Daniel and Kelly’s Extraordinary Universe - What Is The Emptiest Place In The Universe?

Episode Date: May 14, 2019

What constitutes a vacuum? Can space ever really be empty? Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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Hey, Daniel, I've got a dumb question. Uh-oh, those are always the hardest questions to answer. Why, is it hard to come with a dumb answer? Is that what you mean? No, what people call dumb questions are sometimes really simple, deep questions, and those are the hardest, but sometimes the most fun, to tackle. Okay, here's my dumb question, Daniel. Where does space start?

You know, like, technically we are in space, but we don't think of ourselves in space. We're sort of on Earth. There's an official definition, 100 kilometers up. That's the official beginning of space and stuff. And that sounds totally made up because it's a perfectly round number. All right. Well, I guess the question is, what is space, right? It's kind of like when you no longer have air or when there's a vacuum. Yeah, exactly. You know when you're out there, like deep into space, you know when you're not there here on Earth. And the boundary between them is, it's a bit fuzzy. You know, it's sort of like growing up, you know.

Officially, you're grown up when you turn 18, but it's not like a moment when you suddenly get wisdom and context and vision and understanding and perspective. and you can make grown-up decisions. You know, it's something that very slowly happens. Well, officially, the government does give you a certificate when you're 18. That's right. Please register for the Army. Congratulations on being an adult. Yeah.

You're saying technically I haven't grown up. Like, technically, you may never grow up. That's right. You and Peter Pan are officially not grown up. Here, there you go. Peter Pan, the first astronaut. That's probably true, too. Hi, I'm Jorge. I'm a cartoonist and the creator of PhD comics.

Hi, I'm Daniel Whiteson. I'm a particle physicist. I work at CERN smashing stuff together to reveal the secrets of the universe, and I am not a cartoonist. That's right. I forgot to mention I'm also not a physicist. But in any case, welcome to our podcast. Daniel and Jorge explain the universe, a production of IHeart Radio, where we explain all the crazy and amazing things that are out there in the universe, and we have long conversations about it. That's right. We're going to take a mind-blowing tour of all the crazy stuff out there in the universe, and the most important thing is that we're going to do our best

to explain it in a way that actually makes sense to you and hopefully entertains you along the way. I mean, where else can you sit for an hour and hear about nothing? Literally nothing. That's right. We are going to get spacey today, folks. That's right. Today on the program, we're going to be asking the question, Can space be empty? Truly empty, like nothing.

That's right. What's actually out there in space? If you went out into space and you grabbed a big box and closed up some space, what would you capture? Is space pretty empty? Is it mostly full of stuff that's invisible? What's going on out there in space? And you can think of this question, for those of you keeping track at home, As part of our extreme universe series, this one's sort of like, what is the emptiest place in the universe? Where in the universe is space the spaciest? Yeah, I think most importantly, can it be empty? Like, is it possible to have nothingness in space? That's right.

Yeah, and that's a fun question, too. Like, do you mean experimentally? Like, could we build something which makes a cubic meter of truly empty space? Or theoretically, like, is it against the laws of physics for space to be empty? Yeah. Or, I mean, just are there spots out there in the huge universe that we live in that are really truly empty? Do you know what I mean? Like, we know there's stuff right here on Earth on this planet, but are there parts of the universe where there's truly nothing in there? That's right, because the universe is huge. It certainly is a lot of space out there, right? And not that much stuff. You know, you just look up at the night sky and it's mostly space, right? There's not that many stars. Even if you have a really amazing telescope and you can see really, really far away. there's a lot more space than stars. And so that makes me wonder,

and I think other people wonder, like, what's in that space? How empty is it? How much stuff is there in space? How spacey is space. How spacious? I think maybe the question is how spacious is space. Perfect.

How spacious is space? Is there room for me to move out there and really spread out with my stuff? You've got a lot of stuff in storage. You need to take out an unpack. Right, yeah. And we have had podcasts about how big the universe is, right? and what's the biggest thing in the universe?

But this is the first time we're asking, can space actually be empty? Yeah, exactly. How empty is it? So, as usual, before we dig into the topic, I thought I would crowdsource some information, and I walked around the UC Irvine campus, and I asked people,

what do you think would be in a random cubic meter of space? How empty is it? Is there stuff out there, or is it mostly empty? Yeah. So think for a moment before you hear the answers, and ask yourself, if you encountered a random physicist on the street, and they asked you, what do you think is in a one cubic meter of space, what would you answer?

Here's what people had to say. What's in a random cubic meter of empty space, do you think? Matter. What kind of matter? Adams. Adams. Yeah, that's all I can think of. Oh, geez.

