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What did the early Universe sound like? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey or he. Are you a fan of boba tea?
• 0:11
  Speaker 2: You mean like bubble tea?
• 0:12
  Speaker 1: Yeah? Is that what the kids are calling it?
• 0:14
  Speaker 2: I think they call it boba, but I think maybe
• 0:16
  Speaker 2: most people might not know what that is. But yeah,
• 0:18
  Speaker 2: I'm a fan. My kids are really into it, so
• 0:20
  Speaker 2: I've grown to like it.
• 0:22
  Speaker 1: Well, my daughter loves it, but personally, I can't get
• 0:24
  Speaker 1: over the fear of being choked by a floating blob
• 0:27
  Speaker 1: every time they take a sip.
• 0:28
  Speaker 2: Oh. Well, first of all, they don't float, which tells
• 0:30
  Speaker 2: me maybe you don't drink boba very often, Busty. The
• 0:35
  Speaker 2: other thing is they're not that big. I think they're
• 0:37
  Speaker 2: pretty much smaller than your throat.
• 0:39
  Speaker 1: I think maybe these new trends are just not for
• 0:40
  Speaker 1: the faint of heart.
• 0:41
  Speaker 2: So do you not like bubbles in general?
• 0:44
  Speaker 1: No, I'm pro bubbles in the universe, just not in
• 0:47
  Speaker 1: my tea, not as a choking hazard.
• 0:49
  Speaker 2: I see what about economic bubbles? Those are bad news?
• 0:53
  Speaker 3: Mmm.
• 0:54
  Speaker 1: I'm hoping to ride the podcast bubble until it pops.
• 0:56
  Speaker 2: Yeah, there you go. Not all bubbles are bad. Hi
• 1:14
  Speaker 2: am Jorge Mack, cartoonist and the author of All Ours
• 1:16
  Speaker 2: Great Big Universe.
• 1:17
  Speaker 1: Hi, I am Daniel, I'm a particle physicist and a
• 1:19
  Speaker 1: professor at UC Irvine, and I'm actually fascinated by the
• 1:23
  Speaker 1: mathematics of bubbles.
• 1:24
  Speaker 2: Oh yeah, it is, and it just a sphere.
• 1:26
  Speaker 1: Some bubbles are spheres, but you can also get bubbles
• 1:28
  Speaker 1: of all sorts of different shapes, which solve really complicated
• 1:31
  Speaker 1: sets of mathematical equations to like minimize surface area.
• 1:35
  Speaker 2: Now is that math or is that physics.
• 1:37
  Speaker 1: It's using physics to solve math. It's like using the
• 1:40
  Speaker 1: universe as a computer. Whoa bubble computers?
• 1:43
  Speaker 4: Man?
• 1:43
  Speaker 2: That sounds like an awesome topic for a podcast episode,
• 1:46
  Speaker 2: but I'm guessing that's not what we're talking about today.
• 1:49
  Speaker 1: We are not talking about my new Bubble Computers startup,
• 1:52
  Speaker 1: which will be serving bubble tea in the lobby, but
• 1:54
  Speaker 1: we are talking about bubbles.
• 1:56
  Speaker 2: You're going to ride that tech bubble. But anyways, welcome
• 1:59
  Speaker 2: to a podcast Daniel and Jorge Explain the Universe, a
• 2:02
  Speaker 2: production of iHeartRadio in.
• 2:04
  Speaker 1: Which we want you to ride the bubble of understanding.
• 2:07
  Speaker 1: As human thought expands further and further into the universe,
• 2:10
  Speaker 1: we understand more and more about this incredible and crazy cosmos.
• 2:14
  Speaker 1: We decode the messages that come to us from all
• 2:17
  Speaker 1: these distant places and try to piece them together into
• 2:19
  Speaker 1: a fragile bubble of understanding.
• 2:22
  Speaker 2: Because it is an awesome universe inflating every day with
• 2:25
  Speaker 2: more and more awesomeness. We like to inflate your brain
• 2:27
  Speaker 2: here on the podcast until it pops with an epiphany
• 2:31
  Speaker 2: about how the universe works.
• 2:32
  Speaker 1: I don't want anybody to bring the pop man. We
• 2:35
  Speaker 1: want to very gently inflate it.
• 2:38
  Speaker 2: I said, with an epiphany.
• 2:40
  Speaker 1: Oh, that sounds terrifying, but you're right. We do want
• 2:42
  Speaker 1: listeners to have that moment of understanding where suddenly things
• 2:46
  Speaker 1: click into place and you go, oh, I get it.
• 2:49
  Speaker 1: This thing I used to hear in that bit, I
• 2:50
  Speaker 1: thought I understood. Those actually fit together into a holistic
• 2:54
  Speaker 1: idea about how the universe works, and that, in the end,
• 2:57
  Speaker 1: is the goal of this podcast.
• 2:58
  Speaker 2: Yeah, we like to taggle the bit mysteries about the
• 3:00
  Speaker 2: universe from its large scale and what kinds of amazing
• 3:04
  Speaker 2: things you can find out there in the reaches of space,
• 3:06
  Speaker 2: but also in the smallest of scales done at the
• 3:07
  Speaker 2: atomic and particle sizes, from the beginning of the universe
• 3:10
  Speaker 2: to the end of the universe.
• 3:12
  Speaker 1: Exactly, and those little bubbles at the particle level in
• 3:14
  Speaker 1: the early universe turn out to have a ripple effect
• 3:17
  Speaker 1: that create bubbles in our universe billions of years later
• 3:21
  Speaker 1: and millions of light years across. It turns out that
• 3:24
  Speaker 1: bubbles are not just the core idea between my future
• 3:28
  Speaker 1: billion dollar bubble computing startup or the drinks that my
• 3:31
  Speaker 1: daughter enjoys. They are also fundamental to understanding the early
• 3:34
  Speaker 1: universe and the structure of the universe today.
• 3:37
  Speaker 2: But you mean you can tie the Big Band to boba.
• 3:40
  Speaker 1: The Big Bang was basically just a bobba bubble.
• 3:42
  Speaker 2: Big bubba bubble bang boom. Yes, Daniel said, a lot
• 3:47
  Speaker 2: of things that happened at the beginning of the universe,
• 3:49
  Speaker 2: even small, microscopic things that were going on, have a
• 3:52
  Speaker 2: huge impact in what the universe looks like today, and
• 3:55
  Speaker 2: maybe even might have tip things in our favor for
• 4:00
  Speaker 2: to be creative and for our galaxy to be the
• 4:02
  Speaker 2: way it is now.
• 4:02
  Speaker 1: One of my favorite things in physics is figuring out
• 4:04
  Speaker 1: a way to sift through the clues that are left
• 4:07
  Speaker 1: to us about what happened in deep time, what happened
• 4:09
  Speaker 1: in the very early universe. If we can figure out
• 4:12
  Speaker 1: the signs and signals, but those early events left for us.
• 4:15
  Speaker 1: We can actually reconstruct a complete history of what happened
• 4:18
  Speaker 1: in the universe. It's like the biggest detective game ever.
• 4:23
  Speaker 2: I don't think they can even trace how boba was invented,
• 4:26
  Speaker 2: so that would be an amazing feed if we can,
• 4:28
  Speaker 2: you know, trace our origin back to the Big Bang.
• 4:31
  Speaker 1: Are you saying it just organically bubbled up from nothing?
• 4:33
  Speaker 2: I don't know, that's the mystery. Maybe it was aliens.
• 4:39
  Speaker 2: I knew that NASA had secret alien technology. I just
• 4:42
  Speaker 2: didn't realize it was Boba technology. Well not NASA, and
• 4:45
  Speaker 2: NASA's is from Earth. Am saying the conspiracy runs deeper?
• 4:48
  Speaker 1: Oh my gosh, wow, intergalactic Boba bubble conspiracy.
• 4:52
  Speaker 2: There you go. That's what the world needs, more conspiracy theories.
• 4:57
  Speaker 1: But we are here on this podcast breaking down conspiratorial
• 4:59
  Speaker 1: nons sense and telling you the truth about what we
• 5:01
  Speaker 1: do and do not know, how we trace back to
• 5:04
  Speaker 1: the history of the early universe and how it affects
• 5:06
  Speaker 1: our lives today.
• 5:07
  Speaker 2: So today on the podcast, we'll be tackling the question
• 5:14
  Speaker 2: what did the early universe sound like? Interesting questions about
• 5:19
  Speaker 2: the sound of the early universe.
• 5:21
  Speaker 1: Yeah, did it sound like somebody choking onbah?
• 5:25
  Speaker 2: Maybe that is the origin of the universe. Maybe they're
• 5:29
  Speaker 2: all here because some intergalactic god choking a giant boba.
• 5:35
  Speaker 1: Exactly. He took his daughter out for intergalactic boba and
• 5:38
  Speaker 1: the rest is history.
• 5:39
  Speaker 2: Yeah, maybe black holes are like the boba of you know,
• 5:42
  Speaker 2: the higher beings.
• 5:45
  Speaker 1: Black hole boba. I will definitely sell that in the
• 5:47
  Speaker 1: cafe of my bubble computing startup.
• 5:50
  Speaker 4: Yeah.
• 5:50
  Speaker 2: They are pretty dense right in drink, They're like thing
• 5:53
  Speaker 2: in the drink.
• 5:54
  Speaker 1: They're terrifying.
• 5:55
  Speaker 2: Oh my gosh, you're really afraid of boba.
