Speaker 1: Hey, Jorge, is it still true that you get a
Speaker 1: lot of your work done late at night? Yeah? Yeah,
Speaker 1: you know, it's a little quieter. Nobody's calling you, nobody's
Speaker 1: bothering you. It's a little easier to, you know, get
Speaker 1: your thoughts in order. So like you do your best
Speaker 1: thinking when it's dark outside. Yes, that's right, it's like
Speaker 1: I have dark energy. Oh my gosh, I think you
Speaker 1: might have just cracked the mystery. Yeah, what do you mean?
Speaker 1: Maybe that's what's causing the universe to accelerate outwards. Cartoonists
Speaker 1: staying up too late? Oh, man, I think you're right.
Speaker 1: The universe just can't handle so many cartoons, so it
Speaker 1: has to grow to fit them all in. You are
Speaker 1: literally blowing it up. Those are some dark thoughts, man,
Speaker 1: I'll have to stay up late thinking about it. I
Speaker 1: am more handmade. Cartoonists and the co author frequently ask
Speaker 1: questions about the universe. Hi, I'm Daniel. I'm a particle
Speaker 1: physicist and a professor at U c Irvine, and I
Speaker 1: always thought of the two of us, I was more
Speaker 1: likely to blow up the universe. Well, you know, I
Speaker 1: blow people's mind. You blow up the physical universe. What
Speaker 1: can I say, it's a team effort. Together, we are
Speaker 1: unstoppable and potentially dangerous, also one of us more so
Speaker 1: than the other. And now we are here to blow
Speaker 1: your minds. Welcome to our podcast Daniel and Jorge Explain
Speaker 1: the Universe, a production of I Heart Radio, in which
Speaker 1: we do try to blow up the entire universe, but
Speaker 1: not to destroy it and make it unlivable, but so
Speaker 1: that we can zoom in and understand it in detail.
Speaker 1: We want to expand the whole universe as we expand
Speaker 1: your mind, so we can stretch it in and see
Speaker 1: right through it. We can mix our metaphors and we
Speaker 1: can pull things apart as we try to explain all
Speaker 1: of the craziness and the incredible universe to you. That's right,
Speaker 1: We try to explode your understanding of the cost moods
Speaker 1: because it is a pretty big and wonderful universe, and
Speaker 1: it's also getting bigger. It's getting bigger every year, and
Speaker 1: it's getting bigger faster every year, which means the size
Speaker 1: of the mystery, the scale of our ignorance is getting
Speaker 1: larger and larger every year. Literally, there is more stuff
Speaker 1: we don't know this year than last year. Yeah, because
Speaker 1: there is literally more universe today than there was yesterday,
Speaker 1: and tomorrow there's going to be even more universe, which
Speaker 1: means that maybe we'll never get to understand all of it. Daniel,
Speaker 1: Can we keep up with such an expanding universe? We
Speaker 1: can't think faster than the speed of light, But the
Speaker 1: universe is expanding faster than the speed of light, which
Speaker 1: I guess makes it hopeless, doesn't it? Why are we
Speaker 1: even doing this podcast? That's right, just give up, Daniel.
Speaker 1: You should become a cartoonist. Is that what giving up means?
Speaker 1: Giving up? Right? You're you know, upgrading. That's right. Stepping
Speaker 1: up to being a cartoon is stepping up, upgrading? Yes,
Speaker 1: that's what you meant to say. No, I think that
Speaker 1: even though it's unlikely we will ever understand everything about
Speaker 1: the universe, it's really all about the friends we make
Speaker 1: along the way, meaning the ideas that we captured, those
Speaker 1: bits of knowledge that we do manage to extract from
Speaker 1: the universe and digest, those moments when we pull back
Speaker 1: a layer of reality and say, oh my gosh, the
Speaker 1: universe is different from what we imagined. And one of
Speaker 1: the greatest of those moments is when we discovered that
Speaker 1: the universe was expanding, and that expansion was accelerating. Yep,
Speaker 1: the universe is just getting started. Apparently it's getting bigger,
Speaker 1: faster and faster each year. But do you think Daniel dead?
Speaker 1: You know, once you figure out the loss of the universe,
Speaker 1: you don't need to see all of the universe. You know,
Speaker 1: it's like you you once you figure out the basic rules,
Speaker 1: it's like you know, and they're done that. That's gonna
Speaker 1: be the title of my next paper. Actually it's called
Speaker 1: you know, They're done that. They're done that. Um No,
Speaker 1: Actually that's the name of a cafe my wife wants open.
Speaker 1: Being there done that. Oh nice. She's also upgrading tour
Speaker 1: from a biologist. She's in favor of everything being related.
Speaker 1: For black beans for dinner, coffee beans with breakfast, chocolate
Speaker 1: beans for dessert. It's a whole being themed, you know,
Speaker 1: being there, done that. But I think that there's never
Speaker 1: a time when we will not learn from seeing more
Speaker 1: of the universe. And the history of physics is saying, oh,
Speaker 1: we think we figured out how things work from the
Speaker 1: studies of this local neighborhood, and then we generalize me extrapoling,
Speaker 1: and we say, well, the rest of the universe probably
Speaker 1: works that way, and every time we go to check
Speaker 1: we find a surprise waiting for us. It turns out
Speaker 1: that what we learned was a special case because we
Speaker 1: were looking at only certain circumstances, only when things were
Speaker 1: really slow, or when things were really cold, or when
Speaker 1: things were really big. And every time we do turn
Speaker 1: over that stone and look at some part of the
Speaker 1: universe we've never seen before, we always do learn something new.
Speaker 1: So I think there'll never be a time when we
Speaker 1: say we're done looking around. Well. I think that's good
Speaker 1: news for this podcast, because that means we'll that we're
Speaker 1: run out of things to talk about. The stable gigsodes
Speaker 1: almost and going strong. In fact, it's it's accelerating. I
Speaker 1: feel like they're accelerating here, derated, which we're making a
Speaker 1: podcast episodes. Man, we should be doing ten a week
Speaker 1: at this point. But it is an expanding universe. It's
Speaker 1: getting bigger each year, and it's getting bigger at a
Speaker 1: faster rate each time. And it's all because of dark energy,
Speaker 1: that mysterious energy that's through's force. It's expanding space itself.
Speaker 1: It's not just making more room, it's growing room in
Speaker 1: the universe. That's right. Dark energy is the name we
Speaker 1: give to the observation that the universe is expanding, and
Speaker 1: that that expansion is somehow accelerating. The key there is
Speaker 1: the somehow. We call it dark energy because dark means
Speaker 1: we are cluelest. We don't understand what's going on. We
Speaker 1: don't even have a good idea for what could be
Speaker 1: doing it. We just have the observation that is happening
Speaker 1: and energy because it takes about two thirds of all
Speaker 1: the energy in the universe to make this happen. So
Speaker 1: dark energy is a good description for what's going on
Speaker 1: because it's also basically everything we know about it. I
Speaker 1: thought it was called dark energy because it doesn't like
Speaker 1: give off light like it we can't see it like
Speaker 1: we know it's there because we can see the universe
Speaker 1: expanding faster and faster, but we like it doesn't like
Speaker 1: give off a glow or doesn't like make sparkles. It
Speaker 1: doesn't you know, look like anything. That's what you call
Speaker 1: it dark, not because we're in the dark about it.
Speaker 1: It would be cool if it made sparkles. I think
Speaker 1: if a cartoonist head designed the universe, there would be
Speaker 1: sparkles or like, you know, action lines or something to
Speaker 1: show the universe is stretching. Right, every time you have
Speaker 1: motion in a cartoon, there's always some visual guide there
Speaker 1: to tip you off. Are you saying that cartoonists should
Speaker 1: be God's Is that what you're saying. I'm saying it's
Speaker 1: pretty clear that God is not a cartoonist. You know,
Speaker 1: conclude from that what you will. Well, maybe God needs
Speaker 1: to upgrade, just like you know, to everyone else. Step
Speaker 1: up there, dude, Yeah, grab a pencil, add some sparkles.
Speaker 1: You know, if the universe is a simulation and the
Speaker 1: engineers listen to our podcast, or if you're in the
Speaker 1: believer of a deity whoever is in charge this universe,
Speaker 1: I hope they do listen to our podcast so that
Speaker 1: they hear about all the questions that we have. But
Speaker 1: that is a name we've given it, the the expansion,
Speaker 1: the accelerating expansion of the universe, dark energy. But and
Speaker 1: it explains why the universe is it growing bigger and
Speaker 1: bigger each year. But it doesn't quite explain how we
Speaker 1: got here, right, You're right, it doesn't explain how we
Speaker 1: got here. Number one, because we don't even really have
Speaker 1: an explanation for how it works. Right, Like, we can
Speaker 1: add some energy to general relativity, and we can use
Speaker 1: that to expand the universe in our models and to
Speaker 1: accelerate that expansion. We can do that, but you know,
Speaker 1: we don't understand where that energy comes from. We have
Speaker 1: like no description of what that means and where it
Speaker 1: comes from and how it works and what its future is.
