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Speaker 5: Hey, Daniel, if you were Dark Matter, where would you hide?
Speaker 1: I wouldn't hide. If I was Dark Matter, I would
Speaker 1: totally parade myself in front of all the scientists in
Speaker 1: the galaxy.
Speaker 5: Ooh, a parade You mean like a pageant queen?
Speaker 1: Yeah, something like that. You know, just don't be so shy.
Speaker 5: Well, if it turns out you are dark matter, we'll
Speaker 5: definitely throw you a parade. But so far, it seems
Speaker 5: like dark matter is kind of reclusive, right, it's kind
Speaker 5: of shy, so maybe it is hiding. What would be
Speaker 5: some good spots for it to hide it?
Speaker 1: Well, if dark matter doesn't want a tiara and it's
Speaker 1: hiding somewhere, then I don't know where it would hide.
Speaker 1: I mean, if I knew, I would go and look
Speaker 1: for it there.
Speaker 5: What if it's somewhere kind of obvious.
Speaker 1: Like what like right behind me?
Speaker 5: Yeah, or right in front of you or right on
Speaker 5: TV and the Matter universe contest.
Speaker 1: That would be a great twist ending for the m
Speaker 1: Knight Shamanlan version of this story.
Speaker 5: Well, man, do you think he knows I see dark matter?
Speaker 6: Hi?
Speaker 5: I'm Jorge Mack, cartoonist and author of Allor's Great Big Universe.
Speaker 1: Hi, I'm Daniel. I'm a particle physicist, and I wish
Speaker 1: I had a dark matter tiara.
Speaker 5: Oh, but it wouldn't be very shiny or bright. It
Speaker 5: would be dark, So what's the point. Also, when it
Speaker 5: it just fall through your head.
Speaker 1: It would be hard to wear, but it'd be like
Speaker 1: the greatest, most amazing piece of jewelry.
Speaker 5: Ever, how would you even keep it in your house?
Speaker 1: These are just like engineering details.
Speaker 4: You know.
Speaker 1: Once I've solved the physics of a dark matter Tiara,
Speaker 1: I'll just pass that off to the engineers.
Speaker 5: This is just all part of your dream to be
Speaker 5: the universe's darktor universe.
Speaker 1: I would like a little bit of bling. Yeah, you know,
Speaker 1: physics bling would be nice. I'm not gonna win a
Speaker 1: Nobel Prize anytime soon, So dark matter Tirres sounds good.
Speaker 1: I see.
Speaker 5: I see. You could just say you have a dark
Speaker 5: matter Tierra, and they know nobody would be able to
Speaker 5: see it, or feel it or detect it. They would
Speaker 5: just have to believe you.
Speaker 1: I need evidence, man, That's what science is all about.
Speaker 1: You got to have data.
Speaker 5: I don't think those beauty contests depend on data very much.
Speaker 1: But I'm trying to win a science contest.
Speaker 5: But anyway's welcome. Podcast Daniel and Jorge Explain the Universe,
Speaker 5: a production of iHeartRadio in which we enter you in.
Speaker 1: The greatest science contest of all time, the quest to
Speaker 1: understand the nature of the universe. What is it, what's
Speaker 1: in it? What's it made out? Of how does it
Speaker 1: all work. We think these questions are deep and fundamental
Speaker 1: parts of being a human being in this cosmos, and
Speaker 1: unraveling these questions is a joy that everybody should share.
Speaker 1: So on this podcast we take those questions apart and
Speaker 1: try to share our answers and our ignorance with you.
Speaker 5: That's right, because science is the greatest beauty contest in
Speaker 5: the universe. We're the goal is to discover the beauty
Speaker 5: of how this universe is put together, how it works,
Speaker 5: and what is our place in it.
Speaker 1: Over the last fifty one hundred years, we've developed a
Speaker 1: pretty good sense for what's in the universe. We know
Speaker 1: about stars and galaxies and all the bright and shiny
Speaker 1: stuff that's out there in the universe. And we've also
Speaker 1: figured out that there's a lot of the universe that
Speaker 1: we can't see directly using our senses or any of
Speaker 1: the forces that we've discovered except for gravity. We know
Speaker 1: that a huge chunk of the stuff that's out there
Speaker 1: in the universe is invisible. It's intangible, which makes it
Speaker 1: very hard to discover and to figure out how to
Speaker 1: make it into a tiara.
Speaker 5: Yeah, because it turns out that a pretty good understanding
Speaker 5: of the universe only covers about uh five percent of
Speaker 5: what we know is out there. The rest, the ninety
Speaker 5: five percent of the universe that we know is there,
Speaker 5: we have no idea what it is or how it works.
Speaker 1: That sounds like a good title for a book.
Speaker 5: Yeah, I think we wrote one, Daniel, which is available
Speaker 5: for us sale everywhere.
Speaker 1: That's right. The kind of stuff that you and I
Speaker 1: are made out of, atoms specifically, or what physicists called baryons,
Speaker 1: only makes up five percent of the energy budget in
Speaker 1: the universe. There's another twenty five twenty seven percent that's
Speaker 1: dark matter, some kind of stuff that we know is matter.
Speaker 1: We know it's out there, but we don't know what
Speaker 1: it is, and we only have a very rough sense
Speaker 1: of even where it is around us. The rest of
Speaker 1: the universe is something we call dark energy, which is
Speaker 1: contributing to the accelerating expansion of the universe, and we
Speaker 1: have even less clue about what makes that up.
Speaker 5: Yeah, there's a lot we don't know, and it seems
Speaker 5: like these are maybe the defining mysteries of our times
Speaker 5: is to figure out what the universe is actually made
Speaker 5: out of. Given that what we're made out of counts
Speaker 5: is so little of it.
Speaker 1: Yeah, you're right, And in the last few decades there's
Speaker 1: been a huge program of people looking for dark matter.
Speaker 1: We've talked on the podcast about trying to make dark
Speaker 1: matter in the laboratory by smashing particles together. We're searching
Speaker 1: for the dark matter wind. We might be floating through
Speaker 1: with very sensitive underground facilities looking for an individual piece
Speaker 1: of dark matter to bump into liquid xenon, for example,
Speaker 1: or maybe evidence of dark matter annihilating itself in the
Speaker 1: center of the galaxy. But so far, none of these
Speaker 1: experiments have found dark matter, which means we've got to
Speaker 1: get creative about other ways to maybe detect this most
Speaker 1: important or at least most common kind of matter in
Speaker 1: the universe.
Speaker 5: So to be On the podcast, we'll be tackling the
Speaker 5: question could quantum clocks detect dark matter? And how many
Speaker 5: jargon words can we fit into one podcast title?
Speaker 1: I know it does sound like buzzword sound, you know,
Speaker 1: like could we use AI generated crypto bitcoin to detect
Speaker 1: dark matter?
Speaker 5: You mean quantum nano matter, Yes, exactly, quantum nano matter.
Speaker 1: Tiras Wow, I like quantum nanomatter. I'm going to use
Speaker 1: that in a proposal.
Speaker 5: That's good, that's said Daniel. Also, it's probably our on
Speaker 5: sale on Amazon. There's probably some product out there with
Speaker 5: that name.
Speaker 1: So yeah, but you didn't say ching tm after it,
Speaker 1: so I can use it.
Speaker 5: No, you don't have to.
Speaker 1: What I gotta brush up on my podcast property law.
Speaker 5: Yeah, you better or else I'm gonna see you for
Speaker 5: nano dollars for nano bitcoins, you know what?
Speaker 1: Or hey, you can have all of my nano bitcoins.
Speaker 5: What's the price of bitcoin these days?
Speaker 1: Nano bitcoins zero? Yeah, doesn't exist.
Speaker 5: But anyways, it's kind of an intriguing title. Could quantum
Speaker 5: clocks detect dark matter and quantum clocks sounds like it
Speaker 5: does sound like something you could buy an off of Amazon.
Speaker 5: Did you check to see if it's something you can
Speaker 5: just get next day?
Speaker 4: Oh?
