo. And that's not a coincidence. Right. The
Speaker 2: reason the galaxy exists is because of a big dark
Speaker 2: matter blob there that's gathered together all the hydrogen helium
Speaker 2: gravitationally and may it into a galaxy. It's the reason
Speaker 2: we have stars, et cetera.
Speaker 1: Now, when you say like halo, you don't actually mean
Speaker 1: like an angel's halo that looks like a ring. You
Speaker 1: actually mean just like a blob, right.
Speaker 2: Yeah, exactly, like a big fuzzy blob that extends out
Speaker 2: further along the disc and then further above and below
Speaker 2: the disc. But even that we know already is not
Speaker 2: evenly distributed.
Speaker 1: Is it like football shaped? Is it you? Is it
Speaker 1: kind of flat or is it a perfect sphere?
Speaker 2: It's more like a hockey puck, right, It's flat, but
Speaker 2: not as flat as the galaxy. Itself.
Speaker 1: What made it flat?
Speaker 2: Yeah, maybe a hockey puck is the wrong analogy. It's
Speaker 2: not quite that flat. It's more like a big ellipsoid.
Speaker 1: You mean like a slightly squished ball.
Speaker 2: Yeah, exactly, It's like a big basketball that somebody's sitting
Speaker 2: on or something.
Speaker 1: All right, Well, let's get a little bit more into
Speaker 1: the details of what we know about dark matter. How
Speaker 1: much of it can we see? How much can we
Speaker 1: discern about what it's doing in our universe? And we'll
Speaker 1: answer the question of whether you can use a quantum
Speaker 1: clock from Amazon dot com to detect it. So we'll
Speaker 1: get to those questions, but first's take at a quick break.
Speaker 1: All right, we're asking the question can you use quantum
Speaker 1: clocks to detect dark matter? And we've been recapping a
Speaker 1: little bit about what we know about dark matter, Daniel.
Speaker 1: How much of the details of it can we see?
Speaker 2: Not really very much. We have this sense of a big,
Speaker 2: fuzzy halo that surrounds the galaxy, and we can also
Speaker 2: measure the density as a function of distance from the center.
Speaker 2: So if you're a star, for example, orbiting the center
Speaker 2: of the galaxy, the speed at which you orbit depends
Speaker 2: on the force that's holding you in that orbit. So
Speaker 2: the stronger the force, the faster you can go, or
Speaker 2: the faster you can go, the stronger the force that's
Speaker 2: needed to hold you in that orbit. So by measuring
Speaker 2: the speed of a given star, we can essentially measure
Speaker 2: the mass of all all that stuff that's holding on
Speaker 2: to that star. So then if you look at stars
Speaker 2: at different distances from the center, you can basically map
Speaker 2: out the density of stuff in the galaxy as you
Speaker 2: go further and closer to the center of the galaxy.
Speaker 1: Like if dark matter was super condensed in the middle
Speaker 1: of the galaxy, then the stars in the galaxy would
Speaker 1: be rotating a certain way. Or if the dark matter
Speaker 1: was more spread out, then the stars in the galaxy
Speaker 1: would be rotating in a different way.
Speaker 2: Yeah, exactly, if all the dark matter in the galaxy
Speaker 2: was at the center, then everything would act in a
Speaker 2: certain way, would just go like one over are squared.
Speaker 2: It's sort of like the way the Solar system orbits
Speaker 2: the Sun. But if you take some of that mass
Speaker 2: and you spread it out through the galaxy instead, then
Speaker 2: the dark matter that's further out than a given star
Speaker 2: doesn't affect its orbit because its gravity all cancels out,
Speaker 2: so that changes the rotation speed of those stars. And
Speaker 2: that's in fact how we first discover dark matter was
Speaker 2: by looking at these rotation speeds of stars around the
Speaker 2: center of the galaxy and seeing that we couldn't explain
Speaker 2: it by mapping all the mass from the stars and
Speaker 2: the gas and the dust. And that's exactly how you
Speaker 2: can tell where you need to add more mass to
Speaker 2: explain these rotation speeds. It's not just like, hey, add
Speaker 2: a big blob at the center. You need to add
Speaker 2: some of the center and also some further out and
Speaker 2: some further out, and so precise measurements of those velocities
Speaker 2: give you a fairly accurate picture of where the dark
Speaker 2: matter is in the galaxy. And it's not evenly spread out.
Speaker 2: It's more densely clumped at the center, which is something you'd.
Speaker 1: Expect because it is affected by gravity, right, It.