Speaker 1: And also recently we've discovered that even that picture, that
Speaker 1: simplistic picture that like maybe we just add a number
Speaker 1: to Einstein's theory of general relativity, that also doesn't quite work.
Speaker 1: It doesn't really match the story we see out there
Speaker 1: in the acceleration of the universe. This is growing problem
Speaker 1: with our understanding of how fast the universe is accelerating. Right.
Speaker 1: It's sort of related to the idea that the universe
Speaker 1: is maybe bigger than it should be, even with this
Speaker 1: idea of dark energy put into it. Yeah, like maybe
Speaker 1: the universe is bigger than it should be, or that
Speaker 1: it's not as old as we think it is. All
Speaker 1: these ideas are connected because our whole idea of how
Speaker 1: old the universe is and how vast it is, how
Speaker 1: big the portion of what we can see is depends
Speaker 1: on understanding how quickly it's been expanding. Understand how old
Speaker 1: it is. We unwind this picture, we run the clock
Speaker 1: backwards and see how long does it take to get
Speaker 1: back to the Big Bang singularity. So if our understanding
Speaker 1: of the expansion rate is wrong, that our understanding of
Speaker 1: the whole history of the universe, including its age, could
Speaker 1: be wrong. Yeah, it's a big mystery, which we'll talk
Speaker 1: about later. But there is sort of a concept that
Speaker 1: might explain all of this, and it has a very
Speaker 1: imaginative name. Right. Well, I was wondering, you know what
Speaker 1: a cartoonist called this idea. Well, we wouldn't call it anything.
Speaker 1: We just draw it. Right what it could be called
Speaker 1: sparkly dark energy. Everything should be sparkly sequence dark energy.
Speaker 1: But there is a concept that might explain the expansion
Speaker 1: of the universe in the beginning. And so today on
Speaker 1: the program, we'll be tackling the question what is early
Speaker 1: dark energy? Wait, that's the name, Like, that's the whole concept.
Speaker 1: Just put the word early in front of dark energy.
Speaker 1: That is the whole concept. And you know it's not
Speaker 1: just inspired by cartoonists staying up so late at night
Speaker 1: that it actually becomes early in the morning. I was
Speaker 1: gonna say, I'm more of a fan of late dark energy.
Speaker 1: So when I got an email from you at five am,
Speaker 1: is that when you're staying up super duper late, it
Speaker 1: doesn't cross over into early. It means I scheduled my emails.
Speaker 1: You noticed my emails always coming at five am? Exactly?
Speaker 1: Why would you schedule them for five am? That's still
Speaker 1: a bonkers time to send an email. Why don't you
Speaker 1: schedule them for eight am? Or is that for eight
Speaker 1: am on the East coast or something? You just got it, Yeah,
Speaker 1: eight am in an Eastern time, all right? But the
Speaker 1: question still stands, how late do you have to stay
Speaker 1: up before you count it as early or are you
Speaker 1: saying that no matter how late you stay up, if
Speaker 1: you're still up, it's still late from the day before. Boy,
Speaker 1: these big questions about the universe are just too confusing.
Speaker 1: I'm not sure we have a whole episode here to
Speaker 1: talk about my sleeping habits. I'm sure Aristotle had something
Speaker 1: to say on this deep philosophical question, But that is
Speaker 1: the concept that we're going to be talking about here today,
Speaker 1: this idea of early dark energy. And does that mean, Daniel,
Speaker 1: there's late dark energy. Late dark energy is the dark
Speaker 1: energy we have right now that we look around and
Speaker 1: we see because we are in late times of the universe.
Speaker 1: That doesn't mean that we think the universe is about
Speaker 1: to expire or at the end of its life. It
Speaker 1: just means like recent times of people talk about the
Speaker 1: early universe meaning the very beginning, and the late universe
Speaker 1: meaning right now. I see. So maybe we should be
Speaker 1: it should be called a current dark energy or something
Speaker 1: that's right. But one of the mysteries is how the
Speaker 1: universe accelerated in the very early days. Their disagreement about
Speaker 1: how quickly was accelerating in the very first few moments
Speaker 1: and how quickly it's accelerating now. And to solve those problems,
Speaker 1: people are working on ideas to change how quickly the
Speaker 1: universe was accelerating early on, I see, And will late
Speaker 1: dark energy at some point become early dark energy only
Speaker 1: when you go to bed right only Easter standard time.
Speaker 1: We should call it scheduled dark energy. Right there, you
Speaker 1: go just in time dark energy. But this is a
Speaker 1: new concept, early dark energy, one that physicists are thinking
Speaker 1: about and talking about, and so as usual, we were
Speaker 1: wondering how many people out there had heard of this
Speaker 1: idea of early dark energy. So Daniel went out there
Speaker 1: once again to ask people this question, and I'm eternally
Speaker 1: grateful to our cadre of volunteers to answer these questions
Speaker 1: for us so that we can get a sense for
Speaker 1: what people know and what people are thinking about. If
Speaker 1: you'd like to participate, please don't be shy right to us.
Speaker 1: Two questions at Daniel and Jorge dot com. So think
Speaker 1: about it for a second. What do you think early
Speaker 1: dark energy means? What does it do? Here's what people
Speaker 1: had to say. I am not certain, however, I guess
Speaker 1: that it is similar to the background radiation and that
Speaker 1: that it's sort of residue from the initial dark energy
Speaker 1: or the dark energy that initially expanded the universe. I mean,
Speaker 1: dark energy is probably what's responsible for expanding the universe
Speaker 1: and accelerating the expansion. I don't know what early in
Speaker 1: that context means. Was dark energy different in the early
Speaker 1: state of the universe. I don't know. Um well, as
Speaker 1: far as they know, dark energy has been increasing since
Speaker 1: the beginning of the universe. Maybe this is the dark
Speaker 1: energy that was still around, that was around at the
Speaker 1: very beginning that we might be able to find if
Speaker 1: we look far enough back with gravity or something. Probably
Speaker 1: dark energy is the dark energy from the original Big
Speaker 1: Bang or soon thereafter that it's all around today early
Speaker 1: dark energy. I have no idea what it actually is.
Speaker 1: I'm assuming it's the early stuff that comes to the
Speaker 1: party early, like maybe in the early part of the universe,
Speaker 1: kind of like the cosmic micrtive background. Definitely not my wife,
Speaker 1: that would be the late dark energy. I'm going to
Speaker 1: take a guess that early dark energy is essentially the
Speaker 1: same thing as dark energy now, just earlier in our universe,
Speaker 1: before it was the more dominant of the two between
Speaker 1: it and gravity. Well, I can think a guess that
Speaker 1: it's the dark energy right before the Is that just
Speaker 1: another word for inflation? All right, it's a pretty um
Speaker 1: straightforward I feel like everyone you said, it's it's dark energy,
Speaker 1: but early, except it's not my wife. She's late dark energy.
Speaker 1: That's my favorite answer. Wait, what was that answer from you?
Speaker 1: Because I know you're wife's days of late also working, right,
Speaker 1: that's true. Yes, she is on joge time, that's right,
Speaker 1: or a standard time. She needs to step up and
Speaker 1: become a cartoonist. Yeah, she's just she's just a pencil sketch. Away,
Speaker 1: but most people seem to be related to the early university.
