Did the Big Bang REALLY Happen¿

Now, when we look up at the stars, we all wonder, where did all of this come from? And by all of this, I mean the entire universe. Now, I know that you know that the currently accepted theory is called the Big Bang Theory, and I wanna talk about it in detail in this video. But before I get there, I know that a lot of people out there just cannot accept this theory, because a lot of times people think that scientists just put forward these ideas without really any real evidence. So before going into detail here, I want to give you the top few lines of evidence that the Big Bang Theory is not just an idea, it's what fits with what we actually see out in the universe. And then after we do that, we'll talk about the process of the Big Bang and the theory in detail. Now, first off, we have something called Hubble's Law. So when telescopes got big enough to actually look out into the universe and observe galaxies far away from our own galaxy, we can figure out by looking at the light which way the galaxy is moving. And it turns out that no matter what direction you look, that way, that way, or in the Southern Hemisphere, in a totally different direction in the sky, all of the galaxies are basically moving away. And not only are they moving away from our galaxy, the rate or the speed at which they're moving away is related to how far away they are from us. So if you wind the clock backward, then you come to an inescapable conclusion that all of these galaxies at one point in the past must have been right on top of each other. So that's an observable thing that we can see that kind of goes in line with the idea of the Big Bang, which is an origin where everything was very hot and dense and then some sort of rapid expansion event happened. You can think of it as sort of an explosion, if you want to, that created the universe. Now that, by itself, is already a pretty mind-blowing idea that everything is moving away from us and there must have been some origin point where everything was in the distant past. But not only that, when we began to build microwave antennas and start to look at the sky, not in the visible light that you see with your eyes, but with microwaves, what we find, even today, is that when you look at any direction in the sky, up, down, left, right, Southern Hemisphere, or Northern Hemisphere, you see a very constant cosmic microwave background radiation in all directions. And it turns out that when you wind back the clock and go through the math that describes the Big Bang theory, it must have been a hot, dense point and then some sort of rapid expansion or explosion. When you go through the math and see as time and space expands after the Big Bang, the hot radiation that was there at the beginning would be stretched out and cooled off. And after the age of the universe that we have calculated to be, the currently accepted age of the universe, that hot radiation must have been cooled off and guess what? The calculated frequencies that we get for that Big Bang energy, as it has cooled off through expansion of the universe, turns out to be right at a color temperature of about 2.7 Kelvin. In other words, we look around the sky and we see the afterglow of the Big Bang itself, because no matter which way we look, we see the exact correct frequency of radiation that we calculate if everything started at a hot, dense point, exploded, and then all of that radiation cools off as the universe expands. Now, if that's not enough, the third most convincing line of evidence that the Big Bang theory is something that agrees with observations is that, again, it's not just an idea, it's a mathematical theory that predicts what the relative abundances must have been in the early universe for when hydrogen was created, the lightest element, and then when helium was created. Because remember, before the elements coalesced in the Big Bang model, it was just pure energy. And then when things cooled off, atoms actually then formed, and then much, much later, stars formed. So we look around the universe and we see X amount of hydrogen and X amount of helium in all of these ratios around the universe and lithium and other elements, and those ratios exactly agree with the calculations that you get when you go through the Big Bang model and use its predictive power to calculate those ratios. So big picture, the Big Bang model of the universe is not just an idea that people just made up one day. It agrees with what we see in the universe. There are many more lines of evidence than this, but the most compelling is that we see all of the galaxies racing away from us and at a certain rate that's proportional to their distance, and that we also see a uniform, constant microwave background radiation that has a frequency that exactly agrees with what we would see if a hot, dense explosion happened and then cooled off as the universe aged. And when we look around to the elements in the universe, we see the exact ratios of hydrogen and helium and lithium that we calculate using the Big Bang model of the universe. And if I do my job right, almost every single sentence should be literally a wow moment for all of us. I like to talk about exactly what the Big Bang is, what the common misconceptions are, what the nature of time is, and really, really fascinating to me, the so-called fine-tuning of our universe for life. And so today, in a nutshell, I'd like to walk you through a recipe, so to speak, as if you were running through a cookbook for a recipe for creating the universe from scratch, starting from absolutely nothing and ending up with you, with me, with all of the planets, all of the stars, and everything in the entire universe. So before we can actually start our universal cooking show to create a universe, we need to grasp just how small things can actually get. And I mean really, really, really small. Let's start with something that might seem tiny, but is actually enormous by the standards of the Big Bang singularity, and that is a proton. No matter how hard you try, no matter how long you sit and think about it, you will never be able to wrap your head around just how tiny a proton is. And I don't mean just you, I mean me as well. I want you to think about a dot of