Ben Lillie – High-energy particle physicist
So this is Lithium, It’s got 3 electrons, 3 protons and usually 4 neutrons, and you probably don’t think about it very much. Umm, right?
Show of hands, who doesn’t think about Lithium? You probably don’t think about it very much, you probably know that it’s used in a medication, you know that it’s used in batteries, and… that’s it.
A couple of years ago, I was sitting in my room, very emo and depressed, and listening on repeat to the song “Lithium” by Evanescence. You might, if you’re slightly older, know the song “Lithium” by Nirvana, and it struck me as odd that these two intense emotional bands had both written songs about Lithium, and this isn’t really a thing that happens, right? OK, people write songs about Gold and Platinum, but there is no Beryllium song, there is no Boron song. Why this one?
And I started digging, and it turns out that Lithium is one of the strangest elements in the Universe and I want to tell you about it, starting with the fact that it probably shouldn’t be here on Earth at all. So, you’ve all heard the phrase “we’re all stardust.” So what that means is that way back in the early Universe there was a giant cloud of Hydrogen gas, and somewhere in that cloud of gas a little bit became denser than the rest, and the gravity of that part started pulling it in further and further, and as more accumulated, it’s started pulling in faster and faster, and eventually the whole thing began collapsing and heating up and eventually it heated up to the point where nuclear fusion ignited and the force of explosion from that fusion counteracted the implosion from gravity and that’s what a star is.
Then, inside that star, the Hydrogen, element number one with one proton, began fusing with other Hydrogen, one plus one, and you end up with element number two, Helium. And that went on for hundreds of millions of years and then eventually, the Hydrogen was used up, it stopped burning, collapsed, heated up more to the point where it could fuse Helium, element number two. So, one plus one gave us two, element two plus element two gives us element six, that’s right. And that’s because of Quantum Mechanics.
The best thing about being a physicist is anytime you want to skip a long, involved explanation, you just go, “Because Quantum Mechanics.” So, the Helium burns into element number 6, which is Carbon, as well as 7 and 8, Oxygen and Nitrogen, and this process continues, and you start creating more and more elements, all of the ones we know, up to Iron, number 26.
Once it hits Iron, it can’t burn anymore, the star shuts off, and if it’s big enough it collapses more, and as it collapses, it rebounds and explodes as a Supernova, the brightest thing in the Universe, which can outshine a galaxy while it’s exploding. In the hot plasma from that supernova explosion is so intense that all of the heavier elements can be formed from nuclear fusion, all of the Gold, and the Silver, and the Xenon, and the Uranium are made there along with all the others. Throughout this, all these elements are being scattered out into the cosmos, and as they are, they find another cloud of Hydrogen gas, and this one begins to collapse into a star. That star ignites, and around it, these heavier elements form into rocks, and asteroids, and planets, and that’s what Earth is. And that’s why we’re all stardust.
Now, a couple of things about this. First, we skipped Lithium, skipped number 3. So where does it come from? It’s actually even weirder than that, if you had some Lithium, and you took it and you put into a star, it would melt and go away. So not only do stars not produce Lithium, they destroy it, if it existed before. It turns out it comes from a number of places. A small amount of it does come from stars, in that Supernova explosion, and the other ways that stars die in, but a lot of it comes from… – think about what did I mean when I said, “We’re all stardust”? – Turns out that’s not quite right, because in your body, you’re about 10% Hydrogen, and if you remember, the star started from a primordial cloud of Hydrogen gas, where did that come from? And that, it turns out, came from the Big Bang itself.
So, moments after the Big Bang, everything was a hot dense soup of undifferentiated nuclear matter. It eventually cooled, and as it cooled, little droplets of nuclear matter formed, and those droplets became protons, which are the nucleus of a Hydrogen atom. And it goes on.
During that hot era, the protons can fuse with each other and they can make Helium, then, unlike stars in the early Universe, that Helium can fuse to make Lithium, and it’s different there because Quantum Mechanics. But some Lithium is formed in the Big Bang, it’s not a lot, it’s 1 part in ten billion, but that’s enough. And a lot of that comes into this cloud of gas and ends up here on Earth.
The fourth place that we get Lithium from, is actually my favorite, it goes by the wonderful name ‘cosmic rays foliation’ – it’s a lovely word – and what it means is. Out in the Universe, cosmic rays are accelerated, these are protons and electrons and positrons and other things, and they come screaming across the cosmos, occasionally, one of them will intersect with the Earth, I say occasionally, there is a tremendous number of these things, we’re being bombarded by them constantly. Sometimes, these cosmic rays come in through the atmosphere, and they find a big nucleus, like a Nitrogen or an Argon, and they hit that nucleus, they shatter it; the shattered bits of that giant nucleus form other elements, sometimes Lithium.