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Is dark energy a fudge factor? · Daniel and Kelly’s Extraordinary Universe

• 0:07
  Speaker 1: What's going on with the universe? First, we thought it
• 0:11
  Speaker 1: was static, a single galaxy, floating in space forever. Then
• 0:15
  Speaker 1: we learned it's actually expanding. Everything out there is running
• 0:19
  Speaker 1: away from us. More recently, we figured out it's actually accelerating.
• 0:24
  Speaker 1: What's happening? This is one of the biggest questions in
• 0:28
  Speaker 1: modern physics, and the whole area of studies loosely called
• 0:31
  Speaker 1: dark energy. which is also, confusingly sometimes, the name used
• 0:36
  Speaker 1: to refer to the leading hypothesis for what's happening. But
• 0:39
  Speaker 1: do physicists know what they're doing here? Is it physics,
• 0:42
  Speaker 1: or is it just a bit of wonky math they
• 0:45
  Speaker 1: stick in to make their precious equations work out? We're
• 0:48
  Speaker 1: going to dive deep into all of that and hear
• 0:50
  Speaker 1: my rants on the subject, plus we'll have the usual
• 0:53
  Speaker 1: hilarious digressions all on today's episode of Daniel and Kelly's
• 0:58
  Speaker 1: Extraordinarily Dark Universe.
• 1:00
  Speaker 2: Intro Hello, I'm Kelly Wienersmith.
• 1:14
  Speaker 3: I study parasites and space, and this is the second
• 1:17
  Speaker 3: Fudge Factor episode we've done.
• 1:19
  Speaker 1: Hi, I'm Daniel. I'm a particle physicist, and I love
• 1:22
  Speaker 1: thinking about how aliens imagine the universe. And I suspect
• 1:27
  Speaker 1: that there are alien physicists out there like me who
• 1:29
  Speaker 1: don't like fudge.
• 1:30
  Speaker 3: Oh, wait, we've talked about why you don't like fudge before.
• 1:33
  Speaker 3: So two things. First of all, when I saw the
• 1:35
  Speaker 3: outline you sent me, I thought, oh, Daniel didn't realize
• 1:38
  Speaker 3: he sent me the same outline twice. And then I
• 1:41
  Speaker 3: was like, oh, wait, this is different. Where do you
• 1:43
  Speaker 3: think the phrase fudge factor came from?
• 1:45
  Speaker 1: Oh, that's a great question. I'm going to speculate without
• 1:50
  Speaker 1: a chance to research about the history of this word.
• 1:53
  Speaker 1: I don't know. I mean, in general, like to fudge something,
• 1:56
  Speaker 1: means to mess it up or to fake it, right?
• 1:58
  Speaker 1: And I wonder if that came from somebody like me
• 2:01
  Speaker 1: who doesn't like fudge or there's another sort of scatological
• 2:05
  Speaker 1: implication of fudge.
• 2:06
  Speaker 3: Yep, that occurred to me. That occurred to me.
• 2:08
  Speaker 1: And so maybe that's a connection, like, oh, you fudged it.
• 2:12
  Speaker 2: I don't know.
• 2:13
  Speaker 1: That's a great question. What do you think?
• 2:15
  Speaker 3: I have no idea. I also, you know, as a biologist,
• 2:18
  Speaker 3: the scatological connection was made in my brain, but I
• 2:22
  Speaker 3: didn't bother looking it up. I just thought I'll, you know,
• 2:25
  Speaker 3: I'll ask Daniel. Are you looking it up?
• 2:27
  Speaker 1: I'm asking the robot. Let's see. So, based on my
• 2:33
  Speaker 1: internet research, the Oxford Dictionary of Word Origins says that
• 2:37
  Speaker 1: the term fudge expresses annoyance and is traced to the
• 2:41
  Speaker 1: 18th century, originating from another word, fudge, which is sort
• 2:46
  Speaker 1: of meant to fit.
• 2:48
  Speaker 3: So then where did the word fudge as a delicious
• 2:51
  Speaker 3: treat come from? Right.
• 2:54
  Speaker 1: And apparently fudge, the not so delicious treat, is characterized
• 2:58
  Speaker 1: as like an accident. And so somebody was trying to
• 3:01
  Speaker 1: make something else and they fudged it and they made fudge.
• 3:06
  Speaker 3: Oh, interesting. We learned something new today.
• 3:09
  Speaker 1: Yes. And we unnecessarily went for the scatological reference.
• 3:13
  Speaker 2: Well.
• 3:13
  Speaker 1: On brand for us. Exactly. Yes.
• 3:16
  Speaker 4: Yes.
• 3:17
  Speaker 3: Well, we've previously talked about how dark matter is not
• 3:22
  Speaker 3: a fudge factor. Or would you still say dark matter
• 3:25
  Speaker 3: is a fudge factor?
• 3:26
  Speaker 1: Oh, my God. Did you listen to the episode, Kelly?
• 3:28
  Speaker 1: The whole point of the episode was dark matter is
• 3:31
  Speaker 1: not a fudge factor.
• 3:32
  Speaker 2: Okay.
• 3:32
  Speaker 1: And so, I mean, let me give some context here.
• 3:35
  Speaker 1: You know, there's a lot we know about the universe
• 3:36
  Speaker 1: and we do our best to communicate it. But there's
• 3:38
  Speaker 1: also a lot of misinformation out there about what we
• 3:41
  Speaker 1: know and how it works. And a lot of folks
• 3:43
  Speaker 1: out there under the impression that dark matter specifically is
• 3:48
  Speaker 1: just like a number we plop in the equations to
• 3:50
  Speaker 1: make the math work because we're stuck on some dogma
• 3:54
  Speaker 1: and we'll never give it up, even if we have
• 3:56
  Speaker 1: to insert ridiculous fudge factors in it to get it
• 3:58
  Speaker 1: to describe the universe, which is not a fair characterization
• 4:02
  Speaker 1: of dark matter and also avoids the very rich, fascinating
• 4:07
  Speaker 1: field that has surfaced like 10 independent lines of evidence
• 4:11
  Speaker 1: for this thing we call dark matter. So I was
• 4:14
  Speaker 1: inspired to do an episode contrasting this like popular science
• 4:18
  Speaker 1: misinformation with the reality of the research of dark matter.
• 4:21
  Speaker 3: I just like riling you up.
• 4:25
  Speaker 1: Well, button pushed successfully. And in that episode, I made
• 4:29
  Speaker 1: a contrast between dark matter, which is a thing and
• 4:33
  Speaker 1: we have a lot of evidence for it and definitely
• 4:35
  Speaker 1: not a fudge factor. And I used the cosmological constant,
• 4:38
  Speaker 1: which we'll talk about in more detail today, as an
• 4:40
  Speaker 1: evidence of something which kind of is a fudge factor.
• 4:43
  Speaker 1: And a bunch of people wrote in and they were like, wait,
• 4:45
  Speaker 1: are you saying dark energy is a fudge factor? And
• 4:48
  Speaker 1: so I thought, all right, we need to do an
• 4:49
  Speaker 1: episode on is dark energy a fudge factor? Not as
• 4:53
  Speaker 1: a repeat, not as a rehash, but as an even
• 4:55
  Speaker 1: deeper dive into the subject of cosmic fudge factors.
• 4:59
  Speaker 3: Well, I love fudge and I love learning about whether
• 5:03
  Speaker 3: or not something is a fudge factor. So I'm sure
• 5:04
  Speaker 3: we're going to have a lot of fun today.
• 5:06
  Speaker 1: All right. I hope we don't fudge it up.
• 5:08
  Speaker 3: Oh, watch it, Daniel. We don't want Matt to have
• 5:11
  Speaker 3: to start dropping a bunch of bleeps into this episode.
• 5:15
  Speaker 1: Fage is my new favorite archaic term. I'm going to
• 5:18
  Speaker 1: use it everywhere.
• 5:19
  Speaker 3: I'm going to work on incorporating it into my life
• 5:21
  Speaker 3: as well. I'm a little worried about what might happen
• 5:24
  Speaker 3: if I use it in front of my seventh grader
• 5:25
  Speaker 3: and then she uses it at school and slips up
• 5:28
  Speaker 3: a little bit. So, all right. Well, we did what
• 5:31
  Speaker 3: we always do here at DKEU. And the first thing
• 5:34
  Speaker 3: we do when we have an interesting question is we
• 5:36
  Speaker 3: share it with the extraordinaries.
• 5:38
  Speaker 1: That's right. Research step number one is ask our audience.
• 5:42
  Speaker 3: That's right. And so we asked our audience, is dark
• 5:44
  Speaker 3: energy a fudge factor? And if you want to be
• 5:47
  Speaker 3: on the list of people who get our questions that
• 5:49
  Speaker 3: are our first step of research, write to us at
• 5:52
  Speaker 3: questions at danielandkelly.org. And you can get added to the
• 5:55
  Speaker 3: list of folks who get our emails.
• 5:57
  Speaker 1: So think about it for a moment before you hear
• 5:59
  Speaker 1: these answers. Do you think dark energy is a fudge factor?
• 6:03
  Speaker 1: Here's what folks had to say. It doesn't mean that
• 6:06
  Speaker 1: it's not real.
• 6:08
  Speaker 5: Just we don't know what it is or how it
• 6:10
  Speaker 5: is yet.
• 6:11
  Speaker 2: Well, I still don't really know what dark energy is.
• 6:14
  Speaker 2: So I don't know.
• 6:16
  Speaker 1: It seems maybe it's more of a thing than dark matter.
• 6:21
  Speaker 2: I don't know.
• 6:22
  Speaker 4: I have no idea.
• 6:24
  Speaker 1: I think yes, until we know what it is.
• 6:27
  Speaker 3: So I'm also a barista in my other job, and
• 6:30
  Speaker 3: dark energy definitely sounds like a fudgy sort of latte.
• 6:34
  Speaker 3: I would totally drink that.
• 6:36
  Speaker 1: I don't think so.
• 6:38
  Speaker 5: Something is creating space.
• 6:41
  Speaker 2: Yes.
• 6:42
  Speaker 1: We don't know what it is. We don't even know
• 6:43
  Speaker 1: if it's a constant, so... Dark energy is not a
• 6:46
  Speaker 1: fudge factor.
• 6:48
  Speaker 3: Yes, I think it is.
• 6:49
  Speaker 5: Your Honor, I refer you to the previous case of
• 6:52
  Speaker 5: dark matter and whether it's a fudge or not. in
• 6:55
  Speaker 5: which I responded, it isn't. So therefore, I must also
• 6:58
  Speaker 5: respond that dark energy is not a fudge either.
