Stars are helium factories. Older stars use helium as raw material to make other elements like carbon. And yet the vast majority of helium in the universe today wasn’t made in stars. Instead, it had an even more amazing, even more violent origin.
It’s hard to believe that all those stars in all those galaxies, producing vast quantities of helium every second of their existence, haven’t made a difference in the overall abundance of elements in the universe. And yet it’s true. In the beginning, the ordinary matter* of the universe was around 74% hydrogen, 26% helium, and traces of lithium. Today, the ordinary matter is made of 73% hydrogen, 25% helium, and around 2% everything else. This, by the way, is by mass. Remember that since helium is around 4 times more massive than hydrogen, there must be a lot more hydrogen atoms than helium atoms, both today and in the past.
*the dirty little secret (which isn’t really a secret anymore) in all of this is that “ordinary matter” is only a tiny smattering of all the universe has to offer. But that idea, one of the greatest discoveries of our own generation, will have to wait for another time on this blog. Sigh.
So what about the past? Can we say anything about where all this hydrogen and helium came from? Oh, yes we can. Of all the amazing stories this universe has to offer us, this one is among my favorites. We all like to hear about the day we were born. And that’s what this story is all about. But I’m going to start it in a strange place – inside a radio telescope, where two future Nobel prize winners are busy scraping away pigeon poop.
Yes. Pigeon poop. Arno Penzias and Robert Wilson were scientists with Bell Labs. In 1964, they were trying to find the source of static in their fancy new satellite communication antenna in Holmdel, New Jersey. It seemed to be always there, day and night, no matter where they turned the antenna. They couldn’t get rid of this annoying static hum. What could be causing it? Finally they decided it might be due to the local pigeons roosting in the horn of their antenna and doing, well, what pigeons do. Maybe the white clumps of nastiness were the problem. So Wilson and Penzias set about removing them, as well as the pigeons (don’t worry, they used a very humane trap):
But it was all for naught. The static just wouldn’t go away. It hadn’t been caused by pigeon poop, after all.
Amazingly, in nearby Princeton, astrophysicist Robert Dicke and some of his colleagues had been working on a strange idea. The sky, they thought, might contain a fossil. Not a dinosaur, but something much bigger. A fossil of an event called the Big Bang. Dicke and his team thought they might be able to find that fossil as background radiation in the sky. When Penzias and Wilson let Dicke know of their non-pigeon-caused troubles, Dicke knew that they had been scooped. The fossil had been found. Wilson and Penzias had discovered not pigeon poop, but the birth of the universe.
OK, here’s the whole story. Edwin Hubble and his colleague Milton Humason found in the 1920s that the whole universe is rushing away from itself. They did this by looking at faraway galaxies and discovering that the bar code lines in the spectra (that same bar code used to discover helium in the Sun! Isn’t it amazing how it’s all connected?). They found that the lines in the bar code were all shifted toward the red, in the same way that the toot of a train is shifted toward longer frequency as it rushes away from you.
Well if the universe today is expanding, then in the past things must have been much closer together. And when things are closer together, they get hotter (remember the bicycle pump analogy from before – squeeze air and it gets hotter). So in the past, when things were very, very close, they would have been very, very hot. Today, with the universe so spread out, that hot past would still exist as a very, very cold fossil that should appear in all directions all the time. And no amount of pigeon poop scraping can ever get rid of it. Just by looking at the sky with the right kind of poop-free equipment, Wilson and Penzias had discovered the birth of us all.
This event, which I prefer to call the Fireball, is not what most people think it is. It wasn’t an explosion, because there was nothing to explode into. It didn’t make a great big noise, or even (really) a flash, since there was nothing to flash into. It simply was. And (here’s the most amazing thing) it didn’t happen far away. It happened right here. And here. And here. In every point of space you can think of. The Fireball happened right where you are at this very moment.
So what, exactly happened? That’s the big question. You and I are extremely ordered entities. That’s why everything (bacteria, tigers, and the IRS, oh my) wants to eat us. They want our order. But where did that order come from? It came from the Fireball. In an event called inflation, a tiny patch of the universe suddenly grew to enormous size. The potential disorder of this event was gigantic, and yet, because it happened so incredibly fast, the order present in this tiny lump was preserved. Ever since then, we’ve been rolling downhill, toward more disorder, which is why eggs break but never unbreak, why pigeons turn ordered food into disordered poop, and why, in the end, everyone must die.
But think of all we can do in the meantime! We are a way to temporarily recapture a little bit of the magic of those first moments of the fireball. Every bit of energy you will ever use in your life was set into motion in those first moments of the universe. Let’s visit those first moments and find out just what happened.
In the beginning, the fireball was so hot that no matter could exist. Everything was energy. But then, as inflation spread the universe out, matter began to condense out. At first it was just quarks and electrons, the bare constituents of all ordinary stuff. Then the quarks found one another in threes (there’s that number again!) and formed protons (hydrogen) and neutrons. Just as happens today in the Sun, some of those protons slammed into one another, resulting in our friend helium. A tiny bit of an even heavier element called lithium also formed in these collisions. But nothing else. The fireball was spreading out too quickly for that.
That’s a good thing, because as we’ve seen it’s the hydrogen, left over from the first moments of the fireball, that really holds the key to our universe. If we taste good, hydrogen tastes delicious. It’s got so much potential for releasing energy that it, in time, lit up the universe, changing itself into helium and giving us gorgeous sunsets, beautiful starry nights, and a glorious sunrise to follow.
The helium, on the other hand, around a quarter of what we started with, is almost all still there, floating about in space or packed into stars. As we’ve seen, some of that helium turned into carbon, which became you and me. Not only are we all starstuff; we are, each one of us, children of the Fireball.