How Did Everything Begin? The Science of Space & Time Explained by Max Tegmark

How did everything come into existence? How did the planets, stars and galaxies form? Is the universe infinite? Today we will explore these questions in depth and hopefully we will have a sense of how grandiose our universe is. So how big is our cosmos? We humans have again and again underestimated not only the size of our cosmos, realizing that everything that we thought existed was just a small part of a grander structure, a planet, a solar system, a galaxy, a universe and maybe even a hierarchy of parallel universes. But equally importantly, we've repeatedly underestimated the power of our human minds to understand our cosmos. One of the most mind-boggling ideas in cosmology for most people to try and wrap their heads around is whether our universe is infinite. Fortunately, we have very good physical theories that can give us an answer. The best theory we have for what created our space, the inflation theory which stretched out and created this awesome cosmos perhaps that we're in, it actually predicts that not only that space is big, but it generically predicts that it's even infinite. Now we've repeatedly underestimated both our ability to understand the cosmos and also the sheer size of it. And the edge of what we saw here in our exploration of space is the edge of our observable universe. But what is the deal here? What are all these red, yellow and blue spots that adorn the edge of what we can see? To understand this, it's not enough to just talk about our place in space. We also have to understand our place in time. Besides space, the other piece of the puzzle to fully understand how our universe works is time. But nobody can really tell what it actually is. Fortunately, we can learn a lot about our place in time just from looking into the sky, because the sky is like a time machine. When I look at the sun, I see the sun the way it was eight minutes ago. And when I look at some of these galaxies here in the Hubble Ultra Deep Field, I see them the way they were 10 billion years ago. So what have we learned by observing the universe at various stages of its cosmic history? We've learned something really, really surprising. And to make you fully appreciate just how surprising it is, we can understand this exactly because the farther away I look, right, the farther into the past I'm seeing. So when I look at nearby galaxies from my vantage point over here, I see them the way they were pretty recently, when they had had time to mature and become big and modern looking. When I look farther into the past, I'm seeing galaxies long ago that hadn't had time yet to grow up and become big galaxies. And really far away, all I see is baby galaxies that had not had time to do much growing at all. And beyond that, I see no galaxies at all, because I'm looking so far back in time, and I'm witnessing the epoch before there were any galaxies that had time to form. All I'm seeing there is the building, the raw material out of which the galaxies later formed, namely hydrogen gas. In 1842, Austrian physicist Christian Doppler described how the change of pitch heard when a vehicle sounding a horn approaches and recedes from an observer. And his principle has also found use in cosmology. It's exactly the same way, not just with sound, but with light. So a galaxy flying away will have its light shifted to lower frequencies, which here corresponds to the reds. We call this redshift in astronomy. The more redshifted something is, the faster it's flying away. And Edwin Hubble discovered that pretty much all the galaxies he looked at were redshifted. Everything seemed to be flying away from us. And this is what we mean when we say that our universe is expanding. Edwin Hubble's measurements would forever change observational cosmology and our view of the cosmos. Hubble proved that many objects previously thought to be clouds of dust and gas were actually galaxies beyond the Milky Way. What Edwin Hubble discovered when he made these fantastic measurements in the late 1920s was that things weren't expanding just in some random haphazard way, but in a very organized way. Pretty much all the galaxies were moving effectively straight away from Earth. And moreover, the farther away they were, the faster they receded. If they were five times as far away, they receded five times as fast. So what this is saying is that about 13.8 billion years ago, something really crazy happened, because pretty much everything was on top of everything else. Things were extremely dense. Everything is receding from everything else in this very orderly fashion, where the relative patterns stay the same. It's just that all distances keep getting increased by the same factor. That also gives you an alternative way of thinking about the expanding universe that some of you might find more intuitive. Instead of thinking about a static space where these galaxies are flying apart like this, you can think of all these galaxies actually just sitting still, and the space is just expanding. Now all distances are increased by the same factor. That's what we mean when we say that space is expanding, and it's allowed to do that, according to Einstein's general relativity theory. Now, another one of the really surprising things we've discovered about the history of our universe from looking out, when I look at you galaxies here, was that the far wall was