• 7:02
  Speaker 4: We don't know the underlying mechanism with why it happens.
• 7:06
  Speaker 4: So I mean, to me, that seems a lot like
• 7:08
  Speaker 4: dark energy. Like it could be one forces behind there,
• 7:11
  Speaker 4: or it could be three forces.
• 7:12
  Speaker 5: I do not think it is a fudge factor, but
• 7:14
  Speaker 5: I have no idea how to classify it. Dark matter
• 7:17
  Speaker 5: is not a fudge factor. I think dark energy might be.
• 7:22
  Speaker 3: All right, so if I remember correctly from the Dark
• 7:24
  Speaker 3: Matter episode, there was a lot of like.
• 7:27
  Speaker 2: Oh, I don't know.
• 7:29
  Speaker 3: I think people were a little bit less willing to
• 7:31
  Speaker 3: call it a fudge factor. It looks like there's a
• 7:33
  Speaker 3: little bit more willingness to lean into fudge factoriness when
• 7:37
  Speaker 3: it comes to dark energy.
• 7:39
  Speaker 1: Some people here are standing up for dark energy. You know,
• 7:41
  Speaker 1: an empty space has energy, etc. But yeah, definitely a
• 7:45
  Speaker 1: lot more skepticism here. And maybe we'll circle back at
• 7:48
  Speaker 1: the end of the episode and see if that was justified.
• 7:50
  Speaker 3: Yeah, well, I think it shows that they've been listening
• 7:52
  Speaker 3: to what you've been saying. So, all right, let's, you know,
• 7:55
  Speaker 3: we talked a little bit about the etymology of the
• 7:58
  Speaker 3: phrase fudge factor.
• 7:59
  Speaker 4: Yeah.
• 8:00
  Speaker 3: But let's go ahead and dig into, like, what does
• 8:03
  Speaker 3: a scientist mean when they say fudge factor? What is
• 8:06
  Speaker 3: the scientific definition of this term?
• 8:09
  Speaker 1: Yeah, well, I think fudge factor is used in two ways. One,
• 8:12
  Speaker 1: it's used as an insult or a smear, you know,
• 8:15
  Speaker 1: to suggest you have a theory that's not really serious
• 8:19
  Speaker 1: or interesting. You're making the theory work, even though it's
• 8:22
  Speaker 1: not right. You've fudged it. You know, and I think
• 8:25
  Speaker 1: that's the essential implication or accusation in this popular misinformation
• 8:31
  Speaker 1: to say that scientists have an idea and it doesn't
• 8:35
  Speaker 1: really work. And it's not even very convincing because all
• 8:38
  Speaker 1: they've done is tweak the numbers to make it work, right?
• 8:41
  Speaker 1: They've added something to the equation, something mathematical. That's the
• 8:45
  Speaker 1: other implication that this is purely a math trick to
• 8:49
  Speaker 1: and not something physical, not something real, not something that
• 8:51
  Speaker 1: reflects how the universe actually works, because the equations, if
• 8:56
  Speaker 1: you left them alone, would predict something else, and so
• 8:58
  Speaker 1: you had to add a fudge factor. Like if I
• 9:01
  Speaker 1: had some mathematical equation that predicted Kelly's height, and it
• 9:07
  Speaker 1: predicted three feet, and then we were like, well, that's wrong,
• 9:10
  Speaker 1: and I'm just going to add a number to it.
• 9:11
  Speaker 1: I've fudged it so that it gets the right answer.
• 9:15
  Speaker 1: You'd say like, hey, your Kelly height prediction equation is
• 9:18
  Speaker 1: garbage because it's got a big fudge factor and it
• 9:21
  Speaker 1: needs a fudge factor to work. And therefore, it's not
• 9:24
  Speaker 1: any good.
• 9:24
  Speaker 3: But would you learn something if like, you know, if
• 9:26
  Speaker 3: you said, OK, I'm going to predict that Kelly is
• 9:29
  Speaker 3: three feet tall and then I'm going to add a
• 9:31
  Speaker 3: fudge factor. But over time, every time. the fudge factor
• 9:34
  Speaker 3: ended up being the same value. Would that hint at
• 9:38
  Speaker 3: the realness of the importance of that mathematical constant or something?
• 9:42
  Speaker 3: Are fudge factors a way of placeholding? There's something we
• 9:47
  Speaker 3: don't understand, but if it's always the same value, then
• 9:49
  Speaker 3: maybe we're onto something important?
• 9:51
  Speaker 2: Maybe.
• 9:51
  Speaker 1: I think that you have your finger on something useful, though,
• 9:54
  Speaker 1: which is that science is iterative. And often we can
• 9:58
  Speaker 1: have fudge factors on the first attempt. Sometimes a fudge
• 10:02
  Speaker 1: factor isn't a way to lie to people and mislead
• 10:06
  Speaker 1: and to try to pull the wool over your eyes
• 10:09
  Speaker 1: and get you to believe our theory. It's just a
• 10:11
  Speaker 1: way to say, we don't know how this works. Let's
• 10:14
  Speaker 1: try something. And if it doesn't quite work the first time,
• 10:17
  Speaker 1: we'll insert some fudge factors which we'll then intend to
• 10:21
  Speaker 1: come back and revisit and improve on. Like, as you say,
• 10:24
  Speaker 1: if my prediction for Kelly's height is three feet too short,
• 10:27
  Speaker 1: and for Zach's height is three feet too short, and
• 10:29
  Speaker 1: for Katrina's height is three feet too short, I'm gonna
• 10:31
  Speaker 1: go back and look at my prediction and be like,
• 10:33
  Speaker 1: why am I systematically three feet too short? What is
• 10:35
  Speaker 1: wrong with my theory? And then I'm gonna come back
• 10:38
  Speaker 1: with another theory that I hope is more accurate, right?
• 10:41
  Speaker 1: And so in that sense, a fudge factor is not
• 10:44
  Speaker 1: always bad. It just sometimes means you're in the early days.
• 10:48
  Speaker 1: You know, like say, for example, you're walking through your
• 10:51
  Speaker 1: backyard and you see like elephant footprints, right? And so
• 10:54
  Speaker 1: you're like, okay, well, I'm going to assume there's probably
• 10:56
  Speaker 1: some elephants. I don't have direct evidence yet, but I
• 10:59
  Speaker 1: have a theory that there are elephants walking through my backyard.
• 11:02
  Speaker 1: If you come back later and you find like elephant
• 11:04
  Speaker 1: poop and tusk marks and you smell elephants, you're like, okay, yeah,
• 11:07
  Speaker 1: the theory is probably right. But if you don't, or
• 11:09
  Speaker 1: if you come back and you see like cow poop
• 11:11
  Speaker 1: and you smell horses and the evidence doesn't really come together, then,
• 11:15
  Speaker 1: you know, you got to adapt your ideas. And so-
• 11:18
  Speaker 1: It's okay to have initial guesses that aren't totally solid,
• 11:22
  Speaker 1: even sometimes just numbers that you put in there that
• 11:25
  Speaker 1: you don't yet know how they work until you later
• 11:28
  Speaker 1: do figure out why they work. It just reflects that
• 11:31
  Speaker 1: you're not done sometimes.
• 11:33
  Speaker 3: I find myself trying to figure out how many people
• 11:36
  Speaker 3: there are on this planet that could sniff the difference
• 11:39
  Speaker 3: between an elephant, a cow, and a horse. There must
• 11:43
  Speaker 3: be someone who works at a zoo who can do that.
• 11:46
  Speaker 1: I think I can do that.
• 11:47
  Speaker 2: Oh, yeah?
• 11:47
  Speaker 1: I've spent enough time around horses with my daughter that
• 11:50
  Speaker 1: this is a very definite horsey smell, for sure.
• 11:54
  Speaker 3: But is it different than a cow poop smell?
• 11:57
  Speaker 2: Oh, yeah.
• 11:57
  Speaker 3: Because they're all eating grass. Okay, all right.
• 11:59
  Speaker 1: Well, I mean, you know how different animals all have
• 12:02
  Speaker 1: cheeses that taste different, right? Like goat cheese tastes different
• 12:06
  Speaker 1: from cow cheese.
• 12:07
  Speaker 2: Mm-hmm.
• 12:07
  Speaker 1: You ever notice how goats smell different from cows? And
• 12:10
  Speaker 1: how goat smell is sort of related to the way
• 12:13
  Speaker 1: goat cheese tastes.
• 12:14
  Speaker 2: I love it.
• 12:15
  Speaker 1: There's just like a goatiness.
• 12:16
  Speaker 3: Yeah. And the goat milk has a bit of a
• 12:18
  Speaker 3: goatiness too.
• 12:19
  Speaker 1: Yes.
• 12:19
  Speaker 2: I love it all.
• 12:21
  Speaker 3: All right. Point made.
• 12:25
  Speaker 1: I've never had horse cheese before. But I'm pretty sure
• 12:27
  Speaker 1: if somebody made horse cheese, I could be like, this
• 12:30
  Speaker 1: is pretty horsey.
• 12:31
  Speaker 5: You know what?
• 12:31
  Speaker 3: I shouldn't have said, eh, because I do think there
• 12:33
  Speaker 3: are cultures who do a lot with horse milk.
• 12:36
  Speaker 4: Yeah.
• 12:36
  Speaker 3: Just I don't happen to have come from one. I see.
• 12:38
  Speaker 1: You've never had horse milk yourself.
• 12:40
  Speaker 3: I have never had horse milk myself. I have a
• 12:42
  Speaker 3: friend who has had fermented horse milk. It was not
• 12:44
  Speaker 3: his bag. But, you know, it's the bag of many
• 12:48
  Speaker 3: other people.
• 12:49
  Speaker 1: Well, rather than pulling us back from this digression, I'm
• 12:51
  Speaker 1: going to take us even deeper and ask you, what
• 12:53
  Speaker 1: is the most interesting kind of milk you've ever had?
• 12:56
  Speaker 3: Interesting, I mean, I don't think, I haven't had that
• 12:58
  Speaker 3: much milk variety.
• 12:59
  Speaker 1: I have had- You've never had like beaver milk?
• 13:02
  Speaker 3: Have you?
• 13:02
  Speaker 1: No. But you like animals. You have like 65,000 different
• 13:07
  Speaker 1: kinds of things in your farm. Who knows?
• 13:09
  Speaker 3: Doesn't mean I'm suckling all the animals that come across.
