Speaker 1: When you look up at the majesty of the night sky,
Speaker 1: when you marvel at the intricate beauty of our microscopic,
Speaker 1: quantum world, sometimes you just can't help but wonder where
Speaker 1: does it all come from? Why does our universe exist
Speaker 1: at all? Who or what is responsible for all of
Speaker 1: this crazy, beautiful, bonkers universe. That's the biggest hope and
Speaker 1: the biggest challenge for physics, not the small question of
Speaker 1: why are we here, but the much bigger, deeper question
Speaker 1: of why is there here at all? I Daniel, I'm
Speaker 1: a particle physicist, and welcome to the podcast Daniel and
Speaker 1: Jorge Explain the Universe, a production of I Heart Radio.
Speaker 1: On this podcast, we talk about everything in the universe,
Speaker 1: the stuff that's really big and vast and hard to understand,
Speaker 1: and the stuff that's super small and tiny and mind boggling,
Speaker 1: lee weird. We talk about all of it, and we
Speaker 1: explain it to you in a way that we hope
Speaker 1: actually makes sense and leaves you with the feeling that
Speaker 1: you have grappled with a small piece of the world,
Speaker 1: and one that you could import part of the universe
Speaker 1: into your brain and you can make a little model
Speaker 1: inside your head of what's going on out there in
Speaker 1: the universe, and that it can work. It can help
Speaker 1: you understand how the universe works, think about what it's doing,
Speaker 1: and make predictions about what it might mean. The goal
Speaker 1: of this podcast is not just for you to hear
Speaker 1: a bunch of fancy science sounding words and come away
Speaker 1: feeling like you were in the presence of science, but
Speaker 1: to invite you to include you in the process of science,
Speaker 1: because science is a human endeavor, is by the people
Speaker 1: of the people, and for the people, and you are
Speaker 1: the people. You're the people we are doing science for.
Speaker 1: It's not just for a bunch of folks in white
Speaker 1: lab coats and crazy hair. Is for everybody, because humanity
Speaker 1: wonders about the universe, and humanity deserves answers about the universe.
Speaker 1: And that's why humanity has decided to spend a non
Speaker 1: trivial amount of money paying for science. And that's why
Speaker 1: I think it's important that US scientists come back and
Speaker 1: talk to people and explain to them what we have learned,
Speaker 1: what it means, and connect back with that inherent curiosity that,
Speaker 1: in the end, is what's responsible for driving this entire wonderful, crazy,
Speaker 1: frustrating exhilarating project of unraveling the mysteries of the universe. Normally,
Speaker 1: I'm joined by my co host, Orge, him a cartoonist
Speaker 1: and roboticist, and we joke about bananas as he asks
Speaker 1: me crazy questions. But he's not availed well today, so
Speaker 1: I am taking the opportunity to catch up on questions
Speaker 1: from you instead. That's right. Our loyal listeners often send
Speaker 1: us questions things that they think about, that they are
Speaker 1: wondering about. They have imported a little bit of the
Speaker 1: universe into their minds and one piece of it doesn't
Speaker 1: quite make sense. And so I encourage everybody out there
Speaker 1: who has a question about the universe, something they are
Speaker 1: wondering about, something they would like to hear understood, to
Speaker 1: write to us. Send us your questions either on Twitter
Speaker 1: at Daniel and Jorge or via email two questions at
Speaker 1: Daniel and Jorge dot com. We right back to everybody.
Speaker 1: We answer every email. You will get your question answered.
Speaker 1: And sometimes the questions are interesting enough or fun enough
Speaker 1: that I want to answer them here on the podcast
Speaker 1: because I think other people might want to hear the
Speaker 1: answers to these questions. I think that probably a lot
Speaker 1: of people are wondering about those partaicular questions, and so
Speaker 1: on today's episode will be answering listener questions. I love
Speaker 1: all of our episodes, from the science fiction universe to
Speaker 1: the extreme universe to the everyday physics, but maybe closest
Speaker 1: to my heart are these questions that come from you,
Speaker 1: from the listeners who are wondering about the world. Because,
Speaker 1: as I said earlier, questions really are at the heart
Speaker 1: of science. Science doesn't move forward without people, individual folks
Speaker 1: asking questions about the universe and wanting to know the answer.
Speaker 1: Think about that graduate student or that physicist or that
Speaker 1: biologist out there devoting her life to answering one particular
Speaker 1: question about the way microbes work, or about the way
Speaker 1: rings form about a planet. It's because that person has
Speaker 1: a deep curiosity about that one question and needs to
Speaker 1: know the answer. So that's one of the joys of life,
Speaker 1: is figuring out who you are and what you want
Speaker 1: out of it, and what questions you want answered about
Speaker 1: the universe. So please don't hesitate. Send me your questions.
Speaker 1: I'd love to encourage them and to help give you
Speaker 1: a few answers. And particularly I'd like to encourage our
Speaker 1: listeners from Africa and from South America. We get questions
Speaker 1: from all over the world, but I was looking at
Speaker 1: the demographics recently and realizing that there's a group of
Speaker 1: people out there who have been a little more silent
Speaker 1: than the other folks. So if you're a listener in
Speaker 1: Africa or in South America, please take my special encouragement
Speaker 1: to write to us with your questions. We want to
Speaker 1: hear from you and we want to help you understand
Speaker 1: the universe. All right, so let's get to the first
Speaker 1: listener question. This one comes to us from a very
Speaker 1: young listener him names Megan. I'm nine years old. I
Speaker 1: heard my damma the show, and I want to ask
Speaker 1: you a couple of questions. So number one, how long
Speaker 1: does it take to get to a black hole? At
Speaker 1: number two, why are the stars round? Thank you for
Speaker 1: answering my question by well, thank you Megan for sharing
Speaker 1: your questions. I think she overheard her dad trying to
Speaker 1: answer questions for future topics. So thanks very much Megan's
Speaker 1: dad for letting Megan send in her questions and for
Speaker 1: encouraging science and curiosity in the next generation. So Megan
Speaker 1: asked us two questions. First, how long does it take
Speaker 1: to get to a black hole and why our stars around. Well,
Speaker 1: my first thought is like, why does Megan want to
Speaker 1: go visit a black hole? And is that a good idea?