Speaker 2: Is, in the end affected by gravity, and so it's
Speaker 2: pulled itself together. And the whole reason that this exists
Speaker 2: is because of some like early universe perturbation where you
Speaker 2: had a denser blob of dark matter that created this
Speaker 2: whole well gathered together the other dark matter and created
Speaker 2: this over density which then pulled in hydrogen, helium and
Speaker 2: whatever was around to make a galaxy. So it's a
Speaker 2: little bit denser at the center. Though it's not very
Speaker 2: well understood, like if we do calculations simulations to describe
Speaker 2: what we think should happen. If you have a bunch
Speaker 2: of dark matter and you'll give it a few billion
Speaker 2: years to fall together and to form some structure. It
Speaker 2: describes what astronomers call a cusp, which means like a
Speaker 2: point of high density of the center and then very
Speaker 2: steeply falling, should like drop off quickly. But if you
Speaker 2: go out and measure the actual distributions of stars velocities,
Speaker 2: you see something that looks like a bigger core. It's
Speaker 2: not like it's pointing near the center. It's more spread
Speaker 2: out in the inner galaxy. It's like flatter, and so
Speaker 2: this is not something we understand very well. And it
Speaker 2: also gives you a sense of like the scale of
Speaker 2: which we can figure this stuff out. We're talking about
Speaker 2: over light years distances, right, we're not resolving dark matter
Speaker 2: in meters or even in aus with very very coarse
Speaker 2: ways to measure where the dark matter is. Again, because
Speaker 2: its gravity is so weak.
Speaker 1: Are you saying, like the beginning of the universe, dark
Speaker 1: matter was more evenly spread out, Like you know, all
Speaker 1: those light years of empty space between us and Andromeda
Speaker 1: and other galaxies was all filled with dark matter, and
Speaker 1: then it all collapsed into certain clusters.
Speaker 2: Yeah, it definitely gathered itself together. The early universe had
Speaker 2: initial density fluctuations, and that's a whole big question about
Speaker 2: where exactly that came from. And then those seated gravity
Speaker 2: to pull things together. So gravity does form structure, but
Speaker 2: it takes time. And so yeah, dark matter was more
Speaker 2: spread out and now it's less spread out.
Speaker 1: Why would dark matter stay stuck together?
Speaker 2: Well, it's not that dark matter is sticking together. It's
Speaker 2: not like it's bonded to itself. And again we don't
Speaker 2: really know because we don't have a microscopic picture of
Speaker 2: the dark matter. But I think you're asking, like why
Speaker 2: does dark matter form even gravitational structures? Like why does
Speaker 2: it get more dense in some places and then in others?
Speaker 2: Is that what you're asking?
Speaker 1: Yeah, Like I'm imagining at the beginning of the universe
Speaker 1: there's a bit of dark matter that was you know,
Speaker 1: let's say ten light years away, and then it got
Speaker 1: attracted to our galaxy, so it flew over here. But
Speaker 1: then why didn't it just keep flying to the other side.
Speaker 2: Yeah, so as that distant piece of dark matter approaches
Speaker 2: the galaxy, it gains velocity. Right, it's exchanging gravitational potential
Speaker 2: energy for kinetic energy. And then you're imagining, like the
Speaker 2: way a ball rolls down a valley, why doesn't it
Speaker 2: roll back up the other side? And it will, yes,
Speaker 2: but then it comes back right, And so gravity in
Speaker 2: the end is organizing something. There's the second piece to that,
Speaker 2: which is that it doesn't completely grow back up the
Speaker 2: other side. You know, anything that's accelerating is emitting gravitational
Speaker 2: radiation for example. So the reason, for example, two black
Speaker 2: holes orbiting each other will eventually spiral in and collapse
Speaker 2: is that they're emitting gravitational energy. So none of these
Speaker 2: things are really stable. So over long periods of time,
Speaker 2: even without inelastic interactions like electromagnetism or whatever, these things
Speaker 2: will form very large structures and they will gradually collapse
Speaker 2: due to gravitational radiation.
Speaker 1: All right, so we kind of have a fuzzy picture
Speaker 1: of where it is in the universe. So now the
Speaker 1: question of the episode is can we use quantum clocks
Speaker 1: to detect dark matter? How do quantum clocks fit into this?
Speaker 2: So quantum clocks might give us a sense for where
Speaker 2: the dark matter is if we can find a place
Speaker 2: where it's like clumpy, if we can find a place
Speaker 2: in our solar system where it's like gathered together for
Speaker 2: some reason. And that would be really cool because not
Speaker 2: only would it help us detect what dark matter is,
Speaker 2: but it would help us understand where it is. It's
Speaker 2: a really deep mystery, I think, not just because we
Speaker 2: want to understand dark matter, but because we want like
Speaker 2: a map. You know, humans are visual creatures. We want
Speaker 2: to know like where the stuff is, and just not
Speaker 2: knowing where dark matter is in the universe really bugs me.
Speaker 2: So I would love to know where it is and
Speaker 2: understanding its map on a finer scale would be really helpful.
Speaker 2: And quantum clocks might be able to help us map
Speaker 2: where dark matter is if we can send them out
Speaker 2: into space and if they're sensitive to dark matter, if
Speaker 2: their operation changes as they pass through dark matter.
Speaker 1: Okay, I think you're saying that you know, at the
Speaker 1: galaxy level, we know that it looks like a big blob.
Speaker 1: It's sort of like a switchball. It's sort of more
Speaker 1: intense or more dense in the center of the galaxy.