• 13:16
  Speaker 3: We do joke about, you know, should we try pig
• 13:19
  Speaker 3: milk and get pigs or something? But no, I've had
• 13:21
  Speaker 3: sheep milk, goat milk, and cow milk. And I think
• 13:24
  Speaker 3: those are all the milks I've had.
• 13:27
  Speaker 1: I have had pony milk, actually.
• 13:29
  Speaker 2: Oh, when?
• 13:30
  Speaker 1: Not horse milk. Yeah, there's a little organic store near
• 13:33
  Speaker 1: where we used to live when we were at CERN,
• 13:36
  Speaker 1: and they sell pony milk. And I was always like,
• 13:39
  Speaker 1: what is this? We have to try it in these
• 13:41
  Speaker 1: tiny little bottles. And so, yeah, I actually have had
• 13:44
  Speaker 1: pony milk. I forgot about that.
• 13:45
  Speaker 3: Wait, so what's the difference between pony milk and horse milk?
• 13:48
  Speaker 3: I just think of ponies as young horses.
• 13:50
  Speaker 1: Oh my gosh, Kelly, what?
• 13:52
  Speaker 3: Okay, you tell me, horse guy.
• 13:54
  Speaker 2: What's the difference?
• 13:56
  Speaker 1: How far off topic are we now? Really far. All right,
• 13:59
  Speaker 1: we're going to have to bring this back to tell
• 14:01
  Speaker 1: a story about making fudge with pony milk or something. Ponies... Okay. So...
• 14:12
  Speaker 1: Ponies are not baby horses. That's a foal, right? A
• 14:15
  Speaker 1: baby horse is a foal. A pony is a distinct,
• 14:19
  Speaker 1: fully grown, smaller equine, right? So like a mature pony
• 14:23
  Speaker 1: is like five feet tall at the shoulder, while a
• 14:26
  Speaker 1: mature horse is much taller than that. So it's sort
• 14:30
  Speaker 1: of like a, you know, it's like a short version
• 14:32
  Speaker 1: of the horse.
• 14:33
  Speaker 3: But they're the same species, right?
• 14:34
  Speaker 2: Yeah.
• 14:35
  Speaker 1: Yeah, they can interbreed and their offspring are fertile, but
• 14:38
  Speaker 1: it's sort of like, you know, the difference between a
• 14:40
  Speaker 1: Chihuahua and a Great Dane.
• 14:41
  Speaker 2: Okay.
• 14:42
  Speaker 5: Right?
• 14:42
  Speaker 1: It's like a Chihuahua is not a baby version of
• 14:45
  Speaker 1: a Great Dane, right? It's a smaller kind of dog.
• 14:48
  Speaker 3: All right.
• 14:49
  Speaker 2: All right. All right.
• 14:49
  Speaker 3: Well, thank you for this biology lesson, physicist.
• 14:54
  Speaker 1: All right. All because of my elephant example.
• 14:56
  Speaker 3: My biology knowledge is a fudge factor. And let's move
• 15:00
  Speaker 3: back to physics.
• 15:01
  Speaker 1: The point I was trying to make is that often
• 15:04
  Speaker 1: we don't understand something or we understand things partially. And
• 15:07
  Speaker 1: what you want to do the first time is make
• 15:10
  Speaker 1: simplifying assumptions and fill in numbers you don't know and
• 15:13
  Speaker 1: then come back and revisit it. And so you can
• 15:16
  Speaker 1: dig in and understand it better. And so maybe you
• 15:19
  Speaker 1: want to call that a fudge factor while you're still
• 15:22
  Speaker 1: in the process of figuring it out, but not in
• 15:24
  Speaker 1: a negative sense, not in a misleading sense. We're open,
• 15:28
  Speaker 1: we're honest about what we're doing and the status of
• 15:31
  Speaker 1: our understandings. I think fudge factor has too much of
• 15:34
  Speaker 1: a negative connotation for me to say that a first
• 15:37
  Speaker 1: draft of a theory, even with numbers you don't understand,
• 15:40
  Speaker 1: has fudge factors in it.
• 15:42
  Speaker 3: What would you call it instead?
• 15:44
  Speaker 1: I'd say unexplained constants. For example, we measure the coefficient
• 15:49
  Speaker 1: of friction. When two surfaces rub together, how much force
• 15:52
  Speaker 1: is there on those surfaces because of their friction? And
• 15:56
  Speaker 1: if you didn't understand how friction works, that it's due
• 15:59
  Speaker 1: to the microscopic grabbing and dragging- of the little features
• 16:03
  Speaker 1: of those surfaces. You just measure it as a number
• 16:06
  Speaker 1: and say, well, that's what it is. And then if
• 16:08
  Speaker 1: you have a microscope, you can zoom in. You can see, oh,
• 16:11
  Speaker 1: Teflon is a tiny coefficient of friction because it has
• 16:14
  Speaker 1: almost no surfaces. And sandpaper has a high coefficient of
• 16:18
  Speaker 1: friction because look at all these features. And so then
• 16:21
  Speaker 1: you can reveal it and you can even calculate it
• 16:23
  Speaker 1: from those images. And so that's an example of like
• 16:26
  Speaker 1: you start with a fudge factor and then you go
• 16:27
  Speaker 1: off and you explain it, you understand it. And so
• 16:30
  Speaker 1: it's not always a bad thing. Sometimes it's just a
• 16:32
  Speaker 1: first step towards a deeper understanding.
• 16:35
  Speaker 3: So before we take a break, I guess I want
• 16:36
  Speaker 3: to like jump the gun a little bit and know,
• 16:39
  Speaker 3: is dark energy a like, this is a first step.
• 16:43
  Speaker 3: This is the constant we're using to hold in place.
• 16:45
  Speaker 3: Or is it a lot, are we farther than that?
• 16:48
  Speaker 1: Oh, it's so much more nuanced than that, Kelly. You're
• 16:49
  Speaker 1: going to have to listen to the rest of the episode. Sorry.
• 16:52
  Speaker 2: Oh man. All right.
• 16:52
  Speaker 3: Well, let's take a break so I can work up
• 16:54
  Speaker 3: the energy and we'll be right back. all right we're
• 17:17
  Speaker 3: back and we're discussing whether or not dark energy is
• 17:20
  Speaker 3: a fudge factor so daniel catch us up what is
• 17:23
  Speaker 3: what what do we think dark energy is Yeah, it's.
• 17:26
  Speaker 1: Important to separate dark energy into two different categories, which
• 17:30
  Speaker 1: are very closely related, but also really importantly different. One
• 17:35
  Speaker 1: is our observation that the universe is expanding and that
• 17:39
  Speaker 1: that expansion has been accelerating for the last five to
• 17:44
  Speaker 1: six billion years. So that's number one. Observation experimentally, and
• 17:49
  Speaker 1: we'll talk about in more detail, that the universe's expansion
• 17:52
  Speaker 1: is accelerating. Sometimes that's called dark energy. The other side
• 17:57
  Speaker 1: of it is our attempt theoretically to describe that, to
• 18:00
  Speaker 1: make sense of it, to either incorporate it into our
• 18:02
  Speaker 1: theories or to extend our theories to describe it. And
• 18:06
  Speaker 1: that involves something called the cosmological constant. And so those
• 18:11
  Speaker 1: are two big pieces of this concept of dark energy,
• 18:15
  Speaker 1: but it's important to keep them separate because one is
• 18:17
  Speaker 1: something we know, we measure, we see, and the other
• 18:20
  Speaker 1: are theoretical ideas that we're putting together to understand it.
• 18:23
  Speaker 3: Okay, so tell me more about how we know the
• 18:25
  Speaker 3: universe is expanding and how we measure this.
• 18:28
  Speaker 1: Yeah, so we've known that the universe is expanding for
• 18:32
  Speaker 1: more than 100 years. Before Hubble and Henrietta Leavitt, people
• 18:36
  Speaker 1: thought the universe was static. They thought, here we have
• 18:39
  Speaker 1: a galaxy and we're just sitting out here in space
• 18:42
  Speaker 1: and stars are stars and that's it. And they didn't
• 18:45
  Speaker 1: even know that there were other galaxies. And it wasn't
• 18:48
  Speaker 1: until Henrietta Leavitt came up with a way to measure
• 18:51
  Speaker 1: the distance to things in the sky that Otherwise, it's
• 18:54
  Speaker 1: hard to know, are you looking at something that's big
• 18:57
  Speaker 1: and bright and far away or something that's small and
• 19:02
  Speaker 1: dim and close? Those two things look similarly. Until Levitt
• 19:06
  Speaker 1: figured out how to use Cepheids, these variable stars, so
• 19:09
  Speaker 1: you can measure how their brightness changes. And by measuring
• 19:13
  Speaker 1: how their brightness changes, you can tell what their brightness
• 19:15
  Speaker 1: actually is. And then you can, from that, determine how
• 19:18
  Speaker 1: far away they are. So she came up with this
• 19:21
  Speaker 1: method and then Hubble used it. and discovered that, oh
• 19:24
  Speaker 1: my gosh, there's a bunch of stuff in the sky
• 19:25
  Speaker 1: that's not even in our galaxy. It looks like it
• 19:28
  Speaker 1: is because it's sort of mixed up there in the sky,
• 19:31
  Speaker 1: but it's actually really, really far away. And that was
• 19:34
  Speaker 1: the first observation that there's stuff outside our galaxy. There's
• 19:37
  Speaker 1: more than one galaxy in the universe, right? Mind-blowing realization.
• 19:42
  Speaker 1: At the same time, he discovered those galaxies are redshifted,
• 19:46
  Speaker 1: that they're moving away from us. So that's when we
• 19:49
  Speaker 1: went from the universe, is static to the universe is
• 19:52
  Speaker 1: expanding and everything is moving away from us.
• 19:55
  Speaker 3: That sounds like an exciting time to be alive and
• 19:57
  Speaker 3: be in science.
• 19:58
  Speaker 1: Yeah. And for like 80 years or so, that's how
• 20:02
  Speaker 1: we thought the universe worked. And the big question in
• 20:04
  Speaker 1: cosmology at the time was, Is that expansion going to
• 20:08
  Speaker 1: turn around? Is there enough gravity in the universe to
• 20:10
  Speaker 1: pull everything back together to make a big crunch? Or
• 20:14
  Speaker 1: is there not enough gravity in the universe and things
• 20:16
  Speaker 1: will slow down but keep drifting forever? Those are the
• 20:21
  Speaker 1: two options. Keep drifting forever and expanding or slow down,
• 20:26
  Speaker 1: turn around, and come back to a big crunch.
• 20:28
  Speaker 3: Oh boy, existential dread.
