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Speaker 1: When you look up at the majesty of the night sky,

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Speaker 1: when you marvel at the intricate beauty of our microscopic,

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Speaker 1: quantum world, sometimes you just can't help but wonder where

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Speaker 1: does it all come from? Why does our universe exist

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Speaker 1: at all? Who or what is responsible for all of

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Speaker 1: this crazy, beautiful, bonkers universe. That's the biggest hope and

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Speaker 1: the biggest challenge for physics, not the small question of

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Speaker 1: why are we here, but the much bigger, deeper question

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Speaker 1: of why is there here at all? I Daniel, I'm

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Speaker 1: a particle physicist, and welcome to the podcast Daniel and

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Speaker 1: Jorge Explain the Universe, a production of I Heart Radio.

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Speaker 1: On this podcast, we talk about everything in the universe,

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Speaker 1: the stuff that's really big and vast and hard to understand,

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Speaker 1: and the stuff that's super small and tiny and mind boggling,

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Speaker 1: lee weird. We talk about all of it, and we

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Speaker 1: explain it to you in a way that we hope

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Speaker 1: actually makes sense and leaves you with the feeling that

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Speaker 1: you have grappled with a small piece of the world,

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Speaker 1: and one that you could import part of the universe

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Speaker 1: into your brain and you can make a little model

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Speaker 1: inside your head of what's going on out there in

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Speaker 1: the universe, and that it can work. It can help

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Speaker 1: you understand how the universe works, think about what it's doing,

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Speaker 1: and make predictions about what it might mean. The goal

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Speaker 1: of this podcast is not just for you to hear

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Speaker 1: a bunch of fancy science sounding words and come away

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Speaker 1: feeling like you were in the presence of science, but

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Speaker 1: to invite you to include you in the process of science,

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Speaker 1: because science is a human endeavor, is by the people

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Speaker 1: of the people, and for the people, and you are

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Speaker 1: the people. You're the people we are doing science for.

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Speaker 1: It's not just for a bunch of folks in white

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Speaker 1: lab coats and crazy hair. Is for everybody, because humanity

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Speaker 1: wonders about the universe, and humanity deserves answers about the universe.

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Speaker 1: And that's why humanity has decided to spend a non

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Speaker 1: trivial amount of money paying for science. And that's why

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Speaker 1: I think it's important that US scientists come back and

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Speaker 1: talk to people and explain to them what we have learned,

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Speaker 1: what it means, and connect back with that inherent curiosity that,

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Speaker 1: in the end, is what's responsible for driving this entire wonderful, crazy,

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Speaker 1: frustrating exhilarating project of unraveling the mysteries of the universe. Normally,

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Speaker 1: I'm joined by my co host, Orge, him a cartoonist

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Speaker 1: and roboticist, and we joke about bananas as he asks

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Speaker 1: me crazy questions. But he's not availed well today, so

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Speaker 1: I am taking the opportunity to catch up on questions

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Speaker 1: from you instead. That's right. Our loyal listeners often send

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Speaker 1: us questions things that they think about, that they are

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Speaker 1: wondering about. They have imported a little bit of the

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Speaker 1: universe into their minds and one piece of it doesn't

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Speaker 1: quite make sense. And so I encourage everybody out there

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Speaker 1: who has a question about the universe, something they are

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Speaker 1: wondering about, something they would like to hear understood, to

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Speaker 1: write to us. Send us your questions either on Twitter

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Speaker 1: at Daniel and Jorge or via email two questions at

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Speaker 1: Daniel and Jorge dot com. We right back to everybody.

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Speaker 1: We answer every email. You will get your question answered.

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Speaker 1: And sometimes the questions are interesting enough or fun enough

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Speaker 1: that I want to answer them here on the podcast

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Speaker 1: because I think other people might want to hear the

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Speaker 1: answers to these questions. I think that probably a lot

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Speaker 1: of people are wondering about those partaicular questions, and so

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Speaker 1: on today's episode will be answering listener questions. I love

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Speaker 1: all of our episodes, from the science fiction universe to

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Speaker 1: the extreme universe to the everyday physics, but maybe closest

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Speaker 1: to my heart are these questions that come from you,

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Speaker 1: from the listeners who are wondering about the world. Because,

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Speaker 1: as I said earlier, questions really are at the heart

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Speaker 1: of science. Science doesn't move forward without people, individual folks

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Speaker 1: asking questions about the universe and wanting to know the answer.

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Speaker 1: Think about that graduate student or that physicist or that

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Speaker 1: biologist out there devoting her life to answering one particular

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Speaker 1: question about the way microbes work, or about the way

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Speaker 1: rings form about a planet. It's because that person has

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Speaker 1: a deep curiosity about that one question and needs to

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Speaker 1: know the answer. So that's one of the joys of life,

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Speaker 1: is figuring out who you are and what you want

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Speaker 1: out of it, and what questions you want answered about

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Speaker 1: the universe. So please don't hesitate. Send me your questions.

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Speaker 1: I'd love to encourage them and to help give you

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Speaker 1: a few answers. And particularly I'd like to encourage our

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Speaker 1: listeners from Africa and from South America. We get questions

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Speaker 1: from all over the world, but I was looking at

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Speaker 1: the demographics recently and realizing that there's a group of

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Speaker 1: people out there who have been a little more silent

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Speaker 1: than the other folks. So if you're a listener in

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Speaker 1: Africa or in South America, please take my special encouragement

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Speaker 1: to write to us with your questions. We want to

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Speaker 1: hear from you and we want to help you understand

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Speaker 1: the universe. All right, so let's get to the first

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Speaker 1: listener question. This one comes to us from a very

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Speaker 1: young listener him names Megan. I'm nine years old. I

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Speaker 1: heard my damma the show, and I want to ask

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Speaker 1: you a couple of questions. So number one, how long

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Speaker 1: does it take to get to a black hole? At

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Speaker 1: number two, why are the stars round? Thank you for

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Speaker 1: answering my question by well, thank you Megan for sharing

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Speaker 1: your questions. I think she overheard her dad trying to

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Speaker 1: answer questions for future topics. So thanks very much Megan's

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Speaker 1: dad for letting Megan send in her questions and for

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Speaker 1: encouraging science and curiosity in the next generation. So Megan

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Speaker 1: asked us two questions. First, how long does it take

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Speaker 1: to get to a black hole and why our stars around. Well,

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Speaker 1: my first thought is like, why does Megan want to

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Speaker 1: go visit a black hole? And is that a good idea?

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Speaker 1: I mean, I certainly want to go visit a black hole.

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Speaker 1: I want to go see what's inside them and maybe

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Speaker 1: learn something deep about the nature of the universe and

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Speaker 1: help unravel the secrets of quantum gravity. But you know,

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Speaker 1: I'm not nine years old, and so I think it's

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Speaker 1: up to Megan's dad to decide whether or not he

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Speaker 1: should lend Megan the keys to the spaceship for this

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Speaker 1: particular field trip. So how long does it take to

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Speaker 1: get to a black hole? Say you wanted to get

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Speaker 1: into a spaceship and go to visit one. Well, you know,

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Speaker 1: there are two kinds of black holes out there in

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Speaker 1: the universe that we've discovered. There are the one at

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Speaker 1: the centers of galaxies, super massive black holes with masses

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Speaker 1: like millions of times the mass of our sun. Those

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Speaker 1: are spectacular and very interesting, but also really far away

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Speaker 1: and hugely dangerous because they are the centers of galaxies

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Speaker 1: where the radiation is intense and the X rays just

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Speaker 1: from the black holes. Creation disc itself would be really intense,

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Speaker 1: and then just the center of the galaxy is a

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Speaker 1: pretty crazy spot. So there is another kind of black

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Speaker 1: hole which I think would be much more reasonable to visit.

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Speaker 1: And these are stellar black holes, the ones that result

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Speaker 1: from a star aging and no longer having fusion pressure

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Speaker 1: to push back against gravity, trying to squeeze it down,

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Speaker 1: and eventually just giving up the ghost and becoming a

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Speaker 1: black hole. And so the one that's nearest to us

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Speaker 1: is actually only about eleven hundred and twenty light years

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Speaker 1: from the Sun. It's called q V telescopy if you

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Speaker 1: want to put that into your space navigation system. And

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Speaker 1: you might ask, how long does it take to get

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Speaker 1: to something that's eleven hundred light years away? Well, you know,

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Speaker 1: if you traveled at the speed of light, of course,

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Speaker 1: it would take eleven hundred years, which seems like a

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Speaker 1: really long time, and it is. But there's a bit

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Speaker 1: of a relativistic wrinkle we'll dig into there in a minute.

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Speaker 1: But we, of course can't travel at the speed of

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Speaker 1: light unless you develop some technology to like scan your

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Speaker 1: body and convert it into photons and beam yourself somewhere else.