Speaker 1: Yeah, it turns out Amazon will sell you something it
Speaker 1: calls a quantum clock, like a quantum entanglement led wall clock.
Speaker 1: But none of these things are actually quantum clocks the
Speaker 1: way that we understand them.
Speaker 5: Well, technically, isn't everything a quantum something? Well, I mean
Speaker 5: not everything, but you know the five percent that we
Speaker 5: know about in the universe, it's in it all quantum technically,
Speaker 5: like this is a quantum podcast.
Speaker 1: I mean, that's a really interesting philosophical question and not
Speaker 1: one that we really have an answer to, because on
Speaker 1: one hand, you're right that everything is made out of
Speaker 1: quantum particle, so isn't the whole universe quantum. On the
Speaker 1: other hand, we know that when you zoom out things
Speaker 1: behave by different rules. We call that classical. We don't
Speaker 1: really understand why there is that transition, but there definitely
Speaker 1: is a transition. So to call everything quantum is either
Speaker 1: to say that look classical is just big zoomed out quantum,
Speaker 1: or is to say that clackical doesn't really matter, which
Speaker 1: doesn't really sit well with me. Or what if I
Speaker 1: have no class, then you probably have a lot of
Speaker 1: big coin.
Speaker 5: Then I'm not gonna win any beauty contest. I have poise,
Speaker 5: but just no class.
Speaker 1: Yeah, exactly. But you know, for example, a clock that
Speaker 1: just works on mechanical parts would also work in the
Speaker 1: universe where QUANTUMU didn't rule the microscopic because it's not
Speaker 1: sensitive to those microscopic details, and so that wouldn't be
Speaker 1: a quantum clock. For example, like a pendulum clock or
Speaker 1: an old fashioned Swiss gear based.
Speaker 5: Clock a discussion about now mankla Sure that's my favorite.
Speaker 1: Hey you brought it up.
Speaker 5: But anyways, it's a kind of an interesting question and
Speaker 5: so we'll dig into it. But as usual, we were
Speaker 5: wondering how many people out there have thought about putting
Speaker 5: the concepts of dark matter and quantum and clocks all
Speaker 5: together in one sentence.
Speaker 1: So thanks very much to everybody who participates in this
Speaker 1: segment of the podcast. We love that you volunteer, We
Speaker 1: love hearing your thoughts, and we love sharing your voice
Speaker 1: with all of the other listeners. Please chime in if
Speaker 1: you'd like, write to me two questions at Danielanjorge dot
Speaker 1: com and you can't participate.
Speaker 5: So think about it for a second. Do you think
Speaker 5: quantum clocks can be used to detect dark matter? Here's
Speaker 5: what people had to say.
Speaker 7: I've never heard of a quantum clock, but I'm not
Speaker 7: sure how it would be able to detect dark matter
Speaker 7: anymore than a regular clock could. I guess maybe even
Speaker 7: with a regular clock, you could send it out into space,
Speaker 7: and if it hits a huge clump of dark matter
Speaker 7: and therefore gravity, maybe we could learn that there's a
Speaker 7: big well of gravity out in some location that we
Speaker 7: otherwise couldn't detect.
Speaker 3: Not so sure.
Speaker 8: I suppose it's possible, but I have no clue how
Speaker 8: it would Maybe something to do with entanglement.
Speaker 9: Since you're asking, the answer is probably yes, but maybe
Speaker 9: still theoretical. I would think you'd have to use the
Speaker 9: idea of measuring light passing through an area of more density,
Speaker 9: thus possibly dark matter that causes curvature of space and
Speaker 9: also time dilation. How to do that, I'm not sure.
Speaker 1: Since we don't possess a quantum clock, it doesn't seem
Speaker 1: unreasonable to suggest that a non existent clock cannot detect
Speaker 1: dark matter.
Speaker 5: All right, it's pretty uh intense answers here. I feel
Speaker 5: like it's something that some of the listeners had heard
Speaker 5: about before. Did you pull your professor colleagues this time?
Speaker 1: No, these are our listeners online. You know. There's some
Speaker 1: good answers here about entanglement and light passing through areas
Speaker 1: with dark matter density in them, and just in general
Speaker 1: sense that this is a hard problem.
Speaker 5: Maybe you should ask a bunch of beauty queens next time,
Speaker 5: or make it one of the standard questions in a
Speaker 5: beauty pageant. Forget howdy, how would you save the world?
Speaker 5: Or how would you know make things better? What do
Speaker 5: you think about quantum clocks?
Speaker 1: Well, where is the dark matter? Yeah, I'd love to
Speaker 1: hear that answer in the beauty pageant.
Speaker 5: Not that it couldn't happen, of course, no, absolutely. All right, Well,
Speaker 5: let's dig into this intriguing question of whether dark matter
Speaker 5: can be detected by quantum clocks, and let's start with
Speaker 5: the basics. Daniel, what do we know about dark matter?
Speaker 1: So there's a lot that we do and do not
Speaker 1: know about dark matter. So let's start with what we
Speaker 1: do know. We know that it's out there, and we
Speaker 1: know that it's here as well. We know that dark
Speaker 1: matter is something that exists in the universe. And then
Speaker 1: it's matter. We know that because we see its gravity.
Speaker 1: We see it holding galaxies together as they spin. There
Speaker 1: isn't enough gravity from the stars and the gas and
Speaker 1: dust that make up those galaxies to keep the stars
Speaker 1: in place as they swirl around the center of the
Speaker 1: galaxy at very high speeds, and yet they do stay
Speaker 1: in place. Galaxies are mostly not throwing stars out into
Speaker 1: intergalactic space, and so we infer that there must be
Speaker 1: some matter there to hold that galaxy together. But it's
Speaker 1: more than just that one inference, that one fudge factor
Speaker 1: to make that particular equation work. We see evidence for
Speaker 1: dark matter all over the history of the universe, from
Speaker 1: the very first few moments when the early universe plasma
Speaker 1: is slashing around and you have dark matter and normal
Speaker 1: matter and photons all acting very differently and creating different
Speaker 1: slashing patterns. From looking at that slashing in the cosmic
Speaker 1: microwave background radiation, we can figure out that there was
Speaker 1: dark matter and even measure how much of it there is,
Speaker 1: and we can trace the history of dark matter's gravity
Speaker 1: as it shapes the structure formation of the whole universe
Speaker 1: why we have galaxies at all this early in the
Speaker 1: history of the universe, And so dark matter is definitely
Speaker 1: out there as a kind of matter, but we don't
Speaker 1: know really what it is or very specifically where it is,
Speaker 1: because it's so hard to see since it only feels gravity.
Speaker 1: It doesn't feel any of the other forces that we've discovered.
Speaker 5: And we can also sort of see dark matter right like,
Speaker 5: we can see it in the same way that you
Speaker 5: can see a lens or glass lens or example. You
Speaker 5: can see how it distorts the light behind it, right.
Speaker 1: Yeah, exactly. We can see dark matter through gravity, and
Speaker 1: so that means we can see stuff bending around dark matter.
Speaker 1: We can see it holding galaxies together, and that even
Speaker 1: impacts how light moves in the vicinity of dark matter.
Speaker 1: If you have a big blob of dark matter between
Speaker 1: you and some distant galaxy, for example, the photons from
Speaker 1: that distant galaxy will bend as they move through that
Speaker 1: dark matter, creating apparent distortions in your image. You can
Speaker 1: even sometimes see the same galaxy twice in the sky
Speaker 1: because of this gravitational lensing. And so we know that
Speaker 1: it's out there, and we can use some techniques like
Speaker 1: that to sometimes tell roughly where it is. But because
Speaker 1: dark matter is so weak it's particles only feel gravity,
Speaker 1: we think it's very difficult to figure out what exactly
Speaker 1: is made out of to isolate one piece of dark matter,
Speaker 1: because gravity is so weak that essentially a particle's gravity
Speaker 1: is almost impossible to measure.