ink, like maybe the period at the end of a sentence printed in a book. So that's a minuscule little speck. You could probably fit about 500 billion protons inside that tiny dot, and that's more than the number of seconds in half a million years. But here's the thing. A proton is absolutely, positively, literally, gigantic compared to where our story begins with the birth of the universe. So to start our universe, so to speak, we need to think even smaller than a proton. Take one of those impossibly tiny protons that we were just talking about and shrink it down to a billionth of its size. It's already incomprehensible, but when you shrink it down to a billionth of a size, it's totally beyond what I'm capable of visualizing. But give it a shot. Now, you're getting closer to the scale that we need. I want you to pack about an ounce of matter into that inconceivably tiny space, making the density of that dot totally and utterly incomprehensible, and we're ready to begin. But wait, we're getting ahead of ourselves just a little bit. Let's pause for just a second and talk about time for a moment. I know that all of us have pondered the concept of time at one point or another. When we discuss the Big Bang, people often ask, what came before the Big Bang? So it's a perfectly logical question, but it contains a hidden assumption that there was actually a before to begin with. You see, time itself began with the Big Bang. There was no before because time didn't even exist until the Big Bang actually happened. So I know what you're thinking. It's making your brain hurt already. That's part of talking about that stuff. It's bigger than any of us can really truly comprehend. Part of the reason this is so hard for us to visualize or think about is because we're all taught that there's this thing called space, and it's everywhere. And all of the matter, like the Earth, the planets, the coffee cup, whatever, it's stuff inside of this scaffolding called space. And so we have been born and interacted with the world thinking of space as this thing that just exists everywhere. And the same thing about time. You become aware of time when you're a little child and you learn how to tell time, and so it's this thing that's just always going on in the background. Now, along comes Einstein later, and through the theory of relativity, we now know that time is not a concept that is just independent of everything else. Time can tick at different rates depending on how you're moving, depending on how much gravity is around. That is a fact. We know it's a fact because we can build devices like atomic clocks and such that depend on that, on understanding that to actually function. But also space is actually not a rigid thing either. It can change depending on gravity, can warp space and time, and your state of motion and other things as well. But still, even though you might know that, it's really hard for us to shake the concept that time and space are not always everywhere. But you have to try to use your imagination, right? At the Big Bang, if the Big Bang actually happened according to the way the theory is set up, and again, I presented several lines of evidence, which was not exhaustive, that it agrees with observational things that we see in the universe around us. But if the Big Bang happens according to the existing theory that before the Big Bang, there was no time at all. There was nothing ticking, right? There was no change in entropy or anything like that going on before the Big Bang. There was also no space, right? Now, it's not totally true that we understand everything at that exact moment of the singularity. So we don't know if time didn't exist at all or if it manifested in some totally different manifestation that has no relevance or nothing that we've seen before. But the concept of time that we think of as this ticking that just keeps going on and that governs how things change, how things break down, basically the increase of entropy, that thing did not exist before the Big Bang. So asking what happened before the Big Bang or what was present before the Big Bang, it literally makes no sense at all. I want you to think about it this way. Asking what came before the Big Bang is kind of like asking what is north of the North Pole? The question itself doesn't make any sense if you've run out of north. In other words, if you go all the way to the North Pole and then you ask yourself, well, what is north of the North Pole? In any direction you go, if you're standing on the North Pole, then there is no north of that because if you deviate from north, then you've already gotten to the maximally north position. And if you go in any direction, you'd have to turn around and go north again. So asking yourself what is north of the North Pole is a nonsensical question. Asking what happened before the Big Bang or what space and time looked like before the Big Bang makes no sense because it did not exist before the Big Bang. Here's another analogy I've never heard anybody else use, so I'll just tell you and you can decide to discard it or embrace it. Think about a pot of water that you put on the stove and you add heat to the bottom, like a flame from a stove. And it's boiling, right? But before it boils, it's just really, really hot, but it hasn't actually reached a boil yet. If you look down in the bottom of the pot, right before it starts to boil, you will probably see some bubbles on the bottom of the pan that are sticking to the bottom of the pan. They begin to form as these little bubbles all over the bottom of the pan. And as you add more heat or if you just hit the side of the pan, they'll be dislodged and they'll float up and eventually with more and more heat, you reach a rolling boil. But I want you to think about those little bubbles which have formed on the bottom of the pan as I'm adding heat. You can think of those little bitty bubbles as almost like a big bang just about to happen, right? The singularity, so to speak. It's not a great analogy because the singularity is different, but it's something that is there and before you added the heat, it wasn't there at all. And then as you added more heat, it dislodged from the bottom, rapidly expanded and then rose up to the top. You can think of that as