Daniel and Jorge Explain the UniverseListener Questions about aliens, black holes and white holes!
Daniel and Jorge answer questions from listeners like you! Send your questions to questions@danielandjorge.com
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Hey, Daniel, I got a tough question for you.
Oh goodie, that's what I live for, all right.
Well you might regret that, but here it is. Is physics real or pretend?
Boom? Oh my gosh. Wow. I don't even know how to begin to answer that.
What you don't have an answer? You mean it could all just be made up?
Well, you know, physics tries to describe the universe, but it might all just be like a convenient mathematical story in our head.
Yes, math is pretty convenient, I think. I guess my next question is are physicists real or are you also made up?
I'm not sure. I mean, I'm definitely making it up as I go. Well, at least you're keeping it real or pretending to. Hi, am Jorge.
I'm my cartoonist and the co author of Frequently Asked Questions about the Universe.
Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine. Or at least I pretend to be.
Do you have to dress up also like Halloween? Do you have a professor costume you put on every morning?
Yeah, I'm wearing my professor costume right now. He sure, jeans and sandals.
Right right, I guess socks are not part of the costume.
Ever.
No, I believe strongly in the toe liberation movement. Toes should be able to breathe.
You're a big TLM fan activist.
I'm sure how we got started talking about my toes already on the podcast.
Well, toe stands for a theory of everything.
Yes, exactly, And you want to let your theories breathe?
Yeah, so they don't smell, you know, nobody wants a stinky theory.
Hey, I'll take any working theory. I don't care what it smells like.
Oh really, you might regret saying that.
Also, Welcome to the stinky cheese theory of the universe.
We are pretty cheesy, Daniel, but anyways, Welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which we explore the real universe that may actually be out there, all those crazy quantum particles frothing and bubbling and waving and interfering and weaving together to make an incredible experience for me and for you, one chock full of bizarre effects and strange mysteries, mysteries that we hope to be able to unravel with the little brain made up of its own quantum particles, the universe trying to understand itself, and here we are, a tiny little part of the universe trying to explain their rest it to you.
Yeah, it is a mysterious universe. It's huge, It's full of incredible and sometimes unbelievable things. Where you go, what is that for real? Or is that just made up by physicists.
And physics is just sort of like a never ending stream of moments like that where we're like, how could that be possible? How could it be that the universe is actually this way? Think about when people discovered that, Wow, the universe might be describable by physical laws, maybe it's all like clockwork, like deterministic. That must have been an incredible moment to feel like our brains could describe the universe in a way that predicts its future. And then the rug was pulled out from under that big idea when we discovered the universe maybe not predictable, maybe not deterministic, an even crazier, more bonkers realization.
It kind of has to me, Daniel, like keep getting it wrong. Like if you got it write the first time, you wouldn't need to have your mind blown so many times. But you just keep a striking out.
It seems physics is definitely wrong. The goal is to make it less and less wrong over time time, right, is to make it writer and writer as we go. We're hoped to be asymptotically approaching the truth. But you know, we may never get there. We may never find a theory that we say, hmm, this is it. It works, it's satisfying, it's simple. We're done.
So that's like a great model for your department. Just trying to get it less wrong.
I think that's a pretty good goal, right, to be the least wrong. We're trying to be humble. Also, right this, some humility is important in academia.
Right, right, because it's so rare, right, Like, it never happens, it's pretend.
Well, it's one of my favorite qualities actually, in my collaborators, I work with some of the smartest people on the planet, but the ones who are most fun to work with all the ones that still have some humility, that know that anybody can make mistakes.
Nice, And it is an interesting universe on which to guess how it might all be working. And the way we do that is by asking questions about the universe. We wonder how it all works, why things are the way they are, and how did it all come to be.
Yeah. An important part of figuring out how the universe works is asking why is it this way and not some other way? Why does the universe follow this law? Why doesn't this follow this other law, which would seem to make much more sense to us. It's a deep part of being human to ask these questions about the universe, to try to understand what the rules are and what our place is in those rules.
Yeah, because we are all part of the universe, and as humans we seem to be born. I guess with a question asking, gene do you think it's embedded in our genetic instructions? Daniel, This sort of propensity, this tendency to ask questions about the universe, about the things around us.
I don't know. It makes me wonder about the nature of intelligence and whether asking questions and curiosity is all tied up with intelligence, whether it's an evolutionary trait. You know, whether curiosity didn't kill the cat, it fed the cat because the cat was wondering, like, h is that thing tasty? And crunched on it. And sometimes the answer is.
Yes, maybe killed the curious cats, but then it saved like the curious monkeys. You know, maybe it's a double edged sword. Curiosity save some species, but some of them didn't quite make it right because we don't have intelligent cats running around it.
True, cats are pretty intelligent, you know, not as intelligent as dogs, but you can definitely identify curiosity in other species, right. You can tell when your dog is curious about something, or even a rat can sniffing around trying to understand what something is. Of course, we'll never know what it's like to be a rat or a cat or a bat, just like we'll never know what it's like to be another person. But it does feel like being curious is part of being alive. We might not be able to answer that question until we meet aliens and discover whether or not they are also curious about the universe, right.