Speaker 1: I guess you know, most people associate dark energy with
Speaker 1: you know, the universe itself and early I guess you know,
Speaker 1: you might think that it's dark energy that was there
Speaker 1: at the beginning of the universe. And it's confusing also
Speaker 1: because we know that there are multiple periods of expansion
Speaker 1: in our history of the universe. Like we talked about
Speaker 1: dark energy, which has been dominating the expansion of the
Speaker 1: universe for the last five billion years, although it's been around,
Speaker 1: is part of the mix since the very beginning, it's
Speaker 1: just sort of only taken over in the last five
Speaker 1: billion years. But we've also talked many times on the
Speaker 1: podcast about inflation, which is another period of rapid expansion
Speaker 1: in the universe in the first ten to the minus
Speaker 1: thirty seconds of the history of the universe. And as
Speaker 1: we said several times, we don't know if those are
Speaker 1: connect that are those different mechanisms for rapid expansion of
Speaker 1: the universe. Are they related somehow? We don't know, And
Speaker 1: so it's fair to try to lump these periods of
Speaker 1: expansion together and say, like, oh, maybe early dark energy,
Speaker 1: just inflation. That makes a lot of sense. It's kind
Speaker 1: of weird to think that the universe had basically growth spurts,
Speaker 1: right like you might think that a cold, random universe
Speaker 1: which is grow at a steady rate. But somehow the
Speaker 1: universe has had these like periods of expansion and slowing
Speaker 1: down too. And one of the key things to understand
Speaker 1: is that as the universe expands, the mixture that it
Speaker 1: has of matter and radiation and dark energy, that mixture
Speaker 1: changes as it expands, because, for example, as the universe expands,
Speaker 1: matter gets dilute. You have a certain number of particles
Speaker 1: in a box, and you make that box bigger than
Speaker 1: the density goes down. But that dilution is different for
Speaker 1: matter than it is for radiation, for example light. If
Speaker 1: you expand the box and stretch the space, light also
Speaker 1: loses energy because it gets red shifted. So radiation gets
Speaker 1: diluted more quickly, whereas dark energy doesn't get diluted at all.
Speaker 1: As you make more space and expand the box, you
Speaker 1: have the same amount of dark energy per unit space,
Speaker 1: and so the dark energy fraction of the whole universe
Speaker 1: goes up. So as the universe expands, these fractions change,
Speaker 1: and then that changes how the universe responds, and so
Speaker 1: it's this very dynamical system. Right, it's not just like
Speaker 1: the steady state thing hanging out because it's expanding. That
Speaker 1: expansion then changes how it expands. Yeah, that's wild. And
Speaker 1: it's well to think that the universe has things that
Speaker 1: it you know, conserves and keeps the same, and there's
Speaker 1: has things that keep growing, you know what I mean,
Speaker 1: Like matter seems to be constant and it's not increasing,
Speaker 1: but space needs to be, you know, growing out of
Speaker 1: the woodwork. Yeah, it's growing out of the universe work exactly.
Speaker 1: And as the universe expands, dark energy takes over and
Speaker 1: it makes it expand faster. And that's the source of
Speaker 1: this acceleration, which is crazy because it suggests the future
Speaker 1: is all dark energy dominated. Once dark energy is sort
Speaker 1: of in charge, it basically never let's go as far
Speaker 1: as we understand. And so it might be that the
Speaker 1: periods of the universe where matter we're in charge, or
Speaker 1: radiation were in charge, we're just like the first blips,
Speaker 1: you know, the first few moments of like a trillion
Speaker 1: year history. Right, the future is all cartoonists. You should
Speaker 1: join us now. It is inevitable, I see before it
Speaker 1: gets cool right as the universe gets colder and colder.
Speaker 1: But anyways, this idea of early dark energy is really interesting,
Speaker 1: and so let's break it down for people who are
Speaker 1: not familiar with this concept of even dark energy. So, Daniel,
Speaker 1: what is the regular dark energy? So the regular dark
Speaker 1: energy is a name we give to something shocking that
Speaker 1: we discovered about twenty years ago. Now, remember that, like
Speaker 1: only a hundred years ago, we discovered that there are
Speaker 1: other galaxies out there in the universe and that they
Speaker 1: are moving away from us, that the universe is expanding.
Speaker 1: This was sort of a big deal when it was
Speaker 1: discovered in like, you know, Einstein's universe that he imagined
Speaker 1: in general relativity was a static universe, no expansion, no acceleration.
Speaker 1: So the Hubble discovered that, oh, the universe is expanding.
Speaker 1: Things are floating out there. But people thought, okay, well,
Speaker 1: the universe is expanding, but probably it's gonna pull back.
Speaker 1: Probably gravity is going to be strong enough to pull
Speaker 1: everything back together and maybe make a big crunch. Or
Speaker 1: if not, then things are gonna gradually slow down due
Speaker 1: to gravity as they drift away from each other. So
Speaker 1: the question until twenty years ago was how quickly is
Speaker 1: the universe decelerating? How quickly are things slowing down? And
Speaker 1: then they went out and measured this, because, as we
Speaker 1: talked about earlier, you always got to go out and
Speaker 1: see what's really going on in the universe. And they
Speaker 1: discovered by looking at how far away stars were and
Speaker 1: looking back into the past to see how quickly they
Speaker 1: were moving away from us a long time ago, that
Speaker 1: the universe wasn't slowing down at all, that this expansion
Speaker 1: was in fact accelerating, that every year things were moving
Speaker 1: away from us faster and faster. So this blew everybody's minds.
Speaker 1: They're like, oh my gosh, not only is the universe expanding,
Speaker 1: but it's accelerating. What could be doing? And so they
Speaker 1: replaced that big question mark with a fancy phrase called
Speaker 1: dark energy, and that's about where we are today. Dark
Speaker 1: energy is just the name for this discovery for which
Speaker 1: we have no real explanation, right because without that observation,
Speaker 1: I mean, like you said, we would expect the universe
Speaker 1: to crunch back down again, right because gravity sort of
Speaker 1: doesn't give up, Like, even if things are super far away,
Speaker 1: they're still being pulled a little bit by gravity. And
Speaker 1: so eventually that acceleration that floors should bring everything back
Speaker 1: together into a little tiny dot. Right. It depends a
Speaker 1: little bit on the balance between gravity and the initial velocity.
Speaker 1: It's possible, because gravity gets weaker as distance grows, that
Speaker 1: we could have lived in the universe with no dark energy,
Speaker 1: that didn't crunch back down together, that just spread out forever,
Speaker 1: if there was sort of enough initial energy, just in
Speaker 1: the same way that you can, for example, throw a
Speaker 1: ball off the surface of the Earth at high enough
Speaker 1: velocity that it never ever comes back, even in the
Speaker 1: infinite future, has enough energy to escape Earth's potential. Well,
Speaker 1: so it was possible that things expanded out forever. But
Speaker 1: until we discovered dark energy, we never imagined that it
Speaker 1: could actually be accelerating outward, that things could be stretched out,
Speaker 1: that new space could be being made between those galaxies. Right,
Speaker 1: And so you gave that acceleration of the expanding universe
Speaker 1: that's expanding faster and faster. You give it the name
Speaker 1: dark energy because it must be some kind of energy, right,
Speaker 1: because you don't know what else it could be. We
Speaker 1: don't know what else this could be. One sort of
Speaker 1: category of explanations is something we call the cosmological constant.
Speaker 1: And this is just like a number that you stick
Speaker 1: into Einstein's general relativity equations and it reflects some sort
Speaker 1: of like potential energy of the universe. Remember we talked
Speaker 1: to the podcast about how the space is filled with
Speaker 1: quantum fields, right, all of space has fields, and it
Speaker 1: fields for the electrons, fields for photons, feels for all
Speaker 1: the different kinds of particles. And these fields can do
Speaker 1: different things. They can wiggle, which is like having kinetic
Speaker 1: energy the way like a ball rolling down the hill
Speaker 1: has kinnectic or g But the fields can also have
Speaker 1: potential energy energy stored in them because of their configuration,
Speaker 1: like a ball sitting at the top of a hill
Speaker 1: that isn't yet moving really fast. So if you have
Speaker 1: a field with a lot of potential energy, that creates
Speaker 1: this outward pressure due to this cosmological constant that comes
Speaker 1: from that field. And so we sort of like stuck
Speaker 1: this number into Einstein's theory and we gave it the
Speaker 1: right number to explain the expansion that we see. But
Speaker 1: we can't explain that number. It's just like, well, here's
Speaker 1: a number, we measured it. We don't know why it
Speaker 1: is that number or what field could be generating this
Speaker 1: potential energy. It's still a really big mystery, and I
Speaker 1: feel like that's kind of the reason you gave it
Speaker 1: a name, right, It was was sort of because it
Speaker 1: is sort of a term in your equations of the universe,
Speaker 1: in Einstein's equations, Right, like my kids are growing faster
Speaker 1: and faster, but I don't give a name to the
Speaker 1: idea or the phenomenon of them growing faster and faster.
Speaker 1: Or like if the universe he saw that it was
Speaker 1: growing faster and faster, you might just say, oh, the
Speaker 1: universe is growing faster and faster. But because you have
Speaker 1: these equations and you have you have like an actual
Speaker 1: term that kind of describes that or explain this expansion.