like the expansion of the universe, sort of. So a lot of scientists think about the big bang as being kind of like a phase change. So the analogy I'm giving you is not too far off. I mean, obviously it's not right, but if I were to ask you, if one of those bubbles was a universe and by the way, if there's a bubble right next door, maybe that's an adjacent universe totally and independently separated from the first universe. So you could have two universes right next to each other, like the multiverse idea, okay? But if I were to ask you, at the moment that that bubble was there, ready to pop off, and I were to ask somebody living in there, what was this place like? What existed before the big bang? And then they would say, well, there was no before. Why? Because before I added the heat, there was no bubble at all. There was no agitation. There was no big bang. There was nothing. The concept inside of that bubble, of that universe existing, did not appear in that region at all until the big bang event, whatever it was, happened. And so just think about that. And so this is a little bit philosophical, but the idea of space and time did not even come into being until the big bang actually happened. So you can think about the big bang as the moment the stopwatch started moving. I want you to think about what happened when that watch, so to speak, started ticking. Now, when the first fraction of a second in the big bang model, and I'm talking about timeframes so short that they make a lightning bolt look like it's moving through molasses. In other words, really short intervals in time, something really extraordinary happened according to the big bang model. The universe underwent what we call cosmic inflation. Basically, most people think that the big bang is just something that, boom, explosion, and happens. Well, actually, it's a lot more nuanced than that to get the theory to match what we actually see in everyday life. So in the earliest stages, the first few fractions of a second, it underwent rapid inflation. And this is where Alan Guth's inflation theory comes in. In 1979, Guth proposed that in the first 10 to the minus 34 seconds, that's an incomprehensible fraction of a second, 10 to the minus 34 seconds is a decimal point followed by 33 zeros and then a one, the universe underwent an expansion that would make a rocket ship look like it's standing totally still. The universe doubled in size every 10 to the minus 37 seconds. Basically, it was this incredibly fast inflationary period, impossible for us to truly comprehend, 10 to the minus 37 seconds, the universe doubling at that rate in that interval. And after the inflationary period happened, everything slowed down, continued to expand, but slowed down compared to the original inflationary period. Now, this inflationary model of the Big Bang primarily addressed what we call the horizon problem and the flatness problem with the original Big Bang theory. Remember, theories are revised when they don't explain observations. So in this case, the universe appears remarkably uniform across super vast distances, despite not having enough time to reach what we call thermal equilibrium according to the standard or original Big Bang model. So the inflationary period rapidly expanded the universe, smoothing out any initial regions or irregularities and explaining this uniformity. Basically, the original Big Bang theory was proposed and then people start studying it. And they say, well, if this is true, then it doesn't really fit with this piece of data. If this is true, then it doesn't really fit with that piece of data. And instead of throwing away the theory, what people do is they make modifications to it and say, well, maybe it was not a uniform expansion. Maybe there was a super rapid period of expansion in the beginning, which then slowed down a little bit. And that was called the horizon problem. Basically, when you look at different regions of the universe, super, super far apart, they appear very, very uniform. They need to be in contact with each other long enough so that everything can be smoothed out. And then after the expansion happens, we get to the uniformity that we actually see in the sky today. And the inflation problem addresses that. Also, in the original Big Bang theory, before inflationary theory was presented, the universe's geometry was calculated to be a curved geometry. Now, what I mean by that is space and time are curved in their relation to each other across the universe. Think of a flat sheet of paper being a flat geometry, but a curved balloon being a curved geometry. Now, it's hard for us to visualize the three-dimensional curvature instead of a two-dimensional curvature. And also, time is curved in there as well, which means the ticking rate can change as you move around the universe as well. But the concept is the same. Visualize a curved sheet of paper or something bent. So the original theory predicted a bent or a curved model of the universe. But actually, observations that we were able to then do showed when we measured different parts of the sky that the actual flatness of the universe is pretty darn flat. It's not very curved at all. And so that was solved, or at least explained, by the inflationary model of the Big Bang Theory. So what was actually happening during this explosive growth? So this is where the four fundamental forces of nature come into play. So today, we know of four distinct forces. Any force that you've ever experienced has been categorized as one of these four. The first one, which is the weakest one, is called gravity, and that keeps the planets orbiting the stars and you planted on the ground and all that stuff. Then you have electromagnetism, which holds atoms together and also give us light because photons are related to electromagnetism. Then we have the strong nuclear force, which binds the atomic nuclei together into atoms. And then we have the weak nuclear force, which helps to govern radioactive decay processes. Four fundamental forces of nature. Now here's one small caveat. You know, gravity is by far the weakest of these forces, even though we kind of think of it as really strong. It's millions of times weaker than any of the others. The question is, is it a real force? So