Hey Dr Z, I keep getting things in my feed telling me that scientists are smashing atoms or particles together in massive (and massively expensive) particle accelerators, and when they do that, they can somehow figure out what’s inside the particles – sometimes they even create new particles! And I gotta ask – how do they do it? How can they even smash, say, two electrons or two protons together, let alone to see what comes out when they hit? I’m sure it’s all on the up-and-up – but it really sort of boggles the mind.
It’s really impressive, isn’t it? And it’s not sugar, spice, or everything nice (sorry). So much technology, so much computer power, and so much equipment to be able to see what the tiniest things in the universe are made of. But then it sort of makes sense – with our eyes we can see things down to a fraction of a millimeter; grains of flour, silt, even very large microbes. To see anything smaller we need to use a magnifying lens, to see smaller yet we need an electron microscope. The smaller the things we’re trying to see, the larger and more expensive the equipment we need to see it. To see what’s inside an atom we need cyclotrons (you can fit one of these in a bedroom); to see what’s inside the particles that make up an atom we need to use particle accelerators that are tens of miles in circumference and that accelerate those particles to almost unimaginable energies. Don’t worry – I won’t get into the nitty-gritty of it all…largely because I can’t; I don’t understand it at that deep a level. But I know enough to get us to an answer to your questions! Let’s start with how these accelerators work – let’s start with protons.
Protons have a positive electrical charge and charged particles are affected by electrical charge and by magnetic fields. If, like me, you spent part of your childhood chasing magnets around a tabletop you’ll know that the ends of the magnet with the same polarity (e.g. two “north” poles) push each other apart. Electrical charges are the same. So if we can create a wave of positive electrical field moving through space, that wave will push protons along in front of it – almost as though the protons are surfing on the electromagnetic wave. If the wave is moving down a tube, the protons gets pushed down the tube. And if that tube is bent into a circle, we can still move the protons through the tube if we immerse the tube in a magnetic field because charged particles moving through a magnetic field will follow a curved path through space. The stronger the magnetic field, the tighter the curve.
So that’s the very high-level view of how particle accelerators work! The other big things to add are that we can ramp up the strength of the magnetic field, the strength of the electromagnetic wave, and the speed at which the wave moves down the beam tube – this is how we get particles to higher and higher speeds and energies. We can let the beam go around time after time, picking up more energy each time around, until the particles are at the energies we want. At that point we can simply let the protons smash into a chunk of metal to see what flies out, we can smash it into a second beam of particles, or we can find a different target. And we can do this with more than just protons – we can smash entire atoms together, we can produce anti-protons into the beam and smash them into protons, we can smash light particles into heavy ones, and more. These collisions are timed to occur in a test chamber filled with instruments, many of which are the size of a small house; these instruments analyze the bits and pieces that come flying out of the collisions.
Say we’re trying to find out what’s inside a proton so we smash a few beams of protons together. When that happens we’re going to see a burst of debris – particles – flying out into space. The instruments in the target chamber are immersed in a magnetic field so the charged particles will follow a curved path – the tighter the curve the lighter and/or less energetic the particle; no curvature means the particle has no electrical charge. If it’s single particles that are being slammed together – especially if the particles are fairly light – the collisions are “clean” and it’s easier to figure out what’s coming out of the collision; the larger, heavier, and more energetic the collisions, the harder the task becomes.
Think of it this way – say you’re trying to figure out what’s inside a golf ball and the only tool you have is a golf ball accelerator. If you smash two golf balls together fast enough, the cover will split – when you examine the debris you’ll see the cover and a core, but you won’t know what the core’s made of. So you increase the speed and keep smashing golf balls together and, at the right energy, the core will start to split into its components parts – an outer layer and an inner layer maybe – and you can see these flying out of the collision. So now you know what the golf balls are made of! But golf balls are pretty simple – what if you’re trying to figure out, say, what’s inside a Volkswagen bug?
Well, it’s probably not going to take much energy to get the wheels to pop off and fly through the air, to see bits of broken glass, body panels, bumpers, and so forth – so, as with the golf balls, slamming Punch-Buggies into each other will give us a pretty good idea of what the outer layers are made of. But, as before, it’s going to take much more energy to get the seats or the engine flying through the air and a LOT more energy to cause the engines to come apart so we can see the pistons, gaskets, crankshaft, and all the other parts. Not only that, but trying to figure out how they’re all assembled will take a long time and a lot of computer power.
Same thing with particles and collisions – to see what a proton’s made of isn’t too hard, but to see what those components are made of is fiendishly challenging. Not only that, but these particles interact as they’re flying outwards from the collision – as though the metal parts of a car were smashing into each other, maybe fusing together or knocking pieces off. And, in the odd, odd world of high-energy physics, the energy itself can coalesce to form additional particles, in accordance to Einstein’s famous equation E=mc2 that tells us that energy can “condense” to form matter just as matter can turn into energy. Which makes me think…I need to see if I’ve already written about pair production.
Anyhow, this is a very basic overview, but I think it gives you an idea as to the basics of how particle accelerators and high-energy physics work. To get into the next level of description, though, requires a lot more understanding than I’ve got, so this seems like a good place to stop.