Speaker 1: But I think maybe you're saying, can we know in
Speaker 1: finer detail what it looks like between stars within the galaxy,
Speaker 1: like is it clumpy, is it chunky, or is it
Speaker 1: like peanut butter or smooth exactly?
Speaker 2: And people have tackled this problem in the past, Like
Speaker 2: people use the technique you mentioned gravitation lensing to look
Speaker 2: for blobs of dark matter, and that works and it's powerful,
Speaker 2: but only if you have like a really nice galaxy
Speaker 2: behind the blob of dark matter that can show you
Speaker 2: that it's there, So that tells us a little bit
Speaker 2: about the dark matter density. But there aren't like galaxies
Speaker 2: in all the right places to like X ray the
Speaker 2: whole Solar system and figure out where it is, And
Speaker 2: that technique isn't always powerful enough. You need like a
Speaker 2: really big blob of dark matter. Another technique people have
Speaker 2: used is to look for dwarf galaxies. Essentially, our galaxy
Speaker 2: is formed by the combination of lots of galaxies, right,
Speaker 2: we think galaxies formed kind of small and then grew
Speaker 2: together with all sorts of absorptions and collisions. That means
Speaker 2: that our galaxy has other, like many galaxies embedded within it.
Speaker 2: Some of these we call dwarf galaxies because they're small
Speaker 2: and we think they're like very high dark matter density.
Speaker 2: They're very few stars, and so we can look at
Speaker 2: the motion of the stars inside those little galaxies to
Speaker 2: get sensors for like where those blobs are. But we
Speaker 2: don't have a great way to like X ray the
Speaker 2: Solar System and figure out like where is the dark
Speaker 2: matter in our Solar system? Is it hanging out by Jupiter?
Speaker 2: Is it spread evenly like peanut butter? What's going on?
Speaker 1: You want to know it's distribution at the Solar system
Speaker 1: scale exactly.
Speaker 2: That's what I want to do. And I read a
Speaker 2: recent paper which was very clever, which is looking at
Speaker 2: asteroids and trying to track asteroid trajectories and see if
Speaker 2: like tiny little deviations in the trajectory of asteroids or
Speaker 2: comets as they move through the Solar System could reveal
Speaker 2: the presence of dark matter. It's very difficult to do
Speaker 2: because if dark matter is evenly spread out or only
Speaker 2: a little bit clumpy, that be basically no effect on
Speaker 2: those asteroids. But it's the kind of thing that we're
Speaker 2: just on the verge of being able to potentially do
Speaker 2: now that we have better measurements and better computational tools
Speaker 2: to try to like infer this information from really specific measurements.
Speaker 1: All right, So then how would you use a quantum
Speaker 1: clock to de teg dark matter?
Speaker 2: So when we talk about a quantum clock, really what
Speaker 2: we mean is something which is based on fundamental quantum
Speaker 2: mechanical principles. And you know, it sounds fancy, but even
Speaker 2: just like an atomic clock is a quantum clock. An
Speaker 2: atomic clock is something that looks at like the oscillation
Speaker 2: of electron between two energy levels and a caesium atom,
Speaker 2: which is a very precise, very very regular process that
Speaker 2: we can use essentially to tell how time has passed.
Speaker 2: And so on Earth, we have extraordinarily precise atomic clocks
Speaker 2: which now set the standard and in fact define what
Speaker 2: we mean by a second. A second used to have
Speaker 2: a different definition, but now a second is defined as
Speaker 2: like a certain number of cycles of a specific kind
Speaker 2: of atom. That's literally how we measure time now, and
Speaker 2: so it's the standard.
Speaker 1: But it's like the minute, like it used to be
Speaker 1: like a minute with sixty seconds, but now people say, oh,
Speaker 1: it's been a minute to really mean something totally different.
Speaker 2: Yes, it's just like that exactly. And we call it
Speaker 2: a quantum clock because this really is a quantum process.
Speaker 2: We're talking about quantum particles, an electron, there's an atom.
Speaker 2: The electron is moving in the potential well of the atom,
Speaker 2: so it's interacting electromagnetically with the nucleus, and the way
Speaker 2: that it's moving, the way it oscillates between energy levels,
Speaker 2: is completely controlled by quantum processes. This is not a
Speaker 2: clock that you could have in a perfectly classical universe.
Speaker 2: You know, if we lived in a universe where electrons
Speaker 2: really were tiny little balls that went to orbits and
Speaker 2: had smooth classical paths the way planets do, then this
Speaker 2: clock could not exist. And so that's when we meet
Speaker 2: by quantum clock.
Speaker 1: But I guess, if it's a quantum clock, doesn't it
Speaker 1: have a certain amount of uncertainty to it or unknowability?
Speaker 1: How can it be precise? If there's the Heisenberg uncertainty principle.