Speaker 1: You give it a name, and we can also calculate
Speaker 1: how much energy is necessary for this to happen, Like
Speaker 1: you find the number you have to put into Einstein's
Speaker 1: equation to explain this, and then you can calculate what
Speaker 1: sort of energy density is required in space to cause
Speaker 1: that term. Right, this cosmological constant isn't just like an
Speaker 1: abstract idea. It reflects like some potential energy stored in
Speaker 1: space itself, and then we can calculate that energy we
Speaker 1: can compare to other things and we find that, Wow,
Speaker 1: this potential energy is more than all of the energy
Speaker 1: stored in all the stars and the galaxies and the
Speaker 1: dust and all of the dark matter and all of
Speaker 1: the stuff we see in the universe. It's like more
Speaker 1: than twice as much energy as everything else in the universe.
Speaker 1: So it's a huge quantity. It's a big part of
Speaker 1: the recipe of the universe, right, And it's sort of
Speaker 1: energy because I mean, it's one thing to grow space,
Speaker 1: but it's also another thing to like push the things
Speaker 1: along that are in space. Right, Like if I was
Speaker 1: growing my house, they can just grow the house, it
Speaker 1: would also have to like move the beds on the
Speaker 1: table everything out further out towards the walls more, right,
Speaker 1: And so that that takes energy, right, It takes energy. Yeah,
Speaker 1: And what this means is that space has energy in
Speaker 1: it like this stuff because it's part of the potential
Speaker 1: energy of space itself. It doesn't get diluted when you
Speaker 1: make new space. When you stretch out the space between
Speaker 1: two galaxies, then you're creating more dark energy because you
Speaker 1: are creating more space. So it's really weird and counterintuitive.
Speaker 1: You know. It means that like energy is creating more energy.
Speaker 1: And for those of you who worry about, like, well
Speaker 1: where does this energy come from? Right, Like, how can
Speaker 1: you just do that? Doesn't that violate conservation of energy? Yes,
Speaker 1: and biolate it's conservation of energy, which it turns out,
Speaker 1: is not a deep and fundamental principle of the universe.
Speaker 1: Only a fundamental principle of universe is where space is static,
Speaker 1: where the rules are not changing as a function of time.
Speaker 1: But we don't seem to live in that kind of universe.
Speaker 1: We live in the universe where the space is changing
Speaker 1: and so energy is not served. It just like appears
Speaker 1: seemingly out of nowhere, right, But I feel like that's
Speaker 1: only true if you assume that dark energy is sort
Speaker 1: of inherent to space, you know what I mean? Like
Speaker 1: the dark energy also be you know, the result of
Speaker 1: something already in space or something that that is limited.
Speaker 1: A dark energy could be a lot of things. But
Speaker 1: what we do know is that it doesn't get diluted
Speaker 1: as space expands, so you can come up with something
Speaker 1: else that also has that property. The only thing we
Speaker 1: know about is vacuum energy is the potential energy that's
Speaker 1: the only thing that doesn't get diluted as space expand.
Speaker 1: Matter and radiation, those kind of things, they do get
Speaker 1: diluted as space expands. But then again, we don't really
Speaker 1: know what space is, right, and so maybe we need
Speaker 1: a whole new concept for how space works and what
Speaker 1: it means. Right. That's kind of what I mean is that,
Speaker 1: you know, you don't know where it's coming from, and
Speaker 1: like you said, it's changed over the years since the
Speaker 1: beginning of the universe. So even that statement that it
Speaker 1: is sort of inherent to space, we don't really quite
Speaker 1: know for sure, right, We definitely do not know for sure.
Speaker 1: We're in the part to this investigation where we're trying
Speaker 1: to just like build a general structure of an idea
Speaker 1: and ask, like what shape does this idea have to take?
Speaker 1: What can we fit into it? And we start with
Speaker 1: what we think are the simplest ideas. You know, maybe
Speaker 1: it's like this, maybe it's like that, and if that works, great,
Speaker 1: and if it doesn't work, then we need to add
Speaker 1: bells and whistles or come up with new ideas. We're
Speaker 1: definitely in the very early days. Yeah, and even though
Speaker 1: we are still only I guess inventing the general shape
Speaker 1: of the general idea. There are some problems with this
Speaker 1: general idea, ones that have to do with the beginning
Speaker 1: of the universe, and so let's get into what is
Speaker 1: the problem with dark energy, But first let's take a
Speaker 1: quick break. All right, we're talking about dark energy, and
Speaker 1: I guess there's a problem with dark energy. I mean,
Speaker 1: it's not just making the universe bigger and bigger, faster
Speaker 1: and faster, which eventually lead to the heat death of
Speaker 1: the universe, the universe dying out of basically order. There's
Speaker 1: also some problems with it being able to explain the
Speaker 1: early universe exactly. What we've tried so far is saying
Speaker 1: maybe that there's just a number we can stick in
Speaker 1: Einstein's equation, that like every unit of space has a
Speaker 1: certain amount of dark energy. And there's a few different
Speaker 1: things going on here that it's important to sort of unravel.
Speaker 1: One is that, like, we assume that dark energy is constant,
Speaker 1: but when we say constant, we mean like any chunk
Speaker 1: of space has the same amount of this dark energy,
Speaker 1: this potential energy, this cosmological constant. But as the universe expands,
Speaker 1: even if every chunk of space has the same amount
Speaker 1: of dark energy. Dark energy is fraction of the universe
Speaker 1: itself is growing, right, because everything else gets diluted away.
Speaker 1: So the dark energy fraction of the universe we don't
Speaker 1: think is constant dark energy. We thought maybe was constant
Speaker 1: like per chunk of space. That's what the cosmological constant is.
Speaker 1: That was the basic idea, like had a fixed amount
Speaker 1: of dark energy per unit of space, and then see
Speaker 1: if that evolves the universe through time in the way
Speaker 1: that we see it actually happening out there, right, And
Speaker 1: what you found is that it doesn't write like a
Speaker 1: number you have just taken now to the equation to
Speaker 1: explain the current acceleration of the expansion of the universe works.
Speaker 1: But then if you you know, you look back in time,
Speaker 1: that number doesn't work exactly. A cosmological constant doesn't quite
Speaker 1: describe the history that we see. And we can measure
Speaker 1: this in two different ways. We have late time measurements
Speaker 1: and we have early time measurements, and they don't quite agree.
Speaker 1: So the late time measurements are like, let's go out
Speaker 1: and measure the expansion of the universe. How fast are
Speaker 1: things moving and how fast are they accelerating? And these
Speaker 1: are the famous discoveries of dark energy, you know, for example,
Speaker 1: looking at type one A supernova, that kind of stuff.
Speaker 1: We can also look at the very very early universe
Speaker 1: and trying to measure how much dark energy was there
Speaker 1: back then, measure that using like the cosmic microwave background radiation.
Speaker 1: We measure that, and then we plug that into our
Speaker 1: simulations and try to predict how much acceleration there was
Speaker 1: and how fast things should be moving today. And those
Speaker 1: two numbers don't agree, right, and so there's some sort
Speaker 1: of mismatch there, Like there doesn't seem to be enough
Speaker 1: dark energy in the early universe to get us going
Speaker 1: as fast as we seem to be going today. I
Speaker 1: feel like there's two things, and maybe people are getting confused.
Speaker 1: So like, right now the universe is expanding at a
Speaker 1: velocity that's faster than it used to be. That's for sure,
Speaker 1: like the universe expanding faster than it used to expand before.
Speaker 1: But you can also talk about the acceleration of the universe,
Speaker 1: which is the idea that it's growing faster and faster
Speaker 1: each year. And so I think you're saying that even
Speaker 1: the acceleration now is faster than it used to be,
Speaker 1: Like the universe is somehow hitting the gas pedal even harder. Today.
Speaker 1: What we do is we measure this thing called the
Speaker 1: Hubble constant, you know, which is terribly named because it's
Speaker 1: not a constant. It's a measure of how fast the
Speaker 1: universe is expanding. And we can measure it like in
Speaker 1: recent times, because we can look in our neighborhood and
Speaker 1: see like how fast is stuff looking away from us?
Speaker 1: How fast was stuff moving away from us pretty recently.
