Daniel and Jorge Explain the UniverseWhat constitutes a vacuum? Can space ever really be empty?
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Hey, Daniel, I've got a dumb question.
Oh oh, those are always the hardest questions to answer.
Is it hard to come with a dumb answer? He said, what you mean?
You know what people call dumb questions. There's 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? 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 one hundred 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 a space?
Right? It's kind of like when you no longer have air, or when there's a vacuum.
Yeah, exactly. It's 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 eighteen, 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.
Yeah, well, officially, the government does give you a certificate when you're eighteen.
It's right, please register for the army. Congratulations, I'm 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 really true too.
Hi, I am Orgee. I'm a cartoonist and the creator of PhD Comics.
Hi. I'm Daniel Whiteson. I'm a part of the physicist I work at cerns smashing stuff together to reveal the secrets of the universe. And I am not a cartoonist.
That's right.
Also, 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 iHeartRadio 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 can 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 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, end 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 like grabbed a big box and closed up some space. What would you capture a 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 is it against the laws of physics for space to be empty? Yeah?
Or I mean just are there 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 that, you know, we know their 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 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?
How spacious in space? Exactly? Is there room for me to move out there and like really spread out with my stuff? You got a lot of stuff in storage. You're going to 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't 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 here on 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 have to say.
What's in a random cubic meter of empty space? Do you think matter? What kind of matters? Adams?
Adams? That's all I can think of. Oh, jeez, not too sure.
I don't know.
I know the particles is what I'd assume.
Cubic meter a million moleculus million.
I don't know.
Yeah, thanks guessing. It depends where you're on.
I mean, if you're out of space, it'll just be filled with space.
I mean if space is empty, then there's nothing I'm assuming.
Okay, of the matter, we know, probably nothing, but there could be dark.
Energy in that cubic meter or dark dark matter, a.
Third degree of rad nation. Awesome, thanks very much, dark matters, dark quarters, dark matter, And yeah, I mean I'll watch it all dark matter all spaces. What about like far between galaxies? Is it dark matter everywhere or is it just near the galaxies? No, it's I think it's like every open space, you're like like in between like planets and stars and cool. All right, I would say that there's stuff in there. I wouldn't say it was like completely empty space. There's probably a bunch of particles or components of something. I would say, okay, great, us there are different types of particles. Yeah, is it totally empty? I guess, all right, cool?
Something else.
Well, you'd probably get some particles of some sort.
But how many holy up to like eight grade science?
All right?
I like, I like most people just said stuff. I feel like, did you say maybe? I mean you couldn't 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 versatilism 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 and it, then these people were voting for stuff. I think a lot of people had 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 the most people, well didn't say nothing or vacuum.
Do you know what I mean? Like, the most people assumed that it had 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, that there was still some residual stuff in there.
So if you're giving a test annual and a student you ask, like, hey, what is quantum physics and the student rights stuff? What would you would you technically market 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 straight pencil marks. I will give partial credit for sometimes.
Really it's when they leave the space empty that you really could 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 car tune 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 in it, and I ask 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 learn before for the exam.
Yeah, And then I have the ta is 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 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 get more point.
I hope 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 the about physics and 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. It's like, I really think that it helps them understand They have to think about how is this relevant to some situation.
Oh interesting, have them kind of take a step back and try to find a think about the context of the stuff they learn.
Yeah, exactly exactly, because we don't learn everything in the 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 is truly can be truly empty, you might give it zero points, no partial.
Well, you know, the universe is making it ever to talk about it 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. You know, here on Earth we can do things that 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 with the collisions. But it turns out that that vacuum is not really empty, like 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 ten to the twenty five molecules per cubic meter. So that's a huge number, right, like ten with twenty five zeros. I don't even know what the scientific prefix is for it.
And it's all like air molecules and gas molecules.
