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What is early dark energy? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey, Jorge, is it still true that you get a
• 0:10
  Speaker 1: lot of your work done late at night? Yeah? Yeah,
• 0:13
  Speaker 1: you know, it's a little quieter. Nobody's calling you, nobody's
• 0:16
  Speaker 1: bothering you. It's a little easier to, you know, get
• 0:18
  Speaker 1: your thoughts in order. So like you do your best
• 0:20
  Speaker 1: thinking when it's dark outside. Yes, that's right, it's like
• 0:23
  Speaker 1: I have dark energy. Oh my gosh, I think you
• 0:26
  Speaker 1: might have just cracked the mystery. Yeah, what do you mean?
• 0:28
  Speaker 1: Maybe that's what's causing the universe to accelerate outwards. Cartoonists
• 0:33
  Speaker 1: staying up too late? Oh, man, I think you're right.
• 0:36
  Speaker 1: The universe just can't handle so many cartoons, so it
• 0:39
  Speaker 1: has to grow to fit them all in. You are
• 0:42
  Speaker 1: literally blowing it up. Those are some dark thoughts, man,
• 0:45
  Speaker 1: I'll have to stay up late thinking about it. I
• 1:02
  Speaker 1: am more handmade. Cartoonists and the co author frequently ask
• 1:05
  Speaker 1: questions about the universe. Hi, I'm Daniel. I'm a particle
• 1:08
  Speaker 1: physicist and a professor at U c Irvine, and I
• 1:11
  Speaker 1: always thought of the two of us, I was more
• 1:13
  Speaker 1: likely to blow up the universe. Well, you know, I
• 1:18
  Speaker 1: blow people's mind. You blow up the physical universe. What
• 1:21
  Speaker 1: can I say, it's a team effort. Together, we are
• 1:23
  Speaker 1: unstoppable and potentially dangerous, also one of us more so
• 1:29
  Speaker 1: than the other. And now we are here to blow
• 1:31
  Speaker 1: your minds. Welcome to our podcast Daniel and Jorge Explain
• 1:34
  Speaker 1: the Universe, a production of I Heart Radio, in which
• 1:37
  Speaker 1: we do try to blow up the entire universe, but
• 1:40
  Speaker 1: not to destroy it and make it unlivable, but so
• 1:43
  Speaker 1: that we can zoom in and understand it in detail.
• 1:46
  Speaker 1: We want to expand the whole universe as we expand
• 1:49
  Speaker 1: your mind, so we can stretch it in and see
• 1:52
  Speaker 1: right through it. We can mix our metaphors and we
• 1:55
  Speaker 1: can pull things apart as we try to explain all
• 1:58
  Speaker 1: of the craziness and the incredible universe to you. That's right,
• 2:02
  Speaker 1: We try to explode your understanding of the cost moods
• 2:04
  Speaker 1: because it is a pretty big and wonderful universe, and
• 2:08
  Speaker 1: it's also getting bigger. It's getting bigger every year, and
• 2:12
  Speaker 1: it's getting bigger faster every year, which means the size
• 2:15
  Speaker 1: of the mystery, the scale of our ignorance is getting
• 2:19
  Speaker 1: larger and larger every year. Literally, there is more stuff
• 2:22
  Speaker 1: we don't know this year than last year. Yeah, because
• 2:25
  Speaker 1: there is literally more universe today than there was yesterday,
• 2:29
  Speaker 1: and tomorrow there's going to be even more universe, which
• 2:32
  Speaker 1: means that maybe we'll never get to understand all of it. Daniel,
• 2:35
  Speaker 1: Can we keep up with such an expanding universe? We
• 2:37
  Speaker 1: can't think faster than the speed of light, But the
• 2:39
  Speaker 1: universe is expanding faster than the speed of light, which
• 2:43
  Speaker 1: I guess makes it hopeless, doesn't it? Why are we
• 2:45
  Speaker 1: even doing this podcast? That's right, just give up, Daniel.
• 2:48
  Speaker 1: You should become a cartoonist. Is that what giving up means?
• 2:55
  Speaker 1: Giving up? Right? You're you know, upgrading. That's right. Stepping
• 2:59
  Speaker 1: up to being a cartoon is stepping up, upgrading? Yes,
• 3:04
  Speaker 1: that's what you meant to say. No, I think that
• 3:06
  Speaker 1: even though it's unlikely we will ever understand everything about
• 3:09
  Speaker 1: the universe, it's really all about the friends we make
• 3:12
  Speaker 1: along the way, meaning the ideas that we captured, those
• 3:16
  Speaker 1: bits of knowledge that we do manage to extract from
• 3:18
  Speaker 1: the universe and digest, those moments when we pull back
• 3:21
  Speaker 1: a layer of reality and say, oh my gosh, the
• 3:24
  Speaker 1: universe is different from what we imagined. And one of
• 3:27
  Speaker 1: the greatest of those moments is when we discovered that
• 3:30
  Speaker 1: the universe was expanding, and that expansion was accelerating. Yep,
• 3:35
  Speaker 1: the universe is just getting started. Apparently it's getting bigger,
• 3:39
  Speaker 1: faster and faster each year. But do you think Daniel dead?
• 3:42
  Speaker 1: You know, once you figure out the loss of the universe,
• 3:44
  Speaker 1: you don't need to see all of the universe. You know,
• 3:46
  Speaker 1: it's like you you once you figure out the basic rules,
• 3:49
  Speaker 1: it's like you know, and they're done that. That's gonna
• 3:52
  Speaker 1: be the title of my next paper. Actually it's called
• 3:55
  Speaker 1: you know, They're done that. They're done that. Um No,
• 3:58
  Speaker 1: Actually that's the name of a cafe my wife wants open.
• 4:01
  Speaker 1: Being there done that. Oh nice. She's also upgrading tour
• 4:05
  Speaker 1: from a biologist. She's in favor of everything being related.
• 4:09
  Speaker 1: For black beans for dinner, coffee beans with breakfast, chocolate
• 4:13
  Speaker 1: beans for dessert. It's a whole being themed, you know,
• 4:15
  Speaker 1: being there, done that. But I think that there's never
• 4:18
  Speaker 1: a time when we will not learn from seeing more
• 4:21
  Speaker 1: of the universe. And the history of physics is saying, oh,
• 4:25
  Speaker 1: we think we figured out how things work from the
• 4:27
  Speaker 1: studies of this local neighborhood, and then we generalize me extrapoling,
• 4:30
  Speaker 1: and we say, well, the rest of the universe probably
• 4:32
  Speaker 1: works that way, and every time we go to check
• 4:34
  Speaker 1: we find a surprise waiting for us. It turns out
• 4:37
  Speaker 1: that what we learned was a special case because we
• 4:39
  Speaker 1: were looking at only certain circumstances, only when things were
• 4:43
  Speaker 1: really slow, or when things were really cold, or when
• 4:45
  Speaker 1: things were really big. And every time we do turn
• 4:48
  Speaker 1: over that stone and look at some part of the
• 4:50
  Speaker 1: universe we've never seen before, we always do learn something new.
• 4:53
  Speaker 1: So I think there'll never be a time when we
• 4:55
  Speaker 1: say we're done looking around. Well. I think that's good
• 4:57
  Speaker 1: news for this podcast, because that means we'll that we're
• 5:00
  Speaker 1: run out of things to talk about. The stable gigsodes
• 5:04
  Speaker 1: almost and going strong. In fact, it's it's accelerating. I
• 5:07
  Speaker 1: feel like they're accelerating here, derated, which we're making a
• 5:11
  Speaker 1: podcast episodes. Man, we should be doing ten a week
• 5:13
  Speaker 1: at this point. But it is an expanding universe. It's
• 5:15
  Speaker 1: getting bigger each year, and it's getting bigger at a
• 5:18
  Speaker 1: faster rate each time. And it's all because of dark energy,
• 5:21
  Speaker 1: that mysterious energy that's through's force. It's expanding space itself.
• 5:26
  Speaker 1: It's not just making more room, it's growing room in
• 5:28
  Speaker 1: the universe. That's right. Dark energy is the name we
• 5:31
  Speaker 1: give to the observation that the universe is expanding, and
• 5:36
  Speaker 1: that that expansion is somehow accelerating. The key there is
• 5:40
  Speaker 1: the somehow. We call it dark energy because dark means
• 5:43
  Speaker 1: we are cluelest. We don't understand what's going on. We
• 5:46
  Speaker 1: don't even have a good idea for what could be
• 5:49
  Speaker 1: doing it. We just have the observation that is happening
• 5:53
  Speaker 1: and energy because it takes about two thirds of all
• 5:56
  Speaker 1: the energy in the universe to make this happen. So
• 5:59
  Speaker 1: dark energy is a good description for what's going on
• 6:02
  Speaker 1: because it's also basically everything we know about it. I
• 6:05
  Speaker 1: thought it was called dark energy because it doesn't like
• 6:08
  Speaker 1: give off light like it we can't see it like
• 6:10
  Speaker 1: we know it's there because we can see the universe
• 6:12
  Speaker 1: expanding faster and faster, but we like it doesn't like
• 6:15
  Speaker 1: give off a glow or doesn't like make sparkles. It
• 6:18
  Speaker 1: doesn't you know, look like anything. That's what you call
• 6:20
  Speaker 1: it dark, not because we're in the dark about it.
• 6:22
  Speaker 1: It would be cool if it made sparkles. I think
• 6:24
  Speaker 1: if a cartoonist head designed the universe, there would be
• 6:27
  Speaker 1: sparkles or like, you know, action lines or something to
• 6:30
  Speaker 1: show the universe is stretching. Right, every time you have
• 6:32
  Speaker 1: motion in a cartoon, there's always some visual guide there
• 6:35
  Speaker 1: to tip you off. Are you saying that cartoonists should
• 6:38
  Speaker 1: be God's Is that what you're saying. I'm saying it's
• 6:42
  Speaker 1: pretty clear that God is not a cartoonist. You know,
• 6:44
  Speaker 1: conclude from that what you will. Well, maybe God needs
• 6:47
  Speaker 1: to upgrade, just like you know, to everyone else. Step
• 6:51
  Speaker 1: up there, dude, Yeah, grab a pencil, add some sparkles.
• 6:53
  Speaker 1: You know, if the universe is a simulation and the
• 6:55
  Speaker 1: engineers listen to our podcast, or if you're in the
• 6:57
  Speaker 1: believer of a deity whoever is in charge this universe,
• 7:00
  Speaker 1: I hope they do listen to our podcast so that
• 7:03
  Speaker 1: they hear about all the questions that we have. But
• 7:04
  Speaker 1: that is a name we've given it, the the expansion,
• 7:06
  Speaker 1: the accelerating expansion of the universe, dark energy. But and
• 7:10
  Speaker 1: it explains why the universe is it growing bigger and
• 7:13
  Speaker 1: bigger each year. But it doesn't quite explain how we
• 7:16
  Speaker 1: got here, right, You're right, it doesn't explain how we
• 7:18
  Speaker 1: got here. Number one, because we don't even really have
• 7:20
  Speaker 1: an explanation for how it works. Right, Like, we can
• 7:23
  Speaker 1: add some energy to general relativity, and we can use
• 7:26
  Speaker 1: that to expand the universe in our models and to
• 7:28
  Speaker 1: accelerate that expansion. We can do that, but you know,
• 7:31
  Speaker 1: we don't understand where that energy comes from. We have
• 7:34
  Speaker 1: like no description of what that means and where it
• 7:37
  Speaker 1: comes from and how it works and what its future is.