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Speaker 1: But then you need some technology on the other side

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Speaker 1: to receive those photons and reconstruct your body. So a

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Speaker 1: more realistic way to go and visit a black hole

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Speaker 1: is to build a spaceship that's actually capable of such flight. Now,

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Speaker 1: there are two main limits to doing such a thing.

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Speaker 1: One is acceleration. To get up to that speed, you

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Speaker 1: have to speed up, and the human body has some

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Speaker 1: pretty tough limits on how fast we can accelerate. If

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Speaker 1: you try to accelerate more than five or ten GeSe,

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Speaker 1: your insides will get liquefied, and so for comfortable travel

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Speaker 1: over long periods, you really don't want acceleration much more

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Speaker 1: than one G. So let's do the calculation. Say you

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Speaker 1: had a spaceship that could accelerate at one G, you

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Speaker 1: would actually get up to pretty close to the speed

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Speaker 1: of light within just a couple of years, though most

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Speaker 1: of the trip would be spent pretty close to the

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Speaker 1: speed of light. So if you have to travel one thousand,

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Speaker 1: one hundred and twenty light years, it would only take

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Speaker 1: you one thousand, one hundred and twenty two years. Now,

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Speaker 1: the other problem with this scenario, of course, is the fuel.

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Speaker 1: To accelerate, you need fuel, and fuel makes your ship heavier,

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Speaker 1: which means you need more fuel to accelerate it. So

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Speaker 1: you have this rocket equation problem sometimes known as the

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Speaker 1: toothpick problem, because accelerating something even as small as a

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Speaker 1: toothpick up to very high velocities would require an enormous

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Speaker 1: quantity of fuel. And so, for example, if Megan's ship

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Speaker 1: was ten tons, which is really pretty small for a spaceship,

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Speaker 1: it would require something like thirteen million tons of fuel

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Speaker 1: for this kind of trip, and so basically the ship

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Speaker 1: would be all fuel, and most of that fuel is

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Speaker 1: there to help push the rest of the fuel. So

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Speaker 1: this is why we talk about things like black hole

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Speaker 1: power drives and other kinds of things. Of course, it

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Speaker 1: would be kind of silly to have a black hole

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Speaker 1: power drive to go visit a black hole. If you

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Speaker 1: have a black holed power drive, that means either you

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Speaker 1: can capture or make your own black holes anyway. But

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Speaker 1: the relativistic wrinkle is actually quite interesting because while from

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Speaker 1: Earth's point of view, it takes one thousand, one hundred

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Speaker 1: and twenty two years before you reach that black hole.

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Speaker 1: So that's like Megan's dad's clock. If he had a

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Speaker 1: telescope and he was keeping an eye on Megan during

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Speaker 1: her trip, he would see her clock running very slowly,

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Speaker 1: according to him, very very slowly, so that by the

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Speaker 1: time she reaches the black hole, she would only have

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Speaker 1: experienced thirteen points seven years, So she would only be

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Speaker 1: twenty two years old by the time she reached the

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Speaker 1: black hole. Now, of course, for everybody back on Earth,

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Speaker 1: more than a thousand years would have passed. And if

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Speaker 1: she actually wants to turn around and come back to Earth,

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Speaker 1: that's a whole other relativistic ring goal. When she turns around,

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Speaker 1: special relativity gets really complicated because that's another kind of acceleration,

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Speaker 1: and that gets us into the twin paradox, which we

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Speaker 1: can talk about another time on the podcast. So, Megan,

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Speaker 1: the answer is, it would take you more than a

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Speaker 1: thousand years to reach a black hole, but from your

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Speaker 1: point of view, it would only feel like about fourteen years.

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Speaker 1: So factor that into your decision about whether or not

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Speaker 1: to build your spaceship and go business black hole. But

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Speaker 1: if you go and you do discover secrets of the

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Speaker 1: universe and quantum gravity, please send me an email now.

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Speaker 1: Megan's second question was why are things around? Like why

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Speaker 1: are the stars round? Which is related to another really

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Speaker 1: interesting question, you know, like why our planets around. Why

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Speaker 1: is most of the stuff in the universe round? And

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Speaker 1: the answer is gravity. A little bit counterintuitive, but gravity,

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Speaker 1: even though it's the weakest force we know about, is

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Speaker 1: the dominant force when it comes to the structure of

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Speaker 1: astronomical stuff. The shape of the Earth, the shape of

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Speaker 1: the Sun, all this kind of stuff is round because

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Speaker 1: of gravity. And you can think about it pretty simply.

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Speaker 1: Gravity pull stuff down, right, So if you have the

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Speaker 1: Earth with anything sticking up on it, eventually that's going

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Speaker 1: to get knocked down, maybe wind or water, or even

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Speaker 1: if you don't have any atmosphere or water on the surface,

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Speaker 1: any kind of process eventually is going to settle into

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Speaker 1: a lower energy state. And for gravity, the simplest configuration,

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Speaker 1: the lowest energy state is a sphere. So anything that's

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Speaker 1: big enough to have its own gravity is eventually going

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Speaker 1: to be round. That's why small things are not necessarily round,

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Speaker 1: like asteroids and meteors are sometimes weird shaped because they

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Speaker 1: don't have the gravity to pull themselves together into a

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Speaker 1: round object. Whereas things as big as the Earth or

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Speaker 1: even the Moon, or definitely the Sun, gravity does its

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Speaker 1: thing and pulls anything that sticks out a little bit

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Speaker 1: down until eventually you get a sphere. But of course

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Speaker 1: not everything out there in the sky is a sphere, right,

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Speaker 1: I mean, our Solar System is not a sphere. It's

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Speaker 1: like a flat disc, and our galaxy is on a sphere.

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Speaker 1: It's also a flat disc. So why is it that

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Speaker 1: those things are not round? And that's because they have

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Speaker 1: something which can actually overcome gravity, and that's spin, that's rotation.

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Speaker 1: The Solar System is spinning. The Earth is spinning around

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Speaker 1: the Sun. That's why it doesn't fall in due to

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Speaker 1: the Sun's gravity, because it has enough velocity to stay

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Speaker 1: in orbit. And the same thing with the Sun. The

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Speaker 1: Sun is spinning around the center of the galaxy, which

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Speaker 1: is why the Sun and all the other stars don't

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Speaker 1: just fall into the black hole at the center of

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Speaker 1: the galaxy. And that's why black holes have an accretion

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Speaker 1: disk around them, because that rotation keeps stuff from falling in.

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Speaker 1: So you have a couple of forces here at play.

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Speaker 1: Mostly you have gravity dominating for things like the size

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Speaker 1: of the Moon and up to the Sun. But then

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Speaker 1: if things are spinning fast enough, they will turn into

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Speaker 1: a disk. Like if you took the Earth and you

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Speaker 1: spun it faster, it would turn into a disk. In fact,

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Speaker 1: the Earth itself is not exactly sound because it's spinning.

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Speaker 1: The distance from the surface to the center of the

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Speaker 1: Earth is actually greater at the equator because the Earth

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Speaker 1: is spinning, and if you spun the Earth even faster,

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Speaker 1: it would eventually turn into a pancake. And the same

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Speaker 1: with the Sun. So everything out there is balancing a

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Speaker 1: bunch of different forces. Mostly you don't see the effect

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Speaker 1: of electromagnetism or the weak nuclear force, or even the

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Speaker 1: strong force on the shapes of astronomical objects because they're

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Speaker 1: mostly balanced out. The Earth doesn't have an overall positive charge.

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Speaker 1: The Sun doesn't have an overall negative charge. If it did,

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Speaker 1: that force would be so strong, it's so much more

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Speaker 1: powerful than gravity that you would get these streams of

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Speaker 1: basically currents until things did get balanced out. But gravity

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Speaker 1: can't get balanced out. There is no opposite charge to gravity.

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Speaker 1: There's no negative mass that can create anti gravity to

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Speaker 1: balance out gravity. Gravity is always there, it always has

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Speaker 1: to be contended with, has to wait until everything else

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Speaker 1: gets sorted out and neutralized for it basically gets to

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Speaker 1: take the field and dominate. But eventually gravity takes over,

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Speaker 1: and that's why gravity is the dominant force for the universe,

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Speaker 1: and that's why the Sun and the Earth are around.

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Speaker 1: All right, Megan, thanks very much for those wonderful questions.

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Speaker 1: I want to get to some more or lessen our questions,

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Speaker 1: but first let's take a quick break. Hello, we are

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Speaker 1: back and this is Daniel and I'm answering questions from

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Speaker 1: listeners who want to understand the nature of the universe. So,

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Speaker 1: without further ado, here's our next question. Hello Daniel, So

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Speaker 1: what happened wondering for some time about anti matter stars?

