Daniel and Jorge Explain the UniverseIs there dark matter in black holes? Are gravitons and gravitational waves the same thing? Daniel and Jorge answer the most common listener questions!
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Hey Daniel, how's our email in box looking these days? Oh?
It is happening. There are so many fun questions, and there's so many people wondering about the mysteries of the universe.
WHOA do you notice any patterns or trends or maybe frequently asked questions?
Oh for sure. Actually most of the questions we get are question we have seen before.
Oh yeah, really, a lot of people have the same questions.
Yeah, just the same concepts tend to trip up a lot of people.
So if you still don't understand quantum mechanics or relativity. You're not the only one.
No, In fact, you're in very good company because I'm still confused about it.
May you should submitted as a question to our podcast.
And who's going to answer it?
Not me? I am Orge, I'm a cartoonist and the creator of PhD Comics.
Hi.
I'm Daniel. I'm a particle physicist and I've never stopped asking questions about the universe.
And Welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which we dive deep into your questions about the universe, into scientists questions about the universe, into everybody's questions about the universe. How does it work? What is it made of? Why does it work this way and not that way? Why don't I have a taco stand around my corner? Every deep and important question about the universe handled on one podcast?
Have you actually checked all four corners?
I do a scan every day for taco chucks, and there's still not one on my corner.
You live in southern California and you have trouble finding a taka truck. You need to get out more man.
Yes, that's definitely my problem.
Yeah, we all have questions, and it seems to be kind of a innate part of human nature to be curious about what's going on around them and how things work. And fortunately the universe is happy to provide mysteries and strange things for us to ask questions about.
Yeah, we're lucky that the universe is both amazing, beautiful and mysterious. Yet it also seems to be discoverable that we have this incredible technique for divining knowledge from the universe by asking questions and then answering them in a structured way. So we're fortunate to be surrounded by amazing but accessible mysteries.
Yeah, especially you, I guess, because you know, if the universe was simple and easy to understand, we might be out of a job. Daniel. That's right, especially you.
If the whole field of physics lasted like ten minutes of human history, they're like, let's knock that off before lunch.
We done it, We done it. Fire all the physicists. Put them to work somewhere else. Do we have a taga truck age?
You're right, there is this sort of exquisite balance. Their physics was too easy, it'd be done too soon. If it was too hard. Nobody would give us any money because we weren't making any progress. So it's got to be just hard enough to be worth doing.
And so physicists, as part of their jobs, ask questions about the universe, and they all have They have all kinds of amazing questions about how things work. And the public also has a lot of questions. And sometimes those questions are one and the same.
That's right, and we on this podcast do our best to answer those questions, to dig deep, to explain them to you in a way that makes sense. But sometimes our explanations inspire more questions. We'll talk about a topic like black holes, and then we'll get five or ten of very similar questions about some little wrinkle that we didn't cover or something we said that didn't quite make sense to a few people. And so we thought it'd be fun to dig into some of those emails and answer those questions and iron out those wrinkles.
So today on the podcast, we'll be tackling our most common listener.
Question, that's right. We have a series of episodes on this podcast where we talk about the most unusual and interesting listener questions, the ones that are sort of tricky and hard and required me to do a bunch of research. But there's a whole other category of questions that we want to share with you, and these are the common questions, the ones that a lot of people are asking.
And so today we'll be asking most of a lot of the top questions that we get through email, through Twitter, through Instagram, Daniel, do you check Instagram? Do you know what Instagram is? Do we have a TikTok account too?
I don't use grams because you know, I'm an American, and so I use Insta pounds.
Good. That sounds like a bad diet to go on.
I don't recommend it. Actually, that's the name of my taco truck is Insta pounds. Oh, we put sour cream on everything.
Maybe it's good that you don't have a taco truck.
Then maybe that's why I don't have a taco truck.
Yeah. So we're gonna be asking all these questions, and they're all great questions, and they have to do with the dark matter and black holes and particles and all kinds of things, even philosophical questions.
Yeah, and questions about life and how to get involved in physics.
So we'll dive right in. Our first question comes from Thomas Gontredra's and he has a question about is there dark matter inside of black holes? And what about neutrinos?
Now?
Is he asking if there's dark matter inside of neutrinos or is he asking if there are neutrinos inside of a black hole?
I think he's asking if he can get a side of neutrinos with his tacos.