Not too sure. I don't know. I know that particles is what I'd assume. Cubic meter. A million molecules for cubic. Million molecules? I don't know, yeah. Thanks.

I'm guessing it depends where you're on. I mean, if you're out in space, it'll just be filled with space. I mean, if space is empty, then there's nothing, I'm assuming. Okay, great. Of the matter, we know, probably nothing. But there could be dark energy in that cubic meter or dark matter. Third degree of radiation. Okay.

Awesome. Thanks very much. Three quarters, dark matter, and, yeah. I mean, actually, all dark matter. All space is dark. What about, like, far between galaxies? Is there dark matter everywhere, or is it just near the galaxies? No, it's, I think it's, like, every open space.

You're, like, in between, like, planets and stars. Cool. All right. I would say that there's stuff in there. I wouldn't say it was, like, completely empty space. It's probably a bunch of particles or components of something, I would say. Okay, great. dust, dirt, different types of particles.

Is it totally empty? Vacuum energy, I guess. All right, cool. Something else. I feel like you'd probably get some particles of some sort. Like how many? Yeah, I'm only up to like eight-grade science. All right.

I like most people just said stuff. Like, I feel like, you could just say the Big Bang. That would have been a... Physics. Remnants of the Big Bang. I mean, that's always correct, but stuff is also pretty versatile as a physics answer. Well, that's sort of the question. Is space have any stuff in it?

And so if you want to make it binary, like, you know, it's empty or there's stuff in it, then these people were voting for stuff. I think a lot of people have the sense that space is not truly empty, that there's always something in there, even if you can't see it. Oh, I see. You're saying that most people didn't say nothing or vacuum. Do you know what I mean? Like most people assumed it had stuff.

stuff in it. Yeah, exactly. That was the sense that I got from most people, that they weren't quite sure what was in there. They thought it was mostly empty, but not truly empty. There was still some residual stuff in there. So if you're giving a test, Daniel, and a student, you ask like, hey, what is quantum physics and the student writes stuff? I mean, would you technically mark it wrong? Oh, for sure, yeah. But I always give credit, I always give a lot of partial credit, and you always get some points for writing down anything, like even stray pencil. marks, I will give partial credit for sometimes. Really? It's the blank.

It's when they leave the space empty that you really, it bothers you. Exactly. Pure empty space, that bothers me. For that, you get a zero, right? Reflecting the amount of effort you put into the problem. But you write down something, anything. I'll give you some points. Maybe you didn't know this. At the end of all of my

midterms, I also do a physics cartoon contest. Really? Yeah. What do you mean? I pick a random cartoon from the New Yorker, usually, that looks a little physics-y, Like there's a wheel or something, physics-y-in-it. And I asked them to write a physics-related caption for that cartoon related to what they learned on the exam. Well, hopefully they didn't learn it on the exam.

Hopefully they learned it before the exam. For the exam, yeah. And then I have the TA. The TA's always graded. And I tell them, if they write anything, give them a point. If they write something that actually makes you laugh, give them two points. And, you know, sometimes these kids are pretty funny. I can imagine being a stressed out student thinking,

oh my gosh, should I devote my last two minutes to try to come up with a clever caption? Or should I try to solve this quantum physics problem? Well, I hope that it gives them a little bit of stress relief. But it's actually some interesting stuff in the physics education literature that shows that making people think about physics in the context of their real lives

or in real life contexts helps them understand these concepts. So it's not just a joke on my part. I really think that it helps them understand if they have to think about how is this relevant to some situation. Oh, interesting. Have them to kind of take a step back and try to think about the context of the stuff they learn. Yeah, exactly, exactly. Because we don't learn everything in a vacuum, right?

It's not just out there floating in space. Right. Well, now I'm a little nervous for the universe. I feel like if the universe can be truly empty, you might give it zero points. No partial credit. Well, you know, the universe is making it ever. talking about being truly empty. When I was doing some reading for this episode,

I was shocked to discover some things about what we consider empty space here on Earth. Here on Earth, we can do things like create vacuum in the lab, right? People do this to do all sorts of experiments. And we have pretty good vacuum, for example, the Large Hadron Collider where we smash protons together. We suck all the other stuff out because we don't want it to interfere with the collisions.

But it turns out that that vacuum is not really empty at all. If you look at the density of air that we're breathing, like the air that I'm breathing right now, there's about 10 to the 25 molecules per cubic meter. So that's a huge number, right? Like 10 with 25 zeros. I don't even know what the scientific prefixes for it. And it's all like air molecules and gas molecules. And when they make vacuum, they pump the air out, right?

