Listener Questions 49: Black Holes, Neutrinos and Gravitational waves!

00:00:08
Speaker 1: Hey, Daniel, is it true that every electron is identical?

00:00:12
Speaker 2: Well, they all do have the same mass and the same charge, Like exactly, yeah, we think so.

00:00:19
Speaker 1: Isn't that weird? Why don't you expect them to be a little bit different each one.

00:00:23
Speaker 2: It's kind of exactly not weird. It means that no electrons are weird because they are all the same.

00:00:29
Speaker 1: I don't know, man, that's a bit wooky. Like if everyone in your neighborhood looked the same, wouldn't that be weird?

00:00:37
Speaker 2: I mean, I live in Orange County, so that's kind of what most people in the neighborhood are going for.

00:00:43
Speaker 1: Everyone's going for that scruffy physicist.

00:00:45
Speaker 2: Look more like plastic surgery face and beige housing.

00:00:50
Speaker 3: Well.

00:00:50
Speaker 1: I didn't want to say anything, but yeah, I do feel like you need a facelift in or at least a physics lift. Hi. I'm jorm At, cartoonist and the author of Oliver's Great Big Universe.

00:01:14
Speaker 2: Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I'm proud of being one of a kind.

00:01:19
Speaker 1: But what kind is that? Daniel?

00:01:21
Speaker 2: That's the quiet that you. The pride might depend On. Mm, yeah, I define my kind man. There's nobody else like me. M.

00:01:30
Speaker 1: How do you know, though, have you met everyone who's ever existed? What if there was a Daniel with your exact same DNA that you know, lived two hundred years ago or could be living right now.

00:01:41
Speaker 2: It's possible, but they wouldn't have the same experiences. I have actually met another Daniel Whitson. He's an artist in the UK and quite accomplished.

00:01:50
Speaker 1: Ooh are you jealous?

00:01:54
Speaker 2: Am I jealous of the artist lifestyle?

00:01:56
Speaker 3: Oh?

00:01:56
Speaker 2: So many directions to go with that?

00:02:01
Speaker 1: What was that like? I don't think I've ever met a horhe Cham yet, but I think one exists somewhere in Indonesia.

00:02:06
Speaker 2: Maybe isn't there another one who has the Twitter handle at hohorhey.

00:02:11
Speaker 1: Cham somebody got that Twitter handle. I don't know if it is horri ha Jam or not, but I'm waiting for the blackmail email. Mm.

00:02:18
Speaker 2: Yeah, well, at least a digital copy of you exists.

00:02:21
Speaker 1: Or maybe I opened it years ago, but I forgot the password and the email I associated it with, so I don't know. Maybe I am my other meat.

00:02:30
Speaker 2: Yeah. Maybe we're old enough that younger versions of us are like alien minds.

00:02:34
Speaker 1: Oh wait, wouldn't that make you an alien?

00:02:39
Speaker 2: I think we're all still struggling to know ourselves.

00:02:41
Speaker 1: Right, well, we might all be aliens, right that Isn't there a theory that maybe life came to Earth from Mars.

00:02:48
Speaker 2: There is a theory like that called panspermia, that life may have originated somewhere else in the universe and then transported microbially hidden inside asteroids. It's a possibility all immigrants, kind of.

00:03:02
Speaker 1: But anyways, welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio in.

00:03:07
Speaker 2: Which we do our best to digest this alien universe to explain all of the bizarre and amazing effects we see out there in terms of little mathematical stories that your mind and my mind and Jorge's mind can actually understand that we can talk about and digest and explain to you.

00:03:23
Speaker 1: That's right, because it is a pretty vast universe, and it's also pretty weird, full of unexplained phenomenon, unanswered questions, and potentially other versions of you out there.

00:03:33
Speaker 2: Raising all sorts of interesting philosophical questions like what does it mean to have an identical copy? And when you step into a transporter on Star Trek. Is it making a copy or actually transporting you?

00:03:44
Speaker 1: And what if, like there's another Jorge and another Daniel and they start a podcast. Can we sue them technically or maybe just retiring and give them the feat?

00:03:57
Speaker 2: Yeah, maybe it's time for the next generation, right.

00:04:00
Speaker 1: The new Daniel and Jorge explain the universe? Or Daniel and Horry explained the universe the next generation?

00:04:06
Speaker 2: Exactly? Yeah, one of us is Jean Luke and the other one is Riker.

00:04:11
Speaker 1: Wait wait, wait your name comes first, as I mean, I'm number two?

00:04:14
Speaker 2: Make it so? Okay?

00:04:16
Speaker 1: Can I just beque? Like, if I had to pick a character from the next generation, I would pick Q.

00:04:23
Speaker 2: Really not Data. Data might be the smartest one.

00:04:26
Speaker 1: A smart than Q can do anything in time and space.

00:04:30
Speaker 2: Q has no rules, so it doesn't really count exactly exactly, So you basically you want to be God, you're.

00:04:36
Speaker 1: Saying, I mean, who doesn't, come on, Q.

00:04:42
Speaker 2: Has so much responsibility. Every child who's dying of cancer. That's Q's fault, is it?

00:04:47
Speaker 1: Is it?

00:04:47
Speaker 2: Really? If you had the power to save a child and you didn't, then yeah, I think you're kind of responsible. Boy.

00:04:54
Speaker 1: That's a lot of gud killed.

00:04:56
Speaker 2: That's why I'd rather be data.

00:05:00
Speaker 1: Do you want to be data or be data?

00:05:03
Speaker 2: Hmm, Yeah, that's a good question. I actually just want to harness data's computing powers to solve mysteries of the universe. Yeah.

00:05:09
Speaker 1: That's a lot of makeup to put on every data.

00:05:11
Speaker 2: It's pretty heavy.

00:05:13
Speaker 1: Yeah, but anyways, welcome to our podcast. We also like to answer questions, not just talk about the answers that physicists have found. We also like to think about questions about the universe.