Everyone has the side of neutrino's and their tacos, don't they.
Yeah. I think that this question is basically asking, like what kind of stuff gets sucked into a black hole? Dark matter, which we know is out there, this invisible kind of matter giving gravity to the universe even though we can't see it, Does that also get sucked into black holes? And that's I think also why he's asking about neutrinos, Like neutrinos feel hardly anything and have almost no mass. Do they also get sucked into black holes?
So?
I think that's the origin of questions. Are black holes sort of universal sucker uppers?
Or do they only eat regular matter?
Yeah?
Like the kind that we're made at it.
Yeah. And the other angle to this question is, you know, what are the structures of dark matter. If dark matter is here in the universe, is it just big fluffy clouds, or is it making like dark planets, dark stars, dark black holes, and dark podcasts?
Right? So, is there dark matter ins that of black holes? Daniel almost certainly.
Yes. Black holes are basically just very strong sources of gravity, and they can suck in anything, anything that has mass. It doesn't matter if you are moving very fast or if you're moving very slow, if you're low mass or high mass. All forms of energy are trapped by black holes, even if they have no other kinds of interaction. That's the thing that makes dark matter unique is that we think it has no other kinds of interactions that we're aware of. But you can still get sucked into a black hole.
Right Yeah, I guess the question is it can only interact with gravity. I think we have a podcast that covers that. What would keep it inside of the black hole? Couldn't it escape if it wasn't being crunched down by other stuff.
It's not being crunched down by the other stuff, but it's gravity that's holding things inside a black hole. Remember, these days, we don't think about gravity as a force, So you shouldn't think about it like tugging on this stuff and keeping it in the black hole. We think of gravity as the bending of the shape of space. Einstein told us that this is crazy relationship where matter bends space and then space tells matter how to move because of its curvature. And a black hole is this crazy intense bending of space such that essentially becomes one directional. Inside a black hole, you can only move towards the center. Space is one directional inside a black hole, sort of the way time is one directional outside a black hole. Time only moves forward outside a black hole. Space only moves towards the center inside a black hole. So it doesn't really matter what you are. If you have any mass or energy, you are moving towards the center of the black hole once you fall in, right.
But then once it gets to the center, wouldn't it come out the other end.
Once it gets to the center, gravity is going to keep holding it at the center, right, I mean, unless there's like a wormhole at the center attached to a white hole or something crazy. But if you follow general relativity, and you know, we think general relativity is correct, although we don't think it works inside a black hole. But if you're assuming general relativity works inside a black hole, then once you fall in, you're moving towards the singularity, even if you're dark matter. Interesting.
I guess if that's the case, then wouldn't we expect most black holes to be mostly dark matter since there's five times more dark matter in the universe and regular matter.
It's a great question. We don't know what fraction of the stuff inside a black hole came from dark matter. But remember that dark matter is much more diffuse, it's much more spread out through the universe. It doesn't clump as much as a normal matter because it doesn't have those other kinds of interactions like dark matter, these big swirling clouds of stuff that surround our galaxy. But it's harder for dark matter to make dense structures because to make dense structures you need other kinds of interactions. You need other kinds of interactions to hold stuff together, like the electromagnetic force is a thing that's holding you together, not gravity, and you need those interactions to sort of radiate away energy and fall in. Like the reason something doesn't just orbit a black hole forever is that it loses some of its energy and falls in. To do that, you have to be able to like radiate off a photon or a z or something, and dark matter just can't do that. So dark matter is much more spread out. So we don't think that dark matter is sort of the primary seed for black holes. But some of it must have eventually fallen in.
But maybe not as much as you might think, because it's kind of hard for it to fall in.
Yeah, precisely. And if you take, for example, the volume of our solar system, the volume of our solar system is mostly filled with normal matter. There's a lot of dark matter in there, and there's more dark matter in the universe, but in the vicinity of our solar system it's mostly normal matter. So if our star went black hole, it would suck in some of the dark matter that's neearby, but most of the matter in our solar system is normal matter.
And what about neutrinos. Can neutrinos fall into a black hole? I guess anything. I think what you're saying is that black holes bend space and time, so it's more like a space trap rather than it just a gravity trap.
Yeah, exactly, it's a space trap. Space is gravity. Gravity is space, and so You're exactly right. Anything can fall into a black hole and nothing can escape. So the answer to your question, can X fall into a black hole? Is always yes?
