What if gravity were much stronger?

00:00:08
Speaker 1: Hey, Jorge, I have a pitch for a new kind of superhero. I think we're all full up on superheroes. I don't know, but this one, this one stayed with me, will be scientifically accurate. So it'll be like a super physicist. Does he happen to um you know where glasses live in California and be called Daniel not at all? No, No, So you've heard of Magneto, one of the X Men's, those who can control things with magnetism. Of course, So I was thinking, let's have a whole team of superheroes, one for each fundamental force and have them be like accurate. Interesting, except I vote not to be the weak force. So there's going to be like a Gravito then, and a strong Eto. Yeah, and Gravito would be really really really weak, but super patient and in the end will control the shape of the universe. Oh, the bad guys win. That's a twist. You gotta keep the sequels coming until maybe the week Fource gets super strong block twist. Hi'm Poor handmy cartoonist and the creator of PhD Comics. Hi I'm Daniel. I'm a particle physicist and a professor at UC Irvine and I have a superpower, which is that I can sometimes pronounce the title of my job sometimes. What kind of superpower is that it only works in extreme situations through like the Hulk. Well, one listener wrote in to complain that I sometimes mispronounced the word physicist. And I'll admit it's a tricky word. I stumble over it. Physicist, businessicist, It's got a terrible name to it. I guess you never have to say the word very often because you're just surrounded by physicist all the time. Yeah, we say the word physics a lot, but we don't call ourselves physicists very often. You call yourself professors, I guess, explorers of the universe. So when we're feeling grandiose, I see he's walking to the office every day and you're like, hello, fellow explorers of the universe, what's your plan for napping today? Fellow nappers of the universe? Hello, fellow diviners of truth. But you know you are a cartoonist, which means you do cartoons. So you think, since I do physics, I should be a physics ist. But it's not physics ist, it's physicist. Well, English is not my first language, so I'm not even going to pretend to know the difference. And you know, in French, someone who does physics is a physicist, so I think a lot of French physicists call themselves physicians. Interesting. I wonder if people then confuse you with real doctors. I don't real ask people to take off their pants nearly as often. But anyway, we welcome to our podcast. Daniel and Jorge explain the ever. It's a production of I Heart Radio, where we are all explorers of the universe seeking to understand the nature of this bonker's reality, which seems to follow rules as weird and strange as they may be. We encourage you to join us in our journey to understand the nature of those rules and to pick away slowly at the mysteries that remain. Yeah, because it is a pretty mysterious universe, full of head scratching things that happen and mysterious objects out there that are just floating in space, begging us to ask the question what is it? And what's going on with you? And it's not just those of us who can't pronounce our job titles who are curious about the nature of the universe, wondering how the universe works and where it came from and how it all fits together is something almost everybody out there does. Who doesn't want to know where the universe came from and what its final fate will be. Yeah, because curiosity is a very human trade. Everyone looks at the universe and wonderus. You know, what's going on? How did that come to be? And why are we here? And how is it that we are here asking these questions on a podcast, and curiosity is sort of our brand or Hey, we work a lot on projects and encourage people to be curious, from this podcast to our books to our TV show. Do you ever get curious about curiosity? Like? Why are humans so curious? Interesting? Sounds almost like the plot of a movie that's coming out in PBS Kids pretty soon. That sounds like a wonderful journey to me. It is. That is the name of our special for eleanor Wonderus Fly, which is coming out in April, so if you have kids, but please take it out. It's a movie we wrote, It's got awesome songs in it, and it's all about why we ask questions, and we ask questions about the universe, but we also want to hear about your questions. The fact that you're listening to this podcast means that you are curious not just about how butterfly wings evolve, but about how space and time fit together, what we can see at the edge of the universe, and how the universe might fundamentally be different if we tweaked the deepest laws of nature. So, if you are curious about how the universe works and you have a question that you haven't heard an inswer two please it'll be shy right to us two questions at Daniel and Jorge dot com. We answer everybody's questions. Yeah, because everybody has questions. This is a very active podcast. I feel like you cannot just listen to us talking about questions or answering questions. You can also ask questions and you will answer them, and sometimes we even answer them here on the podcast. Yeah, some questions are super fun and I think other listeners would like to hear the answer to them, or they're a little bit tricky and I have to go read something or think carefully about exactly how to praise the answer because there's a lot of subtleties involved, and there's just a lot of fun to talk about on the podcast. Because I know that at least one person out there wants to hear the answer. Yeah, and so today on the podcast will be tackling listener questions. Number twenty seven is twenty seven time we answer listening to questions, Daniel, and I feel like maybe at this point which is dropped the numbers and just go with like, you know, just a fun subtitle, you know, like they do in movies now where there are so many sequels that you don't use. No verst listener questions, no way home and listener questions, return listeners, strike back, listener questions, the questions awakened. Hopefully we won't get to listen to your questions the last question no hopefully yes? Right, but isn't that the goal of all of physics and physicists is to get to the last question ever know the goals to answer today's questions, which will generate tomorrow's questions. We live for questions. We don't want to figure everything out. We want to continuously ask questions. Right, You just want to be able to say your physicists forever. Today I can't say I'm a physicist, so I'm hoping to one day figure that out. You gotta activate that superpower. There. You got to figure out your triggers. But yeah, we have some awesome questions here from listeners like you and there are they're all over the place, or about the observable universe and the cosmic microwave background there about gravity and the forces, and they're also about the disappearing universe. And Daniel, just to be clear, nobody was required to take off their pants to ask these questions. Right, we have a strict Pence policy in this podcast. Right, I'm wearing pants. We don't actually have a strict pants policy. So I have no idea. I can make no statement about what pants these people are or are not wearing. But if you'd like, in the future, I will inquire about what people are wearing when they record these questions. That's maybe not I think we should be pants agnostic. Yeah, yeah, let's be pant pant agnostic. Yeah, alright, well