• 5:58
  Speaker 1: When I take sip of a I want to enjoy
• 6:00
  Speaker 1: a fresh liquid and not worry that something is going
• 6:03
  Speaker 1: to shoot down my throat. Yeah.
• 6:05
  Speaker 2: I think we've established the bow is not for you.
• 6:09
  Speaker 1: But I am a big fan of bubbles, including sound
• 6:11
  Speaker 1: bubbles in the early universe. People don't usually think about
• 6:15
  Speaker 1: what the universe sounds like because they think about space
• 6:18
  Speaker 1: is being mostly empty and so diffuse that sound waves
• 6:21
  Speaker 1: can't effectively travel through it. But that wasn't always the case.
• 6:25
  Speaker 2: Yeah, so this is an interesting question, and it sounds
• 6:27
  Speaker 2: like the early universe sounds are related to bubbles, like
• 6:31
  Speaker 2: bubbles popping or bubbles forming, bubbles.
• 6:33
  Speaker 1: Forming and slashing around, and even oscillating. In physics, this
• 6:37
  Speaker 1: whole field goes by the fancy name of baryon acoustic
• 6:41
  Speaker 1: oscillation b AO or bow.
• 6:44
  Speaker 2: Mm oh, well we should be talking about bows then, buba.
• 6:49
  Speaker 1: Bubble bow.
• 6:50
  Speaker 2: Those you can't probably choke on if you try to
• 6:52
  Speaker 2: eat a whole one at once.
• 6:54
  Speaker 1: Don't put those in your drinks, folks.
• 6:55
  Speaker 2: Yeah, that that's an interesting idea, Daniel. You might have
• 7:00
  Speaker 2: invented the newest trend.
• 7:01
  Speaker 1: Is that going to start a whole new universe?
• 7:03
  Speaker 2: Maybe? Yeah, maybe somebody will struggle to swelling one and
• 7:08
  Speaker 2: originate a whole new universe of lawsuits, I'm guessing. But anyways,
• 7:12
  Speaker 2: it's an interesting question. What did the early universe sound like?
• 7:15
  Speaker 2: And it sounds like it's related to something called the
• 7:18
  Speaker 2: baryon acoustic oscillation, and so, as usual, we were wondering
• 7:21
  Speaker 2: how many people had heard of this concept? Do they
• 7:23
  Speaker 2: know what it is? Do they want to know.
• 7:26
  Speaker 1: What it is? How could they live so long without
• 7:29
  Speaker 1: hearing about it? So thanks very much to everybody who
• 7:31
  Speaker 1: answers these questions for the podcast. If you'd like to
• 7:34
  Speaker 1: join the crew. Please don't be shy. Write to me
• 7:36
  Speaker 1: two questions at Danielandjorge dot com, or contact us on
• 7:40
  Speaker 1: Twitter or join our discord. We'd be happy to send
• 7:43
  Speaker 1: you these questions.
• 7:44
  Speaker 2: So think about it for a second. Do you know
• 7:46
  Speaker 2: what baryon acoustic oscillations are? Here's what people have to say.
• 7:51
  Speaker 3: I have no idea, but it reminds me of something
• 7:54
  Speaker 3: in a video game I used to play. Oscillation is
• 7:57
  Speaker 3: kind of like a ring of something I because in
• 8:01
  Speaker 3: my video game there's like a big circle ring the
• 8:05
  Speaker 3: boss called the ausciliator. Acoustic is like kind of like antiqueish.
• 8:10
  Speaker 1: I think, I'm sorry, I'll pass. Never heard about it.
• 8:15
  Speaker 4: I believe this is pressure waves in the cosmic background
• 8:21
  Speaker 4: radiation that is caused. We can see the slight changes
• 8:26
  Speaker 4: in temperature caused by pressure waves, and because the pressure
• 8:31
  Speaker 4: waves cannot propagate at greater than the speed of light,
• 8:35
  Speaker 4: the size of the acoustic variations gives an excellent estimate
• 8:42
  Speaker 4: of the distance to the cosmic background radiation source, and
• 8:47
  Speaker 4: therefore that, in conjunction with the red shift that we observe,
• 8:54
  Speaker 4: gives us a very good indication of the hubble constant
• 8:57
  Speaker 4: at that one point in time approximately four hundred thousand
• 9:02
  Speaker 4: years after the Big Bang.
• 9:03
  Speaker 5: Based purely on the name, I would guess that baryon
• 9:06
  Speaker 5: acoustic castellation has something to do with either using sound
• 9:11
  Speaker 5: to cause beryons to bump each other or using sound
• 9:17
  Speaker 5: like properties to study how they behave.
• 9:19
  Speaker 6: I have it in my head that baryon acoustic ostellations
• 9:22
  Speaker 6: has something to do with the beginning of the universe
• 9:24
  Speaker 6: and tower. The original quantum fluctuations prior to inflation taking
• 9:29
  Speaker 6: place could be seen as being like waves through the
• 9:32
  Speaker 6: kind of plasmi y stuff at the beginning, and then
• 9:35
  Speaker 6: when that gets blown out by inflation, you can still
• 9:37
  Speaker 6: detect and see those acoustic ostellations today.
• 9:41
  Speaker 3: So Buryon's some atomic particle, and probably.
• 9:49
  Speaker 1: It has acoustic.
• 9:51
  Speaker 3: Oscillation to it, like having a pattern repeating over a
• 9:56
  Speaker 3: period of time.
• 9:57
  Speaker 6: Or something like that.
• 9:59
  Speaker 2: All right, and a lot of answers here. I like
• 10:01
  Speaker 2: the person who said, I'm sorry, I'll pass. What do
• 10:03
  Speaker 2: you say to that, okay next? Or do you try
• 10:08
  Speaker 2: to convince them that they want to know what burying
• 10:10
  Speaker 2: acoustic oscillations are.
• 10:12
  Speaker 1: I don't want to pressure anybody. I'm just impressed that
• 10:14
  Speaker 1: they decided to record their passing and send it in
• 10:17
  Speaker 1: rather than just not responding.
• 10:19
  Speaker 2: Oh, they actually like took the time to record this exactly.
• 10:22
  Speaker 1: They sat down and record their answers and sent it
• 10:24
  Speaker 1: in even though they were passing.
• 10:26
  Speaker 2: I love that, I see. Do you think what do
• 10:28
  Speaker 2: you think happened? Do you think they heard the question?
• 10:30
  Speaker 2: Were like, I don't want to say anything about burying
• 10:31
  Speaker 2: acoustic oscillation.
• 10:32
  Speaker 4: Yeah.
• 10:33
  Speaker 1: Well, the rules are no googling, no looking at the
• 10:35
  Speaker 1: questions ahead of time. I want people's real, spontaneous ideas
• 10:38
  Speaker 1: about what these topics are, because we want to get
• 10:41
  Speaker 1: a sense for what people out there know before they
• 10:43
  Speaker 1: look things up. And so this person was just reading
• 10:46
  Speaker 1: through the questions in real time and recording themselves, and
• 10:48
  Speaker 1: maybe their brain just had a bubble which popped and
• 10:50
  Speaker 1: they decided I got nothing.
• 10:51
  Speaker 2: Okay, I see, it's more like I got nothing not
• 10:54
  Speaker 2: so much A.
• 10:55
  Speaker 1: No, thanks, next question please.
• 10:59
  Speaker 2: Well, people seem to sort of into it or know
• 11:01
  Speaker 2: that it's somehow related to the beginning of the universe.
• 11:04
  Speaker 2: And also I guess to something related to waves, right
• 11:07
  Speaker 2: and sound and oscillations. Nobody gets bows or boba.
• 11:13
  Speaker 1: Nobody made the boba connection. That's just me, all.
• 11:15
  Speaker 2: Right, well, let's jump into it, Daniel. What are baryon
• 11:18
  Speaker 2: acoustic oscillations.
• 11:19
  Speaker 1: Yeah, baryon acoustic oscillations are really fascinating, sort of like
• 11:23
  Speaker 1: fossilized sound waves from very very early universe. You know,
• 11:27
  Speaker 1: like if somebody's playing an acoustic guitar or like an
• 11:29
  Speaker 1: acoustic recording. It refers to the quality and the fabrication
• 11:32
  Speaker 1: of the sound waves that you're hearing. So acoustic there
• 11:35
  Speaker 1: tells you that you're hearing sound waves, and the word
• 11:38
  Speaker 1: buryon tells you what you're hearing those sound waves in
• 11:42
  Speaker 1: that you're hearing it as baryons bump against each other.
• 11:45
  Speaker 2: But I guess maybe not to confuse folks in this case,
• 11:47
  Speaker 2: acoustic doesn't mean necessarily sounds your hearers at the air.
• 11:51
  Speaker 2: They can also mean like sound waves and you hear
• 11:53
  Speaker 2: in the ocean or maybe through even a solid right.
• 11:55
  Speaker 1: Yeah, exactly. Sound Waves can travel through air, but they
• 11:58
  Speaker 1: can also travel through water, or they can travel to steal,
• 12:00
  Speaker 1: they can travel through your body, They can travel through
• 12:03
  Speaker 1: any kind of gas or plasma. Sound Waves are just
• 12:06
  Speaker 1: pressure waves. If you have a bunch of molecules that
• 12:09
  Speaker 1: can interact with each other, that can push against each other,
• 12:11
  Speaker 1: then if you push on one side of that blog,
• 12:13
  Speaker 1: then it's going to push on the next layer, which
• 12:15
  Speaker 1: pushes on the next layer, which it pushes on the
• 12:16
  Speaker 1: next layer. That's what sound waves are. You're hearing us
• 12:19
  Speaker 1: right now because the speaker in your ear is making
• 12:21
  Speaker 1: sound waves that push on layers of air, which push
• 12:24
  Speaker 1: on the next layer of air, etc.