Or any X can the letter X daniel as a concept or fall inside of a black hole?
Oh? Man, can philosophical ideas fall into a black hole? Well, there is this crazy theory that information has mass, and you know that's never really been proven, but so perhaps yeah, you come up with a crazy enough idea that you're it becomes a black hole and you were thinking about the letter X, then yeah, boom.
Well, I know we renamed black holes to space traps. I feel like that's more accurate and more descriptive.
All right, Well, we'll start using that on the podcast from now on and we'll see if it catches on.
Your space trap. All right, Well, I think that answers the questions for to ask contreres. Thank you for asking the question. Our next question is about the universe, small topic and whether it's stretching and expanding. So Steve Slopek, as, if the universe is stretching and expanding, what's it expanding into? Now you said, this is another common question we get.
This is a question we get like once a week people are hearing about how the universe is getting bigger, and they're wondering, like, if the universe is everything, how can it be getting bigger. Doesn't that mean it's sitting inside something else that's holding it, that it's now like filling up. I think people are imagining, like, you know, a blob of molecules inside an empty room spreading out to sort of fill out all those corners. I have that question, and it's an amazing question. But the answer is no, that the universe is not expanding into anything because the expansion is not like relative to some outside external space or metric right. The expansion is intrinsic. It means that distances between points are getting larger. So we don't have our space, you know, our three dimensional space sitting inside some other box. It's just stretching. It's creating new space between existing points.
Well, I feel like what you're saying is that there's nothing outside of space. But isn't nothing something?
There isn't anything outside of space, so I avoid saying the word nothing.
What do you mean? What makes you uncomfortable about the word nothing?
Well, it depends what you mean by space. I mean the origin of space was sort of like the backdrop on which things happen. You know, you like define distances and you could have empty space and then stuff in it. That sort of the origin of the concept of space. But now we know that space is not like that. Space is dynamic. It's flexible. It can shimmer and wiggle and stretch and grow and bend. Right, But you're tempted to put it in some now static, larger space. Right. There's nothing on which this like goo of space actually sits. But we don't have any evidence that that exists. We don't know that there's some other external, true, deep meta space in which our space exists. It seems like all the math is consistent with just our space bending relative to itself.
But I guess the question is if we can expand I think maybe what trips people up is like, what are we expanding into? If we're expanding into something, then you must be able to measure it, and so wouldn't it be like empty space kind of that you can measure.
I think the confusion there is expansion, right, We're not expanding into anything, we're expanding relative to ourselves. So if you have two points in space and you wait you will notice, thanks to dark energy and the expansion of the universe, that they are getting further and further apart. So you can that's how you measure it. You don't step outside of the universe and be like, hey, the universe is fourteen inches wide and last year was thirteen Look how much it's grown. You measure the points between things in space because that's all you can do. You can't step outside of space. It doesn't even really mean anything.
Maybe the way to think about it is that space is not growing. It's almost like it's stained the same size, but we're shrinking inside of it.
You know. Actually, Dan Hooper, who we've had on the program, a cosmologist, likes to make that point that you can't actually tell the difference between the expansion of space and the shrinking of stuff that looks exactly the same.
M there you go. So maybe that will help people from reading confused, because you know, sort of just think about it more like we're the same space is the same, but we're shrinking.
Yeah. I mean that invites lots of other questions, like if I eat somebody tacos, how could I possibly be shrinking?
Because the talkers are shrinking too.
Then, yeah, that's another way to think about it. And you know, remember that we don't understand why the universe is expanding. It's not something that we understand and can make sense of. We don't know why it's happening, why it started happening five billion years ago, whether it will continue to happen. All we have are these observations that distances between things in space are expanding and expanding at an accelerating rate. So it's something we observe, and you have to just go back to the root experiment, like what is it we actually see, rather than you're trying to get tangled up in the various theories of cosmological concepts.
It's almost like the opposite of what happens when you grow up. Like I feel like when you're a kid, distances seem huge, like sitting in the car for an hour it takes forever. But when you grow up and you're an adult, distance is kind of shrunk in a way, right, Like sitting in an hour for get to work doesn't seem long enough actually, And so it's kind of the opposite of that. It's almost like relationship that matter has to space is changing, and that's what this is mean by expansion of the universe.
