How did the universe begin about 12 billion years ago? The question concerns the very large—space, galaxies, etc.—but also the very small, namely the innermost structure of matter. The reason is that the early universe was very hot, so that matter was then decomposed into its constituents. These two topics hang together, and this is what makes them so interesting.
One must start with a few words about the innermost structure of matter. The sketch in Figure 1 indicates, on the very left, a piece of metal.
It is made of atoms. To the right of it you see one of the atoms symbolically designed with a nucleus in the middle and with electrons around it. Here we proceed toward the innermost structure of matter in steps. That’s why I call it the quantum ladder. Further to the right you see the nucleus, consisting of protons and neutrons, which I will call nucleons from now on. We have found out that the nucleons themselves are composite; they are made up of quarks, as seen in Figure 1.
p class=”initial”>Let us look at the forces that keep the constituents together in the four steps of the quantum ladder. The deeper you go, the stronger the forces become. In the piece of metal, the chemical force that keeps the atoms together has the strength of a few electron volts (this is a measure of force strength). In the atom, the electrons are bound to the nucleus by a few tens of electron volts. The protons and neutrons are bound within the nucleus by millions of electron volts, and the forces between the quarks in a nucleus are in the billions of electron volts. This leads us to the concept of conditional elementarity. When we apply small amounts of energy, we cannot overcome the forces that keep the constituents together. For example, if energies of less than a few electron volts are available, atoms cannot be decomposed into electrons and nuclei. They seem to be elementary, which means stable, or unchangeable. When energies above a few hundred but below a million electron volts are available, atoms may be decomposed, but nuclei and electrons seem elementary. For energies over a million electron volts, nuclei are decomposed, but the protons and neutrons are elementary. At a billion electron volts, the nucleons appear to be composed of quarks. Electrons, so far, have never been shown to be composite.
It will be important later on to understand the connection between energy and temperature. Heating a piece of material is equivalent to increasing the energy of motion of the constituents of that piece, be they atoms or electrons or other particles. In a hot material, the atoms or the electrons perform all kinds of motions, oscillations, straight flights, etc. The greater the temperature, the higher the energy of the motions. Thus, temperature is equivalent to energy. For example, one electron volt corresponds to about 12,000 degrees Celsius (about 22,000 degrees Fahrenheit). The temperature…
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