let's jump into it. Our first question here comes from Jeff, and Jeff has a question about the observable universe and the cosmic microwave background. Hi, Daniel, Jorge and special guests contributors. I'm Jeff from Alltown, p A. If the observable universe extends only as far as light as that time to reach us, and that faston the light expansion precludes us from ever seeing galaxies beyond. How is it we can still image the cosmic microwave background, which should predate any cosmic structures. Thank you again for keeping us educated, wondering, curious, and entertained. Awesome. Thank you Jeff for that question, and a shout out to Allentown, Pennsylvania. Daniel. I feel like Jeff asked a pretty good gotcha question, Like I'm wondering how we're going to answer this one. Jeff has a question which really exposes a lot of subtle issues in understanding how far we can see in the universe as the universe is expanding, and as that expansion is accelerating, and so there are a couple of interesting issues here, like what is the oldest thing we can see? And what is it that we cannot see in the universe? Right right, There's a lot of sort of concepts here in this question, Like, first of all, it's the idea of the observable universe. Then also the expansion of the universe, which is presumably maybe at some point going faster than light, and then there's also the concept of the cosmic microwave background, which is kind of like the revenant light from The Big Bang exactly. And so the basic concept to understand is that as we look further and further away, we're seeing things that are older and older. We're looking back in time, and that's just because it takes time for light to get to us from Earth. So we're looking at a distant star that's really far away. We're not seeing it as it is today. We're seeing it as it was when that light left it, and it doesn't look like that today, and it's probably in a different location today. And so as we look further away, we see further back in time, which is actually super awesome and really useful for doing science because we get to see the history of the universe, not just the way it looks today. Right. Yeah, And the whole reason is that light takes a while to get two places. Right, Like, light isn't infinitely fast. It has the speed of light and it's a it's limited, and so space is so big that there's still stuff like coming at us, like coming at us that started maybe billions and billions of years ago. That's right. There are f photons arriving today that left their location billions of years ago and they are just now arriving. You can imagine, like our past light cone. You know, things that are closer can have left more recently and be arriving right now, and things that were really far away the light had to leave a long time ago in order to reach us right now. But those two photons can be arriving at the same moment from different locations and also different times in the past. Yeah, and it's sort of coming at us from all directions, which is which makes it more of a bubble, right than a cone kind of right, it's more of like a bubble around us, which is as far as we can see, because anything further the light just hasn't reached us. Yeah. In one dimensions, it would be like a light triangle, and two dimensions would be like a light cone. But you're right, in three dimensions, it's sort of harder to imagine. It's like a conoid. It would be the geometrical term. I think you need a superpower just to pronounce that. There. And so as we look further back in time, we're looking further into the past, and so we can see, for example, how Gala seas formed. We can see things that happened a billion years after the Big Bang, we can see things that happened five million years after the Big Bang. We can keep looking further and further back in time, right, And so there's this sort of bubble around us of things we can see. But also at the same time, the universe is expanding, so the bubble and the things in it are sort of flying away from us, or at least getting stretched away from us, which is kind of makes it tricky, right, It does make it tricky. The whole thing is pretty complicated and hard to hold in your head. First, let's imagine the universe was not expanding. Then, you know, the bubble we could see would be growing as time went on, and we have no problem seeing the cosmic marcrowave background. We could see things before structure formed. Right, You don't have to see a galaxy in order to see stuff. You just need to see light. So the cosmic microwave background is light from the first plasma before structure was formed. When the universe became transparent. We can't really see before that because the universe was opaque, but we can see past the earliest galaxies all the way to the cosmic microwave background radiation. Right, So that's if the universe was not expanding. Now Jeff says, well, the universe is expanding, and it's expanding fast in the light, which means some parts of the universe we will never see. And he's right. There are things that are so distant past, like sixty five billion light years, where the light will never reach us because the universe is expanding. As we'd like to say, you know, if Hussain Bolt is running towards you and somebody's laying track in front of him faster than he's running, he's never going to get to you. So there are photons moving at us, but they're moving through parts of the universe that are receding fast in the speed of light, so they will never reach us. Right. It's like we can see this bubble around us, but there's also sort of another bubble that's maybe bigger than that of stuff we haven't seen yet. And then we'll also never see because at the same time that we're seeing this bubble, space is expanding, and so there's maybe stuff out there beyond the bubble we can see that may we'll never see, right, because it's moving it too fast. That's right. The current edge of the observable universe is forty six billion light years away, but there's another edge sixty three billion light years away, and stuff beyond that we will never see, Like, it doesn't matter how long you wait, we will never see it because the universe is expanding so fast that those photons will always be moving through space that's moving away from us faster than the speed of light, and so we would just never see it, assuming, of course, the current cosmological model is correct and that expansion continues in the same way that it does. But then Jeff's question is, so, then how is it possible to see the CNB If there are parts of the universe that are moving away from us so fast, we'll never see them, right, Yeah, that's kind of mind blowing to think about. Like, at sixty five billion light years, there's like a son right there that's shining and it's throwing a photon at us, but that photon is like sort of fighting against the stretching of space and just will never get to us. That's right. It's moving through its space at the speed of light, but the distance between us and that photon is actually increasing. Right, The proper stance between us and that photon is growing even though it's moving through space towards us, right, because space in front of it is expanding. It's like there's news space growing between us and that photon rate that's higher than three hundred million meters per second. Right. And if we were relying on seeing light from the CNB that came from super far away cosmic marketway background