• 7:40
  Speaker 1: And also recently we've discovered that even that picture, that
• 7:44
  Speaker 1: simplistic picture that like maybe we just add a number
• 7:47
  Speaker 1: to Einstein's theory of general relativity, that also doesn't quite work.
• 7:51
  Speaker 1: It doesn't really match the story we see out there
• 7:55
  Speaker 1: in the acceleration of the universe. This is growing problem
• 7:58
  Speaker 1: with our understanding of how fast the universe is accelerating. Right.
• 8:02
  Speaker 1: It's sort of related to the idea that the universe
• 8:04
  Speaker 1: is maybe bigger than it should be, even with this
• 8:06
  Speaker 1: idea of dark energy put into it. Yeah, like maybe
• 8:09
  Speaker 1: the universe is bigger than it should be, or that
• 8:12
  Speaker 1: it's not as old as we think it is. All
• 8:14
  Speaker 1: these ideas are connected because our whole idea of how
• 8:16
  Speaker 1: old the universe is and how vast it is, how
• 8:19
  Speaker 1: big the portion of what we can see is depends
• 8:22
  Speaker 1: on understanding how quickly it's been expanding. Understand how old
• 8:25
  Speaker 1: it is. We unwind this picture, we run the clock
• 8:28
  Speaker 1: backwards and see how long does it take to get
• 8:30
  Speaker 1: back to the Big Bang singularity. So if our understanding
• 8:33
  Speaker 1: of the expansion rate is wrong, that our understanding of
• 8:36
  Speaker 1: the whole history of the universe, including its age, could
• 8:39
  Speaker 1: be wrong. Yeah, it's a big mystery, which we'll talk
• 8:42
  Speaker 1: about later. But there is sort of a concept that
• 8:44
  Speaker 1: might explain all of this, and it has a very
• 8:47
  Speaker 1: imaginative name. Right. Well, I was wondering, you know what
• 8:50
  Speaker 1: a cartoonist called this idea. Well, we wouldn't call it anything.
• 8:53
  Speaker 1: We just draw it. Right what it could be called
• 8:56
  Speaker 1: sparkly dark energy. Everything should be sparkly sequence dark energy.
• 9:01
  Speaker 1: But there is a concept that might explain the expansion
• 9:04
  Speaker 1: of the universe in the beginning. And so today on
• 9:06
  Speaker 1: the program, we'll be tackling the question what is early
• 9:15
  Speaker 1: dark energy? Wait, that's the name, Like, that's the whole concept.
• 9:19
  Speaker 1: Just put the word early in front of dark energy.
• 9:23
  Speaker 1: That is the whole concept. And you know it's not
• 9:25
  Speaker 1: just inspired by cartoonists staying up so late at night
• 9:28
  Speaker 1: that it actually becomes early in the morning. I was
• 9:32
  Speaker 1: gonna say, I'm more of a fan of late dark energy.
• 9:35
  Speaker 1: So when I got an email from you at five am,
• 9:37
  Speaker 1: is that when you're staying up super duper late, it
• 9:39
  Speaker 1: doesn't cross over into early. It means I scheduled my emails.
• 9:45
  Speaker 1: You noticed my emails always coming at five am? Exactly?
• 9:50
  Speaker 1: Why would you schedule them for five am? That's still
• 9:52
  Speaker 1: a bonkers time to send an email. Why don't you
• 9:54
  Speaker 1: schedule them for eight am? Or is that for eight
• 9:56
  Speaker 1: am on the East coast or something? You just got it, Yeah,
• 10:00
  Speaker 1: eight am in an Eastern time, all right? But the
• 10:03
  Speaker 1: question still stands, how late do you have to stay
• 10:05
  Speaker 1: up before you count it as early or are you
• 10:07
  Speaker 1: saying that no matter how late you stay up, if
• 10:09
  Speaker 1: you're still up, it's still late from the day before. Boy,
• 10:12
  Speaker 1: these big questions about the universe are just too confusing.
• 10:16
  Speaker 1: I'm not sure we have a whole episode here to
• 10:19
  Speaker 1: talk about my sleeping habits. I'm sure Aristotle had something
• 10:22
  Speaker 1: to say on this deep philosophical question, But that is
• 10:25
  Speaker 1: the concept that we're going to be talking about here today,
• 10:27
  Speaker 1: this idea of early dark energy. And does that mean, Daniel,
• 10:30
  Speaker 1: there's late dark energy. Late dark energy is the dark
• 10:33
  Speaker 1: energy we have right now that we look around and
• 10:35
  Speaker 1: we see because we are in late times of the universe.
• 10:39
  Speaker 1: That doesn't mean that we think the universe is about
• 10:41
  Speaker 1: to expire or at the end of its life. It
• 10:42
  Speaker 1: just means like recent times of people talk about the
• 10:46
  Speaker 1: early universe meaning the very beginning, and the late universe
• 10:48
  Speaker 1: meaning right now. I see. So maybe we should be
• 10:51
  Speaker 1: it should be called a current dark energy or something
• 10:53
  Speaker 1: that's right. But one of the mysteries is how the
• 10:56
  Speaker 1: universe accelerated in the very early days. Their disagreement about
• 11:00
  Speaker 1: how quickly was accelerating in the very first few moments
• 11:02
  Speaker 1: and how quickly it's accelerating now. And to solve those problems,
• 11:06
  Speaker 1: people are working on ideas to change how quickly the
• 11:09
  Speaker 1: universe was accelerating early on, I see, And will late
• 11:12
  Speaker 1: dark energy at some point become early dark energy only
• 11:15
  Speaker 1: when you go to bed right only Easter standard time.
• 11:19
  Speaker 1: We should call it scheduled dark energy. Right there, you
• 11:22
  Speaker 1: go just in time dark energy. But this is a
• 11:25
  Speaker 1: new concept, early dark energy, one that physicists are thinking
• 11:28
  Speaker 1: about and talking about, and so as usual, we were
• 11:30
  Speaker 1: wondering how many people out there had heard of this
• 11:33
  Speaker 1: idea of early dark energy. So Daniel went out there
• 11:36
  Speaker 1: once again to ask people this question, and I'm eternally
• 11:39
  Speaker 1: grateful to our cadre of volunteers to answer these questions
• 11:42
  Speaker 1: for us so that we can get a sense for
• 11:43
  Speaker 1: what people know and what people are thinking about. If
• 11:46
  Speaker 1: you'd like to participate, please don't be shy right to us.
• 11:49
  Speaker 1: Two questions at Daniel and Jorge dot com. So think
• 11:52
  Speaker 1: about it for a second. What do you think early
• 11:55
  Speaker 1: dark energy means? What does it do? Here's what people
• 11:58
  Speaker 1: had to say. I am not certain, however, I guess
• 12:01
  Speaker 1: that it is similar to the background radiation and that
• 12:04
  Speaker 1: that it's sort of residue from the initial dark energy
• 12:09
  Speaker 1: or the dark energy that initially expanded the universe. I mean,
• 12:14
  Speaker 1: dark energy is probably what's responsible for expanding the universe
• 12:18
  Speaker 1: and accelerating the expansion. I don't know what early in
• 12:24
  Speaker 1: that context means. Was dark energy different in the early
• 12:28
  Speaker 1: state of the universe. I don't know. Um well, as
• 12:31
  Speaker 1: far as they know, dark energy has been increasing since
• 12:36
  Speaker 1: the beginning of the universe. Maybe this is the dark
• 12:40
  Speaker 1: energy that was still around, that was around at the
• 12:42
  Speaker 1: very beginning that we might be able to find if
• 12:45
  Speaker 1: we look far enough back with gravity or something. Probably
• 12:50
  Speaker 1: dark energy is the dark energy from the original Big
• 12:55
  Speaker 1: Bang or soon thereafter that it's all around today early
• 13:02
  Speaker 1: dark energy. I have no idea what it actually is.
• 13:05
  Speaker 1: I'm assuming it's the early stuff that comes to the
• 13:07
  Speaker 1: party early, like maybe in the early part of the universe,
• 13:10
  Speaker 1: kind of like the cosmic micrtive background. Definitely not my wife,
• 13:14
  Speaker 1: that would be the late dark energy. I'm going to
• 13:16
  Speaker 1: take a guess that early dark energy is essentially the
• 13:20
  Speaker 1: same thing as dark energy now, just earlier in our universe,
• 13:24
  Speaker 1: before it was the more dominant of the two between
• 13:29
  Speaker 1: it and gravity. Well, I can think a guess that
• 13:34
  Speaker 1: it's the dark energy right before the Is that just
• 13:43
  Speaker 1: another word for inflation? All right, it's a pretty um
• 13:48
  Speaker 1: straightforward I feel like everyone you said, it's it's dark energy,
• 13:51
  Speaker 1: but early, except it's not my wife. She's late dark energy.
• 13:55
  Speaker 1: That's my favorite answer. Wait, what was that answer from you?
• 13:59
  Speaker 1: Because I know you're wife's days of late also working, right,
• 14:02
  Speaker 1: that's true. Yes, she is on joge time, that's right,
• 14:06
  Speaker 1: or a standard time. She needs to step up and
• 14:08
  Speaker 1: become a cartoonist. Yeah, she's just she's just a pencil sketch. Away,
• 14:13
  Speaker 1: but most people seem to be related to the early university.