• 12:26
  Speaker 2: I see so an acoustic wave or acoustic oscillations. They're
• 12:29
  Speaker 2: just like when things propagate through material, because things are
• 12:34
  Speaker 2: bumping into each other basically through electromagnetic forces, or can
• 12:37
  Speaker 2: it be other force.
• 12:38
  Speaker 1: It's almost always electromagnetic forces. The crucial thing is that
• 12:41
  Speaker 1: they bump against each other. If they pass right through
• 12:43
  Speaker 1: each other, then they don't cause pressure waves. The crucial
• 12:46
  Speaker 1: thing is that they're bumping up against each other. That
• 12:48
  Speaker 1: one layer pushes the next layer, which pushes the next layer.
• 12:51
  Speaker 1: The microphysics of how that pushing happens is electromagnetic. You
• 12:54
  Speaker 1: have electrons in one atom are pushing up against the
• 12:56
  Speaker 1: electrons in another atom. They don't like to overlap, they
• 12:59
  Speaker 1: resist each other. It's the same reason why you don't
• 13:01
  Speaker 1: pass through your chair, or when you're leaning against the wall,
• 13:04
  Speaker 1: the wall pushes back or the Earth is pushing up
• 13:06
  Speaker 1: on you. Basically, anything structural is built with electromagnetic forces,
• 13:11
  Speaker 1: because that's the bond of chemistry.
• 13:13
  Speaker 2: Now, for those of us who are not particle physicists,
• 13:16
  Speaker 2: can you remind us what a baryon is.
• 13:18
  Speaker 1: Yeah, Baryons are anything made out of quarks, basically baryon
• 13:21
  Speaker 1: the shorthand for our kind of matter, stuff like protons
• 13:25
  Speaker 1: and neutrons, these are baryons. We call them baryons mostly
• 13:28
  Speaker 1: to distinguish them from the other kind of matter in
• 13:31
  Speaker 1: the universe, dark matter, which is some other kind of
• 13:34
  Speaker 1: stuff that's out there. It feels gravity, it has masks.
• 13:36
  Speaker 1: We think it's made of stuff. We don't know if
• 13:38
  Speaker 1: it's made of particles, but we're very sure that it's
• 13:41
  Speaker 1: not made of our kind of particles. And so when
• 13:44
  Speaker 1: we talk about the very early universe, we have a
• 13:46
  Speaker 1: few components to sort of like that very early universe smoothie.
• 13:50
  Speaker 1: There's baryons, there's photons, there's dark matter, and so we
• 13:53
  Speaker 1: talk about baryon acoustic oscillations because it's the sound waves
• 13:57
  Speaker 1: in those early universe protons mostly that we're thinking about.
• 14:01
  Speaker 2: Does that include electrons as well or electrons something else?
• 14:04
  Speaker 1: So electrons are not technically baryons because they're not made
• 14:08
  Speaker 1: out of quarks. Baryons are particles that are made out
• 14:11
  Speaker 1: of three quarks. Quarks are these incredible particles that feel
• 14:14
  Speaker 1: a strong force in order to have a neutral particle
• 14:16
  Speaker 1: and the strong force and that it doesn't have an
• 14:18
  Speaker 1: overall strong force charge the way, for example, a proton,
• 14:22
  Speaker 1: an electron can make a neutral atom with no overall
• 14:24
  Speaker 1: electric charge. In or for quarks to come together to
• 14:28
  Speaker 1: make an object that doesn't feel a strong force, it's
• 14:30
  Speaker 1: overall neutral. You need either three of them or two
• 14:33
  Speaker 1: of them, and if you put three of them together
• 14:35
  Speaker 1: you get a baryon like a proton or a neutron,
• 14:38
  Speaker 1: or there are other more exotic baryons. So technically an
• 14:41
  Speaker 1: electron is not a baryon, but it is included when
• 14:44
  Speaker 1: you talk about baryonic matter, which is like atoms made
• 14:48
  Speaker 1: out of a baryon and an electron.
• 14:50
  Speaker 2: I see that makes not a lot of sense.
• 14:55
  Speaker 1: Yeah. The short answer is you can lump electrons in
• 14:57
  Speaker 1: with baryonic matter even though technically they're not buryons.
• 15:01
  Speaker 2: Okay, I see, so it's really just regular matter. You're
• 15:04
  Speaker 2: using that shorthand for regular matter or at least the
• 15:07
  Speaker 2: matter that we're made out.
• 15:08
  Speaker 1: Of, exactly the matter that really matters.
• 15:10
  Speaker 2: So then we're talking about the Big Bang. This is
• 15:12
  Speaker 2: the early moments of the universe, and now what was
• 15:14
  Speaker 2: going on there.
• 15:15
  Speaker 1: When we talk about the Big Bang. It's also important
• 15:17
  Speaker 1: to clarify what we really mean by the Big Bang.
• 15:19
  Speaker 1: If you say that to a lot of people, they
• 15:21
  Speaker 1: imagine some very dense dot in space which then exploded
• 15:24
  Speaker 1: to make our universe. But when physicists talk about the
• 15:27
  Speaker 1: Big Bang, they really have a different idea in mind.
• 15:30
  Speaker 1: First of all, we don't go all the way back
• 15:32
  Speaker 1: to the creation of the universe. We don't know how
• 15:34
  Speaker 1: the universe was created, if it was created, if it
• 15:36
  Speaker 1: existed forever, how everything came to be. We only go
• 15:40
  Speaker 1: back as far as our theories can describe, which is
• 15:43
  Speaker 1: some moment around fourteen billion years ago when the universe
• 15:46
  Speaker 1: was filled with a very very hot and dense material.
• 15:49
  Speaker 1: Our theories go back that far, and our observations verify
• 15:53
  Speaker 1: that that happened. Where that stuff came from and how
• 15:56
  Speaker 1: it got there and all that stuff is all very speculative,
• 15:59
  Speaker 1: and we have theories about that inflation, et cetera. But
• 16:01
  Speaker 1: really the Big Bang, when physicists describe it, starts from
• 16:04
  Speaker 1: that very hot, dense state and then watches it expand
• 16:07
  Speaker 1: and form our universe. So the Big Bang is not
• 16:10
  Speaker 1: like a singularity at some point. It's a moment in
• 16:12
  Speaker 1: time when the universe was very hot and dense and
• 16:15
  Speaker 1: filled with plasma.
• 16:16
  Speaker 2: Well, part of it was that there was a lot
• 16:18
  Speaker 2: less space back then in that those early moments of
• 16:21
  Speaker 2: the universe, or at least what we call the early
• 16:23
  Speaker 2: moments of the universe. Like space expanded a lot since then,
• 16:26
  Speaker 2: from then to now, and so basically maybe a way
• 16:29
  Speaker 2: to think about it is just like all space was
• 16:30
  Speaker 2: more compressed, but it had the same amount of stuff
• 16:33
  Speaker 2: and it so everything was hot and dense.
• 16:34
  Speaker 1: Yeah, it's tricky if you think about size and use
• 16:36
  Speaker 1: words like smaller, because we don't know the size of
• 16:39
  Speaker 1: the universe. It might always have been infinite and might
• 16:41
  Speaker 1: still be infinite today. What we do know is about
• 16:43
  Speaker 1: the density. So as you say, it's more compressed, so
• 16:46
  Speaker 1: you should think about a universe, whether it's infinite or not,
• 16:49
  Speaker 1: just as filled with really hot, dense stuff and then
• 16:51
  Speaker 1: space expands. That's the Big Bang as we think about
• 16:54
  Speaker 1: it today, and makes everything more dilute. So things are
• 16:57
  Speaker 1: cooling down and getting more dilute. There's more space per
• 17:01
  Speaker 1: bit of stuff. That doesn't really tell you anything about
• 17:04
  Speaker 1: whether the universe was infinite or not. We obviously don't know.
• 17:07
  Speaker 2: And so I think the early universe went through a
• 17:09
  Speaker 2: lot of different phases, right Like, at some point there
• 17:11
  Speaker 2: weren't even maybe quantum fields or the quantum fields. We're
• 17:14
  Speaker 2: still trying to figure it out. And then things started
• 17:16
  Speaker 2: to change. But as you said, at some point in
• 17:18
  Speaker 2: that history, everything was basically a hot plasma exactly.
• 17:21
  Speaker 1: Things started out so hot and dense that we can't
• 17:23
  Speaker 1: even really use the physics of today to describe it.
• 17:26
  Speaker 1: You can't even really talk about particles because the fields
• 17:28
  Speaker 1: were so filled with energy. But eventually things cooled down
• 17:31
  Speaker 1: and particles formed, and you got quarks, and you've got electrons.
• 17:35
  Speaker 1: Those quarks then cooled down to make protons. And it's
• 17:38
  Speaker 1: really that moment that we want to zero in on today,
• 17:40
  Speaker 1: the moment when we had protons and electrons and photons
• 17:44
  Speaker 1: and also dark matter in this big hot plasma. But
• 17:48
  Speaker 1: that hot plasma is not uniform. It's not like everywhere
• 17:50
  Speaker 1: in space has exactly the same hot plasma, there's little
• 17:53
  Speaker 1: ripples in it. Some parts are denser than others, and
• 17:56
  Speaker 1: the baryon acoustic oscillation describes how the bears in that
• 18:01
  Speaker 1: hot plasma, we're sloshing around and ringing with sound waves.