The universe is just growing up and eventually is gonna have a midlife crisis.
N it's going down, it's pulling out, Benjamin Bunton.
You think for the universe like now a billion years just like flits by in a moment, whereas when it was a kid it took forever.
Yeah, kind of in a way.
Right, yeah, yeah, maybe that that explains time dilation. Man, Man relativity is just about getting mature. I'll take that Nobel price right now. I'll buy your taco.
All right. We have a lot more of these most common questions that we get through the inbox, but first let's take a quick break.
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All right, I know we're answering our most common questions that we get through the inbox and through Twitter, and we've answered questions about black holes and the universe expanding, and we also have questions about particles, which is kind of your field of.
Expertise particles and tacos. Don't forget, I'm quite an expert on talk.
And particle tacos or taco particles.
Let's taco about it?
Is that what ao is?
That's right, that's when your tacos exchanged particles with your friends tacos.
Well, that's that's a no I know these days.
But that's right. Stay safe out there people, all right.
So our next question is asking about the charge of particles. So, for example, Nina Brown asked, I was wondering how particles could be charged and what that even means? Exclamation point question mark.
Oh man, I love this question because I have the same question and we still don't really know what particle charge is. It's very confusing.
Yeah, I like how she asked, what does that even mean?
It's wonderful because you know it's something where that's very familiar. People think about charge and electric charge you're familiar with lightning and whatever, but down at the particle level, like what does it mean for a particle to have electric charge? Like is it carrying something? Is there a charge like stuffed into it somewhere? Why do some of them have it some of them don't. It's a great deep question.
Yeah, because I guess she's really wondering, like because it seems arbitrary, like a particle has charged or it doesn't have charge, or it has positive charge, or it has a color charge. You know what determines that and why do they have it?
And the answer is that we don't know, and we have to just sort of root ourselves and what we have seen. Remember that all of these ideas about particle physics in the universe they come out of experiments that we've done, things we've seen, and that we're trying to describe about the universe. We don't always understand what's going on, and we're just sort of trying to build a structure that lets it all hang together. And for particle charge, the root thing that we see is that some little bits of matter, some particles, are affected by electric fields and magnetic fields, like you put electrons through an electric field, they will get accelerated. You put other particles, you know, particles that don't have electric charge through an electric field, they don't get accelerated. That's what it means to have electric charge. That's the root thing. We've seen that some particles are pulled by electric fields and some particles are not. That's really what a charge means.
So you're saying it's more of a philosophical answer, like they have charge because we've seen them have charged, or at least Daniel has seen them have charged.
Yeah, well, we see that some particles are affected by electric fields, and so we say, all right, let's say that those particles are different, and we'll create this idea of charge, and we'll use that as a description to say which particles are affected by electric fields and which ones are not. And then we'll look for patterns, and we'll look for trends, and we'll look for symmetries, and we'll try to understand that more deeply. But fundamentally, it's just really a label for the things we've observed.
Now, I wonder if what she's trying to get at is whether charge is a property of particles or the fields that make up the particles, you know what I mean, Like, is it something that gets a sign when the particle pops up or is it something that's just like a property of the field that they're part of.
Yeah, that's a great question. Mathematically, we sort of put it in the middle, like we think of particles, you know, as fields. Mathematically we think of its sort of in the middle. Like we write these things into our theories, and we say that the charge is the thing that connects the field with the particle. So for example, the photon field only interacts with things that have electric charge, and so it's really right there between it is how the two talk to each other. It's a thing that lets them talk to each other, the field and the particle. So it's sort of a property of their interaction.
Oh, I see, it's kind of maybe a property of both, kind of what you're saying.
Yeah, exactly. And you know, we have noticed some amazing interesting things about charge, Like charge is conserved. You know, you can't create it or destroy it. No matter how many particles you create or destroy, the total charge is unchanged. And that tells us that it must be something interesting and fundamental to the universe, sort of like energy. We think energy isn't changed in these interactions, and so that tells us it might be something deep, that it's connected somehow to something really deep about the universe and particles and fields. But the truth is we don't exactly know what.
Like it could be a thing itself, you know what I mean, Like it's something that's being conserved. So it's kind of like something that can be quantified in a way.