• 14:15
  Speaker 1: I guess you know, most people associate dark energy with
• 14:18
  Speaker 1: you know, the universe itself and early I guess you know,
• 14:22
  Speaker 1: you might think that it's dark energy that was there
• 14:25
  Speaker 1: at the beginning of the universe. And it's confusing also
• 14:28
  Speaker 1: because we know that there are multiple periods of expansion
• 14:32
  Speaker 1: in our history of the universe. Like we talked about
• 14:34
  Speaker 1: dark energy, which has been dominating the expansion of the
• 14:37
  Speaker 1: universe for the last five billion years, although it's been around,
• 14:41
  Speaker 1: is part of the mix since the very beginning, it's
• 14:43
  Speaker 1: just sort of only taken over in the last five
• 14:45
  Speaker 1: billion years. But we've also talked many times on the
• 14:48
  Speaker 1: podcast about inflation, which is another period of rapid expansion
• 14:52
  Speaker 1: in the universe in the first ten to the minus
• 14:54
  Speaker 1: thirty seconds of the history of the universe. And as
• 14:57
  Speaker 1: we said several times, we don't know if those are
• 14:59
  Speaker 1: connect that are those different mechanisms for rapid expansion of
• 15:02
  Speaker 1: the universe. Are they related somehow? We don't know, And
• 15:06
  Speaker 1: so it's fair to try to lump these periods of
• 15:08
  Speaker 1: expansion together and say, like, oh, maybe early dark energy,
• 15:12
  Speaker 1: just inflation. That makes a lot of sense. It's kind
• 15:13
  Speaker 1: of weird to think that the universe had basically growth spurts,
• 15:17
  Speaker 1: right like you might think that a cold, random universe
• 15:20
  Speaker 1: which is grow at a steady rate. But somehow the
• 15:23
  Speaker 1: universe has had these like periods of expansion and slowing
• 15:27
  Speaker 1: down too. And one of the key things to understand
• 15:30
  Speaker 1: is that as the universe expands, the mixture that it
• 15:33
  Speaker 1: has of matter and radiation and dark energy, that mixture
• 15:38
  Speaker 1: changes as it expands, because, for example, as the universe expands,
• 15:42
  Speaker 1: matter gets dilute. You have a certain number of particles
• 15:44
  Speaker 1: in a box, and you make that box bigger than
• 15:46
  Speaker 1: the density goes down. But that dilution is different for
• 15:49
  Speaker 1: matter than it is for radiation, for example light. If
• 15:53
  Speaker 1: you expand the box and stretch the space, light also
• 15:55
  Speaker 1: loses energy because it gets red shifted. So radiation gets
• 15:59
  Speaker 1: diluted more quickly, whereas dark energy doesn't get diluted at all.
• 16:02
  Speaker 1: As you make more space and expand the box, you
• 16:05
  Speaker 1: have the same amount of dark energy per unit space,
• 16:08
  Speaker 1: and so the dark energy fraction of the whole universe
• 16:10
  Speaker 1: goes up. So as the universe expands, these fractions change,
• 16:14
  Speaker 1: and then that changes how the universe responds, and so
• 16:17
  Speaker 1: it's this very dynamical system. Right, it's not just like
• 16:20
  Speaker 1: the steady state thing hanging out because it's expanding. That
• 16:23
  Speaker 1: expansion then changes how it expands. Yeah, that's wild. And
• 16:27
  Speaker 1: it's well to think that the universe has things that
• 16:29
  Speaker 1: it you know, conserves and keeps the same, and there's
• 16:34
  Speaker 1: has things that keep growing, you know what I mean,
• 16:36
  Speaker 1: Like matter seems to be constant and it's not increasing,
• 16:39
  Speaker 1: but space needs to be, you know, growing out of
• 16:41
  Speaker 1: the woodwork. Yeah, it's growing out of the universe work exactly.
• 16:45
  Speaker 1: And as the universe expands, dark energy takes over and
• 16:48
  Speaker 1: it makes it expand faster. And that's the source of
• 16:51
  Speaker 1: this acceleration, which is crazy because it suggests the future
• 16:55
  Speaker 1: is all dark energy dominated. Once dark energy is sort
• 16:58
  Speaker 1: of in charge, it basically never let's go as far
• 17:01
  Speaker 1: as we understand. And so it might be that the
• 17:03
  Speaker 1: periods of the universe where matter we're in charge, or
• 17:06
  Speaker 1: radiation were in charge, we're just like the first blips,
• 17:08
  Speaker 1: you know, the first few moments of like a trillion
• 17:11
  Speaker 1: year history. Right, the future is all cartoonists. You should
• 17:15
  Speaker 1: join us now. It is inevitable, I see before it
• 17:18
  Speaker 1: gets cool right as the universe gets colder and colder.
• 17:22
  Speaker 1: But anyways, this idea of early dark energy is really interesting,
• 17:26
  Speaker 1: and so let's break it down for people who are
• 17:28
  Speaker 1: not familiar with this concept of even dark energy. So, Daniel,
• 17:32
  Speaker 1: what is the regular dark energy? So the regular dark
• 17:35
  Speaker 1: energy is a name we give to something shocking that
• 17:39
  Speaker 1: we discovered about twenty years ago. Now, remember that, like
• 17:42
  Speaker 1: only a hundred years ago, we discovered that there are
• 17:45
  Speaker 1: other galaxies out there in the universe and that they
• 17:48
  Speaker 1: are moving away from us, that the universe is expanding.
• 17:52
  Speaker 1: This was sort of a big deal when it was
• 17:54
  Speaker 1: discovered in like, you know, Einstein's universe that he imagined
• 17:58
  Speaker 1: in general relativity was a static universe, no expansion, no acceleration.
• 18:03
  Speaker 1: So the Hubble discovered that, oh, the universe is expanding.
• 18:06
  Speaker 1: Things are floating out there. But people thought, okay, well,
• 18:09
  Speaker 1: the universe is expanding, but probably it's gonna pull back.
• 18:13
  Speaker 1: Probably gravity is going to be strong enough to pull
• 18:16
  Speaker 1: everything back together and maybe make a big crunch. Or
• 18:19
  Speaker 1: if not, then things are gonna gradually slow down due
• 18:22
  Speaker 1: to gravity as they drift away from each other. So
• 18:24
  Speaker 1: the question until twenty years ago was how quickly is
• 18:28
  Speaker 1: the universe decelerating? How quickly are things slowing down? And
• 18:32
  Speaker 1: then they went out and measured this, because, as we
• 18:34
  Speaker 1: talked about earlier, you always got to go out and
• 18:36
  Speaker 1: see what's really going on in the universe. And they
• 18:39
  Speaker 1: discovered by looking at how far away stars were and
• 18:42
  Speaker 1: looking back into the past to see how quickly they
• 18:44
  Speaker 1: were moving away from us a long time ago, that
• 18:46
  Speaker 1: the universe wasn't slowing down at all, that this expansion
• 18:50
  Speaker 1: was in fact accelerating, that every year things were moving
• 18:53
  Speaker 1: away from us faster and faster. So this blew everybody's minds.
• 18:56
  Speaker 1: They're like, oh my gosh, not only is the universe expanding,
• 18:59
  Speaker 1: but it's accelerating. What could be doing? And so they
• 19:03
  Speaker 1: replaced that big question mark with a fancy phrase called
• 19:06
  Speaker 1: dark energy, and that's about where we are today. Dark
• 19:09
  Speaker 1: energy is just the name for this discovery for which
• 19:12
  Speaker 1: we have no real explanation, right because without that observation,
• 19:16
  Speaker 1: I mean, like you said, we would expect the universe
• 19:18
  Speaker 1: to crunch back down again, right because gravity sort of
• 19:21
  Speaker 1: doesn't give up, Like, even if things are super far away,
• 19:24
  Speaker 1: they're still being pulled a little bit by gravity. And
• 19:27
  Speaker 1: so eventually that acceleration that floors should bring everything back
• 19:31
  Speaker 1: together into a little tiny dot. Right. It depends a
• 19:35
  Speaker 1: little bit on the balance between gravity and the initial velocity.
• 19:39
  Speaker 1: It's possible, because gravity gets weaker as distance grows, that
• 19:42
  Speaker 1: we could have lived in the universe with no dark energy,
• 19:46
  Speaker 1: that didn't crunch back down together, that just spread out forever,
• 19:49
  Speaker 1: if there was sort of enough initial energy, just in
• 19:52
  Speaker 1: the same way that you can, for example, throw a
• 19:54
  Speaker 1: ball off the surface of the Earth at high enough
• 19:56
  Speaker 1: velocity that it never ever comes back, even in the
• 19:59
  Speaker 1: infinite future, has enough energy to escape Earth's potential. Well,
• 20:03
  Speaker 1: so it was possible that things expanded out forever. But
• 20:06
  Speaker 1: until we discovered dark energy, we never imagined that it
• 20:08
  Speaker 1: could actually be accelerating outward, that things could be stretched out,
• 20:12
  Speaker 1: that new space could be being made between those galaxies. Right,
• 20:16
  Speaker 1: And so you gave that acceleration of the expanding universe
• 20:20
  Speaker 1: that's expanding faster and faster. You give it the name
• 20:23
  Speaker 1: dark energy because it must be some kind of energy, right,
• 20:26
  Speaker 1: because you don't know what else it could be. We
• 20:28
  Speaker 1: don't know what else this could be. One sort of
• 20:30
  Speaker 1: category of explanations is something we call the cosmological constant.
• 20:34
  Speaker 1: And this is just like a number that you stick
• 20:37
  Speaker 1: into Einstein's general relativity equations and it reflects some sort
• 20:40
  Speaker 1: of like potential energy of the universe. Remember we talked
• 20:44
  Speaker 1: to the podcast about how the space is filled with
• 20:46
  Speaker 1: quantum fields, right, all of space has fields, and it
• 20:49
  Speaker 1: fields for the electrons, fields for photons, feels for all
• 20:52
  Speaker 1: the different kinds of particles. And these fields can do
• 20:54
  Speaker 1: different things. They can wiggle, which is like having kinetic
• 20:57
  Speaker 1: energy the way like a ball rolling down the hill
• 20:59
  Speaker 1: has kinnectic or g But the fields can also have
• 21:01
  Speaker 1: potential energy energy stored in them because of their configuration,
• 21:05
  Speaker 1: like a ball sitting at the top of a hill
• 21:07
  Speaker 1: that isn't yet moving really fast. So if you have
• 21:09
  Speaker 1: a field with a lot of potential energy, that creates
• 21:12
  Speaker 1: this outward pressure due to this cosmological constant that comes
• 21:15
  Speaker 1: from that field. And so we sort of like stuck
• 21:17
  Speaker 1: this number into Einstein's theory and we gave it the
• 21:20
  Speaker 1: right number to explain the expansion that we see. But
• 21:23
  Speaker 1: we can't explain that number. It's just like, well, here's
• 21:26
  Speaker 1: a number, we measured it. We don't know why it
• 21:28
  Speaker 1: is that number or what field could be generating this
• 21:31
  Speaker 1: potential energy. It's still a really big mystery, and I
• 21:33
  Speaker 1: feel like that's kind of the reason you gave it
• 21:36
  Speaker 1: a name, right, It was was sort of because it
• 21:38
  Speaker 1: is sort of a term in your equations of the universe,
• 21:41
  Speaker 1: in Einstein's equations, Right, like my kids are growing faster
• 21:44
  Speaker 1: and faster, but I don't give a name to the
• 21:46
  Speaker 1: idea or the phenomenon of them growing faster and faster.
• 21:49
  Speaker 1: Or like if the universe he saw that it was
• 21:51
  Speaker 1: growing faster and faster, you might just say, oh, the
• 21:52
  Speaker 1: universe is growing faster and faster. But because you have
• 21:55
  Speaker 1: these equations and you have you have like an actual
• 21:57
  Speaker 1: term that kind of describes that or explain this expansion.
