Daniel and Jorge Explain the UniverseListener Questions 41: Questions about the mass of the Universe, moons made of gas, and backyard blackholes.
Daniel and Jorge answer questions from listeners like you!
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California from the California Office of Traffic Safety and Caltrans.
Hey or hey, how is your commute to work this morning?
Pretty cured? Taking me about one or two minutes?
Is that your typical commune? Do you ever get stuck in traffic and take like a whole five or six minutes?
Well, there can be a jam up in the kitchen sometimes usually blueberry jam.
Well, I hope your traffic is only caused by the tastiest kinds of accidents like spilled nutella.
Yeah, it's a short community, but it can get kind of nutty.
Only the most delicious of delays.
Nothing like tasty traffic. Hi am Horea. I'm a cartoonist and the author of Oliver's Great Big Universe.
Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I think the whole universe is pretty tasty.
What does it taste like though? Salty? Sweet, bitter?
Astronaut tell us that space smells like barbecue.
So it's a umami universe.
Exactly. It sounds like it's more savory than sweet, spacey savory. It's more French fried than milkshake out there, I.
Think, or it's French fries with milkshakes.
That's what happens in the multiverse when we cross our savory universes with some of the other sweet ones.
That's what happens every time I go to McDonald's. Do you ever dip your French fries in milkshake or ice cream? I'm much of a fan of soggy French fries, So no, you're missing up. But anyways, welcome to our podcast. Daniel and Jorge Explain the Universe, a production of iHeartRadio, in.
Which we sample all of the flavors of the universe, everything that crunches, everything that crisps, everything that gets soggy when you dip it into a milkshake. We think about the tiniest quantum particles what they are really doing. We think about how fluid flows around you on the surface of the Earth, and we think about the centers of black holes. Our goal is to embrace our curiosity, to think widely about everything out there that makes us wonder, and to talk to you about what we do and don't know about what's happening.
That's right. It is a pretty amazing universe. And the universe is everywhere all around you, in fact, even inside of you. The universe is full of amazing facts and questions for us to ask and possibly maybe sometimes answer, Like, for example, if you're an alien, do French fries become Earth fries?
You know, I'm amazed at our abilities to continually generate new questions that nobody has ever asked before, like that one.
Do I get a noble prize for asking questions? Or maybe depends on where you're from as an alien, like if you're from Andromeda, do they become milky Way price.
But you know, sometimes these foods are not well named, like the pastry that in America we call a Danish. The Danish people don't call an American pastry. They actually call it a Vienna pastry.
Wait what and what do they call it in Vienna? A US pastry?
I think they call it a Vienna was so they take credit for it. But we named it after the Danish.
Well, you know, history goes to the conquerors, I guess, so whoever first discovered the Danish maybe they discovered it in Denmark and then they got to call it the Danish.
And I've heard that there's a long debate about the French fry whether it's actually invented in France or in Belgium.
But don't they speak French in Belgium, so technically they would still call it pomfrets. So yeah, it's still a French fry.
I'm going to stay out of that colonial and political discussion.
Let's stick to the universe instead, simpler things like everything.
If Aliens are mad at us for calling them French fries, at least they're not going to write angry emails to us.
Why would they get angry if anything, it would be the French.
I love all the French people and all the Belgian people and all their cuisine and their culture.
But not the Danish. The Danish, you want to steal their national pastry away from them.
They don't claim it as their national pastry. They call it a Vienna pastry. It's not part of their national bride.
What are they call the sausages there? Danish sausage?
You mean wieners in a can. I don't think anybody wants to take credit for that.
That's a whole separate universe. But yeah, the universe is full of amazing questions for scientists to ask and also everyday people to ask.
These questions we ask about the universe are questions that people have been asking for generations, sometimes for thousands of years. How big is the universe? How does it all work? What's out there waiting for us? Are we alone? Because it's just part of being human to look out of the universe and want to understand it, to generate questions, to have that wonder bubble up inside of you. And it's not just professional scientists and cartoonists who are asking these questions, it's everybody.
It's you yeah, it does seem to be kind of a human quality, curiosity and asking questions about the universe. I mean, you don't see a lot of other animals asking questions or doing research, right.
I don't know. I see curiosity in cats and dogs, even rats. There's definitely curiosity out there.
You think cats wonder about the origin of the universe, but gravity, the nature of space and time.
I think they wonder why their dinner is late.
Yeah, yeah, they're just wondering how to kill you probably if they could.
You could call that experimentation, you know, yeah, murderers a feline EXPERIMENTATIONMFI.
But yeah, everybody has questions, and sometimes on this podcast we like to answer them.
We love to answer questions. If you are wondering something about the nature of the universe or this something that doesn't quite click in your mind, we want to help you make its stap together. So please write to us with your questions to questions at Danielandjorge dot com. When we say it all the time, but we really mean it. We love your questions. We answer all of them, and if there's a question that's especially interesting or I think a lot of people might want to hear the answer to we will even play it here on the podcast and joke about it.
So today on the podcast will be taggling Listener Questions number forty one. Maybe we should stop numbering these question episodes. I feel like at forty one we can probably stop counting, or maybe we should stop with forty two, because that is the answer.
That's right and everything. Well. Numbering them helps me keep track of them, because otherwise I'll get confused about whether or not we already answered a question or not.