00:05:24
Speaker 2: Because everybody's got questions. I've got questions, You've got questions. Everybody who looks up at the night sky and wonders how it all works, or stares down between their toes and wants to understand the tiniest particles is yearning to understand how the world works, and that means asking questions. And on this podcast we answer questions at the edge of knowledge, those pose by physicists and those pose by listeners. So if you have questions about the nature of the universe or some explanation you've heard somewhere that didn't quite make sense to you, write to us to questions at Danielandjorge dot com. We really do. Right back to all of our listeners.

00:05:58
Speaker 1: Yeah, we're all curious about how the universe works, why we're in it, and how it's all put together. Although I'm not exactly curious about the particles in your toes or anyone's toes. Maybe we'll leave that part out of our questions.

00:06:11
Speaker 2: Wow, limits to your curiosity. That's disappointing.

00:06:14
Speaker 1: Yeah, I think there should be limits to anyone's curiosity. But yeah, we like to answer questions here on the podcast and plans from listeners, and so thanks to everyone who sent their questions in.

00:06:25
Speaker 2: Often I'll just write back, but sometimes we choose questions to answer on the podcast because we think lots of people will want to hear the answers.

00:06:32
Speaker 1: And so today on the podcast, we'll be tackling listener questions number forty nine. What are we gonna do when we hit fifty, Daniel, We're gonna have a mid podcast live crisis.

00:06:46
Speaker 2: We're gonna have a nice cake with fifty on it, and we're gonna fall asleep before the end of the.

00:06:49
Speaker 1: Party and then burn your house down.

00:06:51
Speaker 2: What it's gonna be virtual, of course, but.

00:06:56
Speaker 1: Yeah, we're answering listener questions here today and we have some awesome questions here from our listeners. There's one about black hole identity, there's one about neutrino and how many there are in the universe. And we also have a question about what it's like to serve a gravitational wave and what happens when you wipe out, Like where do you fall if it's a gravitational wave? But let's jump right in. Our first question comes from Matthew, who comes from Barry, Ontario.

00:07:24
Speaker 4: Hello, Daniel and Jorge. This is Matthew from Barry, Ontario up here in Canada, and like many of your listeners, I spend a bit of time thinking.

00:07:32
Speaker 1: About black holes.

00:07:34
Speaker 4: While I understand that it is impossible for us to see what lurks beyond the event horizon, I was curious if there is consensus in the scientific community about all black holes being the same, or if they could vary inside based on their density. For example, could a smaller black hole be not a black hole at all, but a dark star, while the super massive black holes at the center of some galaxies be a more traditional black hole or a string theory fuzz. Thank you very much for the wonderful show and I look forward to hearing your response.

00:08:04
Speaker 1: All right, I feel like this question ken has an identity problem in itself.

00:08:10
Speaker 2: It's so many questions but also one.

00:08:12
Speaker 1: But I think Matthew's basic question is about the identity of black holes, Like, are all black holes the same? Are they actually black holes? Could they be something else? Is it a case of mistaken identity? Or do all black holes come with an ID tag?

00:08:27
Speaker 2: Yeah, he's basically wondering what's going on inside black holes and if they all have to be the same on the inside, and whether the things we've seen out there in the universe that look like black holes could actually be a bunch of different kinds of stuff that all mimic black holes. So it's a really cool question guess at the heart of what we think is going on inside black holes.

00:08:46
Speaker 1: M Like, maybe what we call black holes are actually maybe a varity of different things.

00:08:53
Speaker 2: Yeah, it's possible. And two black holes with the same mass, do they have to look the same on the inside?

00:08:59
Speaker 1: Wait on how much mass is in it? Or Like, two things that look like black holes, are they actually black holes? Or do you think he's asking if they're the same, if there's any property that sets them apart?

00:09:09
Speaker 2: Yeah, I think he's asking both of those questions, and I think we should start with that. Like, if you have two black holes that have the same mass, are they the same thing? Are they indistinguishable? Or are they different? And this is a big question in general, relativity goes by the name of two black holes have hair? Essentially, are there texture or details? Are there tiny little properties that set two black holes apart the way two Like identical twins are always a little bit different. Are two black holes with the same mass, could they actually be a little bit different on the inside.

00:09:43
Speaker 1: Well, I feel there's two questions. One is like are they the same? And can you tell if they're the same? Aren't those two separate questions?

00:09:50
Speaker 2: Yeah, those are two separate questions. So as you can see, with black holes, we have like a constantly multiplying stream of questions.

00:09:58
Speaker 1: It's like a black hole of questions. It's a bit of a rabbit hole. It's a black rabbit hole. So which which question are we tackling? Can you tell if two black holes are different or whether they're actually different inside?

00:10:10
Speaker 2: Yeah, we can talk about all of it, but let's start with what's going on inside black holes, at least what we think is going on.

00:10:16
Speaker 1: Okay, well, you sort of mentioned the no hair problem, and that one's more of a like can you tell if two black holes are different problem?

00:10:23
Speaker 2: I think it also touches on whether the black holes inherently are different. Are there features to two black holes which tell them apart? Because in general relativity, the idea is that all you can know about a black hole are three different quantities how much mass it has, whether it's spinning, and whether it has electrical charge. And to say that that's all you can know about a black hole means that that's what defines a black hole. So in general relativity, two black holes with the same mass, spin, and charge really are identical according to that theory.

00:10:57
Speaker 1: From the outside right, I mean, it's basically saying that's all you can tell about what's inside a black hole.

00:11:02
Speaker 2: It means those are the only properties of the objects, So even on the inside, they would be identical again according to general relativity. Important caveat we can get to later.

00:11:12
Speaker 1: But I guess, how can they be exactly identical or how can we know or how can the theory know that it's identical because inside the black hole maybe things are arranged differently.

00:11:21
Speaker 2: We can't know currently because we can't see inside black holes, but that doesn't stop the theory from predicting what's there and describing what we think is happening. And according to general relativity, again big caveat there we can get to in a minute. All these black holes, if they have the same mass, spin, in charge, really are identical. They have the same exact internal structure because they're defined just by those three numbers, So there's no whiggle room. There's no opportunity for a black hole made of bananas to be different from a black hole made of bowling balls or squirrels if they have the same mass, spin, and charge. That's again according to general relativity, which is predict what's inside black holes, though it's not something we've seen.

