Chapter Content
Okay, so, um, where do you even start with trying to imagine the scale of the universe, right? Like, even something as tiny as a proton, you can't even really wrap your head around how incredibly small it is. I mean, it's just... it's mind-boggling.
So, protons are these tiny bits that make up atoms, and, you know, atoms themselves are already super small, right? But, like, get this, a single drop of ink, just that little dot over the letter “i”, would contain, like, five hundred billion protons. I mean, that's more than the number of seconds in, like, fifteen thousand years. So, yeah, protons are seriously, seriously tiny.
Now, imagine if you could shrink one of those protons, okay? Make it one billionth of its actual size, like ridiculously small. And then, pack about an ounce of stuff, like 30 grams, into that teeny, tiny space. Well, guess what? You’d basically be ready to, like, create a universe.
Of course, you probably want a universe that expands, right? But even if you're going for a more old-school Big Bang type of universe, you'd still need everything – every single particle that exists, like, from now until the beginning of time – crammed into a point so small it basically has no size at all. This is what they call a singularity.
Either way, you're looking at a pretty massive explosion. Naturally, you'd wanna stand back and watch, but here's the thing: there's nowhere to stand back to, because there's nothing *outside* the singularity. As the universe starts to expand, it’s not expanding *into* anything. The space itself is what it creates as it expands.
It's tempting to think of the singularity as a tiny speck floating in this vast, empty darkness, but that's just wrong. There's no space, there's no darkness. There's no "around" the singularity. There's no space for it to even *be* in, no place for it to exist. We can't even ask how long it was there, whether it just popped into existence like a good idea or if it was just waiting for the right moment. Time itself didn't exist. There's no “before” it.
And so, the universe just… came into being. From nothing.
Then, in a flash, faster and bigger than anything we can describe, the singularity ballooned out, creating unimaginable amounts of space. In the first, like, super-charged second – which, by the way, scientists spend their whole careers trying to understand in even smaller fractions – that second created gravity and all the other forces that govern physics. In less than a minute, the universe was already trillions of miles across and still expanding, like crazy. The heat was intense, like ten billion degrees Celsius, enough to set off nuclear reactions and create the lighter elements, mostly hydrogen and helium, with a tiny bit of lithium thrown in there, too. Like one lithium atom for every ten million other atoms. Three minutes later, 98% of all the matter that exists now, or ever will, was already there. Boom. Universe done. Pretty amazing, right? And all of that, like, in the time it takes to make a sandwich.
Now, when all this exactly happened is still up for debate, you know? Scientists have been arguing for ages whether the universe is, like, ten billion years old, twenty billion years old, or somewhere in between. Right now, the number everyone seems to agree on is around 13.7 billion years. But, honestly, it’s really hard to calculate. So, basically, all we can say for sure is that, at some really, really distant point in the past, for reasons we just don’t understand, this moment called t=0 happened. And that's when the journey started.
And, obviously, there's a *lot* we don’t know. And a *lot* we thought we knew for a long time and then realized we didn't. Even the Big Bang theory itself wasn’t around that long ago. It's been bouncing around since the 1920s, thanks to a Belgian priest and scholar named Georges Lemaître, but it didn’t really take off until the mid-1960s. That's when two young radio astronomers accidentally stumbled onto something amazing.
These guys, Arno Penzias and Robert Wilson, were trying to use a big antenna at Bell Labs in New Jersey in 1965, but they kept getting this weird background noise, this constant, hissing sound, and it was just ruining their experiments. The noise was there all the time, no matter what direction they pointed the antenna, day or night, summer or winter. For a whole year, these guys tried everything to track down and get rid of it. They checked all the equipment, rewired everything, cleaned the connections, you name it. They even climbed inside the antenna and taped up every crack and rivet. They climbed back in with brooms and rags, and carefully cleaned up what they called "white dielectric material," which, to be honest, was just bird poop. But nothing worked.
What they didn’t know was that, just 30 miles away at Princeton University, another group of scientists led by Robert Dicke, was actually *trying* to find the very thing Penzias and Wilson were trying to get rid of! This Princeton group was looking for evidence of something called cosmic background radiation, something a Russian-born astrophysicist named George Gamow had suggested in the 1940s. Gamow thought that if you looked far enough into space, you should find leftover radiation from the Big Bang. He even figured it would have cooled down into microwaves by the time it reached Earth. In fact, he wrote a paper saying the Bell Labs antenna might be just the thing to find it. But, get this, nobody, not Penzias, not Wilson, not even the experts at Princeton, had ever read Gamow's paper.
So, guess what? That noise Penzias and Wilson were hearing was exactly what Gamow had predicted. They had found the edge of the universe, or at least the part we can see, about 15 billion light-years away. They were basically seeing the first photons, the oldest light in the universe, stretched into microwaves by time and distance, just like Gamow said. Alan Guth, the guy who came up with the inflation theory, had this analogy to help you picture it. If looking deep into the universe is like looking down from the 100th floor of the Empire State Building, where the street level is the Big Bang, then the furthest galaxies anyone had seen before Penzias and Wilson were only on, like, the 60th floor. And the furthest known things, quasars, were only on the 20th floor. Penzias and Wilson’s discovery took us down to less than half an inch from the ground.