plasma, then Jeff is right, we would never be able to see it. What we are seeing when we look at the CNB is not light that was emitted from that far away. It was actually emitted from pretty close to us. It's just taken forever to get here because the universe has expanded while those photons fly through the universe. Right. I think maybe what Jeff is thinking is that, you know, there is a background of like light that came from the Big Bang, And you know the word background means like it's in the back, right, So he's probably manna be thinking that this cosmic background comes from like way further out, like since the further out we look, the further back in time we look. He's thinking maybe the source of this light is like the you know, the basically the background of the universe, and so he's wondering, like, if the background is moving away from us faster than light, then how can that background get to us? But you're saying, I think, is that it's not really like in the back, it's like everywhere. It is, in fact, everywhere the CNB was admitted everywhere. There's a patch of the universe where we are right now. There used to be plasma right here, and it emitted CNB light, and that CNB light is flying away from us, and it's been flying away from us fo the whole universe, and it's now almost forty six billion light years away right, not exactly forty six billion light years, because it was admitted a little bit after the universe started, like you know, a few hundred thousand light years. And similarly, the CNB light that we are seeing right now was emitted from stuff which is now almost at the edge of the observable universe, right, so it did have time to get here. It's within the edge of the observable universe. Interestingly, though, when it admitted it, it was much much closer, like it was probably only a few tens of millions of light years away when it emitted that light. But the universe has been expanding so much that took thirteen billion years to cross what was originally forty two million light years, right. The same mystery for the stars that are at that business, right, like the library getting from the edge of the servile universe, is from stars that they used to be closer to us. Exactly. So the patch of the universe which now occupies like a sphere with radius forty six billion light years, used to be much much smaller. At the universe is expanding rapidly, and so basically we are seeing what used to be a tiny little bubble of the universe. Something which was fifty million light years away from us at the very beginning of the universe is now outside the edge of the observable universe. Will probably never see it because it's all expanded. So the CNB light we're seeing today started out forty two million light years away, has been struggling to get to us for billions of years, and has now just arrived. We see it today, and we think the plasma that admitted it that stuff is now forty six billion light years away, right. I think that maybe the key point here is that the cosmic microwave background was sort of like made everywhere in all directions at the same time, you know, Like it wasn't like one event that flashed and then now the light is getting to us. It's like even where we are right now, like this batch of space that I'm occupying here in my podcast studio, like this space around me generated some microwave background radiation at some point in the past, but now that light has just gone right. It's like it's when when, and in all directions. But the same thing happened all over space, like between here and the observable universe the edge of it. There was stuff being generated at every point. Yeah, And I think a lot of people have a misconception that the universe started as a point and then expanded and at some moment it was this little ball of plasma that admitted that light, and they wonder, like, why is it we can see it right now, and you're write the answer is that that's true. But it wasn't just a little ball. The whole univer verse was filled with this plasma. The big band wasn't just when one spot, it was everywhere, and so everywhere in the universe had these little balls of plasma. And as time goes on, we continue to see the CMB, but we see different slices of it. We see light from different pieces of that infinite universe plasma. Right, I wonder if I have a good analogy, is kind of like a rubber band, Like if you're stretching a rubber band, but also all of the rubber band was emitting light. You would see the light that your patch of space emitted, and you're part of the rubber band, but you also over time be seeing the light those generated over other parts of the rubber band. Yeah, and if you think about what's going to happen in a very very far future, we will always see some CMB, but you know, there is a limit of what fraction of the universe we will see. So eventually the CNB will just get red shifted into invisibility. Like the CNB right now is very long wavelengths compared to the light that was emitted at the time. It used to be a very hot plasma hundreds of thousands of degrees. It used to be you know, very high frequent and see wavelength, and it's gotten red shifted down to very long wavelengths, down to like two point seven degrees Calvin. So that's just going to keep happening. The wavelength is gonna get longer and longer until eventually becomes essentially invisible. Right, And I think what's interesting what you just said is that you know, the cosmic microwave background, then we'll be changing over the next couple of billion years, like the picture of it is gonna wiggle and ripple because it's coming from different parts of the universe each time you take the picture exactly, and so as we look at it it does change that it doesn't change very rapidly. Um. You know, we took the original picture of the CNB thirty years ago, and then we're taking more and more refined pictures of it, and over those time periods it doesn't really change in any significantly observable way. So we are seeing slightly different slices of the universe. But you know, in the way that like a star doesn't change very much when you look at it from one year to the next. On these time scales of twenty thirty years, nothing really is changing. If we keep watching it for millions and billions of years and keep doing astronomy for that long and then we will see different slices of the universe. M M. Yeah, And I think Jeff is right that at some point in the future, like the observable universe is going to reach the point where we can't see anything, including the cosmic microwave background. Right, Like, at some point in the future, um, this cosmic microwave is going to disappear. I think we'll always be able to see some CNB, but it will just red shift away to infinity. There's always going to be some point in the universe where light is just now arriving from wherever it was admitted. And since the CNB was everywhere in the universe, there will always be some CNB whose light is just now arriving. But that's going to get more and more stretched out as time goes on, and eventually you'll disappear, right, let's get stretched into nothingness. Oh yes, it disappear in the sense that the wavelength will reach infinity and therefore it be like essentially unobservable. Like if the CNB has a wavelength of the galaxy, then you need a galaxy size detector to see it, and so yeah, it would be invisible to us MM, so it will sort of disappear, So like if humans had come