00:12:03
Speaker 1: I guess what I mean is like a black hole is like a sphere right like to us, it has volume, and so what does general relativity predict is inside of that sphere just a singularity? Like everything just collapses instantly or what.

00:12:17
Speaker 2: Well, a black hole that's had time to settle, everything will fall towards the singularity. So if things are still dynamically falling into a black hole, its state is changing. But after a long time. When it settles, then it's just defined by these three numbers. And yeah, two black holes with the same mass will each have a singularity inside them with the same.

00:12:37
Speaker 1: Mass and nothing between the singularity and the event horizon. What does general relativity say is between the singularity which is at the center, and the event horizon, which is the outer shell of the black hole.

00:12:49
Speaker 2: So it depends a little bit on the mass, spin, in charge. These kinds of black holes have different internal structures, like the simplest kind one with just mass and no spin, no charge, or this is the kind most people talk about and think about, is just a sphere and in the inside you have the singularity and there's nothing else. If it's charged or if it's spinning, then the structure in the inside is a little bit different, Like you don't actually have a singularity if it's spinning, you have a ringularity because you need an object that can spin and singularities can't. And you can have different kinds of horizons inside the black hole or even near the black hole on the outside if it's spinning and if it has charge.

00:13:29
Speaker 1: Well, that's an interesting concept you just mentioned, which is like the settling of a black hole. Now does that happen like instantly over billions of years trillions? Does it ever happen? Doesn't times stop? Inside of a black hole?

00:13:42
Speaker 2: Nothing happens instantly, right. Relativity describes how there's a maximum speed limit to the universe, and so you definitely can't have things instantly collapsing into a singularity. It always takes time. How much time it takes depends on who you are and where you are. Like, if you're outside the black hole and you're watching things fall in, you'll actually not see them fall in because time slows down so much at the event horizon. You'll see them frozen at the event horizon. If you are riding that banana into the black hole, then you will see yourself past the event horizon and you'll fall in, and you'll reach the singularity in a finite amount of time. So how long it takes depends on the observer. In general relativity, these things are very screwy.

00:14:23
Speaker 1: But I guess maybe then the scenario I wonder that Matthew's thinking about me, Like, if I have two black holes, they have the same mass and energy and spin in charge and all that they're identical, But then black hole A eats a banana, and black hole b eats a bowling ball. Like to us, it takes some time for the banana to and bolling bull to make it to the center of the black hole. So are those two black holes different in the meantime.

00:14:49
Speaker 2: In the meantime they are. Yeah, But if the bowling ball and the banana have the same mass, and like that's a tiny bowling ball or a huge banana, then eventually they do reach steady state, which is just described by the mass, spin and charge.

00:15:04
Speaker 1: But could we tell that one aid the banana and the other one ate the bowling ball.

00:15:08
Speaker 2: We couldn't, right, Not after they've settled into the singularity exactly. According to general relativity, that information is lost. Before that information is still within the event horizon. We can't see it, but it does still exist within the black hole after it's settled into the singularity. According to general relativity, that information is gone because the state is perfectly described by the mass, spin in charge.

00:15:31
Speaker 4: Mmm.

00:15:32
Speaker 1: So then it's sort of possible for two black holes to be different, perhaps, but for us to not be able to tell them apart.

00:15:38
Speaker 2: Yeah, that is possible, and that's a transient state.

00:15:42
Speaker 1: Right, Well, black holes are eating all the time, right, So black.

00:15:44
Speaker 2: Holes in the real world yet are always eating are They're always surrounded by something. There's never a true vacuum. There's always a solar wind or particles everywhere. So yeah, absolutely, black holes are always eating in real life. In the sort of thought experiments we construct, you could imagine a black hole surrounded by actually nothing and then you just drop a banana into it. But yeah, and the real universe, black holes are never surrounded by nothing.

00:16:08
Speaker 1: But I think, as you were saying, this all depends on general relativity.

00:16:12
Speaker 2: Yeah, exactly. This is a picture from classical physics that says that singularities can exist within black holes, and that it matter could be compressed into a tiny dot. That's totally incompatible with what we know about the nature of reality that is quantum mechanical. Though, when things get really really small, like the size of singularities, different rules take over and have to be accounted for, rules that general relativity ignores. So we don't think singularities actually do exist at the heart of any black holes in our universe. We think, if black holes are even real, that there's some other kind of thing going on, something dictated by a different theory of physics, not general relativity, one that correctly incorporates the quantum nature of our universe, a theory we don't have today, so we can't say what we actually think is inside a black hole.

00:17:00
Speaker 1: I think maybe Matthew's question is, like, let's say black holes they're all a little bit different inside, depending on their density, Like maybe some of them are super dense but collass into a singularity, or maybe some do, or maybe some are more like uh, let strings every fuzzballs. I wonder if they can be different in that way inside, but to us from the outside they all look the same.

00:17:21
Speaker 2: It's possible, and it depends on your flavor of quantum gravity. If what he's describing is true. There are no classical black holes in the universe. They're all some weird quantum version. And you're right, there could be a variety, right, There could be some fuzzballs and some dark stars and some white holes and some other kind of crazy stuff going on. And whether we could see the difference on the outside also depends on the details of the quantum gravity theory. In some scenarios, you can tell what's inside a black hole by studying the patterns of the hawking radiation, which might be quantum entangled with the details of what's going on inside and leaking that information out. There are other quantum theories of black holes in which you still can't get that information out even though it is inside the event horizon. So it depends on your flavor of quantum black hole. But it's possible that all these things do really exist in our universe.

00:18:12
Speaker 1: Hmmm. It sounds like it sort of depends on what you define as a black hole, right, Like, if you define it as what a general what relativity calls a black hole, then you get one as er. But if you just define it as something that has an event horizon that doesn't let you look inside, it is possible maybe to have different kinds of black holes exactly.

00:18:31
Speaker 2: And remember, not all of these objects even have event horizons. When we talk about a black hole, we sort of imply an event horizon. But it's possible that some of the things out there in the universe that we call black holes don't actually have event horizons. We haven't verified the event horizon nature of those objects. They're just really really small, really really massive, and really really space bendy in the way we expect black holes to be, but we haven't like zoomed up close and proven that they actually have event horizons. And some of these theories don't create objects with event horizons.