Eventually, Penzias and Wilson were so frustrated they called Dicke at Princeton and described their problem, hoping he could explain it. Dicke, he knew right away what the two had stumbled upon. He reportedly hung up the phone and said to his colleagues, "Well, boys, we've been scooped."
Soon after, two articles appeared in the *Astrophysical Journal*. One was by Penzias and Wilson, describing the hissing noise. The other was by Dicke's group, explaining what it was. Even though Penzias and Wilson weren’t even looking for cosmic background radiation, didn’t know what it was when they found it, and didn’t write any paper explaining what it was, they still won the Nobel Prize in Physics in 1978. The Princeton guys just got sympathy. According to Dennis Overbye in his book *Lonely Hearts of the Cosmos*, Penzias and Wilson didn’t even realize how important their discovery was until they saw a story about it in the *New York Times*.
By the way, we all experience this cosmic background radiation all the time. Just tune your TV to a channel with no signal, and about 1% of that static you see is actually leftover radiation from the Big Bang. So, next time you’re complaining about bad reception, just remember, you’re also watching the birth of the universe.
Now, even though everyone calls it the Big Bang, a lot of books point out that you shouldn't think of it like a regular explosion. It was more like a sudden eruption of space and scale that's just beyond comprehension. So, what caused it?
Some people think the singularity was actually the leftover remnant of a previous universe that had collapsed in on itself. Like, our universe is just one in a series of universes, expanding and collapsing over and over, like the bellows of an oxygen pump. Other people blame the Big Bang on something called a “false vacuum,” or a “scalar field,” or “vacuum energy,” basically some kind of substance or thing that introduced a bit of instability into nothingness. It seems unlikely that something could come from nothing, but then again, there *was* nothing, and now there’s a universe, so… clearly, it’s possible. Maybe our universe is just one of many in a larger, ever-shifting cosmos, with Big Bangs popping off all over the place. Or maybe, before the Big Bang, time and space just existed in a completely different form, something so unfamiliar we can’t even imagine it, and the Big Bang was just a transition from that form to something we can *almost* understand. As one cosmologist put it, it’s a lot like a religious question.
The Big Bang theory isn’t actually about the explosion itself. It’s about what happened *after* the explosion. And I mean, very shortly after. Scientists have done a lot of calculations and looked closely at what happens in particle accelerators, and they think they can look back to as early as 10 to the power of -43 seconds after the explosion, when the universe was still so tiny it was microscopic. We don't need to get bogged down in every single crazy number we encounter, but sometimes it's good to understand one, just to keep the scale of everything in perspective. So, 10 to the -43 seconds is 0.000 000 000 000 000 000 000 000 000 000 000 000 000 000 1 seconds, or one hundred-thousand-billion-billion-billionth of a second. A lot of what we know or think we know about the early universe is thanks to this thing called inflation theory, which a young particle physicist named Alan Guth first came up with in 1979. He was working at Stanford back then, and he's at MIT now. He was only 32 and admitted he hadn't really done much before that. If he hadn't gone to this one lecture on the Big Bang, he might never have come up with the theory at all. And guess who gave that lecture? Robert Dicke! The lecture just got Guth interested in cosmology and how the universe formed.
Eventually, he came up with the theory of inflation, which says that in the first, tiny fraction of a second after the Big Bang, the universe suddenly expanded like crazy. It was, like, running away with itself, doubling in size every 10 to the -34 seconds. The whole process might have lasted less than 10 to the -30 seconds, or one million-billion-billionth of a second, but it took the universe from something you could hold in your hand to something at least a billion-billion-billion times bigger. The inflation theory explains the clumping and spinning that made our universe possible. Without it, there would be no clumps of matter, so no stars, just gas and endless darkness.
According to Guth, gravity came into being within that first hundred-thousand-billion-billion-billionth of a second. Then, pretty quickly, electromagnetism, and the strong and weak nuclear forces came along too, the basic ingredients of physics. And then, tons of elementary particles appeared, the ingredients of ingredients. Suddenly, there were all these photons, protons, electrons, neutrons, and tons of other stuff, like 10 to the 79th to 10 to the 89th power of each, according to the standard Big Bang model.
Those are numbers that are, like, impossible to really understand. All we need to know is that, in a flash, we had a giant universe, one that's, according to the theory, at least 100 billion light-years across, maybe even infinitely big. And it was all perfectly set up for stars, galaxies, and everything else.