• 20:30
  Speaker 1: Yeah, and so to know whether it was going to
• 20:31
  Speaker 1: be like option A, drift forever, or option B, big crunch...
• 20:36
  Speaker 1: They had to make more precise measurements of the really
• 20:38
  Speaker 1: far away stuff to look like further back into the
• 20:41
  Speaker 1: history of the universe and see how those distances have
• 20:43
  Speaker 1: been changing with time to see, does it look like
• 20:46
  Speaker 1: it's going to turn over or does it look like
• 20:48
  Speaker 1: it's just going to keep spreading out? So they developed
• 20:50
  Speaker 1: a new way to measure distances, which are type 1a supernova.
• 20:54
  Speaker 1: These are stars that go supernova, they implode, but they're
• 20:57
  Speaker 1: a special kind of supernova. They're stars that didn't initially
• 21:01
  Speaker 1: go supernova. They just became white dwarfs. They didn't have
• 21:04
  Speaker 1: enough mass in them to go supernova. But then later,
• 21:07
  Speaker 1: they get fed extra stuff from their partners in a
• 21:10
  Speaker 1: binary system. And then they go over the threshold and
• 21:13
  Speaker 1: become supernova. And because of this particular way that they
• 21:16
  Speaker 1: do it, it's very easy to measure from how their
• 21:19
  Speaker 1: light curve goes, how bright they actually are, and therefore
• 21:22
  Speaker 1: how far away they are. So then we got this
• 21:25
  Speaker 1: extra candle that we could use to measure really, really
• 21:28
  Speaker 1: far away stuff. And then we had much more lever
• 21:31
  Speaker 1: arm on our fits to understand the whole history of expansion.
• 21:34
  Speaker 1: Because Cephids, these variable stars, tell you about closer up stuff.
• 21:38
  Speaker 1: And type 1 supernova are bright enough to tell you
• 21:41
  Speaker 1: about really far away, really far back in time, longer history.
• 21:45
  Speaker 2: Okay.
• 21:45
  Speaker 3: I think you lost me on the lever arm thing,
• 21:46
  Speaker 3: but then you summarized the point and I'm with you now.
• 21:50
  Speaker 1: Yeah. Well, the point of the lever arm is just
• 21:51
  Speaker 1: like you're trying to understand the trend and you want
• 21:54
  Speaker 1: to be able to predict it. Say, for example, you're
• 21:56
  Speaker 1: looking at like apple stock and you want to know
• 21:58
  Speaker 1: is it going to go up or is it going
• 21:59
  Speaker 1: to go down if you only have three days of
• 22:01
  Speaker 1: data it could go anywhere but if you have like
• 22:03
  Speaker 1: 50 years of data you can make a more confident
• 22:06
  Speaker 1: prediction and so you have a better lever arm you're
• 22:09
  Speaker 1: like theories are more constrained and so in order to
• 22:12
  Speaker 1: predict the future of the universe we had to look
• 22:14
  Speaker 1: deeper into the past and this was one of my
• 22:16
  Speaker 1: favorite moments in science it's around 2001 they made this
• 22:20
  Speaker 1: measurement And they asked the universe, okay, is it scenario
• 22:24
  Speaker 1: A that we're going to expand forever? Or is it
• 22:26
  Speaker 1: scenario B that we're going to come back and do
• 22:28
  Speaker 1: a big crunch? And the universe said, no, it's secret
• 22:31
  Speaker 1: option C. It's something you never considered, which is that
• 22:35
  Speaker 1: neither of those things are going to happen. And instead
• 22:37
  Speaker 1: what's happening is that the expansion is accelerating. Both option
• 22:41
  Speaker 1: A and option B suggested the expansion was decelerating. Things
• 22:45
  Speaker 1: were slowing down. And the difference was like, is it
• 22:47
  Speaker 1: going to slow down enough? To actually go to negative expansion,
• 22:51
  Speaker 1: to collapse, or just sort of drift out towards slower
• 22:54
  Speaker 1: and slower expansion. But secret option C, which is reality,
• 22:58
  Speaker 1: says no, the expansion is increasing. It's getting faster and
• 23:01
  Speaker 1: faster every year. And this was mind-blowing. This was a
• 23:05
  Speaker 1: crazy idea.
• 23:07
  Speaker 3: Where were you when you learned this? Because this was
• 23:09
  Speaker 3: in our lifetime, right?
• 23:10
  Speaker 2: Yeah, absolutely.
• 23:11
  Speaker 1: Absolutely. I was in grad school and I was actually
• 23:14
  Speaker 1: at Berkeley in grad school. And one of the big
• 23:16
  Speaker 1: teams to do this was at Berkeley. Saul Perlmutter was
• 23:18
  Speaker 1: leading that team and he was racing against another team
• 23:21
  Speaker 1: in Australia. It was very exciting. I knew grad students
• 23:24
  Speaker 1: working on that project up at LBL was a big deal.
• 23:27
  Speaker 1: And then of course they won the Nobel prize like
• 23:29
  Speaker 1: five minutes later. So yeah, it was a big deal
• 23:32
  Speaker 1: at Berkeley at the time. It was exciting. You know,
• 23:34
  Speaker 1: anytime you find a surprise, those are the best moments,
• 23:37
  Speaker 1: you know, because, it shocks you. It forces you to
• 23:41
  Speaker 1: upend your understanding, you know, to get rid of the
• 23:44
  Speaker 1: dogma and change the mainstream narrative. The kind of thing
• 23:47
  Speaker 1: that like, you know, pop sign misinformation artists are always
• 23:50
  Speaker 1: saying we never want to do. This is our dream
• 23:52
  Speaker 1: come true.
• 23:53
  Speaker 3: I'm imagining grad student Daniel, like taking the whole weekend off,
• 23:57
  Speaker 3: going out into the woods and just staring at the
• 23:59
  Speaker 3: stars with his mind blown for a whole weekend.
• 24:02
  Speaker 1: Yeah. And also being like, why didn't I work on that?
• 24:04
  Speaker 1: Oh my gosh. I could have won a Nobel Prize
• 24:07
  Speaker 1: in grad school. That was the second time I missed
• 24:11
  Speaker 1: a Nobel Prize. I also had the opportunity to go
• 24:14
  Speaker 1: to Caltech and to work on LIGO, the gravitational wave observatory.
• 24:17
  Speaker 1: And I remember visiting and they were like, you should join.
• 24:20
  Speaker 1: It's a really exciting time. And I remember thinking to myself,
• 24:23
  Speaker 1: these guys are crazy. They're never going to see this.
• 24:26
  Speaker 1: Oh my gosh. They're going to work forever and see nothing.
• 24:29
  Speaker 1: And boy, was I wrong.
• 24:31
  Speaker 2: Oh, man.
• 24:31
  Speaker 1: All right.
• 24:32
  Speaker 3: So if you want to know which projects are going
• 24:34
  Speaker 3: to win the Nobel Prize, check out projects Daniel turns
• 24:36
  Speaker 3: his nose up at.
• 24:37
  Speaker 1: Exactly. They have a great track record. And so this
• 24:42
  Speaker 1: is a big surprise. This is shocking. Already invites a
• 24:46
  Speaker 1: lot of wonder and speculation about the cause of it,
• 24:49
  Speaker 1: because we're talking about accelerating the whole universe. The amounts
• 24:53
  Speaker 1: of energy required and involved are staggering, right? Absolutely staggering.
• 24:59
  Speaker 1: You need some kind of thing which is going to
• 25:01
  Speaker 1: overwhelm gravity and overwhelm all the other forces. So this
• 25:04
  Speaker 1: is a big new opportunity to learn about the universe.
• 25:08
  Speaker 1: And before people were like, well, are you really sure
• 25:11
  Speaker 1: you want to like understand the universe? They're like, let's
• 25:14
  Speaker 1: figure out some other ways to see if this is right.
• 25:17
  Speaker 1: Because what if you like misunderstood how supernova go or
• 25:20
  Speaker 1: misunderstood something else? And then that's misleading. It's confusing you, right?
• 25:25
  Speaker 1: So what we always love to do in experimental science
• 25:27
  Speaker 1: is find other independent lines of evidence that will either
• 25:32
  Speaker 1: contradict the first ones that tell you like, no, you
• 25:34
  Speaker 1: messed up, that the story's not coherent, or tell you
• 25:37
  Speaker 1: the same story. Because if you hear the same story
• 25:40
  Speaker 1: from four different ways that aren't related to each other,
• 25:43
  Speaker 1: then it's much more likely that you're hearing the true story.
• 25:46
  Speaker 1: You know, it's like you see elephant poop and you
• 25:48
  Speaker 1: hear elephants and you smell elephants and you see elephant footprints,
• 25:51
  Speaker 1: you probably got an elephant problem.
• 25:53
  Speaker 3: Yeah, it would be nice to also see the elephant,
• 25:56
  Speaker 3: but sometimes you don't get to do that.
• 25:59
  Speaker 1: And so we've done that. We have other ways to
• 26:00
  Speaker 1: know the universe is expanding and accelerating. One of those
• 26:05
  Speaker 1: is something we've talked about in the show a few times.
• 26:06
  Speaker 1: It's baryon acoustic oscillations. This comes from seeing that the
• 26:11
  Speaker 1: universe used to be a hot, glowing soup of matter
• 26:15
  Speaker 1: and light, and it was really dense. And so you
• 26:18
  Speaker 1: think about sound in space, you think, oh, nobody can
• 26:21
  Speaker 1: hear you scream, but Back in the early universe, the
• 26:24
  Speaker 1: universe was dense enough that sound could travel through that
• 26:27
  Speaker 1: soup and actually traveled like nearly half the speed of light.
• 26:30
  Speaker 1: It was really, really dense. And so sound traveled really,
• 26:33
  Speaker 1: really fast. And then you had these oscillations where like
• 26:37
  Speaker 1: light pushed matter out and then gravity pulled it back
• 26:40
  Speaker 1: in and then it bounces back out. So you get
• 26:42
  Speaker 1: these oscillations and those create sound waves. And you can
• 26:46
  Speaker 1: see those sound waves propagating through the early universe plasma
• 26:50
  Speaker 1: because where things were denser you later on, like billions
• 26:54
  Speaker 1: of years later, you get more galaxies. And where things
• 26:56
  Speaker 1: were less dense, you get fewer galaxies. And when they
• 26:59
  Speaker 1: go out there and they look at the pattern of
• 27:01
  Speaker 1: galaxies in the universe, they can see these rings. These
• 27:04
  Speaker 1: like literal rings in the sky. Those rings are still
• 27:08
  Speaker 1: there because they got frozen in when the universe expanded
• 27:12
  Speaker 1: and the speed of sound dropped. So those sound waves
• 27:14
  Speaker 1: were propagating out. And then they got frozen into the universe,
• 27:19
  Speaker 1: into its structure again. when the universe cooled and expanded
• 27:22
  Speaker 1: enough that the protons and electrons combined to become neutral,
• 27:26
  Speaker 1: so then they were transparent and they weren't getting pushed
• 27:29
  Speaker 1: by the photons anymore, which changed the whole dynamics and
• 27:32
  Speaker 1: then left this imprint. And so we know when that happened.