Oh I see, so I lead to itselful for one person, yes, exactly, out of the entire universe.
And this way I can refer listeners. I can say, check out Listener Questions twenty four, where we talked about exactly that topic. Oh, I see.
They're like issues of a comic book, like ooh, have you heard Listener Questions number thirty seven. That's the one where the dark Phoenix rises from the ashes.
That's the one where we reveal that Jorge is actually Superman.
That's right. Do you think maybe these will be collector items someday? Maybe we should make NFTs out of these episodes.
I think it's more likely that the aliens come and make French fries out of us.
Than somebody would ever want to collect our podcast. Maybe we should record it in French then, But.
We really do love hearing your questions and thinking about them and answering them. So let me just say again, please don't be shy to write to us questions at Danielandhorge dot com.
Yeah, so today we're answering questions from listeners and give them some kind of answer at least, And we have some pretty awesome questions here about the mass of the universe, about gases, about moons made out of gas, and also what would happen if you stuck your finger in a black hole? A physical black hole I imagine.
As opposed to what a French fried black hole.
I don't know, a metaphorical black hole or something called the black hole, but it's not really a black hole.
Mmmm.
I see.
You just got to be in general careful about what do you mean when you say stick your finger in things?
That's true, some of these questions are a figurative rabbit hole.
Yeah, you gotta watch out for those two because the rabbit might bite your finger if you stick your finger in it. So let's get to it. Our first question comes from Eric.
Hello, Daniel and Horaey. I'm a big fan of your podcast. I'm a line haul truck driver who delivers freight from from Utah to Idaho. My question is how many tons of mass would my rig have to pull if I were to drag the whole universe up to Idaho rather than delivering it a few pieces at a time. Please include dark matter in your calculations, though I understand it would be difficult to secure in place. Thank you and keep up the good work.
All right, Thank you, Eric. That's an awesome question, and I love that he's a long haul trucker.
He's out there delivering those fresh strawberries.
Yeah, or do you think he maybe sometimes cargoes frenchies.
Is really those long haul truck drivers that make our economy work and keep everybody's shelves stocked. So thanks to all the truckers who keep us fed.
Yeah, keep on trucking, and I guess we're happy to keep those truckers entertaining thinking about the universe as they drive those long stretches of road between states.
Yeah. One thing makes me worried, though, because a lot of people write in and say that our podcast is very nice to fall asleep too, gives them pleasant dreams or whatever. And I really don't want long haul truckers drifting off while they listen to us joke about the universe.
Has anybody ever written to say it our podcast helps him stay awake or it rarely happens.
I haven't gotten one of those messages yet, but I hope it does that for Eric.
Well, if you're a long haul trucker right now listening to this, wake up.
Don't alarm them, man, keep.
Your eyes on the road. It's right, don't look up, it's the night sky or as space too much.
But Eric asks a really fun question basically about the mass of the whole universe, and I like how he thinks about it in terms of how much his truck can pull.
Yeah, it's kind of a funny question. His question is how many tons of mass would his truck have to pull if it had to pull the whole universe from Utah to Idaho. I guess that's a very specific move.
I wonder what they make in Utah. The people in Idaho especially want because it's not potatoes, right, If anything, those are going in the other direction.
Sounds like Eric got a request for a quote somebody ordered the universe in Idaho.
He brings salt from Salt Lake City to Boise and comes back with potatoes.
Right, they ran out of potatoes in Idaho, so they need to import a whole universe of them from Utah.
No, dude, it must be the opposite. Idaho is where potatoes grow.
That's what I mean. They ran out of potatoes in Ido, so they had to import some from a different universe.
I guess I do think that Utah is a bit of a different universe than Idaho.
Oh, I think they're both different universes. Every state is a different universe.
They're both beautiful, though, I've been to both, gorgeous mountains everywhere.
But it's an interesting question, I guess. Really he's asking how much does the universe weigh? Or how much mass is there in the entire universe as far as we know.
Yeah, it's a really interesting question. And he thinks about in terms of his truck. A typical semi can haul about fifteen thousand kilograms of stuff. But the universe, of course, much much bigger than that. And I don't even know how many muches I need to say to give you the sense for how much bigger the universe is. The actual number is that the mass the part of the universe that we can see is about ten to the fifty three kilograms. So that's ten with fifty three zeros in front of it, whereas his truck and haul fifteen with three zeros in front of it. So it's a lot bigger than what he can pull.
Yeah, I think he probably understands that this truck can pull the whole universe, But I think he's asking how much mass would his truck be required to pull if he had to move it from you to to Idaho. I think he knows.
I'm pretty sure he knows, but the quantity is really staggering. I mean, it's the case where like a kilogram is really the wrong unit to think about the mass of the universe. A kilogram is like something you could hold in your hand, So ten to the fifty three is just too big a number to think about. If you think about the universe in terms of like loads of Eric's truck, his truck can pull about fifteen thousand kilograms. That still comes out to like ten to the forty nine truckloads, So it's still a really really big number.
Oh, you mean, like if he took the universe broke it down into different palettes, how many trips would we have to make to move the whole universe?
Exactly? So, moving the whole universe would require moving ten to the fifty three kilograms. Clearly impossible if he did break it down. I know, Eric, you want to do it all in one hall. But if you did break it down in the chunks your truck could actually handle, it would take about ten to the forty nine truckloads.