• 22:01
  Speaker 1: You give it a name, and we can also calculate
• 22:03
  Speaker 1: how much energy is necessary for this to happen, Like
• 22:06
  Speaker 1: you find the number you have to put into Einstein's
• 22:08
  Speaker 1: equation to explain this, and then you can calculate what
• 22:12
  Speaker 1: sort of energy density is required in space to cause
• 22:15
  Speaker 1: that term. Right, this cosmological constant isn't just like an
• 22:19
  Speaker 1: abstract idea. It reflects like some potential energy stored in
• 22:23
  Speaker 1: space itself, and then we can calculate that energy we
• 22:26
  Speaker 1: can compare to other things and we find that, Wow,
• 22:28
  Speaker 1: this potential energy is more than all of the energy
• 22:32
  Speaker 1: stored in all the stars and the galaxies and the
• 22:35
  Speaker 1: dust and all of the dark matter and all of
• 22:38
  Speaker 1: the stuff we see in the universe. It's like more
• 22:40
  Speaker 1: than twice as much energy as everything else in the universe.
• 22:44
  Speaker 1: So it's a huge quantity. It's a big part of
• 22:47
  Speaker 1: the recipe of the universe, right, And it's sort of
• 22:50
  Speaker 1: energy because I mean, it's one thing to grow space,
• 22:53
  Speaker 1: but it's also another thing to like push the things
• 22:56
  Speaker 1: along that are in space. Right, Like if I was
• 22:59
  Speaker 1: growing my house, they can just grow the house, it
• 23:01
  Speaker 1: would also have to like move the beds on the
• 23:04
  Speaker 1: table everything out further out towards the walls more, right,
• 23:08
  Speaker 1: And so that that takes energy, right, It takes energy. Yeah,
• 23:11
  Speaker 1: And what this means is that space has energy in
• 23:14
  Speaker 1: it like this stuff because it's part of the potential
• 23:17
  Speaker 1: energy of space itself. It doesn't get diluted when you
• 23:20
  Speaker 1: make new space. When you stretch out the space between
• 23:23
  Speaker 1: two galaxies, then you're creating more dark energy because you
• 23:27
  Speaker 1: are creating more space. So it's really weird and counterintuitive.
• 23:31
  Speaker 1: You know. It means that like energy is creating more energy.
• 23:34
  Speaker 1: And for those of you who worry about, like, well
• 23:35
  Speaker 1: where does this energy come from? Right, Like, how can
• 23:38
  Speaker 1: you just do that? Doesn't that violate conservation of energy? Yes,
• 23:41
  Speaker 1: and biolate it's conservation of energy, which it turns out,
• 23:45
  Speaker 1: is not a deep and fundamental principle of the universe.
• 23:48
  Speaker 1: Only a fundamental principle of universe is where space is static,
• 23:51
  Speaker 1: where the rules are not changing as a function of time.
• 23:54
  Speaker 1: But we don't seem to live in that kind of universe.
• 23:55
  Speaker 1: We live in the universe where the space is changing
• 23:58
  Speaker 1: and so energy is not served. It just like appears
• 24:01
  Speaker 1: seemingly out of nowhere, right, But I feel like that's
• 24:04
  Speaker 1: only true if you assume that dark energy is sort
• 24:07
  Speaker 1: of inherent to space, you know what I mean? Like
• 24:10
  Speaker 1: the dark energy also be you know, the result of
• 24:13
  Speaker 1: something already in space or something that that is limited.
• 24:16
  Speaker 1: A dark energy could be a lot of things. But
• 24:18
  Speaker 1: what we do know is that it doesn't get diluted
• 24:20
  Speaker 1: as space expands, so you can come up with something
• 24:22
  Speaker 1: else that also has that property. The only thing we
• 24:25
  Speaker 1: know about is vacuum energy is the potential energy that's
• 24:29
  Speaker 1: the only thing that doesn't get diluted as space expand.
• 24:32
  Speaker 1: Matter and radiation, those kind of things, they do get
• 24:35
  Speaker 1: diluted as space expands. But then again, we don't really
• 24:37
  Speaker 1: know what space is, right, and so maybe we need
• 24:40
  Speaker 1: a whole new concept for how space works and what
• 24:43
  Speaker 1: it means. Right. That's kind of what I mean is that,
• 24:45
  Speaker 1: you know, you don't know where it's coming from, and
• 24:49
  Speaker 1: like you said, it's changed over the years since the
• 24:52
  Speaker 1: beginning of the universe. So even that statement that it
• 24:55
  Speaker 1: is sort of inherent to space, we don't really quite
• 24:57
  Speaker 1: know for sure, right, We definitely do not know for sure.
• 24:59
  Speaker 1: We're in the part to this investigation where we're trying
• 25:01
  Speaker 1: to just like build a general structure of an idea
• 25:04
  Speaker 1: and ask, like what shape does this idea have to take?
• 25:08
  Speaker 1: What can we fit into it? And we start with
• 25:10
  Speaker 1: what we think are the simplest ideas. You know, maybe
• 25:12
  Speaker 1: it's like this, maybe it's like that, and if that works, great,
• 25:15
  Speaker 1: and if it doesn't work, then we need to add
• 25:17
  Speaker 1: bells and whistles or come up with new ideas. We're
• 25:19
  Speaker 1: definitely in the very early days. Yeah, and even though
• 25:22
  Speaker 1: we are still only I guess inventing the general shape
• 25:27
  Speaker 1: of the general idea. There are some problems with this
• 25:30
  Speaker 1: general idea, ones that have to do with the beginning
• 25:33
  Speaker 1: of the universe, and so let's get into what is
• 25:36
  Speaker 1: the problem with dark energy, But first let's take a
• 25:38
  Speaker 1: quick break. All right, we're talking about dark energy, and
• 25:54
  Speaker 1: I guess there's a problem with dark energy. I mean,
• 25:56
  Speaker 1: it's not just making the universe bigger and bigger, faster
• 25:58
  Speaker 1: and faster, which eventually lead to the heat death of
• 26:02
  Speaker 1: the universe, the universe dying out of basically order. There's
• 26:07
  Speaker 1: also some problems with it being able to explain the
• 26:10
  Speaker 1: early universe exactly. What we've tried so far is saying
• 26:15
  Speaker 1: maybe that there's just a number we can stick in
• 26:17
  Speaker 1: Einstein's equation, that like every unit of space has a
• 26:20
  Speaker 1: certain amount of dark energy. And there's a few different
• 26:23
  Speaker 1: things going on here that it's important to sort of unravel.
• 26:26
  Speaker 1: One is that, like, we assume that dark energy is constant,
• 26:29
  Speaker 1: but when we say constant, we mean like any chunk
• 26:31
  Speaker 1: of space has the same amount of this dark energy,
• 26:34
  Speaker 1: this potential energy, this cosmological constant. But as the universe expands,
• 26:39
  Speaker 1: even if every chunk of space has the same amount
• 26:41
  Speaker 1: of dark energy. Dark energy is fraction of the universe
• 26:44
  Speaker 1: itself is growing, right, because everything else gets diluted away.
• 26:48
  Speaker 1: So the dark energy fraction of the universe we don't
• 26:50
  Speaker 1: think is constant dark energy. We thought maybe was constant
• 26:54
  Speaker 1: like per chunk of space. That's what the cosmological constant is.
• 26:58
  Speaker 1: That was the basic idea, like had a fixed amount
• 27:00
  Speaker 1: of dark energy per unit of space, and then see
• 27:03
  Speaker 1: if that evolves the universe through time in the way
• 27:06
  Speaker 1: that we see it actually happening out there, right, And
• 27:09
  Speaker 1: what you found is that it doesn't write like a
• 27:12
  Speaker 1: number you have just taken now to the equation to
• 27:14
  Speaker 1: explain the current acceleration of the expansion of the universe works.
• 27:18
  Speaker 1: But then if you you know, you look back in time,
• 27:20
  Speaker 1: that number doesn't work exactly. A cosmological constant doesn't quite
• 27:24
  Speaker 1: describe the history that we see. And we can measure
• 27:27
  Speaker 1: this in two different ways. We have late time measurements
• 27:30
  Speaker 1: and we have early time measurements, and they don't quite agree.
• 27:33
  Speaker 1: So the late time measurements are like, let's go out
• 27:35
  Speaker 1: and measure the expansion of the universe. How fast are
• 27:38
  Speaker 1: things moving and how fast are they accelerating? And these
• 27:40
  Speaker 1: are the famous discoveries of dark energy, you know, for example,
• 27:43
  Speaker 1: looking at type one A supernova, that kind of stuff.
• 27:46
  Speaker 1: We can also look at the very very early universe
• 27:49
  Speaker 1: and trying to measure how much dark energy was there
• 27:51
  Speaker 1: back then, measure that using like the cosmic microwave background radiation.
• 27:56
  Speaker 1: We measure that, and then we plug that into our
• 27:57
  Speaker 1: simulations and try to predict how much acceleration there was
• 28:01
  Speaker 1: and how fast things should be moving today. And those
• 28:03
  Speaker 1: two numbers don't agree, right, and so there's some sort
• 28:07
  Speaker 1: of mismatch there, Like there doesn't seem to be enough
• 28:10
  Speaker 1: dark energy in the early universe to get us going
• 28:13
  Speaker 1: as fast as we seem to be going today. I
• 28:15
  Speaker 1: feel like there's two things, and maybe people are getting confused.
• 28:18
  Speaker 1: So like, right now the universe is expanding at a
• 28:21
  Speaker 1: velocity that's faster than it used to be. That's for sure,
• 28:25
  Speaker 1: like the universe expanding faster than it used to expand before.
• 28:29
  Speaker 1: But you can also talk about the acceleration of the universe,
• 28:32
  Speaker 1: which is the idea that it's growing faster and faster
• 28:35
  Speaker 1: each year. And so I think you're saying that even
• 28:37
  Speaker 1: the acceleration now is faster than it used to be,
• 28:41
  Speaker 1: Like the universe is somehow hitting the gas pedal even harder. Today.
• 28:45
  Speaker 1: What we do is we measure this thing called the
• 28:46
  Speaker 1: Hubble constant, you know, which is terribly named because it's
• 28:50
  Speaker 1: not a constant. It's a measure of how fast the
• 28:52
  Speaker 1: universe is expanding. And we can measure it like in
• 28:55
  Speaker 1: recent times, because we can look in our neighborhood and
• 28:58
  Speaker 1: see like how fast is stuff looking away from us?
• 29:00
  Speaker 1: How fast was stuff moving away from us pretty recently.