Speaker 1: We can use that to measure this Hubble constant, which
Speaker 1: is like the derivative of the scale factor of the
Speaker 1: universe normalized to itself. And so that's like a measure
Speaker 1: of the expansion rate. And what we can do in
Speaker 1: the early universe is we can measure like how much
Speaker 1: dark energy was there. We can use that to predict
Speaker 1: the acceleration of the universe, which should give us like
Speaker 1: the velocity. It's sort of like saying, all right, you
Speaker 1: started your car, you were pressing on the gas pedal
Speaker 1: a certain amount, how fast should you be going after
Speaker 1: a minute? And if the rate we're measuring, like how
Speaker 1: faster car is going right now is too fast, and
Speaker 1: we're like, maybe you were pressing the gas pedal faster
Speaker 1: than you thought. You were right, right, But I wonder
Speaker 1: if maybe the folks are getting confused with because there
Speaker 1: there's also the idea in the early universe of inflation,
Speaker 1: right and the Big Bang? Now was inflation and the
Speaker 1: Big bank also due to dark energy? Or was it
Speaker 1: you know, that super rapid expansion like a second after
Speaker 1: the Uni verse was born, the universe expanded like tang
Speaker 1: to the twenties something or crazy amount. Was that also
Speaker 1: due to dark energy? Or was that something due to
Speaker 1: something else? Entirely, we just really don't know. We know
Speaker 1: that there are similar right. They both expand space very rapidly.
Speaker 1: We don't know if they're connected. There are some theories
Speaker 1: of inflation that try to connect dark energy with inflation,
Speaker 1: but there's some theories of inflation that are totally separate
Speaker 1: that say, no, it's due to this weird inflaton field
Speaker 1: that has its own potential energy which rapidly expanded space,
Speaker 1: and so we just don't know. We do notice that
Speaker 1: they are similar, right, But these questions about dark energy
Speaker 1: assume just inflation happened, and like, don't ask too many
Speaker 1: questions about it. Let's just start from the post inflation
Speaker 1: universe and try to understand the expansion history from that point. Oh,
Speaker 1: I see, when you're talking about early dark energy, you
Speaker 1: mean like post inflation dark energy exactly, not that early
Speaker 1: that I mean, not pre early, late earlier. That's right,
Speaker 1: because the early this thing that we can actually measure
Speaker 1: comes from about four thousand years after the beginning of
Speaker 1: the universe. This is the cosmic microwave background radiation. And
Speaker 1: we can look at these wiggles in the microwave spectrum
Speaker 1: in the sky, which is light from that very early plasma,
Speaker 1: and we can get a sense from what was going
Speaker 1: on back then, and so that gives us actually a
Speaker 1: measurement of how much dark energy there was back then,
Speaker 1: which let's just calculate the acceleration from that point, not
Speaker 1: all the way back to inflation. Like that's a murky
Speaker 1: mystery for another day, right, But wouldn't that sort of
Speaker 1: confuse things like at what point do you think this
Speaker 1: potential infloton field or whatever it is that costs a
Speaker 1: big bang or the inflation you know, drop off and
Speaker 1: gave way to dark energy, Like couldn't there have been overlapped?
Speaker 1: How do you know? Like what cause inflation isn't like
Speaker 1: affecting us today. Yeah, we don't write it could be connected.
Speaker 1: The basic ideas are the same. That you have some
Speaker 1: field with a lot of potential energy, you put that
Speaker 1: into Einstein's equations. It causes this repulsive effect on the
Speaker 1: universe to stretch it and expand. It could be that
Speaker 1: inflation has a different kind of potential energy from a
Speaker 1: different field, this in photon field, or it could be related. Also,
Speaker 1: we don't understand either of them. We don't understand why
Speaker 1: inflation happened. We don't understand why it stopped. We don't
Speaker 1: understand if it did in fact stop, or if dark
Speaker 1: energy is an extension of it. Yeah, we're clueless about
Speaker 1: all that stuff. So basically we don't know anything. Daniel.
Speaker 1: We're in the dark about the whole dark energy thing.
Speaker 1: We're mostly in the dark. Until very recently, though, it
Speaker 1: seemed like if you assume that there was a fixed
Speaker 1: amount of dark energy after inflation, after somehow the in
Speaker 1: photon field died away or whatever, that if you assume
Speaker 1: there was a fixed amount of dark energy, that it
Speaker 1: mostly described the universe like our rough calculations and early
Speaker 1: measurements suggested things were banging on that the measurements we
Speaker 1: had of this cosmic microwave background radiation told us a
Speaker 1: certain amount of dark energy. You put that into the
Speaker 1: equations and ran them forward in time. You've got a
Speaker 1: universe that looked a lot like the one we see
Speaker 1: out there right now. But as these measurements got more
Speaker 1: and more precise than a problem emerged and they didn't
Speaker 1: quite work. Oh, I see, all right, So I'm trying
Speaker 1: to put my head in the place of a physicist.
Speaker 1: So you're saying that the Big Bang happened, inflation happened, done,
Speaker 1: like we're going to put a market there and ignore
Speaker 1: everything that happened before. Like after information, we're going to
Speaker 1: reset our thinking. We're going to assume that there's something
Speaker 1: called dark energy that's continuing to keep the universe expanding
Speaker 1: at a faster rate. And you're saying that before we
Speaker 1: used to be able to just plug one number in
Speaker 1: and it sort of worked like it it mostly described things,
Speaker 1: But now now it doesn't quite work. Now it doesn't
Speaker 1: quite work exactly. Now the universe seems to be expanding
Speaker 1: at late times more quickly than we can explain with
Speaker 1: the amount of dark energy that we measure from the
Speaker 1: early times. Like whoever was driving the universe back then
Speaker 1: with dark energy, they put their foot on the gas
Speaker 1: pedal at a certain level. But now when we look
Speaker 1: at the speed of the universe, it seems to be
Speaker 1: going faster than can be explained by that amount of gas.
Speaker 1: So that's the question. Is the cosmological constant actually a
Speaker 1: constant or do we need to make it more complicated?
Speaker 1: Right that number used to plug in that used to
Speaker 1: work before now doesn't work before, which means that basically
Speaker 1: it's not a number. Kind of yeah, now it's a function.
Speaker 1: Right now we need a new little bit, meaning like
Speaker 1: the amount of dark energy per block of space is
Speaker 1: or it has been changing. That's the question exactly, And
Speaker 1: so early dark energy is an attempt to try to
Speaker 1: fix this problem is to say, well, maybe there's dark energy,
Speaker 1: which is just a number and it's constant. But now
Speaker 1: let's add a new thing. Let's not just change dark energy.
Speaker 1: Let's add a new kind of expansion to the universe,
Speaker 1: like a new unexplained expansion that's going to only take
Speaker 1: place in the early universe, Like there was dark energy,
Speaker 1: which is accelerating the expansion the universe. Plus let's add
Speaker 1: a new bit which only turned on an early universe,
Speaker 1: got things going extra fast, and then disappeared, which is
Speaker 1: why we don't see it today. So that's the idea
Speaker 1: of early dark energy, is to try to like patch
Speaker 1: up this problem with dark energy, not by saying dark
Speaker 1: energy changes with time, but by saying there was a
Speaker 1: new thing, yet another way to expanding universe, but this
Speaker 1: one only lasted from like zero to four years after
Speaker 1: the Big Bang? Oh? I see wait? So um, so
Speaker 1: you I think you're saying that early dark energy is
Speaker 1: not dark energy. So early dark energy is not dark
Speaker 1: energy exactly. It's a new thing that is like dark
Speaker 1: energy and also kind of like inflation, right, and that
Speaker 1: it expands the universe due to some potential energy field,
Speaker 1: but it's somehow also disappeared before the CNB, right, so
Speaker 1: that it doesn't like mess up everything we see later. Right.
Speaker 1: I guess an early hooge would be so foreign to
Speaker 1: regular hooge that you would have to call it a
Speaker 1: different whoree. I think that's what you're thinking, is a physicist,
Speaker 1: what gives the sense of the scale here? How different
Speaker 1: is this post inflation, post Big Bang dark energy expansion
Speaker 1: than the expansion we have now due to dark energy.
Speaker 1: It's turned out to be pretty significant. You know, early
Speaker 1: on when we were measuring these things for the first time,
Speaker 1: we really didn't know how fast the universe was expanding,
Speaker 1: and we had big error bars on all of our measurements,
Speaker 1: and so things seemed to kind of disagree a little bit,
Speaker 1: but nobody was worried about it. Now these measurements have
Speaker 1: gotten really really precise, and the difference between the predictions
Speaker 1: for how fast we are expanding and how fast we
Speaker 1: should be expanding if dark energy was constant and there
Speaker 1: was no early dark energy are different by about ten
Speaker 1: per cent. So this is measurements of the Hubble constant,
Speaker 1: and like the late measurements, the ones using like supernova
Speaker 1: and sephids and other kinds of stuff, they measured this
Speaker 1: Hubble constant to be about seventy three, where the units
Speaker 1: are kilometers per second per mega PARSEEK and the early ones,
Speaker 1: the ones that come from the CNB where we measure
Speaker 1: what was going on in the early universe, how much
Speaker 1: dark energy there was, and then predict how fast we
Speaker 1: should be accelerating. They predict sixty seven, So that's seventy
Speaker 1: three versus sixty seven, and the uncertainties are getting pretty
Speaker 1: pretty small, Like, these are precise measurements now. The Plank
Speaker 1: satellite gave us really precise measurements of the CMB, and
Speaker 1: we have lots and lots of supernova now and lots
Speaker 1: of other kind of ways to measure the leration today.