Speaker 1: I mean, I certainly want to go visit a black hole.
Speaker 1: I want to go see what's inside them and maybe
Speaker 1: learn something deep about the nature of the universe and
Speaker 1: help unravel the secrets of quantum gravity. But you know,
Speaker 1: I'm not nine years old, and so I think it's
Speaker 1: up to Megan's dad to decide whether or not he
Speaker 1: should lend Megan the keys to the spaceship for this
Speaker 1: particular field trip. So how long does it take to
Speaker 1: get to a black hole? Say you wanted to get
Speaker 1: into a spaceship and go to visit one. Well, you know,
Speaker 1: there are two kinds of black holes out there in
Speaker 1: the universe that we've discovered. There are the one at
Speaker 1: the centers of galaxies, super massive black holes with masses
Speaker 1: like millions of times the mass of our sun. Those
Speaker 1: are spectacular and very interesting, but also really far away
Speaker 1: and hugely dangerous because they are the centers of galaxies
Speaker 1: where the radiation is intense and the X rays just
Speaker 1: from the black holes. Creation disc itself would be really intense,
Speaker 1: and then just the center of the galaxy is a
Speaker 1: pretty crazy spot. So there is another kind of black
Speaker 1: hole which I think would be much more reasonable to visit.
Speaker 1: And these are stellar black holes, the ones that result
Speaker 1: from a star aging and no longer having fusion pressure
Speaker 1: to push back against gravity, trying to squeeze it down,
Speaker 1: and eventually just giving up the ghost and becoming a
Speaker 1: black hole. And so the one that's nearest to us
Speaker 1: is actually only about eleven hundred and twenty light years
Speaker 1: from the Sun. It's called q V telescopy if you
Speaker 1: want to put that into your space navigation system. And
Speaker 1: you might ask, how long does it take to get
Speaker 1: to something that's eleven hundred light years away? Well, you know,
Speaker 1: if you traveled at the speed of light, of course,
Speaker 1: it would take eleven hundred years, which seems like a
Speaker 1: really long time, and it is. But there's a bit
Speaker 1: of a relativistic wrinkle we'll dig into there in a minute.
Speaker 1: But we, of course can't travel at the speed of
Speaker 1: light unless you develop some technology to like scan your
Speaker 1: body and convert it into photons and beam yourself somewhere else.
Speaker 1: But then you need some technology on the other side
Speaker 1: to receive those photons and reconstruct your body. So a
Speaker 1: more realistic way to go and visit a black hole
Speaker 1: is to build a spaceship that's actually capable of such flight. Now,
Speaker 1: there are two main limits to doing such a thing.
Speaker 1: One is acceleration. To get up to that speed, you
Speaker 1: have to speed up, and the human body has some
Speaker 1: pretty tough limits on how fast we can accelerate. If
Speaker 1: you try to accelerate more than five or ten GeSe,
Speaker 1: your insides will get liquefied, and so for comfortable travel
Speaker 1: over long periods, you really don't want acceleration much more
Speaker 1: than one G. So let's do the calculation. Say you
Speaker 1: had a spaceship that could accelerate at one G, you
Speaker 1: would actually get up to pretty close to the speed
Speaker 1: of light within just a couple of years, though most
Speaker 1: of the trip would be spent pretty close to the
Speaker 1: speed of light. So if you have to travel one thousand,
Speaker 1: one hundred and twenty light years, it would only take
Speaker 1: you one thousand, one hundred and twenty two years. Now,
Speaker 1: the other problem with this scenario, of course, is the fuel.
Speaker 1: To accelerate, you need fuel, and fuel makes your ship heavier,
Speaker 1: which means you need more fuel to accelerate it. So
Speaker 1: you have this rocket equation problem sometimes known as the
Speaker 1: toothpick problem, because accelerating something even as small as a
Speaker 1: toothpick up to very high velocities would require an enormous
Speaker 1: quantity of fuel. And so, for example, if Megan's ship
Speaker 1: was ten tons, which is really pretty small for a spaceship,
Speaker 1: it would require something like thirteen million tons of fuel
Speaker 1: for this kind of trip, and so basically the ship
Speaker 1: would be all fuel, and most of that fuel is
Speaker 1: there to help push the rest of the fuel. So
Speaker 1: this is why we talk about things like black hole
Speaker 1: power drives and other kinds of things. Of course, it
Speaker 1: would be kind of silly to have a black hole
Speaker 1: power drive to go visit a black hole. If you
Speaker 1: have a black holed power drive, that means either you
Speaker 1: can capture or make your own black holes anyway. But
Speaker 1: the relativistic wrinkle is actually quite interesting because while from
Speaker 1: Earth's point of view, it takes one thousand, one hundred
Speaker 1: and twenty two years before you reach that black hole.
Speaker 1: So that's like Megan's dad's clock. If he had a
Speaker 1: telescope and he was keeping an eye on Megan during
Speaker 1: her trip, he would see her clock running very slowly,
Speaker 1: according to him, very very slowly, so that by the
Speaker 1: time she reaches the black hole, she would only have
Speaker 1: experienced thirteen points seven years, So she would only be
Speaker 1: twenty two years old by the time she reached the
Speaker 1: black hole. Now, of course, for everybody back on Earth,
Speaker 1: more than a thousand years would have passed. And if
Speaker 1: she actually wants to turn around and come back to Earth,
Speaker 1: that's a whole other relativistic ring goal. When she turns around,
Speaker 1: special relativity gets really complicated because that's another kind of acceleration,
Speaker 1: and that gets us into the twin paradox, which we
Speaker 1: can talk about another time on the podcast. So, Megan,
Speaker 1: the answer is, it would take you more than a
Speaker 1: thousand years to reach a black hole, but from your
Speaker 1: point of view, it would only feel like about fourteen years.
Speaker 1: So factor that into your decision about whether or not
Speaker 1: to build your spaceship and go business black hole. But
Speaker 1: if you go and you do discover secrets of the
Speaker 1: universe and quantum gravity, please send me an email now.