And whether they have alien cats who who don't ask questions? And also Daniel did you say cats are dumber than dogs?
Cats definitely dumber than dogs.
Absolutely lost half of our audience right now, cat lowers are pretty fiers.
I love cats. Cats are wonderful, they're great pets. Well, let me ask you this. Can cats learn? Can cats be trained?
Pretty sure that you can?
Right, certainly able to teach your cat stuff. I think dogs definitely show a larger capacity for learning, so I think they're more intelligent. I'm not an expert on this stuff. So you feel strongly about cats being intelligent, please write to hohorhe and tell him all about it.
Yes, my email is Daniel at Daniel and horrorhea dot com. Now, Well, regardless of whether cats are smarter or dumber than dogs, humans definitely are pretty smart. And we've been asking questions about the universe since we were cave men and women and cave children. Because we have questions about the universe, right, it's sort of a fascinating thing that we all wonder about. How does it all work?
Yeah, and that's all that science is. It's just a bunch of folks asking questions. It's people for whom the questions were the most important thing in life, and every little piece of science that comes out every time you read a news article about like the life cycle of newts, or how plants grow, or why rocks look a certain color. That's because one person decided that was the most important question in the universe, one they had to devote years of their life to understanding. So these questions really do drive now forward.
Yeah, and it sounds like somebody needs to read that article. Are cats Smarter than dogs? Sounds like great clickbait. But it's not just scientists that ask questions. It's everyday people, people like you that are listening to this podcast, and sometimes our listeners send us their questions and sometimes we even answer it on the podcast.
That's right. We want to hear about your questions about the universe. Maybe something we said on the podcast that you didn't understand, or follow up question to something we discuss, or something you read about in the news, or just something you've been thinking about as you stare up at the night sky. You have questions about the universe, we have answers. Please write to us to questions at Danielandjorge dot com. We answer every message and we will answer yours.
So today on the podcast, we'll be tackling listener questions number twenty nine.
The is it real or pretend edition?
Is that the real title or is that just the pretend title.
Well, if you're a cat, then that's the real title of your dog. Then you know, you can make up whatever you like.
Oh lot, now you're giving dogs extra rights. Oh man, you're you're a real cat or presser here.
You know. I used to be a cat person because we had cats for many, many years. Then I had kids, and my kids are allergic to cats, and the kids wanted to get a dog. So now I find myself a dog person. So still love cats, but presently have a dog in the family.
I see, you have to pick a side, you know, your kids or cats. You chose their kids.
I think that was the right choice. I mean also in parenting. I'm just trying to get it less and less wrong every year.
Yeah, yeah, am I. But we do have some awesome questions here today, and there does seem to be a sort of theme about things being real or pretend. There's a lot of sort of a if scenarios here, like what happens to this happens.
And that's an important part of doing science, you know, considering hypotheticals. Testing your ideas by considering what might happen in this scenario, what might happen in that scenario. It's a great way to do physics. You know, somebody tells you about how something works, don't just digest it and go mm hmm. Think about the consequences. What about this scenario? How does that fit with this other idea I learned. That's the way you can weave all these ideas together into a complete and holistic understanding of the universe, which, of course is the goal of physics.
Yeah, because that's kind of what science is. Right. It's like you never stop asking questions. Even if you find an answer, you can get a look for the other question. It's a very annoying hobbit.
Yeah, but it means you always have something to do. And even if you think you understand something in one circumstance, like you think you know what your dog will do if you feed it a treat, you might wonder, h what will my dog do if the treat is inside a box where it can't smell it, but it can see the treat. These questions help you understand more deeply what's going on inside your dog's head.
Yeah, I guess are you saying dogs or physicists also? Or physicist dogs? Where is this analogy going?
Launching a whole new podcast called the Physics of Dogs.
Oh man, you give me the dog physicist coming to the Discovery Channel next season.
We're going to take a bite out of black holes.
Give me a real treat.
All right.
Well, we asked some awesome questions through to today, some of them about aliens, some of them about black holes going too fast, and also some about giant space collisions that are maybe mind blowing or hard to imagine. So our first question comes from Avanni, who is six years old. Hello, my name's Avannie, A mean sick My question is alien? All right? Sorry? Ivanni? I said you were six, but you're nearly six, which is even more impressive that you're asking these questions.
It's a great question. I love this question, such a basic question but also such a deep philosophical question.
Yeah, Avonnie wants to know are aliens real or pretend? Boy? I feel like we could have a whole podcast series just on that question.
You know, there's so many wrinkles there, like, is anything real? Is it all just pretend?
What does it mean? To pretend what does it mean to be an alien? You can go down a real rabbit hole here.
Yeah, A big part of doing physics is coming up with pretend scenarios and asking like, well, could that be real? How do we know? Often before we see things out there, we do come up with the idea for what might be out there. So, you know, before the Higgs particle was observed, was it real or was it pretend? It was just an idea in our minds until we found it?