• 18:05
  Speaker 2: Well, I think maybe a good way to think about
• 18:07
  Speaker 2: plasma is that it's basically just a gas. The only
• 18:10
  Speaker 2: difference between the plasma and a regular gas is that
• 18:13
  Speaker 2: the atoms are broken up, right Like in a regular gas,
• 18:17
  Speaker 2: like the air we're breathing, the electrons are tied together
• 18:19
  Speaker 2: with the protons and neutrons into atoms. But in the plasma,
• 18:23
  Speaker 2: it things are so heated up that they break apart.
• 18:25
  Speaker 2: But it's still basically a gas, right Like it's just
• 18:27
  Speaker 2: things flying around a space.
• 18:29
  Speaker 1: Yeah, exactly. It's a gas of charged particles, and it's
• 18:32
  Speaker 1: sort of a natural evolution of matter. You know, as
• 18:34
  Speaker 1: things get colder, they form more structure because they don't
• 18:37
  Speaker 1: have the energy to escape the power of those bonds.
• 18:39
  Speaker 1: So you think about an individual electron, if it has
• 18:41
  Speaker 1: a lot of energy, in other words, if it's in
• 18:43
  Speaker 1: a really hot gas, then it's going to have too
• 18:46
  Speaker 1: much energy to be captured by a proton. But as
• 18:48
  Speaker 1: things cool down, then those electrons are susceptible to being
• 18:51
  Speaker 1: captured by the proton, and then you get neutral hydrogen.
• 18:54
  Speaker 1: So as the universe cools, you go from having charged
• 18:57
  Speaker 1: plasma like you say, a charged gas, to having neutral gas.
• 19:01
  Speaker 1: And so, yeah, plasma is just a charged version of
• 19:04
  Speaker 1: a normal gas.
• 19:05
  Speaker 2: Right, It's a gas made out of ions, right, electrons
• 19:08
  Speaker 2: and programs lying around on their own, and so like
• 19:10
  Speaker 2: any gas, it would have sound waves.
• 19:12
  Speaker 1: In it exactly, so that hot plasma was not a
• 19:15
  Speaker 1: quiet place, right. It was also super dup or dense,
• 19:18
  Speaker 1: which means that sound propagated through it at shockingly high speeds.
• 19:22
  Speaker 2: All right, well, let's get a little bit more into
• 19:25
  Speaker 2: this hot plasma, how it works, and how those early
• 19:29
  Speaker 2: sound waves in that plasma led to the universe we
• 19:32
  Speaker 2: see today, Boba included. So let's dig into that. But
• 19:34
  Speaker 2: first let's take a quick break. All right, we're talking
• 19:49
  Speaker 2: about the early sounds of the universe. Now, Daniel, what
• 19:52
  Speaker 2: genre of music do you think the universe sounded like
• 19:54
  Speaker 2: at the beginning? Was it like elevator music? Was it
• 19:58
  Speaker 2: like rocking, banging music? What do you think k pop?
• 20:01
  Speaker 1: I think it sounded mostly like white noise and screams.
• 20:04
  Speaker 2: I see, that's right, that's right, because it was some
• 20:07
  Speaker 2: deity choking on a giant black hole wave exactly. It
• 20:11
  Speaker 2: was not a pleasant sound. But yeah, you were saying
• 20:13
  Speaker 2: that the universe was basically at some point it evolved
• 20:15
  Speaker 2: into basically all hot plasma in it, and there were
• 20:19
  Speaker 2: sound waves in it and ripples in it, because I
• 20:22
  Speaker 2: guess it's just the gas. And so even the air
• 20:25
  Speaker 2: we see around us is not perfectly totally completely uniform, right.
• 20:30
  Speaker 1: That's right. There are pressure waves everywhere as you talk,
• 20:33
  Speaker 1: and you're making pressure waves. As the wind blows and
• 20:35
  Speaker 1: makes pressure waves. As there are temperature variations, you've got
• 20:38
  Speaker 1: pressure waves, and so nothing around you is really totally uniform.
• 20:42
  Speaker 2: So then what made those waves in the early universe? Like,
• 20:44
  Speaker 2: if I just have a room here and I leave
• 20:46
  Speaker 2: it alone, the gas is gonna basically all equalize, isn't it.
• 20:50
  Speaker 1: Mm hmm exactly. So to get sound in the early universe,
• 20:53
  Speaker 1: you need a couple of things. First of all, you
• 20:55
  Speaker 1: need some initial over densities. You need some spots be
• 20:59
  Speaker 1: a little hot and a little denser than others. Then
• 21:01
  Speaker 1: you need a way for it to propagate or for
• 21:03
  Speaker 1: it to ring So what are those initial over densities
• 21:05
  Speaker 1: come from. Because if we're imagining the early universe just
• 21:08
  Speaker 1: this big hot plasma, and we say everywhere in the
• 21:11
  Speaker 1: universe is the same, there's no special location to the universe.
• 21:14
  Speaker 1: There's no reason why the universe would put more stuff
• 21:17
  Speaker 1: here and than there. Then it's hard to imagine like
• 21:19
  Speaker 1: where any sort of really initial ripple might come from.
• 21:22
  Speaker 1: And that comes just from quantum fluctuations in the very
• 21:25
  Speaker 1: very early universe. So way back before the plasma even formed,
• 21:30
  Speaker 1: much earlier on, you had just some quantum fluctuations, particles
• 21:33
  Speaker 1: popping in and out of the vacuum, just true quantum randomness.
• 21:38
  Speaker 1: It is true that everywhere in the universe follows the
• 21:40
  Speaker 1: same laws of physics, But if quantum mechanics really is random,
• 21:43
  Speaker 1: then it can do different things in different spots, and
• 21:46
  Speaker 1: that's how you get little, tiny fluctuations. But then inflation
• 21:50
  Speaker 1: or whatever caused the universe to expand dramatically blue those
• 21:52
  Speaker 1: tiny little quantum ripples up to tiny little macroscopic ripples
• 21:57
  Speaker 1: big enough that gravity could do something with them.
• 22:00
  Speaker 2: Well, you call them tiny microscopic quantum fluctuations. But I
• 22:03
  Speaker 2: wonder if back then, when the universe was a lot smaller, basically,
• 22:08
  Speaker 2: like all of the quantum particles and fields were basically
• 22:11
  Speaker 2: more on top of each other. And for example, the
• 22:13
  Speaker 2: size of an electron today it does seem huge back then.
• 22:17
  Speaker 2: Is that a good way to look at it.
• 22:18
  Speaker 1: It's definitely true that everything was much more compressed back then,
• 22:21
  Speaker 1: like you had the same amount of stuff with less
• 22:23
  Speaker 1: space between them. But those electrons probably weren't even born
• 22:26
  Speaker 1: yet when these ripples that were talking about were made.
• 22:28
  Speaker 1: Eventually that same energy did cool down and spread out
• 22:31
  Speaker 1: into specific particles. But the ripples we're talking about are
• 22:34
  Speaker 1: probably pre particle. They're just like ripples in the froth
• 22:38
  Speaker 1: and quantum fields before you can even really identify them
• 22:41
  Speaker 1: as particles.
• 22:42
  Speaker 2: Right right. I didn't mean to say that there were
• 22:43
  Speaker 2: electrons back then, but I just mean like the scale
• 22:46
  Speaker 2: things was very different back then. Like what we might
• 22:48
  Speaker 2: ignore today is a quantum fluctuation because it's so small.
• 22:51
  Speaker 2: Back then, maybe a quantum fluctuation was huge.
• 22:53
  Speaker 1: Right, Yeah, it's a really interesting comparison. I guess. Really
• 22:56
  Speaker 1: the only meterstick we have to compare today with back
• 22:59
  Speaker 1: then is the speed of light, And so you do
• 23:01
  Speaker 1: have this sense of like the horizon that an electron
• 23:04
  Speaker 1: could see, like what fraction of the universe an electron
• 23:06
  Speaker 1: could interact with, and then that did later get blown up.
• 23:09
  Speaker 1: And so back then the electron was sort of in
• 23:11
  Speaker 1: a smaller pond of the universe of sort of a
• 23:13
  Speaker 1: bigger deal.
• 23:14
  Speaker 2: Then, as you said, these small ripples kind of god
• 23:18
  Speaker 2: stretched out as the universe expanded. So maybe take us
• 23:20
  Speaker 2: through a little bit of what was happening as the
• 23:23
  Speaker 2: universe started to expand, like what was going on with
• 23:25
  Speaker 2: dark matter.
• 23:26
  Speaker 1: Yeah, so you have these initial ripples which create over densities,
• 23:29
  Speaker 1: mostly in the dark matter. Remember that there's more dark
• 23:32
  Speaker 1: matter than anything else. And so if your mental image
• 23:35
  Speaker 1: you're imagining some like hot bright plasma, add a layer
• 23:38
  Speaker 1: to that, an invisible layer of dark matter, which has
• 23:41
  Speaker 1: most of the mass of the matter in the universe
• 23:44
  Speaker 1: at the time, not most of the energy. Most of
• 23:45
  Speaker 1: the energy in the universe at this time is still
• 23:47
  Speaker 1: in photons. It's mostly radiation dominated. But most of the
• 23:50
  Speaker 1: stuff in the universe is dark matter. So now you
• 23:54
  Speaker 1: have these little ripples. You have like a little bit
• 23:55
  Speaker 1: more dark matter here and a little bit more dark
• 23:57
  Speaker 1: matter there, and dark matter has gravity of course, it
• 24:00
  Speaker 1: so it starts to pull things in. Because you have
• 24:02
  Speaker 1: a little bit more dark matter, it means it has
• 24:04
  Speaker 1: more gravity than everything around it. It's going to start
• 24:07
  Speaker 1: to pull stuff in, which gives it more density, which
• 24:09
  Speaker 1: gives it more gravity. So dark matter is starting to
• 24:12
  Speaker 1: form clusters, it's starting to amplify those initial quantum fluctuations.