Speaker 1: Megan's second question was why are things around? Like why
Speaker 1: are the stars round? Which is related to another really
Speaker 1: interesting question, you know, like why our planets around. Why
Speaker 1: is most of the stuff in the universe round? And
Speaker 1: the answer is gravity. A little bit counterintuitive, but gravity,
Speaker 1: even though it's the weakest force we know about, is
Speaker 1: the dominant force when it comes to the structure of
Speaker 1: astronomical stuff. The shape of the Earth, the shape of
Speaker 1: the Sun, all this kind of stuff is round because
Speaker 1: of gravity. And you can think about it pretty simply.
Speaker 1: Gravity pull stuff down, right, So if you have the
Speaker 1: Earth with anything sticking up on it, eventually that's going
Speaker 1: to get knocked down, maybe wind or water, or even
Speaker 1: if you don't have any atmosphere or water on the surface,
Speaker 1: any kind of process eventually is going to settle into
Speaker 1: a lower energy state. And for gravity, the simplest configuration,
Speaker 1: the lowest energy state is a sphere. So anything that's
Speaker 1: big enough to have its own gravity is eventually going
Speaker 1: to be round. That's why small things are not necessarily round,
Speaker 1: like asteroids and meteors are sometimes weird shaped because they
Speaker 1: don't have the gravity to pull themselves together into a
Speaker 1: round object. Whereas things as big as the Earth or
Speaker 1: even the Moon, or definitely the Sun, gravity does its
Speaker 1: thing and pulls anything that sticks out a little bit
Speaker 1: down until eventually you get a sphere. But of course
Speaker 1: not everything out there in the sky is a sphere, right,
Speaker 1: I mean, our Solar System is not a sphere. It's
Speaker 1: like a flat disc, and our galaxy is on a sphere.
Speaker 1: It's also a flat disc. So why is it that
Speaker 1: those things are not round? And that's because they have
Speaker 1: something which can actually overcome gravity, and that's spin, that's rotation.
Speaker 1: The Solar System is spinning. The Earth is spinning around
Speaker 1: the Sun. That's why it doesn't fall in due to
Speaker 1: the Sun's gravity, because it has enough velocity to stay
Speaker 1: in orbit. And the same thing with the Sun. The
Speaker 1: Sun is spinning around the center of the galaxy, which
Speaker 1: is why the Sun and all the other stars don't
Speaker 1: just fall into the black hole at the center of
Speaker 1: the galaxy. And that's why black holes have an accretion
Speaker 1: disk around them, because that rotation keeps stuff from falling in.
Speaker 1: So you have a couple of forces here at play.
Speaker 1: Mostly you have gravity dominating for things like the size
Speaker 1: of the Moon and up to the Sun. But then
Speaker 1: if things are spinning fast enough, they will turn into
Speaker 1: a disk. Like if you took the Earth and you
Speaker 1: spun it faster, it would turn into a disk. In fact,
Speaker 1: the Earth itself is not exactly sound because it's spinning.
Speaker 1: The distance from the surface to the center of the
Speaker 1: Earth is actually greater at the equator because the Earth
Speaker 1: is spinning, and if you spun the Earth even faster,
Speaker 1: it would eventually turn into a pancake. And the same
Speaker 1: with the Sun. So everything out there is balancing a
Speaker 1: bunch of different forces. Mostly you don't see the effect
Speaker 1: of electromagnetism or the weak nuclear force, or even the
Speaker 1: strong force on the shapes of astronomical objects because they're
Speaker 1: mostly balanced out. The Earth doesn't have an overall positive charge.
Speaker 1: The Sun doesn't have an overall negative charge. If it did,
Speaker 1: that force would be so strong, it's so much more
Speaker 1: powerful than gravity that you would get these streams of
Speaker 1: basically currents until things did get balanced out. But gravity
Speaker 1: can't get balanced out. There is no opposite charge to gravity.
Speaker 1: There's no negative mass that can create anti gravity to
Speaker 1: balance out gravity. Gravity is always there, it always has
Speaker 1: to be contended with, has to wait until everything else
Speaker 1: gets sorted out and neutralized for it basically gets to
Speaker 1: take the field and dominate. But eventually gravity takes over,
Speaker 1: and that's why gravity is the dominant force for the universe,
Speaker 1: and that's why the Sun and the Earth are around.
Speaker 1: All right, Megan, thanks very much for those wonderful questions.
Speaker 1: I want to get to some more or lessen our questions,
Speaker 1: but first let's take a quick break. Hello, we are
Speaker 1: back and this is Daniel and I'm answering questions from
Speaker 1: listeners who want to understand the nature of the universe. So,
Speaker 1: without further ado, here's our next question. Hello Daniel, So
Speaker 1: what happened wondering for some time about anti matter stars?
Speaker 1: We know matter is everywhere in the universe, and antimatter
Speaker 1: just doesn't exist in quantities that are big enough for
Speaker 1: anything like this. But if there was an ant I'm
Speaker 1: at their star, or if there is, say one in
Speaker 1: the whole universe, how could we tell it's an antime
Speaker 1: matter star? How would it be different? It would shine
Speaker 1: like a normal star or with it? Thank you? All right,
Speaker 1: super fun question. I love this kind of question, like
Speaker 1: how do we know what we know? Is it possible
Speaker 1: for this weird, crazy scenario I've thought of in my
Speaker 1: mind to be our reality? And that's a very important
Speaker 1: kind of thought process, and that's basically what physicists are doing.
Speaker 1: We're always wondering, all right, here's what we know. What
Speaker 1: is that consistent with? Is there a way I could
Speaker 1: imagine the universe to be different and still look the
Speaker 1: same way. Are we being fooled by our preconceptions? So
Speaker 1: it's this kind of creative, out of the box thinking
Speaker 1: that's really vital in science. So let's dig into it first.
Speaker 1: Let's just remind ourselves, like, what is anti matter? What
Speaker 1: do we know about it? The existence of anti particles
Speaker 1: is one of the most incredible and beautiful symmetries for me.
Speaker 1: In the universe. Every particle that we know of, every fermion,
Speaker 1: electrons and corks and neutrinos, and all of these particles
Speaker 1: have a partner particle. There's like this symmetry where you
Speaker 1: reflect all these particles and boom, they all have an
Speaker 1: exact opposite. So the electron, for example, has the positron,
Speaker 1: which is a positively charged version of the electron, and
Speaker 1: the muan, which is naturally negatively charged, also has a
Speaker 1: positively charged version. Each of the corks, like the upcork
Speaker 1: and the down core, have an anti up and an
Speaker 1: anti down. This is stuff that you hear about in
Speaker 1: science fiction, but it's actually real. It's out there in
Speaker 1: the universe. It's a kind of thing that can exist.