Speaker 2: Yeah, you're right, there's no absolutely precise quantum clock. But
Speaker 2: this is about as regular as it gets. And amazingly,
Speaker 2: these quantum clocks are more precise than mechanical clocks, which
Speaker 2: of course also have uncertainty in them, because no mechanical
Speaker 2: device is perfectly created, right, And so this is as
Speaker 2: accurate as they've been able to make them, and recently
Speaker 2: they've been even able to make them small and transportable.
Speaker 2: You might think of an atomic clock as like some
Speaker 2: huge device in the basement of a laboratory in Colorado
Speaker 2: that weighs like ten tons and fills a room. But
Speaker 2: actually these things can be made quite small.
Speaker 1: So a quantum clock is really just an atomic clock,
Speaker 1: or is there another kind that doesn't use atoms?
Speaker 2: There's no atomic clock that's not a quantum clock. So
Speaker 2: quantum clock is just a fancier sounding name for atomic clock.
Speaker 1: Yes, can you have a quantum clock that maybe doesn't
Speaker 1: use an atom, that maybe just relies on electrons or
Speaker 1: quarks or something.
Speaker 2: Yeah, sure, you're not limited to atoms. You can imagine
Speaker 2: quantum clocks made out of like photons interacting or splitting
Speaker 2: or bouncing or something like that. In some sense, lego
Speaker 2: is a clock because it's measuring the time for photons
Speaker 2: to travel along its legs, right, It's just converting that
Speaker 2: to a distance measurement, and so you could have other
Speaker 2: quantum clocks that are not based on atoms. Yes, And
Speaker 2: one day, when we discover dark matter, maybe we could
Speaker 2: build a clock.
Speaker 1: Out of dark matter, which may or may not tell
Speaker 1: you the time.
Speaker 2: And may or may not smell like flatulin.
Speaker 1: Well, I guess, maybe give us an example of like,
Speaker 1: what's a typical or popular or a commonly used quantum
Speaker 1: clock and how does it work.
Speaker 2: Well, the most precise quantum clock is based on the
Speaker 2: caesium one thirty three atom. That's the one that's actually
Speaker 2: used to define what a second is. And so here
Speaker 2: we have two states of electrons. There's a small splitting
Speaker 2: in an energy state here. It's called a hyper fine
Speaker 2: splitting because the difference is very very small, and when
Speaker 2: the electron sits in there, it sort of goes back
Speaker 2: and forth between the two different states.
Speaker 1: Meaning like, this is an electron that's orbiting around the
Speaker 1: caesium atom.
Speaker 2: Yeah, I wouldn't say orbiting if we want to be
Speaker 2: really really technical. But it's captured by the caesium atom.
Speaker 1: And you're saying it's switching energy levels. Why would it
Speaker 1: switch energy levels?
Speaker 2: So you have this caesium atom and you embed the
Speaker 2: whole thing in some microwave radiation that can lift those
Speaker 2: electrons up from the lower state to the higher state.
Speaker 1: Meaning you like put it in a microwave or you
Speaker 1: shoot it with this like a light gun.
Speaker 2: There's not a difference, right, that's what a microwave is.
Speaker 2: A microwave is shooting microwave radiation at your food, and
Speaker 2: microwaves are lights. Though basically a microwave is a light gun.
Speaker 1: Sounds hot. So then you have this atom and you
Speaker 1: you stick it in the microwave.
Speaker 2: Uh huh, yeah, So you stick in the microwave and
Speaker 2: you measure how often it jumps up and then down
Speaker 2: and then up and then down.
Speaker 1: Because the light, as the light passes through it, it
Speaker 1: knocks the electron up and down or what.
Speaker 2: Yeah, the light is tuned to exactly the frequency for
Speaker 2: the electron to jump up into the higher energy level. Remember,
Speaker 2: electrons can go from a lower to a higher energy
Speaker 2: level if a photon of the right energy comes along.
Speaker 2: So they've tuned this microwave to exactly that energy level.
Speaker 2: So electrons and the lower level can absorb these photons
Speaker 2: jump up to the higher level, but then they'll naturally
Speaker 2: decay down because the universe likes to spread energy out,
Speaker 2: and so the time of these oscillations turns out to
Speaker 2: be very very regular, Like an electron will do this
Speaker 2: nine point one nine to two billion times per second.
Speaker 1: And it doesn't depend on the frequency of the light,
Speaker 1: or it does.
Speaker 2: It definitely depends on the frequency of the light. If
Speaker 2: the frequency of the light is not correct, then it
Speaker 2: won't even abso, right, it won't happen.
Speaker 1: Oh but then don't you need to make that frequency
Speaker 1: super precise?
Speaker 2: Yeah, exactly, And this is one source of uncertainty in
Speaker 2: these clocks, right, making those accurate. And you can measure
Speaker 2: these things, like you build two independent ones, you can
Speaker 2: see how their counts drift relative to each other. And
Speaker 2: that's how you measure the accuracy of clocks. In general.
Speaker 2: There's no absolute standard by which you can tell like, oh,
Speaker 2: this clock is off or that clock is off. You
Speaker 2: just build a few of them and you measure them
Speaker 2: relative to each other. And this is something that we
Speaker 2: know well enough. We know how to design the middle
Speaker 2: of the physics and the engineering that you can build
Speaker 2: these things so that atomic clocks in independent locations agree
Speaker 2: to like zero point three nanoseconds per day. It's really
Speaker 2: very incredibly precise.
