Daniel and Jorge Explain the UniverseListener Questions 54: String cosmology, cosmic strings, and alien numbers
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Hey Daniel, I have a new idea for how to solve quantum gravity.
Oh my gosh, I'm so excited. I can't wait to hear you.
Okay, just take any everyday object and add the word theory to the end of it.
What that's it?
Like?
How did that work?
You know? Like string theory or loop theory. Boom, I've solved quantum gravity.
Those are already theories of quantum gravity.
Okay, there are other objects we can use, like table theory or rug theory or Pokemon theory boom. Anyone can be a quantum gravity physicist.
Oh, I wish that's all there was to it.
Wait, there's more.
Physics isn't just about naming things, man, though, that is the hardest part.
Hi am Forehammer, cartoonist and the author of Oliver's Great Big Universe.
Hi. I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I hope that i'm around when quantum gravity gets figured out.
Well, that's a mass of wish. It's a little bit heavy on the responsibility for a theorists.
I just want to be around so that I can hear what name you give it.
It feels a little lazy if you You're like I wish that somebody else would solve this problem for me. Why did you just get down to it, Daniel and solve it yourself.
Not my job, man, not my job. I'm an experimentalist.
I know you're a physicist.
There are different flavors of physicists, you know. And I'm an experimentalist. I go out and discover weird stuff nobody can explain, and theorists job is to come up with ways to explain it.
I feel like you're letting these imaginary or artificial boundaries get in the way of your true dreams. Daniel, Like, imagine if a serious said, oh man, I wish I was an experimental physicist and could press buttons and stuff. What didn't you just be like, just press the button.
No, No, you're right, those boundaries are artificial. Here in my department we have a theoretical physicist who's now running his whole experiment, and last year I wrote quite a few theory papers. So you're right, I'm cowering behind categories.
This could be you, Daniel. Just make up a theory and you can call yourself a theorist. Isn't that how it works?
Yeah? Podcast Theory of Physics d.
Yeah, Like what's the minimum Like in your department, is there a minimum number of theories you have to come up with to be a theorist or number of publications one?
Just one? There? You have to do it once.
That you can be a theorizer today in this podcast, what's your theory of everything? Daniel M Yeah.
I think it's the chocolate theory of everything.
It's a dark theory or is it a white theory?
I hope it's not a white theory. Oh my gosh, I'd be so disappointed in the universe.
Turns out white chocolate is the secret to everything, and so you can just check.
Out sweet and bitter at the same time.
No, that's the whole point of white chocolate. It's not bitter. It's sweet for everybody.
White chocolate sweet.
But I would be bitter, just you, Okay, But anyways, welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which we do our best to understand this sweet, sweet universe without getting bitter about our favorite theories. We hope that everything that's out there in the universe, the tiny particles, the huge black holes, the swirling oceans of magma, all of those things can be explained, can be understood, and we try to talk about all of them here on the podcast, where our goal is to fit all of those theories into your brain.
That's right, because it is a sweet universe. It's also a sour universe, a bitter universe, and assault the universe and a umammy universe. It's got all the flavors of mysteries and unknowns and questions that we can ask of it, and here on the podcast we sometimes try to answer those questions.
That's right, like string theory can explain the fundamental forces, but can it explain why people drink boba.
Because it tastes sweet? I guess it's not bitter, doesn't have a mommy. I don't think it's truly and delicious. I mean, what's not to like? Isn't that the whole point of the universe to be chewy and delicious?
What's not to like the feeling of choking as you're trying to enjoy a beverage.
I keep saying this time, but I feel like you're not drinking boba correctly. Give me. Somebody needs to show you the true theory of boba drinking.
No, I know how to drink boba. You take the boba, you throw it in the trash, you move on with your life. Then you're dead.
That's not technically drinking, Daniel. Maybe maybe that's why you're not a theorist. You don't know how to formerly theories.
I'm generalizing drink. I have a new theory of drinking. Teach me, teach me a wise one.
I'm not sure how we got to Boba's but anyways, it is a wonderful universe, full of interesting mysteries and lots of interesting questions that you can ask of it, and that anyone can ask of it, even our listeners.
Because science is not just about satisfying the curiosity of people who are paid to come up with theories or to do experiments or too fuzz those boundaries, but everybody out there, it's powered by human curiosity. It is fundamental desire to understand the nature of the universe we live in, to make it makes sense. And so we encourage everybody out there to ask questions about how the universe works, try to fit all those various pieces together into their mind, and when they don't make sense, to write to us to questions at Daniel and Jorgey dot com, where every question gets an answer.
That's right. Everybody has answers, and it seems like the more you learn about the universe, the more questions you have of it. And sometimes on this podcast we like to answer some of those questions.
That's right. If you send me a question and I think, hm, I bet a lot of people want to hear the answer to that one, then we'll play for everybody on the podcast and even answer it.
So to the on the podcast, we'll be tackling listener questions number fifty four. Is this like the Studio fifty four version? Are we going to rock out and do a lot of drugs?
I hope you're wearing something appropriate?
Oh yeah, yeah, yeah, No, I'm always fashionable, Daniel. You don't even have to ask.
Do you have your Studio fifty four pajamas on? Right now?