• 27:37
  Speaker 1: We know how big the universe was when they got
• 27:40
  Speaker 1: frozen in. That's like an absolute measure of something. Here's
• 27:44
  Speaker 1: how big it was when it was created, and then
• 27:46
  Speaker 1: we can see how big it is now And that
• 27:48
  Speaker 1: gives us a standard candle, like a metric, a ruler.
• 27:51
  Speaker 1: So we can use that to see the history of
• 27:54
  Speaker 1: the expansion of the universe because we can see it now.
• 27:56
  Speaker 1: We can see it in early days. We can see
• 27:58
  Speaker 1: it 6 billion years ago if we look out into
• 28:01
  Speaker 1: the universe. It's like somebody put a meter stick in
• 28:05
  Speaker 1: the early universe and then we watch it grow through time.
• 28:08
  Speaker 1: And you can just use that to literally measure the
• 28:11
  Speaker 1: expansion of the universe and see it accelerate.
• 28:13
  Speaker 3: That's amazing.
• 28:14
  Speaker 2: Yeah.
• 28:14
  Speaker 3: So at first I thought it was going to be
• 28:16
  Speaker 3: like you get two points of time. You can get
• 28:18
  Speaker 3: that point and then where we are now. But you'd
• 28:20
  Speaker 3: need multiple points of time to be able to say
• 28:22
  Speaker 3: it's accelerating.
• 28:24
  Speaker 1: Exactly. Yeah.
• 28:25
  Speaker 3: But you've got that. So that's amazing.
• 28:26
  Speaker 1: It's very cool.
• 28:27
  Speaker 2: Yeah.
• 28:28
  Speaker 1: And then there's another one which is super cool, which
• 28:29
  Speaker 1: relies on time. These are like cosmic clocks. The idea
• 28:34
  Speaker 1: is to find galaxies who formed stars a long time
• 28:37
  Speaker 1: ago because stars kind of evolve in a predictable way.
• 28:42
  Speaker 1: Older stars look different from younger stars, and we know
• 28:45
  Speaker 1: how long stars last. And so by looking at how
• 28:48
  Speaker 1: blue are the stars and how red are the stars,
• 28:51
  Speaker 1: because blue stars tend to be hotter and brighter and
• 28:53
  Speaker 1: not live as long, and red stars are cooler and
• 28:56
  Speaker 1: dimmer and live longer. So as a population of stars age,
• 29:00
  Speaker 1: they tend to go from having some blue stars to
• 29:03
  Speaker 1: having fewer blue stars. So by measuring how red is
• 29:07
  Speaker 1: this population of stars, you can get a sense for
• 29:09
  Speaker 1: how old it is. So just by looking at a galaxy,
• 29:11
  Speaker 1: you can age it by measuring the redness and the blueness. Now,
• 29:15
  Speaker 1: if you look at two different galaxies at different redshifts,
• 29:19
  Speaker 1: ones that are further away and ones that are closer,
• 29:22
  Speaker 1: then we're seeing clocks at different points in cosmic history. Awesome.
• 29:26
  Speaker 1: Their stellar populations have different ages. And so you don't
• 29:29
  Speaker 1: need to know the absolute age of either galaxy. You
• 29:33
  Speaker 1: just need to know the change of age, which comes
• 29:35
  Speaker 1: from their change in redshift. And that tells you the
• 29:38
  Speaker 1: rate at which the cosmic redshift is changing with time.
• 29:42
  Speaker 1: So the galaxies sort of act as clocks that let
• 29:45
  Speaker 1: us measure how fast the universe was expanding when their
• 29:48
  Speaker 1: light was emitted. And you repeat this like many different redshifts,
• 29:52
  Speaker 1: as you were saying, and you can trace the expansion history.
• 29:55
  Speaker 1: So neither of these are perfect, and there's questions about
• 29:58
  Speaker 1: both of them. One relies on understanding early universe dynamics,
• 30:02
  Speaker 1: another one relies on understanding stellar populations, and there are uncertainties.
• 30:07
  Speaker 1: But the cool thing is that they are different uncertainties.
• 30:09
  Speaker 1: There are questions and things we don't understand that are
• 30:12
  Speaker 1: different in each of those three measurements, but they all
• 30:15
  Speaker 1: paint the same story about the universe's accelerating expansion. So
• 30:20
  Speaker 1: in the same way that dark matter is not a
• 30:22
  Speaker 1: fudge factor because we have lots of independent evidence for
• 30:25
  Speaker 1: it in all sorts of different ways, people thought of
• 30:28
  Speaker 1: so many different ways to check dark matter, and it
• 30:30
  Speaker 1: almost always comes out with the same story. Like, yes,
• 30:33
  Speaker 1: there's a lot of invisible matter out there. In this way,
• 30:36
  Speaker 1: we've also checked the expansion of the universe, and it
• 30:40
  Speaker 1: tells the same story over and over again, that it's
• 30:43
  Speaker 1: been expanding the whole time. In the very early universe,
• 30:46
  Speaker 1: it was decelerating, and about 6 billion years ago, it
• 30:48
  Speaker 1: turned around and started expanding. accelerating, which is amazing. Absolutely amazing.
• 30:53
  Speaker 3: Maybe this is too much to ask, given the uncertainties
• 30:56
  Speaker 3: associated with each of the different methods that we use
• 30:58
  Speaker 3: that you mentioned earlier. But do these various methods sort
• 31:02
  Speaker 3: of clock the accelerations and the decelerations at the same
• 31:06
  Speaker 3: rate or similar rates? Or is there a lot of
• 31:08
  Speaker 3: variability there?
• 31:09
  Speaker 1: Yeah, great question. And this is connected to a big
• 31:12
  Speaker 1: puzzle in cosmology right now, which is the Hubble tension,
• 31:15
  Speaker 1: which tells us about the rate of expansions. The Hubble constant,
• 31:18
  Speaker 1: which is not a constant, it's a number that changes
• 31:21
  Speaker 1: in time.
• 31:21
  Speaker 3: Thanks, physicists.
• 31:23
  Speaker 1: I know. And to be fair to the physicists and naming,
• 31:26
  Speaker 1: the Hubble parameter, which tells you the rate of expansion,
• 31:30
  Speaker 1: is changing. But technically, the Hubble constant is just its
• 31:33
  Speaker 1: value now, which is a single number. The Hubble constant
• 31:37
  Speaker 1: tells you about the rate of expansion, and that changes
• 31:39
  Speaker 1: in time. And so we can measure this in lots
• 31:42
  Speaker 1: of different ways, and we don't see total agreement. There
• 31:45
  Speaker 1: are things we still have to figure out there. And
• 31:48
  Speaker 1: I think that's a sign of a healthy field because
• 31:50
  Speaker 1: people are constantly coming up with new ways to measure this.
• 31:53
  Speaker 1: And the overall story is the same. We know this expansion.
• 31:56
  Speaker 1: We know that expansion is accelerating. There are differences in
• 32:00
  Speaker 1: those expansion rate measurements in early universe and in late universe.
• 32:04
  Speaker 1: And it requires more complicated theories than some of the
• 32:07
  Speaker 1: simple theories that we'll talk about in a minute. And
• 32:10
  Speaker 1: so whether you expect that expansion to be constant in
• 32:13
  Speaker 1: time or not, is a subtlety that you have to
• 32:16
  Speaker 1: address when you build your theory of why this is happening.
• 32:19
  Speaker 1: But yeah, there's also some fuzziness and disagreement about the
• 32:22
  Speaker 1: measurements themselves.
• 32:24
  Speaker 3: Well, I still think we're very clever apes that we
• 32:26
  Speaker 3: figured out any of these methods of trying to explore
• 32:29
  Speaker 3: what's happening in our universe.
• 32:30
  Speaker 1: I know from this tiny little rock that we basically
• 32:33
  Speaker 1: never left just by gathering photons that happened to come
• 32:37
  Speaker 1: our way. We figured out this incredible cosmic story. That's
• 32:40
  Speaker 1: so much bigger than us. It's, it's amazing how, what
• 32:44
  Speaker 1: people can do. As Hazel says, you know, science is
• 32:47
  Speaker 1: just like looking around and figuring out what happened.
• 32:50
  Speaker 3: I mean, but that's a profound question.
• 32:52
  Speaker 1: What happened? What happened?
• 32:55
  Speaker 2: Exactly.
• 32:56
  Speaker 1: I love the way she minimizes it. She's like, you know,
• 32:58
  Speaker 1: you're just figuring out what happened. I'm like, yes, what
• 33:00
  Speaker 1: happened to the whole universe? That's right.
• 33:03
  Speaker 3: Or, you know, through the evolution of our species, there's
• 33:05
  Speaker 3: lots of what happened questions that we want to answer. Okay,
• 33:10
  Speaker 3: so you mentioned that there's sort of two different things
• 33:12
  Speaker 3: people are talking about when they mention dark energy. And
• 33:15
  Speaker 3: the first is the fact that the universe expansion is accelerating.
• 33:19
  Speaker 3: So we've talked about that. So let's take a break.
• 33:21
  Speaker 3: And when we come back, we'll dig into this cosmological
• 33:24
  Speaker 3: constant idea. And we're back and we're talking about whether
• 33:47
  Speaker 3: or not dark energy is a fudge factor. And the
• 33:50
  Speaker 3: second thing that people are usually referring to when they
• 33:53
  Speaker 3: say dark energy is this idea of a cosmological constant.
• 33:57
  Speaker 2: Yeah.
• 33:57
  Speaker 3: So, Daniel, what's the cosmological constant?
• 34:00
  Speaker 1: Yes. So we want to understand how could the universe's
• 34:04
  Speaker 1: expansion be accelerating? What's doing that?
• 34:07
  Speaker 2: Right.