It can definitely can be quantified, yeah, absolutely, And you know there are other kinds of charge also, right, as you mentioned earlier, the strong force has its own equivalent of charge, and we call it color to be confusing and attempting to be poetic, and it has a lot of similar properties to electric charge, and that some particles have it, some particles don't. And there's one for the weak force. Some particles have it, some particles don't. It's one of the deep mysteries the physics is of why some particles have some of these charges and don't have other charges. It's very confusing, and what we're trying to do is make a unified vision understand how this all shook out and why it's this way and not the other way. But the truth is we just really don't know.
It sounds like it's almost like that the language of the universe is this charge, you know. Yeah, like some particles speak like romanitism, some don't, and that's how they interact with the fields around them in other particles.
Yeah, but why right? Why do some particles feel this and others don't? How did that happen?
And what does that even mean?
What does that even mean? Question mark? Exclamation point. That's like the reason I got into physics because I love asking that question what does that even mean? You know? We want to gather together these weird experiments you've seen and get some sort of deep understanding to peel back a layer of reality and reveal the way the universe like actually works.
Man, do you guys use exclamation points and question marks at the same time in your physics papers?
Oh? Only in the best ones?
All right, thanks for that question. Our next question is another common question that we get, and this one in particular, it came from Roger Grene, and the question goes, how do particles which I understand have zero volume make up matter so that stuff has volume. That's a great question.
It is a great question.
If particles have no volume, how can we have volume?
If the recipe for making a view is a bunch of particles and that each have zero volume, then why isn't your volume just the sum of a bunch of zeros which is zero? Right?
Right? Yeah? Or I guess maybe is my volume kind of an illusion? Kind of like if if you drill down and there's no real volume to any of my particles, does that mean that I am also devoid of volume?
Oh, I'll avote a lot of bad jokes there.
But if I eat a taco, Daniel, how does that affect my volume?
Where does that taco actually go? Well, there's lots of ways to attack this problem, and the most philosophical is to ask, like what do you mean by volume? And we had a whole podcast episode about like how small are particles? What do we mean by their size? Et cetera, et cetera. But that's a whole rabbit hole. Let's put that aside and say particles are points. Let's assume for now the particles actually have zero volume. Right, that's a good point. Yeah, So to try to get to the point here, the idea is that you can build something with non zero volume out of particles that have zero volume if you have a way to space them, right, there's something keeping them from overlapping, from crunching on top of each other, and you do, and they have forces. They have electric forces, for example, And so the reason that, like when you build a molecule, the atoms don't just lie on top of each other is that there are electrons circling those atoms that keep the nuclei apart, and the nuclei, how are positively charged, and they keep each other apart. So there are forces there that create sort of like a spacing, like a lattice that keeps everything from collapsing into the tiniest dump.
I guess it. Yeah, you're ready. It does depend on what you mean by volume, because if by volume mean like when something is there and it's not there, then particles almost have zero volume. But they're also kind of infinite volume, right because you can feel a particle all the way across the galaxy.
Technically, Yeah, yeah, technically, And so you could also say that if you're made of zero volume particles, even if they have spacing between them, then your real volume is still just the sum of all those zeros, even though they're distributed into sort of a cloud and you ask like, well, where do you stop If you're made of a bunch of particles that are spaced apart, where do you stop? Do you stop at the edge of the most like right most particle, or where it pushes back, as you were saying, like where it feels something right and where it pushes back is also not very satisfying because then it depends on what you're pushing with or against, Yeah, or against. If you push against dark matter, dark matter will pass right through you like you're not there. If you push against neutrinos, it will very lightly touch you. If you push against you know, a regular object like a stick, then you're pushing against the electromagnetic forces. So it depends on the kind of thing you're probing with. So it's not really very well defined. But if you just say, like, hey, you can make a cloud out of non zero particles that keep their spacing because of the forces between them, then you get a pretty good sense for why you aren't just a tiny dot.
Yeah, I guess maybe, Like if you go by effect and technically we all have infinite volume, Like you know, if someone across the universe feels me in a way and feels the forces that my particles exert. But if you talk, if you call volume, like where are the particles center that make up poorhead? Then because I have more than one, then you can sort of define a range of space like a volume of space, and that's maybe, that's yeah.
And so it's a slippery topic volume, you know, Microscopically, it doesn't really have a great analog to the way we think about it, like intuitively and macroscopically. And this is something we struggle with all the time when we take our common knowledge about how things work mass, volume, velocity, you know, time, and we try to apply them to the microscopic where the rules are really just totally different, and sometimes the very ideas break down and don't really have a great analog.