I got my Studio fifty four cargo pants on and my Studio fifty four on? And what else do you need?
Hmm? It sounds like you're kind of dressed the way you normally are.
Yeah. I live in the eighties. I live the glabor life of the eighties every day shooting we all.
You found the perfect uniform and you're sticking with it.
They stopped changing closing the eighties.
Yes, and now you literally couldn't get them off once.
I like something there's no need to change in right.
That's right. And what I like are hearing questions from listeners wondering what people out there do and do not understand about our universe. Sometimes people hear something on the podcast that doesn't make sense to them, then they write to me or they read some other crazy article that doesn't quite fit in their brain, or they're just thinking deeply about the universe. Thanks everybody who writes in with your questions.
Yeah, and so today we have three awesome questions from listeners. We have questions here about string theory, cosmic strings, and something that is not strings, but maybe aliens?
Are you saying aliens couldn't be made of strings?
Why do you want to string the listener along here and pretend that there's a connection between all of these questions.
We'll find it. We'll find the connection.
I'm sure there are aliens. They use strings. I mean they have to wear clothes. I guess maybe do they? And for that they need strings?
Right? I don't know? Yeah?
Yeah, Well let's jump right into Daniel. Our first question comes from Bruce and he has a question about string theory in the Big Bang.
Hello Daniel and Joy. Bruce labastered here from Lendham, Saskatchewan, Canada. I was just wondering about string theory and the Big Bang? Is there any series around string theory and the Big Bank? If I understand correctly, the specific vibration of the strings creates specific particles. I'm thinking on the frequency of the strings that are everywhere changing to suddenly create the universe, and the particles sort of like they decayed down to the right energy level to create particles. Once again, you guys are awesome. Everything you do is great, and I look forward to your answer.
All right. This feels like taking two big questions and smushing them into one ginormous question or a little tiny question, depending on your perspective.
No, I think it's a really cool question. It's trying to understand whether string theory gives us an idea of where the universe comes from and how we all ended up where we are hating or loving Buba.
Boy, you really have it against What did Bolba do to you? Diana? Did it actually try to choke you?
Yes? The first time I had Boba I almost choked on one. Yes, absolutely, and I will never forgive it.
Well, it sounds more like the user error here than a fault of the product, to be.
Honre fair, fair. You know we're talking about quantum gravity. In last episode we had about it, we interviewed Nathan who likes Boba even though his dad hates it, So that was just running through my mind.
I see, I see, it's really stuck on your head. But there's a connection, right the Big Bang in Boba. It's a little like fuzzy ball right at some point.
Yes, it's dark, mysterious and kind of dangerous.
And you can string Boba's long into to make a Boba pearl necklace.
Boba's got two bes in it, just like the Big Bang. I think Boba's one word, Mmmm, it's got two b's in it.
Though, I see this word has two bees, just like these two other two words have two bees. Got it? Got it exactly?
Okay, connections here, Bruce is asking actually a deep question about the nature of the universe. He wants to know basically what happened before the earliest time that we can understand.
Yeah, And I think he's specifically asking whether, like what's the connection between string theory and the origin of the universe. Like we know about the Bang, and we there's a theory called string theory. How does string theory a factor into the Big Bang? Or what does it say about the Big Bang?
Yeah, string theory, like all theories of quantum gravity, basically pick up where the Big Bang leaves off. And there's a common misconception about the Big Bang. People think of the Big Bang as the universe starting from a single point and all that stuff then exploding out through space. But modern conception of the Big Bang doesn't talk about the actual very beginning of the universe. It says, the universe right now is kind of cold and old, it's very dilute, but we know it's expanding. And so if you wind the clock backwards, what happens if you unexpand the universe gets denser, things get closer together. It also gets hotter, and at some point it gets so hot and so dense that our current theories we don't think they'll work anymore. Because we have theories of general relativity that describes gravity in space and time, and we have theories of quantum mechanics that describes particles and all that fuzziness and uncertainty. And at some point, when the universe gets dense enough, then both of those theories come into play, and we don't know how to fit those together. For that, we need a theory of quantum gravity. So the Big Bang takes us back to some very hot, dense state that's like the limit of our understanding, but doesn't actually say what came before that. Quantum gravity tries to explain what happens when things get that hot and dense, and so it might give you some insight as to what came before the moment that we can describe up to the Big Bang.
I wonder if there's a sort of like a distinction you can make between these theories, like is string theory or maybe just generally quantum theory a theory of matter, and maybe general relativity is more of a theory about space and time.
General relativity is definitely about space and time, but it's also about matter and energy because it's about how all those things interact with each other. String theory is really a unified theory because it involves gravity, it also involves the other forces, like quantum mechanics can describe electromagnetism and the weak force and the strong force in terms of quantum mechanical objects, these quantum fields and ripples passing through them. General relativity can't explain any of that stuff, but string theory can reproduce general relativity and the quantum theory, so it really is a union of these two things. It explains all of it together.
So string theory has things like this, the bending of space and the slowing down of time all that is baked into the theory or did it just sort of like absorb general relativity.