And have you figured that out yet? We pretend to Yeah, absolutely, but do you know Actually, my daughter, I think when she was around five or six, she asked me this almost the same question, like aliens for real or not? I guess when you're that age, you get a lot of like stories about aliens or movies about aliens or shows about aliens, and you're like, you're probably in your little brain you're thinking, is this for real? Or is this just like you know, dragons and unicorns?
Mm hmm, Yeah. I think it comes from seeing fictionalized portrayals of stuff. But you know, you might ask like, well, why are aliens in fiction? Why do we tell stories about aliens? Why are they're in the movies. Why are they on the brains? Right? They're on the brains because we wonder if they are real, because we think about them as a way to explore this question of are we alone in the universe? Right? So it's an important part of doing science is coming up with these pretend scenarios.
Oh boy, I thought you were going to say it's because they're real, like there's some kind of conspiracy going on here.
I want them to be real, obviously, like I would love to talk to aliens about physics and learn all sorts of things about how to look at the universe from a different perspective. But of course we don't know if they're real.
I guess is that the basic answer that you would give up on he is that we don't know if aliens are real or pretend.
Yeah, we don't know currently, they are just pretend. But why do we pretend? We pretend because we hope that they are real, and to discover them, we need to pretend that they are real. We need to think about what they might be like in order to know how to look for them. We need to imagine different scenarios for how they might communicate, how they might live, how they might think, so that we are prepared to discover them, so we know where to look and how to look for them.
Yeah, so I guess they're pretend like the things you see on TV right now, everything you see about aliens is pretend. Somebody just made that up, but we actually don't know if they are real or not, meaning that they could be real.
Yeah, they could be real. Aliens are pretend the same way string theory is pretend like it's a hypothetical, it's a possible scenario. We don't know if it describes our actual universe. We play around with it to see like does this make sense? Could it be real? There's sort of two steps in the question there, right like could this be real? Is it allowed by the laws of the universe? Does it explain the kind of things we see so we can ask questions like how could else could you make life? And could life of all in other places in the universe? Is that consistent with our understanding? Then? Of course there's the second, totally separate question, which is are they actually real. We might live in the universe where aliens are possible but don't exist. Could be that the universe allows for life to start in other places, but that it just didn't.
Well maybe for somebody like Evannie. You can step us through, like why do we think that aliens could be real? We've only been to one planet, Earth, could life in it? What makes us think that there could be other planets put aliens in them.
It's a great question. And I think an important thing to remember is that something we've been learning over the last few hundred years is that where we are in the universe doesn't seem to be very special. Like we're just in one little spot in one galaxy among billions and billions, maybe trillions, maybe an infinite number of galaxies. So there's a huge universe out there, and nothing about where we are seems to be very special so far. Like the kind of star we have is not that unusual a star, and there's billions of stars. The kind of planet we have, we've recently discovered that there are lots of these kinds of planets, planets made out of rock, not too far and not too close to the Sun. That water is everywhere in the universe. It's not too complicated, and so we can imagine ways for life to have started on other planets. In fact, it seems like there may have been many, many opportunities for this to happen. We don't think that the chemicals that we find here on Earth are un unique or special, and so it's not that hard to imagine life starting in other places or maybe even many many other places in the.
Universe, right. I think the idea is that there are a lot of planets out there, and a lot of planets out there are sort of like the Earth. They sort of maybe even look a lot like the Earth with water and like a nice atmosphere, nice clouds in the sky. And so those are the kinds of planets that at least what we know about of life. There could be other living things in those planets.
There could be and here we're just talking about life as we know it. You conditions similar to Earth that might make life in a way that's similar on Earth. And you know, an important part of pretend though, is thinking about different aliens. Rarely in movies you see aliens looking exactly like humans. Because we think that probably some aspects of life here on Earth are basically random, that just evolution happen to follow this path, and it could have followed another path. We don't really know, Like what are the spectrum of possible options, what else could have evolved and have been intelligent. It's hard to think outside this box because we're just so used to life on Earth, and it's possible that life on other planets looks a little bit different from life on our planet, or could be fundamentally radically, mind blowingly different in ways that are hard for us to even imagine.
Right. But I guess even though there are a lot of planets out there, and a lot of them that looked like the Earth, we sort of don't know if what makes you know living things happen in a planet like that is special or whether that's common too, Like there might be a bazillion planet like the Earth out there, but maybe like our planet is the only one where things just happen to come alive. That's a possibility, right.
That's definitely a possibility because there's a gap in our understanding. I said earlier that we think the chemistry of Earth is probably not unique, But what we don't understand is how you get from like the chemistry of Earth to life on Earth. How do you go from a primordial soup of like building blocks of life to actual life, self reproducing objects that can build complexity. We do not understand that step, like we don't understand how it happened here precisely, which means that we can't say how likely it is to happen somewhere else. And our ignorance ranges from like, oh, it could be pretty common. You get it like half the time. If you have a primordial soup and it sits around for a few million years slashing on alien shores, that fifty percent of the time you get life. You know. Arguments in favor of that are that it didn't take that long on Earth for life to start. We think, you know, less than a billion years after the Earth began. We think there might have been like a little microbe. On the other hand, it could be super duper rare. It could be that it takes trillions and trillions of planets for it to happen one time. We could be the only life in the entire universe because it's just so rare. We just don't understand the mechanism for that. So we don't have any idea how rare or how common that crucial step is.