around, may be a couple of billion years later, whichever alien species comes up a few billion years from now may not maybe even be able to see this kind of baby picture of the universe. Yeah, And whenever I think about that, I realized it's lucky that we live now so we can sort of see this stuff in the universe. It makes me wonder what used to be observable in the universe five billion years ago that now we will never see and couldn't discover. What pictures are we missing? What clues? Will we never get to the deep nature of the universe because we came along fourteen billion years after the party started. Yeah, we missed the cosmic microwave foreground because we got here too late. We procrastinated Daniel in our evolution. We shouldn't have spend so much time in the primordial sludge. Yeah, it was pretty warm and cozy. I gotta say, all right, Well that answers the question for Jeff Um. You're right, the same bee will disappear one day, but not for a while because we are still seeing it and because it was generated by every point in space. All right, let's get into our next question, Um, this one is about gravity, magnetism and the different forces. So we'll get to that, but first let's take a quick break. Al Right, we are answering listener questions. Today. We talked about a great question about the server universe and the cosmic microwave background, and now we have a question here about the forces. And this is kind of what you're referencing before, Daniel, about superheroes based on the different forces, because we have different forces in the universe. Yeah, we have these different forces in the universe, and we don't understand why some of them are stronger than others and some of them are weaker. And we think that maybe in the early universe they might have all been one force that had one strength, but we're not sure. Interesting, we had the Avengers before The Avengers was the prequel. It's sort of like, you know, how the Power Rangers can come together into one superpower Ranger. Uh huh, we think the reverse might have happened in our universe. Interesting, it's a prequel. All right. Well, then let's get to the question. This one is from on God who wonders about gravity and magnetism. Hi, Daniel and Jorge really like your podcast because it teaches so much about physics in space. So I got me. I'm wondering what would happen if gravity was as strong as magnetism would So, if the universe started with gravity being as strong as magnetism, what would happen? Would the universe even start expanding or not? Or were it get even donser somehow? Also, what would happen if right now, if the universe is normal, but then right now gravity all of a sudden becomes as strong as magnetism, where it create mega black holes and then things that are so done that time goes backwards. But the bending of the like cone? What would happen? Thank you very much, good luck with the podcast. Oh man, what an awesome question. Thank you on God you do? You have so much going on in your in your little head. That's amazing. That is a future physicist for sure. Yeah, let's get him practicing the how to say the word physicists as soon as possible. Clearly not a prove requisite, however, for becoming one. So maybe it should be Danny should be pants essential pronunciation, not necessarily. I mean, how are you going to recruit more of you if you can't even say the word. So you're saying we should have more physicists in the world. I'm saying you should have more trained physicists. And how to pronounce your job title. It's all about priorities. Yeah, but their question is pretty interesting, uh, And it's about the forces. So the main question is what if gravity was as strong as magnetism? And so gravity is one force, magnetism is another force. And actually gravity you always say is very weak compared to magnetism. Yeah, gravity is the weakest of the forces by a long shot, like not by a tiny little bit or a factor of ten, but by a factor of ten to the thirties seven. You know, like a billion is ten with twelve zeros in front of it. This is ten with thirty seven zeros in front of it. It's really a huge number. They're just like not even on the same playing field at all. Yeah, Like magnetism is the thirty seven orders of magnitude stronger than gravity, meaning like if you have two things that have mass and electric charge, like the force they feel because of the electric charge is much much higher. Yeah, and you're using electric charge there because you know that magnetism is actually part of a unified idea of electro magnetism. Magnetism by itself isn't really a holistic concept. You need electricity to understand it as well. And that's because from different like frames of reference, the same phenomena will produce electricity or magnetism. So really it's one holistic concept we talk about. And as you say, magnetism is much much stronger than gravity. And you can discover this yourself in your kitchen. You know, you have kitchen magnets on your fridge, right, and they stick to your fridge. They don't fall down, even though the entire mass of the Earth, right, the whole planet is tugging on them. And yet a tiny kitchen magnet can totally resist that because magnetism is that much more powerful than gravity. Yeah, Like the kitchen magnet is being pulled towards the Earth by the whole earth gravity, but it's being pulled up by its magnetic attraction to the fridge. Yeah. I like to think that every time I get up in the morning, I'm beating the whole Earth. That's right. Bananas apparently are more powerful than the Earth. You can defeat its gravity. Yea banana and cereal, they'll get me up in the morning every day, and it beats gravity. And the other forces are also not equal, right. The strong force is a hundred and thirties seven times more powerful than electromagnetism, which is even more powerful than the weak force. But all of those are basically the same compared to gravity, which is almost zero compared to the other forces. And yet gravity is the one that dominates the structure of the universe, right. The nature of the Solar System, the shape of galaxies, all that is because of gravity. And that's because there is a lot of mass in the universe and gravity is very, very patient, and eventually it wins. Yeah. And the main reason, I know we've talked about this before is that for the other forces, they sort of cancel each other out. Like there's a plus you know, a magnetic force and a negative magnetic force, and if you're a plus charge or minus charge, you would feel one of them. But because they're able to cancel, they sort of cancel out generally in the universe. But gravity, it's always attracting. Yeah, Gravity, if you think about in terms of a force rather than the curvature of space time, it's basically just got one kind of charge, right, mass is always positive, and so all it can do is attract the other forces as you say it, positives and negatives, or you know, the strong force has three different kinds of color, but they can be balanced out. You can get things that are effectively neutral. It's impossible to get everything neutral gravitationally, unless you like spread everything out through the universe totally homogeneously. There will always be a gravitational force that tugs on things, so eventually gravity will wait, it will pull everything into a black hole, right. I think we covered this in our book or one of our books, where like if the whole Earth was positively charged and the