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Speaker 1: We know matter is everywhere in the universe, and antimatter

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Speaker 1: just doesn't exist in quantities that are big enough for

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Speaker 1: anything like this. But if there was an ant I'm

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Speaker 1: at their star, or if there is, say one in

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Speaker 1: the whole universe, how could we tell it's an antime

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Speaker 1: matter star? How would it be different? It would shine

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Speaker 1: like a normal star or with it? Thank you? All right,

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Speaker 1: super fun question. I love this kind of question, like

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Speaker 1: how do we know what we know? Is it possible

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Speaker 1: for this weird, crazy scenario I've thought of in my

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Speaker 1: mind to be our reality? And that's a very important

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Speaker 1: kind of thought process, and that's basically what physicists are doing.

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Speaker 1: We're always wondering, all right, here's what we know. What

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Speaker 1: is that consistent with? Is there a way I could

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Speaker 1: imagine the universe to be different and still look the

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Speaker 1: same way. Are we being fooled by our preconceptions? So

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Speaker 1: it's this kind of creative, out of the box thinking

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Speaker 1: that's really vital in science. So let's dig into it first.

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Speaker 1: Let's just remind ourselves, like, what is anti matter? What

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Speaker 1: do we know about it? The existence of anti particles

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Speaker 1: is one of the most incredible and beautiful symmetries for me.

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Speaker 1: In the universe. Every particle that we know of, every fermion,

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Speaker 1: electrons and corks and neutrinos, and all of these particles

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Speaker 1: have a partner particle. There's like this symmetry where you

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Speaker 1: reflect all these particles and boom, they all have an

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Speaker 1: exact opposite. So the electron, for example, has the positron,

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Speaker 1: which is a positively charged version of the electron, and

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Speaker 1: the muan, which is naturally negatively charged, also has a

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Speaker 1: positively charged version. Each of the corks, like the upcork

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Speaker 1: and the down core, have an anti up and an

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Speaker 1: anti down. This is stuff that you hear about in

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Speaker 1: science fiction, but it's actually real. It's out there in

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Speaker 1: the universe. It's a kind of thing that can exist.

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Speaker 1: And when we do particle physics, we're often exploring two

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Speaker 1: different questions. One is can this stuff exists? Like what's

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Speaker 1: out there theoretically on Nature's menu, which if you made

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Speaker 1: the right conditions, could exist in the universe. And then like,

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Speaker 1: is there any of it? How do you actually make it?

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Speaker 1: And we created which is a totally separate question. But

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Speaker 1: antimatter is something that's in the universe, and frankly, we

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Speaker 1: don't know why. Why does every particle have this mirror

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Speaker 1: version of itself? Why does that exist? It tells us

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Speaker 1: something deep about the nature of the universe that every

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Speaker 1: particle seems to come in pairs. Maybe it means that

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Speaker 1: we shouldn't even think about the particles as in pairs.

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Speaker 1: Maybe the fundamental object is the pair, not the particle, right,

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Speaker 1: because if everything comes as part of a unit, then

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Speaker 1: maybe that unit is the thing that's part of the universe.

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Speaker 1: This is kind of the deep fundamental theoretical questions. You

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Speaker 1: could have been a lot of time smoking banana appeals

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Speaker 1: and thinking about and we do a lot of experiments

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Speaker 1: to try to understand antimatter. We make it at certain

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Speaker 1: but we can't make a whole lot. You have to

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Speaker 1: smash protons and do a big block of matter, and

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Speaker 1: some little bits of antimatter come out sometimes and we

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Speaker 1: can collect it and do experiments about it. And one

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Speaker 1: really interesting question we have about antimatter is is it

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Speaker 1: actually an exact copy? Is it really the same thing

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Speaker 1: as matter, but with the charges reversed, our anti electrons

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Speaker 1: really just the exact opposite of electron. And one way

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Speaker 1: to think about that, and this is I think the

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Speaker 1: direction of this question about antimatter stars is does antimatter

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Speaker 1: behave the same way as matters? Like can you make

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Speaker 1: big complicated things out of antimatter the same way you

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Speaker 1: can out of matter? And we've done these kinds of

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Speaker 1: experiments so far. We've made things like anti hydrogen, which

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Speaker 1: is an anti proton with an anti electron in orbit

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Speaker 1: around it, and we've studied and we've asked like, well,

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Speaker 1: does it look like hydrogen? Does it radiate energy the

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Speaker 1: same way? Does it follow the same physical laws? And

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Speaker 1: so far the experiment suggests that it does. We've never

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Speaker 1: detected any difference between the way antimatter works and the

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Speaker 1: way that matter works, So it seems like a perfect symmetry.

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Speaker 1: And yet there's a big mystery there because we know

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Speaker 1: it can't be a perfect symmetry. How do we know that, Well,

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Speaker 1: the universe is most be made of matter, right, I'm

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Speaker 1: made of matter, You're made of matter. The Sun is

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Speaker 1: made out of matter, The Solar System is made out

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Speaker 1: of matter. If matter and antimatter are basically symmetric, and

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Speaker 1: the universe treats them exactly the same way, why is

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Speaker 1: there more matter than there is antimatter? This is one

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Speaker 1: of the deepest questions in physics. We just don't know

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Speaker 1: the answer. You know, we imagine that when the universe

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Speaker 1: began that things were symmetric, because it's hard to imagine

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Speaker 1: anything else. If you imagine the universe started out with

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Speaker 1: more matter than antimatter, you're just sort of like presupposing

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Speaker 1: the answer to the question and introducing a new question.

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Speaker 1: If the answer to the question why does the universe

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Speaker 1: have more matter than antimatter is just well it started

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Speaker 1: that way, then you can just ask why did it

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Speaker 1: start that way? So it's more interesting to start from

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Speaker 1: the assumption that the universe began with equal amounts of

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Speaker 1: matter and antimatter. But now we don't have as much matter.

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Speaker 1: So what happened to it? Well, we know what happens

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Speaker 1: when matter and antimatter meet each other. They annihilate. What

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Speaker 1: does that mean? And from a particle physics point of view,

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Speaker 1: it's not magic. It just means that, like when an

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Speaker 1: electron meets a positron, they can turn into a photon.

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Speaker 1: They turn their matter into energy. Right, this is E

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Speaker 1: equals mc squared. Matter is really just a form of energy,

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Speaker 1: and so you can turn that matter into energy and

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Speaker 1: they can annihilate into a photon, or they can annihilate

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Speaker 1: into a z boson. Quarks can meet anti quarks and

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Speaker 1: turn into photons. They can also turn into gluons. So

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Speaker 1: all these kinds of matter can annihilate and turn into energy,

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Speaker 1: which can then do whatever energy wants to do. So,

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Speaker 1: if there was an equal amount of matter and antimatter

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Speaker 1: in the early universe, you would expect it would eventually

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Speaker 1: meet and annihilate itself, and we would have a universe

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Speaker 1: just filled with photons and gluons and z bosons and

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Speaker 1: stuff like that. But we don't. We still have matter

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Speaker 1: left over, and so people wonder, like, is there some

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Speaker 1: process in the universe which preferentially turns antimatter into matter,

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Speaker 1: so that we ended up with a little bit more matter,

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Speaker 1: and then the rest of an annihilated and we had

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Speaker 1: some leftover, which is just matter, which is what we are,

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Speaker 1: which is what created the entire universe that we are

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Speaker 1: living in. So that's the idea, but we've never explained that.

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Speaker 1: We don't have an understanding of how that happens. There

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Speaker 1: are a few processes and particle physics we found which

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Speaker 1: seemed to prefer creating matter to antimatter, and these things

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Speaker 1: are like CP violating processes and be in k masons.

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Speaker 1: And you can listen to our podcast episode about CP

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Speaker 1: violation if you want to hear more about that. But

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Speaker 1: these are not big enough to explain the asymmetry. The

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Speaker 1: account for a tiny fraction of the asymmetry. You need

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Speaker 1: a much more dramatic way to turn antimatter into matter

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Speaker 1: to explain the universe that we see. So we don't

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Speaker 1: understand it. And this suggests to us that there is

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Speaker 1: some asymmetry between matter and antimatter. There really is some

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Speaker 1: reason why the universe prefers matter to antimatter, and we

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Speaker 1: want to know what that is, right, We want to

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Speaker 1: know why, because that seems like a d truth about

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Speaker 1: the universe. But then there's another possibility, the other possibilities.

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Speaker 1: Hold on a second, and this is the question that

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Speaker 1: was asked ret least, how do we know there isn't

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Speaker 1: more antimatter out there? Are we just assuming that all

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Speaker 1: the stars out there are made of matter? What if

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Speaker 1: they were made out of antimatter? Right? The question is

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Speaker 1: wonderful because you're exactly right, and antimatter star would look

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Speaker 1: a lot like a matter of star. If antimatter can

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Speaker 1: do things like make anti hydrogen, then why can't anti

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Speaker 1: hydrogen anti fuse into anti helium. If it did, it

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Speaker 1: would produce photons just like the matter version of that process.