Einstein really showed us that gravity is not a true force. It is just a result of the curvature of space-time. It's a geometric thing. Now in modern particle theory, there is actually a particle that carries the gravitational force, which we call the graviton. And physicists are still wrestling with trying to bring those two ideas together. We still refer to it as a force, even though Einstein says it's more of a geometric thing and not a true force. Particle theories say, yeah, it's a force mediated by something called a graviton, but we've never discovered a graviton as of yet. Just know that some of these ideas are still being worked on. Now back during the early expansion of the universe, it's really fascinating, because in the heat and density of the early universe, which are incomprehensible, these forces, these four forces of nature were calculated or predicted to not be separate at all. The Big Bang Theory predicts that at that point, they were unified into a single super force, so to speak. And as the universe expanded and cooled, these forces separated out, kind of like water freezing into ice or vapor condensing into liquid water, sort of like a phase change for the forces in the universe. So gravity is predicted, according to the model, to have split off first, becoming the weakest, but far more reaching across the universe as the force that we see today that holds galaxies and stars together. Obviously, the holy grail of science is really trying to unify all four of these forces. We see distinct forces, electromagnetism, the strong nuclear force, the weak nuclear force, and gravity. And the theory goes is that maybe those are just different aspects of a single super force, and that when the universe was much smaller and much hotter in the early stages of the Big Bang, there was really only one force. And as everything expanded and cooled, these four forces kind of coalesced, or kind of like phase-changed, for lack of a better word, into the distinct forces that we see today. So people study the Big Bang where the forces are predicted to have been unified to get clues into unifying the four forces. Now, why do people care about a grand unified theory anyway in unifying all of these forces? Well, because if we understand how the forces are cross-linked and how they are related to each other, then we can understand how to manipulate matter and energy, generate power, build spaceships. Pretty much any machine that we have can be built better if we understand the fundamental forces of the universe. So back to the Big Bang expansion. In the first microsecond, the universe was so hot that matter as we know it could not exist at all back then. Instead, it was really just a cosmic soup of quarks and electrons. These are the most fundamental particles that we know of, which are even more fundamental than the atoms that you know about on the periodic table. It wasn't till about three minutes after the Big Bang that the first atomic nuclei could even form at all, mainly hydrogen and helium, with a tiny dash of the third element lithium thrown in. But here's where we hit a puzzle that's been bothering scientists for literally decades. The Big Bang theory predicts that only the lightest elements were created during the initial actual Big Bang expansion. In other words, hydrogen, helium, and a trace of lithium is predicted to be the only elements to have actually been created during the actual initial Big Bang. And these are the first three elements on the periodic table. But as you know, there's like 100 more elements after that that we already know exist. So where did they come from if they didn't come from the Big Bang? I mean, look around you. Your body contains carbon, right? And nitrogen, oxygen, you're breathing it all the time. Dozens of other elements. Your car, your smartphones, they contain metals that are much, much heavier in the silicon transistors and other things that are inside of the microprocessors that you use every day. And if they were not made in the Big Bang itself, where did they come from? Now, the answer quite literally comes from the stars. Now, it's kind of mind-blowing, but every atom of carbon in your body, every oxygen molecule you breathe, every iron atom in your blood, these were all forged in the hearts of dying stars billions of years after the Big Bang. Now, when massive stars explode, as supernova, for instance, they scatter these elements across space. So really, we are quite literally made of stardust. I want you to really sit and think about this. Only hydrogen and helium and a tiny bit of lithium was actually created according to the Big Bang model in the actual Big Bang itself, right? And so what happens is for a long, long time, these elements are attracted gravitationally and they get clumped together. And then eventually when gravity pulls them together and they get big enough, the pressure inside gets so hot and so much pressure that they get fused together into heavier and heavier elements. But when you go through the theory of nucleosynthesis and fusion theory, we know that you really can only get elements up to about iron from nuclear fusion in stars. So the nitrogen and all of these others that we talk about, the oxygen, they were created in the original stars that are long gone because what happens is when a star runs out of fuel, then the pressure inside goes down and then it goes into a very unstable period and very often, depending on its mass, it can explode in a supernova. So the fusion process creates elements up to iron, but actually anything after iron is not made in normal fusion reaction in any star. The only way you get anything after iron is when a star actually explodes. So lots and lots of things that you use every day and smartphones and things have heavier elements in iron, right, all kinds of things. And so all of those must have come from ancient stars that actually exhausted their fuel, exploded, and they formed the heavier elements, which then later coalesced onto our planet to make the heavier elements that we mine out of the ground and use for various things. So think about that. You literally are made of atoms that were inside of stars. Now, I touched on it in the beginning because I wanted to get it out of the