Latest / Daniel and Kelly’s Extraordinary Universe / Daniel answers Listener Questions about the size of the Universe, what's in intergalactic space and why gravity dominates the Universe.

Transcript

Daniel answers Listener Questions about the size of the Universe, what's in intergalactic space and why gravity dominates the Universe. · Daniel and Kelly’s Extraordinary Universe

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  Speaker 1: Does it ever amaze you the sheer arrogance of physics.
• 0:12
  Speaker 1: I don't mean the arrogance of physicists. That's a topic
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  Speaker 1: for another day. I mean the very concept that we
• 0:19
  Speaker 1: could understand the universe, the vast reaches of space, the
• 0:24
  Speaker 1: distant stars in the early moments of the cosmos. We
• 0:27
  Speaker 1: have hardly even left this planet, and yet we imagine
• 0:31
  Speaker 1: that we could understand how distant galaxies are formed and
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  Speaker 1: what happens at the center of neutron stars without ever
• 0:37
  Speaker 1: actually visiting them. What would you think if you heard
• 0:40
  Speaker 1: of a biologist who refused to leave her room studying
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  Speaker 1: Earth's varied life just by peering out of her windows.
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  Speaker 1: And yet it's all that we can do. And so
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  Speaker 1: it's incredible what we have learned about the universe just
• 0:54
  Speaker 1: looking out of our cosmic living room windows. Hi. I'm Daniel.
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  Speaker 1: I'm a particle physicist, but my curiosity about the universe
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  Speaker 1: extends well beyond my living room windows. And welcome to
• 1:21
  Speaker 1: our podcast, Daniel and Jorge Explain the Universe, a production
• 1:25
  Speaker 1: of My Heart Radio. Is just me on the podcast
• 1:28
  Speaker 1: today Jorge can join us, so I'll be talking to
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  Speaker 1: you all about the incredible things in our universe, the
• 1:33
  Speaker 1: things that are close to home, the things that are
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  Speaker 1: far away, the things that make us wonder, the things
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  Speaker 1: that make us want to go and visit. I'd love
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  Speaker 1: to imagine what it's like to go circle a black hole,
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  Speaker 1: or delve deep into the center of a neutron star,
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  Speaker 1: or even just visit another planet and see if there
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  Speaker 1: is life. But of course we can't answer all of
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  Speaker 1: our questions about the universe by actually going places. All
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  Speaker 1: we can do is sit here at home and think
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  Speaker 1: about these things, use our minds and our telescopes to
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  Speaker 1: peer out of our cosmic living room and try to
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  Speaker 1: understand the universe from our tiny little mode of dust.
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  Speaker 1: And that's the question at the heart of physics. Can
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  Speaker 1: we in fact understand our universe? Is it possible to
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  Speaker 1: wrap our puny, little human minds around the incredible mysteries
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  Speaker 1: of this vast and incredibly complicated and surprising universe. And
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  Speaker 1: when you try to do that, when you ask these
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  Speaker 1: questions about the universe, sometimes you come up with a
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  Speaker 1: point of confusion. You think, how does that make any sense?
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  Speaker 1: Or what is this actually doing? And that's the point
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  Speaker 1: of our podcast to try to bring those questions home
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  Speaker 1: to you, to answer your questions about the universe, to
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  Speaker 1: explain everything, and along the way maybe make a few
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  Speaker 1: banana jokes. And today on the program we will have
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  Speaker 1: an episode chock full of questions, not just questions from physicists,
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  Speaker 1: questions from listeners. And I love getting questions from listeners
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  Speaker 1: because they make me ask myself questions. Before I can
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  Speaker 1: explain something clearly and well enough for anybody to understand it,
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  Speaker 1: I have to really understand it thoroughly. Not just well
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  Speaker 1: enough to follow the mathematics and say, hmmm, that must
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  Speaker 1: be right, but well enough to explain it using intuitive
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  Speaker 1: concepts backwards and forwards and sideways, so that you can
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  Speaker 1: really understand it. And for me that's a joy, because
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  Speaker 1: sometimes there are things in physics that I never really
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  Speaker 1: got to dig into, and when somebody asked me a
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  Speaker 1: question about how they work, then it gives me an
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  Speaker 1: excuse to go off for an hour or two and
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  Speaker 1: read all about it and ask myself all the questions
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  Speaker 1: I never quite answered until I have a solid enough
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  Speaker 1: understanding of it to explain it to you. So please,
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  Speaker 1: if you have a question you would like answered about
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  Speaker 1: the universe or something you never really quite understood. Send
• 3:45
  Speaker 1: it to us to questions at Daniel and Jorge dot com.
• 3:49
  Speaker 1: And if you don't like writing emails, you can come
• 3:51
  Speaker 1: to my first ever public office hours, where I'll be
• 3:55
  Speaker 1: hanging out on zoom and answering questions from the general public.
• 3:58
  Speaker 1: Do you have a question about physics you can't find
• 4:00
  Speaker 1: the answer to on Google? Do you want to hear
• 4:02
  Speaker 1: more about black holes and singularities and flying through the
• 4:06
  Speaker 1: universe on rockets and solar sales. Come to my public
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  Speaker 1: office hours. You can find the link on our website,
• 4:12
  Speaker 1: or you can go to sites dot U, c I
• 4:14
  Speaker 1: dot E, d U slash Daniel and you'll find all
• 4:17
  Speaker 1: the information there. It's December four at nine am Pacific
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  Speaker 1: time and it's totally free, so see you there. But
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  Speaker 1: today on the program will be answering questions that people
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  Speaker 1: did send in, things about space, things about the intergalactic medium,
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  Speaker 1: things about huge galaxies, things about gravity. So let's not
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  Speaker 1: waste any more time and let's get right to the
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  Speaker 1: first question on the docket, which comes from Nick. Hey,
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  Speaker 1: Daniel and Torgy. My name is Nick and I'm a
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  Speaker 1: video game programmer from Canada. I have a question for
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  Speaker 1: you about intergalactic space. Now, I've always assumed that there's
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  Speaker 1: pretty much nothing in the space between galaxies, but recently
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  Speaker 1: I read a NASA article that talked about how there's
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  Speaker 1: a ton of extragalactic stars that live inside these huge voids.
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  Speaker 1: So my question for you is just how much stuff
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  Speaker 1: is there inside of intergalactic space? Does it contain mostly
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  Speaker 1: regular stars or is there a lot of other things
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  Speaker 1: like space dust and black holes in dark matter? So
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  Speaker 1: I love this question because Nick is exploring the universe
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  Speaker 1: with his mind. He's wondering what is out there in
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  Speaker 1: the deepest, darkest reaches of space. Is it totally empty?
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  Speaker 1: Is there actually something out there? How does a star
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  Speaker 1: end up outside of its galaxy? And what else is
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  Speaker 1: there in the intergalactic space? So awesome question. Thank you
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  Speaker 1: very much Nick for sending it in. And I thought
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  Speaker 1: it'd be interesting to answer this question by sort of
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  Speaker 1: stepping up into intergalactic space and starting with space that's
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  Speaker 1: sort of near by us. So you know that outer space,
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  Speaker 1: of course isn't empty. So what about this space that's
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  Speaker 1: right outside of our atmosphere? Is that empty? Is there
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  Speaker 1: stuff out there? Well, the space that's in our Solar
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  Speaker 1: system is dominated by stuff produced by the Sun. This
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  Speaker 1: is called the solar wind. So outer space is not empty.