Yeah, that's a great question. One issue with string theory is that there's a lot of string theories. Like if you start putting these things together and saying, look, the universe is made out of these tiny vibrating strings that vibrate in many dimensions more than the ones that we see, you get lots of different possible ways for those string theories to build a universe. And we know that some of those correspond to the universe that we live in. We don't know how many of them and why this one. There's a whole big question there about like why there are so many string theories. But it is possible in some versions of string theory to reproduce general relativity and quantum mechanics, and so that lets you go back further in time than our current theories, back to where the universe was so hot and so dense that you need that theory of quantum gravity.
So string theory does gerald relativity and quantum theory, but it's sort of not proven, right, It's just a sort of a theory, but it hasn't been confirmed yet.
It has definitely not been confirmed. It only describes things that we cannot yet test. We can't create those conditions higher than the Plank temperature, essentially in order to test quantum gravity. Really yet, we had a whole episode about whether you could test quantum gravity with like tabletop experiments. There's some clever ideas there, but currently string theory is just a theory of quantum gravity. It's still got some mathematical issues. Also, we can't describe like dark energy and the expansion very well. But it does give you a cool picture of how the universe might work if it's correct.
Well, okay, so then it can do both things. Then what does it say about the Big Bang?
It says something pretty cool. Actually, it tells you that the universe can't compress beyond a certain point, like there's a minimum size to these strings. General relativity has no problem compressing the universe infinitely until every part of space is infinitely dense. But when you fold the quantum nature of these strings in, it says, look, everything in the universe has made it these vibrating strings, and they have like a minimum size. That tells you the universe could never have gotten denser than a certain level.
Wait, is that what it says or does it say that you can't have things that are smaller than that? But could the universe be smaller than the things it can have?
Ooh wow, that's a debilosophical question. So first of all, we're not talking about the size of the universe. We're talking about density, right, We're talking about the whole universe, which could be infinite anyway, and could have always been infinite and could always be infinite. We talked about changing from high density in the early universe to low density now, so it's really more about density than size. But on your question, I do think the universe has to be at least as big as the stuff in it.
Why can it be compressed more than the things that it can have in it, Like, for example, my car can be compressed smaller than what I can fit in it.
In order something to be in the universe, it has to have a location in the universe, which means the distance from one side of it to the other side of it has to exist, so that space exists, and so that's part of the universe. So therefore the universe has to be at least as big as the stuff in it.
Why can't it be smaller or more dense? Just like why can't my car be smaller than me?
Well, if your car was smaller than you, you couldn't get in it.
Yeah, but it'd still be a car. Like I could take my car and scrunch it down to the size of a basketball, still be my car. I just couldn't fit in it. But it doesn't mean that it's not my car.
That's true. But the universe contains everything that's in the universe. So if you're in the universe, the universe is at least as big as you are. Even if your car has shrunk smaller than you are, right.
Well, it could still have me in it. I would just be squeeced through a bulb.
I see. Well, the thing a quantum strings is they think that there really is a minimum size there, like a quant mechanical minimum beyond which you cannot shrink them. If you add another feature of quantum mechanics, which is time reversibility, that all the laws of physics seem to go equally well backwards and forwards in time, it naturally brings you to a bounce scenario where the universe infinitely far back in time may have been infinitely dilute, and then it gradually gathered together towards a hotter, denser state, and then when it reached the maximum density, it basically bounced back, expanding out again, and then then expanding out again and creating our universe.
They called it the big bounce, right.
Yeah, that's like the big bounce. The big bounce comes in lots of different varieties, but some versions of string theory are very nicely compatible with this kind of big bounce, and it gives you a reason for the bounce. Right, Why didn't the universe just keep compressing until infinite density and go on and on and on the answer is strings pushed back, strings of a minimum length, which means a maximum density, and that is where the bounce comes from.
Does that mean that the era of time continues beyond the Big Bang?
Yeah, it means that that earliest moment that we can describe with our current theories, that's what we typically describe as the Big Bang. We could extrapolate back further to some higher density, but not infinite density, and then even back through that to when the universe is doing the inverse big bang.
WHOA, and was that universe kind of like a mirror image of our universe just running backwards in time, or is it a totally different universe?
We think you should have the same laws of physics because it's built out of the same basic strings. But yes, it's running backwards through time if you're thinking about it in that direction. Really the way to think about it is to start deep in the infinite past, running forwards in time as that universe is compressing. So that'd be a very different universe to live in because that universe wouldn't be expanding like ours is. It would be shrinking.
And would it have the same things like dark energy, which is in our side of the universe mirror expanding the universe. Wouldn't it also have dark energy expanding it?
Well, string theory can't always accommodate or explain dark energy, so that part is still a bit of aqu western mark where that comes from, where that shrinking and then expansion comes from originally, So that's still something to be figured out. As you can tell, this is all a little bit sketchy because string theory itself has so many varieties that there's like a thousand different directions people are exploring it in and so if you read up on like string cosmology, you'll see this scenario, but also like five hundred other ideas for how strings could explain the Big Bang or what came before it.
Did you just call it extreme cosmology?
String cosmology?
String or extreme?
Yeah? It is pretty extreme.
Also they both sounds pretty exciting. Oh, I say it's string, not extreme chrismology exactly.