They suck it all out. Sometimes they even bake it to try to get as much of the air out of it as possible. and you'd imagine they get it down to a really pretty good vacuum. But what they call like ultra-high vacuum in the lab still has like 10 to the 12 or 10 to the 15 particles per cubic meter, which is still a huge number, right? I mean, it's a much smaller number. You're down like 10 or 15 orders of magnitude.

But super high vacuum here on Earth is filled with particles. Wow. What do you think is the limitation? Why can they suck out those last few particles? I mean last few by me I mean the last 10 to the 15 particle exactly it's difficult

you know you're going to have really powerful pumps and you're going to have no leaks you know it's really pretty tricky it's hard to get nothingness like to pull everything out of a space yeah because the pressure on it is tremendous right if there's nothing in it then things are pressing on it from all sides

and there's nothing in it to push back right so things are trying to squeeze in everywhere so you have like the tiniest little gap like an atom size gap in your in your welded seam or something and particles are going to find their way through. It's a very powerful pressure from the outside. And you know, vacuums don't

suck, right? It's not like the vacuum inside this machine is like actively sucking stuff in. It's all the air outside that's pressing down, that's pushing in. Wait, what do you mean? It's not the vacuum? Well, you can think about it in two ways, but I never like thinking about the vacuum is like

actively sucking stuff in. It's not like there's something inside a vacuum chamber that's going right the reason things like things get sucked into a vacuum it's not like like a black hole black hole's actively pulling stuff in the reason things rush into a vacuum is because the air is being pressed into it right well you know my grandma used to say nature appores a vacuum did your grandma invent that phrase I think she invented that I'm not quite sure but she used to say it all my grandma used to say I think therefore I am

Oh, wow. That is so original of her. Maybe our grandmas were contemporaries. Geniuses of modern philosophy. Or maybe she said she abhors vacuuming. I'm not quite sure which one. She's probably the latter. Okay, sorry.

Yeah. Yeah, exactly. Say you're in a spaceship, right, and there's a leak, right? Then is the vacuum sucking all the air? air out of the ship? No, it's the air in the ship is like a balloon. It's under high pressure and you get a leak and the air is pushing itself out, right? So the reason when you, when they open the air lock on a spaceship on a movie and you get that tremendous wind, it's not that space sucking the air out of the spaceship, it's the air pushing itself out because it's under

pressure. Okay, so we're talking about space and whether space can be truly empty, right? And so the question is, is space like the perfect vacuum? Is there really nothing out there? And the point I wanted to make was that even super good vacuums here on Earth are pretty terrible when it comes to when it comes to relationships to space. So I just wanted to set that stage, right? We're going to be talking about a certain number of molecules per cubic meter. And the air you breathe is 10 to the 25 molecules per cubic meter. And the air in a super awesome fancy vacuum is like 10 to the 12 particles per cubic meter. Okay.

So that's like the gold you're saying that's the gold standard for vacuumness here on Earth. That's right, yeah. In terms of human engineering. Exactly, yeah. And so let's take a tour, right? Let's go up from the planet and think about and explore space and talk about how much stuff there is in space as we leave the Earth. Because the fascinating thing to me is the amount of stuff in space,

the emptiness of space, changes depending on where you are in space. So the answer is the question is, can space be empty? You're saying changes depending on what? where you are. Yeah. There's different levels of spaciness. Yeah, different levels of spaciness, exactly. So for example, let's dig into it.

Like if you take off from the Earth and you leave the Earth's atmosphere and you're out in space, then you're in this extended region we call the Heliosphere, which is where the Sun dominates. And the Sun is pumping out particles all the time. We call it the solar wind. So yeah, you're far away from the Earth's atmosphere, but you're in this region of space that's filled with particles streaming from the Sun. the sun. And that's basically the entire solar system, right?

I mean, basically the entire solar system is kind of within the heliosphere. Yeah, exactly. The entire solar system. And if you look, if you Google image search heliosphere, you'll see that the heliosphere is much bigger than like even the orbit of Pluto because the sun dominates the local environment. At some point it peters out and like the magnetic fields inside the galaxy start to take over. But in the environment around the sun, you know, there's the same.

the space in our solar system is dominated by the solar wind. And the solar wind has all these particles that come from the outer level of plasma of the sun, which is obviously glowing hot and shooting out light, but also shooting out electrons and protons and other kind of radiation. So you're saying the space in between planets, like between here and Mars, here, and Jupiter, here in the sun, it's not empty at all. It's like it's full of sun weather. Exactly. It's full of solar weather. And it's about 5 to 10 million protons per cubic meter,

which is still, you know, a hundred or a thousand times better than the vacuum chambers we have on Earth, but it's not zero. So you said protons. Are you saying protons mostly because those are matter particles? Yeah, exactly. Well, the solar wind is mostly electrons and protons and a few other kinds of particles. But mostly it's those protons and electrons.