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Speaker 1: So mostly you're right that antimatter stars would look like

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Speaker 1: normal stars. And so when you're looking out in the sky,

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Speaker 1: it is possible that some of those stars might be

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Speaker 1: anti matter stars. But it's not exactly the same because

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Speaker 1: stars don't just produce photons. Obviously, they produce lots and

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Speaker 1: lots of photons. As you're out there sunning your face

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Speaker 1: on a nice winter morning, it doesn't really matter if

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Speaker 1: those photons came from a star or an antimatter star.

431
00:24:04,080 --> 00:24:06,600
Speaker 1: Because the photon is a boson, it doesn't have an

432
00:24:06,600 --> 00:24:09,719
Speaker 1: antimatter version of itself, and so it could come from

433
00:24:09,760 --> 00:24:14,600
Speaker 1: an antimatter star. But stars make other things too. You're

434
00:24:14,640 --> 00:24:17,800
Speaker 1: familiar with the solar wind, for example, the solar wind

435
00:24:17,840 --> 00:24:20,840
Speaker 1: is a stream of particles that come out of the

436
00:24:20,880 --> 00:24:24,440
Speaker 1: Sun when fusion happens. In the crazy chaos of a star,

437
00:24:24,760 --> 00:24:28,640
Speaker 1: you don't just make light. You make neutrinos, you make electrons,

438
00:24:28,720 --> 00:24:32,560
Speaker 1: you spew off protons, And so that solar wind can

439
00:24:32,600 --> 00:24:34,960
Speaker 1: tell us something about what kind of star it is,

440
00:24:35,119 --> 00:24:39,320
Speaker 1: because an antimatter star would make anti solar wind, right,

441
00:24:39,359 --> 00:24:44,680
Speaker 1: it would preferentially produce anti protons and positrons and anti

442
00:24:44,680 --> 00:24:47,919
Speaker 1: neutrinos and all sorts of other crazy stuff. All right,

443
00:24:48,000 --> 00:24:50,840
Speaker 1: but these stars are still really far away, right, how

444
00:24:50,880 --> 00:24:54,040
Speaker 1: would we know if those stars were making this antimatter

445
00:24:54,160 --> 00:24:58,040
Speaker 1: solar wind. Well, inside our solar system, we're pretty sure

446
00:24:58,080 --> 00:25:00,800
Speaker 1: everything's made of matter, right, don't think that one of

447
00:25:00,800 --> 00:25:03,159
Speaker 1: the planets is made out of antimatter. And then we

448
00:25:03,200 --> 00:25:06,880
Speaker 1: have two ways of figuring out whether other stars might

449
00:25:06,960 --> 00:25:09,520
Speaker 1: be made out of antimatter. One is just to look

450
00:25:09,560 --> 00:25:12,960
Speaker 1: at cosmic rays. Cosmic rays, some of them come from

451
00:25:12,960 --> 00:25:15,360
Speaker 1: the Sun, but a big proportion of them don't come

452
00:25:15,400 --> 00:25:17,600
Speaker 1: from the Sun. They come from the other stars in

453
00:25:17,720 --> 00:25:21,639
Speaker 1: our galaxy. And so this like galaxy solar wind, is

454
00:25:21,680 --> 00:25:25,480
Speaker 1: an accumulation of all the solar wind from other stars,

455
00:25:25,680 --> 00:25:28,080
Speaker 1: and that contains a lot of particles, and some of

456
00:25:28,080 --> 00:25:32,200
Speaker 1: them are antiparticles. Right, There are positrons and there are

457
00:25:32,240 --> 00:25:36,960
Speaker 1: anti protons in that wind. Cosmic rays sometimes are antiparticles,

458
00:25:37,080 --> 00:25:39,560
Speaker 1: but we don't think that comes from anti stars. We

459
00:25:39,600 --> 00:25:42,919
Speaker 1: have an explanation for how you can make antiparticles like

460
00:25:43,000 --> 00:25:47,840
Speaker 1: pretty simply photons sometimes split into positrons and electrons, and

461
00:25:47,880 --> 00:25:50,280
Speaker 1: so we have an idea and we can explain even

462
00:25:50,320 --> 00:25:54,560
Speaker 1: how to make anti protons in solar wind. So basically

463
00:25:54,600 --> 00:25:57,600
Speaker 1: the cosmic rays that we see here on Earth or

464
00:25:57,640 --> 00:26:01,040
Speaker 1: in our telescopes up in space are to totally consistent

465
00:26:01,400 --> 00:26:04,080
Speaker 1: with the stars in our galaxy being made out of

466
00:26:04,160 --> 00:26:07,600
Speaker 1: matter and not antimatter. If there was antimatter, then we

467
00:26:07,640 --> 00:26:11,760
Speaker 1: would see heavier stuff. We would see like anti iron

468
00:26:11,920 --> 00:26:15,720
Speaker 1: or anti uranium or anti oxygen stuff like that. We

469
00:26:15,840 --> 00:26:19,200
Speaker 1: see heavy versions of those elements in cosmic rays. It's

470
00:26:19,240 --> 00:26:21,879
Speaker 1: a tricky topic. We don't have precise measurements, but we

471
00:26:21,920 --> 00:26:26,159
Speaker 1: don't see any anti heavy elements in cosmic rays, so

472
00:26:26,200 --> 00:26:28,520
Speaker 1: we don't think that there are anti stars sort of

473
00:26:28,600 --> 00:26:32,240
Speaker 1: in our galaxy. Now cast your mind a little further, right,

474
00:26:32,359 --> 00:26:35,359
Speaker 1: How do we know that Andromeda, for example, isn't made

475
00:26:35,640 --> 00:26:39,040
Speaker 1: entirely out of anti stars? Are we measuring the solar

476
00:26:39,080 --> 00:26:42,200
Speaker 1: wind from that galaxy? That's a lot harder to do, though.

477
00:26:42,400 --> 00:26:45,800
Speaker 1: We do get particles from Andromeda, of course, but more generally,

478
00:26:45,840 --> 00:26:48,600
Speaker 1: we have another technique for figuring out if there are

479
00:26:48,640 --> 00:26:52,240
Speaker 1: like big antimatter patches to the rest of the universe,

480
00:26:52,400 --> 00:26:55,560
Speaker 1: and that's by thinking about where the matter and antimatter

481
00:26:55,640 --> 00:26:59,280
Speaker 1: patches might cross. Like if our galaxy was made of

482
00:26:59,320 --> 00:27:03,520
Speaker 1: matter and Andromeda was made of antimatter, then the antimatter

483
00:27:03,600 --> 00:27:07,200
Speaker 1: particles from Andromeda would be hitting the matter particles from

484
00:27:07,200 --> 00:27:10,640
Speaker 1: our galaxy somewhere in between. And what would happen while

485
00:27:10,680 --> 00:27:13,760
Speaker 1: they would annihilate and you would see this like surface

486
00:27:13,880 --> 00:27:16,880
Speaker 1: of that was creating photons and other kinds of particles

487
00:27:16,920 --> 00:27:19,880
Speaker 1: at a particular energy, because you'd expect, for example, when

488
00:27:19,920 --> 00:27:23,199
Speaker 1: an electron annihilates with a positron, it turns into a

489
00:27:23,200 --> 00:27:27,280
Speaker 1: photon that mostly has the energy of twice the mass

490
00:27:27,440 --> 00:27:31,200
Speaker 1: of the electron. So there's this characteristic flash of light

491
00:27:31,280 --> 00:27:35,440
Speaker 1: that happens when antimatter and matter annihilate, and we can

492
00:27:35,480 --> 00:27:37,920
Speaker 1: look to see sort of at the boundary between our

493
00:27:37,920 --> 00:27:41,639
Speaker 1: two galaxies if that's being created and we don't see it.

494
00:27:41,960 --> 00:27:44,280
Speaker 1: And this is a very powerful way to look deep

495
00:27:44,359 --> 00:27:47,280
Speaker 1: into the universe and see, like, are there surfaces, there

496
00:27:47,280 --> 00:27:51,639
Speaker 1: are their boundaries between matter and antimatter regions of the universe,

497
00:27:52,080 --> 00:27:54,840
Speaker 1: And so we haven't explored the entire universe this way.