way in the very beginning, but I wanna dive into the evidence for all of these ideas a little bit more. How do we know actually that any of this stuff is actually true? I mean, honestly, it sounds totally absurd that everything started from an infinitesimal speck exploding and then creating time and space as it expands. So I wanna talk about one of the most remarkable discoveries in the history of science. I touched on it earlier. I wanna talk about it in a little more detail, and that is the cosmic microwave background radiation. I personally think that this should be taught to every kid in science class in about fourth grade. This is literally the afterglow of the Big Bang explosion itself, and it was first discovered by accident, total accident, in 1964 by Arno Penzias and Robert Wilson. So these two fellows were working at what's called Bell Labs with a sensitive radio antenna, and they kept picking up this persistent background noise, quite literally static, in what they were receiving. And so they were confused. Why is there static in this thing? They checked everything. They actually went and cleaned out the pigeon droppings, which were on their antenna, and they referred to in their scientific papers as white dielectric materials, bird poop, and they checked all of their equipment, but the noise, no matter what they did, would never go away. There was always this background static at a certain frequency. And they did a lot more than this. They actually pointed their antenna at different areas of the sky. They checked it at different times of the year. They tried disassembling, reassembling everything, and no matter what they did, no matter where they pointed it at this certain frequency, they always picked up this background static at a certain frequency in the sky. So what they stumbled upon was the oldest light in the universe. So when the universe was only about 380,000 years old, it cooled enough for electrons to combine with protons, and those formed neutral hydrogen. Suddenly, light could travel freely throughout space, and that light has been traveling ever since, stretched by the expanding universe until it reached us today as microwave radiation. Now, you might say, if you're paying attention, well, wait a minute, you said the first atoms formed a few minutes after the Big Bang, and now you're telling us that the microwave background radiation came from electrons recombining and forming atoms like 300 and something thousand years after the Big Bang. Well, here's what's really going on. In the first few minutes after the Big Bang, the electrons and the protons could very briefly recombine and form the very first atoms, but everything was so hot that those atoms were not truly stable. So we say that those first atoms kind of formed then, but they were, think about a plasma, a soup of charged ions. I mean, they can recombine and then immediately be broken apart again because it's so hot, something else smashes into it and disrupts it. So the first atoms of hydrogen were formed after the first few minutes, but we really say that the first elements of hydrogen that could actually be stable in bulk without immediately breaking down again into electrons and protons, those didn't happen until much later when the universe cooled off about 300 and some change thousand years after the Big Bang. And much like what happens in a laser or even in a regular light bulb, photons are emitted when an electron comes out from far away away from the atom and drops in and goes into a stable orbit around a nucleus. And so whenever that was done, it releases a photon of a known energy. And by the way, we know that the universe is expanding and as the, according to the Big Bang theory, and as the universe expands and that energy that's in there, the photons that were literally created at the moment of the Big Bang, we know what their frequency should have been back then, their energy levels. And so as the universe expands, it stretches the wavelength out because it's not just that the atoms or the energy are exploding inside of space. You got to remember, space itself is getting stretched out and kind of being formed as the explosion happens, so to speak. And so what's happening is the energy that was there during the Big Bang, the photons, their wavelength is being stretched out. And so we know by looking at the sky, what the wavelength of the energy that we see is up there now. And by going and winding the clock backward, we know that that energy is coming from the Big Bang because we know the energy of the photons, the wavelength and the frequency that must have been emitted when the first atoms formed. And so then if that was stretched out over the given age of the universe that we have calculated, we should get exactly the frequency of the microwave background that we can look up and see everywhere. So when we look up and see that, we're looking at the energy that was first released at the Big Bang. So not only do we look everywhere and see the exact correct frequency, the uniform in all directions that we would calculate if the universe came to being exactly as we talked about there, but there's a precise pattern when you look at that sky because the sky has been mapped and we've measured the microwave background very accurately over the years with satellites. And there's temperature variations in that radiation that observe, that matches the observations and the theoretical predictions with remarkable accuracy. It's like finding a fingerprint or something at a crime scene that matches perfectly our suspect. So it's not just like one number over there, it's the precise variation across the sky matches exactly what we would have calculated. Now, as I mentioned before, we have what's called the abundance of the light elements in the universe. So the Big Bang theory predicts that in the first few minutes, the universe should have created a very specific amount of hydrogen that can be calculated according to the Big Bang model. A very precise amount of helium, a very precise amount of lithium, according to the model. And when we look at the oldest, most pristine parts of the universe in the sky, what do we actually find? Exactly these proportions. It's about 75% hydrogen, about 25% helium, and