Speaker 1: And when we do particle physics, we're often exploring two
Speaker 1: different questions. One is can this stuff exists? Like what's
Speaker 1: out there theoretically on Nature's menu, which if you made
Speaker 1: the right conditions, could exist in the universe. And then like,
Speaker 1: is there any of it? How do you actually make it?
Speaker 1: And we created which is a totally separate question. But
Speaker 1: antimatter is something that's in the universe, and frankly, we
Speaker 1: don't know why. Why does every particle have this mirror
Speaker 1: version of itself? Why does that exist? It tells us
Speaker 1: something deep about the nature of the universe that every
Speaker 1: particle seems to come in pairs. Maybe it means that
Speaker 1: we shouldn't even think about the particles as in pairs.
Speaker 1: Maybe the fundamental object is the pair, not the particle, right,
Speaker 1: because if everything comes as part of a unit, then
Speaker 1: maybe that unit is the thing that's part of the universe.
Speaker 1: This is kind of the deep fundamental theoretical questions. You
Speaker 1: could have been a lot of time smoking banana appeals
Speaker 1: and thinking about and we do a lot of experiments
Speaker 1: to try to understand antimatter. We make it at certain
Speaker 1: but we can't make a whole lot. You have to
Speaker 1: smash protons and do a big block of matter, and
Speaker 1: some little bits of antimatter come out sometimes and we
Speaker 1: can collect it and do experiments about it. And one
Speaker 1: really interesting question we have about antimatter is is it
Speaker 1: actually an exact copy? Is it really the same thing
Speaker 1: as matter, but with the charges reversed, our anti electrons
Speaker 1: really just the exact opposite of electron. And one way
Speaker 1: to think about that, and this is I think the
Speaker 1: direction of this question about antimatter stars is does antimatter
Speaker 1: behave the same way as matters? Like can you make
Speaker 1: big complicated things out of antimatter the same way you
Speaker 1: can out of matter? And we've done these kinds of
Speaker 1: experiments so far. We've made things like anti hydrogen, which
Speaker 1: is an anti proton with an anti electron in orbit
Speaker 1: around it, and we've studied and we've asked like, well,
Speaker 1: does it look like hydrogen? Does it radiate energy the
Speaker 1: same way? Does it follow the same physical laws? And
Speaker 1: so far the experiment suggests that it does. We've never
Speaker 1: detected any difference between the way antimatter works and the
Speaker 1: way that matter works, So it seems like a perfect symmetry.
Speaker 1: And yet there's a big mystery there because we know
Speaker 1: it can't be a perfect symmetry. How do we know that, Well,
Speaker 1: the universe is most be made of matter, right, I'm
Speaker 1: made of matter, You're made of matter. The Sun is
Speaker 1: made out of matter, The Solar System is made out
Speaker 1: of matter. If matter and antimatter are basically symmetric, and
Speaker 1: the universe treats them exactly the same way, why is
Speaker 1: there more matter than there is antimatter? This is one
Speaker 1: of the deepest questions in physics. We just don't know
Speaker 1: the answer. You know, we imagine that when the universe
Speaker 1: began that things were symmetric, because it's hard to imagine
Speaker 1: anything else. If you imagine the universe started out with
Speaker 1: more matter than antimatter, you're just sort of like presupposing
Speaker 1: the answer to the question and introducing a new question.
Speaker 1: If the answer to the question why does the universe
Speaker 1: have more matter than antimatter is just well it started
Speaker 1: that way, then you can just ask why did it
Speaker 1: start that way? So it's more interesting to start from
Speaker 1: the assumption that the universe began with equal amounts of
Speaker 1: matter and antimatter. But now we don't have as much matter.
Speaker 1: So what happened to it? Well, we know what happens
Speaker 1: when matter and antimatter meet each other. They annihilate. What
Speaker 1: does that mean? And from a particle physics point of view,
Speaker 1: it's not magic. It just means that, like when an
Speaker 1: electron meets a positron, they can turn into a photon.
Speaker 1: They turn their matter into energy. Right, this is E
Speaker 1: equals mc squared. Matter is really just a form of energy,
Speaker 1: and so you can turn that matter into energy and
Speaker 1: they can annihilate into a photon, or they can annihilate
Speaker 1: into a z boson. Quarks can meet anti quarks and
Speaker 1: turn into photons. They can also turn into gluons. So
Speaker 1: all these kinds of matter can annihilate and turn into energy,
Speaker 1: which can then do whatever energy wants to do. So,
Speaker 1: if there was an equal amount of matter and antimatter
Speaker 1: in the early universe, you would expect it would eventually
Speaker 1: meet and annihilate itself, and we would have a universe
Speaker 1: just filled with photons and gluons and z bosons and
Speaker 1: stuff like that. But we don't. We still have matter
Speaker 1: left over, and so people wonder, like, is there some
Speaker 1: process in the universe which preferentially turns antimatter into matter,
Speaker 1: so that we ended up with a little bit more matter,
Speaker 1: and then the rest of an annihilated and we had
Speaker 1: some leftover, which is just matter, which is what we are,
Speaker 1: which is what created the entire universe that we are
Speaker 1: living in. So that's the idea, but we've never explained that.
Speaker 1: We don't have an understanding of how that happens. There
Speaker 1: are a few processes and particle physics we found which
Speaker 1: seemed to prefer creating matter to antimatter, and these things
Speaker 1: are like CP violating processes and be in k masons.
Speaker 1: And you can listen to our podcast episode about CP
Speaker 1: violation if you want to hear more about that. But
Speaker 1: these are not big enough to explain the asymmetry. The
Speaker 1: account for a tiny fraction of the asymmetry. You need
Speaker 1: a much more dramatic way to turn antimatter into matter
Speaker 1: to explain the universe that we see. So we don't
Speaker 1: understand it. And this suggests to us that there is
Speaker 1: some asymmetry between matter and antimatter. There really is some
Speaker 1: reason why the universe prefers matter to antimatter, and we
Speaker 1: want to know what that is, right, We want to
Speaker 1: know why, because that seems like a d truth about
Speaker 1: the universe. But then there's another possibility, the other possibilities.