Speaker 5: Yeah, and dark matter is also something that's not just
Speaker 5: out there in space. It's sort of like all around us,
Speaker 5: right like it's floating through us right now, sort of
Speaker 5: like the fourth you know, it flows through us, binds
Speaker 5: us all together. It's made out of medtichlorians.
Speaker 1: Perhaps perhaps, yeah, exactly, you'll only really understand it after
Speaker 1: nine hundred years of study. That's a really good question,
Speaker 1: and that's sort of the central question of this episode
Speaker 1: is exactly where is the dark matter? And can we
Speaker 1: find like concentrations of it? Can we map it out?
Speaker 1: Because dark matter is so weakly interacting like only gravity,
Speaker 1: it takes huge amounts of it to feel anything, and
Speaker 1: so that makes it very hard to tell exactly where
Speaker 1: the dark matter is. It might be that it's mostly
Speaker 1: spread out evenly through the galaxy. It might be more
Speaker 1: clumpy than that depends a lot on your particular theory
Speaker 1: of dark matter. Where it exactly is. So it could
Speaker 1: be that we are in a dark matter wind as
Speaker 1: the Earth orbits the Sun and the Sun moves through
Speaker 1: the galaxy. We could also be in a dark matter
Speaker 1: liss bubble, a bubble of space in which there's comparatively
Speaker 1: little dark matter. Or it could be that dark matter
Speaker 1: is fairly dense in our area.
Speaker 5: You know, I have to say, every time you say
Speaker 5: dark matter wind, it makes me think of dark parts.
Speaker 1: Elevating the discourse every week.
Speaker 5: That's my job. That's why I'm here.
Speaker 1: Smells.
Speaker 5: It's all grounded or grounded or you know, flat as
Speaker 5: in fletch wents. But anyways, so it's sort of all
Speaker 5: around this, and I guess I'm wondering, like, if it
Speaker 5: is all around us, would we be able to tell, Like,
Speaker 5: you know, if let's say dark matter is flowing through
Speaker 5: the Earth right now, or say it wasn't, would you
Speaker 5: be able to tell the difference.
Speaker 1: That's exactly what these experiments are trying to measure. And
Speaker 1: to give you a sense of the difficulty the challenge
Speaker 1: of this, think about like why we didn't discover dark
Speaker 1: matter earlier, just in studying how our Solar system moves.
Speaker 1: We have now very precise measurements of the orbit of
Speaker 1: Jupiter and Mars and all the planets and all the
Speaker 1: little pieces of the Solar System as they orbit the Sun.
Speaker 1: You might think, hey, if dark matter is here in
Speaker 1: our Solar system and it has gravity, wouldn't it change
Speaker 1: the way those things orbit? Shouldn't we be able to
Speaker 1: detect it? But because we think dark matter might be
Speaker 1: spread very thin, probably there isn't that much dark matter
Speaker 1: in the vicinity of our Solar system. So even those
Speaker 1: very very precise measurements you know, like knowing the motion
Speaker 1: of Jupiter to meters or centimeters, can't detect dark matter
Speaker 1: because it would be very thin and very spread out
Speaker 1: and mostly we think homogeneous, which in the end doesn't
Speaker 1: give much gravitational pull on the objects in the Solar System.
Speaker 1: So it takes a very specialized, highly sensitive device to
Speaker 1: be able to detect this dark matter.
Speaker 5: Yeah, and then don't we say once like, if you
Speaker 5: take all the dark matter that is potentially floating through
Speaker 5: the Earth right now, it would only weigh about as
Speaker 5: much as a squirrel or something like that.
Speaker 1: Yeah, exactly, though that's very speculative, right. That assumes that
Speaker 1: dark matter is essentially equally spread out in our galaxy,
Speaker 1: which we don't believe is true. But if you assume
Speaker 1: that there is, then we know our galaxy, for example,
Speaker 1: is ninety five percent dark matter. That means for every
Speaker 1: kilogram of matter made out of atoms like hydrogen and
Speaker 1: helium or whatever, there's nineteen kilograms of matter made out
Speaker 1: of whatever dark matter is made out of. And so
Speaker 1: it's like nineteen to one in our galaxy.
Speaker 5: Which sounds like a lot, but I guess also galaxies
Speaker 5: kind of very empty mostly right, like it's probably like
Speaker 5: ninety nine percent empty.
Speaker 1: Yeah exactly. Now, normal matter clumps up a lot, right,
Speaker 1: Like the Sun is an extraordinarily dense collection of normal matter.
Speaker 1: Normal matter is not spread evenly through the galaxy. But
Speaker 1: if you take dark man and spread it evenly through
Speaker 1: the galaxy, you get a pretty small density. It's like
Speaker 1: ten to the twenty six kilograms per cubic light year,
Speaker 1: which is a huge volume, which means it's like ten
Speaker 1: to the negative twenty two kilograms per cubic meter. So
Speaker 1: then if you add up all the cubic meters in
Speaker 1: the Earth, that adds up to about two thirds of
Speaker 1: a kilogram of dark matter inside the volume of the Earth. Again,
Speaker 1: assuming that dark matter is evenly spread throughout the galaxy,
Speaker 1: which it probably isn't, but it might be.
Speaker 5: Roughly, which is about the size or mass of a squirrel.
Speaker 1: Yeah exactly, So one squirrel of dark matter inside the
Speaker 1: volume of the Earth compared to you know, the many,
Speaker 1: many millions and billions of kilograms of normal matter inside
Speaker 1: the volume of the Earth. That sounds the importance of clumping, right,
Speaker 1: Because normal matter clumps together, it's gravity is much more powerful.
Speaker 1: In our local neighborhood, than dark matter. Even though dark
Speaker 1: matter outweighs normal matter by nineteen to one, if it's
Speaker 1: much more thinly spread out, the local effects of its
Speaker 1: gravity are much harder to detect.
Speaker 5: I think maybe what you're saying is that dark matter,
Speaker 5: in terms of the universe scale, it mostly hangs out
Speaker 5: in galaxies. Like you don't see a lot of dark
Speaker 5: matter floating out there on its own between galaxies.
Speaker 1: Yeah, we can do really precise measurements of where dark
Speaker 1: matter is on the galaxy scale, because galaxies are really
Speaker 1: really big. If we can tell how galaxies are orbiting
Speaker 1: around each other, just the way we can tell how
Speaker 1: stars are moving through the galaxy, so enormous clumps of
Speaker 1: dark matter, absolutely, we can measure their gravity. But when
Speaker 1: you zoom in in a really fine grained way and
Speaker 1: want to say, hey, is there a moon sized blob
Speaker 1: of dark matter anywhere in our solar system, that's a
Speaker 1: tough question to answer.
Speaker 5: So then within the galaxy, you're saying, like, there's a
Speaker 5: lot of dark matter within our galaxy. Ninety five percent
Speaker 5: of the mass of our galaxy is dark matter, And
Speaker 5: what does it look like. Does it look like, you know,
Speaker 5: an intense dense ball of dark matter in the middle,
Speaker 5: is it evenly distributed? And also, like our galaxy looks
Speaker 5: like a disc sort of like a flat disk, is
Speaker 5: dark matter also shaped like a flat disk.
Speaker 1: So we have the best answers the more we zoom out,
Speaker 1: and then as we zoom in things get literally funny.
Speaker 1: But on the scale of the galaxy we have some ideas.
Speaker 1: We think that dark matter is like a big halo.
Speaker 1: So imagine the visible galaxy right the edge of the stars.
Speaker 1: Dark matter is a big halo that goes out beyond
Speaker 1: the visible stars, and it's bigger and fuzzier. It hasn't
Speaker 1: collapsed the way normal matter has because it just doesn't
Speaker 1: clump right. In order to clump, things need other kinds
Speaker 1: of interaction other than gravity. Like if you have two
Speaker 1: dark matter particles they attract each other gravitationally and then
Speaker 1: just passed right through each other. They're just gonna zig
Speaker 1: and zag back and forth oscillate forever. They're not going
Speaker 1: to clump together. To do that, you need like electromagnetism
Speaker 1: or the strong force or something that wants to grab
Speaker 1: onto each other. So dark matter stays a big puffy
Speaker 1: halo and the galaxy is sort of embedded in that halo,
Speaker 1: and that's not a coincidence. Right. The reason the galaxy
Speaker 1: exists is because of a big dark matter blob there
Speaker 1: that's gathered together all the hydrogen helium gravitationally and made
Speaker 1: it into a galaxy. It's the reason we have stars, etc.