498
00:27:55,080 --> 00:27:58,440
Speaker 1: We've looked out past our galaxy cluster in between other

499
00:27:58,520 --> 00:28:01,879
Speaker 1: galaxy clusters, and we've ever seen any evidence of like

500
00:28:02,240 --> 00:28:06,919
Speaker 1: massive annihilation of matter and antimatter into photons, which is

501
00:28:07,000 --> 00:28:09,080
Speaker 1: what you would expect to see again at one of

502
00:28:09,080 --> 00:28:11,760
Speaker 1: these sort of like boundaries between a matter region and

503
00:28:11,800 --> 00:28:15,160
Speaker 1: an antimatter region of the galaxy. So we haven't ever

504
00:28:15,240 --> 00:28:17,879
Speaker 1: detected that. Now, that doesn't mean we can rule it

505
00:28:17,880 --> 00:28:20,919
Speaker 1: out entirely in the entire universe, right there could be

506
00:28:20,960 --> 00:28:23,119
Speaker 1: a portion of the universe that's so distant that we

507
00:28:23,240 --> 00:28:26,640
Speaker 1: just can't probe it yet with these methods. Absolutely, we've

508
00:28:26,680 --> 00:28:29,600
Speaker 1: looked sort of like the ten megapars x scale. We

509
00:28:29,640 --> 00:28:34,199
Speaker 1: know that our large neighborhood doesn't have any significant antimatter

510
00:28:34,240 --> 00:28:36,760
Speaker 1: in it, that doesn't mean that there isn't antimatter in

511
00:28:36,800 --> 00:28:40,120
Speaker 1: the rest of the universe. So yes, absolutely, there could

512
00:28:40,200 --> 00:28:43,600
Speaker 1: be an antimatter galaxy out there somewhere super far away

513
00:28:43,720 --> 00:28:46,360
Speaker 1: and we just haven't seen it yet, or evidence of

514
00:28:46,560 --> 00:28:50,040
Speaker 1: its cosmic rays annihilating with a cosmic rays from a

515
00:28:50,040 --> 00:28:53,040
Speaker 1: matter galaxy. It's certainly possible, and that would be sort

516
00:28:53,040 --> 00:28:56,880
Speaker 1: of a beautiful explanation to this mystery of antimatter. If

517
00:28:56,880 --> 00:28:59,640
Speaker 1: it turns out that the universe actually is symmetric to

518
00:28:59,720 --> 00:29:02,440
Speaker 1: matter an antimatter, If there are matter patches of the

519
00:29:02,520 --> 00:29:05,520
Speaker 1: universe and anti matter patches of the universe, and that

520
00:29:05,560 --> 00:29:07,800
Speaker 1: they're in balance somehow, then of course you have to

521
00:29:07,800 --> 00:29:10,320
Speaker 1: wonder like, well, why did this become a matter patch

522
00:29:10,360 --> 00:29:12,640
Speaker 1: and why did that become an antimatter patch. But you

523
00:29:12,680 --> 00:29:15,920
Speaker 1: can imagine such things being answered by quantum mechanical randomness

524
00:29:15,920 --> 00:29:18,360
Speaker 1: and the formation of structure and all sorts of fun

525
00:29:18,440 --> 00:29:21,040
Speaker 1: stuff like that. But to meanwhile, we're digging into the

526
00:29:21,120 --> 00:29:26,080
Speaker 1: question of whether there are larger asymmetries between matter and antimatter. If,

527
00:29:26,160 --> 00:29:29,360
Speaker 1: as we suspect, the universe is mostly matter, then we're

528
00:29:29,400 --> 00:29:32,080
Speaker 1: trying to understand what that means, because we think that

529
00:29:32,080 --> 00:29:34,240
Speaker 1: that's going to tell us something about like why there

530
00:29:34,480 --> 00:29:37,200
Speaker 1: is matter at all, why we're not just living in

531
00:29:37,200 --> 00:29:41,520
Speaker 1: a universe filled with photons. So if it's true that

532
00:29:41,560 --> 00:29:43,840
Speaker 1: the universe is mostly matter, then we should be grateful

533
00:29:43,920 --> 00:29:46,960
Speaker 1: that there's an asymmetry, because that is in fact why

534
00:29:47,160 --> 00:29:50,800
Speaker 1: we are here. Alright, wonderful question. Thanks very much for

535
00:29:50,920 --> 00:29:53,320
Speaker 1: sending that in. I want to answer one more question,

536
00:29:53,480 --> 00:30:08,880
Speaker 1: but first let's take another break. Okay, we're back and

537
00:30:08,920 --> 00:30:11,840
Speaker 1: we're talking about the nature of the universe, symmetries and

538
00:30:12,040 --> 00:30:15,160
Speaker 1: black holes, and now we have a fun question from listeners.

539
00:30:15,160 --> 00:30:19,600
Speaker 1: That's maybe one of the deepest questions in physics and philosophy. Hi,

540
00:30:19,720 --> 00:30:22,800
Speaker 1: Daniel and Jorge. I know this often gets slumped into

541
00:30:22,840 --> 00:30:26,480
Speaker 1: the realm of philosophy, but is there a physics explanation

542
00:30:26,680 --> 00:30:30,320
Speaker 1: of why there is anything rather than nothing in the universe?

543
00:30:31,200 --> 00:30:34,360
Speaker 1: Why does any of this exist? What may have triggered

544
00:30:34,400 --> 00:30:38,160
Speaker 1: any of the matter, energy and forces we observe? Thanks

545
00:30:38,760 --> 00:30:42,120
Speaker 1: James Chronister, Thank you James for not being afraid to

546
00:30:42,160 --> 00:30:45,520
Speaker 1: ask the biggest and deepest questions and the questions that

547
00:30:45,680 --> 00:30:48,800
Speaker 1: overlap with philosophy. I don't think that's a negative thing

548
00:30:48,840 --> 00:30:51,240
Speaker 1: to be lumped in with philosophy. I think it's wonderful.

549
00:30:51,480 --> 00:30:54,480
Speaker 1: I think it means our questions are relevant. You know,

550
00:30:54,560 --> 00:30:58,280
Speaker 1: philosophy tells us what our questions mean and why they're interesting,

551
00:30:58,360 --> 00:31:00,600
Speaker 1: and why we want an answer to them and how

552
00:31:00,640 --> 00:31:02,800
Speaker 1: to think about them. And so I think that all

553
00:31:02,800 --> 00:31:07,120
Speaker 1: of the deepest questions in physics have philosophical implications. That's

554
00:31:07,240 --> 00:31:10,560
Speaker 1: why they're exciting. You know, if you knew exactly how

555
00:31:10,600 --> 00:31:13,600
Speaker 1: the universe was created, for example, from a physics point

556
00:31:13,600 --> 00:31:17,160
Speaker 1: of view, that would definitely have philosophical implications. So I

557
00:31:17,160 --> 00:31:19,400
Speaker 1: think the most fun questions in physics are the ones

558
00:31:19,440 --> 00:31:22,360
Speaker 1: that also get philosophers excited. And you're right, there's been

559
00:31:22,400 --> 00:31:25,920
Speaker 1: a lot of philosophical discussion back to the ancient Greeks

560
00:31:25,960 --> 00:31:30,120
Speaker 1: about why is there something rather than nothing? And it's

561
00:31:30,120 --> 00:31:32,360
Speaker 1: a really fun question to think about. And first I

562
00:31:32,400 --> 00:31:34,960
Speaker 1: think you should think about, like, what do we mean

563
00:31:35,120 --> 00:31:39,440
Speaker 1: by nothing? What is the opposite idea that we're considering.

564
00:31:39,880 --> 00:31:42,080
Speaker 1: On one hand, we have the universe and us and

565
00:31:42,120 --> 00:31:46,440
Speaker 1: there's definitely something here. What is the alternative that we're

566
00:31:46,480 --> 00:31:48,880
Speaker 1: wondering about. What is the thing that we're trying to

567
00:31:49,280 --> 00:31:52,440
Speaker 1: rule out? What is the nature of nothing? You know?

568
00:31:52,480 --> 00:31:55,240
Speaker 1: And let's knock down first some very simple ideas about

569
00:31:55,280 --> 00:31:57,800
Speaker 1: what nothing might be from a physics point of view.

570
00:31:58,040 --> 00:32:01,000
Speaker 1: It's not just like not having this stuff, not having

571
00:32:01,120 --> 00:32:04,440
Speaker 1: these stars and these galaxies and these particles, right, It's

572
00:32:04,480 --> 00:32:08,240
Speaker 1: something deeper. It's something about the possibility of things being

573
00:32:08,280 --> 00:32:11,560
Speaker 1: in the universe, about the nature of existence itself. It's

574
00:32:11,600 --> 00:32:14,160
Speaker 1: a pretty weird thing to consider, you know, a universe

575
00:32:14,240 --> 00:32:17,880
Speaker 1: with nothing or not a universe. You couldn't ever like

576
00:32:18,240 --> 00:32:22,400
Speaker 1: do an experiment to prove that nothing exists, because of

577
00:32:22,440 --> 00:32:25,240
Speaker 1: course your experiment is a thing, and so we can't

578
00:32:25,280 --> 00:32:26,920
Speaker 1: really prove it. And so that's why this is a

579
00:32:26,960 --> 00:32:29,840
Speaker 1: fun sort of philosophical question. But what I still think

580
00:32:29,880 --> 00:32:32,600
Speaker 1: that we can make progress on if we think about

581
00:32:32,680 --> 00:32:35,160
Speaker 1: what physics has told us about the nature of the

582
00:32:35,200 --> 00:32:39,240
Speaker 1: universe and the nature of nothing. By nothing, do we mean,

583
00:32:39,320 --> 00:32:43,200
Speaker 1: for example, just space, but with no matter in it,

584
00:32:43,520 --> 00:32:47,000
Speaker 1: like delete the stars, delete the galaxies, delete the planets,

585
00:32:47,000 --> 00:32:49,560
Speaker 1: delete all the stuff that's out there in the universe.