But then Bruce is wondering, is it possible for those strings in the very early universe to decay down and create our particles? And the answer is yes, absolutely. If string theory is right, then the universe was much denser than even our quantum field theory of particles can describe a moment when everything was these crazy bouncing strings.
And then those strings became quantum particles, and then those quantum particles became us, and then someone became Boba balls, which try to kill Daniel.
Apparently unsuccessfully unsuccessfully.
So far, so far. They'll get you yet, Daniel, They'll sneak up on you.
That's a horror movie, right there. A man being followed by bubba.
That would be scary for like three people, Yeah, including you, I guess.
But it is possible that we could one day know more than just speculate, because these theories do make some predictions. The very early universe, it's expansion and all the dynamics are predicted to leave gravitational waves bouncing around the universe. These are called primordial gravitational waves. If those are there and we can pick them up and measure them, we could learn something. But what happened in that early stage before quantum field theory can describe basically before the Big Bang?
WHOA, so I guess in this version gravitational waves are not made out of particles then.
No, they're not boba particles or anything. They're real ripples in space time. But these would be very, very subtle. There was an experiment a few years ago they claim to have measured primordial gravitational waves, but it turns out they were just measuring dust. It's a hard problem.
All right. Well that's the answer for Bruce. What a strings theory say about the Big Bang? It says that maybe the Big Bang just came from the big bounds, and that from that came quantum particles in quantum things, including quantum theories, extreme theories of the use. That's right, extreme and string both alike. All right, thanks Bruce for that question. Let's get to our second question. This one is about cosmic strings, which has nothing to do with string cosmology at all, like at all, It's a totally different thing, super interesting. So let's get to that question. But first, let's take a quick break.
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Right, we're answering listener questions here today, and our second question is pretty cosmic, dude. It's about cosmic strings, and it comes from Dame.
Hy Daniel and Jorge in articles about the newly discovered big ring megastructure. I've seen cosmic strings mentioned several times as a possible cause if cosmic strings even exist. What happens when one intersects a black hole?
Also?
What happens when normal matter contacts a cosmic string? Is it pulled into the string? Is a cosmic string effectively a black line? Also? Is there a stable orbital path around a string? If so, what would that be? A ring, a spiral, or corkscrew something else? Thanks for any clarification you can provide. I think cosmic strings are really.
Weird, all right, interesting question here, and again, cosmic strings have nothing to do with string theory.
Yeah, it's almost as if the names and physics are just not very well thought out.
A little bit. I mean I've sort of been saying that for five years.
Yeah, I think you put it very well. Cosmic strings have nothing to do with string cosmology. Totally separate questions.
But they could be related, right, Like, for example, string theory could account for cosmic strings.
For example, if string theory is correct, then it accounts for everything. So then yes, cosmic strings are made out of tiny quantum strings.
Okay, it's like a string made out of strings.
Yeah, exactly. Like if string theory is right, then the yard that major sweater is also made out of quantum strings. So you're wearing like a string theory sweater.
Right, right, But we don't know, I guess there. There hasn't been that connection yet. But cosmic strings is something that comes out of just general relativity.
Right, Cosmic strings is an idea that does come out of general relativity, but it's also related to quantum mechanics. It has to do with how the universe is cooling and how the laws of physics and the sort of state of space itself changes and cracks as the universe cools.
Well, all right, well maybe break it down for us. What is a cosmic string?
So cosmic string is like a topological defect in space.
It's a theoretical concept first of all, right, like nobody's seen one. It's just something people think might exist out there.
Yeah, it's just an idea so far. It would be interesting because they're like a boundary. They're like a spot where space behaves differently, not like the laws of physics themselves are different, but it's like faces in a different phase. If you think about the universe from the very initial days, things are hot and dense. You can use a sort of certain set of laws to describe it the same way that you use like the ideal gas law to describe water when it's a gas, and you use fluid dynamics to describe it when it's a fluid, and use like crystal theory describe it when it's a lattice. Things are a different temperature, you have different effective laws that describe them. We think the universe is the same way. And as the universe cools, as things expand and get more dilute, different effective laws take over. And so the universe sort of has different phases.
Phases with a pH right, like phase like solid or liquid.
Yeah, phases, not faces. I don't know if there are any faces in the universe except for the one on Mars. But yeah, we think about phases more generally than just like the phases of matter. Physicists think about them as like regions where your laws of physics are applicable, because there's always boundaries to where your laws work, just like we're talking about how quantum field theory works up to a certain temperature and beyond that it doesn't work anymore. So there's a fa in which you can talk about quantum fields, and beyond that it's sort of nonsense.
And so it is that after the big bang, everything was super hot and things kind of settle down, and like, for example, around us, the universe settled into a particular phase, like a particular set of laws or arrangement of the quantum fields. But maybe next door to us, a few thousand or bazillion light years away, maybe it started settling in a totally different set of laws or phase.
Because as the universe cools, there's a few different ways that it could cool down. It's like a ball rolling down a hill, but that hill has interesting features in it, so maybe it gets stuck on a shelf, or maybe it goes all the way down to the valley.
And is there an infinite number of bases of the universe that the universe can be or is there a like three or four.