• 34:08
  Speaker 1: And there's a really interesting history here, which goes all
• 34:11
  Speaker 1: the way back to the beginning of the story we
• 34:13
  Speaker 1: told about when people thought the universe was static. So
• 34:17
  Speaker 1: Einstein came up with his theory of general relativity, which
• 34:20
  Speaker 1: tells us about space and time and how things pull
• 34:24
  Speaker 1: away from each other or expand also. And this theory
• 34:27
  Speaker 1: of general relativity, it predates Hubble and Leavitt. Their discovery
• 34:30
  Speaker 1: that the universe was expanding, that wouldn't come for a
• 34:33
  Speaker 1: long time, many years after Einstein developed his theory of
• 34:36
  Speaker 1: general relativity. So, Einstein was dealing with the assumption that
• 34:41
  Speaker 1: the universe was static. And when he put his theory together,
• 34:43
  Speaker 1: he was like, all right, so mass bends space, the
• 34:46
  Speaker 1: universe is filled with mass, so it should curve space
• 34:49
  Speaker 1: and pull stuff together. And then he thought, hmm, well,
• 34:52
  Speaker 1: why hasn't the universe collapsed, right? Like, if space is
• 34:56
  Speaker 1: filled with all this mass, why hasn't it all crunched down? So,
• 35:00
  Speaker 1: his theory essentially predicted the universe should have collapsed already.
• 35:04
  Speaker 1: But he looked out and he said, no, the universe
• 35:05
  Speaker 1: is static, so … What's going on? Well, there's another
• 35:09
  Speaker 1: knob in his theory. General relativity tells us that space
• 35:13
  Speaker 1: is bent by mass. And the sort of pop-side level
• 35:15
  Speaker 1: understanding of general relativity tells you, like, you can think
• 35:19
  Speaker 1: of the force of gravity as the bending of space.
• 35:22
  Speaker 1: But general relativity is much more than that. Different kinds
• 35:25
  Speaker 1: of energy enter into general relativity in a different way. So,
• 35:29
  Speaker 1: for example, if you have internal stored energy, what we
• 35:31
  Speaker 1: call mass, that does bend space and does pull things
• 35:34
  Speaker 1: together effectively, although they're actually in free fall. But if
• 35:38
  Speaker 1: you have another kind of energy, stored potential energy that
• 35:42
  Speaker 1: just fills space, that actually makes space expand. So general
• 35:47
  Speaker 1: relativity broadly doesn't just pull things together. It can also
• 35:52
  Speaker 1: create expansion.
• 35:54
  Speaker 3: Okay. And he recognized that at the time, question mark.
• 35:59
  Speaker 1: He knew that at the time. And so he thought,
• 36:00
  Speaker 1: all right, what if I just stick a number into
• 36:04
  Speaker 1: my theory? If I add potential energy to the universe,
• 36:08
  Speaker 1: no explanation, no idea what it's referring to, just a
• 36:12
  Speaker 1: fudge factor, put that in to balance gravity so that
• 36:15
  Speaker 1: the universe is then static. Because that's what he wanted
• 36:19
  Speaker 1: to achieve. He wanted to describe the universe. He wanted
• 36:21
  Speaker 1: to see if his theory was compatible with the universe.
• 36:23
  Speaker 1: And is that a bogus thing to do? No, it's
• 36:26
  Speaker 1: just essentially asking, well, what would I have to put
• 36:29
  Speaker 1: into my theory to make it describe the universe as
• 36:32
  Speaker 1: I think it works? And remember, he was working on
• 36:34
  Speaker 1: a false premise. He was trying to describe a static
• 36:36
  Speaker 1: universe because that's what they thought we lived in at
• 36:39
  Speaker 1: the time, but they were wrong.
• 36:40
  Speaker 3: The OG fudge factor.
• 36:42
  Speaker 1: Yeah, exactly. So the OG fudge factor was put in
• 36:44
  Speaker 1: to make general relativity agree with the misunderstanding at the
• 36:48
  Speaker 1: time that the universe was static. And the other problem
• 36:52
  Speaker 1: with this fudge factor is that the universe as he
• 36:55
  Speaker 1: described it had these two competing things, the cosmological constant
• 37:00
  Speaker 1: pushing out and gravity pushing in. And for that to
• 37:03
  Speaker 1: give you a static universe, they had to be perfectly balanced.
• 37:06
  Speaker 1: So the universe is like on a knife's edge. It's
• 37:08
  Speaker 1: not stable at all. Somebody like drops an extra raisin
• 37:11
  Speaker 1: in the universe, boom, it collapses. You get a tiny
• 37:14
  Speaker 1: smidge more potential energy, boom, it expands. So it doesn't
• 37:18
  Speaker 1: really make sense as a model of the universe.
• 37:21
  Speaker 3: One more reason to hate raisins.
• 37:23
  Speaker 2: I know.
• 37:24
  Speaker 1: Wait, hold on a second. I love raisins. What are
• 37:27
  Speaker 1: you talking about?
• 37:28
  Speaker 3: You're wrong is what I'm talking about. Yeah, no, raisins
• 37:31
  Speaker 3: and cookies are why I have trust issues.
• 37:34
  Speaker 1: That's only because you think they're chocolate chips and then
• 37:37
  Speaker 1: you're disappointed. But if you're expecting raisins, then you're like, yum, raisins.
• 37:42
  Speaker 3: No, then I'm mad at whoever thought I would like
• 37:44
  Speaker 3: raisin cookies. They don't know me at all.
• 37:47
  Speaker 1: Well, the answer is to put raisins and chocolate chips
• 37:49
  Speaker 1: into your cookies.
• 37:50
  Speaker 2: Oh, no.
• 37:50
  Speaker 1: Porque no los dos.
• 37:52
  Speaker 3: Because then you've ruined the cookie with the raisins.
• 37:56
  Speaker 1: All right.
• 37:56
  Speaker 3: We've had milk digressions, raisin digressions. We should start a
• 37:59
  Speaker 3: food podcast.
• 38:00
  Speaker 1: So then Hubble and Leavitt discover the universe is actually expanding.
• 38:04
  Speaker 1: And this whole point of putting in a cosmological constant
• 38:06
  Speaker 1: to describe a static universe, yeah, that was a mistake.
• 38:09
  Speaker 1: And Einstein said, okay, I'm going to get rid of
• 38:11
  Speaker 1: the cosmological constant. And instead, I'm just going to assume
• 38:14
  Speaker 1: that the universe is decelerating. It's currently expanding, but it's decelerating.
• 38:19
  Speaker 1: So here we're distinguishing between essentially velocity and acceleration. So
• 38:24
  Speaker 1: think about how your car operates. You can have forward velocity.
• 38:28
  Speaker 1: You're going to 50 miles an hour. and you're hitting
• 38:30
  Speaker 1: the brakes. You're decelerating, so you're slowing down. You're still
• 38:34
  Speaker 1: moving forwards, but you're slowing down. That's what Einstein assumed
• 38:38
  Speaker 1: was happening. He said, okay, the universe isn't static. The
• 38:40
  Speaker 1: car is not just sitting on the highway. It's moving forward,
• 38:44
  Speaker 1: and gravity is slowing it down. He thought eventually it
• 38:48
  Speaker 1: will crunch. That was his supposition, but he didn't need
• 38:52
  Speaker 1: cosmological constant anymore, and he got rid of it.
• 38:55
  Speaker 2: Okay.
• 38:55
  Speaker 3: And this was in response to information he learned in
• 38:58
  Speaker 3: his lifetime. He went from thinking the universe was stable
• 39:01
  Speaker 3: to decelerating.
• 39:02
  Speaker 2: Okay.
• 39:02
  Speaker 1: Yeah. And that's the origin of his comment. I don't
• 39:05
  Speaker 1: know the exact quote, that the cosmological constant was his
• 39:08
  Speaker 1: greatest blunder. You know, that he put it in and
• 39:10
  Speaker 1: then he had to take it out.
• 39:12
  Speaker 3: We all make mistakes.
• 39:14
  Speaker 1: Yeah. Now, 80 years later, we discover, okay, the universe
• 39:18
  Speaker 1: isn't just expanding. It's expanding and accelerating, right? And so
• 39:21
  Speaker 1: now people are searching for for a theoretical reason that
• 39:25
  Speaker 1: might happen. What could accommodate that? Not just that it's accelerating,
• 39:29
  Speaker 1: but that it started accelerating recently, right? That the history
• 39:34
  Speaker 1: is that we were always expanding, but that expansion was
• 39:37
  Speaker 1: decelerating for the first 9 billion years. Gravity was winning.
• 39:41
  Speaker 1: And then around 5 billion years ago, 9 billion years
• 39:44
  Speaker 1: into the history of the universe, it turned around and
• 39:46
  Speaker 1: it went from decelerating to accelerating. So like the car
• 39:50
  Speaker 1: was always moving forward, it was slowing down the first
• 39:52
  Speaker 1: 9 billion years. And then we went from brake to gas.
• 39:56
  Speaker 1: And now we're accelerating. We're still moving forward, still expanding.
• 39:59
  Speaker 1: But now that expansion is faster and faster.
• 40:02
  Speaker 3: Somebody was like, would you like a cookie with raisins
• 40:04
  Speaker 3: in it? And you put your foot on the gas
• 40:06
  Speaker 3: to get out of there as fast as you can.
• 40:08
  Speaker 3: The universe is trying to.
• 40:10
  Speaker 1: Escape raisin cookies. I am driving as fast as possible
• 40:13
  Speaker 1: to the oatmeal cookie factory.
• 40:15
  Speaker 3: No, huge mistake.
• 40:15
  Speaker 1: So I can consume them as quickly as possible. Huge mistake.
• 40:18
  Speaker 1: And so the cosmological constant can actually describe this. It's
• 40:22
  Speaker 1: amazing because the cosmological constant says, look, you got some
• 40:26
  Speaker 1: potential energy that fills space. We don't know what it
• 40:28
  Speaker 1: is yet, but say you have something that fills space
• 40:30
  Speaker 1: with potential energy. that will cause some expansion. And the
• 40:34
  Speaker 1: amazing thing is that as the universe expands, matter gets
• 40:38
  Speaker 1: more dilute, radiation gets more dilute, right? By which I
• 40:41
  Speaker 1: just mean like you got more space and the same
• 40:43
  Speaker 1: amount of stuff. So the density of matter goes down,
• 40:47
  Speaker 1: which means essentially gravity is decreasing, but potential energy doesn't.