And and when they make vacuum, they pump the air out right, they suck it all out, and sometimes they even bake it to try to get as much of the air out of it as possible. And you'd imagine they maybe they get it down to a really pretty good vacuum. But what they call like ultra high vacuum in the lab still has like ten to the twelve or ten to the fifteen particles per cubic meter. Wow, which is still a huge number, right, I mean it's a much smaller number. You're down like ten or fifteen orders of magnitude. But super high vacuum here on Earth is filled with particles. Woh, what is is a limitation? Why can't they suck out those last few particles? I mean last few by me, I mean the last ten to the fifteen park exactly. It's difficult. You know, you've got to have really powerful pumps and you've got 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 sized gap in your in your welded seam or something, and particles are gonna 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 a black hole. A black hole is 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 abhors a vacuum.
Did your grandma invent that? Right?
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.
She said she abhours vacuuming. I'm not quite sure which one. Probably she's probably the latter. Okay, sorry, yeah, exactly.
Say you're in a spaceship, right, and there's a leak, right, then is the vacuum sucking all the air out of the sh 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 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 it 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 that we're gonna be talking about a certain number of molecules per cubic meter, and the air you breathe is ten to the twenty five molecules per cubic meter, and the air in a super awesome fancy vacuum is like ten to the twelve particles per cubic meter.
Okay, so that's like the gold you're saying, that's the gold standards for vacuumness here on Earth.
That's right 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 where you are depending on where you are in space.
So the answer is the question is can space be empty? You're saying changes depending on 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.
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, Peter's out and like the magnetic fields inside the galaxy start to take over. But in the environment around the Sun, you know, 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 in Jupiter, or 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 five to ten million in protons per cubic meter, which is still you know, one hundred or one 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 that's that's 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 it's those protons and electrons, and so you count them in turn, and the protons are much heavier than the electrons, so they dominate the calculation.
Oh, I see, they count as stuff, but like photons do they count a stuff?
Photons do photons count as stuff? That's a good question. You know, later when we talk about what's in between, like superclusters of galaxies and all we have is energy, then I think you'll have to count that. But you know, photons are not matter there, they are radiation though. Okay, that's a good question.
Okay, So you're saying within the Solar System, the space is still not empty, it's full of 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 five percent of all the energy in the universe, and it's about twenty percent 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 and galaxies. Whenever 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 twenty five million amount of stuff of dark matter in that space between planets.
Yeah, and now we don't know a whole lot about the structure of dark matter. We know 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 of matter and multiply it 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 ten to the twenty five 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 the normal matter. So you can basically just multiply the normal matter by five, and that tells you how much dark matter there is.
So there's still a lot of stuff out there in the Solar System. The space is not quite into but it's sort of really empty compared to what we can do on Earth, right, Like you're saying here on Earth, we can do ten to the fifteen you're sing out in between in the solar system between planets. It's about ten to the six.
Ten to the six, 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, if you were just out there in a really really thin spacesuit 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 those 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. 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, is it. There's stuff out there and it can kill you. Right, don't run through traffic, folks.
It should be the title our next book, Daniel Space Traffic and all the stuff They can kill you.
Space can kill you.
Well, let's let's take off from the Solar system and let's go into interstellar space. But first let's take a quick break.
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All right, we're talking about how empty is space, and we learned 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.
Mm hmm.
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 numb ber them or name them. I mean, it's 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 as 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 inter interstellar space, like the stuff that the galaxy is made out of.
So you're saying that the stuff that comes at from the Sun, all those protons and ions and stuff, at some point kind of doesn't go on forever, right, Like they maybe they come back because of gravity.
Is that?
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. Right, what there's magnetic field 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. Whoah, yeah, exactly. But then if it peters out right and you're no longer really protected by the Sun's magnetic field, where 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.
So who gives you a certificate that?
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 that 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 of 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, you know, get far enough away from our planet that we're worthy talking to.
May they're just waiting for us to get put us back into our cages.
Is it? Don't make me use the howes exactly? Oh no, anyways, 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 ninety nine percent gas and a little bit of dust and some cosmic rays.