Right, And I guess if I'm a six year old or nearly six year old, like Evanni. I might be wondering right now, like, how can we not know if there are aliens out there? Like can't we just look at them or go to them or see them from Earth?
Yeah, we do know something, right, if there were aliens everywhere, if there were aliens on Mars and on Venus and building civilizations around Jupiter, then we would have seen them. So we know the universe is not like overwhelmed with life. It's not like brimming with life. Even if they were like really fancy aliens the one star over, we might have seen messages from them. We might have heard from them already. So in our little vicinity, it seems like, you know, there isn't any other life that we have found yet. There are still some places in the Solar system we haven't looked, and there are lots of ways for alien life to be like kind of nearby but not that close, and us to not have seen it. But so far our neighborhood seems sort of abandoned except for us.
Right at least for now, right Like, it could also be that there were aliens here or around a long time ago, but they're not anymore. Or it could be that there will be aliens in our neighborhood in the future, just not right now.
Yeah, the universe is a very long trajectory. Our life cycles and the whole history of humanity on Earth is just a blip in the cosmic history. So it might be that aliens lived around a nearby star for a billion years and then died out and we just missed them. That they might arise in two billion years and last for a trillion years, But we're just a little bit too early, so there's lots of ways for us to not see aliens.
All right. Well, then I think the answer for Evannie is that the universe is so big that aliens are probably real, but so far we just have to pretend that they're pretend because we haven't seen any or talk to any yet so far.
Yeah, and that pretending about aliens is an important way of actually discovering them, of thinking about what they might be like.
Yeah, it's part of using your imagination, which is a big part of using your curiosity, which is a big part of science.
And maybe Vannie, you'll grow up and be the one to discover aliens.
All right, Well, let's get to our other questions here about fast moving black holes, and also white hole collitions. But first, let's take a quick break.
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All right, we are answering listener questions here today, and Daniel, are we for real answering them or just pretending to answer them?
I'm not sure I know the difference anymore.
Your life is a blur. You're doing fiction, you're doing physics. What is real? Man?
I'm really pretending to do my best.
All right, Well, we have our second question here of the day, and this one comes from Jeff, and he's wondering what happens when heavy things go really fast?
Hi, Daniel and Jorge my name is Jeff, and I've got a question for you about high energy photo black holes and relativity. I've heard that if you can get enough energy in a small enough volume, a black hole can form. Right, If you had a laser that could shoot ultra high energy photons, those photons could become black holes. But what would an observer moving close to the speed of light relative to that laser sea As those photons in that reference frame would have less energy, they shouldn't observe these photons becoming black holes. It sounds kind of paradoxical. I'm sure I'm missing a subtle point somewhere, But if you could help shine a light on it, that would be appreciated.
All Right, that is a pretty mind blowing question. I'm going to pretend that I understood it. I think what he's asking, Jeff is asking, is a black hole's form because when you have enough energy in one spot, and so if you take a little rock and you get it going really fast, doesn't it get a lot of kinetic energy? And if it has enough kinetic energy, doesn't it at some point become a black hole because of its kinetic energy.
Yes, it's a really good question about like whether observers in different frames, moving at different speeds I'll see a black hole made at the same time, do they agree about whether something is a black hole or not. And it's a great question because energy is relative, right, Like if I'm holding a rock, I see it having no velocity, so it has no kinetic energy. Whereas if you're running by at seventy five percent of the speed of light because you're really fast, you measured that rock to have a lot of velocity relative to you, and so a lot of energy relative to you, So you see that rock as having more energy. So in principle, you could say, oh, that rock has enough energy to form a black hole, and I could say, no, it doesn't have enough energy to form a black hole. But you know, one of us would have to be right, because either it's a black hole or it's not.
Right, because velocity is relative, right, it depends on how you measure it. And so does that mean then that kinetic energy is also relative, like it doesn't really exist.
Kinetic energy is definitely relative. And there's an important difference between things being conserved and things being invariant, right, Like something's invariant if everybody measures it and gets the same answer. Like everybody measures the speed of light to be the speed of light, no matter what frame you're in, how fast you're going, et cetera. Not everybody measures velocity to be the same number. If you're moving relative to me, then you have a different measurement of my velocity and so a different measurement of my energy. Right now, in your frame, energy is conserved, and in my frame, energy is conserved. But we actually measure different amounts of energy. So energy is conserved that is in flat space, right, But it's not invariant, so different people measure different amounts of energy. Yes, it's relative.