Speaker 5: Now, when you say halo, you don't actually mean like
Speaker 5: an angel's halo that looks like a ring. You actually
Speaker 5: mean just like a blob, right.
Speaker 1: Yeah, exactly, like a big fuzzy blob that extends out
Speaker 1: further along the disc and then further above and below
Speaker 1: the disc. But even that we know already is not
Speaker 1: evenly distributed.
Speaker 5: Is it like football shaped? Is it kind of flat?
Speaker 5: Or is it a perfect sphere.
Speaker 1: It's more like a hockey puck, right, It's flat, but
Speaker 1: not as flat as the galaxy itself.
Speaker 5: What made it flat?
Speaker 1: Yeah, maybe a hockey puck is the wrong analogy. It's
Speaker 1: not quite that flat. It's more like a big ellipsoid.
Speaker 5: You mean like a slightly squished ball.
Speaker 1: Yeah exactly. It's like a big basketball that somebody's sitting
Speaker 1: on or something.
Speaker 5: All right, Well, let's get a little bit more into
Speaker 5: the details of what we know about dark matter, how
Speaker 5: much of it can we see, how much can we
Speaker 5: discern about what it's doing in our universe? And we'll
Speaker 5: answer the question of whether you can use a quantum
Speaker 5: clock from Amazon dot com to detect it. So we'll
Speaker 5: get to those questions, but first let's take a quick break.
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Speaker 5: All right, we're asking the question can you use quantum
Speaker 5: clocks to deteg dark matter? And we've been recapping a
Speaker 5: little bit about what we know about dark matter, Daniel.
Speaker 5: How much of the details of it can we see?
Speaker 1: Not really very much. We have this sense of a big,
Speaker 1: fuzzy halo that surrounds the galaxy, and we can also
Speaker 1: measure the density as a function of distance from the center.
Speaker 1: So if you're a star, for example, orbiting the center
Speaker 1: of the galaxy, the speed at which you orbit depends
Speaker 1: on the force that's holding you in that orbit. So
Speaker 1: the stronger the force, the faster you can go, or
Speaker 1: the faster you can go, the stronger the force that's
Speaker 1: needed to hold you in that orbit. So by measuring
Speaker 1: the speed of a given star, we can essentially measure
Speaker 1: the mass of all that stuff that's holding on to
Speaker 1: that star. So then if you look at stars at
Speaker 1: different distances from the center, you can basically map out
Speaker 1: the density of stuff in the galaxy as you go
Speaker 1: further and closer to the center of the galaxy.
Speaker 5: Like, if dark matter was super condensed in the middle
Speaker 5: of the galaxy, then the stars in the galaxy we'd
Speaker 5: be rotating a certain way. Or if the dark matter
Speaker 5: was more spread out then the stars in the galaxy
Speaker 5: we'd be rotating in a different way.
Speaker 1: Yeah, exactly, if all the dark matter in the galaxy
Speaker 1: was at the center, then everything would act in a
Speaker 1: certain way, would just go like one over are squared.
Speaker 1: It's sort of like the way the Solar system orbits
Speaker 1: the Sun. But if you take some of that mass
Speaker 1: and you spread it out through the galaxy instead, then
Speaker 1: the dark matter that's further out than a given star
Speaker 1: doesn't affect its orbit because it's gravity all cancels out.
Speaker 1: So that changes the rotation speed of those stars, and
Speaker 1: that's in fact how we first discover dark matter. Was
Speaker 1: by looking at these rotation speeds of stars around the
Speaker 1: center of the galaxy and seeing that we couldn't explain
Speaker 1: it by mapping all the mass from the stars and
Speaker 1: the gas and the dust. And that's exactly how you
Speaker 1: can tell where you need to add more mass to
Speaker 1: explain these rotation speeds. It's not just like, hey, add
Speaker 1: a big blob of the center. You need to add
Speaker 1: some of the center and also some further out and
Speaker 1: some further out, and so precise measurements of those velocities
Speaker 1: give you a fairly accurate picture of where the dark
Speaker 1: matter is in the galaxy. And it's not evenly spread out.
Speaker 1: It's more densely clumped at the center, which is something you'd.
Speaker 5: Expect because it is affected by gravity, right.
Speaker 1: It is, in the end affected by gravity, and so
Speaker 1: it's pulled itself together. And the whole reason that this
Speaker 1: exists is because of some like early universe perturbation where
Speaker 1: you had a denser blob of dark matter that created
Speaker 1: this whole well, gathered together the other dark matter and
Speaker 1: created this over density which then pulled in hydrogen, helium
Speaker 1: and whatever was around to make a galaxy. So it's
Speaker 1: a little bit denser at the center, though it's not
Speaker 1: very well understood, like if we do calculations simulations to
Speaker 1: describe what we think should happen. If you have a
Speaker 1: bunch of dark matter and you give it a few
Speaker 1: billion years to fall together and to form some structure,
Speaker 1: it describes what astronomers call a cusp, which means like
Speaker 1: a point of high density of the center and then
Speaker 1: very steeply falling should like drop off quickly. But if
Speaker 1: you go out and measure the actual distributions of stars velocities,
Speaker 1: you see something that looks like a bigger core. It's
Speaker 1: not like it's pointing near the center. It's more spread
Speaker 1: out in the inner galaxy. It's like flatter, and so
Speaker 1: this is not something we understand very well. And it
Speaker 1: also gives you a sense of like the scale of
Speaker 1: which we can figure this stuff out. We're talking about
Speaker 1: over light years distances, right, We're not resolving dark matter
Speaker 1: in meters or even in aus with very very coarse
Speaker 1: ways to measure where the dark matter is again, because
Speaker 1: its gravity is so weak.
Speaker 5: Are you saying like the beginning of the universe, dark
Speaker 5: matter was more evenly spread out, like you know, all
Speaker 5: those light years of empty space between US and Andromeda
Speaker 5: and other galaxies was all filled with dark matter, and
Speaker 5: then it all colleutes through certain clusters.
Speaker 1: Yeah, it definitely gathered itself together. The early universe had
Speaker 1: initial density fluctuations, and that's a whole big question about
Speaker 1: where exactly that came from. And then those seated gravity
Speaker 1: to pull things together. So gravity does form structure, but
Speaker 1: it takes time. And so yeah, dark matter was more
Speaker 1: spread out and now it's less spread out.
Speaker 5: Why would dark matter stay stuck together?
Speaker 1: Well, it's not that dark matter is sticking together. It's
Speaker 1: not like it's bonded to itself. And again we don't
Speaker 1: really know because we don't have a microscopic picture of
Speaker 1: the dark matter. But I think you're asking, like, why
Speaker 1: does dark matter form even gravitational structures? Like why does
Speaker 1: it get more dense in some places and then in others?
Speaker 1: Is that what you're asking?
Speaker 5: Yeah, Like I'm imagining at the beginning of the universe
Speaker 5: there's a bit of dark matter that was, you know,
Speaker 5: let's say, ten light years away, and then it got
Speaker 5: attracted to our galaxy, so it flew over here. But
Speaker 5: then why didn't just keep flying to the other side.
