 So let's recap. We've had a look at the theory of quantum mechanics as evidence through the two-slit experiment and we've had a look at the history of quantum mechanics. And to recap the theory everything's a wave. An electron is a wave, a nucleus is a wave, a molecules a wave, an atoms a wave, you're a wave, I'm a wave, the room is a wave, and waves aren't exactly what we thought they were, they do slightly strange things when you measure them. And this theory, although it does sound a little strange to begin with, turns out to explain to the dozen significant figures or more every property of everything we've ever measured. Okay, it has no known bugs. Now we saw, especially through the history, how it explained the existence of atoms and how they work, we saw how it explained absorption and emission, the photoelectric effect, interference, and so forth. But our history only went through to about the 1920s where the modern form of quantum mechanics finally emerged. So what happened after that? So after that the next major advance happened when we tried to marry the theories of relativity with quantum mechanics. Now not only did that help us get the details right so that we could get a dozen digits of significant figure agreement between theory and experiment, it also actually put a lot of restrictions on our quantum mechanical theories. In order for our wave evolution to obey the principle of special relativity, there are only certain theories that would work. And it turns out that some of those theories actually predicted particles that we'd never seen before. And then we went and looked for those particles, they were there. And this was the first time that completely new things had been discovered from theory rather than from experiment first. The normal role of science was that things would be observed, and then theories would be developed to explain those things, and then those theories would be tested by further experiments. In this case, the principles behind the theory suggested a slightly different version of the theory, and that version of the theory made predictions that turned out to be correct. And we saw completely new phenomena, in other words entirely new particles in nature that we hadn't seen before. And it didn't stop there. Quantum field theory, which is what this theory is called when you marry relativity with quantum mechanics, has predicted many new particles which have been observed, and also new forces and relationships between those forces, all of which have been verified to the best of our ability. And our best model of all these particles and forces is called the standard model.