whole Sun was negatively charged, like we'd be toasts, Like the whole Earth would just fly into the Sun super fast, because that's how strong the electroplanknetic forces. But because you know, we have an equal number of plus and minus force charges here on Earth and almost equal mound in the Sun like to the Earth, the Sun is neutral. It doesn't feel any electromagnetic attraction or repulsion exactly. And the reason is that mostly the universe was formed from neutral stuff because electromagnetism is so strong that charged particles sought each other out to balance each other out early on in the universe, and so the universe neutralized from the point of view of electromagnetism, long before gravity really had anything to say about anything. Yeah, and so I'm guess question is that gravity is weaker than the electromagnetic force. But what if it wasn't, Like, what if it was stronger at the beginning of time? And what would happen if it suddenly got stronger? And now it's a great question, and I love running these sort of mental simulations, like what would the universe look like if the knobs were different? And it's a really important question because let's just think about, like, why are the knobs set the way they are? Is it possible they could have been set differently or not? And so in this case, if gravity was just as strong as electromagnetisms, so we're cranking gravity up by ten to the thirty seven, then the whole universe would look very different from the very beginning. Remember that the structure of the universe that we see now galaxies and stars and planets and all this stuff, took a long time to form because gravity is so weak. So gravity was sort of on the sidelines while the universe was cooling, and all these particles buzzing around positive negative charges. The universe cools and the other forces are sort of in charge. So the strong force, for example, pulls together a bunch of quarks to make them neutral from the strong force point of view. So you get like protons, right, which are neutral from the strong force. And then electromagnetism takes over and it pulls protons and electrons together to make neutral atoms like hydrogen. And then finally, thousands and millions of years later, gravity does its job and clumps those together into stars. Now, if gravity was as strong as electromagnetism, then it would have been active much earlier on. It wouldn't have been waiting while electromagnetism form neutral atoms. It would have started clumping protons together before they even neutralized. You would get these like huge positively charged masses. Well, I guess you have to be clear, Like, it's not like gravity turn on at toping, Like it was always there from the beginning. It was just so weak compared to the electroc bannetic corps that basically the universe sort of egbarded for a long time. Exactly. It was irrelevant for a long time because more powerful forces were on the field. Only when those forces finished doing their jobs could gravity even play in the game, because it was the only thing left on the fee basically, And so if gravity was much much stronger than it would have been relevant earlier on and hydrogen, for example, might not have formed in the same way because gravity would have like tugged all those protons together instead of letting them seek out their electrons. And I don't want to overstate it, as you say, gravity is around, and even though it's weaker than the other forces, it does play a role in the early universe. We can see its effect on like the slashing of the barry on plasma. It just wasn't dominant, right or I wonder if even like neutrons or protons would have formed, like could gravity somehow mess up with the way the quarks like buying together could potentially if it was strong enough. In this scenario, though, gravity is as strong as electromagnetism, which is weaker than the strong force, So then in this scenario the strong force would still be stronger than gravity, so you would still form protons of course, would feel those color forces more strongly than they would feel gravity, so they would still form together. But then if it's the same strength as electromagnetism, then you know, gravity and elect a magnetism would be at a tug of war very early on, and you get very weird structures, So the universe would look totally different. You might get like black holes forming very very early on because gravity would be so powerful. Well, I feel like these physics scenarios never end well for us, Like it's always some crazy universe that comes out of it. It wouldn't end well for us. It would form some other, very different universe. It's hard to imagine what like stable structures would form, what it would look like. It might take trillions of years to develop complexity or only last for millions of years, we don't know, And it might evolve very very different forms of life that we can't even imagine, forms of life which you know would have podcasts and speculate about what the universe would be like if gravity was much weaker. I like our podcast better there, but I think I think maybe the main question here is like would you even see structure in this universe or would it all just immediately or very early on, just become all black holes Because if gravity is stronger than write things things, blacks are easier to make, black holes are easier to make. Although to make a black hole you need a lot of mass. And so one question is like, are you gonna get a lot of small clumps or is gravity gonna gather things together into a big clump. Because in the early universe, you know, things are very spread out, very smooth, and you have these micro fluctuations, these slight over densities that let you form structure. Now in this scenario, gravity is much much more powerful, so those over densities form structure much more quickly. But it's not clear to me whether you get a lot of little black holes or a bunch of really big black holes, or if you might just get things like neutron stars. Right, well, but if Grouty was thirty seven times stronger, like those neutron stars will probably become black holes much more quickly. That's right. Neutron stars in our universe wouldn't survive in that universe. But you might get like smaller objects which much less gravity there are still stable somehow, you know, the strong force could resist the force of gravity. In smaller scales, you might get like neutron stars the size of your hand instead of ten kilometers wide, for example. It's really hard to predict because we can't really calculate things using the strong force very well. It's too strong, it's too powerful, it's too chaotic, and so these kind of simulations are very hard to do. All right, Well, then the other part of the question is, like, what if gravity suddenly became stronger? Now, Like what if on Gut went to the control room of the universe and flipped the switch and suddenly we are sitting here, but then suddenly gravity is much stronger. On God, please do not do that. You would be like the double Fanos because everybody you know would die instantly if that happened. Oh my goodness, really straight to death. Well, imagine you're standing on Earth and all of a sudden gravity becomes ten to the thirty seven times more powerful, right, It would pulverize you. The tidal forces from Earth would tear you apart, you would get squished to the surface. You would just not survive. So you're saying Fantasy should have been a physicist, because