• 24:16
  Speaker 2: Well, I guess the big question is what do we
• 24:18
  Speaker 2: know about dark matter in those early moments, Like we
• 24:21
  Speaker 2: know that regular matter, it started to dissociate into protons
• 24:24
  Speaker 2: and electrons, and before that they dissociated even more. Did
• 24:28
  Speaker 2: dark matter break down too, or did it also have
• 24:32
  Speaker 2: quantum fluctuations or does it even have quantumness to it?
• 24:36
  Speaker 1: Yeah? Wow, I wish I knew the answer to any
• 24:37
  Speaker 1: of those questions. We don't know, right because we don't
• 24:41
  Speaker 1: know what particles dark matter is made out of, if
• 24:43
  Speaker 1: it's even made out of particles in this theory. Instead,
• 24:46
  Speaker 1: we treat dark matter sort of as like a collisionless fluid,
• 24:49
  Speaker 1: some that has no interactions other than gravity. We think
• 24:52
  Speaker 1: just about its mass density and the gravitational impact of that.
• 24:56
  Speaker 1: We don't try to break it down into the microphysics
• 24:58
  Speaker 1: because we don't have that story at all. We don't
• 25:01
  Speaker 1: know if dark matter is ten different kinds of dark
• 25:03
  Speaker 1: particles that are all turning into each other and back
• 25:05
  Speaker 1: or not. But because it doesn't interact with the baryons
• 25:09
  Speaker 1: except for gravity, we don't really need to know those details.
• 25:12
  Speaker 1: I mean, we'd love to know, who wouldn't want to know,
• 25:15
  Speaker 1: But it doesn't change the story of the baryon acoustic
• 25:17
  Speaker 1: oscillations that we're focused on today.
• 25:19
  Speaker 2: I see at this point we're just squinting at dark matter.
• 25:22
  Speaker 2: We're sort of waving our hands. We're like, well, I
• 25:24
  Speaker 2: don't care what's happening at the small microscopic level of
• 25:29
  Speaker 2: dark matter. It could be anything, but you just sort
• 25:31
  Speaker 2: of treat it as, like you said, like a cloud
• 25:34
  Speaker 2: or liquid of stuff.
• 25:35
  Speaker 1: Yeah, it's not that we don't care. We deeply care,
• 25:38
  Speaker 1: and we'd love to know. But the game of physics
• 25:40
  Speaker 1: is trying to make progress even when you don't know things.
• 25:43
  Speaker 1: And so here's a question we can focus on even
• 25:45
  Speaker 1: without knowing what's going on with the dark matter. We
• 25:48
  Speaker 1: can still think clearly about what's going on with the
• 25:50
  Speaker 1: baryons because we think we do understand their interactions.
• 25:54
  Speaker 2: Right, So then you're saying that the dark matter was
• 25:56
  Speaker 2: influenced by the quantum fluctuations of the regular matter. But
• 26:00
  Speaker 2: could dark matter itself have had its own quantum fluctuations.
• 26:03
  Speaker 1: Now, they had their own quantum fluctuations for sure. Dark
• 26:06
  Speaker 1: matter and regular matter both come out of these initial
• 26:08
  Speaker 1: quantum fluctuations. So one spot in the universe we have
• 26:11
  Speaker 1: like an over density of energy that turns into more
• 26:13
  Speaker 1: dark matter and more normal matter. And it's mostly the
• 26:16
  Speaker 1: quantum fluctuations in the dark matter itself that spur everything
• 26:20
  Speaker 1: we're talking about, because it's the gravity of the dark
• 26:23
  Speaker 1: matter that triggers everything.
• 26:24
  Speaker 2: Right, because there's more dark matter than regular matter. But
• 26:27
  Speaker 2: then are you assuming that, like the dark matter fluctuations
• 26:31
  Speaker 2: and the regular matter fluctuation, we're somehow in sync in
• 26:33
  Speaker 2: the early universe.
• 26:34
  Speaker 1: The quantum fluctuations we're talking about again predate the formation
• 26:38
  Speaker 1: of the particles themselves, and this division of energy into
• 26:40
  Speaker 1: dark matter and normal matter, which frankly, we don't understand,
• 26:43
  Speaker 1: and to understand it, we'd have to have a better
• 26:45
  Speaker 1: idea of what particles there are and how the quantum
• 26:48
  Speaker 1: fields sort of filter out into the dark matter. So
• 26:50
  Speaker 1: we just say that there's an initial quantum fluctuation and
• 26:53
  Speaker 1: then at each point, if you have more stuff or
• 26:55
  Speaker 1: less stuff, you get about eighty percent of it into
• 26:57
  Speaker 1: dark matter and twenty percent of it into normal matter.
• 27:00
  Speaker 1: So from that point of view, they are correlated because
• 27:02
  Speaker 1: they come from the same initial quantum fluctuations, which are
• 27:05
  Speaker 1: independent from the dark matter or the normal matter nature.
• 27:08
  Speaker 2: I see, you are sort of imagining a point in
• 27:11
  Speaker 2: the universe when even dark matter was maybe dissociated or
• 27:14
  Speaker 2: didn't exist exactly.
• 27:17
  Speaker 1: Those are where the quantum fluctuations are happening before we
• 27:19
  Speaker 1: even have dark matter or normal matter, and then down
• 27:22
  Speaker 1: the road tiny fractions of a second later, when we
• 27:25
  Speaker 1: do have matter, some of that energy has gotten into
• 27:27
  Speaker 1: dark matter and some of it into normal matter.
• 27:29
  Speaker 2: Okay, So then both dark matter and regular matter are
• 27:33
  Speaker 2: kind of have these expanding fluctuations ripples, which, as you said,
• 27:37
  Speaker 2: create pockets of the higher density dark matter and regular matter,
• 27:41
  Speaker 2: which then I guess is what creates the sound ways, right,
• 27:45
  Speaker 2: because when you have something more dense in one side,
• 27:48
  Speaker 2: it tends to try to go to the other side.
• 27:50
  Speaker 1: Exactly, and sort of a push and a push back here.
• 27:52
  Speaker 1: So dark matter is creating these over densities. It's like
• 27:55
  Speaker 1: gravitationally collapsing things, and that's fine for dark matter. Dark
• 27:58
  Speaker 1: matter doesn't really care happy it gets pulled in by
• 28:01
  Speaker 1: gravity and overlap with itself whatever. But baryons are different.
• 28:05
  Speaker 1: Baryons and photons interact with each other, and so if
• 28:08
  Speaker 1: you squeeze them down, then they're going to push back.
• 28:11
  Speaker 1: Like you squeeze a bunch of baryons together, they push
• 28:13
  Speaker 1: against each other and they push back out. And remember
• 28:17
  Speaker 1: that there's a huge number of baryons but also an
• 28:19
  Speaker 1: enormous number of photons. So as you squeeze these protons together,
• 28:24
  Speaker 1: then they're effectively squeezing on the photons, which push back out.
• 28:28
  Speaker 1: So it's sort of like a mini version of what
• 28:30
  Speaker 1: happens in a star where you collapse it gravitationally and
• 28:33
  Speaker 1: then it creates fusion, and that radiation pressure from the
• 28:36
  Speaker 1: fusion keeps the star from collapsing. Here you have dark
• 28:40
  Speaker 1: matter pulling blobs of baryons and photons together, and then
• 28:43
  Speaker 1: those photons and baryons interacting when they get squeezed to
• 28:46
  Speaker 1: push back out, and that's what creates these ripples in
• 28:50
  Speaker 1: the baryons.
• 28:52
  Speaker 2: Like it's like the dark matter collects all of the
• 28:56
  Speaker 2: other the regular matter tries to squeeze it down, but
• 28:58
  Speaker 2: then it bounces back exactly.
• 29:00
  Speaker 1: It bounces back sort of like a mini weaker version
• 29:03
  Speaker 1: of a supernova, you know, gravitational collapse, which then bounces
• 29:06
  Speaker 1: back out in impollusion, which leads to an explosion. Some
• 29:10
  Speaker 1: way I want to get clearing people's minds, which is
• 29:11
  Speaker 1: sort of crazy to imagine, is the ratio of different particles,
• 29:15
  Speaker 1: Like there's about a billion photons for every proton and
• 29:19
  Speaker 1: every electron at this point at the universe, Like the
• 29:21
  Speaker 1: universe is mostly light, so there's a huge number of
• 29:24
  Speaker 1: photons pushing against these baryons.
• 29:27
  Speaker 2: Now, are you sweeping electrons and protons into radiation here
• 29:32
  Speaker 2: or do you actually mean real photons that later got
• 29:35
  Speaker 2: transformed into electrons.
• 29:37
  Speaker 1: Totally fair question, because you're right that if things are
• 29:41
  Speaker 1: moving near the speed of light, we just call it radiation.