glowing with microwaves. Why would it do that? Well, since everything is expanding, so is the gas that fills space. We all know that if you expand the gas, it will cool off. That's how air conditioners and refrigerators work. So if we run this backwards, and imagine going backward in time, the gas is getting more and more compressed, which means it's getting hotter and hotter and hotter. If you heat up a liquid, it turns into gas, steam. If you turn it, if you heat up a gas, what does it turn into? A plasma. So eventually, beyond all of these galaxies, we're going to see a plasma screen of hydrogen plasma, and that's opaque. So it's going to look to us like there's an opaque wall there of plasma, and it's going to look that way in whatever direction I choose to look. I'm going to see galaxies, and I'm going to see nothing, and then there's going to be a plasma screen. So it looks to us actually like we're surrounded by a spherical plasma screen that we're looking at from inside. And we can, and we in fact have, photographed this and gotten these beautiful images from the Wilkinson Microwave Anisotropy Probe. These are baby pictures of what our universe looked like just 400,000 years after our Big Bang. 13.8 billion years it took the light to reach us here. The Planck satellite released even better images of this, going from three megapixels to 50 megapixels. It's really spectacular that we've been able to get this sort of images. These are photos of the most distant thing you can photograph in science. Our universe is bound to four fundamental forces known to exist, and these forces do not appear to be reductible to more basic interactions. We have seen that during the past 13.8 billion years, there were two quite different processes that went on. There was the process of expansion, which transformed our universe from small to big, from hot to cold, from dense to more rarefied. But in parallel with that, there was also this transition from smooth and uniform and boring to clumpy and interesting. And it's interesting that the different forces of nature have actually taken turns tag-teaming, driving this clustering. The strong interaction early on clumped together triplets of quarks to form protons and neutrons, and then bound together these protons and neutrons into atomic nuclei. Then the electric force took over, took the lead and started clumping together nuclei with electrons to form atoms, and then handed over the baton to the gravitational force, which clumped enormous numbers of atoms into stars and also formed planets and ultimately people. Now, although we understand quite well then what happened during the past 13.8 billion years, what happened before this? Why did we start out? A theory of exponential expansion of space in the early universe that explains how we got here is the theory of inflation. But what is it exactly? It's the most popular theory right now for what actually happened early on, for what created our Big Bang. And what is it that the theory says? Well, it has only one single assumption that you need to make. You need to assume that there is a tiny speck of matter, vastly smaller than a proton is plenty enough, that has a strange property that it's very hard to dilute. So that if you expand it into a larger volume, its density stays almost the same. That's very different from everyday stuff like air, where if you put it in a larger volume, density drops because the total mass is the same. If you have this inflation substance, you have one kilogram of it, you put it in twice the volume, well now you've got two kilograms. If you are willing to assume that such a substance exists, then you can prove by just plugging it into the theory of general relativity that it will create a Big Bang for you. Specifically, what comes out of the equations is that it will keep doubling and doubling and doubling itself at regular intervals. To the layperson, predictions of modern cosmology might seem out of touch with reality, but our intuitions are useless when trying to grasp the early universe. The basic inflationary paradigm is accepted by most physicists, and a number of inflation model predictions have been confirmed by observation. Our baby universe in the simplest model doubled every hundredth of a trillionth of a trillionth of a second, then did so maybe 80 times, perhaps a lot more. You only need one assumption to get this, but you get a lot of predictions out. This is a theory that gives much more out than you put into it. What does it predict? Well, first of all, it predicts that there will be a Big Bang. We just saw how this repeated doubling actually causes a Big Bang. So it solves the bang problem in a sense, because there is no explanation. Equations simply assume that it's happened, and it happened. It's very unsatisfactory that you have to start out with an infinite space, which somehow, for some weird reason, all started expanding exactly uniformly, all at the same time, all with the same temperature, all with the same density. Basically, you need to start with some sort of miracle. Inflation, on the other hand, says, no, there's no miracle at all. You just need this puny speck, less mass than that of an apple, much smaller than a proton, and then it predicts a Big Bang, making everything we see here in our cosmos. Thanks for watching. Did you like this video? Then show your support by subscribing and ringing the bell to never miss videos like this.