Speaker 1: So the difference between these two has become pretty significant.
Speaker 1: It's like five or six sigma, which means that it's like,
Speaker 1: doesn't seem to be just a statistical error. It seems
Speaker 1: like it might be real. Well, it's it's it's ten
Speaker 1: percent different, but you're saying that your confidence in that
Speaker 1: ten percent difference is getting stronger. Exactly. People were sort
Speaker 1: of thinking like, okay, these numbers are far apart, but
Speaker 1: the errors are big. And then as we get more
Speaker 1: and more data, sometimes what happens is that the things
Speaker 1: sort of drift together. You're like, oh, two measurements of
Speaker 1: the same thing using different ways as they get more precise,
Speaker 1: if you're really measuring the same thing, they should eventually
Speaker 1: agree and if you've understood all of your uncertainties and biases.
Speaker 1: But these two things, as they've gotten more precise, have
Speaker 1: stayed far apart. And so now yeah, they seem to
Speaker 1: be far apart, and the confidence in both measurements is
Speaker 1: pretty high. All right, So there's about a ten percent
Speaker 1: difference in what we thought was the universe's expansion and
Speaker 1: what it actually was before. And so just regular dark
Speaker 1: energy on time late dark energy doesn't planet, and so
Speaker 1: you need this concept of early dark energy. Early dark
Speaker 1: energy is sort of in the same spirit of dark energy.
Speaker 1: It's like, hold on the universe seems to be doing
Speaker 1: something we can't explain. Let's just add another piece to
Speaker 1: the mix and see if we can use that to
Speaker 1: explain what's going on. Later we'll come in and figure
Speaker 1: out why is this thing here, how does it work,
Speaker 1: what exactly is creating this dark energy. The first step
Speaker 1: is just like, you know, rough out an idea for
Speaker 1: what pieces you need at what time to explain the
Speaker 1: history that we see right right. Basically, it's sort of
Speaker 1: like admitting that dark energy is changing. Right Like, the
Speaker 1: original idea for dark energy was that it was some
Speaker 1: sort of like constant inherent property of space and never changes.
Speaker 1: But now you're sort of being forced to say, hey,
Speaker 1: dark energy kind of is changing, So maybe it's not
Speaker 1: some constant of the universem inherent property of space. Maybe
Speaker 1: it's there are multiple dark energies, or maybe it's the
Speaker 1: dark energy that's changing, yes, exactly. And there's a whole
Speaker 1: category of ideas there. There's ones where there's multiple dark energies,
Speaker 1: like a new one that appears early in the universe
Speaker 1: and then disappears, right, which is why we don't seem
Speaker 1: to see it today. Others where dark energy itself changes
Speaker 1: and then stabilizes to a certain number and then is
Speaker 1: fixed for the rest of the time of the universe.
Speaker 1: There's a whole ridiculous spectrum of ideas. A lot of
Speaker 1: particle theories I talked to say that most of them
Speaker 1: are kind of ridiculous. They call them theoretical shenanigans. But
Speaker 1: you know, it's just an effort to like try to
Speaker 1: cook up a recipe that explains what we see and
Speaker 1: then later figure out the details of that recipe right, right,
Speaker 1: And in the meantime, let's confuse everybody with shortcuts here
Speaker 1: to call things. Why not just call it dark shenanigans.
Speaker 1: That would be valid. Oh man, that would have been awesome.
Speaker 1: I would love if we had called it dark cinnanigans.
Speaker 1: That's right, DS for because I have dark matter, dark energy,
Speaker 1: and dark shenanigans. That seems like a really nice trifecta.
Speaker 1: Sounds like what all physicists, and you know, the theorists
Speaker 1: are going crazy with these ideas because every time you
Speaker 1: give them an opening to be creative, then they come
Speaker 1: up with all sort of silly ideas for like what
Speaker 1: might be creating this. Lisa Randall, who's a famous theorist
Speaker 1: who came up with the idea of extra dimensions. She
Speaker 1: has a paper about rock and roll solutions to the
Speaker 1: early universe that involves like new weird fields in space,
Speaker 1: some of which rock back and forth to explain like
Speaker 1: why they disappear, and some of them would you like,
Speaker 1: roll away gradually and fade out before we could see them. Mhm.
Speaker 1: So she called them rock and roll solutions literally in
Speaker 1: her paper exactly. Her paper really is called rock and
Speaker 1: Roll Solutions. It's pretty fun paper, but it's definitely in
Speaker 1: the theoretical shenanigans category. Yeah, because I guess you, I mean,
Speaker 1: before you saw dark energy was this constant thing, but
Speaker 1: now knowing that it's changing, I mean, you're sort of
Speaker 1: blowing the whole thing open, right, Like you're saying, now
Speaker 1: you could pretty much imagine anything that could explain that change. Yeah,
Speaker 1: although it's a bit more complicated, right, It's simpler to say, oh,
Speaker 1: the universe has this new property, and that property is
Speaker 1: a constant and it just is. It's more complicated to
Speaker 1: come up with a new piece which you have to
Speaker 1: explain and then also explain why it's no longer around.
Speaker 1: It's just as tricky as inflation. Like with inflation, we
Speaker 1: have this very rapid expansion of the early universe which
Speaker 1: you have to explain. You also have to explain why
Speaker 1: that stopped. And so early dark energy is a special
Speaker 1: puzzle for theorists because they have to explain why it
Speaker 1: exists and also why it no longer seems to exist. Right,
Speaker 1: and they also have to get up early, which is
Speaker 1: a big problem. Just stay up late enough, or drink
Speaker 1: a lot of dark coffee. All right, Well, let's get
Speaker 1: into whether this early dark energy is real and what
Speaker 1: we're doing to measure it and or confirm all of
Speaker 1: these dark Shenanigan ideas. But first let's take a quick break.
Speaker 1: All right, we're talking about the mystery of dark energy,
Speaker 1: which apparently, um, it's not this constant thing. It's sort
Speaker 1: of this seems to be this kind of fickle saying
Speaker 1: almost like it was pretty lazy at the beginning of
Speaker 1: the universe after inflation, right, that's the idea. But now
Speaker 1: it's sort of getting steam, and it's maybe getting darker
Speaker 1: and later, and so it's getting more energy exactly. And
Speaker 1: it's amazing to me that dark energy sort of ever worked.
Speaker 1: You know, we look back now the history of the
Speaker 1: universe's expansion and it's incredible that you can add this
Speaker 1: simple term to just say, well, space seems to have
Speaker 1: this weird potential energy in it, which Einstein's equations predict
Speaker 1: cause this expansion, this repulsive force to stretch out the universe,
Speaker 1: and that that mostly describes what we see after inflation.
Speaker 1: We see this period of very slow expansion then sort
Speaker 1: of picked up steam around eight or nine billion years
Speaker 1: after the universe and is now accelerating very very quickly.
Speaker 1: It's sort of amazing that that complex history can in
Speaker 1: fact be described almost by a constant term. I think
Speaker 1: that's pretty cool. I mean, the fact that it doesn't
Speaker 1: quite work means, you know, it needs some new ideas,
Speaker 1: but I think it's sort of awesome that it works
Speaker 1: at all. Well, it's the only sort of sort of
Speaker 1: works right, Like it could just be like totally wrong,
Speaker 1: Like our whole sort of formulation of the universe could
Speaker 1: be totally wrong, and this could be sort of like
Speaker 1: the thing that makes us see that it's wrong, right exactly.