586
00:32:49,760 --> 00:32:52,440
Speaker 1: Is that what we would consider to be nothing. Well,

587
00:32:52,480 --> 00:32:55,120
Speaker 1: I think it's an interesting question, like why doesn't that

588
00:32:55,280 --> 00:32:58,360
Speaker 1: universe exist rather than ours? But I think the question

589
00:32:58,400 --> 00:33:01,320
Speaker 1: goes deeper, right because I think and that's question, you

590
00:33:01,360 --> 00:33:04,640
Speaker 1: will still ask, well, why is there space? Why is

591
00:33:04,720 --> 00:33:07,160
Speaker 1: there a universe for things to be in? Even if

592
00:33:07,200 --> 00:33:09,760
Speaker 1: there don't happen to be anything's in it right now,

593
00:33:10,120 --> 00:33:14,840
Speaker 1: that universe still has the possibility of things. And more specifically,

594
00:33:14,880 --> 00:33:17,800
Speaker 1: we know that physics tells us that even space is

595
00:33:17,840 --> 00:33:21,200
Speaker 1: not really empty a bowl. There's no such thing really

596
00:33:21,240 --> 00:33:24,520
Speaker 1: as empty space. If you somehow remove all the matter

597
00:33:24,560 --> 00:33:27,640
Speaker 1: in space and make as good a vacuum as you can,

598
00:33:28,120 --> 00:33:31,800
Speaker 1: then there's still a thing there, and that's space because

599
00:33:31,800 --> 00:33:35,920
Speaker 1: space has inside of it quantum fields, and those quantum

600
00:33:35,920 --> 00:33:40,200
Speaker 1: fields we know, are always buzzing with energy. Despite your

601
00:33:40,280 --> 00:33:44,040
Speaker 1: best effort to reduce the energy of that space, quantum

602
00:33:44,080 --> 00:33:47,480
Speaker 1: fields can't go down to zero energy. It's a fundamental

603
00:33:47,520 --> 00:33:50,360
Speaker 1: property of quantum fields that their lowest state is not

604
00:33:50,560 --> 00:33:54,120
Speaker 1: add zero energy. And in our universe at least there's

605
00:33:54,160 --> 00:33:57,640
Speaker 1: one field, the Higgs Boson field, which is totally rife

606
00:33:57,680 --> 00:34:00,560
Speaker 1: with energy. It's stuck. It's at this weird a minimum

607
00:34:00,560 --> 00:34:02,800
Speaker 1: that has a lot of energy in it, and so

608
00:34:02,880 --> 00:34:05,080
Speaker 1: there's a lot of energy and even what we think

609
00:34:05,120 --> 00:34:08,640
Speaker 1: about as empty space. And some people who think about

610
00:34:08,680 --> 00:34:11,080
Speaker 1: the nature of the universe and why is there something

611
00:34:11,200 --> 00:34:14,319
Speaker 1: rather than nothing take this as the answer. They say, well,

612
00:34:14,360 --> 00:34:16,960
Speaker 1: there has to be something because space is filled with

613
00:34:17,040 --> 00:34:19,879
Speaker 1: quantum fields, and those fields have energy and so boom,

614
00:34:19,920 --> 00:34:22,879
Speaker 1: therefore there has to be something. I don't really find

615
00:34:22,920 --> 00:34:25,960
Speaker 1: that answer to be satisfactory, because it really just suggests

616
00:34:25,960 --> 00:34:28,239
Speaker 1: another question, which is, you know, well, why do those

617
00:34:28,320 --> 00:34:31,120
Speaker 1: quantum fields even exist? And I like the way that

618
00:34:31,160 --> 00:34:34,000
Speaker 1: a philosopher David Albert put about it. He says, quote,

619
00:34:34,280 --> 00:34:37,400
Speaker 1: the fact that some arrangements of fields happen to correspond

620
00:34:37,440 --> 00:34:40,160
Speaker 1: to the existence of particles and some don't is not

621
00:34:40,280 --> 00:34:42,520
Speaker 1: a whit more mysterious than the fact that some of

622
00:34:42,560 --> 00:34:45,719
Speaker 1: the possible arrangements of my fingers happen to correspond to

623
00:34:45,760 --> 00:34:48,839
Speaker 1: the existence of a fist and some don't. Really, he's

624
00:34:48,880 --> 00:34:51,640
Speaker 1: saying that it's not really that interesting to think about

625
00:34:51,960 --> 00:34:54,839
Speaker 1: why are the fields sometimes making a planet and why

626
00:34:54,880 --> 00:34:57,919
Speaker 1: are the fields sometimes making empty space? The question really

627
00:34:58,000 --> 00:35:00,799
Speaker 1: is why are the fields right? Why do we have

628
00:35:01,080 --> 00:35:04,359
Speaker 1: fields at all? Why do we have space even that

629
00:35:04,640 --> 00:35:08,040
Speaker 1: has the possibility for fields. And this is the deep

630
00:35:08,120 --> 00:35:10,640
Speaker 1: question I think that physics should answer, and this is

631
00:35:10,680 --> 00:35:13,440
Speaker 1: sort of where physics is. We know that space is

632
00:35:13,480 --> 00:35:16,319
Speaker 1: out there, We know that every bit of space is

633
00:35:16,360 --> 00:35:19,960
Speaker 1: filled with quantum fields, and those quantum fields have energy.

634
00:35:20,080 --> 00:35:22,560
Speaker 1: And so from that starting point we can ask the question,

635
00:35:22,880 --> 00:35:26,560
Speaker 1: what does physics have to say about the nature of

636
00:35:26,680 --> 00:35:30,239
Speaker 1: nothing and why there is anything? Because remember, the goal

637
00:35:30,239 --> 00:35:32,680
Speaker 1: of physics is to try to grapple with the universe

638
00:35:32,719 --> 00:35:35,640
Speaker 1: to make sense of it. And I think an important

639
00:35:35,640 --> 00:35:38,600
Speaker 1: part of making sense of the universe is just understanding

640
00:35:39,040 --> 00:35:41,960
Speaker 1: why it exists. You know, we want to understand that

641
00:35:42,280 --> 00:35:44,879
Speaker 1: if the universe exists, it should be because it has

642
00:35:44,920 --> 00:35:49,160
Speaker 1: to exist or because it cannot not exist. The nature

643
00:35:49,160 --> 00:35:53,080
Speaker 1: of physics is to get the simplest possible explanation for

644
00:35:53,280 --> 00:35:55,719
Speaker 1: the universe as we see it. You know, we use

645
00:35:55,760 --> 00:35:59,160
Speaker 1: Acam's razor and we remove anything from our explanation that's

646
00:35:59,239 --> 00:36:02,200
Speaker 1: not necessary. We want to boil it down to the smallest,

647
00:36:02,360 --> 00:36:04,840
Speaker 1: simplest description. That doesn't mean we want to boil it

648
00:36:04,840 --> 00:36:07,480
Speaker 1: down to nothing, right, That's why I think about the

649
00:36:07,560 --> 00:36:11,279
Speaker 1: question in this way, is the simplest thing something or

650
00:36:11,480 --> 00:36:15,080
Speaker 1: is the simplest thing nothing. It might be that nothing

651
00:36:15,200 --> 00:36:17,439
Speaker 1: is sort of incoherent. You know, what do we even

652
00:36:17,560 --> 00:36:20,799
Speaker 1: mean by nothing? So from that point of view, if

653
00:36:20,840 --> 00:36:25,160
Speaker 1: we understood the simplest, deepest nature of the universe, we

654
00:36:25,239 --> 00:36:27,360
Speaker 1: might be able to point to it and say, oh, look,

655
00:36:27,440 --> 00:36:31,440
Speaker 1: this is the simplest possible thing. It's even simpler than nothing.