M all right, mind bending question, All right. Our next question from our most common question pile is a bit of a career question. I'm curious as to why you get this a lot. So the question goes, I've always loved physics but studied something else. Is it too late for me to learn physics for real? I'd like it for real.
At the end, we do get this question a lot, and I think that that's because our podcast has attracted folks who are really interested in questions at the universe and have a passion for understanding these things, but because of whatever happened to them in life, didn't end up studying physics. They studied computers or ended up in something else in their life. And maybe this has reignited their interest a little bit, and they're wondering, like, is the door closed? Is there still a path for me to like go back to school and get a degree in physics and actually do physics for real? Yeah?
And the answer is no, Right, anyone can study physics even for real.
Yeah, it's never too late. And it depends on your life and your personal situation, of course, and whether you have the time available and the financial means to go back to school. But there are lots of paths back into physics. And something I think that a lot of people don't understand is that you don't need like a formal physics undergraduate degree from a fancy university to get back into physics. I can tell the story of somebody here in Irvine who was always interested in physics but ended up in computers and working in software for fifteen years and then came to me one day to my office and said, look, I want to get back into physics. What can I do? And he just ended up taking a bunch of classes at UCI, not as an enrolled student, just like taking classes which you can do at most universities without getting into it like a degree program. You don't need to apply to become a freshman. You just take the classes you need. Then you can apply to graduate schools and you can say, look, I've done these courses, I got reasonable grades in them. And that student, for example, he's now a grad student at an Ivy League university in physics. And so it's totally possible. If you have the interest and you can do it in your spare time and sort of build up the basic knowledge you need, then you can jump right back in and the doors can still be open.
Yeah, you can still be like a physicist at any point in your life. I mean, people change careers all the time. I mean I know this one guy who was an engineer, but then he turned into a cartoonist. It sounds crazy, but you can change careers.
I heard he's now running a taco truck.
Isn't that true? Unfortunately it doesn't have a happy ending. It's actually worse, he's doing a podcast.
But the other side to this is that you don't need to be an official physicist with a capital P to ask interesting questions about the universe and to think about it and even to make progress. You know, there are lots of people out there who have figured that stuff out on their own, And physics is not owned by physics professors. It belongs to everybody. Wondering and curiosity about the universe belongs to everybody. So even if you aren't in a situation in your life where you can't go back to grad school in physics, you can still enjoy wondering about the universe and learning about physics.
All right, we have a couple of more questions here from our most commonly asked Questions pile, and we'll get into them. They are about black holes and gravitational waves. But first, let's take another quick break.
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Slash Live. All right, Daniel, we are going down our list of most commonly asked questions to the podcast, and our next question has to do with black holes. Question goes, do black holes move? And does this moving black hole leave any trail quote unquote trail a stretch space? And this is a question from a six year old in particular.
That's right?
Are you saying that a lot of six year olds ask this question? Or does this six year old ask one of our most common questions?
Yeah, this six year old put his finger on a question that we get a lot, which is, you know, are black holes sitting around or are they moving? And did they leave us some sort of like wake in space as they move the way like a boat leaves a wake in a lake. But I love that this question came from a six year old thinking about black hole. So congrats to is Sean and to his parents for encouraging wonder and care about the universe.
Yeah.
So I guess the question is, first of all, can black holes move or are they so massive and monumental that they're basically static in space?
It's a great question, and we have to remember, first of all that motion and position is always relative, right, So there's no like absolute motion. You can't ask is a black hole moving without saying what is it moving? Relative? Too? But the other side of that is that black holes follow the same rules as everything else, Stars and planets and galaxies, right, they all can move through space or relative to each other, just like black holes. And sometimes you'll see two black holes that are bound to each other and orbiting each other. So yes, they definitely can move through space just like everything else.
Yeah, and they can. I mean they basically act like any other object in space to the things around them, right, Like, you can have a black hole orbiting our solar system for example.