• 29:04
  Speaker 1: We can use that to measure this Hubble constant, which
• 29:06
  Speaker 1: is like the derivative of the scale factor of the
• 29:09
  Speaker 1: universe normalized to itself. And so that's like a measure
• 29:12
  Speaker 1: of the expansion rate. And what we can do in
• 29:14
  Speaker 1: the early universe is we can measure like how much
• 29:17
  Speaker 1: dark energy was there. We can use that to predict
• 29:20
  Speaker 1: the acceleration of the universe, which should give us like
• 29:24
  Speaker 1: the velocity. It's sort of like saying, all right, you
• 29:27
  Speaker 1: started your car, you were pressing on the gas pedal
• 29:30
  Speaker 1: a certain amount, how fast should you be going after
• 29:33
  Speaker 1: a minute? And if the rate we're measuring, like how
• 29:36
  Speaker 1: faster car is going right now is too fast, and
• 29:39
  Speaker 1: we're like, maybe you were pressing the gas pedal faster
• 29:41
  Speaker 1: than you thought. You were right, right, But I wonder
• 29:44
  Speaker 1: if maybe the folks are getting confused with because there
• 29:47
  Speaker 1: there's also the idea in the early universe of inflation,
• 29:50
  Speaker 1: right and the Big Bang? Now was inflation and the
• 29:53
  Speaker 1: Big bank also due to dark energy? Or was it
• 29:56
  Speaker 1: you know, that super rapid expansion like a second after
• 29:59
  Speaker 1: the Uni verse was born, the universe expanded like tang
• 30:02
  Speaker 1: to the twenties something or crazy amount. Was that also
• 30:05
  Speaker 1: due to dark energy? Or was that something due to
• 30:07
  Speaker 1: something else? Entirely, we just really don't know. We know
• 30:10
  Speaker 1: that there are similar right. They both expand space very rapidly.
• 30:14
  Speaker 1: We don't know if they're connected. There are some theories
• 30:17
  Speaker 1: of inflation that try to connect dark energy with inflation,
• 30:21
  Speaker 1: but there's some theories of inflation that are totally separate
• 30:23
  Speaker 1: that say, no, it's due to this weird inflaton field
• 30:26
  Speaker 1: that has its own potential energy which rapidly expanded space,
• 30:31
  Speaker 1: and so we just don't know. We do notice that
• 30:34
  Speaker 1: they are similar, right, But these questions about dark energy
• 30:37
  Speaker 1: assume just inflation happened, and like, don't ask too many
• 30:39
  Speaker 1: questions about it. Let's just start from the post inflation
• 30:42
  Speaker 1: universe and try to understand the expansion history from that point. Oh,
• 30:46
  Speaker 1: I see, when you're talking about early dark energy, you
• 30:49
  Speaker 1: mean like post inflation dark energy exactly, not that early
• 30:54
  Speaker 1: that I mean, not pre early, late earlier. That's right,
• 30:59
  Speaker 1: because the early this thing that we can actually measure
• 31:02
  Speaker 1: comes from about four thousand years after the beginning of
• 31:04
  Speaker 1: the universe. This is the cosmic microwave background radiation. And
• 31:07
  Speaker 1: we can look at these wiggles in the microwave spectrum
• 31:10
  Speaker 1: in the sky, which is light from that very early plasma,
• 31:13
  Speaker 1: and we can get a sense from what was going
• 31:15
  Speaker 1: on back then, and so that gives us actually a
• 31:17
  Speaker 1: measurement of how much dark energy there was back then,
• 31:20
  Speaker 1: which let's just calculate the acceleration from that point, not
• 31:23
  Speaker 1: all the way back to inflation. Like that's a murky
• 31:25
  Speaker 1: mystery for another day, right, But wouldn't that sort of
• 31:28
  Speaker 1: confuse things like at what point do you think this
• 31:31
  Speaker 1: potential infloton field or whatever it is that costs a
• 31:34
  Speaker 1: big bang or the inflation you know, drop off and
• 31:38
  Speaker 1: gave way to dark energy, Like couldn't there have been overlapped?
• 31:41
  Speaker 1: How do you know? Like what cause inflation isn't like
• 31:44
  Speaker 1: affecting us today. Yeah, we don't write it could be connected.
• 31:48
  Speaker 1: The basic ideas are the same. That you have some
• 31:51
  Speaker 1: field with a lot of potential energy, you put that
• 31:53
  Speaker 1: into Einstein's equations. It causes this repulsive effect on the
• 31:58
  Speaker 1: universe to stretch it and expand. It could be that
• 32:01
  Speaker 1: inflation has a different kind of potential energy from a
• 32:04
  Speaker 1: different field, this in photon field, or it could be related. Also,
• 32:07
  Speaker 1: we don't understand either of them. We don't understand why
• 32:09
  Speaker 1: inflation happened. We don't understand why it stopped. We don't
• 32:12
  Speaker 1: understand if it did in fact stop, or if dark
• 32:15
  Speaker 1: energy is an extension of it. Yeah, we're clueless about
• 32:18
  Speaker 1: all that stuff. So basically we don't know anything. Daniel.
• 32:22
  Speaker 1: We're in the dark about the whole dark energy thing.
• 32:24
  Speaker 1: We're mostly in the dark. Until very recently, though, it
• 32:27
  Speaker 1: seemed like if you assume that there was a fixed
• 32:29
  Speaker 1: amount of dark energy after inflation, after somehow the in
• 32:33
  Speaker 1: photon field died away or whatever, that if you assume
• 32:36
  Speaker 1: there was a fixed amount of dark energy, that it
• 32:37
  Speaker 1: mostly described the universe like our rough calculations and early
• 32:41
  Speaker 1: measurements suggested things were banging on that the measurements we
• 32:44
  Speaker 1: had of this cosmic microwave background radiation told us a
• 32:48
  Speaker 1: certain amount of dark energy. You put that into the
• 32:50
  Speaker 1: equations and ran them forward in time. You've got a
• 32:52
  Speaker 1: universe that looked a lot like the one we see
• 32:54
  Speaker 1: out there right now. But as these measurements got more
• 32:56
  Speaker 1: and more precise than a problem emerged and they didn't
• 32:59
  Speaker 1: quite work. Oh, I see, all right, So I'm trying
• 33:02
  Speaker 1: to put my head in the place of a physicist.
• 33:04
  Speaker 1: So you're saying that the Big Bang happened, inflation happened, done,
• 33:09
  Speaker 1: like we're going to put a market there and ignore
• 33:10
  Speaker 1: everything that happened before. Like after information, we're going to
• 33:14
  Speaker 1: reset our thinking. We're going to assume that there's something
• 33:17
  Speaker 1: called dark energy that's continuing to keep the universe expanding
• 33:22
  Speaker 1: at a faster rate. And you're saying that before we
• 33:24
  Speaker 1: used to be able to just plug one number in
• 33:26
  Speaker 1: and it sort of worked like it it mostly described things,
• 33:29
  Speaker 1: But now now it doesn't quite work. Now it doesn't
• 33:32
  Speaker 1: quite work exactly. Now the universe seems to be expanding
• 33:35
  Speaker 1: at late times more quickly than we can explain with
• 33:38
  Speaker 1: the amount of dark energy that we measure from the
• 33:40
  Speaker 1: early times. Like whoever was driving the universe back then
• 33:44
  Speaker 1: with dark energy, they put their foot on the gas
• 33:46
  Speaker 1: pedal at a certain level. But now when we look
• 33:49
  Speaker 1: at the speed of the universe, it seems to be
• 33:50
  Speaker 1: going faster than can be explained by that amount of gas.
• 33:54
  Speaker 1: So that's the question. Is the cosmological constant actually a
• 33:57
  Speaker 1: constant or do we need to make it more complicated?
• 34:00
  Speaker 1: Right that number used to plug in that used to
• 34:02
  Speaker 1: work before now doesn't work before, which means that basically
• 34:05
  Speaker 1: it's not a number. Kind of yeah, now it's a function.
• 34:08
  Speaker 1: Right now we need a new little bit, meaning like
• 34:10
  Speaker 1: the amount of dark energy per block of space is
• 34:14
  Speaker 1: or it has been changing. That's the question exactly, And
• 34:17
  Speaker 1: so early dark energy is an attempt to try to
• 34:20
  Speaker 1: fix this problem is to say, well, maybe there's dark energy,
• 34:23
  Speaker 1: which is just a number and it's constant. But now
• 34:25
  Speaker 1: let's add a new thing. Let's not just change dark energy.
• 34:28
  Speaker 1: Let's add a new kind of expansion to the universe,
• 34:31
  Speaker 1: like a new unexplained expansion that's going to only take
• 34:35
  Speaker 1: place in the early universe, Like there was dark energy,
• 34:38
  Speaker 1: which is accelerating the expansion the universe. Plus let's add
• 34:41
  Speaker 1: a new bit which only turned on an early universe,
• 34:45
  Speaker 1: got things going extra fast, and then disappeared, which is
• 34:48
  Speaker 1: why we don't see it today. So that's the idea
• 34:50
  Speaker 1: of early dark energy, is to try to like patch
• 34:52
  Speaker 1: up this problem with dark energy, not by saying dark
• 34:55
  Speaker 1: energy changes with time, but by saying there was a
• 34:57
  Speaker 1: new thing, yet another way to expanding universe, but this
• 35:01
  Speaker 1: one only lasted from like zero to four years after
• 35:05
  Speaker 1: the Big Bang? Oh? I see wait? So um, so
• 35:08
  Speaker 1: you I think you're saying that early dark energy is
• 35:10
  Speaker 1: not dark energy. So early dark energy is not dark
• 35:14
  Speaker 1: energy exactly. It's a new thing that is like dark
• 35:17
  Speaker 1: energy and also kind of like inflation, right, and that
• 35:21
  Speaker 1: it expands the universe due to some potential energy field,
• 35:24
  Speaker 1: but it's somehow also disappeared before the CNB, right, so
• 35:28
  Speaker 1: that it doesn't like mess up everything we see later. Right.
• 35:30
  Speaker 1: I guess an early hooge would be so foreign to
• 35:33
  Speaker 1: regular hooge that you would have to call it a
• 35:36
  Speaker 1: different whoree. I think that's what you're thinking, is a physicist,
• 35:41
  Speaker 1: what gives the sense of the scale here? How different
• 35:44
  Speaker 1: is this post inflation, post Big Bang dark energy expansion
• 35:49
  Speaker 1: than the expansion we have now due to dark energy.
• 35:52
  Speaker 1: It's turned out to be pretty significant. You know, early
• 35:54
  Speaker 1: on when we were measuring these things for the first time,
• 35:57
  Speaker 1: we really didn't know how fast the universe was expanding,
• 35:59
  Speaker 1: and we had big error bars on all of our measurements,
• 36:02
  Speaker 1: and so things seemed to kind of disagree a little bit,
• 36:04
  Speaker 1: but nobody was worried about it. Now these measurements have
• 36:07
  Speaker 1: gotten really really precise, and the difference between the predictions
• 36:10
  Speaker 1: for how fast we are expanding and how fast we
• 36:13
  Speaker 1: should be expanding if dark energy was constant and there
• 36:16
  Speaker 1: was no early dark energy are different by about ten
• 36:19
  Speaker 1: per cent. So this is measurements of the Hubble constant,
• 36:22
  Speaker 1: and like the late measurements, the ones using like supernova
• 36:25
  Speaker 1: and sephids and other kinds of stuff, they measured this
• 36:27
  Speaker 1: Hubble constant to be about seventy three, where the units
• 36:30
  Speaker 1: are kilometers per second per mega PARSEEK and the early ones,
• 36:35
  Speaker 1: the ones that come from the CNB where we measure
• 36:37
  Speaker 1: what was going on in the early universe, how much
• 36:39
  Speaker 1: dark energy there was, and then predict how fast we
• 36:42
  Speaker 1: should be accelerating. They predict sixty seven, So that's seventy
• 36:46
  Speaker 1: three versus sixty seven, and the uncertainties are getting pretty
• 36:49
  Speaker 1: pretty small, Like, these are precise measurements now. The Plank
• 36:52
  Speaker 1: satellite gave us really precise measurements of the CMB, and
• 36:56
  Speaker 1: we have lots and lots of supernova now and lots
• 36:58
  Speaker 1: of other kind of ways to measure the leration today.