And how long does each trip take?
So it's about five hours from Salt Lake City to Boise. I'm not sure exactly where he's driving, which makes it like a ten hour round trip. Now if he never sleeps, and that means he has about time for nine hundred trips in a year back and forth, So that's like almost a thousand trips a year. But it's going to take him ten to the forty nine truckloads. That comes out to ten to the forty seven years of driving back and forth, NonStop, no sleeping, no bathroom breaks to bring the whole universe back and forth between Salt Lake City and Boise.
Oh man, but can he listen to our podcast? While he's driving, might make him drive faster. He's like, oh God, this is torture. I just want to get this over with with. I have to listen to this podcast.
You know, we got like five hundred hours of podcast out there. But even still he would run out pretty quick. He would have to listen to every episode a lot of times.
Interesting. I guess maybe the question is how do we know how much the universe ways? First of all, we don't know if the universe is finite or infinite.
Right, We certainly don't. The universe could be infinitive, could go on forever, or it could also be finite. The part of the universe that we can see, what we call the observable universe, is just the part where light has had time to get to us from those far reaches beyond that we literally can't see, because even though it might exist and photons from it could be racing through space to reach us, it hasn't arrived yet because the universe it's only like fourteen billion years old, so photons that take fifteen billion years to get here haven't arrived. Yets, we haven't seen that part of the universe. So there's like a sphere surrounding us that we call the observable universe, and that's the part we can see and we can measure how much stuff is in it, and so we can talk about the mass of that part. But that could be literally a zero percent fraction of the infinite universe, or it could be most of the stuff that's out there. We don't know what's beyond the boundary of the observable Yeah.
The universe can be pretty big, but I guess then the question is, how do we know how much it weighs or how much mass it has, Like we have a hard time knowing exactly how much mass the Earth has, right, Didn't we have a whole episode about that.
Yeah, we did have an episode about measuring the gravitational constant, and that's a fun episode because we talk about how they're trying to make that very very precise. What we do when we measure the universe is that we measure the typical energy density, like how much stuff is there in a cubic light year of space an average cubic light year of space. So we go out there and we look at like all the stars and the gas and the dust, and we add up all the dark matter as Eric suggested that we include and we measured that by looking at how like galaxy swirl and the large scale structure the universe which is influenced by dark matter. We also add of the energy of the expansion dark energy. So there's all these different components of the sort of energy budget of the universe. Some of them we can measure independently, some of them when we measure together all of them. We have multiple different ways of measuring. So we're pretty confident we know all those various pieces of the pie.
But I think Eric is asking about the mass of the universe, not the energy of it. Right, Energy doesn't necessarily have to haul if you have to move it from Utah to Idaho.
Yeah, that's right. Therese different components. Is matter, there's radiation, there's dark energy. So just the matter part of it, right, we can measure that as well. Just the matter part we can measure separately. And we've done that.
How do we do that? Like, how do we even know how much the Earth weighs? So a giant scale we can put the whole Earth on.
Well, once we measure the gravitational constant, which required using like a pendulum and a weird Mountain in Scotland that we knew the density of then we could measure the mass of the Earth by understanding how it moves around the Sun. Because once you have the gravitational constant, do you know the force?
But when do we need to know? Also the mass of the Sun and how do we know that?
So the mass in general of stars we can connect to their brightness because there's a model that tells us that brighter stars are heavier, and that's somewhat theoretical but also pretty well established. So in general we can tell the massive stars by looking at how bright they are.
Interesting, but it's based on a theory sort of, right, Yeah.
It is based on a theory. We have this theory of how stars form, how they operate, how the mass of those stars determines their temperature, which it determines how bright they are. It has to do with how fusion happens at various temperatures, and that works pretty well. Of course, there's still big unanswered questions about what's going on at the heart of star, the plasma flux tubes that are snapping in the magnetic fields that don't really make any sense. But on the whole we're pretty confident in our understanding of how massive stars are. Sometimes we get lucky. We see like a binary star system and we can use that to calibrate this because by the relative motion we understand their masses.
Okay, so that's stars out there. What about like planets and gas and does like have we measured the mass of planets around other stars or do we just sort of ignore that it's and say it's negligible.
That really is negligible, Like even in our solars, the mass of things that are not the Sun is about one percent. We can measure the mass of some planets around other stars because we can see their size as they eclipse their star, and we can get their mass from the period, and so that tells us their density, et cetera, et cetera. So we can study a few planets outside our solar system, but on the whole we have not observed very many of them. But mostly it's stars. And then there's gas and dust. A huge fraction of the mass of the universe that's not dark matter, just the normal mass is in gas and dust. A lot of that is in galaxies, but also a lot of that is between galaxies, like the gas that flows between galaxies that's still falling into galaxies is a huge fraction of the normal matter in the universe.
And then how do you measure that. I mean, it's so far away and it doesn't shine like a star. How do you know how much of that stuff is out there?
That's pretty difficult to measure because it's diffuse. One way we can do it is by looking at quasars. Quasars send out these bright rays of light, these like pencil beams of light, and when they pass through these filaments, they get distorted, or they get diffracted, or they get bent. So in some cases we have these beams that penetrate this cosmic web and give us a measurement for what's there, though it can be pretty tricky and those are pretty rare. So again, we have models that describe like the overall evolution of the universe, like the large scale structure of the universe, that tell us roughly how much gas there is, but a lot of it has not been directly seen. We actually had a fun episode about how slime molds teach us about the large scale structure of the universe and where these cosmic filaments are because they tend to form in patterns that are similar to that cosmic structure, but a lot of it is not observed. It's extrapolated from a few observations.