Yeah, you can't tell the difference gravitationally between a black hole and another object of the same mass. You're at the same distance between those two, you just can't tell the difference. They have the same gravitational effect. So yeah, we could orbit a black hole the way we orber the Sun. We could have a tiny black hole as part of our solar system that we wouldn't even have noticed. In fact, there are those folks that wonder about Planet nine whether it's a primordial black hole that's somehow stuck out there in the depth of our solar system. So black holes can move through space, and you know, there's even the possibility of black hole could move through space and come disrupt our solar system. We did a whole podcast episode about that. So, yeah, they're not like nailed in place there. They can move just like everything else.
Yeah, I wonder if what trips people of is that people often talk about black holes, or should I say, space traps as being kind of these like holes punctured in space time itself, or like these bubbles of space time. And so maybe it's hard to think about it moving around because it's I mean, when you punch a hole through a piece of paper, it doesn't you can't move it.
That's a good point, but remember that's true for everything. All kinds of matter change the shape of space, they change the curvature, they bend space, and where that is just depends on your frame of reference, and whether it's moving depends on whether you're moving. So if you can move past a black hole, then a black hole can move past you. Right, there's no like absolute frame in which these black holes are anchored.
All right, Well, I guess then the answer is yes, they can move. Space traps can move. And so if you're at there in space, watch out like you should look both ways before crossing the Solar System lane.
That's right, and the other part of his question was whether or not they like leave any trail behind them, any like wake through space. And we said earlier that the location of a black hole and its velocity depends just on its frame of reference, like are you moving with respect to it? If so, then it has velocity. But if a black hole is accelerating, if it's changing its velocity, then it absolutely will leave a wake through space the way a boat will when it moves through a lake. And those waves are called gravitational waves. They'll make these ripples in space.
It's like the change in velocity of something that is what generates a gravitational wave.
Yeah, exactly, because these frames of reference are called inertial frames of reference, and you can't tell the difference between any of them as long as they have no relative acceleration. But as soon as something has acceleration is changing its velocity, then it leaves a signal through space, and those signals are these gravitational waves. And that's what we've detected. In those underground detectors where they have the long laser beams to measure the stretching of space itself, they see two black holes, for example, orbiting each other and leaving all these ripples in space.
Which leads us to our next question. Speaking of gravitational waves, another common question we get is are gravitational waves the same as a graviton? Meaning is a graviton a gravitational wave or can a gravitational wave be a graviton or can you just have a wave without a graviton?
Great question, and it's very natural because people think about like electromagnetic waves, you know that think about light, and they know that light is made out of photons, these little quantized units of electromagnetic radiation, and so it's very natural to think about, well, for gravity, if you have gravitational waves, you know, is that the same thing as a graviton, this whole particle wave duality, And the answer is no. And the reason basically is that gravitational waves are really really big. They are huge effects in gravity, and gravitons if they exist, we expect them to be really really really small. So a gravitational wave might be made out of like zillions and zillions of gravitons, the way, for example, like a beam of light is made out of lots and lots of photons, So they're not the same thing. There are different scales and also gravitational waves. We know they exist. Gravitons still totally theoretical.
Right, We don't know if they're actually real because we don't know if gravity is quantum.
That's right. The only theory we have of gravity is this classical theory that says that gravity is smooth and continuous. It's not like chopped up into little units like everything else is. Like electromagnetic waves are made out of little units we call photons. You can't have an arbitrarily small size of them that come in discrete bits. And we don't know that about gravity. We think probably it is because everything else is, but we don't actually know that. We don't have a theory for it. So the graviton is the particle you would invent if you did have a theory of gravity. But we know the gravitational waves are real. So those things are out there, we've seen them. We don't know if they're made out of tiny little gravitons.
Right.
It's kind of like a water I guess, you know, like a wave in water. It's not the same as a molecule of water.
Yeah, we'd love to discover those water molecules. We'd love to figure out if gravity is quantum and if it's made out of gravitons, but we haven't seen those yet. And it's really hard because even the gravitational waves are hard to spot because gravity is really really weak compared to all the other forces. It's like billions and trillions times weaker, which means it's very hard to set its effects. And so to see a graviton would be to see an even tinier little bit of gravity. We're just not nearly sensitive enough.
All right, So I guess the answer is a gravitational wave is a gravity knot not necessarily a graviton. All right, Dan, I think we have time for one more of our most commonly asked question pile, and I'm going to pick this one here, which says, if he equals mc squared and a photon is massless, then how does a photon have any energy? How can a photon have energy if it's massless?