Speaker 1: Yeah, So as that distant piece of dark matter approaches
Speaker 1: the galaxy, it gains velocity. Right, it's exchanging gravitational potential
Speaker 1: energy for kinetic energy. And then you're imagining like the
Speaker 1: way a ball rolls down a valley, why doesn't it
Speaker 1: roll back up the other side? And it will, yes,
Speaker 1: but then it comes back right, And so gravity in
Speaker 1: the end is organizing something. There's the second piece to that,
Speaker 1: which is that it doesn't completely roll back up the
Speaker 1: other side. You know, anything that's accelerating is emitting gravitational
Speaker 1: radiation for example. So the reason, for example, two black
Speaker 1: holes orbiting each other will eventually spiral in and collapse
Speaker 1: is that they're emitting gravitational energy. So none of these
Speaker 1: things are really stable. So over long periods of time,
Speaker 1: even without inelastic interactions like electromagnetism or whatever, these things
Speaker 1: will form very large structures and they will gradually collapse
Speaker 1: due to gravitational radiation.
Speaker 5: All right, so we kind of have a fuzzy picture
Speaker 5: of where it is in the universe. So now the
Speaker 5: question of the episode is can we use quantum clocks
Speaker 5: to detect dark matter? How do quantum clocks fit into this?
Speaker 1: So quantum clocks might give us a sense for where
Speaker 1: the dark matter is if we can find a place
Speaker 1: where it's like clumpy, if we can find a place
Speaker 1: in our solar system where it's like gathered together for
Speaker 1: some reason. And that would be really cool, because not
Speaker 1: only would it help us detect what dark matter is,
Speaker 1: but it would help us understand where it is. It's
Speaker 1: a really deep mystery. I think, not just because we
Speaker 1: want to understand dark matter, but because we want like
Speaker 1: a map. You know, humans are visual creatures. We want
Speaker 1: to know like where the stuff is, and just not
Speaker 1: knowing where dark matter is in the universe really bugs me.
Speaker 1: So I would love to know where it is, and
Speaker 1: understanding its map on a finer scale would be really helpful.
Speaker 1: And quantum clocks might be able to help us map
Speaker 1: where dark matter is if we can send them out
Speaker 1: into space and if they're sensitive to dark matter, if
Speaker 1: their operation changes as they pass through dark matter.
Speaker 5: Okay, I think you're saying that you know, at the
Speaker 5: galaxy level, we know that it looks like a big blob.
Speaker 5: It's sort of like a switch ball. It's sort of
Speaker 5: more intense or more dense in the center of the galaxy.
Speaker 5: But I think maybe you're saying, can we know in
Speaker 5: finer detail what it looks like between stars within the galaxy,
Speaker 5: like is it clumpy, is it chunky, or is it
Speaker 5: like peanut butter.
Speaker 1: Smooth exactly, And people have tackled this problem in the past,
Speaker 1: Like people use the technique you mentioned gravitation lensing to
Speaker 1: look for blobs of dark matter, and that works, and
Speaker 1: it's powerful, but only if you have like a really
Speaker 1: nice galaxy behind the blob of dark matter that can
Speaker 1: show you that it's there, so that tells us a
Speaker 1: little bit about the dark matter density. But there aren't
Speaker 1: like galaxies in all the right places to like X
Speaker 1: ray the whole Solar system and figure out where it is.
Speaker 1: And that technique isn't always powerful enough. You need like
Speaker 1: a really big blob of dark matter. Another technique people
Speaker 1: have used is to look for dwarf galaxies. Essentially, our
Speaker 1: galaxy is formed by the combination of lots of galaxies, right,
Speaker 1: we think galaxies formed kind of small and then grew
Speaker 1: together with all sorts of absorptions and collisions. That means
Speaker 1: that our galaxy has other like mini galaxies embedded within it.
Speaker 1: Some of these we call dwarf galaxies because they're small,
Speaker 1: and we think they're like very high dark matter density
Speaker 1: therew stars, and so we can look at the motion
Speaker 1: of the stars inside those little galaxies to get sensors
Speaker 1: for like where those blobs are. But we don't have
Speaker 1: a great way to like X ray the Solar System
Speaker 1: and figure out, like where is the dark matter in
Speaker 1: our Solar system? Is it hanging out by Jupiter? Is
Speaker 1: it spread evenly like peanut butter? What's going on?
Speaker 5: You want to know it's distribution at the Solar system
Speaker 5: scale exactly.
Speaker 1: That's what I want to do. And I read a
Speaker 1: recent paper which was very clever, which is looking at
Speaker 1: asteroids and trying to track asteroid trajectories and see if
Speaker 1: like tiny little deviations in the trajectory of asteroids or
Speaker 1: comets as they move through the Solar System could reveal
Speaker 1: the presence of dark matter. It's very difficult to do
Speaker 1: because if dark matter is evenly spread out or only
Speaker 1: a little bit clumpy, that'd be basically no effect on
Speaker 1: those asteroids. But it's the kind of thing that we're
Speaker 1: just on the verge of being able to potentially do
Speaker 1: now that we have better measurements and better computational tools
Speaker 1: to try to like infer this information from really specific measurements.
Speaker 5: All right, So then how would you use a quantum
Speaker 5: clock to deteg dark matter?
Speaker 1: So when we talk about a quantum clock, really what
Speaker 1: we mean is something which is based on fundamental quantum
Speaker 1: mechanical principles. And you know it sounds fancy, but even
Speaker 1: just like an atomic clock, is a quantum clock. An
Speaker 1: atomic clock is something that looks at like the oscillation
Speaker 1: of electron between two energy levels and a caesium atom,
Speaker 1: which is a very precise, very very regular process that
Speaker 1: we can use essentially to tell how time has passed,
Speaker 1: and so on Earth, we have extraordinarily precise atomic clocks
Speaker 1: which now set the standard and in fact define what
Speaker 1: we mean by a second. A second used to have
Speaker 1: a different definition, but now a second is defined as
Speaker 1: like a certain number of cycle of a specific kind
Speaker 1: of atom. That's literally how we measure time now, and
Speaker 1: so it's the standard.
Speaker 5: It's like the minute, like it used to be like
Speaker 5: a minute with sixty seconds, but now people say, oh,
Speaker 5: it's been a minute to really mean something totally different.
Speaker 1: Yes, it's just like that exactly, and we call it
Speaker 1: a quantum clock because this really is a quantum process
Speaker 1: we're talking about quantum particles. There's an electron, there's an atom.
Speaker 1: The electron is moving in the potential well of the atom,
Speaker 1: so it's interacting electromagnetically with the nucleus. And the way
Speaker 1: that it's moving, the way it oscillates between energy levels,
Speaker 1: is completely controlled by quantum processes. This is not a
Speaker 1: clock that you could have in a perfectly classical universe.
Speaker 1: You know, if we lived in a universe where electrons
Speaker 1: really were tiny little balls that went to orbits and
Speaker 1: had smooth classical paths the way planets do, then this
Speaker 1: clock could not exist. And so that's when we meet
Speaker 1: by quantum clock.
Speaker 5: But I guess, if it's a quantum clock, doesn't it
Speaker 5: have a certain amount of uncertainty to it or unknowability?
Speaker 5: How can it be precise if there's the Heisenberg uncertainty principle.
Speaker 1: Yeah, you're right, there's no absolutely precise quantum clock. But
Speaker 1: this is about as regular as it gets. And amazingly,
Speaker 1: these quantum clocks are more precise than mechanical clocks, which
Speaker 1: of course also have uncertainty in them, because no mechanical
Speaker 1: device is perfect created, right, And so this is as
Speaker 1: accurate as they've been able to make them, and recently
Speaker 1: they've been even able to make them small and transportable.
Speaker 1: You might think of an atomic clock as like some
Speaker 1: huge device in the basement of a laboratory in Colorado
Speaker 1: that weighs like ten tons and fills a room. But
Speaker 1: actually these things can be made quite small.
Speaker 5: So a quantum clock is really just an atomic clock
Speaker 5: or is there another kind that doesn't use atoms?
Speaker 1: There's no atomic clock that's not a quantum clock. So
Speaker 1: quantum clock is just a fancier sounding name for atomic clock.
Speaker 5: Yes, can you have a quantum clock that maybe doesn't
Speaker 5: use an atom, that maybe just relies on electrons or
Speaker 5: quarks or something.