Speaker 1: Hold on a second, and this is the question that
Speaker 1: was asked ret least, how do we know there isn't
Speaker 1: more antimatter out there? Are we just assuming that all
Speaker 1: the stars out there are made of matter? What if
Speaker 1: they were made out of antimatter? Right? The question is
Speaker 1: wonderful because you're exactly right, and antimatter star would look
Speaker 1: a lot like a matter of star. If antimatter can
Speaker 1: do things like make anti hydrogen, then why can't anti
Speaker 1: hydrogen anti fuse into anti helium. If it did, it
Speaker 1: would produce photons just like the matter version of that process.
Speaker 1: So mostly you're right that antimatter stars would look like
Speaker 1: normal stars. And so when you're looking out in the sky,
Speaker 1: it is possible that some of those stars might be
Speaker 1: anti matter stars. But it's not exactly the same because
Speaker 1: stars don't just produce photons. Obviously, they produce lots and
Speaker 1: lots of photons. As you're out there sunning your face
Speaker 1: on a nice winter morning, it doesn't really matter if
Speaker 1: those photons came from a star or an antimatter star.
Speaker 1: Because the photon is a boson, it doesn't have an
Speaker 1: antimatter version of itself, and so it could come from
Speaker 1: an antimatter star. But stars make other things too. You're
Speaker 1: familiar with the solar wind, for example, the solar wind
Speaker 1: is a stream of particles that come out of the
Speaker 1: Sun when fusion happens. In the crazy chaos of a star,
Speaker 1: you don't just make light. You make neutrinos, you make electrons,
Speaker 1: you spew off protons, And so that solar wind can
Speaker 1: tell us something about what kind of star it is,
Speaker 1: because an antimatter star would make anti solar wind, right,
Speaker 1: it would preferentially produce anti protons and positrons and anti
Speaker 1: neutrinos and all sorts of other crazy stuff. All right,
Speaker 1: but these stars are still really far away, right, how
Speaker 1: would we know if those stars were making this antimatter
Speaker 1: solar wind. Well, inside our solar system, we're pretty sure
Speaker 1: everything's made of matter, right, don't think that one of
Speaker 1: the planets is made out of antimatter. And then we
Speaker 1: have two ways of figuring out whether other stars might
Speaker 1: be made out of antimatter. One is just to look
Speaker 1: at cosmic rays. Cosmic rays, some of them come from
Speaker 1: the Sun, but a big proportion of them don't come
Speaker 1: from the Sun. They come from the other stars in
Speaker 1: our galaxy. And so this like galaxy solar wind, is
Speaker 1: an accumulation of all the solar wind from other stars,
Speaker 1: and that contains a lot of particles, and some of
Speaker 1: them are antiparticles. Right, There are positrons and there are
Speaker 1: anti protons in that wind. Cosmic rays sometimes are antiparticles,
Speaker 1: but we don't think that comes from anti stars. We
Speaker 1: have an explanation for how you can make antiparticles like
Speaker 1: pretty simply photons sometimes split into positrons and electrons, and
Speaker 1: so we have an idea and we can explain even
Speaker 1: how to make anti protons in solar wind. So basically
Speaker 1: the cosmic rays that we see here on Earth or
Speaker 1: in our telescopes up in space are to totally consistent
Speaker 1: with the stars in our galaxy being made out of
Speaker 1: matter and not antimatter. If there was antimatter, then we
Speaker 1: would see heavier stuff. We would see like anti iron
Speaker 1: or anti uranium or anti oxygen stuff like that. We
Speaker 1: see heavy versions of those elements in cosmic rays. It's
Speaker 1: a tricky topic. We don't have precise measurements, but we
Speaker 1: don't see any anti heavy elements in cosmic rays, so
Speaker 1: we don't think that there are anti stars sort of
Speaker 1: in our galaxy. Now cast your mind a little further, right,
Speaker 1: How do we know that Andromeda, for example, isn't made
Speaker 1: entirely out of anti stars? Are we measuring the solar
Speaker 1: wind from that galaxy? That's a lot harder to do, though.
Speaker 1: We do get particles from Andromeda, of course, but more generally,
Speaker 1: we have another technique for figuring out if there are
Speaker 1: like big antimatter patches to the rest of the universe,
Speaker 1: and that's by thinking about where the matter and antimatter
Speaker 1: patches might cross. Like if our galaxy was made of
Speaker 1: matter and Andromeda was made of antimatter, then the antimatter
Speaker 1: particles from Andromeda would be hitting the matter particles from
Speaker 1: our galaxy somewhere in between. And what would happen while
Speaker 1: they would annihilate and you would see this like surface
Speaker 1: of that was creating photons and other kinds of particles
Speaker 1: at a particular energy, because you'd expect, for example, when
Speaker 1: an electron annihilates with a positron, it turns into a
Speaker 1: photon that mostly has the energy of twice the mass
Speaker 1: of the electron. So there's this characteristic flash of light
Speaker 1: that happens when antimatter and matter annihilate, and we can
Speaker 1: look to see sort of at the boundary between our
Speaker 1: two galaxies if that's being created and we don't see it.
Speaker 1: And this is a very powerful way to look deep
Speaker 1: into the universe and see, like, are there surfaces, there
Speaker 1: are their boundaries between matter and antimatter regions of the universe,
Speaker 1: And so we haven't explored the entire universe this way.