Speaker 1: WHOA, so what are you measuring? How are you measuring
Speaker 1: whether these electrons are going up and down?
Speaker 2: When the electron goes back down, it emits radiation, right,
Speaker 2: and so you can gather that as.
Speaker 1: Well, like it shoots off light, like it will blink.
Speaker 2: Basically exactly little flash.
Speaker 1: All right. So then, and you're saying you can build
Speaker 1: these things now to be the size of a toaster
Speaker 1: or or a microwave oven.
Speaker 2: A quantum toaster. They have them now and they've deployed
Speaker 2: them out in space. They actually built the Deep Space
Speaker 2: Atomic Clock Mission and they sent an atomic clock out
Speaker 2: into space to see, like, hey, can we operate one
Speaker 2: of these things out in space? And you might wonder
Speaker 2: like is this just a bunch of nerds trying to
Speaker 2: do something that seems cool?
Speaker 1: Yes? Is always the answer, Like can we shoot a
Speaker 1: microwave into space and will it still heat up my burrito?
Speaker 1: My seizing Burritoah? Is that the challenge?
Speaker 2: That's the challenge. But also if we want to do
Speaker 2: things like navigate in space, navigation needs timing. You need
Speaker 2: to know like how long you're going in one direction.
Speaker 2: If you want to do dead reckoning, you want to
Speaker 2: know where you are. Timing is absolutely crucial. Or if
Speaker 2: you want to use like nearby pulsars to triangulate your position,
Speaker 2: my whole episode about how that works, you also need
Speaker 2: very accurate timing so you can measure the time between
Speaker 2: the pulses. So this was like a technological challenge that's
Speaker 2: going to lay the groundwork for all sorts of cool innovations.
Speaker 2: And this was totally successful, this deep space atomic clock mission.
Speaker 1: Well, let's get into how you would actually use these
Speaker 1: and how the timing might tell you where dark matter
Speaker 1: is within our Solar system and maybe even within the Earth.
Speaker 1: So let's dig into that. But first let's take another
Speaker 1: quick break. All right, we're talking about using a microwave
Speaker 1: stuck inside of a microwave to detect dark matter so
Speaker 1: you can win a Tierra for being the prettiest scientist.
Speaker 2: Yeah, exactly. Does it take longer to heat up your
Speaker 2: burrito when there's dark matter around?
Speaker 1: So the idea is that you take these atomic or
Speaker 1: basically an atomic clock, which is a quantum clock, but
Speaker 1: it seems like the most popular ones use atoms, and
Speaker 1: so you shrink them down to the size of a
Speaker 1: toaster or microwave and then you shoot them in space,
Speaker 1: and then how does that help you measure dark matter?
Speaker 2: Well, there were a bunch of physicists who thought, okay,
Speaker 2: this is that's cool because now we not only have
Speaker 2: all some super precise atomic clocks, but now we have
Speaker 2: them spread out through the Solar System, like in principle
Speaker 2: the way we like scent devices near the Sun with
Speaker 2: a Parker solar probe. People are, what if we built
Speaker 2: a bunch of these things and we spread them out
Speaker 2: in the Solar system, could they give us a picture
Speaker 2: of where the dark matter is in the Solar system
Speaker 2: if they operate differently when there's dark matter around, like
Speaker 2: if they're sensitive to the dark matter density, Like if
Speaker 2: your atomic clock gets off if it drifts when there's
Speaker 2: more or less dark matter around, than having a bunch
Speaker 2: of these atomic clocks spread out through the Solar system
Speaker 2: could give you a picture for where in the Solar
Speaker 2: System the dark matter is.
Speaker 1: But I guess what's the mechanism by which dark matter
Speaker 1: would affect the timing of these clocks.
Speaker 2: Yeah, so mostly it wouldn't. For many theories of dark matter,
Speaker 2: dark matter is just some wimp. It's a massive particle
Speaker 2: that only interacts gravitationally, and so it has essentially no
Speaker 2: effect on these clocks except for gravitational time dilation. We
Speaker 2: know the areas with greater mass more curvature, and a
Speaker 2: curvature causes time dilation, but that would be very, very
Speaker 2: difficult to measure even with these quantum clocks.
Speaker 1: But wait, wait, why would it be difficult.
Speaker 2: You can measure gravitational time dilation with quantum clocks, and
Speaker 2: we've done that. You can do it on the surface
Speaker 2: of the Earth, for example, and you could put a
Speaker 2: quantum clock one meter above another one and you can
Speaker 2: see the difference between them because one of them is
Speaker 2: deeper in the curvature than the other. Super duper awesome,
Speaker 2: but that's because the Earth has a huge amount of
Speaker 2: gravity and this significant curvature. Here. Dark matter doesn't contribute
Speaker 2: significantly to the curvature because it's pretty spread out, and
Speaker 2: we would already know if dark matter wasn't pretty spread out,
Speaker 2: because we would have seen deviations and like Jupiter's orbit
Speaker 2: and whatever. So in principle you can, but we don't
Speaker 2: think it's going to be very sensitive. If you had
Speaker 2: a lot of quantum clocks and there were much more sensitive,
Speaker 2: then you could probably detect dark matter local density variations
Speaker 2: using that.