Speaker 1: Yeah, sure, you're not limited to atoms. You can imagine
Speaker 1: quantum clocks made out of like photons interacting or splitting
Speaker 1: or bouncing or something like that. In some sense, lego
Speaker 1: is a clock because it's measuring the time for photons
Speaker 1: to travel along its legs, right, it's just converting that
Speaker 1: to a distance measurement. And so you could have other
Speaker 1: quantum clocks that are not based on atoms. Yes, And
Speaker 1: one day, when we discover dark matter, maybe we could
Speaker 1: build a clock out of dark.
Speaker 5: Matter, which may or may not tell you the time.
Speaker 1: And may or may not smell like flatulence.
Speaker 5: Well, I guess maybe give us an example of, like
Speaker 5: what's a typical or popular or a commonly used quantum
Speaker 5: clock and how does it work.
Speaker 1: Well, the most precise quantum clock is based on the
Speaker 1: caesium one thirty three atom. That's the one that's actually
Speaker 1: used to define what a second is. And so here
Speaker 1: we have two states of electrons. There's a small splitting
Speaker 1: in an energy in state here. It's called a hyper
Speaker 1: fine splitting because the difference is very very small, and
Speaker 1: when the electron sits in there, it sort of goes
Speaker 1: back and forth between the two different states.
Speaker 5: Meaning like, this is an electron that's orbiting around the
Speaker 5: caesium atom.
Speaker 1: Yeah, I wouldn't say orbiting if we want to be
Speaker 1: really really technical, But it's captured by the caesium atom.
Speaker 5: And you're saying it's switching energy levels. Why would it
Speaker 5: switch energy levels?
Speaker 1: So you have this caesium atom and you embed the
Speaker 1: whole thing in some microwave radiation that can lift those
Speaker 1: electrons up from the lower state to the higher.
Speaker 5: State, meaning you like put it in a microwave or
Speaker 5: you shoot it with it like a light gun.
Speaker 1: There's not a difference, right, that's what a microwave is.
Speaker 1: A microwave is shooting microwave radiation at your food, and
Speaker 1: microwaves are lights. Though basically a microwave is a light gun.
Speaker 5: Sounds hot. So then you have this atom and you
Speaker 5: you stick it in the microwave.
Speaker 1: Uh huh, yeah, So you stick in the microwave and
Speaker 1: you measure how often it jumps up and then down
Speaker 1: and then up and then.
Speaker 5: Down because the light, as the light passes through it,
Speaker 5: it knocks the electron up and down or what.
Speaker 1: Yeah, the light is tuned to exactly the frequency for
Speaker 1: the electron to jump up into the higher energy level. Remember,
Speaker 1: electrons can go from a lower to a higher energy
Speaker 1: level if a photon of the right energy comes along.
Speaker 1: So they've tuned this microwave to exactly that energy level.
Speaker 1: So electrons and the lower level can absorb these photons
Speaker 1: jump up to the higher level. But then they'll naturally
Speaker 1: decay down because the universe likes to spread energy out
Speaker 1: and so the time of these oscillations turns out to
Speaker 1: be very very regular, Like an electron will do this
Speaker 1: nine point one nine two billion times per second.
Speaker 5: And it doesn't depend on the frequency of the light,
Speaker 5: or it does.
Speaker 1: It definitely depends on the frequency of the light. If
Speaker 1: the frequency of the light is not correct, then it
Speaker 1: won't even absorb it, right, it won't happen.
Speaker 5: Oh, but then don't you need to make that frequency
Speaker 5: super precise?
Speaker 1: Yeah, exactly, And this is one source of uncertainty in
Speaker 1: these clocks, right, making those accurate. And you can measure
Speaker 1: these things, like you build two independent ones, you can
Speaker 1: see how their counts drift relative to each other. And
Speaker 1: that's how you measure the accuracy of clocks. In general.
Speaker 1: There's no absolute standard by which you can tell like, oh,
Speaker 1: this clock is off or that clock is off. You
Speaker 1: just build a few of them and you measure them
Speaker 1: relative to each other. And this is something that we
Speaker 1: know well enough. We know how to design the mean
Speaker 1: of the physics and the engineering that you can build
Speaker 1: these things so that atomic clocks in independent locations agree
Speaker 1: to zero point three nanoseconds per day. It's really very
Speaker 1: incredibly precise.
Speaker 5: WHOA, so what are you measuring? How are you measuring
Speaker 5: whether these electrons are going up and down?
Speaker 1: When the electron goes back down. It emits radiation, right,
Speaker 1: and so you can gather that as well.
Speaker 5: Like it shoots off light like an a blink.
Speaker 1: Basically exactly little flash.
Speaker 5: All right. So then, and you're saying you can build
Speaker 5: these things now to be the size of a toaster
Speaker 5: or a microwave oven.
Speaker 1: A quantum toaster. They have them now and they've deployed
Speaker 1: them out in space. They actually built the Deep Space
Speaker 1: Atomic Clock Mission and they sent an atomic clock out
Speaker 1: into space to see, like, hey, can we operate one
Speaker 1: of these things out in space? And you might wonder
Speaker 1: like is this just a bunch of nerds trying to
Speaker 1: do something that seems cool? Yes, is always the answer.
Speaker 5: Like can we shoot a microwave into space and will
Speaker 5: it still heat up my burrito? My season Burritoah? Is
Speaker 5: that the challenge?
Speaker 1: That's the challenge. But also if we want to do
Speaker 1: things like navigate in space, navigation needs timing. You need
Speaker 1: to know like how long you're going in one direction.
Speaker 1: If you want to do dead reckoning, you want to
Speaker 1: know where you are. Timing is absolutely crucial. Or if
Speaker 1: you want to use like nearby pulsars to triangulate your position,
Speaker 1: I have whole episode about how that works. You also
Speaker 1: need very accurate timing so you can measure the time
Speaker 1: between the pulses. So this was like a technological challenge
Speaker 1: that's going to lay the groundwork for all sorts of
Speaker 1: cool innovations, and this was totally successful in this deep
Speaker 1: space atomic clock mission.
Speaker 5: Well, let's get into how you would actually use these
Speaker 5: and how the timing might tell you where dark matter
Speaker 5: is within our Solar system and maybe even within the Earth.
Speaker 5: So let's dig into that. But first, let's take another
Speaker 5: quick break.
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Speaker 5: All right. We're talking about using a microwave stuck inside
Speaker 5: of a microwave to the tech dark matter so you
Speaker 5: can win a Tierra for being the prettiest scientist.
Speaker 1: Exactly does it take longer to heat up your burrito
Speaker 1: when there's dark matter around?
Speaker 5: So the idea is that you take these atomic or
Speaker 5: basically an atomic clock, which is a quantum clock. But
Speaker 5: it seems like the most popular ones use atoms, and
Speaker 5: so you shrink them down to the size of a
Speaker 5: toaster or microwave, and then you shoot them in space.
Speaker 5: And then how does that help you measure dark matter?
Speaker 1: Well, there were a bunch of physicists who thought, Okay,
Speaker 1: this is cool because now we not only have all
Speaker 1: some super precise atomic clocks, but now we have them
Speaker 1: spread out through the Solar system, like in principle the
Speaker 1: way we like scent devices near the Sun with a
Speaker 1: Parker solar probe. People are like, what if we built
Speaker 1: a bunch of these things and we spread them out
Speaker 1: in the Solar system? Could they give us a picture
Speaker 1: of where the dark matter is in the Solar system?
Speaker 1: If they operate differently when there's dark matter around, like
Speaker 1: if they're sensitive to the dark matter density, Like if
Speaker 1: your atomic clock gets off if it drifts when there's
Speaker 1: more or less dark matter around, than having a bunch
Speaker 1: of these atomic clocks spread out through the Solar system
Speaker 1: could give you a picture for where in the Solar
Speaker 1: System the dark matter is.
Speaker 5: But I guess what's the mechanism by which dark matter
Speaker 5: would affect the timing of these clocks.
Speaker 1: Yeah, so mostly it wouldn't For many theories of dark matter.