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  Speaker 1: It's filled with particles that come from the Sun. These
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  Speaker 1: our trons and protons and sometimes alpha particles, and they're
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  Speaker 1: produced by the same processes that creates all the light
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  Speaker 1: for which the Sun is quite famous. All that crazy
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  Speaker 1: fusion that's going on in the Sun also injects a
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  Speaker 1: lot of particles, so we call this the solar wind.
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  Speaker 1: It's not wind in the sense that there's any air
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  Speaker 1: in space, of course. It's just a huge stream of particles,
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  Speaker 1: a flux of particles, and it's a lot. There are
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  Speaker 1: like five to ten million protons per cubic meter, and
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  Speaker 1: these things are moving at four hundred kilometers per second,
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  Speaker 1: so that's definitely not nothing. And ten million protons sounds
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  Speaker 1: like a lot, but remember that in a drop of
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  Speaker 1: water there's like ten to the twenty three protons. So
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  Speaker 1: it's quite diffuse compared to like our atmosphere or anything
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  Speaker 1: on the surface, but it's definitely not empty. You also
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  Speaker 1: have to remember that out there in space is a
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  Speaker 1: lot of matter that we cannot see. We think that
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  Speaker 1: there's five times as much dark matter as there is
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  Speaker 1: normal matter in the universe, and that it's clustered roughly
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  Speaker 1: the same way that normal matter is. It's a bit
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  Speaker 1: more diffused. It's not localized into planets and stars. It's
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  Speaker 1: fluffy and spread out, but it's out there in space.
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  Speaker 1: So if you build a box in space that's a
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  Speaker 1: cubic meter, you're probably also capturing some dark matter, one
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  Speaker 1: or two protons worth of dark matter per cubic meter. Alright,
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  Speaker 1: So that's inside our solar system. We already see that
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  Speaker 1: space is not empty. If you take a step outside
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  Speaker 1: our solar system, so into interstellar space, but still within
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  Speaker 1: our galaxy, then we have something that's called the interstellar medium.
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  Speaker 1: This is gas. It's just hydrogen and helium that's floating
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  Speaker 1: out there, stuff that didn't coalesce into a star or
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  Speaker 1: sort of left out the last time stars were made,
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  Speaker 1: and it could also be the building blocks of future stars.
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  Speaker 1: You know that our stars were made when huge clouds
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  Speaker 1: of gas and dust were sort of shocked maybe by
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  Speaker 1: a supernova or something else, and coalesced into star forming regions.
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  Speaker 1: And this kind of stuff can still will happen, and
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  Speaker 1: it could happen in the interstellar medium. So this is
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  Speaker 1: gases like one percent dust, which are these tiny little
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  Speaker 1: grains of stuff left over from other stars. And it's
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  Speaker 1: mostly hydrogen out there, and there's not a lot of stuff.
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  Speaker 1: There's about one molecule of hydrogen every ten thousand to
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  Speaker 1: one million cubic meters, so it's not a whole lot
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  Speaker 1: of stuff out there. It's pretty empty, but you know,
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  Speaker 1: it's not empty space. And of course inside our galaxy
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  Speaker 1: you still have to multiply by five for dark matter,
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  Speaker 1: because there's a lot of dark matter in our galaxy,
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  Speaker 1: even out there between the stars, right, the dark matter
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  Speaker 1: is spread out more diffusely than the normal matter, but
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  Speaker 1: it's still there. So if you're inside the galaxy, there's
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  Speaker 1: still a lot of dark matter, all right. So that's
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  Speaker 1: just sort of the setup. Now let's get directly to
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  Speaker 1: NIXT question. NIXT question is about what's an intergalactic space.
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  Speaker 1: So here we have our galaxy, for example, the Milky Way,
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  Speaker 1: and this Andromeda just for example, several million light years away.
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  Speaker 1: Nick through asking about what's between here and there, and
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  Speaker 1: now we're still inside our cluster of galaxies. Remember, galaxies
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  Speaker 1: are not just like floating out there in space randomly.
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  Speaker 1: They are also organized into structures we call these galactic clusters,
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  Speaker 1: and gravity is strong enough to hold these things together.
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  Speaker 1: All these galaxies are orbiting some central point. So what's
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  Speaker 1: in intergalactic space inside one of these galaxy clusters. Well,
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  Speaker 1: it's something very cleverly named the intergalactic medium, which basically
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  Speaker 1: means the stuff between galaxies. Well what is this stuff, Well,
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  Speaker 1: it's basically plasma. It's ionized hydrogen. So hydrogen is just
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  Speaker 1: the proton and an electron when it's neutral, But ionized
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  Speaker 1: hydrogen is when there's too much energy in that electron
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  Speaker 1: so it can't be held onto by the proton, so
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  Speaker 1: there to part their way. So ionized hydrogen is basically
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  Speaker 1: just a proton. And this stuff is called a plasma
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  Speaker 1: because it's ionized and and that's what a plasma is.
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  Speaker 1: You take a ga asking you strip away the electrons
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  Speaker 1: and you call that a plasma. So this stuff is
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  Speaker 1: the intergalactic medium, and it stretches sort of between galaxies.
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  Speaker 1: And you might think, well, that doesn't sound like a
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  Speaker 1: lot of stuff, but it's surprising. There's so much space
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  Speaker 1: out there between galaxies that even though there's not a
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  Speaker 1: lot of it's like, you know, maybe one hydrogen atom
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  Speaker 1: per cubic meter. It really adds up. So there's these
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  Speaker 1: incredible reaches of space. Right, Like the space between us
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  Speaker 1: and the next galaxy is millions of light years, So
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  Speaker 1: even if the stuff between us and them isn't very dense,
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  Speaker 1: there's a huge volume. So actually, about half of the
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  Speaker 1: baryonic matter in the universe, half of the atoms in
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  Speaker 1: the universe, are in this intergalactic medium. So half of
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  Speaker 1: it is in galaxies, which means stars and planets and
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  Speaker 1: hamsters and bananas and all that crazy stuff, and the
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  Speaker 1: other half is between galaxies. So yes, Nick, there is
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  Speaker 1: stuff between the galaxies, like half of all the familiar
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  Speaker 1: matter in the universe is between galaxies. And these filaments
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  Speaker 1: are crazy. They stretch between the galaxies, and you can
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  Speaker 1: think of the galaxies is sort of like the bright
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  Speaker 1: spots in this web, and there are these connections between
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  Speaker 1: the galaxies, these streams between the galaxies. And we talked
• 11:16
  Speaker 1: on the podcast recently about the magnetic fields that are
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  Speaker 1: out there in deep space. One of the really fascinating
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  Speaker 1: things is that you can use these streams of stuff
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  Speaker 1: between galaxies, this intergalactic medium to measure those magnetic fields.