• 37:01
  Speaker 1: So the difference between these two has become pretty significant.
• 37:03
  Speaker 1: It's like five or six sigma, which means that it's like,
• 37:07
  Speaker 1: doesn't seem to be just a statistical error. It seems
• 37:10
  Speaker 1: like it might be real. Well, it's it's it's ten
• 37:13
  Speaker 1: percent different, but you're saying that your confidence in that
• 37:16
  Speaker 1: ten percent difference is getting stronger. Exactly. People were sort
• 37:20
  Speaker 1: of thinking like, okay, these numbers are far apart, but
• 37:23
  Speaker 1: the errors are big. And then as we get more
• 37:25
  Speaker 1: and more data, sometimes what happens is that the things
• 37:27
  Speaker 1: sort of drift together. You're like, oh, two measurements of
• 37:29
  Speaker 1: the same thing using different ways as they get more precise,
• 37:33
  Speaker 1: if you're really measuring the same thing, they should eventually
• 37:35
  Speaker 1: agree and if you've understood all of your uncertainties and biases.
• 37:38
  Speaker 1: But these two things, as they've gotten more precise, have
• 37:41
  Speaker 1: stayed far apart. And so now yeah, they seem to
• 37:44
  Speaker 1: be far apart, and the confidence in both measurements is
• 37:47
  Speaker 1: pretty high. All right, So there's about a ten percent
• 37:49
  Speaker 1: difference in what we thought was the universe's expansion and
• 37:53
  Speaker 1: what it actually was before. And so just regular dark
• 37:57
  Speaker 1: energy on time late dark energy doesn't planet, and so
• 38:00
  Speaker 1: you need this concept of early dark energy. Early dark
• 38:03
  Speaker 1: energy is sort of in the same spirit of dark energy.
• 38:05
  Speaker 1: It's like, hold on the universe seems to be doing
• 38:07
  Speaker 1: something we can't explain. Let's just add another piece to
• 38:11
  Speaker 1: the mix and see if we can use that to
• 38:14
  Speaker 1: explain what's going on. Later we'll come in and figure
• 38:16
  Speaker 1: out why is this thing here, how does it work,
• 38:19
  Speaker 1: what exactly is creating this dark energy. The first step
• 38:22
  Speaker 1: is just like, you know, rough out an idea for
• 38:25
  Speaker 1: what pieces you need at what time to explain the
• 38:28
  Speaker 1: history that we see right right. Basically, it's sort of
• 38:30
  Speaker 1: like admitting that dark energy is changing. Right Like, the
• 38:34
  Speaker 1: original idea for dark energy was that it was some
• 38:36
  Speaker 1: sort of like constant inherent property of space and never changes.
• 38:40
  Speaker 1: But now you're sort of being forced to say, hey,
• 38:42
  Speaker 1: dark energy kind of is changing, So maybe it's not
• 38:45
  Speaker 1: some constant of the universem inherent property of space. Maybe
• 38:49
  Speaker 1: it's there are multiple dark energies, or maybe it's the
• 38:51
  Speaker 1: dark energy that's changing, yes, exactly. And there's a whole
• 38:54
  Speaker 1: category of ideas there. There's ones where there's multiple dark energies,
• 38:57
  Speaker 1: like a new one that appears early in the universe
• 39:00
  Speaker 1: and then disappears, right, which is why we don't seem
• 39:02
  Speaker 1: to see it today. Others where dark energy itself changes
• 39:05
  Speaker 1: and then stabilizes to a certain number and then is
• 39:08
  Speaker 1: fixed for the rest of the time of the universe.
• 39:10
  Speaker 1: There's a whole ridiculous spectrum of ideas. A lot of
• 39:13
  Speaker 1: particle theories I talked to say that most of them
• 39:15
  Speaker 1: are kind of ridiculous. They call them theoretical shenanigans. But
• 39:19
  Speaker 1: you know, it's just an effort to like try to
• 39:21
  Speaker 1: cook up a recipe that explains what we see and
• 39:24
  Speaker 1: then later figure out the details of that recipe right, right,
• 39:27
  Speaker 1: And in the meantime, let's confuse everybody with shortcuts here
• 39:32
  Speaker 1: to call things. Why not just call it dark shenanigans.
• 39:35
  Speaker 1: That would be valid. Oh man, that would have been awesome.
• 39:39
  Speaker 1: I would love if we had called it dark cinnanigans.
• 39:41
  Speaker 1: That's right, DS for because I have dark matter, dark energy,
• 39:45
  Speaker 1: and dark shenanigans. That seems like a really nice trifecta.
• 39:49
  Speaker 1: Sounds like what all physicists, and you know, the theorists
• 39:53
  Speaker 1: are going crazy with these ideas because every time you
• 39:56
  Speaker 1: give them an opening to be creative, then they come
• 39:59
  Speaker 1: up with all sort of silly ideas for like what
• 40:02
  Speaker 1: might be creating this. Lisa Randall, who's a famous theorist
• 40:05
  Speaker 1: who came up with the idea of extra dimensions. She
• 40:08
  Speaker 1: has a paper about rock and roll solutions to the
• 40:10
  Speaker 1: early universe that involves like new weird fields in space,
• 40:15
  Speaker 1: some of which rock back and forth to explain like
• 40:18
  Speaker 1: why they disappear, and some of them would you like,
• 40:20
  Speaker 1: roll away gradually and fade out before we could see them. Mhm.
• 40:25
  Speaker 1: So she called them rock and roll solutions literally in
• 40:27
  Speaker 1: her paper exactly. Her paper really is called rock and
• 40:31
  Speaker 1: Roll Solutions. It's pretty fun paper, but it's definitely in
• 40:34
  Speaker 1: the theoretical shenanigans category. Yeah, because I guess you, I mean,
• 40:39
  Speaker 1: before you saw dark energy was this constant thing, but
• 40:41
  Speaker 1: now knowing that it's changing, I mean, you're sort of
• 40:43
  Speaker 1: blowing the whole thing open, right, Like you're saying, now
• 40:46
  Speaker 1: you could pretty much imagine anything that could explain that change. Yeah,
• 40:50
  Speaker 1: although it's a bit more complicated, right, It's simpler to say, oh,
• 40:54
  Speaker 1: the universe has this new property, and that property is
• 40:56
  Speaker 1: a constant and it just is. It's more complicated to
• 40:59
  Speaker 1: come up with a new piece which you have to
• 41:00
  Speaker 1: explain and then also explain why it's no longer around.
• 41:04
  Speaker 1: It's just as tricky as inflation. Like with inflation, we
• 41:07
  Speaker 1: have this very rapid expansion of the early universe which
• 41:10
  Speaker 1: you have to explain. You also have to explain why
• 41:12
  Speaker 1: that stopped. And so early dark energy is a special
• 41:16
  Speaker 1: puzzle for theorists because they have to explain why it
• 41:18
  Speaker 1: exists and also why it no longer seems to exist. Right,
• 41:22
  Speaker 1: and they also have to get up early, which is
• 41:24
  Speaker 1: a big problem. Just stay up late enough, or drink
• 41:27
  Speaker 1: a lot of dark coffee. All right, Well, let's get
• 41:29
  Speaker 1: into whether this early dark energy is real and what
• 41:32
  Speaker 1: we're doing to measure it and or confirm all of
• 41:35
  Speaker 1: these dark Shenanigan ideas. But first let's take a quick break.
• 41:52
  Speaker 1: All right, we're talking about the mystery of dark energy,
• 41:54
  Speaker 1: which apparently, um, it's not this constant thing. It's sort
• 41:58
  Speaker 1: of this seems to be this kind of fickle saying
• 42:00
  Speaker 1: almost like it was pretty lazy at the beginning of
• 42:02
  Speaker 1: the universe after inflation, right, that's the idea. But now
• 42:05
  Speaker 1: it's sort of getting steam, and it's maybe getting darker
• 42:09
  Speaker 1: and later, and so it's getting more energy exactly. And
• 42:13
  Speaker 1: it's amazing to me that dark energy sort of ever worked.
• 42:15
  Speaker 1: You know, we look back now the history of the
• 42:17
  Speaker 1: universe's expansion and it's incredible that you can add this
• 42:21
  Speaker 1: simple term to just say, well, space seems to have
• 42:24
  Speaker 1: this weird potential energy in it, which Einstein's equations predict
• 42:27
  Speaker 1: cause this expansion, this repulsive force to stretch out the universe,
• 42:31
  Speaker 1: and that that mostly describes what we see after inflation.
• 42:35
  Speaker 1: We see this period of very slow expansion then sort
• 42:38
  Speaker 1: of picked up steam around eight or nine billion years
• 42:41
  Speaker 1: after the universe and is now accelerating very very quickly.
• 42:44
  Speaker 1: It's sort of amazing that that complex history can in
• 42:47
  Speaker 1: fact be described almost by a constant term. I think
• 42:51
  Speaker 1: that's pretty cool. I mean, the fact that it doesn't
• 42:53
  Speaker 1: quite work means, you know, it needs some new ideas,
• 42:56
  Speaker 1: but I think it's sort of awesome that it works
• 42:58
  Speaker 1: at all. Well, it's the only sort of sort of
• 43:00
  Speaker 1: works right, Like it could just be like totally wrong,
• 43:04
  Speaker 1: Like our whole sort of formulation of the universe could
• 43:07
  Speaker 1: be totally wrong, and this could be sort of like
• 43:09
  Speaker 1: the thing that makes us see that it's wrong, right exactly.