Well, we don't really know. It depends on the nature of all those quantum fields. For example, we know that in our portion of the universe we have not settled into like the lowest energy possible state of the universe. Some of the fields that fill space got stuck, like the Higgs field. The Higgs field has a lot of energy in it, and that's why we have mass. And then when things interact with the Higgs fild. There's a lot of energy stored in that field. It hasn't fully relaxed, and we talked about how if it did spontaneously collapse, that would change the nature of physics. It would lead to a new phase essentially of the universe, in which the same fundamental laws might apply. But you know, everything we've learned about atomic physics and chemistry and whatever wouldn't apply. So in our region of the universe, we're in a certain phase, like space is cooled in a certain way. Are there different options? We don't really know, because we don't fully understand the nature of the Higgs field and the other fields that might be out there once for dark matter or dark energy. There's lots of potential fields out there in the universe.
So there might be part of the universe out there beyond the observable universe, right, because as far as we know, the observable universe is the same phase.
Right.
I imagine, as far as we can tell, the same laws of physics do apply everywhere in the observable universe. So yeah, most likely these things would exist past the observable universe.
Then the idea is that maybe beyond the observable universe, there's a in the same universe, there's another phase expanding or growing or settling just like we are, and at some point they have to meet. And if they meet, it's Is it like a big disaster or can both types of universes coexist next to each other?
Well, the theory of cosmic strings is that they can coexist, and then you get this weird boundary, and that's the cosmic string. It's like a crack in space where the laws are different on one side and the other. These can be like two dimensional, like a whole surface where the laws are on different on one side and the other. They could even be like one dimensional. That's where the idea of a cosmic string comes in. These like long, weird cracks in space, but the laws are a little bit different just in that like one femtometer wide cosmic string that could be like ninety billion light years long.
Well, I guess I'm thinking of like bubbles. Like if we're in a bubble and there's a bubble next to us, where the two bubbles meet, you get a wall basically, right, mm hmmm. Is that what we're talking about in terms of the interface between two phase is like it could be a wall. Or sometimes if you get like three bubbles, then you can sort of get a line between the three bubbles. Is that what you mean by a string?
Yeah, here we're talking about a line, and the bubble analogy mostly works.
Okay, let's go with boba. It've got three boba balls.
It's my mental kryptonite. I can't even think now. I'm just worried about choking the whole time.
Get over it, Daniel, it's the new thing.
I can't. I can't. That what roughly works, the boba analogy. But it is possible for space to crack as it's cooling in this sort of uneven way and create these one dimensional ripples in space.
WHOA, what does that mean?
Like?
How can a string have two sides to it?
Right?
Because if you're saying it's the intersection between two universes, like which side is what.
This scenario we have like a cosmic wall give an interface between two portions of three D space. But you can also get space just cooling in this way where you have a line that's a different phase and the rest of space is all the same. So it's like a tube of space that's different than the rest of it.
Oh wait, wait, wait does a cosmic string is more like a cosmic tube?
Yeah, because it's not really one dimensional. It's like one femtometer wide, but very very long, So it's like a cosmic hair or something that's very very long.
Whoa, and inside of that hair is a whole different universe.
Yeah, exactly, And they think they's probably higher energy. The universe hasn't cooled in those places as much. It's like hotter and denser. So these things, if they exist, they are gravitational objects because they're immensely dense. They're basically stuffed filled with original primordial energy. Imagine like a tube of the original hot dense universe that never cooled. It got like stuck at some hot dense statement's still around.
Like it somehow got trapped, right, Is that the idea like maybe like the universe started settling into our kind of universe all around it, and as those things grew, there's a certain amount of primordial energy you got trapped and squeeze into uh, basically a spaghetti.
Yes, exactly, cosmic pasta.
Yeah, that's a better name for it, cosmic city or RIGATONI. I don't know. Oh no, wait, Bugatoni. That's the right, right, right here you go, that would be the right.
Well, not an expert sounds good. All right, So now I think we're finally ready to answer Dane's question.
Oh right, right, what was this question again?
What happens when a cosmic string hits a black hole?
Oh?
Okay, he wants to throw that spaghetti against the wall.
I see, he wants to throw the spaghetti against like a meat ball.
Yeah. And the short answer is, we're not sure because cosmic strings are features of a kind of theory of quantum gravity, because as you hear, they're all about how quantum fields are cooling, but they also involve space. You know, you have energy density deformation of space, and black holes are a feature of general relativity. They don't know how to talk to quantum mechanics, and so we're not exactly sure what would happen because we don't really have a full theory of quantum gravity that would explain Lane how quantum fields behave near a black hole.
Well, I guess the question are they both even compatible? Like, does the theory that predict cosmic strings also predict black holes or are they sort of mutually exclusive?
Now in the theory where you have cosmic strings, you also are allowed to have black holes. Yes, we don't know if cosmic strings are real. We could look for them with gravitational lensing gravitational waves of their own, because we think they're dynamic. They can like wiggle and whip around and stuff, but of course we've never seen one.
Well, technically we don't even know if black holes are real.
Yeah, technically that's true. There are some very compact massive objects, but we don't know if they actually are general relativistic black holes or something else.