a tiny trace of lithium. It's kind of like discovering that the recipe card matches perfectly with a cake that you randomly find somewhere in a store. And thirdly, as I mentioned before, there's a expansion of the universe first discovered by Edwin Hubble. We actually named the expansion after Edwin Hubble. Every distant galaxy we look at is actually moving away from us. And the farther away that it is from the Earth, which we can measure, the faster it is moving away from us. If you run this cosmic expansion backwards, like rewinding a video or something, everything converges to a single point in the past. And remember, it's time and space that's actually being shrunk down as well because that was created during the expansion. And this observation was actually made before we had all of the other evidence. And it was the first big hint that led to the Big Bang Theory in the first place. The fourth line of evidence for the Big Bang, which is honestly really striking, is what we call the perfect sky problem. Look at any direction in space and the temperature of the cosmic microwave background radiation. It's almost exactly the same in any direction that you point your instrument at. It's varying only by about one part in 100,000. Now this uniformity was a mystery until cosmic inflation theory came along. And when you run the calculations, the inflation theory explains how the regions of space that could have never communicated with each other because they're so far apart in the sky today, they were somehow on top of each other, intermingled when the inflation period happened at the same temperature. And it's like finding out that sort of like two people on opposite sides of the earth somehow wrote exactly the same story without ever actually interacting. But then you figure out that, oh, they were in the same place in 1900 or something, and that's where they chatted about the stories that they were gonna write. So these four pieces of evidence, and there are actually others as well, but these four taken together form an incredibly strong case for the Big Bang Theory. Each one independently, because they're independent measurements, points to the same conclusion. And unlike many other scientific theories, the Big Bang makes very specific prediction that we can actually test and that we actually have tested, predictions that have been confirmed again and again by actual observations. But perhaps the most compelling aspect of all of this stuff is that no other theory has been able to explain all of these observations simultaneously in the same framework for a same alternative theory. And so alternative theories might explain one or two pieces of evidence, but they fall apart when trying to explain everything we see and the totality of everything that we measure when we actually look at the sky. And so the Big Bang Theory not only explains what we observe, but it explains what we have predicted several of these phenomenon before we actually had the technology to observe them. So in other words, we have in many cases predicted what should happen before we even had the instruments. And then later the instruments were invented, pointed at the sky, 10 years happened to measure these things like the galaxy recession or something like this, and then, oh, it matches exactly what the calculation said. So let's talk about the age of the actual universe. Based on multiple lines of evidence, including the cosmic microwave background that we talked about so much, the rate of expansion of the galaxies that we can measure, and the ages of the oldest stars that we can also measure, we now know that the universe is about 13.8 billion years old. But what does that number actually really mean? Now, I can't speak for you, but I think I can visualize 100 years. That's about a human lifetime, roughly. 1,000 years, I can kind of visualize it because that's like roughly 10 human lifetimes, maybe a little bit more, okay? You start getting into hundreds of thousands of years and it starts to get difficult for me. You get to a million years, I kind of comprehend it because it's a nice multiple of 1,000, but it's basically hard for me to figure out. You get to 300 million years and then you get into billions, then suddenly my conception of what it is stops and basically it just becomes a really big number. It's basically impossible for us to understand how long that is, but it's long enough for multiple sets of stars to have coalesced, exhausted their fuel, exploded, made heavy elements, and coalesced again into other planetary bodies and stars. Let's try an alternative way to visualize how old that is. If we actually compress the entire history of the universe into a single year, with the Big Bang actually happening on January 1st, our solar system wouldn't even form until September. Think about that, September. Life on Earth would start in late September. Dinosaurs, which we think about as being so old, they would appear on December 25th of this year and they would go extinct on December 30th of this year. And all of recorded human history, which we also think of as being pretty old, would take place in the last 14 seconds of December 31st. Now stop and actually think about that for a second. If the Big Bang happens on January 1st, then all of human history, the rise and fall of Rome, the building of the pyramids, the invention of language and agriculture and math, and all of the leaders and the wars and all that stuff in this framework, it takes place, all of it, during the last 14 seconds of this year with the Big Bang on January 1st. So we have talked so much about how the universe began, but a question that's been asked for just as long is how will the universe end? Or will the universe actually end? Now scientists used to actually think that there were three main possible fates for our universe when it ends. So the first one is it could expand for a while until gravity causes it to collapse, slow down, and collapse back in on itself. Or it could expand forever, just getting bigger and bigger and bigger. Or it could be perfectly balanced somewhere in the middle where it kind of just slows down and kind of peters out. Now we know, thanks to observations of distant supernovae and also the microwave background