• 29:43
  Speaker 1: But here we're talking about real radiation. We're just talking
• 29:45
  Speaker 1: about photons. We're treating electrons, protons, and photons separately, and
• 29:50
  Speaker 1: it really is mostly photons. But those photons they push
• 29:53
  Speaker 1: on the baryons, they push on the protons, they push
• 29:56
  Speaker 1: on the electrons in a way that they of course
• 29:58
  Speaker 1: don't push on the dark matter. So the dark matter
• 30:01
  Speaker 1: is collapsing into the center and the baryons get pushed
• 30:04
  Speaker 1: back out because they have this electric interaction that dark
• 30:08
  Speaker 1: matter doesn't have.
• 30:09
  Speaker 2: But the photons are not being pulled together by gravity,
• 30:12
  Speaker 2: are they?
• 30:12
  Speaker 1: Photons are affected by gravity? Right, Photons bend around the Sun,
• 30:16
  Speaker 1: or can bend around a black hole. So as dark
• 30:18
  Speaker 1: matter curved space, photons are also gathered into that well
• 30:22
  Speaker 1: together with the protons. But then they push back and
• 30:25
  Speaker 1: there's so many protons, so many photons that you get
• 30:27
  Speaker 1: a sound, right, This is the sound of the early universe.
• 30:30
  Speaker 1: Is this pressure wave in the buryons created by the
• 30:34
  Speaker 1: baryons and the photons being squeezed down by dark matter.
• 30:37
  Speaker 2: M it's the sound of regular matter being uncomfortable, like whoa, whoa,
• 30:43
  Speaker 2: I don't want to be so close to my neighbors.
• 30:45
  Speaker 1: Exactly, it's here, Exactly. It's the sound on the subway
• 30:49
  Speaker 1: when another ten people get on and squeeze you into
• 30:52
  Speaker 1: the back and you're like, hell, I can't breathe back here.
• 30:54
  Speaker 2: It's the groan of a million introverts.
• 30:58
  Speaker 1: What you're saying, Yeah, Another one rides. That was the
• 31:00
  Speaker 1: sound of the early universe.
• 31:03
  Speaker 2: Another one gets gathered by dark matter against its well.
• 31:07
  Speaker 1: Exactly, and the density of the universe is really really high,
• 31:10
  Speaker 1: and the density controls the speed of sound. Like sound
• 31:14
  Speaker 1: travels faster through water than does through air because those
• 31:17
  Speaker 1: molecules are more tightly packed together, so the soundwave propagates
• 31:21
  Speaker 1: more quickly, and their bonds are more rigid because they're denser.
• 31:24
  Speaker 1: So the soundwave propagates faster through denser materials like steel
• 31:28
  Speaker 1: than it does through water, than does through air, than
• 31:31
  Speaker 1: it does through really diffuse gases like the upper atmosphere.
• 31:34
  Speaker 1: And in the early universe, things are super duper crazy dense,
• 31:38
  Speaker 1: So the speed of sound in the early universe is
• 31:40
  Speaker 1: like half the speed of light.
• 31:42
  Speaker 2: Whoa wouldn't you have to call it radiation wave?
• 31:48
  Speaker 1: Fair point? Fair point?
• 31:50
  Speaker 2: All right? So then there were these waves from the
• 31:54
  Speaker 2: material sort of bouncing back, and that means that like
• 31:56
  Speaker 2: those waves propagated at which made things more dents in
• 32:00
  Speaker 2: some places than others, right, because that's what a wave.
• 32:03
  Speaker 1: Is, yeah, exactly, So you have this dark matter core
• 32:06
  Speaker 1: and then you have this density wave of baryons propagating out.
• 32:10
  Speaker 1: But this doesn't last forever, right, Things in the universe
• 32:12
  Speaker 1: are happening fast, and the universe is expanding and it's cooling,
• 32:15
  Speaker 1: and at some point, around three hundred and eighty thousand
• 32:18
  Speaker 1: years after this first moment, we can describe what we
• 32:21
  Speaker 1: call the beginning of the universe, or at least the
• 32:22
  Speaker 1: Big Bang. Things cool down enough that the protons and
• 32:25
  Speaker 1: the electrons did bond together to make neutral hydrogen. The
• 32:29
  Speaker 1: electrons no longer had enough energy to escape the pull
• 32:32
  Speaker 1: of the protons, so the universe became transparent to photons
• 32:35
  Speaker 1: instead of opaque. So now when photons are flying through
• 32:38
  Speaker 1: the universe, instead of interacting with all the protons and
• 32:40
  Speaker 1: the electrons, they see now they just see neutral hydrogen.
• 32:43
  Speaker 1: So they no longer push on it. Now they just
• 32:46
  Speaker 1: fly through it. And so the universe can expand and cool,
• 32:49
  Speaker 1: and these photons can dissipate, and so the sound wave
• 32:52
  Speaker 1: basically got frozen.
• 32:54
  Speaker 2: It's sort of like if you suddenly frozy ocean, you
• 32:57
  Speaker 2: would see all these water molecules frozen in the shape
• 33:00
  Speaker 2: of a wave.
• 33:01
  Speaker 1: Yeah, that's right. Or say you slap your hand in
• 33:03
  Speaker 1: your bathtub and it creates a wave and then you
• 33:06
  Speaker 1: suddenly cool it to freeze it. You can come back later.
• 33:09
  Speaker 1: You can still see that water wave. Otherwise it would
• 33:11
  Speaker 1: have kept propagating and slashing around. But now it's frozen
• 33:14
  Speaker 1: because your bathtub, the water has cooled so it can
• 33:17
  Speaker 1: no longer propagate. And the same thing happened in the universe.
• 33:20
  Speaker 1: The universe became transparent, it became cooler, became less dense,
• 33:24
  Speaker 1: and the photons passed through this wave overcame it. So
• 33:27
  Speaker 1: now that single ring of sound is like frozen in
• 33:30
  Speaker 1: the structure of the early universe.
• 33:32
  Speaker 2: Right, But I guess maybe the confusing thing is is
• 33:34
  Speaker 2: that it's like a sound wave in the density of photons. Right.
• 33:39
  Speaker 2: It's like there were sound waves propagating because the regular
• 33:42
  Speaker 2: matter was interacting with photons and with itself. There were
• 33:44
  Speaker 2: waves in that slash. But then it's almost like you
• 33:47
  Speaker 2: took away the regular matter, you took all the protons
• 33:50
  Speaker 2: and electrons out of it, and now suddenly the light
• 33:54
  Speaker 2: was kind of stuck in these like oscillations of density.
• 33:57
  Speaker 2: And that's what we see today.
• 33:58
  Speaker 1: The light was really powering these oscillations. It's the thing
• 34:01
  Speaker 1: that was pushing the baryons and the electrons along. Once
• 34:04
  Speaker 1: the electrons and baryons cooled so they became neutral, they're
• 34:07
  Speaker 1: no longer like riding this wave of the light, so
• 34:10
  Speaker 1: they sort of jump off the train. They get frozen
• 34:11
  Speaker 1: where they are, and the light continues on and it
• 34:14
  Speaker 1: just passes right through and it diffuses around, and that
• 34:17
  Speaker 1: becomes the cosmic microwave background light that we still see today.
• 34:20
  Speaker 1: So we see the echoes and the ripples of that
• 34:22
  Speaker 1: light today and we can measure it. But the baryons
• 34:24
  Speaker 1: electrons got left behind after that moment when they could
• 34:27
  Speaker 1: no longer ride the light train, because they became neutral.
• 34:31
  Speaker 2: Right, Yeah, that's kind of what I mean is that
• 34:33
  Speaker 2: it's not like the photons continue to ripple with this sound.
• 34:36
  Speaker 2: It's more like you took out the regular matter and
• 34:39
  Speaker 2: so the photons that were creating those waves stayed in
• 34:42
  Speaker 2: those different layers of density, and.
• 34:45
  Speaker 1: The photons can keep propagating out and rippling, and they did.
• 34:48
  Speaker 1: In truth, it's a little bit more complicated, it's like
• 34:50
  Speaker 1: sloshing back and forth. But basically the picture you should
• 34:53
  Speaker 1: have in your head is like a core of dark
• 34:55
  Speaker 1: matter and then these rings of frozen sound waves. At
• 34:59
  Speaker 1: the time, we're talking about like five hundred thousand light
• 35:02
  Speaker 1: years across, where you should have like more baryons, like
• 35:05
  Speaker 1: a higher density of baryons, this baryons frozen sound wave
• 35:09
  Speaker 1: like five hundred thousand light years across, and then the
• 35:11
  Speaker 1: light continuing on and slashing through the whole universe.
• 35:14
  Speaker 2: Right, It's almost like the light the photons were holding
• 35:17
  Speaker 2: the regular matter in these wave patterns, and then you
• 35:20
  Speaker 2: took away the wave the water basically, and so you
• 35:23
  Speaker 2: have this light kind of stuck in that pattern.
• 35:25
  Speaker 1: And we think that basically this seated the structure of
• 35:28
  Speaker 1: the whole universe. After this point, gravity takes over. In
• 35:31
  Speaker 1: places that you have more dark matter and more baryons,
• 35:34
  Speaker 1: things are going to get clustered together more and more
• 35:37
  Speaker 1: and more, and that's where you're going to end up
• 35:38
  Speaker 1: getting galaxies, and that's where you're going to end up
• 35:40
  Speaker 1: getting gas clouds, and then stars and planets and people
• 35:43
  Speaker 1: and podcasts and eventually boba.