00:19:03
Speaker 1: But some do, right, Like you could have a dark star that does have event horizon.

00:19:07
Speaker 2: Perhaps, yeah, some of them do. It depends on the flavor or quantum gravity.

00:19:12
Speaker 1: Hmm, all right, well then so then the answer for Matthew is, uh, it depends and we don't.

00:19:19
Speaker 2: Know that summarizes most of physics.

00:19:23
Speaker 1: Yes, it depends that black hole that's in your backyard.

00:19:27
Speaker 2: What it means is that there's still so much to learn about the nature of these objects. And the answer to the question might not be it's this kind or it's that kind, but it's all the kinds. I love that possibility.

00:19:37
Speaker 1: Mmm. So it sort of maybe depends on what's actually going on, which we don't have a clear theory about.

00:19:43
Speaker 2: And we might not ever know.

00:19:45
Speaker 1: Ever.

00:19:46
Speaker 2: It might be that the universe prevents us from ever seeing inside these black holes, or that the information in the Hawking radiation doesn't reveal what's inside them. It might be that we're not smart enough to figure out the universe.

00:19:57
Speaker 1: Who knows, Boy, I wish you had left the question on a more positive note, But it could.

00:20:03
Speaker 2: Be that we figure it all out and then you go in ten generations the latest. Daniel and Jorge are explaining it all to you on their podcast.

00:20:11
Speaker 1: All right, all right, yeah, that's good. That doesn't leave us in a black hole. All right, let's tackle some of our other questions. We have questions here about the number of neutrinas in the universe and also about what it's like to bob up and down on a gravitation wave. So let's stick into those. But first let's take a quick break. Right we're answering questions from listeners, and our next question comes from Sam from British Columbia.

00:20:50
Speaker 3: Hello, Daniel and Jorge, this is Sam from British Columbia and thank you for your podcasts and availability to answer our questions. It is really appreciated about neutrinos. You always mention how many trillions are passing through the Earth every second. This got me wondering about how many neutrinos are estimated to exist in the universe, as well as proportions for the other main particle groups.

00:21:13
Speaker 2: In the standard model.

00:21:14
Speaker 3: It has often estimated that there are ten to the eighty particles in the universe. When he asked chat gpt for help, I got back that each of the groups of leptons, quarks, and bow sounds each were in the order of ten to the eighty, and then that there were significantly more electrons than neutrinos, and also that there were about ten to the eighty of each. I think chat gpt once again was confused, and I'm hoping you can help unconfuse me.

00:21:40
Speaker 1: Thanks all right, Well, I'm glad that we were his second choice for answering questions about the universe.

00:21:48
Speaker 2: Oh man, chat GPT.

00:21:51
Speaker 1: I guess chat gpt is free. I guess you don't have to listen to ads d I.

00:21:57
Speaker 2: Think you have to pay for some version of chat GPT. No version of it can be relied on to answer physics questions. I see, well, you know what they say, you get what you pay for. You can do get what you paid for.

00:22:09
Speaker 1: It sounds like chat jipt did not answer Sam's question or game of an answer that maybe it was confusing.

00:22:15
Speaker 2: Well, it's also not designed to answer physics questions. It's designed to generate text which looks like the answers to questions it's not designed to do any reasoning, or have a model of the universe, or actually think in any way, or be accurate or explain things. So I wouldn't rely on chat gpt to answer any questions. Yet you could say that about anything. Man, your toaster hasn't replaced you yet.

00:22:39
Speaker 1: Well, you know, it's like they say, chat chipet is not designed to do basic math, right, Like, if you ask it a math question, it may not give you the right answer. But I've seen examples of like asking Chad Gipt to check using some sort of math toolbox, and then it gives you the right answer.

00:22:53
Speaker 2: Yeah, you know a stop clock is right a few times a day, right, yeah?

00:22:57
Speaker 1: Yeah, So you could ask chat gipt twice a day to go read every physics paper in the universe and then come back to you with an answer, which is basically what we do in this podcast.

00:23:07
Speaker 2: And it's the wrong tool for the job. You know. Its job is to generate text which resembles answers, not to reason and think and provide explanations. I don't think it'll ever be a good place to ask physics questions. I say, I see somedays somebody might actually develop an AI which is good at the reasoning and thinking and explaining. I'm not ruling that out. I'm pretty sure that will happen one day, but large language models won't get there.

00:23:32
Speaker 1: I think what you're saying is that we're the right tools.

00:23:34
Speaker 2: Yes, ask us where we were, just the pair tools, just like data on Star Trek.

00:23:42
Speaker 1: Right, there you go, There you go. Maybe the next chat GBT should be called Daniel and Cordy Chat DJ. All right, well, let's get to Sam's question here. Samon wants to know how many neutrinias there are in the universe, right, Like, what's a good estimate for the number of neutrinos in the universe?

00:23:59
Speaker 2: Such an awesome question because there are so many neutrinos in the universe, it's mind boggling.

00:24:06
Speaker 1: Well, there's a lot of everything in the universe, right, Well, there's only one me and one you. How do you know.

00:24:12
Speaker 2: Ship a theseus man, if there's another copy of me, it's not me.

00:24:18
Speaker 1: Well, there could be one you that has gone through the same experiences as you. Wouldn't that be the same Anyways, let's get back on track here. It's a big universe. Asne wants to know how many neutrinios are Why do you think he wants to know how many there are? Like, why neutrinos? Why not how many electrons or quarks there are in the universe?

00:24:37
Speaker 2: I think because neutrinos give us a window into a deeper understanding of what's out there in the universe. Like we're made out of quarks and electrons, and that feels like, Oh, that's the universe, what's all that made out of? But as soon as you realize that our senses are limited and that there's so much more going on in the universe than the little bits of matter that you and I are made out of, it makes you wonder what's out there, how much of it is there? And new trinos are like the tip of that invisible matter Iceberg.