All right, well, then what would happen if you have this crack, this spaghetti of super primorial energy hitting a black hole. Wouldn't the black hole just win?
Probably that's what would happen, because black holes always win. I mean they are event horizons. So cosmic strings and the cosmic string is just like a tube of super high energy density, and so it probably just gets slurped up and make it like a really monster black hole.
Or could the string maybe like slice the black hole apart? Is that a possibility? Like it? Because these strings aren't just sitting out there, they're also bending space and time around them, right, Like they're super extreme I think we've talked about maybe like doing a lub around one of these and going back in time and things like that. Couldn't one of these strings just kind of like disrupt the black hole.
There's one way to theoretically go back in time, which involves doing orbits around an infinite string of cosmic dust. But that's a different kind of string. That's a third kind of string. But could cosmic strings slice a black hole in half? I don't think so, because cosmic strings are just energy density. Although there are energy density where the rules of the universe are in a different phase, those quantum fields are still very, very high, but there's something about them that's preserving that there's like a crack in space itself, is an interface there that's keeping this from just like diffusing out into space, And so the rules are a little bit different. But my money would be on the cosmic string getting gobbled by the black hole. You never bet against the black hole.
But a cosmic string, isn't it super long? So would it just get split in half or what would happen? Or would it get disrupted by the black hole and then rejoin up again?
They can be super duper long, like maybe one hundred billion light years. But if a black hole hits the middle of it, it would just start slurping it from both sides. It's like if you eat a piece of spaghetti from the middle and you can just slurp both ends in.
Oh, cosmic string is a thing like you can move?
Yes, yeah, they can whip around and slide through space absolutely, and make gravitational waves, which is how we might one day be able to detect them.
It would slur bit interesting. But isn't it like a feature of space?
Yes, but everything's a feature of space. You're a feature of space. I'm a feature of space, right.
Like I guess I mean, like, would it get slurred by the black hole?
Like?
Can it move through space? If it's a feature of space.
You can move through space the same way that we can. Right, We're just like our energy slides through the quantum fields that fill all of space. Cosmic strings can also moved, so it's sort of like persistent in that way. They don't just diffuse out into nothing. They persist and move through space, keeping their structure.
All right, So then I guess that answers Dane's question that your best guess is that the black hole wins. It slurps up the cosmic string like a string of bugatoni pasta.
That's right, because as dense as the cosmic string is, it's not dense enough to make its own black hole. So it's probably less dense than the black hole, and that's why the black hole wins. And even if the cosmic string was dense enough to make like a black line of singularities, that would also just be a black hole. And black hole plus black hole means black.
Hole, it would be a black line or black pasta.
Squid pasta cosmic squid pasta.
There you go, a new recipe for the universe. All right, well, thank you Dane for that question. Now let's get to our third question, and this one is about Daniel's favorite topic, aliens and also nano things, and so let's get to that question. But first let's take a quick break.
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All right, we're answering listening to questions here today, and our last question of the day comes from I'll be.
Hi, Daniel and Jorge. In trying to communicate with extraterrestrials, we need to demonstrate that our signals are intelligent. We can't broadcast say the speed of light or the ground energy of hydrogen using our preferred units like meters per second or electron volts, because who's to say that et doesn't measure speeds in quad lutes per Now? Now, how do we then demonstrate in a unit free or natural way that we know stuff?
All right? Interesting question? I feel like this is a question about how to talk to aliens.
Yeah, basically, how do we convince aliens that we're smart, that we're here. How do you can send a message to aliens that when they read it they're like, oh yeah, those guys know what they're doing, or there are even people out there.
Like how do we pass the test? Like, if you want to talk math to aliens? I think obvious question is like what sort of units would you use if you can? Are there like units that they would recognize?
Yeah, it's a really cool question. There's a couple directions go with this, like could you come up with numbers that don't need units? Are there physical numbers in the universe that are unitless? Because he's right, units are things we made up, you know, Like the speed of light is three times ten of the eight meters per second. But that number three times ten of eight is only that number because of the length of a meter in the length of a second. If you change that to something else, the speak of light would be a different numbers. You can't just send that number without explaining whe the units are. The units are just something we invented.
Right yeah, And I think we don't even know exactly what a meter is or it's like it's a little bit somewhat arbitrary or changeable.
It used to be that a meter was the length of some platinum rod in Paris, but then people finally realized that's ridiculous because Paris has different weather, and so the rod gets longer and shorter, and we all get like taller and shorter as that happens. Now they fine the meter in terms of the speed of light, how far light goes in a certain amount of time.
Even a unit of time are oursho arbitrary, right, Like a second which is one sixty eight of a minute and sixty of an hour and twenty fourth of a day. That's arbitrary, right, like we could have twenty four hours in a day.
The units of time are arbitrary. You're absolutely right. We just made them up. But they are also physical. Like we define the second in terms of oscillations of an atom, and when atom oscillates a certain number of times, we call that a second. That's a new definition of a second. So one approach to making something universal is to say, let's just get rid of units altogether, and we can talk about that. The other approach is to make the units physicals and say, like, look, here's a very natural choice for a clock. Let's use that as our definition of time and hope the aliens follow along. That's actually what Carl Saign tried to do on the Pioneer plaque, this plaque that went on the Pioneer probe and was sent out into deep space and is right now zooming out towards aliens.