So I think that's the paradox that Jeff pointed to, is that you're there holding your rock to you. The rock has no energy, right, it's just sitting there in the palm of your hand. But for me that I'm going at seventy five percent of the speed of light zooming past you, I'm seeing you from my point of view, I'm seeing you and the rock have a ton of energy, right, because you have fast and you're moving really fast relative to me. So I'm thinking, oh my goodness, there's so much energy there. Well, first of all, I can't believe Daniel's moving that fast, but there's so much energy there that a black hole should be forming there. I mean, it would be a really short moment there, I'd be like, well, oh, are Arety gone? Would a wonder about it too long?
It's a really fun question, and it gives us an opportunity to understand a little bit more about general relativity. The short answer is that, remember, a black hole is curvature of space, and that it forms when you have enough energy density in a certain location. But it's not that simple exactly. It's not just like more energy density means more curvature and eventually you hit a threshold and you get a black hole. It's more complicated than just like a certain amount of energy density. It's not just like one number that controls the solution to Einstein's equations. Einstein's equations are a big complicated nightmare, and different pieces of it feed in slightly differently. It's not just like you measure the energy density. This's this thing called the stress energy tensor. And kinetic energy feeds in differently from potential energy, which feeds in differently from other kinds of energy. So it also of dances together and to get a solution.
Well, I guess maybe the basic question is does kinetic energy bend space? Also, like, if I have a rock moving really fast, is that kinetic energy bending the space around the rock as it's moving. Or even if I just have a like a photon which has sort of momentum, right, kinetic energy, is that photon bending space? Also?
It can? Right, it does contribute, Right, It's not like the universe just ignores kinetic energy. It does contribute to the effects on space, right. But it's not trivial. It's not like you can just add up all the energy and say here you have enough to have a black hole. Eindsense equations, Remember, are very complicated, so it's not easy to say, here's this configuration. Now we know exactly what happens. And in fact, it's really a nightmare to solve Einstein's equations for anything with kinetic energy. I mean it's a nightmare to solve it in almost any circumstances. We've only ever solved Einstein's equations under a few very specific, very simple situations, like a huge amount of mass at rest or the universe filled homogeneously with matter. We haven't even solved different simple things like to objects orbiting each other. Right, that's too complicated for us to figure out. And so to solve these problems, what we typically do is we use a trick. We say, well, this problem is too hard to solve. We don't know how to solve the problem of I have a rock moving past me with a lot of kinetic energy. I can't solve that one, But can I solve a different problem that I know has the same answer. So one thing we know about general relativity is that it is invariant. Everybody should agree about what happens about whether there's a black hole, regardless of your coordinates, how you choose your reference frame, how you organize space time, right where you put your axes shouldn't matter. Everybody should agree about whether or not there is a black hole. So that's a short answer. Or hey, and I can't disagree about whether the rock forms into a black hole. It's not like he could see a form of black hole and I don't. We have to agree. We know that the equations of general relativity are invariant, so we say, well, let's solve the problem in the easier case. Or I'm just holding the rock and I can ask the question does it have enough mass to form a black hole? Yes? Or no? And then we say, well or hey, must see the same answer. We don't know how to solve the equation for or, but we know what the answer has to be.
Meaning that because you don't see a black hole in the rock in you're the palm of your hand, then I shouldn't see a black hole when I'm moving past you seventy five percent of the speed of light. You're saying, we should all come out with the same observation exactly.
And if we were better at math and we knew how to solve that problem in the case of an object moving really, really fast, then we would get the same answer. We know that that's true because we know that general relativity is invariant that no matter what frame you solve it in, you do get the same answer. We just can't work through the details of that math right now because we don't know how to solve those equations in every possible scenario. So typically we just say, well, let's solve it in an easier case and then argue that the answer must be the same in this other case.
Sounds like a pretend argument, But I guess is why does it have to be that way, you know, Like, why couldn't you see no black hole? But to me, it looks like you are holding a black hole, you know, like it maybe somehow it sort of looks like it nothing can escape there. But do you it does seem like something can escape from the palm of your hand. Why couldn't that be true?
Well, remember what the condition for a black hole is. We're talking about an event horizon, talking about our region in space where nothing can ever leave. So it'd be a paradox, right if you see an event horizon but I don't. Right, that means that I could see a photon leave this rock and strike you. But you're saying that no photon could ever leave that rock and strike you. Right, Those two things are in contradiction with each other. And remember that there's lots of relativity In relativity, right, people can disagree about the order of events, for example, But you know, whether two things strike each other, for example, whether that photon reaches johe or not are things that all observers do have to agree.
On, all right, So then what's kind of the answer here If we both have to see a black hole not forming the palm of your hand, then does that mean that my velocity is irrelevant, like kinetic energy doesn't go into really the formation of a black hole, Because I feel like that's kind of what you're saying, is that me moving fast is irrelevant and therefore it can't affect whether or not a black hole forms or not.