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  Speaker 1: Because the magnetic fields affect how those streams flow. It's
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  Speaker 1: really pretty super awesome. But that's not the only stuff
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  Speaker 1: that's out there in between galaxies. As Nick said, there
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  Speaker 1: are sometimes stars out there. How do stars end up
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  Speaker 1: in between galaxies? Well, they don't typically form out there
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  Speaker 1: on their own in the darkness of space. Remember that
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  Speaker 1: the structure of the universe forms bottom up, meaning that
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  Speaker 1: you start out with like denser clouds of hydrogen, and
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  Speaker 1: then in those clouds you get stars, and those stars
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  Speaker 1: come together or to form galaxies. So in the very
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  Speaker 1: early universe you may have had stars more distributed through
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  Speaker 1: the universe than we have today, but then they came
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  Speaker 1: together and they formed galaxies. And dark matter also plays
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  Speaker 1: a really important role in that structure formation. Remember that
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  Speaker 1: there's more dark matter than anything else in the universe,
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  Speaker 1: and so where there was more dark matter, all that
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  Speaker 1: stuff fell in and formed the galaxies. All right, so
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  Speaker 1: we expect to find the stars mostly inside the galaxies.
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  Speaker 1: How does stars end up outside the galaxies? Well, stars
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  Speaker 1: can get thrown out of a galaxy. You know, most
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  Speaker 1: of the stars are swirling around the center, but sometimes
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  Speaker 1: there are collisions. You know, stars will bump into each other,
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  Speaker 1: not physically like splash, like a stellar collision, like the
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  Speaker 1: way a particle physicist might build a collider. This smashes
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  Speaker 1: two stars together, but just sort of gravitationally tugging on
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  Speaker 1: each other. If stars passed near each other, one of
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  Speaker 1: them might fling the other one outside of the galaxy.
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  Speaker 1: Because just like the Earth has an escape velocity, and
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  Speaker 1: if you throw a ball, it's going to come back
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  Speaker 1: to Earth, but if you threw a ball hard enough,
• 13:03
  Speaker 1: it would go out into space. And in the same way,
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  Speaker 1: our Sun has an escape velocity. If you shoot a
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  Speaker 1: rocket out into space fast enough, it will leave the
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  Speaker 1: Sun's gravitational hold. And if a star ends up with
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  Speaker 1: just the right velocity and the right angle, it can
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  Speaker 1: also escape the gravitational hold of the galaxy. And that happens,
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  Speaker 1: and so you end up with some stars out there
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  Speaker 1: in intergalactic space. But most of the stuff in intergalactic
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  Speaker 1: space is this rarefied plasma, this intergalactic medium. And the
• 13:34
  Speaker 1: other really weird thing about that medium is that it's
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  Speaker 1: really really hot. Like you think about deep space as
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  Speaker 1: being cold and frozen, and if you got dropped out there,
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  Speaker 1: you would crystallize instantly and that's probably true, but remember
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  Speaker 1: that temperature is a weird thing. There's temperature and then
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  Speaker 1: there's heat. So we call this plasma very very hot.
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  Speaker 1: In fact, it's temperature ranks in the millions of kelvin's.
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  Speaker 1: But that's just because the individual particles in the plasma
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  Speaker 1: are zooming along, so they have a lot of speed,
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  Speaker 1: and microscopically, that's what temperature is. You ask, why is
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  Speaker 1: this gas hot or that gas cold, it's because the
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  Speaker 1: particles inside it are zooming around if they're hot, or
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  Speaker 1: not zooming around if they're cold. And so these particles
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  Speaker 1: are zooming around, which technically makes this intergalactic medium hot.
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  Speaker 1: But it's also not very dense, and so if you're
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  Speaker 1: out there, it wouldn't be able to warm you up. Yes,
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  Speaker 1: you'd be hit by these zippy little protons slamming into you,
• 14:32
  Speaker 1: but you would still not have enough heat to stay warm,
• 14:35
  Speaker 1: and you would freeze. So you could get dropped into
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  Speaker 1: the super hot intergalactic medium and still freeze into an
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  Speaker 1: ice cube. Space is weird, and if you want to
• 14:46
  Speaker 1: go further, you know, the deeper reaches of space are
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  Speaker 1: the ones that are outside our galactic cluster. These filaments
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  Speaker 1: they tied together galaxies in our cluster, But our cluster
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  Speaker 1: itself is part of a larger structure we call a supercluster,
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  Speaker 1: and these superclusters, it's not entirely clear how gravitationally bound
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  Speaker 1: they are. Some people think that they're too big, that
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  Speaker 1: gravity is not really holding them together, that they're getting
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  Speaker 1: separated by dark energy. Other people think that parts of
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  Speaker 1: the supercluster might be small enough to be tied together.
• 15:17
  Speaker 1: In either case, there are also these filaments between galaxy clusters.
• 15:22
  Speaker 1: This was recently discovered by scientists trying to understand how
• 15:25
  Speaker 1: far into space magnetic fields go, and they used the
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  Speaker 1: filaments between galaxies to figure out that there are magnetic
• 15:32
  Speaker 1: fields out there in deep space. And then they found
• 15:35
  Speaker 1: these filaments between galaxy clusters that showed that there are
• 15:38
  Speaker 1: also magnetic fields out there in deep space. Now, the
• 15:42
  Speaker 1: dark matter dark matter, remember, clumps together like normal matter does.
• 15:46
  Speaker 1: So there are huge blobs of dark matter associated with
• 15:49
  Speaker 1: each galaxy. But then dark matter peters out and there's
• 15:52
  Speaker 1: less of it out there and intergalactic space. So Nick,
• 15:55
  Speaker 1: to answer your questions, in intergalactic space, it's mostly this
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  Speaker 1: rarefied plasmate, These filaments of protons that extend between galaxies.
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  Speaker 1: There's a little bit of dark matter out there, but
• 16:05
  Speaker 1: not as much. But remember that all of the universe
• 16:08
  Speaker 1: also is bathed in dark energy, something we don't understand,
• 16:12
  Speaker 1: but it's two thirds of the energy budget of the
• 16:15
  Speaker 1: universe that's busy pulling the universe apart, accelerating the expansion
• 16:19
  Speaker 1: of the universe, and tearing all of these galaxy clusters
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  Speaker 1: apart from each other. Great question, Thank you very much,
• 16:25
  Speaker 1: Nick for sending that in super vun stuff to talk about.
• 16:29
  Speaker 1: I want to get to the next question, but first,
• 16:31
  Speaker 1: let's take a quick break. All right, we're back and
• 16:46
  Speaker 1: we're answering listener questions. Today. We're helping you explore the
• 16:50
  Speaker 1: things you are curious about. What's out there in deep space?
