At the very beginning of modern physics part 1, we have summarized the development of modern physics into the generalizations of general physics in a lot of directions. For example, higher, stronger, faster, etc. Now, after introducing modern physics part 1 and part 2, we have summarized them in a more logical order, that there are a few driving forces to push physics forward. The one driving force is relativity that a lot of our common concepts, which we thought are absolute, are actually relative. This is the driving force towards special relativity, general relativity, and the modern understanding of our universe. The other driving force is quantum mechanics, that if we go smaller and smaller, eventually, at the scale of atom, we end up with a set of rules which are completely unfamiliar to us. That set of rules is characterized by some fundamental building blocks known as quanta. From quantum mechanics, we have atoms, we have quantum information, etc. These two, relativity and quantum mechanics, are indeed the major driving forces of physics in the past 100 years. However, they are not the only ones. There are a lot of other driving forces to push physics to advance together. In the part 3 of modern physics, I'm selecting a few other perspectives and driving forces for the past 100 years of physics, including universality, that would like to treat all the possible physical entities in a universal way. What is the universal motion laws? Even, what are the laws of laws that some of the laws, we thought they were fundamental, they may not be fundamental. Reductionism that would like to study smaller and smaller things. Ourself for example, made of atoms, atoms made of nuclei and electron, and the nuclei made of protons and neutrons, protons made of quarks, etc. What are the laws of the electrons and the quarks? Are they the most fundamental or is there another layer of fundamental physics? This try to reduce bigger things into smaller things and to understand that smaller building blocks. As another perspective, we may not only think about the laws of physics, in the laws governing how things move, but also, when we think about that, as how information flows, how information is preceded. In the sense, we have talked about information at least twice. The one time is about in causality in special relativity, that the real constraint is information is not passing faster than light. The other is in quantum information thinking about what is the quantum version generalization of information. It motivate us to think about, is information considered to be something very fundamental? We even put it into a very fancy sentence, It from bit. Is it from bit? Also, complexity, that there are some phenomena in our universe, actually, most of the phenomena in our universe, they are so complicated. They are so complicated that we cannot give an analytical solution from their equations of motion. For these kinds of phenomena, among the most complicated phenomena, can we actually find some universal rules, not from reducting them to smaller elements, but from the collective, from the emergent motion of the complex bodies? Can we find some rules for them? This is complexity. These are some other driving forces of physics in the past 100 years, which we will cover in the modern physics part 3.