• 40:52
  Speaker 1: It's just built into space. So if you get twice
• 40:55
  Speaker 1: as much space, you get the same density of potential
• 40:58
  Speaker 1: energy everywhere, which means more energy. So as the universe expands,
• 41:04
  Speaker 1: the cosmological constant becomes more and more important because everything
• 41:08
  Speaker 1: else has energy density that's decreasing with expansion, but it's
• 41:11
  Speaker 1: staying constant, which means that it gets a larger and
• 41:14
  Speaker 1: larger fraction. So expansion leads to more expansion because as
• 41:19
  Speaker 1: time goes on, as the universe expands, the cosmological constant
• 41:23
  Speaker 1: becomes more and more important, which according to the equations
• 41:26
  Speaker 1: of general relativity means more expansion until at some point,
• 41:30
  Speaker 1: it starts to win and it's overwhelming everything. And that's
• 41:33
  Speaker 1: what happened 5 billion years ago. So it actually goes
• 41:36
  Speaker 1: to accelerating expansion, a runaway effect. And this predicts that
• 41:40
  Speaker 1: as time goes on, it's just going to get more
• 41:42
  Speaker 1: and more important. We're in a dark energy dominated universe.
• 41:46
  Speaker 3: So my brain is trying to make a connection to Noether.
• 41:49
  Speaker 3: And Noether, did she play a role in helping us
• 41:52
  Speaker 3: understand this?
• 41:53
  Speaker 1: So she didn't help us understand it, but she helps
• 41:55
  Speaker 1: us understand the implications. Because you're probably remembering that Noether
• 41:59
  Speaker 1: has her amazing theory about conservation laws and symmetries. And
• 42:04
  Speaker 1: there's a connection between whether the laws of physics and
• 42:07
  Speaker 1: space are constant in time and conservation of energy. And
• 42:12
  Speaker 1: she says, if space is not expanding and the laws
• 42:14
  Speaker 1: of physics don't change, actually, if the action is invariant
• 42:18
  Speaker 1: over time, then energy is conserved. Check out our whole
• 42:21
  Speaker 1: podcast episode about action if you want to learn more
• 42:24
  Speaker 1: about that. But now we know that the action is
• 42:27
  Speaker 1: not invariant, that as time goes on, space is expanding
• 42:30
  Speaker 1: and accelerating. And that's how we know that energy can't
• 42:33
  Speaker 1: actually be conserved in our universe. It shouldn't be conserved
• 42:37
  Speaker 1: in our universe because the symmetry that you would need
• 42:40
  Speaker 1: to get energy to be conserved is broken, right? Space
• 42:44
  Speaker 1: is expanding. The action is not invariant. So that's the
• 42:47
  Speaker 1: connection to Emmy Noether. Is that what you're asking about?
• 42:49
  Speaker 3: Yeah, and so I guess now I'm trying to connect
• 42:51
  Speaker 3: that to... So as the universe is expanding, you're getting
• 42:55
  Speaker 3: more dark energy being made.
• 42:56
  Speaker 2: Yeah.
• 42:57
  Speaker 3: Is that the same thing as the cosmological constant? Or
• 43:00
  Speaker 3: is that like a part of understanding the cosmological constant?
• 43:04
  Speaker 1: It's a great question because that's the essential piece of
• 43:06
  Speaker 1: this theory that helps us make it work. That as
• 43:09
  Speaker 1: the universe expands, cosmological constant is constant. It's a constant density, right?
• 43:15
  Speaker 1: It does not get diluted. That's the reason that it works. Okay.
• 43:18
  Speaker 1: And it's sort of amazing that our theory of general
• 43:21
  Speaker 1: relativity already has a knob in it, which if you
• 43:25
  Speaker 1: crank it up to a certain number, explains perfectly, well,
• 43:28
  Speaker 1: not perfectly, but very, very well, this accelerating expansion of
• 43:32
  Speaker 1: the universe. You don't have to reach for totally crazy
• 43:35
  Speaker 1: new theory of physics, but what you do need is
• 43:38
  Speaker 1: potential energy that fills all of space and doesn't get diluted.
• 43:42
  Speaker 1: And that's the big mystery. So we've made sort of
• 43:44
  Speaker 1: a step forward by saying like, oh, there's feature of
• 43:47
  Speaker 1: general relativity, which can create this thing which we've observed,
• 43:51
  Speaker 1: which we know is happening. But it also kicks the
• 43:54
  Speaker 1: can down the road and invites more questions like, well,
• 43:56
  Speaker 1: what is this potential energy? You just put it in there.
• 44:00
  Speaker 1: You haven't said what it is. Potential energy is not
• 44:02
  Speaker 1: just some abstract thing. You can have potential energy stored
• 44:06
  Speaker 1: in a field, for example. We know that the Higgs
• 44:09
  Speaker 1: boson is a particle that's an oscillation in a field
• 44:12
  Speaker 1: that's out there. And one of the most interesting things
• 44:15
  Speaker 1: about the Higgs field, the reason it does what it does,
• 44:18
  Speaker 1: is because it's filled with potential energy, unlike other fields.
• 44:21
  Speaker 1: The photon field and the electron field don't have this
• 44:24
  Speaker 1: kind of potential energy, but the Higgs does. It's potential
• 44:27
  Speaker 1: energy that fills all of space. And you might think, oh, wow,
• 44:32
  Speaker 1: is the Higgs boson field providing the potential energy you
• 44:36
  Speaker 1: need to explain the cosmological constant? Wouldn't that be incredible?
• 44:40
  Speaker 1: If you came out from one direction, you're like, hey,
• 44:43
  Speaker 1: the universe is expanding, and that suggests maybe there's potential
• 44:46
  Speaker 1: energy in all of space. And you came out from
• 44:48
  Speaker 1: the other direction, you're like, hey, particle physicists have discovered
• 44:51
  Speaker 1: a field that fills all of space with potential energy.
• 44:53
  Speaker 1: And you might be like, oh my gosh, am I
• 44:55
  Speaker 1: about to make the best understanding in the history of
• 44:57
  Speaker 1: the universe? And you put these two numbers together and say,
• 44:59
  Speaker 1: do they agree? And the answer is no. And not
• 45:03
  Speaker 1: even to within 10% or 50%. They're different by 10
• 45:07
  Speaker 1: to the 120.
• 45:08
  Speaker 3: And so let me guess, this is a project you
• 45:11
  Speaker 3: decided you wanted to be part of because it was
• 45:13
  Speaker 3: destined to not get a Nobel Prize.
• 45:16
  Speaker 2: Oh my gosh.
• 45:17
  Speaker 1: Understanding theoretically the source of dark energy would definitely get
• 45:20
  Speaker 1: somebody the Nobel Prize. And so we have no explanation.
• 45:24
  Speaker 1: We have this mechanism, the cosmological constant, which if you
• 45:27
  Speaker 1: put into general relativity can explain the accelerating expansion of
• 45:32
  Speaker 1: the universe. But we have no idea what the cosmological
• 45:37
  Speaker 1: constant really is. It's just like a first idea. It's
• 45:39
  Speaker 1: a number we put in to make things work. And
• 45:42
  Speaker 1: then we come back and say, well, what could be
• 45:44
  Speaker 1: causing it? And our first idea, all the quantum fields
• 45:47
  Speaker 1: that we know about, definitely is not explaining that. That
• 45:50
  Speaker 1: does not work.
• 45:51
  Speaker 2: No.
• 45:51
  Speaker 1: We don't have another better idea yet. So is that
• 45:55
  Speaker 1: a fudge factor? I mean, I think it's a little
• 45:57
  Speaker 1: bit of a fuzzy question because it's not a bad
• 46:00
  Speaker 1: fudge factor. It's not like, hey, we discover the universe
• 46:03
  Speaker 1: is expanding and accelerating and we really want to stick
• 46:06
  Speaker 1: with general relativity. So we're going to do anything to
• 46:08
  Speaker 1: make it work. And we're just going to stick this
• 46:10
  Speaker 1: number in here. We're going to pretend it makes sense,
• 46:12
  Speaker 1: even though it doesn't, right? That's the cartoon version of
• 46:16
  Speaker 1: conspiratorial physicists trying to defend general relativity or something. I mean,
• 46:21
  Speaker 1: which makes no sense because in reality, everybody, especially the
• 46:23
  Speaker 1: conspiracy folks out there, are trying to disprove Einstein. I
• 46:27
  Speaker 1: get Einstein was wrong emails 10 times a day. So
• 46:30
  Speaker 1: I don't know why they think that physicists don't also
• 46:33
  Speaker 1: want to disprove Einstein.
• 46:34
  Speaker 3: Because then your face would be on all the posters.
• 46:37
  Speaker 3: What would your quote be, Daniel?
• 46:41
  Speaker 1: My quote would be, this is never going to work.
• 46:43
  Speaker 1: Daniel was wrong again.
• 46:44
  Speaker 3: Oh, I'd put that poster up.
• 46:46
  Speaker 1: Yeah.
• 46:48
  Speaker 3: Good to always be skeptical.
• 46:49
  Speaker 1: And the issues go deeper, right? It's not just that
• 46:52
  Speaker 1: we don't know where this number, the cosmological constant, comes from.
• 46:57
  Speaker 1: We'd love to be able to derive it from first
• 46:59
  Speaker 1: principles to say, oh, the Higgs field, and you calculate it,
• 47:02
  Speaker 1: and here's the potential energy, and here's the number you
• 47:04
  Speaker 1: put in, and it works. We're not there yet. We're
• 47:06
  Speaker 1: nowhere close to there. The other issue is that, as
• 47:09
  Speaker 1: I was saying earlier— Even just having a single number,
• 47:13
  Speaker 1: the cosmological constant, doesn't quite work because we see the
• 47:16
  Speaker 1: number you would need changing over time a little bit,
• 47:20
  Speaker 1: like the early universe measurements, the late universe measurements. So
• 47:23
  Speaker 1: it might be that there's two different kinds of expansion
• 47:26
  Speaker 1: happening there. So there's a theory of early dark energy
• 47:30
  Speaker 1: that is another kind of dark energy that turned on early,
• 47:35
  Speaker 1: kicked things off, and then turned off, which maybe explains
• 47:39
  Speaker 1: why we're seeing inconsistent measurements. So there's like complexity to
• 47:43
  Speaker 1: this fudge factor. And there's, you know, even other people
• 47:46
  Speaker 1: out there with totally different theories. Like a couple of
• 47:49
  Speaker 1: years ago, there was all this excitement because people noticed
• 47:51
  Speaker 1: a correlation between supermassive black holes at the hearts of
• 47:55
  Speaker 1: galaxies and the expansion of the universe and the accelerating expansion.
• 48:00
  Speaker 1: And so there was thought for a while, like maybe
• 48:02
  Speaker 1: supermassive black holes in the hearts of galaxies are the
• 48:05
  Speaker 1: dark energy. Maybe somehow they are doing this to the universe.