00:25:05
Speaker 1: I see, Well, how would you answer the question of how many new trinos there are?

00:25:10
Speaker 2: Yeah, so it takes a few steps. Basically, you have to know how many protons there are in the universe, and then you have to try to figure out how many neutrinos there are per proton. And it turns out that we can do both of those calculations.

00:25:21
Speaker 1: Wait, why do we have to go through protons?

00:25:24
Speaker 2: Because the way we figure out how many new trinos there are in the universe is by going back to the very very early universe and understanding how photons and protons and neutrinos and dark matter all slashed around and pushed against each other. It's this plasma soup at the very beginning of the universe that reveals the answers to all of these questions. From measurements of the cosmic microwave background, we can learn a lot about that plasma and how it was slashing, and it tells us the answers to all of these things. Then, specific ways it tells us some ratios allow us to get to these answers.

00:25:56
Speaker 1: Like the beginning of the universe tells you the original recipe of the universe kind.

00:26:00
Speaker 2: Of yeah, exactly, And some of that hasn't changed, and some of that has changed, and we know how that has changed, and we can evolve that through time. But it basically starts the machine and tells us how things evolve through time.

00:26:12
Speaker 1: But is it even possible to get this answer because aren't neutrino's being created, for example, all the time in the sun? Like, are new neutrinos being made all the time?

00:26:21
Speaker 2: Yeah? The specific number like to the individual neutrino is not very well defined because neutrinos are quantum particles, and so they even have probabilities of existing. Like you have a certain reaction that might generate neutrinos. Whether it actually did or not isn't even determined until it interacts with some classical objects. So from a quantum mechanical point of view, getting the answer down to like the individual neutrino is not technically possible, and even zooming out a little bit as you say, there are neutrino factories in the universe and neutrinos being annihilated. Neutrinos can be created and destroyed, so the number is changing. But it turns out that the number of neutrinos being created in roid in the universe is really tiny compared to like the huge reservoir of neutrinos we already have.

00:27:06
Speaker 1: Well, how do you.

00:27:07
Speaker 2: Know, because we think we understand those processes, and we've measured neutrinos that come from space and neutrinos that pass through the Earth. Neutrino physics is something we're really starting to get a grip on in like the last twenty years. So we are a pretty good handle on how many neutrinos are out there and how many are being made by the Sun. We even see neutrinos generated by crazy sources in other galaxies. Neutrino astronomy is something that's really come into its own in the last couple of decades.

00:27:34
Speaker 1: And so what's the picture. It's like the Sun is making bazillions of neutrinos, but that's very like a drip of water compared to like we're swimming in an ocean of neutrinos.

00:27:43
Speaker 2: Zechon what you're saying exactly. It's like asking what's the volume of the Pacific? Well, you don't really have to worry about evaporation and rain because those are tiny details relative to massive volume of water there.

00:27:54
Speaker 1: And so then what's the connection to protons? Why do we need to know how many protons there are?

00:28:00
Speaker 2: Know how many neutrinos there are per proton. That's a measurement we can make back in the very early universe. If you wind the universe backwards, we see that it gets hotter and denser. Right now, the universe is kind of old and cold, very dilute, very chill. But as you wind time backwards and you undo the expansion, things get very hot and very dense. Back to some early state where there were protons and there were photons, and there were electrons, and there were also neutrinos zipping about, and we can see photons from that moment. This is the moment we call the surface of last scattering, when the universe became transparent to those photons, so they're still around. So we can see a picture of what that early universe plasma looked like. It's called the cosmic microwave background radiation, and we can see patterns in it. We see wiggles and we see waves. Those wiggles and waves are determined by how it's slashing, which depends on how many protons there are, how many photons there are, how much dark matter there is. As you change those fractions, that early universe plasma slashed differently because those different pieces all behave differently.

00:29:03
Speaker 1: But even neutrinos were consequential at the beginning of the universe because I thought neutrinos were basically massless and they're ghostly and they they don't really interact with anything much. Isn't there like a wide range of neutrino proportions that could have been there at the beginning of the universe.

00:29:20
Speaker 2: Yeah. Absolutely. Neutrinos don't interact very much, but they do have energy, and so they affect the energy density of the universe, which changes its expansion. And because neutrinos are very very light, they sort of fall into the same category as photons. Back in the early universe, everything that was moving almost at the speed of light or at the speed of light gets counted kind of as radiation. Remember we talked about this once, and stuff that's moving very very slowly gets counted as matter. And so things that are moving as radiation do affect the expansion of the universe because they affect the energy density in this complicated way. So you're right, the neutrinos are weak, but they still have energy and that affects the old overall balancing of these equations in general relativity.

00:30:03
Speaker 1: There's stills a piece of the pot.

00:30:05
Speaker 2: Yeah, exactly. And it turns out there's a huge number of them, so they have a pretty big influence.

00:30:10
Speaker 1: Oh, how big of a number, Like if you had a pie chart of the universe at the beginning in the Big Bang, how big is the neutrino slice.

00:30:17
Speaker 2: Yeah, so you wouldn't even be able to see the protons on that pie chart because there are approximately one billion neutrinos for every proton.

00:30:25
Speaker 1: Well in terms of quantity, but in energy, how big of a slice is it there?

00:30:30
Speaker 2: The numbers are much more closely balanced. There are many fewer protons, but protons have a huge mass compared to neutrinos that have almost no mass. On the other hand, the neutrinos have a lot more kinetic energy. Right they're moving really really fast, They're almost at the speed of light, so the energy is there are much better balanced that are in the same order of magnitude. The numbers aren't exactly determined, but the original question was about the number of neutrinos in the universe, and so there we need the number ratio, and the cosmic microwave background radiation tells us that there are like three hundred and thirty million neutrinos per cubic meter of space back then, and there was less than one proton per cubic meter, so the ratio is about a billion I.

00:31:12
Speaker 1: See, so neutrino's were a pretty significant slice of the universe, but in terms of quantity, like number of neutrinos because they're so small at night that the number of them dwarfs the number of protons around us exactly.