Speaker 1: We've looked out past our galaxy cluster in between other
Speaker 1: galaxy clusters, and we've ever seen any evidence of like
Speaker 1: massive annihilation of matter and antimatter into photons, which is
Speaker 1: what you would expect to see again at one of
Speaker 1: these sort of like boundaries between a matter region and
Speaker 1: an antimatter region of the galaxy. So we haven't ever
Speaker 1: detected that. Now, that doesn't mean we can rule it
Speaker 1: out entirely in the entire universe, right there could be
Speaker 1: a portion of the universe that's so distant that we
Speaker 1: just can't probe it yet with these methods. Absolutely, we've
Speaker 1: looked sort of like the ten megapars x scale. We
Speaker 1: know that our large neighborhood doesn't have any significant antimatter
Speaker 1: in it, that doesn't mean that there isn't antimatter in
Speaker 1: the rest of the universe. So yes, absolutely, there could
Speaker 1: be an antimatter galaxy out there somewhere super far away
Speaker 1: and we just haven't seen it yet, or evidence of
Speaker 1: its cosmic rays annihilating with a cosmic rays from a
Speaker 1: matter galaxy. It's certainly possible, and that would be sort
Speaker 1: of a beautiful explanation to this mystery of antimatter. If
Speaker 1: it turns out that the universe actually is symmetric to
Speaker 1: matter an antimatter, If there are matter patches of the
Speaker 1: universe and anti matter patches of the universe, and that
Speaker 1: they're in balance somehow, then of course you have to
Speaker 1: wonder like, well, why did this become a matter patch
Speaker 1: and why did that become an antimatter patch. But you
Speaker 1: can imagine such things being answered by quantum mechanical randomness
Speaker 1: and the formation of structure and all sorts of fun
Speaker 1: stuff like that. But to meanwhile, we're digging into the
Speaker 1: question of whether there are larger asymmetries between matter and antimatter. If,
Speaker 1: as we suspect, the universe is mostly matter, then we're
Speaker 1: trying to understand what that means, because we think that
Speaker 1: that's going to tell us something about like why there
Speaker 1: is matter at all, why we're not just living in
Speaker 1: a universe filled with photons. So if it's true that
Speaker 1: the universe is mostly matter, then we should be grateful
Speaker 1: that there's an asymmetry, because that is in fact why
Speaker 1: we are here. Alright, wonderful question. Thanks very much for
Speaker 1: sending that in. I want to answer one more question,
Speaker 1: but first let's take another break. Okay, we're back and
Speaker 1: we're talking about the nature of the universe, symmetries and
Speaker 1: black holes, and now we have a fun question from listeners.
Speaker 1: That's maybe one of the deepest questions in physics and philosophy. Hi,
Speaker 1: Daniel and Jorge. I know this often gets slumped into
Speaker 1: the realm of philosophy, but is there a physics explanation
Speaker 1: of why there is anything rather than nothing in the universe?
Speaker 1: Why does any of this exist? What may have triggered
Speaker 1: any of the matter, energy and forces we observe? Thanks
Speaker 1: James Chronister, Thank you James for not being afraid to
Speaker 1: ask the biggest and deepest questions and the questions that
Speaker 1: overlap with philosophy. I don't think that's a negative thing
Speaker 1: to be lumped in with philosophy. I think it's wonderful.
Speaker 1: I think it means our questions are relevant. You know,
Speaker 1: philosophy tells us what our questions mean and why they're interesting,
Speaker 1: and why we want an answer to them and how
Speaker 1: to think about them. And so I think that all
Speaker 1: of the deepest questions in physics have philosophical implications. That's
Speaker 1: why they're exciting. You know, if you knew exactly how
Speaker 1: the universe was created, for example, from a physics point
Speaker 1: of view, that would definitely have philosophical implications. So I
Speaker 1: think the most fun questions in physics are the ones
Speaker 1: that also get philosophers excited. And you're right, there's been
Speaker 1: a lot of philosophical discussion back to the ancient Greeks
Speaker 1: about why is there something rather than nothing? And it's
Speaker 1: a really fun question to think about. And first I
Speaker 1: think you should think about, like, what do we mean
Speaker 1: by nothing? What is the opposite idea that we're considering.
Speaker 1: On one hand, we have the universe and us and
Speaker 1: there's definitely something here. What is the alternative that we're
Speaker 1: wondering about. What is the thing that we're trying to
Speaker 1: rule out? What is the nature of nothing? You know?
Speaker 1: And let's knock down first some very simple ideas about
Speaker 1: what nothing might be from a physics point of view.
Speaker 1: It's not just like not having this stuff, not having
Speaker 1: these stars and these galaxies and these particles, right, It's
Speaker 1: something deeper. It's something about the possibility of things being
Speaker 1: in the universe, about the nature of existence itself. It's
Speaker 1: a pretty weird thing to consider, you know, a universe
Speaker 1: with nothing or not a universe. You couldn't ever like
Speaker 1: do an experiment to prove that nothing exists, because of
Speaker 1: course your experiment is a thing, and so we can't
Speaker 1: really prove it. And so that's why this is a
Speaker 1: fun sort of philosophical question. But what I still think
Speaker 1: that we can make progress on if we think about
Speaker 1: what physics has told us about the nature of the
Speaker 1: universe and the nature of nothing. By nothing, do we mean,
Speaker 1: for example, just space, but with no matter in it,
Speaker 1: like delete the stars, delete the galaxies, delete the planets,
Speaker 1: delete all the stuff that's out there in the universe.
Speaker 1: Is that what we would consider to be nothing. Well,
Speaker 1: I think it's an interesting question, like why doesn't that
Speaker 1: universe exist rather than ours? But I think the question
Speaker 1: goes deeper, right because I think and that's question, you
Speaker 1: will still ask, well, why is there space? Why is
Speaker 1: there a universe for things to be in? Even if
Speaker 1: there don't happen to be anything's in it right now,
Speaker 1: that universe still has the possibility of things. And more specifically,
Speaker 1: we know that physics tells us that even space is
Speaker 1: not really empty a bowl. There's no such thing really
Speaker 1: as empty space. If you somehow remove all the matter
Speaker 1: in space and make as good a vacuum as you can,
Speaker 1: then there's still a thing there, and that's space because
Speaker 1: space has inside of it quantum fields, and those quantum
Speaker 1: fields we know, are always buzzing with energy. Despite your
Speaker 1: best effort to reduce the energy of that space, quantum
Speaker 1: fields can't go down to zero energy. It's a fundamental
Speaker 1: property of quantum fields that their lowest state is not
Speaker 1: add zero energy. And in our universe at least there's
Speaker 1: one field, the Higgs Boson field, which is totally rife
Speaker 1: with energy. It's stuck. It's at this weird a minimum
Speaker 1: that has a lot of energy in it, and so
Speaker 1: there's a lot of energy and even what we think
Speaker 1: about as empty space. And some people who think about
Speaker 1: the nature of the universe and why is there something
Speaker 1: rather than nothing take this as the answer. They say, well,
Speaker 1: there has to be something because space is filled with
Speaker 1: quantum fields, and those fields have energy and so boom,
Speaker 1: therefore there has to be something. I don't really find
Speaker 1: that answer to be satisfactory, because it really just suggests
Speaker 1: another question, which is, you know, well, why do those
Speaker 1: quantum fields even exist? And I like the way that
Speaker 1: a philosopher David Albert put about it. He says, quote,
Speaker 1: the fact that some arrangements of fields happen to correspond
Speaker 1: to the existence of particles and some don't is not
Speaker 1: a whit more mysterious than the fact that some of
Speaker 1: the possible arrangements of my fingers happen to correspond to
Speaker 1: the existence of a fist and some don't. Really, he's
Speaker 1: saying that it's not really that interesting to think about
Speaker 1: why are the fields sometimes making a planet and why
Speaker 1: are the fields sometimes making empty space? The question really
Speaker 1: is why are the fields right? Why do we have
Speaker 1: fields at all? Why do we have space even that
Speaker 1: has the possibility for fields. And this is the deep
Speaker 1: question I think that physics should answer, and this is
Speaker 1: sort of where physics is. We know that space is
Speaker 1: out there, We know that every bit of space is
Speaker 1: filled with quantum fields, and those quantum fields have energy.