• 35:46
  Speaker 2: And bows as well. All right, well, let's dig into
• 35:50
  Speaker 2: how we can see this cosmic microwave background. Well, we
• 35:53
  Speaker 2: know about it and also what it means about how
• 35:55
  Speaker 2: we ended up here today, So let's dig into that.
• 35:57
  Speaker 2: But first let's take another quick break. All Right, we're
• 36:12
  Speaker 2: talking about the sound of the early universe, and it
• 36:15
  Speaker 2: sounds like. It sounded kind of uncomfortable. It was really
• 36:18
  Speaker 2: hot and crowded, and the regular matter in the universe
• 36:21
  Speaker 2: did not like it exactly.
• 36:23
  Speaker 1: Very loud but very short lived early universe scream.
• 36:26
  Speaker 2: And so you were saying that you had these ripples
• 36:28
  Speaker 2: of matter kind of bouncing back from being compressed. Things
• 36:31
  Speaker 2: were slashing around, things had sound waves in it. But
• 36:34
  Speaker 2: then at some point the regular matter kind of froze
• 36:37
  Speaker 2: into place. They got together into atoms, which then let
• 36:40
  Speaker 2: the light continue on. Does that mean that at that
• 36:43
  Speaker 2: point the universe went silent?
• 36:46
  Speaker 1: Yeah, basically that's when the universe quieted down and the
• 36:49
  Speaker 1: speed of sound dropped really really fast. Right, So things
• 36:53
  Speaker 1: couldn't propagate nearly as fast.
• 36:55
  Speaker 2: Why not, Like we wouldn't regular atoms carry those waves.
• 36:58
  Speaker 1: Well, regular atoms can still carry waves the way they
• 37:00
  Speaker 1: do today, Like the sound we hear today is mostly
• 37:03
  Speaker 1: in neutral atoms in the air. Right, So neutral atoms
• 37:05
  Speaker 1: certainly can bump into each other and can certainly carry
• 37:08
  Speaker 1: sound waves. But the pressure was just a lot lower
• 37:11
  Speaker 1: because the photons had decoupled, and so the density was
• 37:14
  Speaker 1: a lot lower, and so the speed of sound just
• 37:16
  Speaker 1: dropped very quickly, and so there still was sound, it
• 37:19
  Speaker 1: was just much slower moving. It's no longer anywhere close
• 37:22
  Speaker 1: to the speed of light, and so it's effectively frozen
• 37:25
  Speaker 1: because soundwaves can still propagate, but just very very slowly.
• 37:28
  Speaker 1: So things are not going to change very fast the
• 37:30
  Speaker 1: way they had initially.
• 37:31
  Speaker 2: I wonder if you can still measure those waves in
• 37:33
  Speaker 2: the regular matter, you know what I mean? Like, I
• 37:35
  Speaker 2: wonder if like collectively all the galaxies in the universe
• 37:38
  Speaker 2: still has ours kind of slashing around or being moved
• 37:42
  Speaker 2: around by those sound waves.
• 37:44
  Speaker 1: Absolutely you can, and we have looked for this and
• 37:46
  Speaker 1: we have actually seen it. We can see these waves
• 37:49
  Speaker 1: in two different ways. One, we can look back at
• 37:51
  Speaker 1: those photons from the early universe and see these ripples,
• 37:55
  Speaker 1: like there were more photons in some places than in others.
• 37:58
  Speaker 1: We can look back at those photons ones that we're
• 38:00
  Speaker 1: created when the universe just became transparent, that's the cosmic
• 38:03
  Speaker 1: microwave background radiation, and we see these ripples and we
• 38:06
  Speaker 1: see exactly what we expect. But we can also see
• 38:09
  Speaker 1: it in the structure of the universe today. Those rings
• 38:12
  Speaker 1: that were five hundred thousand light years across, they expanded
• 38:15
  Speaker 1: as the universe expands and now we expect them to
• 38:18
  Speaker 1: be about five hundred million light years across. So what
• 38:21
  Speaker 1: people have done is they've looked at the distribution of
• 38:23
  Speaker 1: galaxies and they say, hm, our galaxies just like sprinkled
• 38:26
  Speaker 1: randomly everywhere, or is there a typical distance between the galaxies?
• 38:31
  Speaker 1: How are they clustered? So they gathered a bunch of
• 38:33
  Speaker 1: galaxies together, they did these redshift measurements to see how
• 38:37
  Speaker 1: far away they are, so we can have a three
• 38:39
  Speaker 1: D map of the galaxies in the universe. And then
• 38:42
  Speaker 1: they just like counted up what is the distance between
• 38:44
  Speaker 1: all the pairs of galaxies? Is there any preferred distance?
• 38:49
  Speaker 2: And what did they find? Did they find that there's
• 38:51
  Speaker 2: so even or did they find that this distance varied
• 38:54
  Speaker 2: according to leg a soundwave?
• 38:55
  Speaker 1: So they found that it was not smooth, that there
• 38:58
  Speaker 1: was a bump there, that you were more like you
• 39:00
  Speaker 1: have galaxies about five hundred million light years apart than
• 39:03
  Speaker 1: you were other distances. And this is exactly what they
• 39:06
  Speaker 1: expected to see because those rings the sound horizon from
• 39:09
  Speaker 1: the early universe was five hundred thousand light years across
• 39:13
  Speaker 1: at that time. But the universe has expanded since right
• 39:16
  Speaker 1: We've had deceleration and acceleration. We know the expansion history
• 39:19
  Speaker 1: of the universe, and we expect those rings to now
• 39:22
  Speaker 1: be five hundred million light years across. And when you
• 39:24
  Speaker 1: look at the distribution of galaxies, you see many more
• 39:27
  Speaker 1: at that distance apart than you do at like four
• 39:29
  Speaker 1: hundred million or six hundred million. So this is like
• 39:31
  Speaker 1: twenty years ago. In two thousand and five, they saw
• 39:33
  Speaker 1: this statistical evidence for the Bury on acoustic ostellations that
• 39:38
  Speaker 1: when you add up all these galaxies and compare their distances,
• 39:40
  Speaker 1: you tend to see the more at exactly the size
• 39:43
  Speaker 1: of this sound ring.
• 39:46
  Speaker 2: No wait, are you saying that somehow this early sound
• 39:49
  Speaker 2: wave got frozen and the distances between galaxies and the
• 39:53
  Speaker 2: structure of the universe, or are you saying this sound
• 39:55
  Speaker 2: wave is still rippling through the structure of the universe.
• 39:58
  Speaker 1: They got frozen in the early universe and then gravity
• 40:01
  Speaker 1: took over it like seeded the structure. It's like if
• 40:04
  Speaker 1: somebody sprinkled a bunch of seeds in a circle and
• 40:06
  Speaker 1: you came back one hundred years later and you found
• 40:08
  Speaker 1: a bunch of oak trees and you wondered, like, why
• 40:10
  Speaker 1: are there oak trees in a circle? It comes from
• 40:12
  Speaker 1: the initial distribution of seeds. And so here we're talking
• 40:15
  Speaker 1: about slashing around the very early universe when things were
• 40:18
  Speaker 1: still very chaotic, left this over density of baryons in
• 40:22
  Speaker 1: these sound rings which no longer were able to ripple
• 40:26
  Speaker 1: as fast because the photons the decoupled and weren't pushing
• 40:28
  Speaker 1: them anymore, and things got cooler and less dense. And
• 40:31
  Speaker 1: those are likely initial seeds which formed galaxies, which grew
• 40:35
  Speaker 1: up to be galaxies.
• 40:37
  Speaker 2: I see. So we also see these frozen sound waves
• 40:40
  Speaker 2: out there exactly.
• 40:41
  Speaker 1: And so about twenty years ago people saw the statistical evidence.
• 40:44
  Speaker 1: They're like, oh, the galaxies tend to be more far
• 40:46
  Speaker 1: apart at this particular distance than other distances. And that
• 40:49
  Speaker 1: was evidence that the baryon acoustic ostellations were real, that
• 40:52
  Speaker 1: we were seeing them in the universe. But very excitingly,
• 40:54
  Speaker 1: just a few weeks ago, people see an actual single bubble.
• 40:58
  Speaker 1: When you look out into the unit, you can actually
• 41:01
  Speaker 1: see like a ring, a huge structure, ring of galaxies
• 41:04
  Speaker 1: and superclusters lined up into a massive bubble. How big
• 41:09
  Speaker 1: this thing is, a ring structure about two hundred and
• 41:11
  Speaker 1: fifty mega parsecs around, And we're sort of near the
• 41:15
  Speaker 1: center of it, and at the actual center of it
• 41:17
  Speaker 1: is this huge supercluster called the Buches supercluster, which we
• 41:21
  Speaker 1: think was gathered together because there's a huge dark matter
• 41:23
  Speaker 1: blob at the center of this ripple. And then along
• 41:26
  Speaker 1: the edges are other superclusters that we found, like the
• 41:29
  Speaker 1: Slow and Great Wall and other pieces that we've been
• 41:33
  Speaker 1: discovering of structure here and there in the universe. Turns
• 41:36
  Speaker 1: out they assemble themselves into this incredible, enormous ring two
• 41:40
  Speaker 1: hundred and fifty mega parsex across.
• 41:43
  Speaker 2: Now it's a bubble because, as you said, the early
• 41:45
  Speaker 2: universe dark matter brought together this barren matter, the barrion
• 41:49
  Speaker 2: matter bounce back, and when it bounced back, I guess
• 41:52
  Speaker 2: it looked like a bubble, right, that's what you're saying.