Speaker 1: Principle, meaning these clocks would take at a different frequency
Speaker 1: depending on how close it was to big sources of
Speaker 1: mass or even sources of mass, because that's just how
Speaker 1: relativity works.
Speaker 2: Yeah, that's how relativity works. Remember, in relativity, it is
Speaker 2: two kinds of time dilation. One is based on speed.
Speaker 2: If you see a clock moving quickly, then you see
Speaker 2: it ticking slowly, and that's very confusing because it's relative,
Speaker 2: and so it depends on two observers. But there's another
Speaker 2: kind of time dilation, gravitational, which is absolute. It just
Speaker 2: says anybody in curvature their clock is going to tick slowly,
Speaker 2: no matter who's looking at it, and everybody's going to
Speaker 2: agree about whose clock is ticking slowly. So that's very powerful,
Speaker 2: and that's something you can use to measure just like
Speaker 2: how much stuff is there in general, because clocks tick
Speaker 2: slower near stuff. Really kind of an awesome feature of
Speaker 2: the universe.
Speaker 1: Meaning like if I had two of these atomic clocks
Speaker 1: and one of them is out there in the middle
Speaker 1: of empty space, and the other one is near a
Speaker 1: big blob of dark matter. The one near the blob
Speaker 1: of dark matter would take slower.
Speaker 2: Right, Yeah, that's exactly right.
Speaker 1: And so you might like start them out in the
Speaker 1: same spot. But then after being for a while and
Speaker 1: two different spots, one near the dark matter, and you
Speaker 1: run a back, you would see that one of them
Speaker 1: take more ticks than the other.
Speaker 3: Yeah.
Speaker 2: So now imagine like a grid, you have a quantum
Speaker 2: clock every ten meters in the solar system, right, you
Speaker 2: start them all out at the same time, and then
Speaker 2: you monitor it, and by measuring the difference in that
Speaker 2: number of ticks after a year on your reference clock,
Speaker 2: the one that's hanging out with you, you can tell where
Speaker 2: stuff is in the solar system.
Speaker 1: Like which spots in the solar system have slower time.
Speaker 2: Yes, exactly, because slower time means more matter, more curvature,
Speaker 2: more energy density.
Speaker 1: Really, I guess, on top of what you already know
Speaker 1: about the Solar system right like right now, even if
Speaker 1: we didn't have dark matter, a clock near the Sun
Speaker 1: would take slower than a clock here exactly.
Speaker 2: And we've done some basic version of this, as I
Speaker 2: said earlier, If a few clocks on Earth at different altitudes,
Speaker 2: those are different distances from the matter of the Earth
Speaker 2: and the ones closer do ticks more slowly, and satellites
Speaker 2: up in space their clocks tick faster than atomic clocks
Speaker 2: here on the surface of the Earth. And you've got
Speaker 2: to take that new account famously when you're doing GPS,
Speaker 2: et cetera.
Speaker 1: But you're saying, we're not going to be using this effect,
Speaker 1: this time dilation from relativity to measure dark matter. Dark
Speaker 1: matter is just too weak.
Speaker 2: Dark matter is too weak, and we think it's not
Speaker 2: cluppy enough to really detect that, though it would be
Speaker 2: super awesome. There's a special kind of dark matter which
Speaker 2: might give much larger effects, which would be much easier
Speaker 2: to discover. And this is a theory called fuzzy dark matter.
Speaker 1: Sounds fuzzy. But wait, so you're saying, like this idea
Speaker 1: of using atomic clocks to measure dark matter would only
Speaker 1: work for a certain theoretical meaning guessie type of dark matter,
Speaker 1: which we don't know whether it's true or not or
Speaker 1: exists or not. M So this is a huge sources
Speaker 1: in white scheme that you don't really know if it's
Speaker 1: going to work.
Speaker 2: You know, you were talking about nomenclature and now you're
Speaker 2: using the words guess and scheme. You know, really kind
Speaker 2: of undermine the credibility of science, but you know, this
Speaker 2: is good faith stuff. This is like, hey, what if
Speaker 2: dark matter is this other weird particular thing. How could
Speaker 2: we see that and yet be best if we had experiments
Speaker 2: which could detect any kind of dark matter. But you know,
Speaker 2: there might be kinds of dark matter which we could
Speaker 2: only detect in certain ways or easier to spot in
Speaker 2: some ways. And so it's good to be creative and
Speaker 2: think about how we could detect specific kinds of dark
Speaker 2: matter as well, even though we don't know what dark
Speaker 2: matter is. And if this theory is at.