Speaker 1: And so from that starting point we can ask the question,
Speaker 1: what does physics have to say about the nature of
Speaker 1: nothing and why there is anything? Because remember, the goal
Speaker 1: of physics is to try to grapple with the universe
Speaker 1: to make sense of it. And I think an important
Speaker 1: part of making sense of the universe is just understanding
Speaker 1: why it exists. You know, we want to understand that
Speaker 1: if the universe exists, it should be because it has
Speaker 1: to exist or because it cannot not exist. The nature
Speaker 1: of physics is to get the simplest possible explanation for
Speaker 1: the universe as we see it. You know, we use
Speaker 1: Acam's razor and we remove anything from our explanation that's
Speaker 1: not necessary. We want to boil it down to the smallest,
Speaker 1: simplest description. That doesn't mean we want to boil it
Speaker 1: down to nothing, right, That's why I think about the
Speaker 1: question in this way, is the simplest thing something or
Speaker 1: is the simplest thing nothing. It might be that nothing
Speaker 1: is sort of incoherent. You know, what do we even
Speaker 1: mean by nothing? So from that point of view, if
Speaker 1: we understood the simplest, deepest nature of the universe, we
Speaker 1: might be able to point to it and say, oh, look,
Speaker 1: this is the simplest possible thing. It's even simpler than nothing.
Speaker 1: So that might be why the universe sort of has
Speaker 1: to exist. So we're jumping ahead of us a little
Speaker 1: bit and digging into the implications of the answer. But first,
Speaker 1: let's talk a little bit more about what quantum physics
Speaker 1: and general relativity tell us about the nature of space
Speaker 1: and what that says about why it exists. So, of
Speaker 1: course we have two different voices in this story. We
Speaker 1: have the voice of quantum mechanics and the voice of
Speaker 1: general relativity, which tell us two very different stories about
Speaker 1: the nature of space and give us two very different
Speaker 1: answers about why the universe should or shouldn't exist. So
Speaker 1: let's start with quantum mechanics. Quantum mechanics treats space and
Speaker 1: time very very differently. Quantum mechanics says space is the
Speaker 1: place where quantum fields are. Every point in space is
Speaker 1: just a place where quantum field has a value over here,
Speaker 1: the electron field has one value. Over there, the electron
Speaker 1: field has another value. That's all a quantum field is.
Speaker 1: It's just a point in space with a value in it.
Speaker 1: Sometimes that values a vector, Sometimes it's a number, sometimes
Speaker 1: it's more complicated. Whatever, it's just a point in space.
Speaker 1: But time is separate. Time is how those fields evolved.
Speaker 1: And the most famous equation in quantum mechanics the Shortinger equation.
Speaker 1: That's what that equation is about. It tells you if
Speaker 1: you have a quantum wave function or graduate that to
Speaker 1: a quantum field. It tells you how that changes with time.
Speaker 1: And the most important thing about the Shorteninger equation is
Speaker 1: that it says that quantum information is never lost. Like
Speaker 1: a quantum wave function, changes as time goes on. Maybe
Speaker 1: a photon spreads out, or maybe interact with the wall
Speaker 1: or something happens, but the information is not lost. According
Speaker 1: to quantum mechanics and the shorting Your equation, everything about
Speaker 1: the past is encoded in the present. This means that
Speaker 1: you can reconstruct what happened in the past just by
Speaker 1: looking at the information about the arrangement of quantum particles
Speaker 1: now and the really fascinating thing about this is that
Speaker 1: it says that this works backwards and forwards. Right. The
Speaker 1: shorting your equation can tell you how your wave functions
Speaker 1: will change as the future goes on. It won't tell
Speaker 1: you what the actual outcomes of experiments are, right. That
Speaker 1: depends on this whole measurement problem that we're not going
Speaker 1: to dig into today. But it tells you how the
Speaker 1: probabilities evolved and how they have evolved in the past.
Speaker 1: What that means is that quantum mechanics says the universe
Speaker 1: should basically be eternal because quantum information can't be destroyed,
Speaker 1: which means if it exists now, it always has to
Speaker 1: exist and it can't have not existed in the past.
Speaker 1: So from the wanting to you quantum mechanics, the universe
Speaker 1: has to have always existed. There can't be a point
Speaker 1: in the time line of the universe where it doesn't
Speaker 1: exist if it does exist today. So it sort of
Speaker 1: requires this like consistency as a function of time. Now,
Speaker 1: the mystery is that general relativity tells us a different story. Right.
Speaker 1: General relativity tells us that space and time are very
Speaker 1: very closely connected. It prefers a tightly bundled space and
Speaker 1: time where the two react together to the presence, for example,
Speaker 1: of mass in the universe and general relativity is what
Speaker 1: helps us understand the fact that the universe is expanding.