00:31:23
Speaker 2: So there's this incredible ocean of neutrinos back in the early universe and still today. Like the density of neutrinos has dropped because the universe expands and everything gets more dilute except for dark energy, but most of those neutrinos are still around. It's called the cosmic neutrino background, and it's something we're searching for in neutrino experiments.

00:31:44
Speaker 1: Does it depend still on the number of protons? Is it the same ratio like three hundred and thirty million to one or billion to.

00:31:51
Speaker 2: One, depends a little bit what you count as a proton. Like some of those protons go on to make helium. There's still protons in there, but like now we call them helium instead of protons or hydrogen. But most of those protons are still around, and most of those neutrinos are still around, and because they're both matter, they both get diluted in the same way as the universe expands, and so their ratio is approximately the same.

00:32:14
Speaker 1: Then to get account of the number and neutrinos, we need a count of the number of protons, So how many protons are there in the universe.

00:32:20
Speaker 2: So in the observable universe, we don't know what's in the full universe right past where we can see. We know the density of protons, which is about a fifth per cubic meter, and we know roughly the volume of the observable universe, which is like ten to the eighty cubic meters or so, and that means around ten to the seventy nine protons in the observable universe. That's ten with seventy nine zeros. It's not even like a name for that.

00:32:47
Speaker 1: Number, Sure there is, we can make one.

00:32:49
Speaker 2: Up, right, there will be soon.

00:32:52
Speaker 1: What's the number bananion?

00:32:56
Speaker 2: Coincidentally, there's exactly one bananion of protons in the universe.

00:33:00
Speaker 1: Oh my gosh, such a coincidence.

00:33:03
Speaker 2: Which means that there's a billion bananians of neutrinos in the universe, because it's about a billion neutrinos per.

00:33:10
Speaker 1: Proton, So ten to the what eighty eight.

00:33:13
Speaker 2: About ten to the eighty eight neutrinos in the observable universe.

00:33:17
Speaker 1: Observable universe, but the observable universe is getting bigger every day. Right, So that number is going up.

00:33:23
Speaker 2: Actually depends a little bit how you think about distance. The universe is expanding faster than the speed of light, so the fraction of stuff in the universe we can see is actually shrinking, right, And eventually a lot of stuff is going to fall outside of our horizon. So the number of particles in the observable universe is actually decreasing.

00:33:40
Speaker 1: WHOA, the universe is its outgrowing how far we can see.

00:33:45
Speaker 2: Yeah, exactly. The universe is expanding faster than our horizon is, so particles are disappearing from the observable universe. That's another reason why the number is not fixed.

00:33:55
Speaker 1: Well, it may not even be fixed, right, Like, maybe the universe is infinite, in which case there's maybe an infinite number of neutrinos.

00:34:02
Speaker 2: Yeah, exactly. In that case, you could still measure the density of neutrinos like three hundred and thirty million per cubic meter, but the total number in the whole universe would be infinite. If the universe is infinite, and if the universe beyond a horizon is similar to the bits that we see here, could be that what's beyond the horizon is very different, right, And then we live in a weird patch of the universe.

00:34:23
Speaker 1: Right right, It depends and we don't know, is what you're saying. But what do you think is the ratio of like in the universe, the ratio between neutrinos and Daniels. Is it infinite to one or is there a fixed number?

00:34:41
Speaker 2: That's the question philosopher has been wondering about for thousands of years, and we're not going to answer it today on the podcast.

00:34:48
Speaker 1: That's right. We don't have the time. That's why we're not answering.

00:34:50
Speaker 2: That's right, exactly. No, I think if there are other Daniels out there, there's still not me because I'm not experiencing them, even if they think that there Daniel. I'm experien think this one, which makes this one different, which makes me unique. I'm only experiencing one Daniel.

00:35:05
Speaker 1: Unless they're having the exact same experience you are, in which case, in which case, there the outside can't tell the difference.

00:35:13
Speaker 2: But we can from inside, right inside the Daniel horizon, you can tell which Daniel you are.

00:35:19
Speaker 1: But your feeling of uniqueness is the same feeling of unique is the other Daniel's having.

00:35:23
Speaker 2: Yeah, that's right, But I'm only feeling my feeling of uniqueness. I'm not feeling bears. Oh, I see.

00:35:28
Speaker 1: So to you, there's only one Daniel, yeah, but maybe to someone outside of the universe there is an infinite number of Daniels.

00:35:34
Speaker 2: Yeah. And it means and we don't know, And to me is all that matters, because I'm the only consciousness I'm actually aware of in the universe.

00:35:41
Speaker 1: But I'm not asking what matters to you. I'm wondering what matters to me, Daniel.

00:35:50
Speaker 2: I don't know if you're even real.

00:35:51
Speaker 1: So that's right, We're all in them some AI's imagination. All right, Well, I think that answers the question for Sam. The estimate of the number of neutrinos in the observable universe is ten to the eighty eight neutrinos plus or minus ten to the what eighty seven.

00:36:10
Speaker 2: Seven pluster minus infinity.

00:36:12
Speaker 1: Probably there's our pleasure minus infinity. All right, Well, let's get to our last question of the episode, which is about gravitational waves and can you serve one? So let's get into that, but first let's take another quick break. All right, Our last question of the day comes from Klai wants to know about gravitational waves.

00:36:43
Speaker 5: Howdy Daniel and Jorge. I was wondering how would feel to be hit by a gravitational wave? We have detected infinitely weak waves from Earth, but imagine if we were close to two black holes revolving around each other and eventually colliding and merging. How would it feel to get hit by a gravitational wave? And would it be the same as a wave? And finally, would your organs be damaged?

00:37:11
Speaker 1: Interesting question. It sounds like Clay is planning a trip. Perhaps.

00:37:18
Speaker 2: I think Klay wants to experience the universe, wants to feel gravitation waves, not just read about it online.

00:37:25
Speaker 1: Well, I think one of the things is that, first of all, we're all experiencing gravitation waves right now.

00:37:30
Speaker 2: Right, Yeah, that's true. Gravitational waves are everywhere. They fill the universe because they're generated anytime any mass is accelerated. So you're in orbit, you're generating gravitational waves. You get out of bed, you're generating gravitational waves. Gravitational waves are everywhere, right.

