What would happen if we could zoom in with a microscope infinitely? Would we keep seeing more detail or is there a ‘cut off’ where we can’t see any more detail?
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Let’s say you want to look at a Hydrogen atom in the DNA of an animal with your theoretical microscope. At normal zooms, everything looks normal, and as you zoom in on the cell you see more detail of smaller things. You keep zooming and eventually you see the chromosones all coiled up. It’s probably around this point that things start to look fuzzy.
As other people have mentioned, seeing smaller things means using smaller wavelengths, and using smaller wavelengths means using more energy. To see smaller and smaller things, you need to put more and more energy into a smaller and smaller space. That doesn’t bode well for the strands of DNA you’re about to look at! As you keep zooming, you keep throwing photons (or electrons) at the DNA to be able to see it, and as you get closer in, the energy you’re adding is enough to break the bonds, breaking the DNA molecule up.
No bother, you’re really interesting in that Hydrogen atom! As you get closer, you start to see bumps where the different atoms are, and they may even be moving around each other. These bumps are the electron clouds of the atoms. The electrons exist in the space around the nucleus of the atom, and the amount of space depends on two things: the force between them, and the mass of the electron. If the force between them is large, the space the electrons exist in is smaller. If the electrons had a larger mass, the space the electrons exists in would be smaller. (There are experiments with atoms that contain muons, which are heavier than electrons, and those atoms have smaller muon clouds than electron clouds.)
After a while you get bored of seeing these bumps and clouds, because that’s not what you expect. You want to see where the electron is, and what it’s made of. You crank up the zoom again and pump some more energy in. That cloud shrinks in size and then disappears from view. The electron hasn’t exploded, you’ve given it enough energy to escape the atom and it’s gone. It’s a bit like trying to squeeze an oily rubber ball. Squeeze it hard enough and it shoots off in some random direction and is gone forever. Even if you could zoom in on the electron, you’d see no substructure to it. But let’s pursue the electron a bit more. Let’s say you catch it in an electromagnetic field and can zoom in as much as you want. What would you see? As you zoom in more and more, you pump in more energy. You start to see electrons, positrons, and photons coming out of the region of space where the electron is. What’s happening is that the energy you’re adding is creating more particles. But still, the electron itself is just a very tiny cloud, so tiny that it looks like a particle. Don’t be fooled though, the electron cloud is only small because the forces acting on it (the electromagnetic field) are stronger than the forces acting on it when it was in the atom. The more you zoom in, the more particles you create, and the more variety, but ultimately, you see nothing new in terms of substructure of the electron. How disappointing.
You’re not done though. You notice that the Hydrogen atom is still there, and another electron has wandered in to fill the gap left by the previous electron. You zoom in on the Hydrogen atom, this time looking at the proton. The proton cloud is smaller than the electron cloud because the forces holding it together are much stronger. In fact, they are called the “strong force”. The proton, like the electron, exists in a small cloud. You crank up the zoom and notice that the proton is wobbling and pulsating slightly. As you zoom in more, this becomes more pronounced. It turns out that the proton does have some substructure! As you crank up the zoom, you notice you can see the cloud actually looks like three sub clouds, all overlapping each other.
You notice that your microscope has a “chargeometer” for measuring electric charge. This is because at these zooms, you are literally firing photons (light particles) at the target and seeing where they bounce off. These light particles interact with electric charge, so the more charge the microscope looks at, the more light particles get reflected back. You point your microscope at the electron cloud to calibrate it and it comes back with a charge reading of -3. Now you point it at the proton again, zoomed out a bit, and it comes back with a charge reading of +3. Interesting… the electron and proton have equal and opposite charge readings. That must be something to do with how atoms form and they are electrically neutral. You zoom in again and try to focus on the sub clouds in the proton. They keep moving about, but you can just about point the chargeometer at them, and you get readings of +2, +2, and -1. It seems that the proton has three smaller particles inside, each with their own cloud, and with different charges. These are in fact the quarks that make up the proton, and you can see them dancing around.
You press on and zoom in even more. As you do so, the dancing of the clouds slows down, and you start to see faint traces of other clouds between them. (The slowing down is because of special relativity and quantum mechanics. Everyone sees the same things happening, but from different perspectives. From the point of view of someone in the “centre of mass” frame of references, the proton and photon move towards each other with equal and opposite momentum. As you crank up the zoom, the photon carries more energy, so in this “centre of mass” frame, the proton has to move faster to match it. The faster the proton moves, the slower time passes for it. You see the outcome of this, not as time slowing down, but as interactions between the photon and proton becoming less frequent.) Essentially, as you crank up the zoom further, you start to “freeze out” the quarks, and their clouds become more distinct.
Around this level of zoom, you also start to notice the other particles around the quarks, known as “gluons”. Gluons hold the nucleus together, and they are, as the name suggests “sticky”. They don’t have electric charge, so you can’t see them directly. Instead you see other particles bouncing off them, first the quarks, and then new particles you are creating. This is just like with the electron cloud. You pump in more energy, and you get more particles. You crank up the zoom to see what happens. The proton starts to wobble and the quarks shift apart, It looks like you’re about to split the proton apart! But no, a new particle, this time a “pion” shoots out the side, and the proton goes back to how it was before. No matter how much try to zoom in, and give the proton more energy, you will never split it up. You will never separate out a quark or a gluon. Instead you will just create more and more particles. In fact this is how the LHC works. The LHC smashes protons into each other at super high speeds. The quarks and gluons get “frozen out”, and as they fly past each other, a tiny fraction interact and make new particles. Of those new particles, an even tinier fraction are the Higgs boson.
You decide to keep zooming. You create more and more particles, until eventually you have a sea of quarks, antiquarks and gluons. This is known as a quark gluon plasma, and it acts like a strange fluid. It’s hard to see “inside” it, because the quarks and gluons absorb nearly all the light they produce. You press on further, and see a handful of new particles (W and Z bosons, Higgs bosons, occasionally a neutron or even a Helium nucleus).
Edit: Wow, thanks for all the awards and lovely comments! 😀
Edit 2: Clarified the size of the electron cloud and proton cloud vs the size of the electron and proton.
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