• 41:54
  Speaker 2: And then the universe expanded, things froze, and we still
• 41:56
  Speaker 2: see that bubble today exactly.
• 41:58
  Speaker 1: And you can look at this paper. You can see
• 42:00
  Speaker 1: in this distribution of galaxies this sort of faint ring.
• 42:03
  Speaker 1: It's not crisp and clear.
• 42:05
  Speaker 2: It's not like there're no legs a ring or a bubble.
• 42:07
  Speaker 1: It's definitely a bubble. It's a sphere. But you know
• 42:09
  Speaker 1: this is a physics paper, which means it's two dimensional slices.
• 42:12
  Speaker 1: So if you look at the slices, you know, we
• 42:13
  Speaker 1: don't publish in three D yet, we're not three D
• 42:15
  Speaker 1: printing our papers. But actually, if you look online, they
• 42:18
  Speaker 1: have a really cool animation of which you can see
• 42:21
  Speaker 1: the three D version, So it definitely has a three
• 42:22
  Speaker 1: D structure. But in two D slices you see rings.
• 42:25
  Speaker 2: I see. But was the analysis done in rings or
• 42:28
  Speaker 2: was it done in a bubble? Or were you saying
• 42:29
  Speaker 2: ring because that's how you read it in the paper.
• 42:31
  Speaker 1: Well, originally they spotted it as a ring. They were
• 42:33
  Speaker 1: just like, hold on, is that a huge ring? And
• 42:36
  Speaker 1: then they started looking in three D They're like, wow,
• 42:38
  Speaker 1: look at that. It really is kind of a bubble.
• 42:39
  Speaker 1: And then they calculated the size of it and they
• 42:41
  Speaker 1: were like, huh, this is exactly the size you would
• 42:43
  Speaker 1: expect from a single baryon acoustic ostellation bubble, which nobody
• 42:47
  Speaker 1: had ever seen before. And these folks, they weren't looking
• 42:49
  Speaker 1: for this. They were doing some other studies of galaxies
• 42:52
  Speaker 1: and their distributions, and they just like spotted this visual
• 42:55
  Speaker 1: and they were like, hold on a second, this is
• 42:57
  Speaker 1: literally a frozen scream from the early universe.
• 43:01
  Speaker 2: Whoa They were like, that's a big boba.
• 43:04
  Speaker 1: It's a big that's when you would choke on for sure.
• 43:07
  Speaker 2: Yeah, they choke Maybe they were drinking boba at the time.
• 43:09
  Speaker 2: They're like, well, what what is that?
• 43:12
  Speaker 1: And I think it's super cool because it gives us
• 43:14
  Speaker 1: a way to understand not just how our universe was
• 43:17
  Speaker 1: formed and why we have galaxies over here and why
• 43:19
  Speaker 1: we have galaxies over there, but also how the universe expanded,
• 43:24
  Speaker 1: Like we know how big that sound wave when it
• 43:26
  Speaker 1: was created, because it just comes down to like the
• 43:28
  Speaker 1: physics of protons and photons and dark matter, how they
• 43:31
  Speaker 1: push on each other, and we know how big they are.
• 43:33
  Speaker 1: Now we can measure them, and so that gives us
• 43:35
  Speaker 1: like an independent way to measure the expansion of the universe,
• 43:39
  Speaker 1: which of course is a big question and a deep mystery,
• 43:41
  Speaker 1: like the source of dark energy and how that all works.
• 43:44
  Speaker 2: I guess maybe a question is why do we see
• 43:46
  Speaker 2: more of these bubbles, Like wasn't the universe filled with
• 43:49
  Speaker 2: these sound ways and these screams of the early universe.
• 43:52
  Speaker 2: We aren't these bubbles more obvious?
• 43:54
  Speaker 1: Yeah, great question. We haven't seen that much of the universe.
• 43:57
  Speaker 1: You know, our precision maps of the locations of galaxies
• 44:00
  Speaker 1: basically are just big enough to include one of these.
• 44:03
  Speaker 1: If you look online and check this thing out, you
• 44:06
  Speaker 1: see that this one bubble occupies a huge fraction of
• 44:09
  Speaker 1: the known galaxies we've seen. We just haven't looked out
• 44:12
  Speaker 1: far enough to see one of these things before.
• 44:14
  Speaker 2: Oh wow, it's that big of a bubble, Like it's
• 44:16
  Speaker 2: almost the size of the observable universe.
• 44:18
  Speaker 1: You're saying, it's almost the size of the set of
• 44:20
  Speaker 1: galaxies that we have mapped. Well, yeah, as things get
• 44:23
  Speaker 1: further out, it's harder and harder to map these things.
• 44:26
  Speaker 1: You need more and more precise measurements. Like if we
• 44:29
  Speaker 1: could use a James Webspace telescope and pointed in every
• 44:31
  Speaker 1: direction for a month, we would get an awesome map
• 44:34
  Speaker 1: of the galaxies in the universe. But the map we
• 44:37
  Speaker 1: have is really sporadic, and in some places it goes
• 44:39
  Speaker 1: really far. In some places it doesn't because we just
• 44:41
  Speaker 1: don't have enough telescopes and enough telescope time to do
• 44:45
  Speaker 1: these careful surveys.
• 44:46
  Speaker 2: Well, as you said, it sort of gives us sort
• 44:48
  Speaker 2: of like a marker in the history of the universe
• 44:50
  Speaker 2: and how it expanded. And now what's the connection to
• 44:53
  Speaker 2: dark energy.
• 44:53
  Speaker 1: Well, dark energy is our word for how the universe
• 44:56
  Speaker 1: expanded and how that expansion has accelerated. The picture we
• 44:59
  Speaker 1: have is that the early universe was dominated by matter
• 45:02
  Speaker 1: and radiation early on and expanded and things cooled. But
• 45:06
  Speaker 1: then that matter radiation starts to decelerate the expansion of
• 45:09
  Speaker 1: the universe, start to slow it down, because that's what
• 45:11
  Speaker 1: energy density does. It curves space and pulls things back together.
• 45:14
  Speaker 1: But at the same time, some new force was waking up,
• 45:17
  Speaker 1: something we call dark energy, was pushing the other direction
• 45:20
  Speaker 1: and accelerated the expansion of the universe. And this is
• 45:23
  Speaker 1: something we'd like to understand the detail because we don't
• 45:25
  Speaker 1: understand the mechanism for it, but we want to understand
• 45:28
  Speaker 1: the history so we can get a better sense for
• 45:30
  Speaker 1: what might have been causing this. So measuring the precise
• 45:33
  Speaker 1: rate of the expansion and how the universe has grown
• 45:36
  Speaker 1: over time is very, very valuable.
• 45:38
  Speaker 2: I see, because I guess these bubbles can't just come
• 45:40
  Speaker 2: up randomly, right.
• 45:41
  Speaker 1: Yeah, these bubbles have a fixed size in the early universe,
• 45:44
  Speaker 1: just determined by like the physics of acoustic oscillations which
• 45:47
  Speaker 1: we think we understand, and then they're stretched by dark
• 45:50
  Speaker 1: energy to a new size which we can measure. So
• 45:53
  Speaker 1: measuring the size of these bubbles now and comparing them
• 45:56
  Speaker 1: to the size we knew they had in the early
• 45:58
  Speaker 1: universe gives us a way to say how much has
• 46:00
  Speaker 1: the universe been stretched, which, of course is something we're
• 46:03
  Speaker 1: very interested in.
• 46:04
  Speaker 2: All right, Well, another interesting exploration into our origins and
• 46:08
  Speaker 2: how much we can and how much we still don't
• 46:10
  Speaker 2: know about what was happening.
• 46:12
  Speaker 1: To me, it's amazing how cosmology has gone from a
• 46:14
  Speaker 1: field where it's like mostly hand wavy stories with rough
• 46:18
  Speaker 1: numbers to a field where we can measure things and
• 46:20
  Speaker 1: do precise calculations and compare this and that and know
• 46:24
  Speaker 1: things about the early universe from these calculations. We have
• 46:27
  Speaker 1: filtered through crazy data to get these stories of the universe,
• 46:31
  Speaker 1: to find these clues to build back this history of
• 46:35
  Speaker 1: what happened and how we all got here.
• 46:37
  Speaker 2: I see it's now precision handwaiting.
• 46:42
  Speaker 1: Baby steps, man, baby steps, Boba steps.
• 46:44
  Speaker 2: You need a thicker straw.
• 46:47
  Speaker 1: Well, we need are more smart people thinking hard about
• 46:49
  Speaker 1: how the universe works and asking questions and listening to podcasts.
• 46:53
  Speaker 2: All right, Well, the next time you're in a crowded subway,
• 46:55
  Speaker 2: think about how the universe felt back then, how it's
• 46:58
  Speaker 2: screamed out in a discomfort, and how we still see
• 47:01
  Speaker 2: those screams today in the shape and the distribution of
• 47:05
  Speaker 2: galaxies and also light.
• 47:07
  Speaker 1: And please continue to enjoy your boba at your own risk.
• 47:10
  Speaker 2: Well, we hope you enjoyed that. Thanks for joining us,
• 47:13
  Speaker 2: see you next time.
• 47:22
  Speaker 1: Thanks for listening, and remember that Daniel and Jorge Explain
• 47:25
  Speaker 1: the Universe is a production of iHeartRadio. For more podcasts
• 47:29
  Speaker 1: from iHeartRadio, visit the iHeartRadio Apple Apple Podcasts, or wherever
• 47:33
  Speaker 1: you listen to your favorite shows.