00:37:47
Speaker 1: We're experiencing them. We're generating them like if a car accelerates in front of me, technically gonna feel or I'm going to experience the gravitational wave generated by the car.

00:37:58
Speaker 2: Right, It's very hard to feel these things because they're very, very gentle. Remember that gravity is like the dominant force and the structure of the universe, but it's also the weakest force, if you even call it a force, so much weaker than the forces that hold your body together for example.

00:38:13
Speaker 1: Right, they're super mellow, hard to detect, but we can detect some of the ones that come from deep in outer space, that come from black holes or heavy things circling each other and then colliding.

00:38:25
Speaker 2: Exactly. The way to detect gravitational waves is to look for extremely loud sources of them, things that make very dramatic gravitational waves. And so two black holes, which are two enormous masses orbiting each other very very quickly just before they collide, are very loud sources of gravitational waves. So even though we're very far from them, we can be like a billion light years away, we can still detect those gravitational waves here on Earth with super sensitive detectors.

00:38:54
Speaker 1: Right here on Earth. By the time that they get to us, they're super weak because I guess, like a ripple in a laketational waves get weaker as they expand right from their source.

00:39:03
Speaker 2: Yeah, as you get further from the source, they get weaker and weaker.

00:39:06
Speaker 1: Right, And as you said, the ones we're detecting now with LIGO, which is the big physics instrument we have here on Earth, those happen billions of light years away. And I think the Khalist question is, like, what if you're closer to that source of gravitational waves, Like, what if you're right next to those two black holes glide in? What would it feel like to have this giant gravitation wave pass three?

00:39:29
Speaker 2: Yeah, it's a really cool question to think about it. I think we should like zoom in on what happens first to like individual particles in your body, and then think about what that would feel like.

00:39:40
Speaker 1: There's a way. Wait, but the scenario is how close am I to these gravitational waves?

00:39:43
Speaker 2: So imagine we're just like a few tens of thousands of kilometers away from these two black holes that are orbiting each other.

00:39:50
Speaker 1: Aren't black holes usually bigger than a few tens of thousands of kilometers or are you imagining like two small ones?

00:39:56
Speaker 2: Well, the kind of collisions we've seen are between black holes that have like thirty to fifty solar masses, and those have an event horizon radius of like one hundred kilometers or less, So if you're thirty thousand kilometers away, you're definitely not inside the event horizon.

00:40:10
Speaker 1: Okay, so these are pretty small black holes.

00:40:12
Speaker 2: Yeah, but these are the kinds of black holes we've been able to see collide.

00:40:16
Speaker 1: Ooh, all right, so then we're a few tens of thousands of kilometers away from these two black holes smashing into each other exactly.

00:40:23
Speaker 2: And on a human, if you're like thirty fifty thousand kilometers away from two black holes that have like the mass of thirty or fifty times the sun, then you're going to feel what's called a strain of about one millimeter. The strain is how much your body is getting squeezed by the gravitational wave. And this is what we measure also here on Earth with LEGO, we have these innerferometers, these very long laser legs that get squeezed and lengthened as the gravitational wave passes by. The ones here on Earth are so faint that the measure strains of like one times ten to the negative twenty one, which means that like the two mile leg of the inferometer gets shorter by that factor. It's a really really tiny factor.

00:41:05
Speaker 1: But unless how much like space is being stretched or compressed, right, Like, not necessarily something in space, right, because it's something in space is sort of holing on to itself. But you're talking about the stretching of space itself.

00:41:20
Speaker 2: Yeah, the changing of the distance between two particles. For example, So imagine you have two particles and you're a few tens of thousands of kilometers away from these black holes that are e merging, and they're generating gravitational waves. What's going to happen is they're going to change the distance between the two atoms. Right, So, for example, that the distance gets longer than those two atoms, if they were like bound together somehow, then they're going to feel an attractive force to pull them back to where they were in equilibrium. If the gravitational wave is very slow, they're going to be able to basically stain in equilibrium and nothing really happens. But if the gravitational frequency is high, if the sort of squeezing and pulling and pushing is fast, they'll effectively feel a force and they might start to oscillate back and forth. That's kind of what happens in Lego.

00:42:07
Speaker 1: Like the stretching of space is kind of like how much space wants to stretch you.

00:42:13
Speaker 2: Yeah, the distance between those two particles or the two mirrors in Lego gets longer or shorter based on the gravitational wave. But then the interaction between the two particles, or the structural strength of the thing, whatever, has a natural length that it wants to be at, so to try to return to that natural length. Like if you imagine a spring between these two particles, you pull them apart, well, the spring is going to pull them back.

00:42:35
Speaker 1: Together, right, So then you're saying, like, if I'm a few tens of thousands of kilometers from these black holes, and I would feel about a one millimeter stretch in my body, or space would want to stretch my body about one millimeter mm hmm.

00:42:47
Speaker 2: And based on the frequency, you're going to get shaken by one millimeter. It's not like you just get pulled by one millimeter in one direction and then you stay there. A gravitational wave is a wave. It's oscillating, and depending on the frequency, if it's like a fast wave or a slow wave, it's going to shake you at that speed, so it might like pull you in one direction and then squeeze you in that direction and pull you in the other direction. So there's this pulling, the stretching, and the squeezing. So right now we're talking about the amplitude about one millimeter, but the frequency of that is also important, and that depends on the orbits of these black holes. How many times are they passing around each other. That determines the frequency of this gravitational wave. If you're nearby these black holes, you're basically going to get shaken from the inside.

00:43:31
Speaker 1: Right, And you're saying kind of depending on the frequency, it might be dangerous or not. Like if it was shaking really slowly, you probably your body can probably adjust to that shaking. But if it's shaking super fast, then it might scramble your insides.

00:43:46
Speaker 2: You might scramble your insides. You might also experience it in a weird way, like it might be like being at a concert. Sound waves at a concert also shake your body and you experience them as sound. If you're out in space near two black holes, you might literally hear the gravitational waves because like the drums in your ear will get shaken.

00:44:08
Speaker 1: Whoa as put everything else in your body.