• 43:11
  Speaker 1: And that's why we do these studies in more and
• 43:13
  Speaker 1: more detail. You know, when you're first looking at something,
• 43:15
  Speaker 1: if you have like a simple explanation that sort of
• 43:18
  Speaker 1: mostly describes it, that's kind of cool. Like if you're
• 43:20
  Speaker 1: plotting to quantities that you've measured and they follow along
• 43:23
  Speaker 1: a straight line, you're like, that's interesting, and then as
• 43:26
  Speaker 1: you get more points, you're like, oh, it turns out
• 43:27
  Speaker 1: it's not quite a straight line, it's almost. Then you
• 43:30
  Speaker 1: know you need to refine your understanding, your theory. But
• 43:33
  Speaker 1: the fact that like mostly a straight line describes it,
• 43:35
  Speaker 1: it is already pretty powerful. Well, I think a big
• 43:37
  Speaker 1: question that you also rais is whether or not this
• 43:40
  Speaker 1: changing dark energy effect is actually real, because I think,
• 43:45
  Speaker 1: as you said, it's it's sort of based on two
• 43:47
  Speaker 1: very different kinds of measurements, right, Like we measure dark
• 43:50
  Speaker 1: energy now using one thing, but then early in the
• 43:53
  Speaker 1: universe we measure doing using something else. So like, you know,
• 43:57
  Speaker 1: like a ten percent difference using to totally different measurement
• 44:01
  Speaker 1: systems seems sort of reasonable. It does, depending on those uncertainties, right,
• 44:05
  Speaker 1: Each of these things are very different styles and measurement
• 44:08
  Speaker 1: and we do this on purpose because we're interested in
• 44:11
  Speaker 1: something deep and true in the universe, so we try
• 44:14
  Speaker 1: to get a handle on it in different ways to
• 44:16
  Speaker 1: make sure that we're not getting biased by one of
• 44:18
  Speaker 1: our measurement techniques. And these really are very very different measurements.
• 44:22
  Speaker 1: It's important to understand, like the early measurements are very indirect.
• 44:26
  Speaker 1: You know, what we do when we look at the
• 44:27
  Speaker 1: cosmic microwave background radiation is we don't actually see dark
• 44:31
  Speaker 1: energy directly. What we do is we measure like how
• 44:34
  Speaker 1: much dark matter was there, how much normal matter was there.
• 44:37
  Speaker 1: We can tell that because we can see those two
• 44:39
  Speaker 1: things sloshing around in the early universe plasma and creating
• 44:43
  Speaker 1: like weird sound waves. It's called bury on acoustic oscillation
• 44:47
  Speaker 1: that we talked about once on the podcast. And we
• 44:49
  Speaker 1: can also measure how much energy there was overall in
• 44:52
  Speaker 1: the universe, a measurement of the curvature of space back then.
• 44:56
  Speaker 1: So the measurement of dark energy from the early universe
• 44:59
  Speaker 1: is actually just a a traction. It says how much
• 45:01
  Speaker 1: energy was there in total? How much can we account for.
• 45:04
  Speaker 1: We're using dark matter and normal matter, the rest of
• 45:06
  Speaker 1: which we call dark energy, So it's sort of like,
• 45:09
  Speaker 1: just by subtraction we assume how much dark energy there
• 45:13
  Speaker 1: was back then. It's very indirect. Well, I guess, because
• 45:16
  Speaker 1: it's so indirect, it makes me kind of feel like
• 45:19
  Speaker 1: it's just kind of a big guess. I mean, you're
• 45:22
  Speaker 1: looking at this picture from the early universe and you're
• 45:24
  Speaker 1: trying to, you know, throw it out these little tiny
• 45:27
  Speaker 1: nuances in the ripples of it. In in you're sort
• 45:30
  Speaker 1: of assuming all these proportions about the universe. Like how
• 45:34
  Speaker 1: confident are physicists about these measurements. There's a lot of
• 45:36
  Speaker 1: debate about that because in order to extract from that
• 45:40
  Speaker 1: the measurement of dark energy, you've got to make some assumptions,
• 45:43
  Speaker 1: like this data comes from the Plank satellite, which is
• 45:45
  Speaker 1: an exceptional instrument, very high precision measurement of the cosmic
• 45:49
  Speaker 1: microwave background radiation like revolutionized cosmology. But in order to
• 45:53
  Speaker 1: interpret this stuff, you need to have some models in
• 45:55
  Speaker 1: your head that you're using to interpret this data. So
• 45:58
  Speaker 1: what people have been doing in the last two years
• 46:00
  Speaker 1: as this discrepancy has arisen between this measurement from Plank,
• 46:04
  Speaker 1: from the early data from the CNB and the late
• 46:06
  Speaker 1: measurements from the supernova is to try to revisit those
• 46:09
  Speaker 1: things and ask questions. It's like, is there another way
• 46:12
  Speaker 1: to interpret this data? Can we see it another way?
• 46:14
  Speaker 1: Are there assumptions that we're making that we can change
• 46:16
  Speaker 1: And they've tried like changing those assumptions and starting from
• 46:19
  Speaker 1: scratch and using other ideas, and the measurement is persistently
• 46:23
  Speaker 1: too small, like they've banged on it and banged on
• 46:26
  Speaker 1: it and banged on it some more, and it just
• 46:28
  Speaker 1: seems to be very consistent. So that's the early expansion
• 46:31
  Speaker 1: of the universe. What about the late expansion of the universe?
• 46:33
  Speaker 1: How are we measuring that one? So that we have
• 46:35
  Speaker 1: to find some way to measure distance in the current universe,
• 46:39
  Speaker 1: that's the key. We want to know how far away
• 46:41
  Speaker 1: things are and how fast are they moving away from us.
• 46:45
  Speaker 1: So in order to measure the velocity of a function
• 46:47
  Speaker 1: of time in the universe, we need to measure velocity
• 46:50
  Speaker 1: of the function of apparent distance. Because things that are
• 46:53
  Speaker 1: far away from us, we see them in the past. Right,
• 46:56
  Speaker 1: something that's a billion light years away, we're not seeing
• 46:59
  Speaker 1: light from it today. We're seeing life from a billion
• 47:01
  Speaker 1: years ago. So in order to understand the expansion the
• 47:04
  Speaker 1: universe over time, we need to understand the velocity of
• 47:06
  Speaker 1: the universe as a function of distance from us today.
• 47:09
  Speaker 1: It's really the same thing. And to measure those distances
• 47:12
  Speaker 1: is always very very tricky, because how can you tell
• 47:14
  Speaker 1: something that's really close by and dim or really far
• 47:17
  Speaker 1: away and bright. Right, You can't tell unless you know
• 47:21
  Speaker 1: how bright it's supposed to be. So the key to
• 47:23
  Speaker 1: all of these late time measurements are calibrations of how
• 47:28
  Speaker 1: far away things are. So we have things like type
• 47:30
  Speaker 1: one A supernova which blow up in a very predictable way.
• 47:34
  Speaker 1: We know basically how bright they should be. And they
• 47:37
  Speaker 1: have other ways to do this, like these sephids, these
• 47:39
  Speaker 1: variable stars where their pulsation is very closely connected to
• 47:43
  Speaker 1: how bright they are at their source. And people have
• 47:46
  Speaker 1: been really creative and finding other ways to measure this
• 47:48
  Speaker 1: expansion using other calibratable objects neutron star, gravitational waves, and quasars,
• 47:54
  Speaker 1: and this recent measurement about red giants, and all of
• 47:58
  Speaker 1: these things are uncertain, uncertain different ways, Like we don't
• 48:01
  Speaker 1: quite know our measurements of the sefids reliable. Are we
• 48:05
  Speaker 1: accounting for the amount of dust between us and those
• 48:07
  Speaker 1: stars correctly? That's why we try to do it in
• 48:09
  Speaker 1: several different ways. The amazing thing is that all these
• 48:12
  Speaker 1: different measurements using ways ours or supernova or sephids or
• 48:16
  Speaker 1: red giant stars that have a helium flash in a
• 48:19
  Speaker 1: very predictable way, they all mostly agree with each other,
• 48:22
  Speaker 1: and they all disagree with this early measurement. So it's
• 48:25
  Speaker 1: really compelling and fascinating. Right, But is there another way
• 48:29
  Speaker 1: I guess to kind of link the two measurements other
• 48:32
  Speaker 1: than this dark energy discrepancy? Do you know what I mean? Like,
• 48:34
  Speaker 1: if I measure something with one ruler and I measure
• 48:36
  Speaker 1: another thing with a different, totally different ruler way of
• 48:39
  Speaker 1: measuring things, and they disagree, I wouldn't necessarily say that
• 48:43
  Speaker 1: that's a whole new constpant in the universe. I like
• 48:45
  Speaker 1: try to find other ways to see that the two
• 48:48
  Speaker 1: rulers or the two measurement systems agree in other things, right, Yeah,
• 48:52
  Speaker 1: And that's what they haven't done by trying to come
• 48:54
  Speaker 1: up with essentially other rulers. They got their Type one
• 48:56
  Speaker 1: a supernova ruler, and their SEFID ruler and their tip
• 49:00
  Speaker 1: of the red giant branch ruler, and all these different
• 49:03
  Speaker 1: rulers all basically seem to agree with each other, and
• 49:06
  Speaker 1: they should all make sort of different kinds of mistakes
• 49:08
  Speaker 1: if they do make mistakes. So that's a clue that like,
• 49:12
  Speaker 1: maybe this is real. Maybe the universe really is expanding
• 49:16
  Speaker 1: in this surprising way, because we haven't found a problem
• 49:19
  Speaker 1: with any of these measurements, right, but have you tied
• 49:22
  Speaker 1: the early universe CMB measurements to things like the say,
• 49:25
  Speaker 1: facifits or the red giant measurements. The only way we
• 49:29
  Speaker 1: can tie them is by taking that measurement from the
• 49:31
  Speaker 1: early universe and using it to predict how fast things
• 49:34
  Speaker 1: should be accelerating today, and that's where the disagreement is.