That's right, and that sort of makes sense. You know, if I'm sitting here holding a rock and you're running by me a mile away, how could you're running by me make my rock implode into a black hole? Right? It doesn't even make sense. And then whether or not a black hole existed would depend on like everybody else's speed in the universe. It shouldn't make sense, right, Your intuition tells you that it's either a black hole or it's not. And no matter how fast Orge runs, he can't turn my rock into a black hole.
Well, I hate to run, so yeah, that wouldn't happen anyways. I think what you're saying is that you know the formulas that say what makes a black hole or what turns into a black hole somehow sort of cancel out the effects of kinetic energy, because you said earlier that kinetic energy does bend space, so you would think that it would help form a black hole, but the equations of the black hole are such that it actually sort of ignores the kinetic energy.
Yeah, it all gets woven in a very complicated way that frankly, you don't even really understand how to solve in an exact way. We have like numerical solutions to this stuff, but most of the solutions to general relativity are done using these kind of assumptions, like that everything is invariant, that you get the same answer in every frame, So let's find the one where it's easiest. And we do this all the time in physics. You want to solve a problem where like a ball is rolling down a plane, then you choose axes that make that simple. You know, where your x axis is like aligned along the plane rather than with the ground, because it makes the math simpler. So we're always doing this kind of thing where we transform the problem to be a simpler one that has the same answer.
Well, all right, well it sounds like you're waving your hands with some math here a little bit, But it sounds like the answer is that to answer Jeff's question, is that fast moving objects do have extra energy because of their kinetic energy depending on who measures it, but that kinetic energy can't affect the formation of whether or not it forms a black hole exactly.
And Jeff actually asked his question in terms of photons. But the same kind of principles apply. Either you have enough energy to form the black hole or you don't, and it's the same in every frame.
Well, we have one more question here today, and it's about what happens when white holes collide with black holes. And I'm guessing it's not just that they form a grayhole. We'll get into the real answer here and not the pretend one. But first let's take another quick break.
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All Right, we were answering listener questions and I feel like I've gotten my mind blown twice already. First of all, that there's a nearly six year old kid thinking about aliens in the universe. That's amazing. That's awesome. And also that black holes don't depend on how fast you're moving.
Yep, black holes are mind blowing and they're really fun hypothetical questions to think about them. Make sure that you understand how they work and what the rules are and how it all comes together. It's really useful to think about crazy hypotheticals.
All right, Well, we have one more question here, and this one comes from Carson.
Hid On Jora, Carson, here, I have a question about black holes and white holes. Could you please explain what would happen if the two were to quiet? And thanks for answering all my questions.
All right, awesome question, Carson. That is a great question because I also wonder about this myself. Carson's question is what happens if I take a black hole and I make it crash or collide with a white hole?
It is a wonderful question. I really love this. When I first got this question, I thought, WHOA, I've never even thought about that. How have I never considered what might happen in this scenario? So I had to go off and think about it a little bit, and I also reached out to a quantum gravity expert. Will chime in a little bit later on.
You can just pretend that you came up with that information.
I can't pretend to be a quantum gravity expert as hard as I try.
Well, what happens when a white hole collides with a black hole? That's a great question. And so let's step through this. What is it exactly a white hole?
So a white hole is a really weird theoretical object, and it's one of these things where it's not even really well to fined what it is. There's sort of like a few white hole kind of ideas out there that all sort of fall in this general category. So the answer to the question depends a little bit on what a white hole is. And there's sort of like three different ideas that might be worth thinking about for what a white hole is.
I guess, first of all, is this a real thing that physicists feel that really exists, or is this just like it's possible in the equations but we don't really have sort of dug into it to get the sense whether or not it can't exist in the universe.
Are you asking me if white holes are real or pretend?
Yeah, well, I'm asking if the theory is pretend.
So white holes do exist in the theory. We don't know if white holes are real in our universe, And as you'll hear about, some of the parts of the theory are a little bit speculative and a little bit fuzzy, So we're not sure whether white holes. Nobody's ever seen a white hole, but there are parts of the theory that suggests that they might be real. And if that sounds pretty speculative, remember that until a few decades ago, black holes were in the same category and the kind of thing that we're in the theory, and a lot of people thought, well, that would never actually happen in reality. And now we're pretty sure black holes are real, that they are out there, So white holes might be real or they might just be pretend. We're not sure.
But that's where we are with white holes, is that we're like three decades behind black holes, because I feel like black holes we thought they were maybe met real or maybe not. Then we sort of saw evidence of their presence, and then only until very recently do we have actual pictures of them. We're still in the maybe they're not real phase.
Right, We're never one hundred percent sure with black holes because the only way we know they are real is by looking at the stuff that's nearby them, and black holes are sort of like the only thing that fits that bill until recently. Now we have some like alternative theories for like what might be going on inside black holes, So maybe they're not actually gr black holes, And we'll talk about that actually in a minute, But yeah, white holes are behind black holes. Black holes we thought of, you know, in the early part of the nineteen hundreds, and then discovered indirectly fifty years later. White holes weren't really thought about it until like the sixties or seventies, where people were understanding the nature of general relativity a little bit more deeply. So, yeah, they're about fifty years behind black holes, all right.