So then you extrapolate that to hold galaxies. Like, how do you know how much mass is in a galaxy? We only see it from far away.
We can mensure the mass of a galaxy by looking at the brightness of the stars, which tells us the mass of the stars, and then also watching its spin, which tells us how much invisible mass there is. Because most of the mass of most galaxies is actually in dark matter, like eighty to ninety percent, and that we can't see directly in any way. We can only see its gravitational effects on the rest of the galaxy. So galaxies that are spinning really really fast, the only way to understand why they are held together, why they're not throwing their stars into intergalactic space, is to imagine that they have a lot of dark matter in them. Sometimes we can also see that dark matter directly through gravitational lensing, as it distorts the light from other background galaxies.
I'm sort of getting the idea that you don't know how much the universe wasys a lot of it seems sort of based on theories and models and what we think is out there, but it sort of doesn't feel like you've gone out there and measured how much mass there is.
There's definitely a lot of extrapolation. And you know, something that's happened recently is that cosmology has become a precision science. It used to be the cosmologist people who think about like the whole universe only really cared about getting answers correct within like a factor of two or factor of five. You know, that was precision cosmology a few decades ago. These days, things have gotten better. Now we can measure these things down to like five percent, one percent, a tenth of one percent, and we're being more and more careful about those uncertainties, asking questions like you're asking, like, how do we really know them? Could we be getting this wrong and in what ways? And do we have another way to test this independently? So cosmology has really become more and more precise. And you're certainly right that we don't know exactly how much mass there is in the universe. We have a pretty good picture to within, you know, like one percent.
I guess even if you're off by you know, a factor of ten or even one hundred, it's still a lot. Like it would be the difference between ten to the forty nine truckloads or ten to the forty eight truckloads, which is still a lot of truckloads, which is a truckload of truckloads.
It's still a lot of truckloads. Yeah, exactly. And we try to be careful about what we don't know, but there's always room for surprises, right. The history of physics is filled with examples of times when we thought we knew what we were doing and then it was all blown up because we discovered something which shakes the foundations. So we could certainly be wrong about it, but I'd be surprised.
All right, Well, I think that's the answer. For he asked how many tons of mass would his truck have to pull if he were to move it from Utah to Idaho, and the answer is about approximately. We think ten to the fifty three kilograms, which is a truckload of truckloads.
Better get some coffee, Eric.
And maybe put this podcast on repeat unless it makes you fall asleep, in which case maybe not. All right, let's get to our other questions here. There's one about moves made out of gas, and also what would happen if you stuck your finger in a black hole. So we'll get to those, but first let's take a quick break.
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All right, we're answering questions from listeners. We're just answered a great one about the mass of the entire universe, or at least the observable universe, And our next question comes from Tim from Virginia.
Hey, Daniel and Jorge. This is Tim from Virginia. I was thinking recently about gas, giant planets, and moons and was curious why all of the moons that I've ever heard of are rocky and there are no gas moons that exist or do they?
Why and why not?
Thanks for answering, cheers.
Why and why not? That's the fundamental human question, my dad. This is a great question from Tim. Thank you Tim. And his question is are there moons out there, at least in our Solar system that are made out of gas?
Yeah? A really find question because he's noticing that there's like two different kinds of planets, rocky planets where you can like walk around on the surface, and then like gas giants like Jupiter and Saturn that are being blobs mostly of gas that you would just like gently sink into if you try to walk on. All the moons, of course, seem to be rocky, and so it's a great question. Are the Moon's made of gas? And why not?
Yeah? And why skip from solid to gas? Could there be liquid moons out there?
Are you? Especially if they're sty today? You want to drink a whole moon, You're going to put your straw up to it and just.
Like shop Yeah inhil a moon, eat the moon, drink a moon worm? Are menu options for moons?
I want a moon boba, right, just like floating tapioca inside the moon with a huge straw.
Yeah, like is it gonna hit your eye like a big pizza pie or you know, is it going to hit your face like a big puff of air?
And I like this question because it makes us think about like why we have gas giants in the first place, Like how do you get a gas planet to anyway?
I guess it's sort of like that's how things form in space, Like if you have a big cloud of gas out there, it's eventually going to collapse into a gas body, right.
Yeah, And most of the universe are these lighter elements hydrogen, helium, et cetera, which we think of as gases, and so the Sun is mostly made of hydrogen and Jupiter is mostly made of hydrogen. Hydrogen dominates the whole universe, and so of course it also dominates the Solar System the other fun stuff that make us up carbon and oxygen and nyitrogen. It's a tiny fraction of the universe and also a tiny fraction of the Solar System.
Like the most of the regular mass of the universe is what percent of hydrogen.
So hydrogen is like ninety one percent of the universe by atoms, Like if you count the number of atoms, but it's only like seventy four percent of the mass fraction of the universe because it's so light. So uranium, for example, is many many times heavier than hydrogen. So a single uranium atom outweighs hundreds of hydrogen atoms.
But there aren't that many uranium atoms in the universe.
No, there really are not very many uranium atoms, So like ninety one percent of all atoms out there are just hydrogen.