radiation detailed studies that the universe is not only expanding, but it's actually accelerating in its expansion. Now if I could do a record scratch, it would be record scratch right now. Nobody should ever expect this to happen. You've got this exploding thing. You would think gravity would slow it down and maybe pull it back in, or maybe it would expand forever or whatever. You would never, ever, ever guess that it would be accelerating. How in the heck is that possible? But that's what we find. They did a multi-year studies, which can only have been done very recently, by the way, with modern instruments and modern computers. And we see that not only is everything moving away from us, which is what I told you from the beginning of the video, but everything is accelerating away from us, going away faster and faster and faster over time. Now the currently accepted idea, which is just an idea and a theory, is that this acceleration is driven by something we call dark energy. And it's one of the biggest mysteries in modern physics that people are studying right now. So theoretically, it makes up about 68% of the universe's energy content, but we don't actually exactly know what it is. It seems to be a property of space itself causing the fabric of the cosmos to stretch faster and faster over gigantic periods in space. So the idea here is that basically the expansion of the universe or the acceleration, if I look around, everything in the room with me, it's not accelerating away from me, right? And the sun is not accelerating away from me. And Jupiter and Saturn are not accelerating away from me. But the dark energy that's fueling the expansion of the universe, it only is really additive over huge distances. So you only notice it over enormous distances, like the distance between galaxies. Something about what empty space is, even though we think of it as being empty, it contains some sort of unseen energy, or maybe it's a property of space itself that fuels this rapid acceleration in the space that we see. So the existence of this dark energy has really profound implications for the fate of our universe, how it might end. So rather than collapsing back on itself, the universe appears like it might just expand forever, accelerating all the time, growing increasingly cold and increasingly empty, which I admit is a little bit of a depressing thought, but that's where we're at. Galaxies will just drift apart until they're no longer visible to each other. Gravity will pull matter together, forming larger and larger black holes, but eventually those will evaporate away through something called Hawking radiation, which is another topic for another day. And basically, since black holes, you can't really see them, the cosmos will become a vast, dark, lonely place and just kind of fade away. But there's another mystery that's equally profound and interesting, the size of the universe itself. So this thing called the observable universe, the part that we can see, it's something like 93 billion light years across, but that's just our cosmic horizon, the limit of what light has had the time to actually reach us since the Big Bang because light travels at a finite speed and the universe is only so old, so we can only see so far. The actual universe could be much, much larger, which is honestly totally impossible for me to actually comprehend. And by the way, if you remember, I told you that there was a flatness problem so that the universe, the geometry of the universe looks remarkably flat where we kind of expect it to be curved. It's possible that the universe is much, much, much bigger than what we can actually see due to the finite time and light speed. And so it might actually be curved on huge distances, but we can only see like a tiny distance, kind of like when you're standing on Earth. You can only see to the horizon, so everything looks flat, but actually the whole planet is curved and you would never know that it is actually curved until you could get above it and start to see the curvature. It's possible that the universe is actually curved on huge scales, but we'll never be able to see anything beyond the horizon that we can see due to the speed of light. Now, there are those that actually also say that our universe is uniquely fine-tuned, that's a word people use, fine-tuning, for matter to exist and for life to exist. So I'd like to take just a second and talk about these so-called cosmic numbers, the six fundamental constants that make our universe possible. And so these aren't just random numbers, they're the cosmic dials, so to speak, that basically have to be set just right for atoms to form and thus for life to form. The first of these six numbers is actually called epsilon, that determines how firmly atomic nuclei actually bind together. And it's set in our universe to about 0.007. If that number were even slightly different, let's say it was 0.0006, the universe would be nothing but hydrogen, no complex elements at all. What if you make it a little big, 0.008, for instance, and all of the hydrogen would have fused into heavier elements billions of years ago, leaving no water and no stars burning today? Seems like that value is perfectly set to exactly what it means to be for us to exist. Then there's the number N. It's the ratio of the electromagnetic force to the gravitational force. It's an enormous number, 10 to the 36, more or less. If it were a little bit smaller, stars would be tiny. They'd be short-lived things burning out before life had a chance to evolve. And so if it were larger, stars would be too cold to spark the nuclear fusion process that actually creates the energy that powers life on the planet. So again, this number seems perfectly suited for atoms and matter and life to exist. Now, there's a third number. It's called omega. It represents the amount of matter in the entire universe if you were to scoop it up and add it all up together. Now, if it were too high, the universe would have collapsed before stars could form due to gravity. And if it were too low, and matter would have spread out too quickly for galaxies to actually form in the first place. The fourth of these numbers is called lambda, the cosmological constant. It's now what we actually call dark