Mysteries of the universe: Expansion and gravity

CHILD 1: You're listening to Brains On where we're serious about being curious.

CHILD 2: Brains On is supported in part by a grant from the National Science Foundation.

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MOLLY BLOOM: You're listening to Brains On from American Public Media. I'm Molly Bloom. And today, we're going to start the new year off with something that we love here at Brains On, mysteries about our universe, and questions without easy answers. We're going to revisit a couple of big questions from some of our favorite episodes.

Have you ever wondered what's beyond the edge of the universe? Or maybe a better question, is there even an edge of the universe? And what does it mean that the universe is expanding?

We're about 15 seconds into this episode, and my brain already hurts from thinking about these big questions. So it's a good thing that we have help. Today, we're going to be listening in on a conversation between two very smart people who are wrestling with these very big and very mind-blowing questions.

The first is an astrophysicist.

KATIE MACK: Hi, my name is Katie Mack. I am a theoretical astrophysicist. And I study the early universe and dark matter and stuff like that.

MOLLY BLOOM: And the second is Thea Hutchins.

THEA HUTCHINS: Hi, my name is Thea. I'm nine years old. And I live in Sydney, Australia.

MOLLY BLOOM: Thea wrote what is perhaps our favorite email that has ever been written to Brains On.

THEA HUTCHINS: I don't understand how the universe can be expanding into nothing. Like, what is the nothing the universe is going into? Also, before the Big Bang, there was nothing. So what made the bang? Usually, explosions blowing up something, but there was nothing to blow up. How can everything have come from nothing?

What is nothing anyway? How can there be no space? I can't understand how to think about nothing. Too many questions. Thanks. Thea.

MOLLY BLOOM: In our book, too many questions is always a good thing. We arranged a conversation with Thea and Katie. And we are very excited to share it with you. Now we can all stare into the infinite together.

Thea started by asking about the expansion of the universe. I understand how the universe can be growing and can be expanding into nothing. Like, what is the nothing that the universe is going into?

KATIE MACK: There's nothing that we see that indicates that there's any edge to the universe. There seems to be just no edge. And if there's no edge, if it really does go on forever, which we don't know, then it could go on forever and it could be just getting bigger. Even though it's already infinite, it could be getting more infinite.

But I mean-- and that's a weird idea. But really, all we see is that we see that galaxies are moving apart from each other. Distant galaxies are getting farther apart from other distant galaxies, and they're getting farther apart from us.

And so all we really can say is that things in the universe are getting farther apart from each other. And we interpret that as like the space in between is expanding. And it really looks like all of space is expanding. I mean, the galaxies themselves are not getting bigger, but the spaces in between them are.

And so it's possible that the universe is already infinitely big. There are lots of galaxies in this already infinitely big space. But the galaxies in this big space are getting farther apart from each other. And that's something you can do in an infinitely big space. You can have everything in the infinitely big space getting farther apart from each other, which would be like the infinitely big space getting more infinitely big.

And so that's totally possible. And that's consistent with all our observations. It could also be that the universe wraps around itself at some point. So like if you're on the surface of a balloon, and the balloon is being blown up on the surface, there's no center of that expansion. Different points on the surface are just getting farther apart from other points on the surface.

It could be something like that, but we don't know at the moment. And if it were like that, then that would be like a really big balloon. Because as far as we can tell, we can't see that curving around. To us, the universe doesn't seem to be wrapping around on itself. But that could just be that it's doing it on such a large scale that we can't see it.

So either of those things are possible. And in one case, you don't need any space outside of our universe. And in the other case, you do. But in both cases, all we really see is that things in the universe are getting farther apart.

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THEA HUTCHINS: When I heard that the universe is always expanding, and-- I thought about, if you go to the edge of the universe, if there is an edge of the universe, then I would think the universe is just a square of black and then there's white around it, like there's-- if you get-- if you get to the edge of the black, then there's just empty white, like infinite white.

KATIE MACK: There was an interesting discussion about this back in the ancient times. I don't remember who the people who were talking about this. But they were talking about the edge of the universe. And they had this thought experiment. The thought experiment is where you can't do the experiment, but you can think about it, and you can talk about what would happen.

And they were saying like, what if you go to the edge of the universe and you take an arrow, like a bow and arrow. And you shoot the bow and arrow-- you shoot the arrow off the edge of the universe. Then that arrow has to go somewhere. And that somewhere must be part of the universe.

And so then the universe isn't-- there's not an edge of the universe. Then that can't be the edge, because the arrow went somewhere else. And then so they were thinking like, well, what if you just keep doing that? Then you can't ever have an edge.