Yeah, so it's sort of a hydrogen universe. But then I guess the question is can you form a moon out of hydrogen or any gas?
Yeah?
So I think to answer that question we have to think about why we have also planets made out of gas and some planets made out of rocks, right, like why do we have rocky planets and why do we have gas planets? And as you said, everything forms out of the original blob that created the Solar System, a blob of gas and dust, etc. Then collapsed and made the star. Not all of it falls into the star, because some of it's spinning really really fast and ends up in orbit, and some of that stuff has enough gravity of its own to gather itself together to make planets, and there's this division between the inner Solar System and the outer Solar system. The inner Solar System is where we get like rocky planets, and the outer Solar system is where we get like gas giants. And the division comes from where water is able to freeze, like in the inner Solar system, so much radiation from the Sun that water is basically a vapor even when it's out in space, but outpast what we call the snow line, and you're far enough away from the Sun, water can form crystals. So those crystals gather together and they help build those planets. So as the Solar system is forming, those water crystals help seed the formation of the gas giants, help them gobble up their own helping of gas, which is why Jupiter got such a big scoop of hydrogen.
Right, Isn't it also a little bit because like any gas that was close to the Sun sort of fell in right away because it's so light.
Yeah, there's actually two different effects there. One is, you're right, the Sun gobbles up a lot of gas and dust, and then once it starts using, it blows away all remaining gas and dust, like the solar wind blew away the Earth's atmosphere in the early formation of the Solar System, so any hydrogen in the Inner Solar System either fell into the Sun or got blown out by the Sun's radiation, which is why we end up with only the heavier stuff making planets in the Inner Solar System and in the Outer Solar System far enough away from the Sun that you can capture some hydrogen and you have the assistance of these water crystals to seed your gravitational attraction. Plus you're far enough away from the Sun that its radiation doesn't blow all of your hydrogen out into deep.
Space, all right, So there was sort of a big band of hydrogen gas in the Outer Solar System, which is where you know Jupiter and Saturn and all of those gas planets came from. But I guess the question is can you make a moon out of gas?
So in principle, you can make a moon out of gas, but you probably can't keep a moon out of gas because in order to hold onto gas, you have to have enough mass, Like the Earth holds onto its thin layer of atmosphere because of its mass. The gravity of the Earth is holding the atmosphere to it. Mars, which is smaller, has much less mass than a much thinner atmosphere. Our moon, which is even smaller than Mars, has much much less gravity and has essentially no atmosphere for that reason. So you make something that's too small, even if it started out with a little envelope of gas, or even a lot of gas, it's just gonna lose it. It's just gonna boil away into space.
I guess if you're like a gas molecule and you're hanging out in the Moon, you could be like, oh, this moon is not so attractive. I'll just fly off into space. That's what you mean by boil off.
Right, Yeah, Every hydrogen molecule in the vicinity of the Moon basically has escape velocity. It's not that hard to escape the gravity of the Moon because the Moon doesn't have that much mass. So any hydrogen atom that's out there is basically hot enough and has enough speed that if it's pointed in the direction of space, it'll just keep going and the Moon can't hold onto it. That's also partially true for the Earth, like the Earth is losing some of its hydrogen. That's one reason why hydrogen is a tiny fraction of our atmosphere because it's the hardest to hold onto because it's so light.
So now let's say what happens if I made a moon out of gas, Like I just took a tag of hydrogen out into space and I released it, creating a cloud of hydrogen. Is that cloud going to keep orbiting around the Earth or is it just gonna disperse?
It depends a little bit also on the temperature. If you could chill that hydrogen down and keep it cold, then it might stay together. If it was kind of more, if you'd like sprayed it out of a nozzle and it's moving pretty fast, then it's just going to disperse.
H It'd be liquid? Do you mean, like if it was super cold it would be liquid? Or would it stay in gas form?
The pressure is essentially zero out there, so the phases get a little bit weird you think about it in terms of vapor versus crystals. Really there's no like flowing liquid.
All right, So then could you form any moon out of gas?
If possible, if you made it really really cold and really really massive, But then basically you're making another planet. That's basically what the gas giants are.
So like, for example, if I take the mass of our moon and made it into gas. Would it stay as a you know, as a satellite or would that just disperse?
It would just disperse. Yeah, there are some moons in the Solar System that do have an atmosphere, like Titan. For example, a moon of Saturn does have an atmosphere, and its atmosphere is actually a little bit thicker than the Earth's atmosphere. Of course, it's not a small moon. It's a really massive thing. It's like ten times the mass of our moon.
I think you're saying that there aren't any then gas moons in our solar system.
There aren't any gas moons in our solar system. And almost every moon in our solar system doesn't even have an atmosphere because they don't have the mass to hold it together. Titan is really an exception. It's the only one that has enough mass to hold an atmosphere. That's probably because it's really cold, and also because it's around Saturn instead of Jupiter. Jupiter has more radiation to blast its moons than Saturn does. If you took a huge, massive blob of gas and made it really, really cold, it might collapse into a gas moon, but it would take very special conditions.
All right, It sounds like gas is just too slippery to wispy to really kind of hold together unless you have a lot of gravity, in which case you would be a gas planet like Jupiter or Set.