• 16:54
  Speaker 1: How does it all work? So sit down and enjoy
• 16:56
  Speaker 1: a mental journey into the deep dark reaches of the
• 16:59
  Speaker 1: universe as we use physics to try to understand how
• 17:02
  Speaker 1: it all works. And so we're answering listener questions, and
• 17:06
  Speaker 1: here comes our second one. What I've been struck by
• 17:09
  Speaker 1: from your podcast is that scale wise, we seem to
• 17:12
  Speaker 1: lie in the middle of the universe. On one end,
• 17:16
  Speaker 1: there's all these tiny tiny particles, and on the other extreme,
• 17:19
  Speaker 1: there is this enormous scale of all these countless galaxies,
• 17:22
  Speaker 1: and we happen to be somewhere in the middle. Separately,
• 17:26
  Speaker 1: quantum physics has this weird observer effect, a situation where we,
• 17:31
  Speaker 1: no matter what we do, have an impact on the
• 17:34
  Speaker 1: state of something that we are trying to study. It's
• 17:36
  Speaker 1: like our presence or our attention partly to find the
• 17:39
  Speaker 1: state of things when we try to analyze it. My
• 17:43
  Speaker 1: question is whether these are somehow related. I find it
• 17:46
  Speaker 1: hard to believe that we just happened to be in
• 17:48
  Speaker 1: the middle, we're just seeing our version of the universe,
• 17:51
  Speaker 1: that this perception of being in the middle scale wise,
• 17:54
  Speaker 1: is actually because we are observing the universe and we
• 17:57
  Speaker 1: are the center of how it is presented up. Wow,
• 18:01
  Speaker 1: thanks so much for that question, super fun. I love
• 18:04
  Speaker 1: the general concept behind this question, this idea that the
• 18:07
  Speaker 1: universe as we see it is somehow a product of
• 18:10
  Speaker 1: how we are looking and who we are, because remember
• 18:14
  Speaker 1: that physics is often trying to separate ourselves from the
• 18:17
  Speaker 1: essential humanity of the way we think. We're trying to
• 18:20
  Speaker 1: get some universal understanding of the universe, something that when
• 18:24
  Speaker 1: aliens come we could use it to compare notes with them,
• 18:27
  Speaker 1: We could talk to them using mathematics and understand the
• 18:30
  Speaker 1: same physics questions. The kind of stuff we put on
• 18:33
  Speaker 1: the Voyager and the Pioneer probes is our like most
• 18:36
  Speaker 1: distilled understanding of the universe that we hope that we
• 18:39
  Speaker 1: think alien intelligence could also understand. And that's because physicists
• 18:43
  Speaker 1: are trying to understand the universe not just from a
• 18:46
  Speaker 1: human perspective, but from a fundamental perspective. We imagine, we
• 18:49
  Speaker 1: hope that there's a way to understand the universe separated
• 18:53
  Speaker 1: from the biases of the human perspective. But is that
• 18:56
  Speaker 1: even possible because we know that quantum mechanics tells us
• 19:00
  Speaker 1: us that observing things changed it. So I think that's
• 19:03
  Speaker 1: what's at the heart of this question. So thank you
• 19:05
  Speaker 1: very much for asking it. Let's begin by talking about
• 19:08
  Speaker 1: the scale. The question started by talking about how we
• 19:11
  Speaker 1: are in the middle of everything, between the tiny, tiny
• 19:15
  Speaker 1: particles and the huge, huge galaxies. So is that actually true? Well,
• 19:20
  Speaker 1: what is the smallest thing that we can see? What
• 19:22
  Speaker 1: is the smallest thing that humans have observed? Well, if
• 19:26
  Speaker 1: you take atoms, for example, and strip them apart, you
• 19:28
  Speaker 1: get down to the nucleus, and inside the nucleus are
• 19:31
  Speaker 1: protons and neutrons, and inside those protons and neutrons are quirks.
• 19:35
  Speaker 1: If you get down to the smallest stuff, then we're
• 19:38
  Speaker 1: talking about fundamental particles. And we had a whole episode
• 19:41
  Speaker 1: in the podcast about what is a fundamental particle? How
• 19:44
  Speaker 1: big is it? What does it even mean? And unfortunately
• 19:47
  Speaker 1: it's sort of a philosophical question, like what is the
• 19:50
  Speaker 1: size of an electron or what is the size of
• 19:52
  Speaker 1: a quirk? And in our theory, we think about these
• 19:55
  Speaker 1: things as point particles like dots in space with no volume,
• 19:59
  Speaker 1: which they don't have a well defined size. If you
• 20:03
  Speaker 1: ask three different theoretical physicists how you define the size
• 20:06
  Speaker 1: of a particle, you might get three different answers. But
• 20:09
  Speaker 1: what we decided on that podcast was that it sort
• 20:12
  Speaker 1: of makes sense to talk about the size of a
• 20:13
  Speaker 1: particle based on its interactions, like how it touches other stuff,
• 20:18
  Speaker 1: because that really determined sort of how it fits into
• 20:20
  Speaker 1: the nature of the universe, how close you can get
• 20:23
  Speaker 1: to it. If you think about the size of something,
• 20:25
  Speaker 1: it's like, you know the distance between its left edge
• 20:28
  Speaker 1: and its right edge. Those edges are determined by when
• 20:30
  Speaker 1: it pushes back on other things. So just as an exercise,
• 20:34
  Speaker 1: you can imagine the size of quarks is like how
• 20:37
  Speaker 1: big is the proton? Because quarks come together to make
• 20:41
  Speaker 1: a proton, so you can imagine the corks are sort
• 20:43
  Speaker 1: of inside their own little bubble inside the proton. So
• 20:47
  Speaker 1: the distances involved inside the proton are crazy tiny numbers,
• 20:52
  Speaker 1: things like ten to the minus fifteen meters. You know,
• 20:55
  Speaker 1: that's zero point zero, zero zero, or fifteen zeros and
• 21:00
  Speaker 1: then one. So it's a really unfathomily tiny scale, and
• 21:04
  Speaker 1: you know, it's hard for a physicist or hard for
• 21:06
  Speaker 1: anybody to imagine what's really going on down there. And
• 21:09
  Speaker 1: this is where we have to rely in the mathematics.
• 21:12
  Speaker 1: We look at that number, we say, well, I assume
• 21:14
  Speaker 1: that means something it's hard to really understand. Is that
• 21:17
  Speaker 1: really a distance? Is someone down there with a ruler
• 21:20
  Speaker 1: and you could measure the distance between the quarks, But anyway,
• 21:24
  Speaker 1: protons are down there about ten to the minus fifteen meters,
• 21:28
  Speaker 1: so fifteen orders of magnitude smaller than a human human
• 21:32
  Speaker 1: is about one meter, right to a physicist, within a
• 21:36
  Speaker 1: factor of to a human is one meter. We don't
• 21:38
  Speaker 1: really care about factors of two or even five. We're
• 21:41
  Speaker 1: mostly just trying to figure out, like roughly, what is
• 21:43
  Speaker 1: the order of magnitude of stuff? And you know, of
• 21:46
  Speaker 1: course we've designed the meter to be approximately a human
• 21:49
  Speaker 1: size because it's it's the kind of thing we used
• 21:51
  Speaker 1: to measure, all right. So then zooming out how big
• 21:55
  Speaker 1: are cosmic structures like our Milky Way or a milky
• 21:58
  Speaker 1: way is about a hundred thousand light years across. Translate
• 22:02
  Speaker 1: that into meters and you get about ten to the
• 22:05
  Speaker 1: twenty meters. So already the scale extends further on the
• 22:08
  Speaker 1: big side than on the small side. Like a proton
• 22:12
  Speaker 1: or a cork is like fifteen orders of magnitude smaller
• 22:15
  Speaker 1: than us, but the Milky Way is twenty orders of
• 22:18
  Speaker 1: magnitude bigger than us. And that's a big deal. That
• 22:21
  Speaker 1: five orders of magnitude is a huge factor. You know,
• 22:24
  Speaker 1: that's a hundred thousand If I have to borrow a
• 22:27
  Speaker 1: hundred thousand dollars and then I pay you back just
• 22:29
  Speaker 1: one dollar, that would make a pretty big difference to
• 22:31
  Speaker 1: your life. But the Milky Way is not the biggest
• 22:33
  Speaker 1: thing that's out there. Clusters of galaxies are these structures
• 22:37
  Speaker 1: of galaxies that come together, and superclusters are these clusters
• 22:42
  Speaker 1: of clusters, and that's probably the biggest thing in the
• 22:45
  Speaker 1: universe because if you zoom out even further, you see
• 22:47
  Speaker 1: it's just like a vast ocean of superclusters. And so
• 22:51
  Speaker 1: the scale of the supercluster is like ten to the
• 22:53
  Speaker 1: twenty four meters. So that means that the smallest things
• 22:57
  Speaker 1: we can see are fifteen orders of magnitudes smaller than
• 23:01
  Speaker 1: we are, but the biggest things we can see are
• 23:04
  Speaker 1: twenty four orders of magnitude bigger than we are. So
• 23:08
  Speaker 1: are we really at the center? We're actually sort of
• 23:11
  Speaker 1: on the small edge of things. Something that's about in
• 23:13
  Speaker 1: the middle, you know, that's between a proton and a
• 23:16
  Speaker 1: supercluster is something that's like a hundred kilometers wide, so
• 23:20
  Speaker 1: you know, I don't know, take the city of Los
• 23:22
  Speaker 1: Angeles for example, that's about a hundred kilometers wide. So
• 23:26
  Speaker 1: Los Angeles has the same relationship to a proton as
• 23:29
  Speaker 1: a supercluster does to Los Angeles, which is pretty incredible, right.