Speaker 1: Dark matter is just some whimp. It's a massive particle
Speaker 1: that only interacts gravitationally, and so it has essentially no
Speaker 1: effect on these clocks except for gravitational time dilation. We
Speaker 1: know the areas with greater mass have more curvature, and
Speaker 1: a curvature causes time dilation, but that would be very,
Speaker 1: very difficult to measure even with these quantum clocks.
Speaker 5: But wait, why would it be difficult.
Speaker 1: You can measure gravitational time dilation with quantum clocks, and
Speaker 1: we've done that. You can do it on the surface
Speaker 1: of the Earth, for example, and you can put a
Speaker 1: quantum clock one meter above another one and you can
Speaker 1: see the difference between them because one of them is
Speaker 1: deeper in the curvature than the other. Super duper awesome,
Speaker 1: but that's because the Earth has a huge amount of
Speaker 1: gravity and this significant curvature. Here. Dark matter doesn't contribute
Speaker 1: significantly to the curvature because it's pretty spread out. And
Speaker 1: we would already know if dark matter wasn't pretty spread out,
Speaker 1: because we would have seen deviations and like Jupiter's orbit
Speaker 1: and whatever. So in principle you can, but we don't
Speaker 1: think it's going to be very sensitive. If you had
Speaker 1: a lot of quantum clocks and there were much more sensitive,
Speaker 1: then you could probably detect dark matter local density variations
Speaker 1: using that principle.
Speaker 5: Meaning these clocks would tick at a different frequency depending
Speaker 5: on how close it was to big sources of mass
Speaker 5: or even light sources of mass, because that's just how
Speaker 5: relativity works.
Speaker 1: Yeah, that's how relativity works. Remember, in relativity, it is
Speaker 1: two kinds of time dilation. One is based on speed.
Speaker 1: If you see a clock moving quickly, then you see
Speaker 1: it ticking slowly, and that's very confusing because it's relative,
Speaker 1: and so it depends on two observers. But there's another
Speaker 1: kind of time dilation, gravitational, which is absolute. It just
Speaker 1: says anybody in curature their clock is going to tick slowly,
Speaker 1: no matter who's looking at it, and everybody's going to
Speaker 1: agree about whose clock is ticking slowly. So that's very
Speaker 1: powerful and that's something you can use to measure just
Speaker 1: like how much stuff is there in general, because clocks
Speaker 1: tick slower near stuff. Really kind of awesome feature of.
Speaker 5: The universe, meaning like if I had two of these
Speaker 5: atomic clocks and one of them is out there in
Speaker 5: the middle of empty space, and the other one is
Speaker 5: near a big blob of dark matter. The one near
Speaker 5: the blob of dark matter would take slower.
Speaker 1: Right, Yeah, that's exactly right.
Speaker 5: And so you might like start them out in the
Speaker 5: same spot. But then after being for a while and
Speaker 5: two different spots, one near the dark matter, and you
Speaker 5: brun them back, you would see that one of them
Speaker 5: take more ticks than the other.
Speaker 1: Yeah. And so now imagine like a grid, you have
Speaker 1: a quantum clock every ten meters in the solar system, right,
Speaker 1: you start them all out at the same time, and
Speaker 1: then you monitor it, and by measuring the difference in
Speaker 1: that number of ticks after a year on your reference clock,
Speaker 1: the one that's hanging out with you, you can tell
Speaker 1: where stuff is in the solar system.
Speaker 5: Like which spots in the solar system have slower time.
Speaker 1: Yes, exactly, because slower time means more matter, more curvature,
Speaker 1: more energy density.
Speaker 5: Really, I guess, on top of what you already know
Speaker 5: about the Solar system right like right now, even if
Speaker 5: we didn't have dark matter, a clock near the Sun
Speaker 5: would takes lower than a clock here exactly.
Speaker 1: And we've done some basic version of this, as I
Speaker 1: said earlier, if a few clocks on Earth at different altitudes.
Speaker 1: Those are different distances from the matter of the Earth,
Speaker 1: and the ones closer do ticks more slowly, And satellites
Speaker 1: up in space their clocks tick faster than atomic clocks
Speaker 1: here on the surface of the Earth, And you've got
Speaker 1: to take that new account famously when you're doing GPS,
Speaker 1: et cetera.
Speaker 5: But you're saying, we're not going to be using this effect,
Speaker 5: this time dilation from relativity to measure dark matter. Dark
Speaker 5: matter is just too weak.
Speaker 1: Dark matter is too weak, and we think it's not
Speaker 1: cluppy enough to really detect that, though it would be
Speaker 1: super awesome. There's a special kind of dark matter which
Speaker 1: might give much larger effects, which would be much easier
Speaker 1: to discover. And this is a theory called fuzzy dark matter.
Speaker 5: Sounds fuzzy. But wait, so you're saying, like this idea
Speaker 5: of using atomic clocks to measure dark matter would only
Speaker 5: work for a certain theoretical meaning guessie type of dark matter,
Speaker 5: which we don't know whether it's true or not, or
Speaker 5: exist or not.
Speaker 4: Mm hmmm.
Speaker 5: So this is a huge sources in white scheme that
Speaker 5: you don't really know if it's going to work.
Speaker 1: You know, you were talking about nomenclature and now you're
Speaker 1: using the words guess and scheme, you know, really kind
Speaker 1: of undermine the credibility of science. But you know, this
Speaker 1: is good faith stuff. This is like, hey, what if
Speaker 1: dark matter is this other weird particular thing, how could
Speaker 1: we see that? And yet it'd be best if we
Speaker 1: had experiments which could detect any kind of dark matter,
Speaker 1: But you know, there might be kinds of dark matter
Speaker 1: which we could only detect in certain ways or easier
Speaker 1: to spot in some ways. And so it's good to
Speaker 1: be creative and think about how we could detect specific
Speaker 1: kinds of dark matter as well, even though we don't
Speaker 1: know what dark matter is. And if this theory is at.
Speaker 5: All correct, well, I'm just trying to understand the scheme.
Speaker 5: So are you saying there's a theoretical kind of dark
Speaker 5: matter called fuzzy dark matter? So what is it?
Speaker 4: So?
Speaker 1: Fuzzy dark matter suggests that maybe dark matter isn't very massive,
Speaker 1: like some people suggest that dark matter could be like
Speaker 1: one hundred GeV like the mass of a w or
Speaker 1: a z boson, like one hundred times the mass of
Speaker 1: a proton, a pretty hefty particle, almost as massive as
Speaker 1: a Higgs. That's sort of the classic strategy, and there's
Speaker 1: reasons for that. There's something called the Wimp miracle. Check
Speaker 1: on our podcast about that, which argues strongly that dark
Speaker 1: matter should be around one hundred gv based on how
Speaker 1: much of it there is in the universe. But people
Speaker 1: are like, well, maybe that's all wrong, and there's an
Speaker 1: assumption there that's wrong. What if dark matter is super
Speaker 1: duper light, like a trilliance the mass of an electron.
Speaker 1: So now there's an enormous number of these dark matter particles,
Speaker 1: so many more than you could even imagine, because you
Speaker 1: have to somehow make like a big fraction of the
Speaker 1: mass of the universe out of particles that are a
Speaker 1: tiny fraction in the mass of the electron, which is
Speaker 1: already very very light.
Speaker 5: Well, first of all, I think this whole podcast is
Speaker 5: a Wimp miracle, Daniel. But I think you're saying, like
Speaker 5: this version of dark matter, instead of being maybe marble
Speaker 5: sized particles, they're like super tiny BB sized particles, And
Speaker 5: some of that makes it fuzzier.
Speaker 1: Yeah, it makes it fuzzier because if they're very very
Speaker 1: low mass, then their wavelengths are more spread out. Some
Speaker 1: of these things can have a wavelength like the size
Speaker 1: of the galaxy.
Speaker 5: What do you mean a wavelength.