So you were saying, there are three kinds of white hole ideas or possibilities. What are they?
So the simplest one to think about is the end point of a wormhole. A wormhole is like a connection between two points in space where you can like enter in one spot and come out somewhere else. And this is possible because general relativity tells us not just the space can do things like wiggle or bend in the presence of mass. It can also be like connected in weird ways. You can like stitch it together to say, this point in space over here is actually also next to that point in space, meaning instead of just being able to go like up, down, left, right, side to side to adjacent points, now one of those adjacent points is actually like somewhere else in space, but also at the same time adjacent to this point in space. So these wormholes can sometimes be like a black hole linked to a white hole. We fall into the black hole and you get spat out the white hole on the other side.
It's like the almost like the opposite of a black hole.
Yes, so conceptionally a white hole is the opposite of a black hole. Where a black hole has an event horizon where nothing can escape, a white hole has an event horizon where nothing can enter. It's like you arrange the shape of space in such a way that nothing can ever cross that event horizon going in the way in a black hole, nothing can ever cross the event horizon going out. Or a white hole, it's like the opposite.
I guess, meaning like if you shoot a photon at a white hole, will just bounce back.
You will never reach the event horizon exactly.
And maybe turn around and come back.
Well, the answer to that depends a little bit on the form of the white hole that you're talking about. In some theories, it'll fall forever towards the event horizon but never actually cross it.
All right, Well, what's the second kind of white hole?
So the second kind of white hole is sort of like a pure gr white hole. It comes from looking at the solutions to Einstein's equations. Say you have like a big mass of stone, so much stuff that you could get a black hole, right, that's a solution to the equations. Turns out that general relativity has this symmetry in it that every solution to general relativity also works backwards in time. General relativity doesn't seem to prefer one direction in time. Like the description going forward and description going backwards both are solutions to Einstein's equation. So what that means is that if you have a massive stuff that can give you a black hole where nothing can ever escape the event horizon, then it also can give you a white hole, and like the opposite solution, the time reversed solution of a black hole is also a solution to the equations. So I put a big blob of stuff in the universe. It can give you a black hole where space is bent so everything falls in crosses the event horizon and never leaves. But it could also give you a white hole, the opposite structure of space that nothing can ever enter the event horizon.
Wait, what it would be because you have a lot of stuff, But would it be random if it turns to a white hole or a black hole, like it'd be like a flip of a coin.
We don't really understand whether these solutions are physical. Right, this is like a solution to the equation, but we don't really understand, like does that mean these things can actually exist? But you've never seen one. It's sort of like when you're solving an equation in math and you have like an X squared equal to nine. X could be three or x could be minus three, right, And sometimes that makes sense, and sometimes it just doesn't. Right. Sometimes that's like a non physical solution, so you just ignore it. We don't know if this is like a physical solution or a non physical solution. One problem with this time reverse scenario is that requires the black hole or the white hole to be eternal for it to always be there for the time reversal solution to exist. It has to like exist all the way back to negative infinity, otherwise the symmetry would be broken. Right the black hole is formed at some moment by a collapsing star for example, that's how many black holes are formed. Then the solution doesn't work backwards in time anymore. That was required the start of like uncollapse somehow.
So it's like the opposite of a black hole mathematically, but we don't know if that could be physically possible.
We don't know if that could be physically possible, and it requires this weird thing called an eternal black hole, which we also don't know if it's physically possible at all. So it's sort of like, you know, it's a theoretical playground. It's like, here's something the math does and it has a cool name and weird physical effects, but we don't really know if that's real or if it could appear in our universe. And there's no physical way we know of to like create this thing, this backwards in time eternal black hole.
All right, and then there's one last kind of white hole here that has to do with quantum physics.
Yeah. One issue is that we think that general relativity is not complete, right, It can't really describe the universe as we know it. We don't think that singularities are real. We think that the infinity predicted by general relativity is like a failure of the theory, and that if things get actually that compact quantum effects takeover. But we don't have like a quantum theory of gravity. We don't know how gravity interacts with quantum mechanics. But we did talk on the program once about a possibility, possibility that maybe black holes don't actually have singularities at their heart. Maybe the curvature of space creates time dilation, so like time moves really really slowly, And what we're seeing is a star collapsing and super slow motion. It's going to collapse to some point and then it's going to bounce back and explode again, and it just hasn't happened yet because the black holes are in super slow motion. So this is the idea of a dark star, like the quantum version of a collapsing black hole that's going to eventually bounce back. It just hasn't happened yet.
Right, I remember we talked about this, is that it's the idea that maybe even black holes don't exist, like maybe black holes aren't real. Like you never get to an actual black hole. You only have super dense star that is never going to collapse to a singularity. It's going to explode before it collapses. And you're saying, I think that that explosion, when it finally collapses, maybe a long time from now, you can call that a white hole.