otherwise he would have known what to do to do to be a little more fitting exactly, and not only would you not vibe, but most of the structures we know in the universe would collapse very very quickly, because you know, what we have today is a balance between gravity and the other forces. The reason the Earth doesn't collapse a new black hole is because it's internal tensile strength of the materials from the electromagnetic bonds are strong enough to prevent that. And the reason the Sun hasn't collapsed into a black hole is because it's powered by fusion, which is preventing its collapse. Now suddenly you're changing half of that equation. Gravity is much much stronger. Everything is going to collapse very very quickly. So the hearts of stars, for example, will instantly become super duper hot because the gravitational pressure. Basically every Sun goes supernova instantly. Well, the whole universe just goes up in a big explosion kind of and emplosion at the same time, like with the Earth, the Earth suddenly become a black hole. Yeah, the Earth becomes a black hole. The Sun goes supernova and leaves behind a black hole, and then you know, the eventual future of our universe we imagine is things driping further apart. But getting pulled together into black holes. And so basically this just speeds that up and turns everything into a black hole much much sooner than it otherwise would. Right, But then the universe is still expanding, So the gravity bring everything together or would the universe continue to expand. The universe would continue to expand we think that dark energy is not a function of the strength of gravity. But you know, there's a balance between dark energy and gravity. Dark energy is pulling the universe apart, and gravity is pulling stuff together. And currently that balance is at the level of like galaxy clusters. We think that gravity wins at the level of galaxy clusters. It holds that stuff together and prevents it from getting pulled apart by dark energy and anything further away, dark energy is winning. Now, if you make gravity much much stronger, then dark energy is still gonna win at some distances, but gravity is gonna win at much bigger things than it did before. So it's going to pull together superclusters and clusters of superclusters, and so you get these really big monster black holes that would contain like, you know, maybe all the stuff in our current observable universe. Yeah, I get called them mega black hole, which is a cool word. It is a super cool word. It's a mega cool word. It's make a cool world. There you go from a mega physicist. Alright, well, I think that answers the question. Things would be really different, right. The universe would have still formed, right, You would still get the Big Bang because that expansion is not depending on gravity like you said. But um, I guess the universe would have just a lot more black holes exactly. If gravity was much more powerful early on, you get very different structures and early black hole formation. If gravity suddenly turned on to be very powerful today, you would get in in supernova and then a lot of black holes. So I got pleased. Don't press that button, at least not yet. You know exactly. I know it's tempting. It's the big red button. You want to press it. The please take a step back, take a step back. Alright, Well, we have one more question here, and it's about things disappearing from space, from the universe. So let's get into that. But first let's take another quick break. We are answering questions from listeners, and our last question here is from Keith from Cleveland, who is wondering if things are going to disappear in the universe at some point. Hi, Daniel and Jorge. This is Keith from Cleveland. I love the podcast and I'm amazed at how much time you spend answering random listener questions. I don't know how Daniel has time left to be a working physicist and have an actual life outside of podcasting and question answering, But I'm going to add to that burden anyways by asking questions. And that is, have we been observing deep enough into space for a long enough time that something we used to be able to see has receded to a point where it can no longer be seen due to the expansion of the universe. For example, is our galaxy that we detected, say by, that has since disappeared for from our view because it is no longer within our hubble volume, and thus that galaxy's photons will now never reach us. Do we know of such an object? And if not, how long do we need to wait between observing a very distant object and it disappearing forever? Thanks so much and keep up the great work all right. Thank you. Keith from Cleveland. That's a little bit hard to say, Keith from Cleveland. I wonder if he became a physicists really extra hard to pronounce. This is his Keith from Cleveland. Yeah, but he asked a really cool question about the nature of the universe and what we can see in it. He also has a great question about the nature of Daniel. Daniel, how do you find at the time to do all everything you do? Time dilation? You know, you move fast enough and clocks go slow? Interesting? Interesting? Or do you get close to a black hole? Right? Is that great? Do you have one in your house? But then I would slow down and the rest of the universe would speed up, So then you need to put the rest of the universe near a black hole while you get your work done. So I see, maybe have a white hole in your house. You are Oh, you aren't called whitesn you figured it out. I am Carlott Holmes Elementary. But not to answer you keeps question. I am still a working physicist. I'm doing data analysis from the Large Agon Collider. I got undergrads and grad students and post docs working with me, and we're just having a lot of fun answering questions about the universe. Yeah. Yeah, you're still working as a physicist. You're just not pronouncing it as well as he could not part of the job. As far as I understand, you don't listen on your resume can pronounce my job title, Joe is. I can't even really spell it. There's so many scenes and asses in it. I get it wrong every single time. Do you spell it like a psychic baby? Yeah, it's like trying to spell the word license. It's like where does that see you go? And a good thing. I don't need a physics license because I couldn't spell either world my goodness or that you're a real doctor too, you'd be a physicians physicist licensee. Al Right, Well, this question was it sort of related to what we're talking about before, the idea that there are parts of space that we can see now and there are parts of space that we maybe we will never see because the universe is expanding faster and faster, And I think he's is asking like, have we gotten to that point yet, Like have we noticed that there are things we can't see anymore? Yeah, it's a really interesting question. You right, he's asking about whether things are falling off the edge of the observable universe. And first of all, he's right that things will fall off the edge of the observable universe. And that's because space is expanding faster than light, right, so space is stretching out right, Well, the observable universe expands that a light year per year. Space itself is expanding faster than that, and so there are things that are moving into parts of the universe that are expanding faster than the speed of light, where their photons will no longer ever reach us. So there are things falling off the edge of the observable