And so you count them in turn. And the protons are much heavy than the electrons, so they dominate the calculation. Oh, I see. They count it stuff. But like photons, do they count as stuff? Photons? Do photons count as stuff?

Hmm, that's a good question. You know, later when we talk about what's in between, like, super clusters of galaxies and all we have is energy, then I think you'll have to count that. But, you know, photons are not matter. They are radiation, though. Okay. That's a good question. Okay.

So you're saying, within the solar system, space is, still not empty. It's still full of stuff from the sun. That's right. And we should remember that all the stuff that we know about, everything that's made of atoms, right? That's a little fraction of the universe, right? That's only 5% of all the energy in the universe. And it's about 20% of all the matter, the stuff in the universe. The rest of it is dark matter. And dark matter and normal matter both cluster into structures like, you know, planets, galaxies, whatever. Those are the structures of normal matter. Dark matter follows those. So, Basically, you can think of it like anywhere you see blobs of matter, there's also dark matter there and about five times as much.

So if there's five million protons, you're saying there's probably 25 million amount of stuff of dark matter in that space between planets. Yeah, and we don't know a whole lot about the structure of dark matter. We know it clumps at the center of the galaxy and then spreads out. We don't know how clumpy it is if it's pretty smooth or if it's not. But on average, yeah, you can just take the amount. matter of matter and multiplied by five. And that's a pretty good estimate for how much dark matter there is. Like in this room with me right now, you know, in the air I'm breathing, there's what, 10 to the 25 molecules of air, right? That much mass, there's five times as much dark matter in this

room per cubic meter with me right now. And the same is true out in space. Dark matter follows a normal matter. So you can basically just multiply the normal matter by five. And it tells you how much dark matter there is. So there's still a lot of stuff out there. the solar system, the space is not quite empty, but it's sort of really empty compared to what we can do on Earth, right? Like you're saying here in Earth we can do 10 to the 15, but you're saying out in between the solar system, between planets, it's about 10 to the 6.

10 to the 6, which is much better than vacuums on Earth. But it's not that small. And in fact, if you're an astronaut, you need like really, really good sunscreen because it's enough radiation to fry you and give you cancer pretty quickly. So the fact that it's not empty has consequences. Oh, you're saying if it was, hmm. If you were just out there in a very, really thin space suit without a whole lot of protection from radiation, you would get fried from that radiation.

Wow. So the fact that it is pretty empty means that you feel that light from the sun a lot stronger. Exactly. We have an atmosphere between us and the sun and that protects us from the solar wind, right? The solar wind doesn't come down to the surface because we're protected by the buffer the atmosphere. atmosphere. But out in space, you're not shielded by that. And so you feel a full brunt of the solar solar radiation. And yeah, it's dangerous stuff. It's dangerous stuff. It is it. There's stuff out there and it can kill you, right? Don't run through traffic, folks.

I mean, it should be the title of our next book, Daniel. Don't play in traffic. And all the stuff that can kill you. Space can kill you. Well, let's take off from the solar system and let's go into interstellar space. But first, let's take a quick break. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys.

Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion, actually, impelled metal, glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and Order Criminal Justice System is back.

In Season 2, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order. criminal justice system on the iHeart radio app apple podcasts or wherever you get your podcasts my boyfriend's professor is way too friendly and now i'm seriously suspicious oh wait a minute sam maybe her boyfriend's just looking for extra credit well dakota it's back to school week on the okay story time podcast so we'll find out soon this person writes my boyfriend has been hanging out with his young professor a lot he doesn't think it's a problem but i don't trust her now

he's insisting we get to know each other but i just don't water gone. Now hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor and they're the same age. It's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe

him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcast, or wherever you get your podcast.

I'm Dr. Scott Barry Kaufman, host of the psychology podcast. Here's a clip from an upcoming conversation about exploring human potential. I was going to schools to try to teach kids these skills, and I get eye rolling from teachers or I get students who would be like, it's easier to punch someone in the face. When you think about emotion regulation, like you're not going to choose an adaptive strategy which is more effortful to use unless you think there's a good outcome as a result of it, if it's going to be beneficial to you. Because it's easy to say, like, go blank yourself, right?

It's easy. It's easy to just drink the extra beer. It's easy to ignore, to suppress, seeing a colleague who's bothering you and just, like, walk the other way. Avoidance is easier. Ignoring is easier. Denial is easier. Drinking is easier. Yelling, screaming is easy.