• 48:08
  Speaker 1: And there were some problems with that theory and it
• 48:10
  Speaker 1: sort of went away, but You know, what it shows
• 48:12
  Speaker 1: you is not a field that's out there to convince
• 48:16
  Speaker 1: you of one idea of whether or not it works,
• 48:18
  Speaker 1: but it shows you a group of people being curious
• 48:21
  Speaker 1: about the universe, scratching their heads, being open about what
• 48:24
  Speaker 1: works and what doesn't work. Like the big mysteries that,
• 48:28
  Speaker 1: you know, we write 10,000 pop-sci articles about a year,
• 48:30
  Speaker 1: the Hubble constant and all this kind of stuff. We're
• 48:33
  Speaker 1: open about what's not working, and it's a work in progress,
• 48:35
  Speaker 1: and it's a work in progress that's out there in public.
• 48:38
  Speaker 1: You can see people making progress, people disagreeing about it,
• 48:42
  Speaker 1: people suggesting new ideas. There's no defense of the dogma here.
• 48:47
  Speaker 1: This is just like you're watching it in action. Welcome
• 48:51
  Speaker 1: to the forefront of ignorance. This is how science works.
• 48:54
  Speaker 1: We're confused about how stuff is happening, and we're trying
• 48:58
  Speaker 1: to figure it out. There are some older questions that
• 49:01
  Speaker 1: we're much less confused about, and we're not very excited
• 49:04
  Speaker 1: about revisiting, like, is the speed of light constant? Maybe
• 49:08
  Speaker 1: we're wrong about that, I don't know, but it doesn't
• 49:10
  Speaker 1: seem as interesting as other questions that we know we're
• 49:13
  Speaker 1: wrong about, and we have no explanation for, like, you know,
• 49:17
  Speaker 1: what is the source of dark energy, theoretically. So that's
• 49:20
  Speaker 1: why some questions get more attention and other questions get
• 49:23
  Speaker 1: less attention because, hey, we're humans and we're driven by
• 49:25
  Speaker 1: our curiosity, and curiosity is frankly subjective and personal and And,
• 49:30
  Speaker 1: you know, driven by what gets you excited to get
• 49:32
  Speaker 1: out of bed and spend your day doing science.
• 49:35
  Speaker 2: Yeah. All right. End rant. And this is the process.
• 49:39
  Speaker 3: You know, you do what you can with the information
• 49:41
  Speaker 3: you have. You try to collect more information so that
• 49:44
  Speaker 3: you can ask more specific and better questions. And sometimes
• 49:47
  Speaker 3: you're going to be wrong. You just always need to
• 49:48
  Speaker 3: be open to that.
• 49:49
  Speaker 1: Yeah.
• 49:50
  Speaker 3: And you move forward the way you can.
• 49:52
  Speaker 1: Yeah. And, you know, let's also acknowledge that there are
• 49:55
  Speaker 1: structural incentives in science and in every human endeavor, right?
• 50:00
  Speaker 1: for people to defend an idea even after we're clear
• 50:04
  Speaker 1: it's not working. You know, there are people who have
• 50:07
  Speaker 1: an idea and stake their reputation on it. And, you know,
• 50:10
  Speaker 1: it was their baby. And when it doesn't look like
• 50:12
  Speaker 1: it's working, they try to make it work and they
• 50:14
  Speaker 1: stick to it. And there are definitely structural incentives for
• 50:17
  Speaker 1: people to not do the right thing. But, you know,
• 50:19
  Speaker 1: people have lots of incentives and they're not always necessarily
• 50:23
  Speaker 1: just going to follow one set of incentives. There are
• 50:26
  Speaker 1: also incentives to figure out how things work and to
• 50:28
  Speaker 1: be a reasonable human being. And in reality, people's actions
• 50:32
  Speaker 1: are complex and this is not a perfect system. And
• 50:35
  Speaker 1: I don't want to suggest that like science is a
• 50:37
  Speaker 1: pure meritocracy and every idea rises to the top perfectly.
• 50:41
  Speaker 1: And that we always work on the most useful thing.
• 50:44
  Speaker 1: Absolutely not. It's a messy political human endeavor, but it's
• 50:48
  Speaker 1: also the best system we've ever had for building knowledge
• 50:52
  Speaker 1: about the universe. So anyway- I was supposed to end
• 50:55
  Speaker 1: my rant a minute ago, but this is the real end.
• 50:57
  Speaker 3: That's rant part two. But I mean, there's like, you know,
• 51:00
  Speaker 3: different people have different incentives. So if you've got somebody
• 51:02
  Speaker 3: whose incentive is to like not back down, even when
• 51:05
  Speaker 3: it's clear that their theory isn't explaining things as well
• 51:07
  Speaker 3: as they thought, there's an incentive for the like lab
• 51:09
  Speaker 3: at the other university across the ponds to prove you wrong.
• 51:12
  Speaker 3: Or there's the incentive of your grad students who like maybe,
• 51:16
  Speaker 3: you know, when they start their own lab realize, oh,
• 51:18
  Speaker 3: I'd really like to be remembered as someone who was right.
• 51:22
  Speaker 3: And so maybe they slowly push back against the ideas
• 51:25
  Speaker 3: of their advisor because they don't want to spend their
• 51:28
  Speaker 3: whole careers on an idea that's wrong. And so, you know,
• 51:30
  Speaker 3: it's different people have different motivations. And hopefully in the end,
• 51:33
  Speaker 3: science pushes everybody towards the right answer.
• 51:35
  Speaker 2: Mm hmm.
• 51:37
  Speaker 1: Yeah, and another note for people who have ideas that
• 51:41
  Speaker 1: they're excited about and they can't get the community to engage.
• 51:46
  Speaker 1: You've written grant proposals and they've all been rejected or
• 51:49
  Speaker 1: nobody will read your theory. Remember that resources are limited.
• 51:53
  Speaker 1: In a perfect world, we could give everybody money to
• 51:55
  Speaker 1: investigate the universe, no matter whether their theories were popular
• 51:59
  Speaker 1: or not. But we have limited funding, we have limited time,
• 52:02
  Speaker 1: we have limited attention. We have to make decisions about
• 52:05
  Speaker 1: where to put those resources. And so rather than having
• 52:09
  Speaker 1: one random YouTuber decide this is what's most important and
• 52:12
  Speaker 1: everybody else is wasting their time, we have panels. We
• 52:15
  Speaker 1: have consensus. We argue over it. We do it in
• 52:17
  Speaker 1: public so that we try to get as many perspectives
• 52:21
  Speaker 1: as possible. But in the end, yes, we do want
• 52:23
  Speaker 1: to put resources towards the things we think are going
• 52:26
  Speaker 1: to lead to discoveries. And that means investing in the
• 52:29
  Speaker 1: mainstream ideas, not always giving money to everybody out there
• 52:34
  Speaker 1: with a crazy new idea, which may be promising and
• 52:36
  Speaker 1: may even be correct, right? But in the same way
• 52:38
  Speaker 1: that like the best screenplays aren't always turned into movies
• 52:42
  Speaker 1: in Hollywood, right? Like the system isn't perfect because of
• 52:46
  Speaker 1: limited resources. And that's just the unfortunate reality. And the
• 52:49
  Speaker 1: way to fix that is not to burn academia to
• 52:52
  Speaker 1: the ground, but to spend more money to fund more
• 52:57
  Speaker 1: of these ideas further from the mainstream, right? If we
• 53:00
  Speaker 1: instead invest in academia, then we get more crazy blue
• 53:04
  Speaker 1: sky ideas. We can take more risks. Anyway, for the
• 53:07
  Speaker 1: third time, I'll say end rant then.
• 53:09
  Speaker 3: Yeah, yeah, sure.
• 53:10
  Speaker 1: We'll see.
• 53:10
  Speaker 3: We'll see.
• 53:12
  Speaker 1: I should stop saying that.
• 53:14
  Speaker 3: That's right. It's like when you title a document or
• 53:17
  Speaker 3: a grant or a manuscript final version, you are making
• 53:21
  Speaker 3: it certain that there will be a final version two
• 53:24
  Speaker 3: and a final version three.
• 53:25
  Speaker 2: Yeah.
• 53:25
  Speaker 3: But, okay, to try to bottom line, we have this
• 53:28
  Speaker 3: observation that we feel pretty darn confident about because we've
• 53:32
  Speaker 3: seen it using a bunch of different methods.
• 53:33
  Speaker 2: Yes.
• 53:33
  Speaker 3: We're doing our best to explain it. We realize that
• 53:36
  Speaker 3: there's shortcomings in our explanations. We are trying to figure
• 53:39
  Speaker 3: it out. It is an open conversation.
• 53:42
  Speaker 2: Yeah.
• 53:42
  Speaker 3: And this is one of the big exciting questions in
• 53:45
  Speaker 3: physics that, you know, hopefully we'll figure out in the
• 53:47
  Speaker 3: next generation or two or this generation.
• 53:49
  Speaker 2: Yeah.
• 53:50
  Speaker 3: And if Daniel thinks the lab is probably not on
• 53:52
  Speaker 3: the right path, those guys and gals are getting a
• 53:55
  Speaker 3: Nobel Prize.
• 53:57
  Speaker 1: That's my backwards seal of approval.
• 53:58
  Speaker 2: Exactly. That's right.
• 54:00
  Speaker 1: All right. Well, thank you, everybody, for going on this
• 54:02
  Speaker 1: journey with us back into history to our understanding of
• 54:05
  Speaker 1: the universe and how the universe evolves and how our
• 54:07
  Speaker 1: understanding of it has evolved to try to predict the
• 54:10
  Speaker 1: future and how our understanding will eventually, we hope, coalesce
• 54:15
  Speaker 1: into a crystal clear picture of the history and future
• 54:18
  Speaker 1: of the universe.
• 54:19
  Speaker 3: Good luck, physicists.
• 54:29
  Speaker 1: Thanks, everybody, for listening. Please go and do us a
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• 54:35
  Speaker 1: It really helps people find us.
• 54:37
  Speaker 3: Daniel and Kelly's Extraordinary Universe is edited by the amazing
• 54:41
  Speaker 3: Matt Kesselman.
• 54:42
  Speaker 1: He really is a wizard. You can also find us
• 54:45
  Speaker 1: online on Blue Sky, Instagram, and X, D & K Universe.
• 54:50
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• 54:52
  Speaker 3: You can email us at questions at danielandkelly.org. We really
• 54:56
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• 54:57
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• 55:02
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• 55:08
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