Speaker 1: All correct, well, I'm just trying to understand the scheme.
Speaker 1: So are you saying there's a theoretical kind of dark
Speaker 1: matter called fuzzy dark matter? So what is it? So?
Speaker 2: Fuzzy dark matter suggests that maybe dark matter isn't very massive,
Speaker 2: like some people suggest that dark matter could be like
Speaker 2: one hundred GeV like the mass of a w or
Speaker 2: a z boson, like one hundred times the mass of
Speaker 2: a proton, a pretty hefty particle, almost as massive as
Speaker 2: a Higgs. That's sort of the classic strategy, and there's
Speaker 2: reasons for that. There's something called the wimp miracle check
Speaker 2: in our podcast about that, which argues strongly that dark
Speaker 2: matter should be around one hundred gv based on how
Speaker 2: much of it there is in the universe. But people
Speaker 2: are like, well, maybe that's all wrong, and there's an
Speaker 2: assumption there that's wrong. What if dark matter super duper light,
Speaker 2: like a trilliance the mass of an electron. So now
Speaker 2: there's an enormous number of these dark matter particles, so
Speaker 2: many more than you could even imagine, because you have
Speaker 2: to somehow make like a big fraction of the mass
Speaker 2: of the universe out of particles that are a tiny
Speaker 2: fraction of the mass of the electron, which is already
Speaker 2: very very light.
Speaker 1: Well, first of all, I think this whole podcast is
Speaker 1: a wimp miracle, Daniel. But I think you're saying, like
Speaker 1: this version of dark matter, instead of being maybe marble
Speaker 1: sized particles, they're like super tiny bb sized particles. And
Speaker 1: some of that makes it fuzzier.
Speaker 2: Yeah, it makes it fuzzier because if they're very very
Speaker 2: low mass, then their wavelengths are more spread out. Some
Speaker 2: of these things can have a wavelength like the size
Speaker 2: of the galaxy.
Speaker 1: What do you mean a wavelength?
Speaker 2: The wavelength of a particle is like the distance on
Speaker 2: which these quantum interference effects appear, and so you can
Speaker 2: calculate this quantity. It's called the Debrogely wavelength. You'll see
Speaker 2: wave like effects for a particle when you interact over
Speaker 2: these kinds of distances, and that's the wavelength of a particle.
Speaker 1: Meaning sort of like the size of it kind of right.
Speaker 2: Sort of, Yeah, it's when it stops acting like a
Speaker 2: blob like a particle and starts acting more like a wave.
Speaker 2: Things that have wavelike behaviors. Really, it's always acting like
Speaker 2: a wave. It's just that when you zoom out you
Speaker 2: can approximate it as a particle.
Speaker 1: Because they have low mass. What's the relationship between having
Speaker 1: low mass and being having big wavelengths.
Speaker 2: Well, the wavelength depends on your momentum and your mass,
Speaker 2: So lower mass just means a larger wavelength because it's
Speaker 2: really like a ratio between the momentum and the mass.
Speaker 2: When things have a lot of kinetic energy relative to
Speaker 2: their mass, they act more like light because light is
Speaker 2: pure kinetic energy. When things have very small amounts of
Speaker 2: energy relative to their mass, they're stationary, so they act
Speaker 2: more like bits of sand, like particles, and so it's
Speaker 2: just sort of a rough way to understand where that
Speaker 2: transition happens.
Speaker 1: Okay, So, then if dark matter is this kind of
Speaker 1: fuzzy kind of dark matter, you're saying that each particle
Speaker 1: would be super duper light, and it would also have
Speaker 1: huge variations in their size. That's what you mean by fuzzy.
Speaker 1: It's like they might be some of them might be
Speaker 1: super big and somewhere might be super small.
Speaker 2: Yeah. Well, the wavelengths could be very very large, which
Speaker 2: means they can interact over long distances. But the fascinating
Speaker 2: thing is that in simulations of this dark matter, it
Speaker 2: predicts like a mini halo of dark matter in our
Speaker 2: Solar system, essentially that this stuff would be clumped up
Speaker 2: in and near the Sun. That most of the dark
Speaker 2: matter in the Solar System might be like clumped up
Speaker 2: near the Sun. It might be like hiding in the Sun.
Speaker 1: And if it wasn't this kind of fuzzy dark matter,
Speaker 1: it wouldn't.
Speaker 2: Now, this kind of fuzzy dark matter is the kind
Speaker 2: we think would clump up like a.
Speaker 1: Halo near the Sun, and the other kinds wouldn't.
Speaker 2: Yeah, the other kinds wouldn't necessarily, I mean, I've heard
Speaker 2: of other theories of dark matter clumping in the Sun.
Speaker 2: There's all sorts of theories, but this particular one tends
Speaker 2: to make a halo near the Sun and would affect
Speaker 2: the operation of quantum clocks because of its special fuzziness.
