In this first lesson, we will be discussing the elementary particles as we know it. And after this lesson, you should have an understanding of what these elementary particles really are. During the first period of our universe right after the Big Bang, normal matter as we know it today, did not yet exist. The universe consisted of elementary particles each with a large amount of energy. And only later, after approximately 380,000 years, the particles slowed down. Enough so that atoms could be formed. In this lesson, we concentrate on the period before the existence of atoms. We will talk about the ultimate building blocks of matter, the constituents of atoms. And one of the most interesting questions in particle physics today is where we understand not only the formation of these atoms but also the whole evolution of the universe in all its complexity. In terms of these building blocks. And you will see that science has produced a lot of knowledge. But very fundamental questions remain unanswered today. If you split the atom, you come across a number of constituents. And on the outside of the atom, you find the electron. An elementary particle that carries a negative electric charge. You have to realize what elementary means, it means that within the limits of the experimental resolution, we observe no size for elementary particles. They really are point particles. And it may actually be that at even shorter distances we discover that the electron is built from yet smaller constituents. But this is outside the reach of experiments today. A century ago, the atom was elementary, and today, the electron is elementary. Atoms further have a nucleus. The nucleus consists of a proton and a neutron. Hydrogen, the most simple atom, has a single proton as a nucleus, and in the 1950s, it was discovered that the protons themselves have a finite size, and hence are not elementary. They consist of yet smaller particles. And it took until the 1970s before the experimental observation of the constituents inside the protons were found. And these are called quarks, a name invented by the physicist Murray Gell-Mann. The resolution of the experimental equipment we reached today is about ten to the minus 19, it's extremely small number, it's equivalent to one thousandths of the diameter of a proton. And this is the smallest size that we can actually observe experimentally. And these quarks inside the nuclei, they form the building blocks of protons and neutrons, and there are a number of types of quarks. First, there is the up quark. We call it up quark and it has an electric charge of two thirds of the election and there is a down quark with a minus one-third charge, and a proton and a neutron each consist of three types of quarks. The proton has two up type quarks and two down type. And the neutron has one up type and two down type quarks. And this quarks are like the electron elementary, that means we do not absorb any size of the quarks within our current experimental set ups. And the elementary building blocks of atoms are there for the electron, the up-type quark, the down-type quark and there is actually a fourth particle, which we call the electron-neutrino. This is a rather mysterious particle that is very difficult to observe. It has a very small mask compared to the other three particles and does not bound in atoms. Neutrinos freely traverse universe and occasionally hit other particles. The number of neutrinos in the universe is huge. Every second 100 billions of these particles traverse through the size of your thumbnail, completely unnoticed. And the properties of neutrinos are not yet fully known, and they may actually play a very crucial role in the understanding of the evolution of the universe. But that remains to be seen. However, these four particles is not the end of the story. Einstein realized in 1905, when he published the theory of special relativity, that energy and matter are actually equivalent to each other, and can transform into each other. And this is expressed by his famous equation E=mc², where E stands for energy and m is the mass. And the factor c squared is just the conversion number. Now, the consequence of this insight is huge. Suddenly it was realized that if you concentrate enough energy, you may be able to transform that energy into mass, into new matter. For example, new elementary particles. Before going into more detail about the transformation of energy into matter, I have to tell you about the existence of antimatter. Antimatter was predicted to exist in 1926 by the theoretician Paul Dirac, and the first antimatter was then subsequently discovered in 1930. It's perhaps one of most beautiful predictions in quantum theory, the theory that describes the behavior of elementary particles. We know today that for every elementary particle, there exists an anti-particle. The anti-particles have opposite charge compared to the particles, but have the same mass. Hence, for the electron, with the charge minus one, there exists an anti-electron with the charge plus one. And the anti-electron is called a positron. Also the quarks have anti-quarks, so you have the anti-up quark, the anti-down quark, and also the anti-neutrino. And the beauty is that when you bring matter and anti-matter particles together, something weird happens. They actually cease to exist. They lose their identity. And what is left is pure energy, the amount of which is given by the famous equation E=mc², where with m then the mass of this particles and the anti-particles. And now you can also turn this around. From the pure energy, you can also create particles and anti-particles always in pairs. And in this way, you can generate new particles, and the mass of the particles that you create depend on the energy that is available. Since energy equals mass times c squared. So if you want to create a heavy particle and anti-particle. You just need a lot of energy. This is exactly the idea behind particle accelerators. In the accelerator, you smash particles against anti-particles, and if they collide, they cease to exist. Lose their identity. And all that is left is energy. And from this energy, new or other particles can be formed. And the crucial thing is, of course, that the energy that you have available to generate new particles depend on the energy of the collision. The larger the collision energy, the heavier the new particles can be. And this is the reason why particle physicists always want bigger accelerators. Because then they need more energy in the collision to be able to make heavier particles. During the last century, new elementary particles were produced and discovered into high energy collisions. Surprisingly, what was found is that the family of four particles that we discussed earlier was repeated in a second family. All the particles in the second family are heavier than the first family and it consist of a chunk quark and a strange quark as the heavy brothers of the upper and down quark. The muon particle is the heavy electron brother and it is also a new type of neutrino, which we call the muon neutrino. The particles of the second family I have here but otherwise, have identical properties as these from these first families. We do not completely understand why nature has chosen for the second family and one of these physicist renounce, who ordered this. All these quarks and leptons, which is the name for the electron, neutrino and muon, are produced in particle accelerators or have been found in energetic cosmic particles hitting the atmosphere of our planet using again, E=mc². Situation is even more obscure by the third family of particles. There you find the top quark, the bottom quark, the tau lepton, and the tau neutrino. The top quark is the heaviest elementary particle as we know today and has a mass equivalent to that of 175 particles. Yet it is a point particle, without any size. It was discovered in 1995 in a big accelerator of 6.8 kilometer circumference called Tevatron at Fermilab near Chicago. And this is the status of elementary particles today. For all these particles, also the anti-particles have been observed, but we don't know exactly what is the rationale behind the fact that we have three families. Are there any more families? Is there a fourth family? What is the relation of the masses of all these elementary particles? Why do we see this structure? On all of these questions, we don't have answers.