Yeah, though, as we talked about recently on the podcast, the distinction between a moon and a planet is a little bit fuzzy. Might have For example, a pair of planets that are orbiting each other, call one a planet and one a moon, and that's both of them could really be gas planets. The one of them, technically you might call a moon of the other one. You make the thing big enough to be able to hold its gas, it's basically a planet.
Like you could have a situation where like a Saturn Neptune is orbiting around a Jupiter out there in another Solar system, in which case you would have a gassy moon.
Yeah, although it might be like a binary planet system sharing an orbit. But yeah, then it's just a question of names.
I wonder if, technically, like our atmosphere sort of is like a gas moon, right, I mean, technically all of the gas in our atmosphere is kind of in orbit around the Earth, right, It's not stuck to the Earth.
Technically, that's an interesting question, and we did talk in that episode about moons that there's no lower limit to the definition of moon. It's basically any natural satellite. If you go far out past the atmosphere to Earth's exosphere, you have these little particles which really are in orbit around the Earth. In the atmosphere, it's not really fair to say it's in orbit because a lot of the forces on those objects from neighboring gas molecules. Out in the exosphere where it's really collisionless, where the molecules don't really talk to each other. Then yeah, you could say those things are in orbit around the Earth. So each one is like a particle sized moon.
There you go. I guess you can have a gas moon, but you can have a gas sort of moon or orbit around the planet.
Yeah, you can't have a gas giant moon, but you can have a gas particle moon. I suppose.
All right, Well, I think that answers Tim's question. Are there moons made out of gas? Not that we know of, at least not here in our Solar system. There might be out there binary planet systems that are made out of gas, in which case you might call one of them a gas moon. But also maybe there are particle moons going around the Earth right now, they're just too small to see. All right, let's get to our last question from Stuart about what happens when you stick your finger in a black hole. So we'll get to that, but first stick another quick break.
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All right, we're answering listener questions and we've answered questions about the mass of the universe and about whether moves can be made out of gas. Our last question comes from Stewart from New Zealand.
Hey, Daniel and Jorge Stuart here. I grew up in South Africa, but live in Auckland, New Zealand now boog fund of the show. Been listening since the very beginning. I've got a bit of a hypothetical that's been making my brain hurt. I was wondering, what if we could create a stable black hole, say roughly Earth mass, which I know is going to be about the size of a ping pong ball, or maybe a bit larger to say the size of a tennis ball, but critically small enough that it's not going to suck us in. And I then wondered, what would happen if I stuck my fingertip in and pulled my finger out again. I presume my fingertip would get ripped off, But then I was wondering about what forignification effects might occur on my actual finger, and then also made me wonder would I then see an image of my fingertip on the surface of the black hole. And then also if I was to come back, say a week later, would I still see that image of my finger on the black hole. I'm hoping you can help me out with the answers, because this one's really been making up right head love the show for the next episode.
Than guys awesome question or should I say questions from Stewart, one of our og listeners from NZ New Zealand, it sounds like he basically just wants to pull a prank on a black hole and be like, hey, black hole, pull my finger.
It sounds like he's really curious and if we put a black hole in front of him, he would not be able to resist sticking something inside.
Well, I'm glad he's going to do it, because I definitely don't want to see try with my finger. So that's an interesting question. I guess he really just kind of wants to know what happens to things as they go into a black hole. You know, because it's so weird to think about what happens in the vicinity of a black hole. And I guess he's painting the scenario where we somehow create a black hole with the same mass as the Earth, which would be I think about the size of a pigpunk ball or a small lemon, right, and like, what if you had it right in front of you, why did you stuck your finger in it? What would happen?
Yeah? I love this question because it makes it immediate. Right. Black hole seem weird and missed. Is an out in deep space that makes you want to like explore a concretely, like have one in front of you and poke it and prod it. And you know, that's what physics labs are all about. And that's why we are trying to make black holes the large Hatren Collider so we can do these kinds of experiments. I mean, not with Stuart's fingertips, but yeah, we want to play with black holes.
It sounds like you're playing with everybody's fingers by making black holes here on Earth? Have you asked everyone's permission to pull their fingers? But yeah, I guess it's an interesting scenario because you know, we are used to thinking about black holes as being humongous, right, I mean, the one at the center of our galaxy is many millions of times bigger than our sun or heavier than our sun, And so you imagine that if you're right next to a black hole, it just looks like a gigantic thing that covers your entire field of vision. But maybe if it's small, like about the size of a lemon or a peck one ball, maybe it'd be small enough to like do little experiments on it, like stick your finger in it.
Yeah, you're right. The black holes are not about enormous amounts of mass. They're really about the density of mass. So you could take almost anything and if you squeeze it down enough into a small enough radius, high enough density, then you'll form an event horizon. The calculation is called the short stiled radius. It tells you the radius of the event horizon for a given mass. So as long as you get all the mass of something within that radius, then it becomes a black hole. You get an event horizon. And if you plug the numbers in for the Earth, then the radius of that event horizon is just under one centimeter. So if you were able to take the Earth and somehow squeeze it down to something with the radius of a centimeter, it would have an event horizon. All that mass inside of it would have so much gravity that it would bend space and create that threshold.
So if you could do that, you would have a black hole possibly in front of you, right like on your desktop.