Yeah, this is a great question, and I love that people are doing this thinking they're like, I have this one idea, I have this other idea. Can I bring them together? Does this make sense? And that's physics, right, that's doing physics. It's saying I have this rule, where does it apply. Let me check make sure that it applies everywhere I understand it. And so it's great kudos to everybody who thinks about this and to ask this question. This one came from James Chad And so the answer is that the formula equals mc squared is not false. It's true, but it's not the most general formula. It's only talking about the energy that you get from mass. And there are lots of forms of energy. Right, there's energy and mass. There's also energy of motion, right, there's energy of rotation, there's energy of vibration. These are other forms of energy.
Right, But don't they all get lumped in the same energy at the end, right, Like if I have a slow moving particle and a fast moving particle, then the fast moving particle has more energy and can transform into heavier particles.
Yes, that's true, and so the most general expression for energy is not E equals mc squared. That's the expression you would use for a particle that's essentially not moving. There's a more general expression that says E equals mc squared plus momentum times the speed of light p time c. So there's another term there. And so for a photon, mass is zero. It doesn't have any of this rest mass that the other particles have, but it does have momentum. Essentially are pure momentum. They're the wiggle of the electromagnetic field. They are pure motion. There's no mass to them.
But wait, doesn't momentum imply mass like it? I remember an engineering when you study momentum, it's M times V, so mass times velocity.
Yeah, that's the non relativistic expression for momentum M times V. In relativity, we have a more general expression for momentum, and we can dive deeper into that rabbit hole. But now you do not have to have mass to have momentum, and photons we know have momentum. We talked about, for example, solar sales. Photons themselves from the Sun can push on something. When they bounce off of it, they transfer their momentum to the solar sale. So we know physically empirically the photons definitely do have momentum and they are essentially pure momentum. And so equals mc squared is the best known formula, but it's not the most general case, and in particle physics we use equals mc squared plus pc, and so for the photon M equals zero and the energy is just momentum times the speed of light P time c.
So it does have energy. Photons have energy, it just doesn't come from it having mass. It just comes from its emotion.
That's right. There are other ways to have energy, and that's what photons do. And they're weird because they have exactly zero masks.
And this more general formula applies to me and you too, Like my energy is both how much I weigh but also how much I'm moving.
Yeah, exactly, you have more energy if you're in motion than when you're sitting on your couch. Cool.
All right, well those are some of our most common questions, Daniel. What do you sort of make of all these questions?
I make that we have smart listeners, and that we have people out there that are intrigued by the way the universe works, and that this stuff is complicated, and that if you try to download it into your brain and play around with it, you'll find little rough edgcy you don't quite understand, or little bits that don't quite click together, and that that's not unusual, and that there are a lot of other people out there wondering about those same tricky bits. So I hope that these answers have helped a lot of people click those pieces together, and if not, feel free to write into us. We would love to help you resolve little questions you have about your understanding about the universe.
Yeah, and in some cases I feel like your answer was we don't know, which means that these are questions that physicists are also asking themselves at the forefront of science.
Yeah. Basically, at the end of every question, you could add and what does that even mean?
Exclamation point question mark? And we'll add a few more question marks there at the end.
Two. That should be the alt title for our podcast, exclamation point question.
Mark or maybe our next book, Daniel, what does that even mean? Exclamation point question mark?
To which the answer is the title of our first book.
We have no idea. It's a recursive book.
Really, that's right. Book three. Let's just go get takos.
Yeah, go back and read our first book while eating some takas and increase in your volume. All right, Well, we hope you enjoyed that and maybe connected a little bit more with people out there, because we all have a lot of the same questions about the.
Universe and don't be shy about writing to us, or engaging with us on Twitter at Daniel and Jorge or sending us email to questions at Daniel and Jorge dot com. We love your listener questions and we answer all of our email.
Yeah, and don't be shy about asking questions and pursuing knowledge and even maybe getting a physics degree late in life. 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. How is us dairy tackling greenhouse gases? Many farms use anaerobic digesters to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's last sustainability to learn more.
As a United Explorer Card member, you can earn fifty thousand bonus miles plus look forward to extraordinary travel rewards, including a free checked bag, two times the miles on United purchases and two times the miles on dining and at hotels. Become an Explorer and seek out unforgettable places while enjoying rewards everywhere you travel. Cards issued by JP Morgan Chase Bank NA Member FDIC subject to credit approval Offer subject to change.
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