Speaker 1: And that's why we do these studies in more and
Speaker 1: more detail. You know, when you're first looking at something,
Speaker 1: if you have like a simple explanation that sort of
Speaker 1: mostly describes it, that's kind of cool. Like if you're
Speaker 1: plotting to quantities that you've measured and they follow along
Speaker 1: a straight line, you're like, that's interesting, and then as
Speaker 1: you get more points, you're like, oh, it turns out
Speaker 1: it's not quite a straight line, it's almost. Then you
Speaker 1: know you need to refine your understanding, your theory. But
Speaker 1: the fact that like mostly a straight line describes it,
Speaker 1: it is already pretty powerful. Well, I think a big
Speaker 1: question that you also rais is whether or not this
Speaker 1: changing dark energy effect is actually real, because I think,
Speaker 1: as you said, it's it's sort of based on two
Speaker 1: very different kinds of measurements, right, Like we measure dark
Speaker 1: energy now using one thing, but then early in the
Speaker 1: universe we measure doing using something else. So like, you know,
Speaker 1: like a ten percent difference using to totally different measurement
Speaker 1: systems seems sort of reasonable. It does, depending on those uncertainties, right,
Speaker 1: Each of these things are very different styles and measurement
Speaker 1: and we do this on purpose because we're interested in
Speaker 1: something deep and true in the universe, so we try
Speaker 1: to get a handle on it in different ways to
Speaker 1: make sure that we're not getting biased by one of
Speaker 1: our measurement techniques. And these really are very very different measurements.
Speaker 1: It's important to understand, like the early measurements are very indirect.
Speaker 1: You know, what we do when we look at the
Speaker 1: cosmic microwave background radiation is we don't actually see dark
Speaker 1: energy directly. What we do is we measure like how
Speaker 1: much dark matter was there, how much normal matter was there.
Speaker 1: We can tell that because we can see those two
Speaker 1: things sloshing around in the early universe plasma and creating
Speaker 1: like weird sound waves. It's called bury on acoustic oscillation
Speaker 1: that we talked about once on the podcast. And we
Speaker 1: can also measure how much energy there was overall in
Speaker 1: the universe, a measurement of the curvature of space back then.
Speaker 1: So the measurement of dark energy from the early universe
Speaker 1: is actually just a a traction. It says how much
Speaker 1: energy was there in total? How much can we account for.
Speaker 1: We're using dark matter and normal matter, the rest of
Speaker 1: which we call dark energy, So it's sort of like,
Speaker 1: just by subtraction we assume how much dark energy there
Speaker 1: was back then. It's very indirect. Well, I guess, because
Speaker 1: it's so indirect, it makes me kind of feel like
Speaker 1: it's just kind of a big guess. I mean, you're
Speaker 1: looking at this picture from the early universe and you're
Speaker 1: trying to, you know, throw it out these little tiny
Speaker 1: nuances in the ripples of it. In in you're sort
Speaker 1: of assuming all these proportions about the universe. Like how
Speaker 1: confident are physicists about these measurements. There's a lot of
Speaker 1: debate about that because in order to extract from that
Speaker 1: the measurement of dark energy, you've got to make some assumptions,
Speaker 1: like this data comes from the Plank satellite, which is
Speaker 1: an exceptional instrument, very high precision measurement of the cosmic
Speaker 1: microwave background radiation like revolutionized cosmology. But in order to
Speaker 1: interpret this stuff, you need to have some models in
Speaker 1: your head that you're using to interpret this data. So
Speaker 1: what people have been doing in the last two years
Speaker 1: as this discrepancy has arisen between this measurement from Plank,
Speaker 1: from the early data from the CNB and the late
Speaker 1: measurements from the supernova is to try to revisit those
Speaker 1: things and ask questions. It's like, is there another way
Speaker 1: to interpret this data? Can we see it another way?
Speaker 1: Are there assumptions that we're making that we can change
Speaker 1: And they've tried like changing those assumptions and starting from
Speaker 1: scratch and using other ideas, and the measurement is persistently
Speaker 1: too small, like they've banged on it and banged on
Speaker 1: it and banged on it some more, and it just
Speaker 1: seems to be very consistent. So that's the early expansion
Speaker 1: of the universe. What about the late expansion of the universe?
Speaker 1: How are we measuring that one? So that we have
Speaker 1: to find some way to measure distance in the current universe,
Speaker 1: that's the key. We want to know how far away
Speaker 1: things are and how fast are they moving away from us.
Speaker 1: So in order to measure the velocity of a function
Speaker 1: of time in the universe, we need to measure velocity
Speaker 1: of the function of apparent distance. Because things that are
Speaker 1: far away from us, we see them in the past. Right,
Speaker 1: something that's a billion light years away, we're not seeing
Speaker 1: light from it today. We're seeing life from a billion
Speaker 1: years ago. So in order to understand the expansion the
Speaker 1: universe over time, we need to understand the velocity of
Speaker 1: the universe as a function of distance from us today.
Speaker 1: It's really the same thing. And to measure those distances
Speaker 1: is always very very tricky, because how can you tell
Speaker 1: something that's really close by and dim or really far
Speaker 1: away and bright. Right, You can't tell unless you know
Speaker 1: how bright it's supposed to be. So the key to
Speaker 1: all of these late time measurements are calibrations of how
Speaker 1: far away things are. So we have things like type
Speaker 1: one A supernova which blow up in a very predictable way.
Speaker 1: We know basically how bright they should be. And they
Speaker 1: have other ways to do this, like these sephids, these
Speaker 1: variable stars where their pulsation is very closely connected to
Speaker 1: how bright they are at their source. And people have
Speaker 1: been really creative and finding other ways to measure this
Speaker 1: expansion using other calibratable objects neutron star, gravitational waves, and quasars,
Speaker 1: and this recent measurement about red giants, and all of
Speaker 1: these things are uncertain, uncertain different ways, Like we don't
Speaker 1: quite know our measurements of the sefids reliable. Are we
Speaker 1: accounting for the amount of dust between us and those
Speaker 1: stars correctly? That's why we try to do it in
Speaker 1: several different ways. The amazing thing is that all these
Speaker 1: different measurements using ways ours or supernova or sephids or
Speaker 1: red giant stars that have a helium flash in a
Speaker 1: very predictable way, they all mostly agree with each other,
Speaker 1: and they all disagree with this early measurement. So it's
Speaker 1: really compelling and fascinating. Right, But is there another way
Speaker 1: I guess to kind of link the two measurements other
Speaker 1: than this dark energy discrepancy? Do you know what I mean? Like,
Speaker 1: if I measure something with one ruler and I measure
Speaker 1: another thing with a different, totally different ruler way of
Speaker 1: measuring things, and they disagree, I wouldn't necessarily say that
Speaker 1: that's a whole new constpant in the universe. I like
Speaker 1: try to find other ways to see that the two
Speaker 1: rulers or the two measurement systems agree in other things, right, Yeah,
Speaker 1: And that's what they haven't done by trying to come
Speaker 1: up with essentially other rulers. They got their Type one
Speaker 1: a supernova ruler, and their SEFID ruler and their tip
Speaker 1: of the red giant branch ruler, and all these different
Speaker 1: rulers all basically seem to agree with each other, and
Speaker 1: they should all make sort of different kinds of mistakes
Speaker 1: if they do make mistakes. So that's a clue that like,
Speaker 1: maybe this is real. Maybe the universe really is expanding
Speaker 1: in this surprising way, because we haven't found a problem
Speaker 1: with any of these measurements, right, but have you tied
Speaker 1: the early universe CMB measurements to things like the say,
Speaker 1: facifits or the red giant measurements. The only way we
Speaker 1: can tie them is by taking that measurement from the
Speaker 1: early universe and using it to predict how fast things
Speaker 1: should be accelerating today, and that's where the disagreement is.