I think that there could be an edge based on the way that we think about physics and dimensions now because there could be a limit to our dimensions of space. We have three dimensions of space, we have up and down, and left and right, and front and back, right?

It could be-- it could be that you can't go-- one of these directions doesn't go forever, or maybe, all of the directions don't go forever. And then there really could be an edge. I don't know what color it would be. We don't know that. And it might be that you'd have to find some other direction to shoot your arrows into that we haven't invented yet.

But yeah, I mean, that's totally-- it's totally possible that there is an edge. And yeah, I don't-- but I have no idea what it looks like. And it's interesting. I never thought about it as white. I always think about it as black.

THEA HUTCHINS: Yeah.

KATIE MACK: [LAUGHS] So that's-- yeah, that's cool.

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MOLLY BLOOM: What do you visualize when you think of the universe or the Big Bang? Send us a drawing. We would love to see it. You can email it to hello@brainson.org, or you can find our mailing address on our website, brainson.org.

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We're going to take a short break from pondering the mysteries of the universe to mull over a more bit-sized one. It's time for the mystery sound.

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CHILD 1: (WHISPERING) It's the sound.

MOLLY BLOOM: Here it is.

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Any guesses? Let's hear it again.

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We'll be back with the answer and more from Thea's conversation with Katie a little later in the show. But first--

RICHARD ARNOLD: Do you want my full name? It's-- my full name is Richard R. Arnold. But I go by Ricky. Well, it depends how long me, but-- and I'm a NASA astronaut.

MOLLY BLOOM: Richard is going to tell us a little bit about what it's like to float in space while we get ready to wrap our heads around another mystery of the universe, gravity.

WOMAN: 5, 4, 3, 2, 1, 0, and liftoff.

RICHARD ARNOLD: When you are on a rocket and you ride, take that 8 and 1/2 minute ride to space, it's constant acceleration, constant acceleration. You just went faster and faster. And then all of a sudden, the main engine cuts off. And you float up out of your seat.

Once it stops your free float until you decide to turn around and come back home, for my first mission, it was 13 days. But for the last few years, missions have been six months long.

MOLLY BLOOM: Six months without needing to put your feet on the ground. Whoa.

RICHARD ARNOLD: By and large, it's a lot of fun, because you're just able to do things that you always dreamed about doing. You can fly from one module to the next in the International Space Station. You can sleep on the walls. You can sleep on the ceilings. It doesn't matter how you're oriented.

You get used to managing your personal life and your personal effects. But you misplace something for a second, and you could spend days looking for it because it's all floating. In whatever direction it started moving, that's the way it's heading. And unless it happens to be picked up by a fan and you can find it against the filter, you could spend days looking for something as simple as a fork or a toothbrush. Whereas, in your house, if you drop something, you've got a pretty good idea of where it's going to be.

MOLLY BLOOM: You might think that everything Richard is talking about is happening with zero gravity. But that's not the case at all. When astronauts go into space, they're still in the Earth's gravitational field. They call it microgravity.

RICHARD ARNOLD: We're only 200 miles up. So what's really happening is you're not really experiencing much difference in gravity. What you're experiencing is being in freefall around a planet for an extended period of time. It's like taking a baseball and throwing it so far over the horizon that it's going to eventually curve to the ground make a parabola to the ground, but you throw it so far and so fast that it's falling around the horizon all the time. And that's what we do when we launch rockets.

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MOLLY BLOOM: We know you're curious about the universe and everything in it. And it's your questions that power this show. If you have one you'd like us to tackle, you can send it to hello@brainson.org. That's what Rowan did when he sent us this question about what happens when you jump.

ROWAN: Do you physically get longer when in mid-air? Are basketball players tall because they jump a lot? Or can they jump high because they are tall?

MOLLY BLOOM: We'll have an answer to that question during our Moment of Um at the end of the show. And if you have mystery sounds or drawings you'd like to share with us, you can also send those to hello@brainson.org. If you do, we'll add your name to the Brains Honor Roll, and read it in an upcoming episode. You can hear the latest group to be added at the end of the show. Keep listening.

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All right. Before we delve back into the mysteries of the universe, let's go back to a smaller mystery. Let's hear that mystery sound again.

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Any guesses? Well, you don't have to hold your breath for the answer. Here it is.

EZRA: My name is Ezra. And that was my mom having the hiccups. And I like it because it's noisy and surprising. That was my mom again, hiccuping.

MOLLY BLOOM: Thanks, Ezra. And if you want to find out more about why you get the hiccups and how you can make them go away, check out our Body Bonanza episode. It's all there.