You would have a black hole in front of you. Though it would be very, very powerful. There's a couple confusing things going on here. On one hand, Stewart's on the right track that if you can pack the Earth into a black hole, you're not fundamentally changing the amount of mass that's there. You're just squeezing it down. So if you stay at the same distance you were before, you're still going to feel the same amount of gravity. He's imagining an Earth mass black hole is not going to be that powerful because the Earth's gravity doesn't feel that powerful. I mean, I'm standing on the Earth's surface. I can jump and avoid it, right, but that's because I'm pretty far away from the center of mass of the Earth. If I formed an earth mass black hole and then got really really close to it, like a centimeter, two centimeters, even a meter, its gravity would be much more powerful than the gravity we feel here on the surface of the Earth, because I'd be much much closer.
Right, Like, if I made a black hole like that, I would the same mass as to Earth, and I put it in the center of the Earth, and I'm standing about an earth radius away from it, i would feel the same gravity that I'm feeling right now, which is doesn't seem like a lot, but I'm pretty far away from the black hole, right It's like ten ten thousand miles or something like that.
You're pretty far from the center of mass of the Earth. If instead you compacted all that mass into one centimeter and then you stood right next to it, then you be seven hundred million times closer to the center of mass than you are in the surface of the Earth. And because gravity gets stronger with distance squared, like twice as close means four times as strong, then the gravity of the earth mass black hole, if you're one centimeter away from it, would be quadrillions of times more powerful than Earth's gravity.
Right, it would be like five times ten to the seventeen right five with seventeen zeros basically.
G exactly, so it would gobble steward up there wouldn't be like time to think about which finger to stick into it. It's be incredibly powerful gravity. You would slurp him up in a moment.
Yeah, I think you're saying, if you're close enough to touch it, that means you're at arm's length from it. Yes, in which case the gravity would be super duper strong, but maybe more important, the tidal forces would be shredding you apart exactly.
The tidle forces come from the variation of gravity across distance. If you're a point mass, you don't feel any tidle forces. You just feel gravity. But if you're larger, so that parts of you are closer to the black hole and parts of you are further away than they're feeling different amounts of gravity. And basically the black hole is tugging you apart because it's pulling on different parts of you with different.
Strengths, right Like that happens right now. As you're sitting there or standing there on the surface of the Earth, your feet are getting pulled more than your head.
Yeah, your feet are getting pulled more than your head. So your Earth is trying to pull your head off of your body. And as you get closer to the black hole. The difference in those two forces grows, and so the effective force the Earth trying to decapitate you also grows, and eventually it overcomes your body's ability to keep your head on your shoulders.
So like if you were maybe a meter from a small black hole like that and you raise your arm to point your finger towards it, your finger would suddenly feel a huge amount more force than the rest of your body. So basically it would pull your finger right, it will shred pull your finger out of your body.
Yeah, you can calculate the safe distance with which you can approach a black hole, and it depends on the mass the black hole, of course, because the tile forces go by like the derivative of the gravitational force, And for an earth mass black hole, it's between one and ten thousand kilometers. So you can't get very close to an earth mass black hole without its churading you apart.
Whoa, So you'd have to be pretty much as far away from it as we are from the center of the Earth right now.
For an earth mass black hole, you need to still stay at least a thousand kilometers away from the edge of the black hole to avoid being pulled apart.
So basically you can't stick your finger inside of that black.
Hole, and less your thanos and you have like more body integrity and ability to resist the tidal forces somehow, then yeah, you can never even get close enough to stick your finger in.
Well, I guess you could. I mean you'd raise your hand, the hole will rip your arm out, your finger out, and then technically it would get sucked in and you'd be sort of sticking your finger in, but you wouldn't be attached to that finger.
Yeah, and your finger would be a long string of particle pulled into spaghetti by the tidal forces before it even got to the black hole.
But I think maybe Stuart's question was, like, you know, let's say that you made a black hole. Maybe it's smaller, or maybe you're somehow able to create a stick that is strong enough to hold together that you can poke into a black hole. I think he's asking, what would you see? What would happen? Because I know we've talked about like a round a black hole, time freezes to stop, right.
Yeah, when space gets curved, it time goes slow. So things that fall into a black hole, for an outside observer, their time goes slower So if you drop a clock into a black hole and then you watch it with a telescope, you'll see that the time on that clock will tick slower than the clock that you are holding. That also controls how quickly it falls into a black hole. So as things approach the event horizon, their time gets slower and slower, and they get more and more smeared out. Also, they get red shifted by that curvature, so things get slowed down and smeared out into the red pininy.
I guess if you take this stick that you're going to stick into the black hole, you put an indestructible watch at the end of it, and then you use that to poke the black hole, you would see it, I guess you would see it approach the black hole the event horizon. You would see that the takes in the clock start going slower, taking slower, And then would you actually see that the rod the event horizon if you keep pushing it towards it.
So this is a little bit tricky and a common source of misunderstanding. People often say you can never see anything enter a black hole because time slows down. You have to wait till the end of the universe to see something actually fall into the black hole. That's true, if you just drop like a particle into a black hole, it'll take forever for it to actually fall in. But what's happening as it falls in is that the event horizon is already growing, like as it approaches the black hole, it contributes its gravitational energy to the mass of the black hole. So the event horizon is actually growing out to meet it. It's not like it has to pass over the event horizon to contribute to the black hole. The two approach each other very slowly. What that means is if you then throw something else in, like a second particle, that second particle will pull the event horizon out even further and you will see the first one absorbed. So it's true that if you drop a single particle and then nothing else into a black hole, it will never enter the event horizon. But if you use a stick, which is like a long string of particles, then the next particle pulls the event horizon over the previous one, et cetera, et cetera, so you actually would see the tip enter the black hole.