universe. It's like, you know, somebody stretching out the fabric faster than we're looking at it, and so we're seeing a smaller and smaller fraction of the stuff in the universe. Well, but it's not sort of like alling off. It's more like the observable universe is growing, but it's just not there are things that are outpacing it, or they're running away from us faster than that bubble is expanding. Yeah, they're not falling off from the edge into like the mouth of dragons or something like that. We think there probably is still space out there for this stuff to be in, but it's sort of disappearing from our view. So you're right, the expansion is outpacing the speed of line, right, And it's not like it's they're falling out of our view. It's just that they never were in our view and they never will. Well, there's things in different categories. There's stuff that was observable and in the future will not be observable, things that sort of move out of the observable universe. There are things which started out not observable, and we're in parts of space that we're expanding faster than the speed of light and then briefly are observable and then fall out. And then there are things that never will be observable, things that, no matter how much time passes, photons from them will never reach us. Oh, you just blew my mind a little bit. That was like four categories of things. Let's let's maybe take one out a time. So there are our silver universe is expanding, there's stats of the stuff we can see for sure. We talked about before earlier in this episode. How there's things like out there beyond sixty five billion light years away that will never see because space is expanding and so it will never like our our silver universe will never catch up to that, right, that's right. It's sixty three billion light years in radius. Things further than that, the recession velocity is greater than the speed of light and always will be, and so those photons will never reach us because they'll always be in parts of space where the recession velocity is greater than the speed of light. So there are distance to us will always be getting larger, even though they're technically moving towards us through their space. Right. And when you say always, you mean as long as the universe keeps expanding, right, that's right. And this is assuming the current cosmological model and that the expansion continues in the way that it has, which is fascinating, you know, because there was very early expansion inflation the first few moments of the universe, and then there's late time expansion, this time around eight billion years after the universe started, when they started accelerating again, the sort of two modes of expansion. And what we're doing now is we're assuming that that recent expansion in the last few billion years just sort of continues forever. But we don't know, right, it could be different. It could be that the future is is something else, right, But as far as we know, it seems like there's stuff we can see stuff we will never see. And then very interestingly, he said, there are two kinds of things that we can see now but that we won't see in the future. So what are those two things? So one is stuff that has been in our observable universe, but eventually we'll fall out of our observable universe because it's moving within space. Well, because space is expanding. You know, things for example, that we're between us and forty two million light years away, very very early on in the universe, like around the CMB time. That's stuff we can see right now. Oh, I see you're saying. I would have thought like once we see something like we can see it forever. No, So if you go back to the very beginning, right T equal zero, technically we could see nothing, right, so we couldn't see any part of the observable universe was a sphere of zero volume. Then as time goes on, that expands and we start to be able to see things in the universe, right, and so things enter the observable universe. Not everything is going to enter that however, right there's still things so far away that they will never enter the observable universe because at the same time, space is expanding, so you know, you have this race between the observable universe, which is growing at one light year per year, and space expanding, which is tugging things away from us. So in the very beginning, nothing's in the observable universe. Then as time goes on, some things come into the observable universe and we can see them, though not everything. There's some things that will never enter the observable universe. But the stuff that falls into the observable universe that comes into the observa universe, so we can see it. Eventually, also it will leave because space is expanding fast in the speed of light, so that will win and eventually everything will get pulled out out of our universe. And even though technically the observing universe will be large, will essentially be nothing in it anymore. Right, Well, I think, maybe just to be clear, like the space within the observable universe right now, it's not expanding faster than the speed of light, but it's accelerating all the time, and space is stretching faster and faster. So I think what you're saying is that eventually the space within the observable universe. That stuff is gradually going to be going faster than the speed of light, and then at some point it's gonna you know, catch up to the observable universe and even pass it, in which case we won't be able to see it. Ye, So the bubble that we can see keeps growing, but stuff gets accelerated away from us faster than that bubble keeps growing, and so eventually everything sort of falls out of our I like to say falls out, but you're right, it's not like tripping over the edge. It's outpacing the growth of that bubble. I feel like it's it's a very exciting race. It's like, you know, the observable universe was winning, but then the expansion was winning, but then that one was losing. And there's some people caught in some stars in the middle that are unfortunately going to be winning but then losing. And it's a pretty pretty dramatic story. It's a pretty dramatic story. And you think about an individual thing, it starts out invisible, right, and essentially you can think about that is like having infinite red shift. Red shift in infinity is totally invisible. So things that are going to be in our observa universe, start out an infinite red shift, and then they come into our observa universe, and at some point in time they reach like their minimum red shift, and then they turn around and they start to grow their redshift again as the universe acceleration takes over and they go back to infinite redshift. So everything sort of starts in infinity, comes to a minimum redshift, and then goes to infinite red shift. Some things are always an infinite redshift and will never see them, those things past our eventual particle horizon. Well, I think keith question though, is like has that started to happen? Right? Like, has stuff within our absorbable universe started to accelerate faster than the speed of light? Because it's possible that it hasn't started right. Well, there's always something right at the edge. There's something that is falling off. Right, Since the universe started accelerating about eight billion years ago, things that are right there at the edge started to lose that race. So there's always something that's passing that threshold, but but