Speaker 2: It can also slightly interact with electrons through sort of
Speaker 2: like a back door in quantum mechanics, which would change
Speaker 2: the way a quantum clock operates. It's like it changes
Speaker 2: the electrons math and how it responds to photons because
Speaker 2: of oscillations in this fuzzy dark matter field, and so
Speaker 2: effectively it changes the frequency of these clocks. And so
Speaker 2: you can detect in principle whether you're near a dense
Speaker 2: blob of this ultra light dark matter by looking at
Speaker 2: a quantum clock and counting its ticks very carefully. And
Speaker 2: this would be a bigger effect than the effect we
Speaker 2: talked about earlier, the gravitational curvature.
Speaker 1: But I thought that dark matter couldn't interact with regular
Speaker 1: matter only through it could only do it through gravity.
Speaker 2: Yeah, it could only do it through gravity in general,
Speaker 2: But this one takes a back door through the Higgs field.
Speaker 2: It like interacts with the Higgs field and it changes
Speaker 2: how the Higgs field works, and so near the presence
Speaker 2: of this ultra light dark matter, electrons effectively have a
Speaker 2: different mass.
Speaker 1: But I guess if that was true, wouldn't we see
Speaker 1: it effect regular matter on a larger scale.
Speaker 2: You would see it happen, but it's a subtle effect,
Speaker 2: and so you need to be near a dense clump
Speaker 2: of it. So the idea is, take something that's very
Speaker 2: very sensitive to the electron mass, like a quantum clock,
Speaker 2: and try to put it near a dense clump of
Speaker 2: this special ultra light dark matter, maybe near the Sun.
Speaker 2: So that's the idea is, like launch a bunch of
Speaker 2: quantum clocks, have them orbit near the Sun, and look
Speaker 2: for deviations in their timekeeping, and see if that's evidence
Speaker 2: for ultra light dark matter interfering with the masses of
Speaker 2: the electrons in these quantum clocks.
Speaker 1: We mean that you would maybe like throw a bunch
Speaker 1: of the sun, have them kind of form a half
Speaker 1: ring around the Sun to see if time changes there,
Speaker 1: sort of like a giant tirra, like.
Speaker 2: A giant tr a quantum cosmic tira.
Speaker 1: All right, But I guess which one would you be proving?
Speaker 1: Would you be proving that dark matter is fuzzy, or
Speaker 1: would you be proving that it's there? Or are they
Speaker 1: both related?
Speaker 2: They're both related.
Speaker 4: Though.
Speaker 2: You know, if we saw this thing, there would instantly
Speaker 2: be like fifty other theories to explain it as well.
Speaker 2: It probably wouldn't be a unique prediction of this kind
Speaker 2: of dark matter. Theories are very very clever people, and
Speaker 2: they'll always come up with another way to explain the
Speaker 2: data that we were seeing. But it's cool because it's
Speaker 2: a prediction that this theory makes and we go out
Speaker 2: and we see it. That's really fascinating, and then we
Speaker 2: can think about ways to distinguish all the different ideas
Speaker 2: that might also explain this kind of observation. It would
Speaker 2: just be cool to see something different. Currently, all of
Speaker 2: our dark matter experiments basically see nothing. It would be
Speaker 2: cool to have a signal somewhere.
Speaker 1: So you're thinking, hey, let's put a bunch of microways
Speaker 1: in space and see if it sticks exactly.
Speaker 2: Let's see if one burrito is a little bit colder
Speaker 2: than another.
Speaker 1: All right, Well, an interesting idea for how we could
Speaker 1: maybe possibly crack sort of a theoretical version of one
Speaker 1: of the biggest mysteries in the universe.
Speaker 2: That's right. Physicists are being very creative and trying to
Speaker 2: come up with new theories of dark matter and new
Speaker 2: ways to discover them, including using super duper sets in
Speaker 2: quantum clocks distributed through the solar system, which also would
Speaker 2: just be fun to do.
Speaker 1: You just want to parade, Daniel, I just want a Tiara?
Speaker 2: Is that too much to ask?
Speaker 1: How about we just buy you a Tiara?
Speaker 2: Is it made of dark matter? Are you using your bitcoin?
Speaker 1: It can be, but in any way that you want.
Speaker 1: But if it's saves tax dollars billions of dollars, you know,
Speaker 1: it would be a pretty good investment.
Speaker 2: Yeah, there we go. That was my scheme the whole time.
Speaker 1: Yeah, to get us to buy you at tiara without
Speaker 1: actually having to run in a beauty contest.
Speaker 2: I'm busted.
Speaker 1: Well, you are the most beautiful podcaster with a show
Speaker 1: called Daniel Jorge Explaining the Universe. So whose name is Daniels?
Speaker 2: I'll take very highly qualified compliments, thank you.
Speaker 1: It's a very specific tiara based on a very theoretical
Speaker 1: model of the universe.
Speaker 2: Fuzzy compliments from Morehey, all.
Speaker 1: Right, well we hope you enjoyed that. Thanks for joining us.
Speaker 1: See you next time.
Speaker 2: For more science and curiosity, come find us on social media,
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Speaker 2: and Jorge Explain the Universe is a production of Iheartworting.
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