00:44:11
Speaker 2: As would everything else, Just like at a concert. Right when you're in the moshpit at that concert, your toes are getting shaken, even though your ears are the only ones actually transmitting sound to your brain. The same way a gravitational wave can be squeezing and pulling on your whole body, but your ears might be the only ones picking it up.

00:44:27
Speaker 1: I've never been in a moshpit, but I'll take your word for it, so you might feel it. But is it dangerous? Like if it's high frequency enough, and these things are pretty high frequency by the time they smash together, it's like super high frequency, right.

00:44:41
Speaker 2: Yeah, they can get to be very high frequency. And actually the frequency they experience is even higher than we observe because there's gravitational time dilation. These black holes, of course have super high curvature, and now one black hole is near another one, it's experiencing the gravitational time dilation of that black hole, so time is super slowed down. So what we're observing is the slow down gravitational wave being emitted by these event horizons. That's already taken into account. If it wasn't, then the frequency would be much much higher.

00:45:15
Speaker 1: Well, I guess from what we know of these smashing black holes or the ones we've seen, then the frequency we've seen, and how fast there actually are closer to the source, would they actually kill you at this distance? Like at some point they'll start to rip apart the bonds between the proteins in your body, right, or you know, it'll basically scramble your brain.

00:45:37
Speaker 2: I don't think I can say. It depends a lot on the internal biological friction, like how much energy is actually going to get absorbed, and how squishy your body is, how resilient it is, depends a lot on the exact kind of tissue. I think all I can do is treat your body as a sphere with ears and say you'll probably hear it happening.

00:45:58
Speaker 1: But you can probably make that calculation, right, Like you can calculate this spignification point of a black hole, right, like the point at which it would actually tear you apart falling into a black hole. You can probably do that for gravitational wave, right.

00:46:10
Speaker 2: Yeah, But the energy that gets absorbed depends on this internal friction. Like if there's no internal friction to your object, it can get squeezed and squished and then be totally unharmed. So how much energy is deposited, how much damage is done depends entirely on the internal friction of that object. It's not just dependent on the tidal forces.

00:46:31
Speaker 1: Right right, But I imagine, I mean, we don't have to do it now, or there's no pressure for you to come up with an answer. But like, if you could make the calculation for like a typical brain, what are some of the maximum accelerations a brain can withstand before it turns into you know, mush, and you can maybe backtrack to find what kind of frequency of gravitation waves would kill you.

00:46:51
Speaker 2: Yeah, probably somebody who knows something about the brain could figure that out.

00:46:56
Speaker 1: What do we know about brains? We just use them.

00:46:59
Speaker 2: I'm going to guess the answer is it depends, and we don't know exactly.

00:47:03
Speaker 1: You read my brain. That's exactly what I was.

00:47:06
Speaker 2: Thinking, exactly. I just got a gravitational wave idea into my brain.

00:47:10
Speaker 1: But again, I feel like this is just firm standing tens of thousands of kilometers away. May you say, maybe we might survive this. I don't know, because don't these things go pretty high frequency? Even a one millimeter strain might be enough to mois your brain.

00:47:24
Speaker 2: One milimeter strain is pretty big, so I think it might be enough. I mean, I think one millimeter strain is much more than you ever experienced at a concert. Even very very high intensity sound waves don't actually like move the molecules in your body by a millimeter. That's a pretty huge displacement. And you've got lots of really sensitive things inside your body that are much smaller than one millimeter, So one millimeters squeezing and stretching could totally destroy like really sensitive little biomachineries.

00:47:52
Speaker 1: So smash bit, not moshpit, like your brain gets washed.

00:47:59
Speaker 2: Yeah, I think it might be like being in a blender.

00:48:02
Speaker 1: Great, then I imagine if you get closer to these circling black holes and it just gets more dangerous, right, because then the waves could get much more intense.

00:48:12
Speaker 2: Exactly, the amplitude of the waves just grows as you get closer. The strain gets larger and larger.

00:48:17
Speaker 1: What if you're just a thousand kilometers away, how big would the strain be.

00:48:21
Speaker 2: Well, it goes like one over r a little, which is a little bit weird, And so a thousand million three times closer would be thirty times if you're like thirty or ten times closer. If you're ten times closer, it's going to be ten times as.

00:48:35
Speaker 1: Strong, times times ten to the three. No, I mean a q because because your are went down a tenth, So then doesn't the intensity go up by a queue?

00:48:46
Speaker 2: The strain goes like one over r oh linear? You sure it's inverse linear? Yeah?

00:48:51
Speaker 1: Oh, it's linear, all right, So then you would experience it a one centimeter strain.

00:48:56
Speaker 2: Yeah, ten times closer you get one centimeter strain.

00:48:58
Speaker 1: Oh wait, yeah, that would be a lot.

00:49:02
Speaker 2: That would definitely be a lot. CLI's asking how would it feel to get hit by a gravitational wave? Would your organs be damaged? It depends a lot on the distance you get close enough, it could definitely scramble you. You get not too close, then you could probably hear it, like physically hear it without being destroyed. But I don't know exactly where that line is, and I don't recommend you figure it out.

00:49:24
Speaker 4: Mmmm.

00:49:25
Speaker 1: That's right. Keep it a thought experiment, Keep it a brain experiment to save your brain. All right. Well, I think that answers all of our questions. Some pretty interesting ideas here. Overall, the picture is that the universe is still mysterious. There's a lot we don't know, and there's still a lot of questions we can ask about it for us to explore.

00:49:45
Speaker 2: But we love that you ask these questions, and we love trying our best to answer them. We don't always know the answer. That's sort of the game of physics, figuring out where the edge of knowledge is and trying to push it forward a tiny little.

00:49:56
Speaker 1: Bit at least. That's one of the games one Daniel can play.

00:50:00
Speaker 2: What can we figure out if we have even more Daniels.

00:50:04
Speaker 1: All right, well, we hope you enjoyed that. Thanks for joining us. See you next time.

00:50:14
Speaker 2: For more science and curiosity, come find us on social media where we answer questions and post videos. We're on Twitter, Discorg, Insta, and now TikTok. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.