Speaker 1: So what we're trying to do is make other measurements
Speaker 1: from the early universe. And there's some pretty exciting, very
Speaker 1: recent results from a telescope in Chile called the Atacama
Speaker 1: Cosmology Telescope that also looks at the CNB, but in
Speaker 1: a way that's different from the Plank satellite, right, And
Speaker 1: that sounds super exciting, But I guess maybe my question is,
Speaker 1: and we like confirm these measurements or confirm our ability
Speaker 1: to measure the expansion of the universe using the CMB
Speaker 1: with other ways or other ways of measuring the expansion. Now,
Speaker 1: like you're saying, the early universe expansion is measured by
Speaker 1: the cosmic microwave background radiation CNB, but the current expansion
Speaker 1: is measured in a totally different way, and they come
Speaker 1: up with different numbers, which may be something about dark
Speaker 1: energy that's changing, or it could just be maybe that
Speaker 1: our two measurements are not quite linked together or calibrating. Yeah,
Speaker 1: it could be an issue with calibration. We can't measure
Speaker 1: the dark energy today the same way we can from
Speaker 1: the CMB. Right, That measurement we could make because we
Speaker 1: had this special window where we get this life from
Speaker 1: the cosmic microwave background radiation. We can't make that same
Speaker 1: kind of measurement today. That would be really awesome if
Speaker 1: we had a late time CMB that we could use
Speaker 1: to measure and compared to the early time CMB. That's
Speaker 1: just not available. Right. The universe doesn't give you everything
Speaker 1: you want. You just got to look around for opportunities
Speaker 1: and and your understanding must be wrong right now. Yeah,
Speaker 1: I mean, it's amazing that we can do any of
Speaker 1: these measurements at all, or that we have these amazing
Speaker 1: instruments to measure these expansion of the universe. Now, and
Speaker 1: before I guess, I'm just saying, I'm just trying to
Speaker 1: understand what it is that the mystery is. And it
Speaker 1: seems like there's a discrepancy, a difference between measuring the
Speaker 1: early expansion of the universe using the CMB and measuring
Speaker 1: the current expansion of the universe using you know, other
Speaker 1: methods like supernovas and and seffords and red giants and
Speaker 1: things like that. And you know, one possibility for this
Speaker 1: difference is that there is something weird about dark energy
Speaker 1: that's changing or I wonder another possibility, just to you know,
Speaker 1: give us some context, is that maybe these two ways
Speaker 1: of measuring the expansion of the universe are not quite calibrated, right, Yeah,
Speaker 1: exactly one of them could be wrong. They could both
Speaker 1: be wrong, exactly. And people are digging into the details
Speaker 1: of how these measurements were made to look for potential
Speaker 1: sources of error or bias that's why it's so valuable
Speaker 1: to measure these things in multiple different ways, because it
Speaker 1: checks your understanding and because they have different potential sources
Speaker 1: of uncertainty, right, you know, all affected by the same bias.
Speaker 1: And that's one reason why they built this telescope in Chile,
Speaker 1: because it has different sensitivity than plank and so it
Speaker 1: probes the cosmic microway background radiation in a slightly different way,
Speaker 1: which gives a different power to answer this question. Right, Yeah,
Speaker 1: I guess it's an ongoing work. But um, I guess
Speaker 1: assuming then that our early measurement of expansion and our
Speaker 1: lading measurement of expansion are both correct and the same
Speaker 1: and have the same sort of basis in reality, then
Speaker 1: that's a big deal. That means dark energy is changing, right,
Speaker 1: So it's not a constant thing, and it may even
Speaker 1: change in the future. It may change in the future. Yeah, exactly.
Speaker 1: It means that the story is more complicated than just
Speaker 1: you have one field which has some potential in it
Speaker 1: and it has this constant contribution per unit of space,
Speaker 1: which tells you this story of the expansion has to
Speaker 1: be more complicated than that. You need some like extra
Speaker 1: bitted gas in the early universe to get us going
Speaker 1: so that we are expanding as fast as we see today.
Speaker 1: And you're right, we don't understand what that is. We
Speaker 1: don't know if it will come back, like and some
Speaker 1: of these raw can roll theories like that early dark
Speaker 1: energy rolls away, but hey, it could rock back, you know.
Speaker 1: It could be that the future has more accelerated expansion,
Speaker 1: or that it could go the opposite directions somehow. What
Speaker 1: it really means is that we just don't know very
Speaker 1: much about the future of the universe. Right. We could
Speaker 1: be headed towards a heavy metal rock universe or a
Speaker 1: easy listening universe. One of the things that is really
Speaker 1: interesting for me is that these new measurements from this
Speaker 1: Chilean telescope, they support this idea of early dark energy.
Speaker 1: They measure the cosmic microwave background radiation in a different
Speaker 1: way than plunk like. The details are kind of technical,
Speaker 1: but you know, ground based telescopes always have different sensitivities
Speaker 1: than space satellites, and when they analyze their data they
Speaker 1: see something consistent with theories of early dark energy, Like
Speaker 1: their data are more consistent with their being early dark
Speaker 1: energy than with their not being early dark energy. So
Speaker 1: they sort of disagree with Plank a little bit. Wait,
Speaker 1: what do you mean? Did they disagree Plank? When they
Speaker 1: look at their data, they don't see any specific evidence
Speaker 1: for early dark energy. Early dark energy, if it existed,
Speaker 1: would be this like extra expansion of the universe just
Speaker 1: before the CNB plasma was formed, and it would change
Speaker 1: a little bit how those ripples look. And Plank doesn't
Speaker 1: see that. But this new telescope, the ACT in Chili,
Speaker 1: it does see some weird ripples in the CNB that
Speaker 1: seemed consistent with their being an extra bit of expansion
Speaker 1: just before that plasma recombined, and so it's sort of
Speaker 1: more consistent with their being early dark energy than with
Speaker 1: their not. It's like a three sigma effect in their data.
Speaker 1: M I see. So again, just kind of maybe confirming
Speaker 1: that dark energy has changed and may change in the future. Right,
Speaker 1: It's more consistent with this complicated story of dark energy
Speaker 1: than with the simple idea of dark energy just being
Speaker 1: a number. Right, But wait, I thought the same B
Speaker 1: also confirmed that, Yeah, the Plank measurements don't agree with
Speaker 1: the late time, but they also don't see evidence for
Speaker 1: early dark energy. These measurements agree with Plank about how
Speaker 1: much dark energy there was, but they also see this
Speaker 1: extra effect which seems consistent with early dark energy. So
Speaker 1: it's new telescope disagrees with Plank a little bit. Maybe
Speaker 1: you need earlier dark energy or mid mid to late
Speaker 1: morning dark energy, sparkly dark energy. Well, and I think
Speaker 1: all this again means that the future is unpredictable, right,
Speaker 1: I think I think that's kind of the bigger deal
Speaker 1: is that, you know, if dark energy was constant and
Speaker 1: just the number that wasn't changing, then we sort of
Speaker 1: know how what's gonna happen in the future, and we
Speaker 1: know how the universe is going to end. But if
Speaker 1: we don't, if it's something totally complicated and different, who
Speaker 1: knows what's gonna happen, right, it could turn off for example, Yeah,
Speaker 1: we don't know what's going to happen in the future.
Speaker 1: It also, I think it's super fascinating affects our vision
Speaker 1: of the past. You know, if the universe has been
Speaker 1: expanding more rapidly than we thought, that means that it's
Speaker 1: younger than we thought because it didn't take as much
Speaker 1: time to get this expansion happening as we thought it did.
Speaker 1: Because the foot was on the gas pedal more strongly
Speaker 1: than we thought it was. So concretely, it might mean
Speaker 1: that the universe is only twelve and a half billion
Speaker 1: years old, not thirteen point eight, right, So we might
Speaker 1: have just like deleted a billion and a half years
Speaker 1: of history. Boom, you're all younger, everybody. Yeah, well, we're
Speaker 1: not younger. We're definitely not getting younger. But maybe the
Speaker 1: universe is younger than we thought exactly. And so that
Speaker 1: just goes to show you how will we know about
Speaker 1: the future of the universe, and how will we really
Speaker 1: understand about its past? How this picture of the universe
Speaker 1: and its expansion is still a big question mark. Yeah,
Speaker 1: I mean it's still dark basically, right, dark energy is
Speaker 1: that it's dark. It's a mystery. It's definitely probably not
Speaker 1: a constant. Who knows what it could be, right, that's right.
Speaker 1: Dark history even more fun than drunk history. Yeah, it
Speaker 1: could be cartoonist um drawing crazy things in the universe.
Speaker 1: I hope that's our future as well. Yeah, and I
Speaker 1: think it just confirms my theory that, you know, staying
Speaker 1: up late keeps you young, right, it seems to work
Speaker 1: so far exactly. Let's keep taking measurements all right, We'll
Speaker 1: stay tuned as we learn more about dark energy and
Speaker 1: what it could mean for our history of the universe
Speaker 1: and also the future. Maybe somebody out there listening to
Speaker 1: this could be the person who discovers what's really going
Speaker 1: on with early or late or mid to late morning
Speaker 1: dark energy. There's certainly a whole lot left to discover,
Speaker 1: a lot of time for a dark energy cook to
Speaker 1: come in. Basically, you might not even have to stay
Speaker 1: up late to figure it out. Well, thanks for joining us.
Speaker 1: We hope you enjoyed that. See you next time. Thanks
Speaker 1: for listening, and remember that Daniel and Jorge Explain the
Speaker 1: Universe is a production of I Heart Radio. For more
Speaker 1: podcast For my heart Radio, visit the i heart Radio app,
Speaker 1: Apple Podcasts, or wherever you listen to your favorite shows.
Speaker 1: Yeah