• 49:38
  Speaker 1: So what we're trying to do is make other measurements
• 49:40
  Speaker 1: from the early universe. And there's some pretty exciting, very
• 49:43
  Speaker 1: recent results from a telescope in Chile called the Atacama
• 49:46
  Speaker 1: Cosmology Telescope that also looks at the CNB, but in
• 49:50
  Speaker 1: a way that's different from the Plank satellite, right, And
• 49:53
  Speaker 1: that sounds super exciting, But I guess maybe my question is,
• 49:56
  Speaker 1: and we like confirm these measurements or confirm our ability
• 50:00
  Speaker 1: to measure the expansion of the universe using the CMB
• 50:02
  Speaker 1: with other ways or other ways of measuring the expansion. Now,
• 50:06
  Speaker 1: like you're saying, the early universe expansion is measured by
• 50:08
  Speaker 1: the cosmic microwave background radiation CNB, but the current expansion
• 50:13
  Speaker 1: is measured in a totally different way, and they come
• 50:16
  Speaker 1: up with different numbers, which may be something about dark
• 50:20
  Speaker 1: energy that's changing, or it could just be maybe that
• 50:23
  Speaker 1: our two measurements are not quite linked together or calibrating. Yeah,
• 50:27
  Speaker 1: it could be an issue with calibration. We can't measure
• 50:29
  Speaker 1: the dark energy today the same way we can from
• 50:32
  Speaker 1: the CMB. Right, That measurement we could make because we
• 50:35
  Speaker 1: had this special window where we get this life from
• 50:38
  Speaker 1: the cosmic microwave background radiation. We can't make that same
• 50:41
  Speaker 1: kind of measurement today. That would be really awesome if
• 50:43
  Speaker 1: we had a late time CMB that we could use
• 50:46
  Speaker 1: to measure and compared to the early time CMB. That's
• 50:49
  Speaker 1: just not available. Right. The universe doesn't give you everything
• 50:52
  Speaker 1: you want. You just got to look around for opportunities
• 50:54
  Speaker 1: and and your understanding must be wrong right now. Yeah,
• 50:57
  Speaker 1: I mean, it's amazing that we can do any of
• 50:59
  Speaker 1: these measurements at all, or that we have these amazing
• 51:01
  Speaker 1: instruments to measure these expansion of the universe. Now, and
• 51:05
  Speaker 1: before I guess, I'm just saying, I'm just trying to
• 51:07
  Speaker 1: understand what it is that the mystery is. And it
• 51:10
  Speaker 1: seems like there's a discrepancy, a difference between measuring the
• 51:14
  Speaker 1: early expansion of the universe using the CMB and measuring
• 51:17
  Speaker 1: the current expansion of the universe using you know, other
• 51:20
  Speaker 1: methods like supernovas and and seffords and red giants and
• 51:25
  Speaker 1: things like that. And you know, one possibility for this
• 51:28
  Speaker 1: difference is that there is something weird about dark energy
• 51:31
  Speaker 1: that's changing or I wonder another possibility, just to you know,
• 51:34
  Speaker 1: give us some context, is that maybe these two ways
• 51:37
  Speaker 1: of measuring the expansion of the universe are not quite calibrated, right, Yeah,
• 51:41
  Speaker 1: exactly one of them could be wrong. They could both
• 51:43
  Speaker 1: be wrong, exactly. And people are digging into the details
• 51:47
  Speaker 1: of how these measurements were made to look for potential
• 51:50
  Speaker 1: sources of error or bias that's why it's so valuable
• 51:53
  Speaker 1: to measure these things in multiple different ways, because it
• 51:56
  Speaker 1: checks your understanding and because they have different potential sources
• 51:59
  Speaker 1: of uncertainty, right, you know, all affected by the same bias.
• 52:02
  Speaker 1: And that's one reason why they built this telescope in Chile,
• 52:04
  Speaker 1: because it has different sensitivity than plank and so it
• 52:07
  Speaker 1: probes the cosmic microway background radiation in a slightly different way,
• 52:11
  Speaker 1: which gives a different power to answer this question. Right, Yeah,
• 52:14
  Speaker 1: I guess it's an ongoing work. But um, I guess
• 52:17
  Speaker 1: assuming then that our early measurement of expansion and our
• 52:20
  Speaker 1: lading measurement of expansion are both correct and the same
• 52:25
  Speaker 1: and have the same sort of basis in reality, then
• 52:28
  Speaker 1: that's a big deal. That means dark energy is changing, right,
• 52:31
  Speaker 1: So it's not a constant thing, and it may even
• 52:34
  Speaker 1: change in the future. It may change in the future. Yeah, exactly.
• 52:37
  Speaker 1: It means that the story is more complicated than just
• 52:40
  Speaker 1: you have one field which has some potential in it
• 52:42
  Speaker 1: and it has this constant contribution per unit of space,
• 52:45
  Speaker 1: which tells you this story of the expansion has to
• 52:47
  Speaker 1: be more complicated than that. You need some like extra
• 52:50
  Speaker 1: bitted gas in the early universe to get us going
• 52:52
  Speaker 1: so that we are expanding as fast as we see today.
• 52:55
  Speaker 1: And you're right, we don't understand what that is. We
• 52:57
  Speaker 1: don't know if it will come back, like and some
• 52:59
  Speaker 1: of these raw can roll theories like that early dark
• 53:02
  Speaker 1: energy rolls away, but hey, it could rock back, you know.
• 53:05
  Speaker 1: It could be that the future has more accelerated expansion,
• 53:09
  Speaker 1: or that it could go the opposite directions somehow. What
• 53:11
  Speaker 1: it really means is that we just don't know very
• 53:14
  Speaker 1: much about the future of the universe. Right. We could
• 53:16
  Speaker 1: be headed towards a heavy metal rock universe or a
• 53:20
  Speaker 1: easy listening universe. One of the things that is really
• 53:24
  Speaker 1: interesting for me is that these new measurements from this
• 53:26
  Speaker 1: Chilean telescope, they support this idea of early dark energy.
• 53:31
  Speaker 1: They measure the cosmic microwave background radiation in a different
• 53:34
  Speaker 1: way than plunk like. The details are kind of technical,
• 53:36
  Speaker 1: but you know, ground based telescopes always have different sensitivities
• 53:39
  Speaker 1: than space satellites, and when they analyze their data they
• 53:43
  Speaker 1: see something consistent with theories of early dark energy, Like
• 53:47
  Speaker 1: their data are more consistent with their being early dark
• 53:50
  Speaker 1: energy than with their not being early dark energy. So
• 53:52
  Speaker 1: they sort of disagree with Plank a little bit. Wait,
• 53:55
  Speaker 1: what do you mean? Did they disagree Plank? When they
• 53:58
  Speaker 1: look at their data, they don't see any specific evidence
• 54:01
  Speaker 1: for early dark energy. Early dark energy, if it existed,
• 54:04
  Speaker 1: would be this like extra expansion of the universe just
• 54:07
  Speaker 1: before the CNB plasma was formed, and it would change
• 54:10
  Speaker 1: a little bit how those ripples look. And Plank doesn't
• 54:13
  Speaker 1: see that. But this new telescope, the ACT in Chili,
• 54:16
  Speaker 1: it does see some weird ripples in the CNB that
• 54:20
  Speaker 1: seemed consistent with their being an extra bit of expansion
• 54:23
  Speaker 1: just before that plasma recombined, and so it's sort of
• 54:25
  Speaker 1: more consistent with their being early dark energy than with
• 54:28
  Speaker 1: their not. It's like a three sigma effect in their data.
• 54:31
  Speaker 1: M I see. So again, just kind of maybe confirming
• 54:35
  Speaker 1: that dark energy has changed and may change in the future. Right,
• 54:38
  Speaker 1: It's more consistent with this complicated story of dark energy
• 54:42
  Speaker 1: than with the simple idea of dark energy just being
• 54:44
  Speaker 1: a number. Right, But wait, I thought the same B
• 54:46
  Speaker 1: also confirmed that, Yeah, the Plank measurements don't agree with
• 54:49
  Speaker 1: the late time, but they also don't see evidence for
• 54:51
  Speaker 1: early dark energy. These measurements agree with Plank about how
• 54:54
  Speaker 1: much dark energy there was, but they also see this
• 54:57
  Speaker 1: extra effect which seems consistent with early dark energy. So
• 55:00
  Speaker 1: it's new telescope disagrees with Plank a little bit. Maybe
• 55:03
  Speaker 1: you need earlier dark energy or mid mid to late
• 55:06
  Speaker 1: morning dark energy, sparkly dark energy. Well, and I think
• 55:12
  Speaker 1: all this again means that the future is unpredictable, right,
• 55:15
  Speaker 1: I think I think that's kind of the bigger deal
• 55:18
  Speaker 1: is that, you know, if dark energy was constant and
• 55:21
  Speaker 1: just the number that wasn't changing, then we sort of
• 55:22
  Speaker 1: know how what's gonna happen in the future, and we
• 55:24
  Speaker 1: know how the universe is going to end. But if
• 55:26
  Speaker 1: we don't, if it's something totally complicated and different, who
• 55:29
  Speaker 1: knows what's gonna happen, right, it could turn off for example, Yeah,
• 55:32
  Speaker 1: we don't know what's going to happen in the future.
• 55:34
  Speaker 1: It also, I think it's super fascinating affects our vision
• 55:38
  Speaker 1: of the past. You know, if the universe has been
• 55:41
  Speaker 1: expanding more rapidly than we thought, that means that it's
• 55:44
  Speaker 1: younger than we thought because it didn't take as much
• 55:47
  Speaker 1: time to get this expansion happening as we thought it did.
• 55:51
  Speaker 1: Because the foot was on the gas pedal more strongly
• 55:54
  Speaker 1: than we thought it was. So concretely, it might mean
• 55:57
  Speaker 1: that the universe is only twelve and a half billion
• 56:00
  Speaker 1: years old, not thirteen point eight, right, So we might
• 56:03
  Speaker 1: have just like deleted a billion and a half years
• 56:06
  Speaker 1: of history. Boom, you're all younger, everybody. Yeah, well, we're
• 56:10
  Speaker 1: not younger. We're definitely not getting younger. But maybe the
• 56:13
  Speaker 1: universe is younger than we thought exactly. And so that
• 56:16
  Speaker 1: just goes to show you how will we know about
• 56:18
  Speaker 1: the future of the universe, and how will we really
• 56:20
  Speaker 1: understand about its past? How this picture of the universe
• 56:23
  Speaker 1: and its expansion is still a big question mark. Yeah,
• 56:27
  Speaker 1: I mean it's still dark basically, right, dark energy is
• 56:30
  Speaker 1: that it's dark. It's a mystery. It's definitely probably not
• 56:34
  Speaker 1: a constant. Who knows what it could be, right, that's right.
• 56:36
  Speaker 1: Dark history even more fun than drunk history. Yeah, it
• 56:39
  Speaker 1: could be cartoonist um drawing crazy things in the universe.
• 56:43
  Speaker 1: I hope that's our future as well. Yeah, and I
• 56:45
  Speaker 1: think it just confirms my theory that, you know, staying
• 56:47
  Speaker 1: up late keeps you young, right, it seems to work
• 56:51
  Speaker 1: so far exactly. Let's keep taking measurements all right, We'll
• 56:54
  Speaker 1: stay tuned as we learn more about dark energy and
• 56:57
  Speaker 1: what it could mean for our history of the universe
• 57:00
  Speaker 1: and also the future. Maybe somebody out there listening to
• 57:03
  Speaker 1: this could be the person who discovers what's really going
• 57:06
  Speaker 1: on with early or late or mid to late morning
• 57:10
  Speaker 1: dark energy. There's certainly a whole lot left to discover,
• 57:14
  Speaker 1: a lot of time for a dark energy cook to
• 57:16
  Speaker 1: come in. Basically, you might not even have to stay
• 57:18
  Speaker 1: up late to figure it out. Well, thanks for joining us.
• 57:20
  Speaker 1: We hope you enjoyed that. See you next time. Thanks
• 57:30
  Speaker 1: for listening, and remember that Daniel and Jorge Explain the
• 57:33
  Speaker 1: Universe is a production of I Heart Radio. For more
• 57:36
  Speaker 1: podcast For my heart Radio, visit the i heart Radio app,
• 57:40
  Speaker 1: Apple Podcasts, or wherever you listen to your favorite shows.
• 57:45
  Speaker 1: Yeah