Complex problem solving. Meditating. You know, takes effort. Listen to the psychology podcast on the IHartRadio app, Apple Podcasts, or wherever you get your podcast. All right, we're talking about how empty is space and we learned that that interplanetary space like between us and other planets in our solar system

is pretty empty but not quite empty, right? There's still millions and millions of protons and stuff in like a cubic meter of space, right? And there's a lot of cubic meters in that space. So you're talking a huge amount. of particles. Like, if you have to count them or number them or name them, I mean, it's too big a number to really think about, which is sort of strange, just cognitively dissonant from the fact that we think of it is empty, right? So remember, it's just like chalk full of

particles. Right. It's like you're swimming in protons and stuff. Exactly. You're literally swimming in it. But then once you leave our solar system, you go past the heliosphere. And only a couple of man-made objects have ever done this, like the Voyager probes, they've been traveling for decades, and they finally broke past into like the interstellar space, like the stuff that the galaxy is made out of. So you're saying that the stuff that comes out from the sun, all those protons and ions and stuff, at some point kind of doesn't go on forever, right?

Like maybe they come back because of gravity? Is that kind of what happens? Like they cluster around the solar system? Well, they peter out there. The intensity gets less and less just because the volume gets larger and larger. And then also they hit the interstellar magnetic field. field, right? What?

There's magnetic fields inside the galaxy. You mean, and that's different than the one we feel inside the solar system? Yeah, because our solar system, the magnetic field is dominated by the magnetic field of the sun, right? And the same way the Earth's magnetic field also helps shield us from the solar wind, right? The sun's magnetic field helps shield us from like the galactic wind. Whoa. Oh.

Yeah, exactly. But then it peters out, right? And you're no longer really protected by the sun's magnetic field. field. The point where the sun's magnetic field is about as strong as the magnetic field of the galaxy, right? And you're really, really far away. And so the density of these particles, the solar wind is dropping. That's when we say you're in the interstellar space. You've left the heliosphere. Wow. So who gives you a certificate then? At that point, you can make your own certificate because you can do anything because you've

accomplished something nobody's ever done before. Just bring your own printer and print yourself a little certificate well that's probably where the you know our alien overlords are waiting for us oh i see so you're saying they're just waiting to hand you something as we step out there yeah sometimes i think that the reason we've never heard from alien species is that they're running some massive cosmic zoo you know and they're just out there watching us laughing at all our antics and then all we need to do to figure that out is just get out there and say hello and maybe they're like hanging out there waiting for us to um you know get far enough away from our planet that we're really talking to Maybe they're just waiting for us to get, put us back into our cages.

Don't make me use the hose. Yeah, exactly. Oh, no, the humans escaped again. Again, for the first time. So if you do get out there, if you do get out there past our solar system and the area dominated by the sun, then you're in what we call the interstellar medium. And this is mostly gas. It's like 99% gas and a little bit of dust in some cosmic rays.

Okay. different between gas and dust? Is it like more complex atoms and stuff? Yeah, dust is like pulverized rock, right? So you have like the stuff from the inside of supernova and old planets that got destroyed and whatever. And so yeah, you have like metals and all the, and silicates and all sorts of stuff. That's what dust is. Gas is basically just hydrogen, right? Okay. Most of the, most of the universe is gas and most of that is hydrogen. So it's a proton with an electron whizzing around it. Well, and what's the concentration at that point? It actually, varies a lot once you get out of the solar

system past the heliosphere. At the high end, it's about a million molecules per cubic meter, which is just a little lower than the density inside the solar system. But then at the low end, it goes down to about 100 particles per cubic meter. It's because the galaxy is just not that smooth, right? They're like

hot spots and cold spots. The spots where it's more dense and spots towards less dense. So it varies between like 100 and a million molecules per cubic meter in the interstellar medium, the spaces between solar systems. Well, here's a question.

How do we know what space is like out there if we've never been there personally? Yeah, that's a great question. Well, we haven't been there personally, but we have sent, for example, the Voyager probes, right? And after that, we have models, right? We have models that describe how galaxies are formed and how stars work and the radiation we expect from them. and so we can see activity from that gas

because it ionizes or it deflects light and so we can probe it even without going there just by seeing like stuff go through it right? Okay, cool. So we're sort of guessing in a way

I mean we have models but we think that's what the emptiness is like up there. Yeah, well if there was a lot more for example then we would see more absorption of light if there was a lot less we would see less absorption of light Remember, gas absorbs photons.