MAN: (SINGING) Baba, baba, baba, bababa, ba, Brains On.

MOLLY BLOOM: Now that we have that mystery taken care of, we're all ready to wrap our minds around the Big Bang, right? Here's Thea again.

THEA HUTCHINS: Before the a Big Bang, there was nothing. So what made the bang? Usually, explosion is blowing up something, but there was nothing to blow up. How can everything here come from nothing?

KATIE MACK: People usually imagine the Big Bang as an explosion. And that's how it's usually drawn or animated or whatever. But that's not really very accurate because an explosion is like a ball of fire happening in a bigger space, and it expands out.

It's possible that the universe started in an infinitely dense point, right? But it's not really like a point in a larger space, it's like all of space would have been wrapped up tighter. So like if you imagine that balloon I was talking about, if you imagine taking a balloon that you haven't blown up yet and crumple it up into a little ball. And then you start blowing it up. And the surface of the balloon gets bigger and bigger, points on the surface are getting farther apart from each other. But every point on the surface was at the center at the beginning.

So that's one way you can think of the Big Bang that every part of the universe was the center of the universe. And every part of the universe is moving away from every other part of the universe as it's getting bigger. But it's not like an explosion in a larger space necessarily.

And we don't even know for sure that that singularity that infinitely dense point happened. What we do know is that there was a time very, very early in the universe where the universe was expanding really, really quickly. And we call that inflation. And that kicked off this expansion of the universe that was-- first, it was extremely fast, and then it slowed down. And since then, it's been slowing down, except that recently, it started speeding up again, which is a whole other topic.

THEA HUTCHINS: One more question. What is nothing anyway? How can there be no space?

KATIE MACK: Yeah. So one of the ideas behind this concept of the singularity, the infinitely dense point, one idea behind that is that there was that point that was the beginning of space and the beginning of time. So in physics, we talk about space time, where space and time are wrapped up together.

And the way you move through space affects how you move through time. And so it's this weird space time fabric. So there's an idea that at the very beginning, the singularity was the beginning, the origin the thing that created both space and time.

And if that was the case, then outside of that point or before that point, there wouldn't have been either space or time. So you couldn't really call it before. There's no before because time hadn't been created yet. And the thing is like, nobody knows how to do that in terms of what could create that stuff.

This is still an area of research, where we try and think about what could have happened before the Big Bang, if there was a before? Maybe there was a big crunch, and then a bang, and then a crunch, and then a bang expanding and collapsing.

That might be the case. There could be all these-- there are these different models where there's a parallel universe. And we smash into the parallel universe. And that creates the Big Bang. And then the two universes come apart for a while, and then they come back together.

And in those kinds of situations, there can be spaces in dimensions other than our own dimensions, like directions we can't access. And those spaces might have something in them or might not.

But in terms of nothing, it's hard because in our concept of our universe, there isn't anything that's-- there's no nothingness. Because even empty space, even the vacuum of space has energy in it. We call it the vacuum energy. There's little virtual particles being created and destroyed all the time.

And so there isn't nothing in our universe. But it might be that there was a time when the whole universe began and there could have been-- and if that was-- if the universe had a beginning, like a true beginning where there was nothing before that, then there was nothing before that. And so you could say that nothing is anything outside of our universe.

But you could also just define the universe as being everything in the entirety of what we can think about. So like a lot of times, in physics, when we talk about things that we can't observe, we don't really have a lot to say about those because physics is all about having an idea, and then testing it with the data, and trying to refine these theories by comparing them to data.

And if we don't have any data, then that's really hard to do. And then it's hard to know if that's even science because we-- it's just speculation.

So we can't-- we know that there are parts of the universe that we'll never be able to observe. And we know that there are times in the universe like the first moments of the universe that we don't have any information about. And so it's hard to-- it's hard to really do any science about those things. And that's where the nothing would be if there were really nothing.

So we avoid that because it's so hard to learn about. That's the fun part about theoretical physics, though. It's that I really like the brain hurting part. That's why I do this.

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MOLLY BLOOM: Now gravity is something I think a lot of us take for granted. We know what gravity feels like on Earth. It's the force that keeps your feet planted on the ground. When you throw a ball in the air, it comes back down. That's gravity. It's essential to everything we do. But there's a lot about it that's a mystery.

Mass is the measure of how much matter is in a thing. And matter means stuff, the molecules, atoms, the tiny building blocks that make up everything. One of the things we know about gravity is that it's created by mass. Earth is really large, has a lot of mass, and therefore, has gravity, so do other planets and stars. But why? Why does gravity exist? To find out, I called my friend Chris.