energy. It's bizarrely small, 10 to the negative 120th power. And even if it were tiny bit larger, space would expand so fast that galaxies couldn't form at all. And the fact that it is so precisely tiny is one of the biggest puzzles in physics. The fifth number is called Q, and it represents the strength of the cosmic ripples from the early universe. It's about one 100,000th, a very, very tiny fraction. But if Q were even a little bit smaller, the universe would be dark and lifeless with no stars, no galaxies. But if it were larger, space would be dominated by enormous black holes. Lastly, there's a number called D, the number of spatial dimensions in our universe set to three in our current universe, three dimensions. With two dimensions, complex structures like brains couldn't really exist on a flat plane. With four spatial dimensions, orbital systems like solar systems would be totally unstable. So take a moment and think about that. These six numbers had to be exactly what they are, or we wouldn't be here to talk about them. Now on the surface, it kind of seems compelling, right? Because we have these six numbers and they have to be set exactly right, and if they're set wrong, then nothing can exist. But here's the thing, we actually don't know if these numbers can be changed at all. Like we don't know if it's even possible to change omega or any of these other numbers. And we also don't know if changing them, if you can even change them independently. In other words, if you change one, it might automatically be cross-correlated with a bunch of other constants that also change. And we also don't know if these constants, so to speak, are things that kind of fall out of the Big Bang process. Like it's possible, just like during a supernova explosion, the heavier elements are created, and it's difficult to predict exactly how much of every element will be created in that process. It's a little bit random in a way, but we know that those heavier elements are created. It's possible that during the Big Bang process, these constants of nature are related to the Big Bang process itself, and maybe they fall out in a semi-random way after a Big Bang actually happens. Whatever that process is, these constants, so to speak, might fall out of that process in semi-random way that we can't comprehend. Now, this so-called fine-tuning, which I don't really love that title because it leads you to believe that there has to be a tuner that's turning knobs or something, but it's led some people to propose something called the multiverse theory. And that's the idea that our universe is maybe just one of perhaps infinitely many parallel universes separated from one another, but also in existence near each other, each with its own totally different physical laws in each pocket universe. And we exist in this particular universe because the laws that are in this universe, which are semi-random, remember, in this theory, maybe provide for our existence. So in other words, it might seem that these numbers are perfectly tuned so that atoms could exist and stars could exist and life could exist. But it's possible that there are parallel universes all around us, each with totally different sets of constants and almost all of them could be totally empty with nothing interesting because the constants in those universes didn't provide atoms or photons or black holes or stars. And we evolve and we exist in one of the universes where those constants were such that atoms could exist. Let me give you a rough analogy of that. Remember the pan of water I mentioned earlier where the bubbles, when you start adding heat, right before boiling are starting to form on the bottom. And then if you watch it, as you add a little more heat, one of them floats up and one of them floats up and another and another and another and then faster and faster and then suddenly it's boiling. Well, imagine that each of those bubbles stuck to the bottom, maybe you see hundreds or thousands of them down there, that those are each a pocket universe separate from the bubbles that are adjacent to it. And when agitated or when the right amount of energy or release mechanism happens, it incurs a rapid expansion that they would call a big bang where the bubble detaches, expands, rapidly floats to the top. The creatures living inside of that thing would never be able to comprehend that they're inside of a pan and they would never be able to see any of the parallel universes or ever interact with them. And they would never know that there's a heat source on the bottom or any of this stuff. They would just know that, boy, aren't we lucky that we live in the bubble where atoms can form. But all the other bubbles nearby may have different constants that don't have any atoms and don't have any photons. Or maybe there are totally different kinds of creatures with totally different laws of the universe in the parallel universes that are surrounding each other. So as we reach the end of our lesson or our recipe on how to create a universe from scratch, I'd like to take a second and recap what we talked about. You start with an unimaginably small point containing all the matter and all the energy in the universe. Then you add something called cosmic inflation, very rapid initial expansion. And then things slow down a bit but continue to expand and you let it expand for about 13.8 billion years. You sprinkle in some fundamental forces which may have been unified in the past but then split apart and the result that you get is a universe that's vast beyond comprehension yet precise enough to allow for stars, for planets, and eventually for beings with a thinking brain capable of understanding their own origins. And I think I'd like to leave you with that thought, ponder that, that maybe we're a way, because we're made of atoms, for the universe to study and understand itself. Carl Sagan said that. Thanks for hanging out with me today. Please do drop me a line. Let me know, did you like it? Was it too much detail? Was it not enough? Did you disagree? Do you not like it at all? Do you love it? Please let me know. And as you ponder what's out there, when you look up at the night sky, I want you to always remember to stay curious. Learn anything at mathandscience.com.