And so we can have some measure of the gas and the dust in our galaxy just by seeing how light is absorbed. Cool. So that's kind of the space inside the galaxy between stars and between solar systems. That's the interstellar medium. That's right. And remember to multiply by five for a dark matter, because there's a lot of dark matter in the galaxy. The galaxy is mostly dark matter. And between the stars, there's definitely oodles and oodles of dark matter.

on average, right? On average, yeah. We don't really know very well the distribution. We know, again, it peaks near the center of the galaxy and that the amount of dark matter extends past the visible edge of the galaxy, but we don't know that much about exactly how it's distributed. Okay, so pretty empty. Yeah, it starts to drop off exactly once you get out past the edge of the solar system.

But it's still pretty full of, like, dark matter and some gas. Mm-hmm. All right. So now what happens if you keep going? Like if you keep going past our solar system, past other solar systems, and out of the galaxy, what do we get? Well, out there between the galaxies is something we very cleverly call the intergalactic medium. And this is not very exciting. And it's basically these, it's mostly empty.

It's these strands of plasma, really, really, really dilute plasma. And so it's mostly ionized hydrogen. That's what we mean by plasma. and it's on average like one to 10 molecules of hydrogen per cubic meter. Wow. So for a cubic meter, which is like a large moving box, right, you would only see one to 10 atoms of stuff. Yeah, exactly. And so that's pretty empty, right?

You could like take a whole cubic meter and look all around and see like one or two or a few atoms inside the entire box. that's so much more empty than a vacuum here on Earth. Wow. Between galaxies is what you're saying. Yeah, exactly. You're between galaxies. And the thing that kind of blows in my mind about this is that remember that galaxies are really, really, really far apart. So even though the density of stuff out there is almost zero, if you add it all up, all the stuff, all the matter between galaxies accounts for about half the atoms in the entire universe.

What? Yeah. So, like, half the atoms in the universe are in galaxies. Half the atoms in the universe are not in galaxies. And the reason that makes sense is that galaxies are tiny compared to the space between galaxies. So if you want to fill all the space between galaxies with even a really, really low density of molecules, it takes a lot of molecules to spread it out. It's like spreading your frosting really thin across the cake. Wow, that's amazing to think that there's more, there's as much stuff in,

empty space, quote-unquote, what we would call empty space, as there are in like all those black holes and stars. And stars. And hamsters. Don't forget the hamsters. Hamsters, bananas. Half as much stuff is just floating out in this super ultra vacuum. Yeah, exactly. And between these galaxies, also we think there must be some

dark matter. We don't know because it's really hard to see dark matter. Remember, we only see dark matter because of its gravitational effects, which means we can only really see it when it's pretty dense, like the center of a galaxy or a big blob. And so between galaxies, there might be these filaments, this rarefied, thin strands of dark matter,

but it's pretty hard to see them. We can't see those directly. And again, we know this because if it was not that empty, then we wouldn't be able to see other galaxies so clearly. That's right. That's how we know about the composition of intergalactic space, because we can measure the absorption of photons between here and there. And so we can sort of like integrate over here to there

and figure out how much life. was absorbed. How clear the spaces. Yeah, yeah. And the other interesting thing that happens when you go between galaxies is that you have to start to account for the other crazy thing in the universe, which is the dark energy, right? We said before that matter is 5% of the stuff in the universe.

Dark matter is five times as much as there's like 25% of that. The rest of it is this thing we call dark energy. And the really weird thing about dark energy is that it's not clustered at all. Right. Matter, it gets pulled together by gravity. You get planets and stars and galaxies. Dark energy is spread uniformly. Right. So it's equally present everywhere. Right. Even here with us right now, right? That's right. Between me and this microphone, between you and your seat everywhere. But because the universe is so big, spreading it uniformly means it's not very dense. So like if you added up how much dark energy there is here on Earth or in this room with me, there's almost none. But once you start getting out there into really, really far stretches of space, where space becomes huge, then it starts to take over. Huge and empty, right? Huge and emptier and emptier, exactly. Right.

I mean, I think what you're saying is that out there, there's so little stuff matter that basically dark energy is like the main thing going on out there. That's right. Once you get outside our galaxy and then you get like outside the cluster of galaxies that we're in, we're inside this cluster of like 30 or 50 galaxies that are all sort of orbiting each other. and there's this plasma between us, this intergalactic medium, this sort of in filaments between the galaxies.

Once you get past the cluster, then you're in intercluster space, and that's mostly dark energy. I'm going to take a wild guess and say that you guys call it the intercluster medium. Did I get that? You got it right,

and again, I wish that you had been there the day that that name was given, because I'm sure you would have come up with a much better name. So out there is mostly just dark energy because it really sort of is kind of empty space, right? There's no, not very little

stuff. Yeah, exactly. You can't go much lower than one atom per cubic meter, right? You start to get to like less than an atom per cubic meter. And so that's what happens, like, out there between the clusters of galaxies, the number density of matter drops to almost zero.