• 23:33
  Speaker 1: That tells you how training a proton is compared to
• 23:36
  Speaker 1: the glorious city of l a and also how big
• 23:39
  Speaker 1: a supercluster is compared to l A. And I know
• 23:42
  Speaker 1: is sometimes it feels like you're driving all the way
• 23:44
  Speaker 1: across a supercluster when you're stuck in traffic in l A.
• 23:47
  Speaker 1: But trust me, supercluster is much bigger than Los Angeles.
• 23:51
  Speaker 1: So we're not actually in the middle. Humans are not
• 23:54
  Speaker 1: really in the middle of these two scales. But still
• 23:57
  Speaker 1: your point holds. I mean, we are much close to
• 24:00
  Speaker 1: the middle than we are to the edges. Right, We're
• 24:03
  Speaker 1: not proton sized, we're not super cluster sized. We're roughly
• 24:07
  Speaker 1: speaking between these two scales. And it's definitely true that
• 24:12
  Speaker 1: the size of us controls what we can see. Right,
• 24:16
  Speaker 1: Our ability to probe things that are really really small
• 24:19
  Speaker 1: depends on the tools that we build to probe them.
• 24:22
  Speaker 1: On the other hand, our ability to see things that
• 24:25
  Speaker 1: are really really big doesn't really depend on our size.
• 24:28
  Speaker 1: It's limited more on the speed of light, like the
• 24:31
  Speaker 1: time it takes information to get to us from these
• 24:34
  Speaker 1: vast structures, and our ability to build telescopes to gather
• 24:38
  Speaker 1: that light. For example, if we could build a huge
• 24:41
  Speaker 1: number of telescopes that surrounded the Earth that gathered light
• 24:44
  Speaker 1: from all over the universe, we could build an incredible
• 24:47
  Speaker 1: three D map of the universe and understand the structure
• 24:50
  Speaker 1: of superclusters and their distribution and stuff like. We still
• 24:54
  Speaker 1: don't even really know what the map of the universe,
• 24:57
  Speaker 1: the observable universe, looks like, only because haven't spent enough
• 25:01
  Speaker 1: time looking. The only thing that limits us to building
• 25:04
  Speaker 1: this map is just gathering the light in telescopes. So
• 25:07
  Speaker 1: on the small side, I think there definitely is an
• 25:09
  Speaker 1: effect because we have to use objects that we can
• 25:12
  Speaker 1: control in order to see things that are small, like
• 25:15
  Speaker 1: we'd like to see things that are much much smaller,
• 25:18
  Speaker 1: but we're limited to building tools out of the objects
• 25:21
  Speaker 1: that we can control. That's how we've gotten down to
• 25:24
  Speaker 1: tend of the minus fifteen meters. We've used particle colliders,
• 25:27
  Speaker 1: for example, to smash these things together. If we were
• 25:30
  Speaker 1: made out of much smaller particles, we could manipulate even
• 25:33
  Speaker 1: smaller particles and we could probe even further. But then
• 25:37
  Speaker 1: one might ask, well, how small can you probe? Right,
• 25:40
  Speaker 1: And we don't know if there's a minimum size to
• 25:43
  Speaker 1: stuff in the universe. It might be that things just
• 25:46
  Speaker 1: get smaller and smaller. That inside the cork there are
• 25:49
  Speaker 1: smaller particles, and inside that there are smaller particles. And
• 25:52
  Speaker 1: inside that there are smaller particles, and it literally just
• 25:54
  Speaker 1: goes on forever. It might be the things can get
• 25:58
  Speaker 1: infinitely small. But I suspect that's not the case, because
• 26:02
  Speaker 1: the universe is quantum mechanical, which means it likes to
• 26:05
  Speaker 1: have discrete units. You'd like to have a basis. It
• 26:08
  Speaker 1: likes to be built out of fundamental building blocks. And
• 26:12
  Speaker 1: we don't know what that scalely is. We don't know
• 26:14
  Speaker 1: what the size of the smallest thing is. But we
• 26:17
  Speaker 1: suspect that the universe follows these rules of quantum mechanics,
• 26:20
  Speaker 1: and we can make some very bad estimates for how
• 26:23
  Speaker 1: small the smallest thing might be. We take the numbers
• 26:26
  Speaker 1: that we have around, like planks constant and the speed
• 26:29
  Speaker 1: of light and the gravitational constant, and we can squish
• 26:32
  Speaker 1: those numbers together, multiply them by each other, and divide
• 26:35
  Speaker 1: and do all sorts of stuff, and do we get
• 26:36
  Speaker 1: a number that has distance units? Right, It's just a
• 26:40
  Speaker 1: number that means a distance. Doesn't mean that it is
• 26:43
  Speaker 1: the size of the smallest particle or the scale of
• 26:46
  Speaker 1: space pixels or anything like that. It just means like, hey,
• 26:48
  Speaker 1: this is the number we can get. And we do
• 26:51
  Speaker 1: this kind of estimate because we don't have any better
• 26:53
  Speaker 1: way of understanding what the smallest thing in the universe is.
• 26:57
  Speaker 1: This is like the dumbest thing you can do. Also
• 26:59
  Speaker 1: the only thing we can do at this point, so
• 27:02
  Speaker 1: better to do the dumbest thing than to do nothing.
• 27:05
  Speaker 1: And you put all those numbers together, you get something
• 27:08
  Speaker 1: like ten to the minus thirty five ms, and that
• 27:11
  Speaker 1: suggests that we could continue exploring the universe twenty more
• 27:15
  Speaker 1: orders of magnitude smaller than we have. Right, we've gotten
• 27:19
  Speaker 1: down to like ten to the minus fifteen meters, So
• 27:21
  Speaker 1: there's like twenty more orders of magnitude left to explore
• 27:25
  Speaker 1: in the universe, maybe, we think, but we suspect there
• 27:28
  Speaker 1: might be a minimum size there. On the other side,
• 27:32
  Speaker 1: is there a maximum size of something we can explore? Well,
• 27:35
  Speaker 1: we think that the largest thing in the universe is
• 27:38
  Speaker 1: a supercluster, meaning that after that there isn't any organized structure.