What's so amazing from our point of view is how incredibly perfect it all was. If the universe had been even a little bit different, if gravity had been a little stronger or weaker, if the expansion had been a little slower or faster, then there might never have been any stable elements to make us, or the ground we stand on. If gravity had been just a tiny bit stronger, the universe would have collapsed like a tent without poles, and there wouldn't have been the right values to give it the size, density, and ingredients it needed. But if it had been weaker, then nothing would have come together. The universe would have been a forever boring, scattered, and empty place.
That’s one reason some experts think there might be multiple Big Bangs, maybe trillions of them, scattered across eternity. We happen to exist in this specific universe because it's the one that's right for us. As one physicist put it, our universe is just one of those things that happens from time to time. And even though creating a universe might be unlikely, no one's ever counted the number of failures.
One astronomer thinks there are many universes, probably infinite, all with different properties and combinations, and we just happen to live in one where the combination is just right for us to exist. He uses the example of a big clothing store. With so many clothes, it's easy to find something that fits. And with so many universes, each governed by a different set of numbers, there's bound to be one where the numbers are just right for life. We just happen to be in that one.
He thinks our universe is governed by six numbers, and if any of those values changed even a tiny bit, things wouldn't be the way they are now. For example, for our universe to exist, hydrogen needs to convert to helium in a precise and fairly stable way, specifically, by converting about 0.7% of its mass into energy. If that value was a little lower, like 0.6%, then the conversion couldn't happen, and the universe would just be hydrogen. If it was a little higher, like 0.8%, the conversion would happen too fast, and all the hydrogen would have been used up a long time ago. Either way, a slight change in that one number, and the universe as we know it wouldn't exist.
So far, everything has been just right. In the long run, gravity might get a little stronger, and one day, it might stop the universe from expanding, and just crush it back down into another singularity, and the whole thing could start again. Or, gravity might get too weak, and the universe would just expand forever, until everything is so far apart that nothing can really interact anymore, and it becomes a very empty, stagnant, and lifeless place. The third possibility is that gravity is just right, what cosmologists call the "critical density," and it keeps the universe in just the right range, so things can just keep going forever. Cosmologists sometimes call this the "Goldilocks effect," where everything is just right. These three possibilities are called closed, open, and flat universes, respectively.
Sooner or later, you start wondering, what if you went to the edge of the universe and stuck your head out? Where would your head be? What would you see on the other side? Well, the answer is kind of disappointing. You can never get to the edge of the universe. Not because it takes too long, although it does, but because even if you went in a straight line, and kept going, you would never reach the edge. Instead, you'd end up back where you started. The reason is that, according to Einstein's theory of relativity, the universe is curved. How it's curved is hard to imagine. For now, just know that we're not floating in some ever-expanding bubble. Instead, space is curved in a way that makes it both infinite and finite. You can't even really say that space is expanding, because, as physicist Steven Weinberg pointed out, the solar system and the galaxies aren't expanding, and neither is space itself. Instead, the galaxies are just moving away from each other. It's all pretty mind-bending. As one biologist famously said, "The universe is not only queerer than we suppose, but queerer than we *can* suppose."
To explain how space is curved, people often use this analogy about someone from a flat universe, who's never seen a sphere, coming to Earth. No matter how far he walks on the surface of the planet, he'll never reach an edge. He might eventually end up back where he started, and he'd be totally confused about how it happened. We're in the same situation with space. We're just more confused.
Just like you can't find the edge of the universe, you also can't stand at the center and say, "This is where it all started. This is the middle of everything." We're all at the center of everything. We're not totally sure about that, though. We can't prove it mathematically. Scientists just guess that we're at the center of the universe, which is a huge thing to think about, but that it looks the same to everyone, everywhere. We're just not totally sure.
As far as we know, the universe has only developed far enough since its formation for light to have traveled billions of years. This visible universe, the one we know about and are talking about, is trillions and trillions of miles across. But according to most theories, the whole universe, sometimes called the mega-universe, is much bigger. According to one astronomer, the number of light years to the edge of this larger, invisible universe isn’t "ten zeroes, or a hundred zeroes, but millions of zeroes." Basically, there’s more space than you can imagine, and you don’t even need to think about what’s beyond that.
For a long time, the Big Bang theory had this giant hole in it, that people just couldn't figure out. It couldn't explain how we got here. Even though 98% of all the matter in the universe was created by the Big Bang, that matter was all made up of light gases, like helium, hydrogen, and lithium. Not a single particle of the heavy stuff, like carbon, nitrogen, oxygen, the stuff that's absolutely essential for us to exist, came out of the Big Bang. But, and here's the tricky part, you need the kind of heat and energy released by the Big Bang to create those heavy elements. But the Big Bang only happened once, and it didn't create heavy elements then. So where did they come from? It's kind of funny that the guy who actually found the answer to that question was a cosmologist who totally didn't like the Big Bang theory, and actually coined the term "Big Bang" to make fun of it.
We'll get to him soon. But before we talk about how we got here, it might be worth taking a few minutes to think about what exactly "here" is.