So are you saying that if it drops below one atom per cubic meter, it means that there are some cubic meters that have no atoms. There are definitely cubic meters with no atoms, yeah. If you have 0.1 atoms per cubic meter, it doesn't mean that every cubic meter has a tenth of an atom. It means you need 10 cubic meters to, on average, have one atom. To find an atom, which means there's nine of them without it.

Oh, wow. Okay. So that sounds pretty empty. Isn't that basically empty? It's basically empty, but, you know, it's not totally empty, right? And there's always dark energy in there. And the fascinating thing to me is that there's no, box of space that has no energy, right? Space itself always comes with dark energy, right? Like dark energy makes space and space contains dark energy.

We don't understand it. We don't know what it is. We don't know where it comes from or how it's happening, but we know it's there. And what that means is that every place in space has energy. And energy and mass are not that different, right? E equals MC squared. So what that means is that anywhere there's energy, you can create mass. Like, you have a little density of energy, it can turn into particles very briefly and then turn back into energy.

Right. But that's kind of as far as we know, right? Because you're saying we don't really know that much about dark energy. I mean, as far as you know, it could maybe have little variations in it, couldn't it? It could. The current thinking is that it's uniform, that it's spread everywhere through space, that it's a property of space itself. But you're right. We're pretty clueless.

And so it could be the dark energy is totally something different. and that we're wrong and it has interesting structure, I suppose. That would be amazing. But the current thinking is that it's uniform. All right, we've gone all the way from planet Earth, vacuums and emptiness on planet Earth, all the way to solar systems and galaxies and intercluster space. So let's go even beyond that, Daniel.

Let's go way past that. But first, let's take another break. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal glass. The injured were being loaded into ambulances, just a chaotic, chaotic.

scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and Order Criminal Justice System is back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Well, wait a minute, Sam, maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon.

This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's, former professor and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them.

I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the Iheart radio app, Apple Podcasts, or wherever you get your podcast. I'm Dr. Scott Barry Kaufman, host of the Psychology Podcast. Here's a clip from an upcoming conversation about exploring.

human potential. I was going to schools to try to teach kids these skills and I get eye rolling from teachers or I get students who would be like, it's easier to punch someone in the face. When you think about emotion regulation, like you're not going to choose an adapted strategy which is more effortful to use unless you think there's a good outcome as a result of it if it's going to be beneficial to you. Because it's easy to say like go you go blank yourself, right? It's easy. It's easy to just drink the extra beer. It's easy to ignore, to suppress, seeing a colleague who's bothering you and just like walk the other way. Avoidance is easier. Ignoring is easier. Denials is easier. Drinking is easier. Yelling, screaming is easy. Complex problem solving, meditating, you know, takes effort.

Listen to the psychology podcast on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts. Okay, so we've gone from the Earth, emptiness of space on Earth, to the solar system, to the galaxies, to inner clusters of galaxies. And we get pretty empty, you're saying, you know, with maybe less than one atom per cubic meter out there between clusters. But you're saying that there's still kind of an inherent energy, inherent stuff to space itself. That's right. If you zoom out even further, remember that clusters form their own. kind of clusters that we call cleverly super clusters, right? And that these super clusters then form these big sheets, these vast stretches which enclose enormous voids. So they're really like

frothing bubbles, right, where the edges of the bubbles are all these super clusters of clusters of galaxies of stars. And so what's inside those voids? Well, this essentially no matter. I mean, we don't know. We can't like, we haven't measured it the way we've measured these other things. So we know it's a very, very, very small amount of matter, like a number of protons is tiny. But, you know, there's dark energy there and there's energy in space itself. You know, for example, the Higgs boson. The Higgs field is something which even if there's no particles there, it still has energy. Something we call the vacuum expectation value is non-zero. Like the ground state of the Higgs field is not at zero, which means this energy in every space and energy can get turned into mass.

There's this fun thing about quantum mechanics where you can create virtual particles. You have energy, you can briefly create mass out of it and then back into energy. And so that's probably happening everywhere in the universe. You take a random box of space inside one of these super voids inside the bubble, and briefly particles will be being created and destroyed. But that's a quantum physics thing, right, isn't it? Yeah, exactly. That's quantum mechanical. There's this uncertainty and there's randomness.

And so particles are always fluctuating in and out. of the vacuum. So you're saying theoretically, you might be able to have truly empty space, but it's sort of not empty all the time forever. Yeah.