Speaker 1: It's not just that we have a universe, and not
Speaker 1: just like why is there something? Why is there every
Speaker 1: year more of that something than there was before? Right,
Speaker 1: the universe is expanding, it's growing, and when we think
Speaker 1: about the nature of that space, right, it tells us
Speaker 1: that space can be created. What's happening now between us
Speaker 1: and other galaxies is the stretching of space, the creation
Speaker 1: of new space. That means that space isn't eternal. It's
Speaker 1: being made right now by some process that we do
Speaker 1: not understand, and that tells us a different story about
Speaker 1: the nature of space, this basic fundamental thing that we're
Speaker 1: struggling to understand why it has to exist. Maybe it
Speaker 1: doesn't have to exist because there's some process that can
Speaker 1: make it, which means maybe the opposite is true as well.
Speaker 1: And in fact, because we don't understand the mechanism of
Speaker 1: this creation of space, is suggests that the mechanism might
Speaker 1: be reversible. And there's still this possibility that dark energy
Speaker 1: will stop and it will halt the accelerating expansion of
Speaker 1: the universe and turn things around and bring it all
Speaker 1: back and crunch it back together to make a new singularity,
Speaker 1: the time symmetric version of the Big Bang right pulled
Speaker 1: together down to a big crunch. And this would involve
Speaker 1: not just the compactification of space, but the destruction of space,
Speaker 1: the shrinking of distances between things, exactly the same way
Speaker 1: that dark energy right now is expanding the distances between
Speaker 1: things by creating new space. This would involve the compactification.
Speaker 1: This would involve the destruction of space, the shrinking of
Speaker 1: distances between things, not just moving things through space, but
Speaker 1: actually destroying the space between them. That's pretty hard to
Speaker 1: think about, but it gives you a clue about like
Speaker 1: what's fundamental to the universe. Now. The problem is, we
Speaker 1: don't really believe that either these theories are correct. We
Speaker 1: look at general relativity and we look at the history
Speaker 1: of the universe, and we say, it doesn't really make
Speaker 1: sense for the universe to always have existed. The quantum
Speaker 1: mechanical view that the universe can't have had a beginning
Speaker 1: because the information in the wave function of the unverse
Speaker 1: can't be destroyed doesn't seem quite right. It doesn't job
Speaker 1: with our observation that the universe does seem to have
Speaker 1: had a beginning, it seems to only have been fourteen
Speaker 1: billion years old. On the other hand, if we retreat
Speaker 1: to the corner of general relativity, we say some problems
Speaker 1: with this theory also. First of all, it ignores the
Speaker 1: obvious quantum mechanical nature of our universe. All of our
Speaker 1: particle physics experiments and investigations in the last hundred of
Speaker 1: years have revealed that the fabric of reality is quantum mechanical,
Speaker 1: and general relativity ignores that. But more importantly, when we
Speaker 1: look back at the very beginning of the universe and
Speaker 1: try to understand, like, well, if the universe is being created,
Speaker 1: what is the beginning of that process, general relativity leaves
Speaker 1: us with a question mark. That singularity, the moment of
Speaker 1: infinite density that begins our universe in the general relativistic story,
Speaker 1: doesn't make any sense. Infinite curvature and infinite density is
Speaker 1: not something we think is physically true. We don't think
Speaker 1: it's a historical, actual accounting of events. It's a failure
Speaker 1: of general relativities. When the theory breaks down and can
Speaker 1: no longer give us a sensible answer. So what does
Speaker 1: physics tell us about why there is something rather than nothing?
Speaker 1: It tells us that we have a lot of work
Speaker 1: to do before we understand what is the thing that
Speaker 1: we are trying to explain. If we want to understand
Speaker 1: why there is something rather than nothing, we need physics
Speaker 1: to lead us closer to understanding what that thing is.
Speaker 1: Because when we know what that thing is, that we
Speaker 1: can ask interesting and fascinating questions about why it should
Speaker 1: exist and what it would be like for it to
Speaker 1: not exist. But we don't even know the fundamental nature
Speaker 1: of the universe. We need that unification of quantum mechanics
Speaker 1: and general relativity into some theory of quantum gravity so
Speaker 1: that we can look at it. We can say, okay,
Speaker 1: the basic element of the universe is a string. For example,
Speaker 1: why do strings have to exist? Would it be simpler
Speaker 1: to not have them? There are some people who think
Speaker 1: really interesting and fascinating thoughts sort of about that future
Speaker 1: without actually knowing what that future is. For example, one
Speaker 1: of my favorite books is Our Mathematical Reality by Max
Speaker 1: tad Mark, and he makes a fascinating argument which I
Speaker 1: don't actually believe but I think it's super fun. He
Speaker 1: says essentially that because our universe can be this scribed mathematically,
Speaker 1: therefore it is a mathematical construct, and that's why it exists.
Speaker 1: In his mind, you have to imagine, like every set
Speaker 1: of mathematical laws that do hold together and make a
Speaker 1: consistent universe, that universe exists because the mathematics works. I'm
Speaker 1: not sure I can take that last step that every
Speaker 1: mathematical self consistent universe that you can write down on
Speaker 1: paper actually does exist out there. It seems like you
Speaker 1: would have more really really simple universes than like vastly
Speaker 1: complex universes like ours. And then you also have to imagine,
Speaker 1: like what is the mathematical substrate on which all of
Speaker 1: these like meta universes are running on. But it's a
Speaker 1: really fun question, so I hope that answers your question.
Speaker 1: Physics basically doesn't yet know what the thing is in something,
Speaker 1: so we can't really answer the question why is there
Speaker 1: something rather than nothing? Thank you everybody who sent in
Speaker 1: all your super fun questions. Keep thinking deeply about the
Speaker 1: nature of the universe and how quant particles work, and
Speaker 1: please keep sending us your questions. They are the light
Speaker 1: of our day. We will answer all of your emails,
Speaker 1: trust me, or interact with us on Twitter if that's
Speaker 1: what you prefer. So please keep thinking deeply about the
Speaker 1: universe and keep asking questions. Tune in next time. Thanks
Speaker 1: for listening, and remember that Daniel and Jorge explained The
Speaker 1: Universe is a production of I Heart Radio. Or more
Speaker 1: podcast from my heart Radio, visit the I heart Radio app,
Speaker 1: Apple Podcasts, or wherever you listen to your favorite shows.
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