Yeah. I think that was in that movie Contact too, wasn't They Like they use the hydrogen atom as a sort of like baseline, and you make a drawing of the hydrogen atom and hopefully the aliens will be like, oh, that's the hydrogen atom, and from there you can kind of figure out units of time and length.
Yeah, exactly. There's a spin flip transition. The electron has a certain spin. It can sometimes flip from one spin to the other spin, and it's very well known time from a very basic thing, and the universe. Hydrogen is like most of the universe. So if you can somehow describe hydrogen and describe this spin flip and communicate to the aliens like, look, can we all agree that this is a basic unit of time, then you can start to talk about things that take time, and then you can use like the speed of light. The speed of light helps you relate meters and seconds, right, relates distance and time, and so from there you could build up what you imagine would be maybe a universal set of units, one at least other science minded aliens might understand.
Right, And that doesn't depend on the conditions of the hydrogen. Like if you hot hydrogen and cold hydrogen, they all have the same timing.
This is for an electron in the lowest state. But you know that's pretty common and we think anybody who studies hydrogen is going to understand this transition. It's pretty well known. But you know, there are a lot of assumptions there, like that the aliens are doing science that they stand we're talking about hydrogen, that they think about time the same way we do. There's a lot of things built into that, right, right.
But I think you were saying that, like units is maybe not the biggest of our problems in communicating with aliens.
You could even get rid of units, and you could say, look, are there numbers in the universe that don't have units? And there are absolutely, Like in our theories of physics, there are numbers that define the theory that if you change those numbers you get a different description in the universe. And those numbers don't have any units to them, like, they're just pure numbers. And so if you wanted to communicate to aliens that were also doing physics the way we were, then you might want to communicate those numbers. And an example is like the cosmological constant, which we think is what's controlling the expansion of the universe. That's a number we can measure it. It doesn't have any units.
It doesn't have any units because it's like a ratio of something, right.
Like any number that doesn't have units, you can calculate them from ratios, but most naturally they're just numbers, you know. Like other examples of things are like the coupling of particles to other particles. These are just numbers that go in our quantum field theory. They don't have units to them. Like every particle that gets mass from the Higgs, there's a number associated with that particle and it controls how much mass that particle gets. That's just a number. Like the top quark has a number, the bottom pork as a number, the electron has a number. It's just a pure number with no units whatsoever.
Is it kind of like pi, which is, you know, like a feature of geometry.
Hmm.
That's another great example. You could use the number of spatial dimensions. That's a pure number that describes our understanding of the geometry of the universe. Pie is another great one because pie is a ratio that works in flat space, or like if you live in curved space, the ratio between the radius and the circumference of a circle actually isn't pie. So there are these numbers that are special that are important to the understanding of the universe that don't have any units at all. You could try to communicate those. But even still, as you were saying, you have a problem, like how do you communicate numbers to a bunch of aliens, Well.
I would imagine maybe you like use one finger for one, Like, if they are aliens living in the universe, they're probably familiar with the concept of a unit, right like one, two, three, and then you build up a number system from that, right.
I think Abby was not talking about aliens that have arrived here on Earth that we're interacting with, and you can, you know, point two apples and say one apple, two apples, three apples, But communicating with extraterrestrials like broadcasting a message the way that we have done in the way that like the pioneer Plaqua is like, how do you build this in and send it out to the universe so you can be understood without us, so that somebody out there getting that message would be like, oh look there's smart people over there.
M Like, how do you basically communicate in more quote kind of.
M Yeah, how do you encode a signal? So if you're sending radio waves to the universe, how do you modulate the frequency or the pulses or whatever to send a message that indicates, Look, we're smart physics people over here. They don't know how to name anything, but we are making some progress and understanding the universe.
Wasn't that in the movie Contact Too? I feel like we're referencing this movie a lot, But wasn't that part of the signal we got from aliens, Like there was a certain number of pulses and the number of pulses followed the digits of pie or something like that.
Yeah. Absolutely, And you're touching on the core issue, which is in the end, any message you send is symbols like pulses or digits or wiggles or whatever. They only represent the pure idea. There's a connection between the idea in your head and the idea in these symbols. But the symbols themselves are actually kind of arbitrary. You come up with lots of different ways to encode the same idea in order to decode it. To look at the symbols and have the idea in your mind, you need to have some commonality. You need to have some frame of reference to say, oh, maybe this is how they're doing it. Which is why it's so challenging to look at the sky and understand whether there are signals from aliens because there's so many different ways they could encode it or represent it. We might just be totally missing it.
Well, I feel like all these questions has maybe two dimensions to it, Like one is, how do we just demonstrate that we're smart and that we know stuff about the universe? And the other one is like, how do you actually like have a conversation about physics with an alien? Like if you just wanted to demonstrate, like, hey, we know math and we know things about the universe, like you could just send the digits of pie as pulses, and somebody would have to interpret that as saying, wait, this is not a random sequence of pulses. This is a secreence of pulses that followed the digits of pie.