• 27:42
  Speaker 1: We don't think superclusters have gathered together to make super
• 27:45
  Speaker 1: duper clusters, that those have pulled together to make super
• 27:49
  Speaker 1: duper duper clusters. And that's for a good reason. That's
• 27:52
  Speaker 1: just because gravity hasn't had enough time to organize that stuff.
• 27:56
  Speaker 1: Remember that structure in the universe is organized bottom up.
• 28:00
  Speaker 1: Stars are formed, they come together to make galaxies. Those
• 28:02
  Speaker 1: galaxies come together to make clusters. Those clusters come together
• 28:06
  Speaker 1: to make superclusters, and all this stuff takes time because
• 28:09
  Speaker 1: gravity is pretty weak. So after billions of years, it's
• 28:12
  Speaker 1: formed these superclusters which are like just barely held together gravitationally.
• 28:17
  Speaker 1: Will it make super duper clusters in the future, we
• 28:20
  Speaker 1: don't know, because there's an opposing force, the dark energy.
• 28:24
  Speaker 1: Dark energy is pulling the universe apart. So anything that
• 28:27
  Speaker 1: gravity is not like holding together the way your body
• 28:31
  Speaker 1: holds itself together, or the Earth holds you on it,
• 28:33
  Speaker 1: or the Sun holds the Earth around it, will get
• 28:36
  Speaker 1: pulled apart by dark energy. So gravity has had its
• 28:39
  Speaker 1: moment to build structures, and it might be that it's
• 28:42
  Speaker 1: run out of time that anything that's not now gravitationally
• 28:45
  Speaker 1: held together will get torn apart and separated by dark energy.
• 28:49
  Speaker 1: So that suggests that even though the universe itself might
• 28:52
  Speaker 1: be infinite, the biggest thing in the universe might already
• 28:56
  Speaker 1: have been formed. It might be that it maxes out.
• 28:59
  Speaker 1: Attend to the toy be four meters. Now there's one
• 29:02
  Speaker 1: more aspect of this wonderful question I want to touch on,
• 29:05
  Speaker 1: which is this quantum observer effect. It's true that every
• 29:08
  Speaker 1: time you observe something in the universe, you affect it.
• 29:12
  Speaker 1: You can't measure anything in the universe without interacting with it.
• 29:15
  Speaker 1: Even just looking at something requires that you bounce a
• 29:18
  Speaker 1: photon off of it, because you can't see something unless
• 29:22
  Speaker 1: there are photons coming from that thing to your eyeballs.
• 29:26
  Speaker 1: So there's literally no way to know anything about the
• 29:28
  Speaker 1: universe without interacting with it, and interacting with things changes them.
• 29:33
  Speaker 1: So there's this intimate relationship between the observer person making
• 29:37
  Speaker 1: a measurement trying to understand the universe, and the thing
• 29:40
  Speaker 1: that's being observed. There's no way to separate those two things.
• 29:44
  Speaker 1: So if aliens come and they do physics differently, they
• 29:47
  Speaker 1: might see different observations. They will definitely have different ways
• 29:50
  Speaker 1: of thinking about the universe. But it's impossible to try
• 29:53
  Speaker 1: to develop a system of understanding a set of observations
• 29:57
  Speaker 1: that are separate from the person doing the observer. So
• 30:01
  Speaker 1: it's certainly there is an influence there the way we
• 30:04
  Speaker 1: do observations, the way we think about the universe. But
• 30:07
  Speaker 1: I don't see a direct connection between this idea that
• 30:09
  Speaker 1: you affect things when you observe them in the universe
• 30:12
  Speaker 1: and the size of things in the universe. I think
• 30:15
  Speaker 1: we're much more limited just by the light that we
• 30:17
  Speaker 1: can gather to see biggest things in the universe and
• 30:21
  Speaker 1: by the probes we can use to see the smallest
• 30:23
  Speaker 1: things in the universe. Alright, so are we in the
• 30:26
  Speaker 1: middle of everything? Sort of things seem to be more
• 30:30
  Speaker 1: big than they are small at this point. We don't
• 30:33
  Speaker 1: know if we can drill down smaller to see even
• 30:35
  Speaker 1: smaller things, but we suspect we might have already seen
• 30:39
  Speaker 1: the biggest things in the universe. So it is sort
• 30:41
  Speaker 1: of amazing that over all those orders of magnitude were
• 30:44
  Speaker 1: much closer to the middle than we are to the edges.
• 30:48
  Speaker 1: So thanks very much for thinking so grandly about the
• 30:51
  Speaker 1: universe and wondering about our place in it. That's exactly
• 30:53
  Speaker 1: what makes physics so much fun. All right, I want
• 30:57
  Speaker 1: to answer one more question, but first let's take another break. Yeah,
• 31:12
  Speaker 1: all right, we're back, and we are exploring the universe
• 31:15
  Speaker 1: with our minds. We are wondering about the way things work.
• 31:18
  Speaker 1: We're asking questions, and we're hoping to do some answering.
• 31:22
  Speaker 1: So I'm here on my own because Jorge can't be
• 31:24
  Speaker 1: here today, and I'm catching up on listener questions. And remember,
• 31:28
  Speaker 1: if you have a question about the universe and you
• 31:30
  Speaker 1: can't find the answer on Google, then please write to
• 31:33
  Speaker 1: us two questions at Daniel and Jorge dot com. All right,
• 31:37
  Speaker 1: let's get to our last question of the day, which
• 31:39
  Speaker 1: is a super awesome one. Hi, guys, this is Foreignce
• 31:42
  Speaker 1: in Texas. I have a question about gravity. You've described
• 31:46
  Speaker 1: it before as the weakest force, and you said, in
• 31:50
  Speaker 1: fact that it's so weak that when you're picking up
• 31:52
  Speaker 1: an object with a magnet, you're overpowering the entire Earth's gravity.
• 31:57
  Speaker 1: So that's pretty weak. My problem is more, I start
• 32:00
  Speaker 1: thinking about the objects and the Kuiper Belt. They're thirty
• 32:03
  Speaker 1: two fifty astronomical units away and that's billions and billions
• 32:07
  Speaker 1: of miles, and yet the Sun's gravity is still able
• 32:10
  Speaker 1: to keep them in orbit, and that just gives me
• 32:12
  Speaker 1: the impression that gravity is really strong, not weak. So
• 32:17
  Speaker 1: those two thoughts really don't go together. Um, would you
• 32:20
  Speaker 1: help me with that? Thank you, bye, Thank you so
• 32:23
  Speaker 1: much for that question, Florence. I love this question, and
• 32:26
  Speaker 1: I love the way you phrased it. At the end,
• 32:28
  Speaker 1: those two thoughts don't go together. That's doing physics right there.
• 32:32
  Speaker 1: You are a physicist, Lawrence, because you are trying to
• 32:35
  Speaker 1: reconcile two ways of thinking about things, because you think, well,
• 32:39
  Speaker 1: the universe has got to make sense, right, and so
• 32:41
  Speaker 1: if I understand idea A and idea B, then I
• 32:44
  Speaker 1: have to somehow be able to bring them together to
• 32:47
  Speaker 1: one holistic idea. And that's exactly what we do in physics.