Exactly. This would be a transition from a black hole to a white hole, because at that moment things would spray out, so you'd have this incredible source of energy, incredible source of radiation in the curvature space would be inverted so much so that it would effectively be a white hole. So I reached out to one of the authors of that paper, Francesca vi Dotty. She wrote it together actually with Carlo Rovelli, who's been a guest on our podcast as an excellent science writer, to ask her about what would happen if a black hole hit a white hole the kind that she thinks about these quantum gravity white holes.
All right, here's the audio professor Francesca vi Dotty talking about quantum gravity.
Okay, so we have to divide this question into two pieces because it really depends whether we are talking about microscopic of microscopic black holes. So let's imagine it's possible to have a two microscopic object to one a black hole and one it's a white hole. And let's imagine that they are turning around the other very much like the black coal binaries that we are now proving with the gravitational wavee telescopes like Lisa and so so in that case, what I would expect is just to have a merging between these two objects that is quite similar to what I would observe for the merging of two black holds. The probably, I'm not sure what the calculation would give exactly, but we have a prediction for the rinkdown face. So after the two black holes merges, there is a specific wave form that we observe in gravitational waves. There could be differences for a black and a white or merging, but I expect something very similar. And the reason't why I expect something similar is because in the moment in which a white hole gets perturbed by another object like a black colt, then very quickly the white hole turns back into a black hole. So basically the two objects that would be merging would be just two black holes. A completely different story is the case of two microscopic black and white holes. First of all, it's more complicated to create such a situation because being a microscopic well is not so easy maybe to create abounded pair that would merge like in the microscopic case. And the other complication is that in the moment in which you have microscopic objects is not so clear the distinction between the black and the white one in the sense that you can have objects that are so small that are basically at the plank scale. The plank scale, those objects behave like quantum objects. They are kind of quantum particle that have at the same time a black and the white nature like particles that could be in a superposition of spin up and spin down, or if you want to, like the shooting a gut that could be alive and at the same time. So those objects that can be black and white at the same time, So what you are merging and in fact a gray hole and another gray hole together.
All right, thank you, professor Francesca. But dirty it sounds like she's saying, there are two scenarios here that can happen when a white hole, or a theoretical white hole hits a probably real black hole.
Yeah, exactly. And one of them is actually the joke that you made, right, you might actually get a gray hole.
Really, oh, I should get the Nobel price.
Then the idea is, if they're macroscopic, they're like big classical objects, then they spiral in together. Then when they touch the black hole will convert the white hole into another black hole, and you'll get like a really big black hole. Basically, the black hole eats the white hole and becomes a super black hole.
What the black hole winds, Basically.
The black hole winds exactly. And if the microscopic if they're super duper tiny, because you know, there's nothing stopping you from having a tiny black hole or a tiny white hole, and they're quantum objects, then quantum effects take over and they can be in this weird superposition where like each one could be like fifty percent chance of being a black hole or fifty percent chance of being a white hole, which is crazy, and that's what she's calling a gray hole.
Whoa wait, So it kind of depends on the sizes of these white and black holes. If they're really big, she said that the black hole would win, I guess, but why does it have to win white can't it just kind of so much together? Why does the black hole win?
Because white holes are fragile objects. They're like not as stable as black holes in her conception of them. So but basically a black hole is still collapsing star it's like sucking all matter in. It doesn't really matter what's your throw in there. Another star, another black hole, even a white hole.
Really, like, what if I take a really really really big white hole and a tiny little black hole. Couldn't the white hole overwhelm the tiny little black hole or would the tiny little black hole still win.
We're in the Macrosky topic region where we're ignoring quantum effects, and she's saying the black hole would win, that it would convert a white hole into another black hole.
Well, no matter like how big or small each of them are.
Yeah, as long as you're above quantum properties. Yeah. And then the other scenario is if we're tiny enough, the quantum effects take over. And again this is speculative because she's using the theory of quantum gravity, which we don't know if it's true or not. It's just like something we're thinking about. In that scenario, you could even stranger quantum effects where it'd be in a weird super position of being a black hole or a white hole.
Interesting. And this is if the white hole and the black hole are really tiny.
Small enough, the quantum effects dominate. You know, we're talking about like particle size black holes and white holes.
All right, Well, I guess that answers the question then for Carson, Basically, Jorge was right. If the black hole and the white hole are small enough, then you get a little, tiny gray hole. But if they're big, then the black hole always wins and the whole thing turns into a giant black hole. Mm hmm exactly, So it's not really much of a collision. I guess it's more like the black hole will always eat the white hole.
That's the prediction, least according to the quantum gravity expert.
All right, well, thank you Carson for that great question, and thank you to all of our listeners who send in their questions. We love to answer them here on the podcast.
We'd like you to think about the way the universe works, the way it might work, the way we pretend that it could work, and then to ask the questions about whether or not they are real.
So if you have a question, feel free to send them to us. We might answer it here on the podcast, or Daniel's dog will answer the question. Apparently it's a pretty smart dog.
It can be pretty rough sometimes with these answers.
Well, we hope you enjoyed that. Thanks for joining us. See you next time.
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 usdairy dot COM's Last Sustainability to learn more.
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