But you'd also have to figure out how to encode digits, Like how do you represent different digits in terms of pulses? That right, there is an encoding scheme, and that's going to be cultural, that's going to be symbolic, that's going to be fundamentally arbitrary. So you have to do it in a way that you think they could reverse engineer.
Oh, I see what you're saying. Because you're saying, like the digits of pie assumes a base of ten, maybe the aliens are doing base of fifty.
Yeah, so how do you send them number four? Right? Did you break it down into binary? All right? But you know you're assuming that they understand that that they know what a one is in a zero and all this stuff.
Well, if you send four pulses, wouldn't that be four in any number system?
Yeah, if you're counting the pulses and that's the way you're representing it. You're talking about like a unary number system, you know, where you just have like one digit, and that's cool, But then they have to know to interpret your message that way that it doesn't mean something totally different. Right. If you know that what system somebody is using, it's not so hard to decode their message. But if you have no idea, then you don't know. We actually talked to a philosopher on the podcast like a year ago who argue that it's probably impossible without any cultural context to know for sure what aliens are saying. You might get a message and decode it and you don't have no idea what they're trying to say, So you have no idea whether you've done it right. You could be lucky and be like, oh my gosh, I'm guessing this encoding and it turns out to give me all the digits a pie. That must be right. That would be a cool experience. You essentially have to randomly guess how they're encoding their message, or in reverse, they would have to guess.
Yeah, because I guess even three, one, four, one, whatever the digits of pie. That's only those numbers. If you're using the same base ten system that we do, right, like PI in binary is totally different.
Yeah, exactly, all right, So.
Then what's the answer for albi It's hopeless, forget about it.
The answer is that it's not hopeless if we have a lot in common with the aliens. I mean, if there are human like aliens doing human like science and a human like way, then we can just send them a text basically and they'll get it and understand it.
They'd be like, who this new number?
Yeah. The more we have in common with them, the easier it is for them to understand us and for us to understand them. The real question is how much in common do we have with them. The most interesting aliens are the ones that have the least in common with us, that have like evolved in some weird situation or doing science in some totally different way, using not even using mathematics or something. Those would be the ones we could learn the most from about the universe. But those would also probably be the ones it's hardest to make contact with because they have different fundamental assumptions about how to communicate and what encoding systems work and whether they even use language. You know.
Well, I mean that's sort of maybe according to you. Maybe somebody else might argue that those are the least useful aliens to talk to, Like, maybe the more useful aliens to talk to might be the ones that we do have things in common with.
Yeah, the ones we have most in common with will definitely have fun stuff to talk about. That philosophy we talked to about that scenario said you have to be careful though, because almost anything you say could be interpreted as aggression, and the aliens could launch a first strike. So the best thing to do in that scenario is not to talk to aliens.
Oh boy, I feel like now you're getting into like cosmic paranoia and the whole like, you know, the three body problem, the creatures in the forest scenario.
Yeah, it's a real concern, which.
Sounds like a whole different thing. Yeah, which maybe goes outside of all they's questions.
That's true. Yeah, maybe Abby is not being responsible and just thinking I'm going to broadcast messages to aliens and I don't care if they want to kill us or not. But in that scenario where you don't worry about deathly aliens, then you should try lots of different schemes. You should talk to people from different cultures and have different ways of encoding it and representing it, hoping that one of them will overlap with the aliens. I think the best shot is to use numbers without units, because those are the ones that are the most universal, we think, at.
Least, like we talked about it. I mean, if they don't have units, you don't know if they're you're using the same base numbers, right.
Yeah, No, absolutely, there's always going to be a challenge there for how you represent those numbers in your message. But if they think similarly to us, maybe they'll unpuzzle it. You know, if there are smart enough aliens out there, they might figure out how to crack the human code.
Well, I guess I wonder if you could make an argument for like digital being maybe the one with the biggest shot at being universal, Like here, on Earth. We had base ten other bases, but ultimately we had to build computers. We built them out of binary.
Those are sort of most natural for us because they represent this dates of the electronics on which our computers are built. Yeah, aliens could have like quantum computers as their first computing right, you never know, in which case binary doesn't really make sense.
All right, Well, I guess then the answer for Auby is there isn't maybe a good way to do this to broadcast our intelligence, But that maybe doesn't mean that we shouldn't do it.
Right, Yeah, absolutely, we can broadcast things in a way that makes sense to us and hope that somebody out there gets it and here's our message and knows that we were for at least a little while here wondering about the universe and surviving Boba.
Is right, we could be like, we'll just speak English, let everyone else figure it out. It's very American.
That's basically the approach. Yeah.
All right, Well, thanks Auby for asking that question, and thanks to all of our question askers here today. I guess there's no end to human curiosity.
For which we are eternally grateful. So if you are a curious person with questions about the universe, don't be shy and write them to us to questions at Daniel and Horne.
All right, we hope you enjoyed that. Thanks for joining us. See you next time.
For more science and curiosity, come find us on social media where we answer questions and post videos. We're on Twitter, Discord, Instant, 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. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. House US dairy tackling greenhouse gases. Many farms use anaerobic digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you asdairy dot COM's last sustainability to learn more. Vitamin water was born in New York because New Yorkers wanted more flavor to pair with all the amazing food in the city. Vitamin water is so New York.
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