Speaker 1: The wavelength of a particle is like the distance on
Speaker 1: which these quantum interference effects appear, and so you can
Speaker 1: calculate this quantity. It's called the Debrogely wavelength. You'll see
Speaker 1: wave like effects for a particle when you interact over
Speaker 1: these kinds of distances, and that's the wavelength of a particle.
Speaker 5: Meaning sort of like the size of it.
Speaker 1: Kind of right, sort of, Yeah, it's when it stops
Speaker 1: acting like a blob like a particle and starts acting
Speaker 1: more like a wave. Things that have wavelike behaviors. Really
Speaker 1: it's always acting like a wave. It's just that when
Speaker 1: you zoom out you can approximate it as a particle.
Speaker 5: Because they have low mass. What's the relationship between having
Speaker 5: low mass and being having big wavelengths.
Speaker 1: Well, the wavelength depends on your momentum and your mass.
Speaker 1: So lower mass just means a larger wavelength because it's
Speaker 1: really like a ratio between the momentum and the mass.
Speaker 1: When things have a lot of kinetic energy relative to
Speaker 1: their mass, they act more like light because light is
Speaker 1: pure kinetic energy. Have very small amounts of energy relative
Speaker 1: to their mass their stationary so they act more like
Speaker 1: bits of sand like particles. And so it's just sort
Speaker 1: of a rough way to understand where that transition happens.
Speaker 5: Okay, so then if dark matter is this kind of
Speaker 5: fuzzy kind of dark matter, you're saying that each particle
Speaker 5: would be super super light, and it would also have
Speaker 5: huge variations in their size. That's what you mean by fuzzy.
Speaker 5: It's like they might be some of them might be
Speaker 5: super big and somewhere might be super small.
Speaker 1: Yeah, well, the wavelengths could be very very large, which
Speaker 1: means they can interact over long distances. The fascinating thing
Speaker 1: is that in simulations of this dark matter, it predicts
Speaker 1: like a mini halo of dark matter in our Solar system,
Speaker 1: essentially that this stuff would be clumped up in and
Speaker 1: near the Sun. That most of the dark matter in
Speaker 1: the Solar System might be like clumped up near the Sun.
Speaker 1: It might be like hiding in the Sun.
Speaker 5: And if it wasn't this kind of fuzzy dark matter,
Speaker 5: it wouldn't.
Speaker 1: Now, this kind of fuzzy dark matter is the kind
Speaker 1: we think would clump up like a halo near the Sun.
Speaker 5: And the other kinds wouldn't.
Speaker 1: Yeah, the other kinds wouldn't. As I mean, I've heard
Speaker 1: of other theories of dark matter clumping in the Sun.
Speaker 1: There's all sorts of theories, but this particular one tends
Speaker 1: to make a halo near the Sun and would affect
Speaker 1: the operation of quantum clocks because of its special fuzziness.
Speaker 1: It can also slightly interact with electrons through sort of
Speaker 1: like a back door in quantum mechanics, which would change
Speaker 1: the way a quantum clock operates. It's like it changes
Speaker 1: the electrons' mass and how it responds to photons because
Speaker 1: of oscillations in this fuzzy dark matter field, and so
Speaker 1: effectively it changes the frequency of these clocks. And so
Speaker 1: you can detect in principle whether you're near a dense
Speaker 1: blob of this ultra light dark matter by looking at
Speaker 1: a quantum clock and counting its ticks very carefully. And
Speaker 1: this would be a bigger effect than the effect we
Speaker 1: talked about earlier, the gravitational curvature.
Speaker 5: But I thought that dark matter couldn't interact with regular
Speaker 5: matter only through it could only do it through gravity.
Speaker 1: Yeah, it could only do it through gravity in general,
Speaker 1: But this one takes a back door through the Higgs field.
Speaker 1: It like interacts with the Higgs field and it changes
Speaker 1: how the Higgs field works. And so near the presence
Speaker 1: of this ultra light dark matter, electrons effectively have a
Speaker 1: different mass.
Speaker 5: But I guess if that was true, wouldn't we see
Speaker 5: it affect regular matter on a larger scale.
Speaker 1: You would see it happen, but it's a subtle effect,
Speaker 1: and so you need to be near a dense clump
Speaker 1: of it. So the idea is, take something that's very
Speaker 1: very sensitive to the electron mass, like a quantum clock,
Speaker 1: and try to put it near a dense clump of
Speaker 1: this special ultra light dark matter, maybe near the Sun.
Speaker 1: So that's the idea is, like launch a bunch of
Speaker 1: quantum clocks, have them orbit near the Sun, and look
Speaker 1: for deviations in their timekeeping and see if that's evidence
Speaker 1: for ultra light dark matter interfering with the masses of
Speaker 1: the electrons in these quantum clocks.
Speaker 5: We mean that you would maybe like throw a bunch
Speaker 5: of the sun, have them kind of form a half
Speaker 5: ring around the Sun to see if time changes there,
Speaker 5: sort of like a giant tirra.
Speaker 1: Like a giant tr a quantum cosmic tiara.
Speaker 5: All right, but I guess which one would you be proving.
Speaker 5: Would you be proving that dark matter is fuzzy or
Speaker 5: would you be proved that it's there? Or are they
Speaker 5: both related?
Speaker 1: They're both related.
Speaker 4: Though.
Speaker 1: You know, if we saw this thing, there would instantly
Speaker 1: be like fifty other theories to explain it as well.
Speaker 1: It probably wouldn't be a unique prediction of this kind
Speaker 1: of dark matter. Theories are very very clever people, and
Speaker 1: they'll always come up with another way to explain the
Speaker 1: data that we're seeing. But it's cool because it's a
Speaker 1: prediction that this theory makes and we go out and
Speaker 1: we see it. That's really fascinating, and then we can
Speaker 1: think about ways to distinguish all the different ideas that
Speaker 1: might also explain this kind of observation. It would just
Speaker 1: be cool to see something different. Currently, all of our
Speaker 1: dark matter experiments basically see nothing. It would be cool
Speaker 1: to have a signal somewhere.
Speaker 5: So you're thinking, hey, let's put up a bunch of
Speaker 5: microways in space and see if at sticks exactly.
Speaker 1: Let's see if one burrito is a little bit colder
Speaker 1: than another.
Speaker 5: All right, Well, an interesting idea for how we could
Speaker 5: maybe possibly crack sort of a theoretical version of one
Speaker 5: of the biggest mysteries in the universe.
Speaker 1: That's right. Physicists are being very creative and trying to
Speaker 1: come up with new theories of dark matter and new
Speaker 1: ways to discover them, including using super duper sets in
Speaker 1: and quantum clocks distributed through the solar system, which also
Speaker 1: would just be fun to do.
Speaker 5: You just want to parade, Daniel, I.
Speaker 1: Just want a tiara? Is that too much to ask?
Speaker 5: How about we just buy you a tiara?
Speaker 1: Is it made of dark matter? Are you using your bitcoin?
Speaker 5: It can be, but in any way that you want.
Speaker 5: But if it saves tax dollars billions of dollars, you know,
Speaker 5: it would be a pretty good investment.
Speaker 1: Yeah, there we go. That was my scheme the whole time.
Speaker 5: Yeah, to get us to buy you a tiara without
Speaker 5: actually having to run in a beauty contest.
Speaker 1: I'm busted.
Speaker 5: Well, you are the most beautiful podcaster with a show
Speaker 5: called Daniel Jorge is playing the universe. So whose name
Speaker 5: is Daniels?
Speaker 1: I'll take very highly qualified compliments, thank you.
Speaker 5: It's a very specific tiara based on a very theoretical
Speaker 5: model of the.
Speaker 1: Universe fuzzy compliments from Warhead.
Speaker 5: All right, well, we hope you enjoyed that. Thanks for
Speaker 5: joining us. See you next time.
Speaker 1: For more science and curiosity, come find us on social
Speaker 1: media where we answer questions and post videos. We're on Twitter, Disport, Instant,
Speaker 1: and now TikTok. Thanks for listening and remember that Daniel
Speaker 1: and Jorge Explain the Universe is a production of iHeartRadio.
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