All right, well, maybe let's do it play by place. I have this long indestructible stick with a watch at the end of it, I pointed towards the black hole. I poke the black hole, and I stop at the moment the tip touches the black hole. It's at the edge of the black hole, and I push it in an inch. Are you saying that that that inch of indestructible rod that I push it into this black hole is enough to grow the event horizon an inch?
The mount of the event horizon grows depends on the mass of the thing that you're putting into it, So it depends if this rod is made out of like lead or titanium or hidi or whatever. But just because you'll put an inch worth of rod doesn't mean the event horizon grows an inch.
So then let's say it's not right. Then if I push it an inch into the black hole, am I going to see it go into the black hole?
Then you are because you're pushing it in, right, You're not just waiting for the event horizon to grow out to gobble it. You're pushing it in. When I say the event horizon is growing out. This just to help people understand how something can actually fall into the event horizon when an object falls into the event horizon. It's because the next thing falling in has pulled the event horizon out over it.
M right, Okay, so then maybe let's not think about that scenario. Let's think about the one Steward is thinking about, which is sticking your finger into the black hole. If I stick this metal finger into the black hole, I would see it going.
You would see it go in. Time would slow down and it would get red shifted still right, Your finger would get redder and redder and darker and darker and then eventually invisible right in black. But you would see it going. You would have your finger sticking out of a black hole.
It would hurt or at least the back part of your metal indestructible finger and sticking out of the black hole. Now what if I pull it?
Then you're gonna have a finger tipless finger?
You mean I lost my watch? Yeah?
Exactly?
Could you pull it? I guess? I guess, yeah, I guess could you? It'd be hard, but you could, right, I guess.
Yeah. If we're talking about a really small black hole, one you could stand next to safely, then it actually wouldn't have that much gravity, Like if you take the empire States Building and you squeeze it down into a black hole, it's going to have as much gravity as the Empire States Building. And that's not that much, right, You can stand next to the mPire States Building without like leaning over because if it's gravity, because remember gravity is super duper weak, so even something as big as a building doesn't have that much gravity.
Well, but then gravity increases the closer you get to it, so maybe it would still shred you if you got, you know, within an inch of it.
Maybe m m. You can get closer to a building mass black hole than you can actually to the center of mass of a building.
Absolutely, So then if I stick a metal finger into it, I would see it go in. I could pulk the black hole. But then when I pulled my finger, it will have eaten whatever was inside of the event horizon.
And the last things in there would be smeared across the surface of the event horizon because the last thing you tried to stick in would take forever to actually fall in until something else comes along and it pulls out the event horizon over it all?
Right, Well, I think that answers Stuart's question. Don't stick your finger in a black hole?
Don't stick your finger in a black hole, Stewart, This is not medical advice, but it's physics advice.
Well, I wonder if like the black hole is so little, like like you said, with the mass of the Empire state building, I imagine it would be you know, super duper tiny small, right, like micron small?
Right?
Yeah. Absolutely, The masses of the black holes we try to make the large Hadron collider are even tinier, and their event horizons are really really small. Yeah, we're talking microscopic.
What happens if you stick your fingers in those you'll make a hole in your finger.
Yeah, I suppose it'd be like a laser beam. But there's another effect there which is really really microscopic. Black holes don't last very long. So if you make a black hole that's really really small, it'll hawking reation away. It's really really fast because the rate of hawking radiation depends on the temperature, which is inversely proportional to the mass, So really small black holes are hotter and have more hawking radiation, so they actually don't last very long.
So you'd have to have a fast finger. Yeah, you have to be pretty quick cook it before it viborates. You'd have to be determined to hurt yourself. All right, well, I think that answers Stuart's question. It's sort of It's not necessarily a case that you would never see what happens. You would see what happens if you start something into a black hole.
That's right. If you manage to somehow s arrive getting next to a black hole, you can actually stick stuff into it and lose.
It, and then the joke would be on the black hole. You can make the fart sound if you like, but I guess the black hole keeps your finger, so then the joke's on.
You don't try this at home, folks, but.
Do try it in a large particle collider. I don't understand the message here.
Well, if those black holes are actually made, they would evaporate very, very rapidly because they're super duber tiny.
Just don't let Stuart near them because he might want us stick his fingers quickly. All right, well, those are three awesome questions. Thanks again to our listeners for sending us these amazing questions.
Thank you everybody out there for being curious and wondering about the nature of the world, which is the reason why we get to do science and think about how the universe works. If you have a question about how something works, please don't be shy. Send it to us to questions at Danglandjorhey dot com.
Yeah, as you sit out there in the long call of life wondering about the universe, staring out at the sky, wondering what you can stick your finger in, just remember it's an amazing.
Universe and dip your French fries into shakes, not into black holes.
Oh what would happen then? Would they still be French?
They wouldn't be cunchy.
It would be decapitated, beheaded like in the French Revolution. All right, Well, we hope you enjoyed that. Thanks for joining us, See you next time.
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. 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 digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you asdairy dot COM's Last Sustainability to learn more.
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