Okay, what's the difference between gas and dust. Is it the 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 silicates and all sorts of stuff. That's what dust is. Gas is basically just hydrogen, right, most of the universe is gas, and most of that is hydrogen. So it's a proton with 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 one hundred 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 where it's less dense. So it varies between like one hundred 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, been there personally.
Yeh, 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 how stars work and the radiation we expect from them. And so we can we can see you know, activity from that gas because you know, it ionizes or it 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 by 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 that's the interstellar medium.
That's right. And remember to multiply by five for dark matter, because there's a lot of dark matter in the galaxy, and the galaxy is mostly dark matter, and between the stars is definitely oodles and oodles of dark matter on average, right on average. 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.
It starts to drop off exactly once you get out past the edge of the.
Solar System, but still pretty full of like dark matter and and some gas.
Mm hmm.
Right, So now what happens if you keep going, 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 ten 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 ten 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 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, the 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, a counter 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, we call it empty space as there are in like all those black holes in stars.
Stars and ham stuff.
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 there's 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 many how much light was absorbed.
Yeah, 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 four that matter is five percent of the stuff in the universe. Dark matter is five times as much as like twenty five percent 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 those right now, right.
Right, that's right between me and this microphone, between you and your seat, everywhere. But because the universe is so big, spreading it uniformally means it's not very dense. So like, if you add it up, how much dark energy there is here on Earth or in this room with me, that is 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.
Yeah, I mean, I think what you're saying is that out there there's so little stuff matter that basically dark energy is like that 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 thirty or fifty galaxies that are all sort of orbiting each other, and there's this plasma between us, this intergalactic medium, the sort of in filaments between the galaxies. Once you get past the cluster, then you're in inter cluster space, and that's mostly dark energy.
I'm gonna I'm going to take a wild guess and say that guess that you guys call it the intercluster medium?
Is that?
Did I get that?
Yeah? 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's really sort of is kind of empty space, right, there's no very little stuff.
Yeah, exactly, you can't go much lower than one atom per cubic meter, right, They 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 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 zero point one atoms per cubic meter, it doesn't mean that every cubic meter has a tenth of an atom. It means you need ten cubic meters to on average have one atom to find, which means which means it's nine of them without it.
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, it 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 were 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, could in.
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 it 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 the planet Earth vacuums and emptiness't planet 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.
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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, 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 superclusters, right, and that these superclusters then form these big sheets, these big, these vast stretches which enclose enormous voids. So they're really like frothing bubbles right where the edges of the bubbles are all these superclusters 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 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 supervoids inside the bubble, and briefly particles will be being created then and destroyed.
But that's a quantum physics thing, right, isn't it.
Yeah, exactly, that's quantum mechanical. There's this uncertainty and this randomness, and some 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 like did the painstaking job or removing every single particle you found from a cubic meter, then you go back to be like, wait a second, I just found another particle. What 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 say you can effectively not ensure that there's no matter, right. 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 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, no energy and therefore no energy. That might be possible, but that wouldn't be empty space. That would be emptyness or nothing, niss 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 they speak 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 anty would be sort of like can you have water pure water, right like water would no contaminants and it just pure H two O. 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 of. 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 you know, past the edge of the universe where there where the space ends, but we don't know. That's that part is really speculative.
And maybe there is a part of the universe that is all water with fish scientists asking that's a question.
Where all the podcasts are all wet, and.
I think their podcasts are called caughdcasts.
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 one 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 question that 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. 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, but not all the time, right, Like you could my mic 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 ten to the minus twenty three seconds. So yeah, congratulations and your accomplishments.
That's what my grandma would call it. A Panamanian minute.
I don't know what that means, but it sounds.
Awesome, all right.
I hope that podcast filled your space with interesting ninety is 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 Danielandhorge dot com.
Thanks for listening, See you next time.
Before 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 Danielandhorge dot 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 podcast, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact, but the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. House US Dairy tackling greenhouse gases. Many farms use anaerobic digesters to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as Dairy dot COM's Last Sustainability to learn more.
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