not necessarily right. It could have been right because the universe's expressed out and it could be like like right, now, it could be that the observerable universe it's expanding at the speed of light. But it could be that maybe the expansion up to the point hasn't reached that right. Well, remember that the recession velocity is linear, that's hubbled laws. So things that are close to us are not moving away from us that fast, And as you go further and further away, things are moving away from us faster and faster, and that's linear. So as you go far enough away, there's always something that's moving away from us faster than the speed of light. Yes, but that thing could be outside of our observable universe right now, or it could be inside of our observable universe. Right If it's outside the observable universe, then right now we can see everything. But eventually it's going to catch up. So things are moving away from as faster as they're more distant. Currently, in order to be moving away from us faster than the speed of light, you only need to be about fifteen billion light years away, So most of the observable universe is moving away from us faster than the speed of light. Oh. Interesting, So there are things that are falling out of our view, but in the past, there wasn't, but now there is. I think there are always things that are falling out of our view if the universe is expanding and accelerating at the same rate. But wasn't the universe expanding slower before? Yeah, the expansion has been accelerating exactly. So now there are things falling out of the edge of our durable universe or getting outpaced by the expansion. I think is your phrase, which I think is better interesting. Alright, So Keith was right these I mean he was asking when that's going to happen, and you're saying it's already happened. We're losing the universe. Yeah, And Keith was asking whether we've seen something disappear, which is a really cool question and similar to your question before about like seeing the CMB change. So if you're like looking at an object that you know is really far away now, right, And remember that when we're talking about seeing an object that's really far away, there's a subtlety here. If we say something that we're seeing is forty six billion light years away, we mean that's where it is right now, right, So we're seeing light from it that was admitted when that object was closer to us, but now where it is is forty six billion light years away. That's when we mean when we say the edge of the observable universe. Right, we're not seeing that stuff today. We're seeing it from when it was actually closer from where it was when it sent us a photon. Anyway, we are looking at stuff at the edge of the observd a universe. And so for example, there's a galaxy people have looked at that might be the most distant object. You know, the CNB is older and more distant. But this is an object near the edge of the observable universe. It's called g n Z eleven and it was a galaxy formed about four hundred million years after the Big Bang. If you look at the pictures of it, it just sort of looks like a blob that the James Webb Space Telescope. Of course, we'll get very very crisp pictures of this object and help us understand like the early universe and galaxy formation. So this is a candidate for the kind of thing we expect to disappear from our universe because it's very close to the edge. Right, interesting, you know, but I guess you're saying that it's not gonna like blink out at some point where it's not going to blink out in the space of ten years. It's gonna slowly red shift into sort of blackness, right. Exactly. The reason the James Webb is a good telescope to look at it is because its wavelengths are already really red shifted into the I, R and two infrared wavelengths, and as the time goes on, it's just going to gradually get more and more red shifted until it gets to red shift of infinity. So you're right, it's not going to just disappear one day. It's gonna gradually get redder and redder. It's not going to be very dramatic, unfortunately, and it's gonna take a long time to really even notice any differences. These things take cosmological time periods to change, not days or weeks or years. Kase, just watch what you eat and you might live long enough to see it disappear. But it sort of makes me a little sad. I feel like you're telling me that we've already started to, you know, see less of the universe, like our view of the universe, like as has already started to disappear. Does that mean that, like what we see today is the most we'll see of the universe. Ever, while there are things disappearing, there are also things that we have not yet seen that we will see. Things that have been flying through the universe the whole history of the universe and have not yet arrived. But they will arrive because right now they're flying through space that's not moving away from us faster than the speed of light. They've made it inside the hubble radius, and they will eventually reach us. So, for example, there are things that are sixty three billion light years away the very first flashes they sent in the very early universe. Those will eventually reach us. Nothing else afterwards that they send will ever reach us, right so they'll very briefly dip into our observable universe at the very end of time. So there are some things where the light is still on its way that will reach us. But there are also things that right now there are ready disappearing from the universe. So every photon as it passes through the universe sort of passes through a different universe because space is expanding, and that expansion is changing with time. So photons that left a long time ago have had a chance to make it within the sphere that's no longer expanding faster than the speed of light, so they will eventually get here, although later photons from the same super distant objects won't get here. All right, Well, I think the answer for Keith is that things have started disappearing now, or they they are starting to disappear, but it might be a little bit before we stopped getting new things into our field of view. Like, we haven't peaked yet in terms of our view of the universe, but we will something That's right, the most distant thing we see will be sixty three billion night years away. We haven't yet seen that. We will see it very briefly at the end of time, and we will never see anything more distant than that. At the same time, there are some things which are closer, which spend more time in our abservable universe, but are already being outpaced by the accelerating expansion in the universe. Unfortunately, they don't blink out dramatically, They just sort of read shift away. All right, Well, um, stay tuned. I guess until the end of time we'll find out the answer that hopefully we'll be making this podcast until the end of time. Hopefully you'll learn how to pronounce the word physicists by then. That will take two or three universes, I think, Yeah, maybe in the next universe. You'll flick it out. In the next universe. All right, I'll put it on my two do list for next universe. That's right, it's stay tuned for the sequel. Uh the universe. The dark matter returns correctly pronounced with pants on. Alright, 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 I Heart Radio. For more podcast from my Heart Radio, visit the I Heart Radio app, Apple Podcasts, or wherever you listen to your favorite show. M