• 32:51
  Speaker 1: We say, huh, this thing over here works this way.
• 32:53
  Speaker 1: I wonder if that's related to that or there, or
• 32:55
  Speaker 1: how do we get these two things to agree? The
• 32:58
  Speaker 1: whole program of physics is to get a single understanding
• 33:00
  Speaker 1: of the universe. So thank you for doing that exercise.
• 33:03
  Speaker 1: That's exactly what I love seeing. So let's help you
• 33:05
  Speaker 1: bring these two ideas together. So idea number one is
• 33:09
  Speaker 1: that gravity is really really weak. It's the weakest of
• 33:12
  Speaker 1: the forces, and yet somehow it seems to control the
• 33:16
  Speaker 1: structure of the universe, things orbiting around the Sun, the
• 33:20
  Speaker 1: Sun overing around the center of the galaxy. How is
• 33:23
  Speaker 1: it possible for gravity to be at the same time
• 33:25
  Speaker 1: the weakest force in the universe and the dominant force
• 33:29
  Speaker 1: in the universe. Awesome question. And so first let's review
• 33:32
  Speaker 1: what does it mean when we say gravity is the
• 33:34
  Speaker 1: weakest force in the universe. So we know about a
• 33:37
  Speaker 1: bunch of forces. Forces are things that push and pull.
• 33:40
  Speaker 1: They create little fields of particles can tug on each
• 33:43
  Speaker 1: other without actually touching. We know about electromagnetism. That's the
• 33:47
  Speaker 1: force that makes like lightning and electricity and photons and stuff.
• 33:51
  Speaker 1: We know about the nuclear weak force, which is actually
• 33:54
  Speaker 1: part of electromagnetism. We call that electro weak, but it's
• 33:57
  Speaker 1: the thing that like can push and pull on neutrinos
• 34:00
  Speaker 1: and it's responsible for radioactive to kay of a nucleus.
• 34:03
  Speaker 1: Then there's the strong force that holds the nucleus together
• 34:05
  Speaker 1: and also binds protons and neutrons together using these funky
• 34:09
  Speaker 1: particles called gluons. And then there's gravity, and gravity is
• 34:13
  Speaker 1: the weakest of those forces. So in order, the strong
• 34:17
  Speaker 1: force is well named because it's the strongest force as
• 34:20
  Speaker 1: the most energy held into it. And then there's electromagnetism,
• 34:24
  Speaker 1: which is also a powerful force. Then there's the weak force,
• 34:27
  Speaker 1: which is well named because it's much weaker than the
• 34:30
  Speaker 1: rest of electromagnetism, and the reason it's weak is because
• 34:33
  Speaker 1: the particles that it uses to communicate the force are
• 34:36
  Speaker 1: the w and the z bosons, and they're very massive,
• 34:39
  Speaker 1: so they don't live for very long. The sort of
• 34:40
  Speaker 1: peter out very very quickly compared to the photon. And
• 34:43
  Speaker 1: then there's gravity at the bottom. And you know, if
• 34:46
  Speaker 1: you organize these things into a race, like, the difference
• 34:49
  Speaker 1: between the strong force and electromagnetism and the weak force
• 34:52
  Speaker 1: is really pretty small compared to gravity. Gravity is not
• 34:56
  Speaker 1: even in their league. Gravity is ten to the forty
• 35:00
  Speaker 1: times weaker than all of these other forces. So, for example,
• 35:04
  Speaker 1: if you take two electrons and you put them a
• 35:07
  Speaker 1: centimeter apart, and you ask, well, what's the strength of
• 35:10
  Speaker 1: the electromagnetic force between them? They're repelling each other because
• 35:13
  Speaker 1: then their negative charges compared to the gravitational attraction, Well,
• 35:18
  Speaker 1: it's ten to the forty times stronger. Right, Gravity is
• 35:22
  Speaker 1: basically zero in comparison. So that's what we mean when
• 35:25
  Speaker 1: we say that gravity is super duper weak. And the
• 35:27
  Speaker 1: example you gave me your question is another excellent one.
• 35:30
  Speaker 1: You can overcome all of the gravity of Earth tugging
• 35:34
  Speaker 1: on a magnet. Just by using another tiny magnet and
• 35:37
  Speaker 1: a super weak fridge magnet can overpower the gravity of
• 35:41
  Speaker 1: a celestial body an entire planet. Right, So that's what
• 35:45
  Speaker 1: we mean when we say gravity super duper weak. And
• 35:48
  Speaker 1: yet you're right, it seems to dominate the universe. Right.
• 35:52
  Speaker 1: If you're talking about why does the neptune move around
• 35:55
  Speaker 1: the Sun, well, it's because of the gravity of the Sun.
• 35:58
  Speaker 1: It's not like the Sun has a positive stric charge
• 36:00
  Speaker 1: and and Neptune as a negative electric charge, and it's
• 36:03
  Speaker 1: using that electromagnetic force to hold Neptune in place. And
• 36:07
  Speaker 1: it's definitely not the strong force of the weak force.
• 36:09
  Speaker 1: It's gravity. So why is that? And the short answer
• 36:13
  Speaker 1: is because gravity cannot be neutralized. It can't be balanced.
• 36:17
  Speaker 1: All objects have mass and those objects feel gravity. You
• 36:22
  Speaker 1: can't be neutralized the way you can, for example, with electromagnetism.
• 36:25
  Speaker 1: Think about, for example, what would happen if the Earth
• 36:27
  Speaker 1: had an overall negative charge and the Sun had an
• 36:30
  Speaker 1: overall positive charge. That would be an enormous force that
• 36:35
  Speaker 1: would be crazy strong, much stronger than the Sun's gravity
• 36:39
  Speaker 1: on the Earth. And what would happen is that particles
• 36:42
  Speaker 1: would very quickly get transmitted between the Earth and the
• 36:45
  Speaker 1: Sun to neutralize that force. Because the force would be
• 36:48
  Speaker 1: so powerful that it would pull negative particles out of
• 36:52
  Speaker 1: the Earth and positive particles out of the Sun. The
• 36:54
  Speaker 1: force itself would neutralize itself right, it would balance itself out.
• 36:58
  Speaker 1: The force acts on charge particles and moves them around
• 37:02
  Speaker 1: in a way to neutralize itself. This is, for example,
• 37:06
  Speaker 1: why you can't get a cell phone signal inside an elevator,
• 37:10
  Speaker 1: because the cell phone signal is electromagnetic radiation. It moves
• 37:13
  Speaker 1: particles around, and if it hits the wall of the elevator,
• 37:17
  Speaker 1: it moves those particles around in order to balance out
• 37:20
  Speaker 1: to cancel out the electromagnetic radiation. So electromagnetism, because it
• 37:25
  Speaker 1: has a plus and a minus, it can be balanced out.
• 37:29
  Speaker 1: And that's also true for the other forces. Most of
• 37:32
  Speaker 1: the things in the universe that are made out of
• 37:34
  Speaker 1: the strong force, that are held together by the strong force.