656
00:36:31,600 --> 00:36:34,600
Speaker 1: So that might be why the universe sort of has

657
00:36:34,680 --> 00:36:37,040
Speaker 1: to exist. So we're jumping ahead of us a little

658
00:36:37,040 --> 00:36:40,000
Speaker 1: bit and digging into the implications of the answer. But first,

659
00:36:40,160 --> 00:36:43,240
Speaker 1: let's talk a little bit more about what quantum physics

660
00:36:43,239 --> 00:36:46,400
Speaker 1: and general relativity tell us about the nature of space

661
00:36:46,680 --> 00:36:50,239
Speaker 1: and what that says about why it exists. So, of

662
00:36:50,280 --> 00:36:52,920
Speaker 1: course we have two different voices in this story. We

663
00:36:53,000 --> 00:36:55,120
Speaker 1: have the voice of quantum mechanics and the voice of

664
00:36:55,160 --> 00:36:59,800
Speaker 1: general relativity, which tell us two very different stories about

665
00:36:59,800 --> 00:37:02,160
Speaker 1: the nature of space and give us two very different

666
00:37:02,160 --> 00:37:06,200
Speaker 1: answers about why the universe should or shouldn't exist. So

667
00:37:06,400 --> 00:37:09,880
Speaker 1: let's start with quantum mechanics. Quantum mechanics treats space and

668
00:37:09,960 --> 00:37:13,880
Speaker 1: time very very differently. Quantum mechanics says space is the

669
00:37:13,920 --> 00:37:17,480
Speaker 1: place where quantum fields are. Every point in space is

670
00:37:17,520 --> 00:37:20,480
Speaker 1: just a place where quantum field has a value over here,

671
00:37:20,520 --> 00:37:23,200
Speaker 1: the electron field has one value. Over there, the electron

672
00:37:23,239 --> 00:37:26,000
Speaker 1: field has another value. That's all a quantum field is.

673
00:37:26,040 --> 00:37:28,520
Speaker 1: It's just a point in space with a value in it.

674
00:37:28,800 --> 00:37:31,520
Speaker 1: Sometimes that values a vector, Sometimes it's a number, sometimes

675
00:37:31,560 --> 00:37:34,520
Speaker 1: it's more complicated. Whatever, it's just a point in space.

676
00:37:34,880 --> 00:37:38,320
Speaker 1: But time is separate. Time is how those fields evolved.

677
00:37:38,400 --> 00:37:41,960
Speaker 1: And the most famous equation in quantum mechanics the Shortinger equation.

678
00:37:42,360 --> 00:37:45,080
Speaker 1: That's what that equation is about. It tells you if

679
00:37:45,080 --> 00:37:47,319
Speaker 1: you have a quantum wave function or graduate that to

680
00:37:47,360 --> 00:37:51,000
Speaker 1: a quantum field. It tells you how that changes with time.

681
00:37:51,480 --> 00:37:54,520
Speaker 1: And the most important thing about the Shorteninger equation is

682
00:37:54,560 --> 00:37:57,960
Speaker 1: that it says that quantum information is never lost. Like

683
00:37:58,040 --> 00:38:01,360
Speaker 1: a quantum wave function, changes as time goes on. Maybe

684
00:38:01,360 --> 00:38:04,040
Speaker 1: a photon spreads out, or maybe interact with the wall

685
00:38:04,200 --> 00:38:08,440
Speaker 1: or something happens, but the information is not lost. According

686
00:38:08,480 --> 00:38:12,040
Speaker 1: to quantum mechanics and the shorting Your equation, everything about

687
00:38:12,080 --> 00:38:15,600
Speaker 1: the past is encoded in the present. This means that

688
00:38:15,640 --> 00:38:18,120
Speaker 1: you can reconstruct what happened in the past just by

689
00:38:18,160 --> 00:38:21,680
Speaker 1: looking at the information about the arrangement of quantum particles

690
00:38:21,719 --> 00:38:24,840
Speaker 1: now and the really fascinating thing about this is that

691
00:38:24,920 --> 00:38:28,239
Speaker 1: it says that this works backwards and forwards. Right. The

692
00:38:28,239 --> 00:38:31,080
Speaker 1: shorting your equation can tell you how your wave functions

693
00:38:31,080 --> 00:38:33,880
Speaker 1: will change as the future goes on. It won't tell

694
00:38:33,920 --> 00:38:36,680
Speaker 1: you what the actual outcomes of experiments are, right. That

695
00:38:36,760 --> 00:38:39,560
Speaker 1: depends on this whole measurement problem that we're not going

696
00:38:39,600 --> 00:38:41,560
Speaker 1: to dig into today. But it tells you how the

697
00:38:41,600 --> 00:38:45,200
Speaker 1: probabilities evolved and how they have evolved in the past.

698
00:38:45,560 --> 00:38:48,400
Speaker 1: What that means is that quantum mechanics says the universe

699
00:38:48,440 --> 00:38:53,360
Speaker 1: should basically be eternal because quantum information can't be destroyed,

700
00:38:53,400 --> 00:38:56,000
Speaker 1: which means if it exists now, it always has to

701
00:38:56,080 --> 00:38:58,960
Speaker 1: exist and it can't have not existed in the past.

702
00:38:59,440 --> 00:39:01,760
Speaker 1: So from the wanting to you quantum mechanics, the universe

703
00:39:01,920 --> 00:39:05,640
Speaker 1: has to have always existed. There can't be a point

704
00:39:05,880 --> 00:39:08,440
Speaker 1: in the time line of the universe where it doesn't

705
00:39:08,440 --> 00:39:11,239
Speaker 1: exist if it does exist today. So it sort of

706
00:39:11,239 --> 00:39:15,120
Speaker 1: requires this like consistency as a function of time. Now,

707
00:39:15,160 --> 00:39:19,480
Speaker 1: the mystery is that general relativity tells us a different story. Right.

708
00:39:19,560 --> 00:39:23,120
Speaker 1: General relativity tells us that space and time are very

709
00:39:23,200 --> 00:39:26,880
Speaker 1: very closely connected. It prefers a tightly bundled space and

710
00:39:26,920 --> 00:39:30,280
Speaker 1: time where the two react together to the presence, for example,

711
00:39:30,320 --> 00:39:33,759
Speaker 1: of mass in the universe and general relativity is what

712
00:39:33,880 --> 00:39:37,240
Speaker 1: helps us understand the fact that the universe is expanding.

713
00:39:37,440 --> 00:39:39,960
Speaker 1: It's not just that we have a universe, and not

714
00:39:40,040 --> 00:39:42,560
Speaker 1: just like why is there something? Why is there every

715
00:39:42,640 --> 00:39:46,120
Speaker 1: year more of that something than there was before? Right,

716
00:39:46,160 --> 00:39:49,160
Speaker 1: the universe is expanding, it's growing, and when we think

717
00:39:49,200 --> 00:39:52,239
Speaker 1: about the nature of that space, right, it tells us

718
00:39:52,280 --> 00:39:56,000
Speaker 1: that space can be created. What's happening now between us

719
00:39:56,000 --> 00:39:59,560
Speaker 1: and other galaxies is the stretching of space, the creation

720
00:40:00,040 --> 00:40:04,319
Speaker 1: of new space. That means that space isn't eternal. It's

721
00:40:04,320 --> 00:40:06,680
Speaker 1: being made right now by some process that we do

722
00:40:06,760 --> 00:40:09,799
Speaker 1: not understand, and that tells us a different story about

723
00:40:09,800 --> 00:40:13,279
Speaker 1: the nature of space, this basic fundamental thing that we're

724
00:40:13,280 --> 00:40:16,759
Speaker 1: struggling to understand why it has to exist. Maybe it

725
00:40:16,840 --> 00:40:19,960
Speaker 1: doesn't have to exist because there's some process that can

726
00:40:20,080 --> 00:40:23,840
Speaker 1: make it, which means maybe the opposite is true as well.

727
00:40:23,920 --> 00:40:26,759
Speaker 1: And in fact, because we don't understand the mechanism of

728
00:40:26,800 --> 00:40:30,440
Speaker 1: this creation of space, is suggests that the mechanism might

729
00:40:30,480 --> 00:40:33,680
Speaker 1: be reversible. And there's still this possibility that dark energy

730
00:40:33,719 --> 00:40:36,960
Speaker 1: will stop and it will halt the accelerating expansion of

731
00:40:37,040 --> 00:40:40,439
Speaker 1: the universe and turn things around and bring it all

732
00:40:40,600 --> 00:40:44,240
Speaker 1: back and crunch it back together to make a new singularity,

733
00:40:44,560 --> 00:40:48,000
Speaker 1: the time symmetric version of the Big Bang right pulled

734
00:40:48,000 --> 00:40:51,120
Speaker 1: together down to a big crunch. And this would involve

735
00:40:51,360 --> 00:40:56,080
Speaker 1: not just the compactification of space, but the destruction of space,

736
00:40:56,520 --> 00:41:00,359
Speaker 1: the shrinking of distances between things, exactly the same way

737
00:41:00,400 --> 00:41:04,040
Speaker 1: that dark energy right now is expanding the distances between

738
00:41:04,080 --> 00:41:08,200
Speaker 1: things by creating new space. This would involve the compactification.