CHRIS MENDILLO: So my name is Chris Mendillo. I'm an astronomer at University of Massachusetts in Lowell, Massachusetts.

MOLLY BLOOM: I asked him what seems like a pretty basic question, do we know where gravity comes from?

CHRIS MENDILLO: We don't really. It's strange because it's the most familiar of the forces in the universe to us. I mean, we deal with it every day. It's something we take for granted. We know that it has a lot to do with mass. And that mass-- for 300 years, we've known that mass creates gravity. But we don't really know where it comes from. And we don't know where it comes from as well as we know or we think we know where the other forces in the universe come from.

MOLLY BLOOM: Chris said there are a couple of different avenues through which scientists are trying to figure it out, string theory and quantum gravity. Explaining those is definitely a task for a future episode, but the very basic premise is this.

CHRIS MENDILLO: I mean, in science, everything is about if you have a theory, it has to produce a prediction that you can test. And if you test it and it works, then it might be true. And if you test it and it doesn't work, then it's definitely not true. And that's how all science works. No one's been able to come up with an origin theory of gravity that if you could test it, you could show it's possible or that it's true.

MOLLY BLOOM: So if we already know so much about how gravity behaves, does it matter if we know where it comes from?

CHRIS MENDILLO: Understanding the origin of gravity would certainly help figure out how black holes work.

MOLLY BLOOM: I had always had this idea in my head that a black hole was literally a hole in space that sucked things into it. I think I got it from cartoons. But Chris set me straight.

CHRIS MENDILLO: There's nothing magic about it. It's normal matter. It's just confined to a very small space. We really well how they form. They form when giant, massive stars collapse.

One of the basic things about black holes is they don't-- it's not like they produce more gravity than what you started with. If the sun just turned into a black hole right now, the Earth's orbit wouldn't change. Everything would be fine. We wouldn't have a sun, so that would be bad. But the gravity wouldn't increase. It's the same-- it's the same matter. It's the same amount of mass. It's just it would be compressed down into the size of a baseball instead of the size of the sun.

MOLLY BLOOM: And the reason they're called black holes, we can't see into them.

CHRIS MENDILLO: We can't see into them because gravity distorts and bends light. Well, in a black hole, the gravity is so strong that light can't escape. That's why they're black. There's nothing we can measure.

MOLLY BLOOM: And knowing more about gravity in black holes would help us learn a lot about our universe.

CHRIS MENDILLO: Black holes are the reason we're here. The only reason we have a galaxy that looks like our galaxy is because there's a giant supermassive black hole at the center of it that holds the whole thing together. So understanding the origin of gravity, yeah, is certainly important for knowing why we're here, why anything is here. [LAUGHS]

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MOLLY BLOOM: Now before we go, it's time for our Moment of Um.

[CHORUS OF PEOPLE SAYING"UM"]

ROWAN: Hello, my name is Rowan. And I'm from Silver Spring, Maryland. My question is, do you physically get longer when in mid-air? Are basketball players tall because they jump a lot? Or can they jump high because they are tall?

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[CHEERING]

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DR. ED LASKOWSKI: Hello. I'm Dr. Ed Laskowski. And I'm co-director of Mayo Clinic Sports Medicine.

The short answer is no, jumping really doesn't make you taller, but practicing jumping can help you to jump higher, and then-- and also train more explosive power. So it doesn't really increase your height, but it may increase how high you can go.

When you jump, you extend your body. So it probably will go to its most extreme length. But the length of the body itself doesn't change with jumping.

By doing that movement pattern, you're training the explosive muscles that are used in helping us to jump, and you're getting them better and better and better. So even though your actual height may not change, and that's a lot genetically determined, your muscles will develop more strength and explosive power, so you'll be able to jump higher. So in essence, your opponents may think you're taller, but you're just jumping higher.

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MOLLY BLOOM: I'm going to jump, leap, and fly through this list of names. It's time for the Brains Honor Roll. These are the kids who power our show by sharing questions, ideas, and mystery sounds with us. Here's the most recent group.

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[LISTING HONOR ROLL].

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MAN: Brains On.

MOLLY BLOOM: That's it for this episode of Brains On. Brains On is produced by Marc Sanchez, Sanden Totten, and me, Molly Bloom. Brains On is supported, in part, by a grant from the National Science Foundation. We had production help this week from Lauren Dee and Marcus Archibold.

You can send your questions, drawings, mysteries sounds, and high fives to hello@brainson.org. We'll be back soon with more answers to your questions. Thanks for listening.

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