• 37:37
  Speaker 1: Proton and neutron have no overall strong charge, or you
• 37:41
  Speaker 1: don't feel the strong force between two protons, usually unless
• 37:45
  Speaker 1: you bring them close enough to bind them into a nucleus.
• 37:47
  Speaker 1: But most of the stuff in the universe doesn't have
• 37:49
  Speaker 1: a strong charge or a weak charge or an electric charge,
• 37:53
  Speaker 1: because if it did, it would get balanced out. But
• 37:56
  Speaker 1: gravity cannot be balanced out. There's no negative man us object, right,
• 38:01
  Speaker 1: everything feels the same kind of gravity was just just attraction.
• 38:05
  Speaker 1: So what happened in the early universe is at first
• 38:08
  Speaker 1: those other forces were more important and they pulled the
• 38:11
  Speaker 1: particles together, so protons were attracted to electrons to make
• 38:14
  Speaker 1: for example, neutral hydrogen, and then everything god balanced out
• 38:18
  Speaker 1: except for gravity. Because if you make a universe filled
• 38:22
  Speaker 1: with neutral hydrogen, for example, then nothing can tug on
• 38:26
  Speaker 1: anything except for gravity because gravity cannot be balanced out.
• 38:30
  Speaker 1: And that's exactly what happened in our universe, is that
• 38:33
  Speaker 1: all the other forces did their thing, neutralized themselves, and
• 38:37
  Speaker 1: then gravity got to do its thing. Now, gravity has
• 38:39
  Speaker 1: been around since the very beginning, but it's been basically
• 38:42
  Speaker 1: ignorable because it's so weak. But once the other the
• 38:46
  Speaker 1: big powerful forces have done their thing and left the field,
• 38:49
  Speaker 1: then it's gravity's turn to take over. So gravity clumped
• 38:52
  Speaker 1: together that neutral hydrogen to make stars and planets and
• 38:56
  Speaker 1: everything else. So the reason that gravity is that we
• 39:00
  Speaker 1: get force and also the dominant force in the universe
• 39:03
  Speaker 1: is because it's patient. It just waits for all the
• 39:06
  Speaker 1: other players to leave the field, and then it takes
• 39:09
  Speaker 1: over because it cannot be neutralized, it cannot be balanced,
• 39:13
  Speaker 1: it cannot be ignored. No matter what goes on in
• 39:16
  Speaker 1: the universe, you are going to feel gravity. And that's
• 39:20
  Speaker 1: why the most powerful things in the universe, like black holes,
• 39:22
  Speaker 1: they are gravitational objects, right, They're crazy, dense blobs of
• 39:28
  Speaker 1: gravity that have bent and torn space time into forms
• 39:32
  Speaker 1: that are not even recognizable. So there's a lesson in there. Right,
• 39:35
  Speaker 1: Even if you're the weakest force out there, you can
• 39:38
  Speaker 1: still win as long as you play the long game.
• 39:42
  Speaker 1: So if you think about things in the Kuiper Belt,
• 39:44
  Speaker 1: you know they're thirty AU away. They're very, very far
• 39:48
  Speaker 1: from the Sun, and even the gravity of the Sun
• 39:51
  Speaker 1: is not very strong. Right. Remember that gravity falls by
• 39:54
  Speaker 1: one over R squared, So if you're twice as far
• 39:57
  Speaker 1: away from something, gravity gets four times weaker. So if
• 40:01
  Speaker 1: you're thirty au away, that's thirty times the distance from
• 40:04
  Speaker 1: the Earth to the Sun. Then the gravity out there
• 40:07
  Speaker 1: is nine hundred times weaker than it would be if
• 40:10
  Speaker 1: you were at the same distance of the Earth and
• 40:12
  Speaker 1: the Sun. But there's nothing else acting on these objects.
• 40:16
  Speaker 1: These are cold, dead objects. They're electrically neutral. Only thing
• 40:20
  Speaker 1: acting on them is the Sun's gravity, and the Sun
• 40:23
  Speaker 1: is pretty massive, and so that does really add up.
• 40:26
  Speaker 1: And the same thing happens not just for our Solar system,
• 40:29
  Speaker 1: but for our galaxy. Right, what is our galaxy? It's
• 40:32
  Speaker 1: a big swirling mass of stars. What's holding them together?
• 40:36
  Speaker 1: Not electrical forces, not magnetism, not the strong force. It's gravity.
• 40:41
  Speaker 1: And gravity is also the reason we have these galaxies. Remember,
• 40:45
  Speaker 1: the galactic formation came because there were these deep gravitational
• 40:49
  Speaker 1: wells formed by dark matter. The gravity of dark matter.
• 40:53
  Speaker 1: The gravity of dark matter created these wells. It clustered
• 40:57
  Speaker 1: together first and it formed these gravitational wells, then pulled
• 41:00
  Speaker 1: in all this other matter to form our galaxy. So
• 41:03
  Speaker 1: in the end, it really is gravity that dominates the
• 41:06
  Speaker 1: structure of the universe. The other forces are what's responsible
• 41:09
  Speaker 1: for making sort of the tiny little building blocks, the
• 41:12
  Speaker 1: protons and neutrons, the atoms, those are tied together by
• 41:15
  Speaker 1: the other forces. But once they build their little neutral blobs,
• 41:18
  Speaker 1: it's gravity that pulls it together into stars and planets
• 41:22
  Speaker 1: and galaxies and clusters and superclusters. And in the end,
• 41:27
  Speaker 1: it's gravity that wins all right. Thanks very much for
• 41:30
  Speaker 1: all of those really fun questions. I had a great
• 41:33
  Speaker 1: time thinking about all the crazy stuff that's out there
• 41:35
  Speaker 1: in the universe, from the very very big to the
• 41:38
  Speaker 1: very very small, from the very very weak to the
• 41:40
  Speaker 1: very very strong, from the very very dense stuff in
• 41:43
  Speaker 1: a star to the very dispersed stuff of the intergalactic medium.
• 41:48
  Speaker 1: So please keep asking questions, think about the universe, try
• 41:51
  Speaker 1: to make sense of it yourself, because remember that science
• 41:55
  Speaker 1: is nothing but people, people like me and people like you,
• 41:58
  Speaker 1: thinking and wondering about the universe and trying to grapple
• 42:01
  Speaker 1: with it. We don't know if the universe is a
• 42:03
  Speaker 1: place that we can understand, but we can do our best.
• 42:06
  Speaker 1: We can form these models in our head and try
• 42:09
  Speaker 1: to map them to the whole universe and wrangle this entire, crazy,
• 42:12
  Speaker 1: beautiful cosmos into our minds. It might seem like an
• 42:16
  Speaker 1: impossible task, and it might be an impossible task, but
• 42:20
  Speaker 1: so far it's worked pretty well. So let's keep using
• 42:23
  Speaker 1: physics to explore the universe and to come to some
• 42:25
  Speaker 1: sort of beautiful understanding of this gorgeous cosmos. Thanks for listening,
• 42:38
  Speaker 1: Thanks for listening, and remember that Daniel and Jorge explained
• 42:41
  Speaker 1: the Universe is a production of I heart Radio. For
• 42:44
  Speaker 1: more podcast for my heart Radio, visit the i heart
• 42:47
  Speaker 1: Radio app, Apple Podcasts, or wherever you listen to your
• 42:50
  Speaker 1: favorite shows.