739
00:41:08,360 --> 00:41:11,960
Speaker 1: This would involve the destruction of space, the shrinking of

740
00:41:12,040 --> 00:41:15,719
Speaker 1: distances between things, not just moving things through space, but

741
00:41:15,840 --> 00:41:19,480
Speaker 1: actually destroying the space between them. That's pretty hard to

742
00:41:19,480 --> 00:41:22,440
Speaker 1: think about, but it gives you a clue about like

743
00:41:22,760 --> 00:41:26,799
Speaker 1: what's fundamental to the universe. Now. The problem is, we

744
00:41:26,840 --> 00:41:30,480
Speaker 1: don't really believe that either these theories are correct. We

745
00:41:30,560 --> 00:41:32,800
Speaker 1: look at general relativity and we look at the history

746
00:41:32,840 --> 00:41:35,520
Speaker 1: of the universe, and we say, it doesn't really make

747
00:41:35,560 --> 00:41:38,920
Speaker 1: sense for the universe to always have existed. The quantum

748
00:41:38,920 --> 00:41:42,080
Speaker 1: mechanical view that the universe can't have had a beginning

749
00:41:42,160 --> 00:41:44,360
Speaker 1: because the information in the wave function of the unverse

750
00:41:44,480 --> 00:41:47,640
Speaker 1: can't be destroyed doesn't seem quite right. It doesn't job

751
00:41:47,680 --> 00:41:49,920
Speaker 1: with our observation that the universe does seem to have

752
00:41:50,080 --> 00:41:52,640
Speaker 1: had a beginning, it seems to only have been fourteen

753
00:41:52,680 --> 00:41:55,760
Speaker 1: billion years old. On the other hand, if we retreat

754
00:41:55,800 --> 00:41:58,960
Speaker 1: to the corner of general relativity, we say some problems

755
00:41:58,960 --> 00:42:01,719
Speaker 1: with this theory also. First of all, it ignores the

756
00:42:01,800 --> 00:42:05,200
Speaker 1: obvious quantum mechanical nature of our universe. All of our

757
00:42:05,360 --> 00:42:08,960
Speaker 1: particle physics experiments and investigations in the last hundred of

758
00:42:09,080 --> 00:42:12,880
Speaker 1: years have revealed that the fabric of reality is quantum mechanical,

759
00:42:12,920 --> 00:42:16,839
Speaker 1: and general relativity ignores that. But more importantly, when we

760
00:42:16,880 --> 00:42:18,880
Speaker 1: look back at the very beginning of the universe and

761
00:42:18,920 --> 00:42:22,480
Speaker 1: try to understand, like, well, if the universe is being created,

762
00:42:22,760 --> 00:42:26,200
Speaker 1: what is the beginning of that process, general relativity leaves

763
00:42:26,239 --> 00:42:29,560
Speaker 1: us with a question mark. That singularity, the moment of

764
00:42:29,680 --> 00:42:34,000
Speaker 1: infinite density that begins our universe in the general relativistic story,

765
00:42:34,200 --> 00:42:37,600
Speaker 1: doesn't make any sense. Infinite curvature and infinite density is

766
00:42:37,640 --> 00:42:40,480
Speaker 1: not something we think is physically true. We don't think

767
00:42:40,520 --> 00:42:44,360
Speaker 1: it's a historical, actual accounting of events. It's a failure

768
00:42:44,560 --> 00:42:47,480
Speaker 1: of general relativities. When the theory breaks down and can

769
00:42:47,560 --> 00:42:51,359
Speaker 1: no longer give us a sensible answer. So what does

770
00:42:51,400 --> 00:42:55,360
Speaker 1: physics tell us about why there is something rather than nothing?

771
00:42:55,719 --> 00:42:57,399
Speaker 1: It tells us that we have a lot of work

772
00:42:57,400 --> 00:43:00,680
Speaker 1: to do before we understand what is the thing that

773
00:43:00,760 --> 00:43:03,960
Speaker 1: we are trying to explain. If we want to understand

774
00:43:03,960 --> 00:43:07,120
Speaker 1: why there is something rather than nothing, we need physics

775
00:43:07,120 --> 00:43:11,040
Speaker 1: to lead us closer to understanding what that thing is.

776
00:43:11,440 --> 00:43:13,200
Speaker 1: Because when we know what that thing is, that we

777
00:43:13,200 --> 00:43:17,280
Speaker 1: can ask interesting and fascinating questions about why it should

778
00:43:17,280 --> 00:43:19,440
Speaker 1: exist and what it would be like for it to

779
00:43:19,640 --> 00:43:22,560
Speaker 1: not exist. But we don't even know the fundamental nature

780
00:43:22,600 --> 00:43:26,080
Speaker 1: of the universe. We need that unification of quantum mechanics

781
00:43:26,160 --> 00:43:29,799
Speaker 1: and general relativity into some theory of quantum gravity so

782
00:43:29,840 --> 00:43:31,800
Speaker 1: that we can look at it. We can say, okay,

783
00:43:31,880 --> 00:43:35,080
Speaker 1: the basic element of the universe is a string. For example,

784
00:43:35,239 --> 00:43:37,840
Speaker 1: why do strings have to exist? Would it be simpler

785
00:43:37,880 --> 00:43:40,319
Speaker 1: to not have them? There are some people who think

786
00:43:40,560 --> 00:43:44,160
Speaker 1: really interesting and fascinating thoughts sort of about that future

787
00:43:44,200 --> 00:43:47,319
Speaker 1: without actually knowing what that future is. For example, one

788
00:43:47,320 --> 00:43:51,040
Speaker 1: of my favorite books is Our Mathematical Reality by Max

789
00:43:51,080 --> 00:43:53,759
Speaker 1: tad Mark, and he makes a fascinating argument which I

790
00:43:53,760 --> 00:43:56,360
Speaker 1: don't actually believe but I think it's super fun. He

791
00:43:56,440 --> 00:44:01,280
Speaker 1: says essentially that because our universe can be this scribed mathematically,

792
00:44:01,480 --> 00:44:06,279
Speaker 1: therefore it is a mathematical construct, and that's why it exists.

793
00:44:06,520 --> 00:44:09,280
Speaker 1: In his mind, you have to imagine, like every set

794
00:44:09,320 --> 00:44:13,080
Speaker 1: of mathematical laws that do hold together and make a

795
00:44:13,120 --> 00:44:18,560
Speaker 1: consistent universe, that universe exists because the mathematics works. I'm

796
00:44:18,560 --> 00:44:20,960
Speaker 1: not sure I can take that last step that every

797
00:44:21,000 --> 00:44:24,440
Speaker 1: mathematical self consistent universe that you can write down on

798
00:44:24,560 --> 00:44:27,800
Speaker 1: paper actually does exist out there. It seems like you

799
00:44:27,800 --> 00:44:31,080
Speaker 1: would have more really really simple universes than like vastly

800
00:44:31,160 --> 00:44:34,640
Speaker 1: complex universes like ours. And then you also have to imagine,

801
00:44:34,680 --> 00:44:37,400
Speaker 1: like what is the mathematical substrate on which all of

802
00:44:37,440 --> 00:44:40,320
Speaker 1: these like meta universes are running on. But it's a

803
00:44:40,320 --> 00:44:43,280
Speaker 1: really fun question, so I hope that answers your question.

804
00:44:43,480 --> 00:44:47,800
Speaker 1: Physics basically doesn't yet know what the thing is in something,

805
00:44:48,000 --> 00:44:50,600
Speaker 1: so we can't really answer the question why is there

806
00:44:50,680 --> 00:44:55,000
Speaker 1: something rather than nothing? Thank you everybody who sent in

807
00:44:55,160 --> 00:44:58,279
Speaker 1: all your super fun questions. Keep thinking deeply about the

808
00:44:58,360 --> 00:45:00,920
Speaker 1: nature of the universe and how quant particles work, and

809
00:45:00,960 --> 00:45:03,680
Speaker 1: please keep sending us your questions. They are the light

810
00:45:03,719 --> 00:45:06,240
Speaker 1: of our day. We will answer all of your emails,

811
00:45:06,280 --> 00:45:09,200
Speaker 1: trust me, or interact with us on Twitter if that's

812
00:45:09,239 --> 00:45:11,799
Speaker 1: what you prefer. So please keep thinking deeply about the

813
00:45:11,840 --> 00:45:23,200
Speaker 1: universe and keep asking questions. Tune in next time. Thanks

814
00:45:23,239 --> 00:45:25,880
Speaker 1: for listening, and remember that Daniel and Jorge explained The

815
00:45:25,920 --> 00:45:29,040
Speaker 1: Universe is a production of I Heart Radio. Or more

816
00:45:29,120 --> 00:45:32,480
Speaker 1: podcast from my heart Radio, visit the I heart Radio app,

817
00:45:32,760 --> 00:45:36,200
Speaker 1: Apple Podcasts, or wherever you listen to your favorite shows.

818
00:45:37,880 --> 00:45:41,840
Speaker 1: Ye