Say you did the painstaking job or removing every single particle you found from a cubic meter. Then you go back, you're like, wait a second, I just found another particle. It disappeared. Oh, wait, there's another one over here.

It's sort of like playing quantum whack-a-mole. Because you can never get all the energy out of that box and so you can effectively not ensure that there's no matter. You can't ensure there's zero matter in there because you can't get all the energy out.

And energy can always fluctuate back into matter. And that's a property you're saying a property of space itself. Like space by itself has energy to it, meaning it has the propensity to make matter always. Yeah. And remember that space is a thing, right? It's not like emptiness, right? Space itself is a thing. It can ripple, it can expand, it can bend.

And so there's some, it has properties. right and it's not nothingness I'm not saying nothing has energy I'm saying space has energy and we're only just now beginning to grapple with what space itself is so if you think space having energy sounds weird then remember that

space is a thing it's like you know fish scientists swimming through water and discovering that water is a thing space is definitely a thing and it has some energy now another deeper question is are there places without space right is there past the edge of the universe if the universe is finite are there

places where there is no space and no energy and therefore no energy that might be possible but that wouldn't be empty space that would be emptiness or nothingness or something but that's pretty hard to grapple with you know conceptually you're saying it's sort of like if fish scientists would be like asking having a podcast a couple of fish talking on a podcast asking themselves it can water be empty and basically to us the answer is ridiculous because we know water is stuff that's right and then they're having trouble thinking about like

is there an edge to the pond like what's above the surface of the pond man what does it mean to not have water I think they would be

sort of what they mean by empty would be sort of like can you have water pure water right like water with no contaminants in it

just pure H2O that would be the question for them that we are sort of asking can if space can be empty yeah exactly and then the deeper question

for them would be can you have places without water. And so we would ask, can you have places without space? Does that even mean anything? And that's pretty hard to think about. So I think the answer is we're pretty sure you can't have

totally empty space because of quantum mechanics and dark energy and the Higgs boson vacuum expectation value. But you might be able to have places without space or past the edge of the universe where space ends. But we

don't know. That part is really speculative. And maybe there is a part of the universe that is all water with fish scientists asking these questions. Where all the podcasts are all wet. And I think their

podcasts are called Codcasts. And so to recap, near the earth, we have like a few million molecules per cubic meter. And then once you get outside the solar system,

it drops to like, between a million and a hundred molecules per cubic meter, then between galaxies, it gets down to like one to ten per cubic meter. But the emptiest place in space is out there in the voids between the bubbles of superclusters,

which is crazy empty. Well, I guess the answer to the question, can space be empty is yes, sort of, but not all the time or not on average or not for long, kind of? I would say most of the space we see is not empty. and as you get further out it gets emptier and emptier and emptier

to get pretty empty but never totally truly empty right but not not all the time right like um you could my might get a cubic meter with nothing absolutely nothing in it no matter but before long you'll see matter popping in and out all the time yeah before long meaning like 10 to the minus 23 seconds yeah congratulations in your accomplishment that's what my that's what my grandma would call it a Panamanian minute. Okay. I don't know what that means, but it sounds awesome.

All right. I hope that podcast filled your space with interesting knowledge and ideas to think about. That's right. I hope we blew your mind and injected some space in there. And remember that we live in a vast universe filled mostly with nothing. Yeah, except in the space around you. So take some time to appreciate all this stuff around you because it could be pretty empty out there.

All right. Thanks, everyone for listening. and if you have questions, send them to Feedback at Danielandhorpe.com. Thanks for listening. See you next time. If you still have a question after listening to all these explanations, please drop us a line we'd love to hear from you. You can find us at Facebook, Twitter, and Instagram at Daniel and Jorge, that's one word,

or email us at Feedback at Danielandhorpe.com. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of IHeartRadio. For more podcasts from IHeartRadio, visit the IHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then everything changed. There's been a bombing at the TWA terminal, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts.

My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want her gone. Hold up. Isn't that against school policy? That seems inappropriate.

Maybe. Find out how it ends by listening. the OK Storytime podcast and the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. The U.S. Open is here and on my podcast, Good Game with Sarah Spain. I'm breaking down the players, the predictions, the pressure, and of course the honey deuses, the signature cocktail of the U.S. Open. The U.S. Open has gotten to be a very wonderfully experiential sporting event. To hear this and more, listen to Good Game with Sarah Spain, an IHeart women's sports production in partnership with Deep Blue Sports and Entertainment on the IHeart Radio app,

Apple Podcasts, or wherever you get your podcasts. Brought to you by Novartis, founding partner of IHeart Women's Sports Network. This is an IHeart podcast.