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Context: Scientists have long wanted to find the most basic building blocks of the universe. They asked, what are the fundamental particles of matter that cannot be subdivided into smaller, simpler particles, and what holds these particles together? The quest for fundamental particles began thousands of years ago. Scientists thought they had finally found them when John Dalton discovered the atom in 1803 (see the timeline in Table 1.1). The word atom means indivisible, and Dalton thought that the atom could not be divided into smaller, simpler particles. Year Discovery Year 1803 Discovery John Dalton discovers the atom. 1897 J.J. Thomson discovers the electron, the first lepton to be discovered. 1905 Albert Einstein discovers the photon, the first boson to be discovered. 1911 Ernest Rutherford discovers the proton, the first particle to be discovered in the nucleus of the atom. Year 1932 Discovery James Chadwick discovers the neutron, another particle in the nucleus. 1964 Murray Gell-Mann proposes the existence of quarks, the fundamental particles that make up protons and neutrons. 1964-present Through the research of many scientists, many other fundamental particles (except gravitons) are shown to exist. For almost 100 years after Dalton discovered atoms, they were accepted as the fundamental particles of matter. But starting in the late 1890s with the discovery of electrons, particles smaller and simpler than atoms were identified. Within a few decades, protons and neutrons were also discovered. Ultimately, hundreds of subatomic particles were found. Today, scientists think that electrons truly are fundamental particles that cannot be broken down into smaller, simpler particles. They are a type of fundamental particles called leptons. Protons and neutrons, on the other hand, are no longer thought to be fundamental particles. Instead, they are now thought to consist of smaller, simpler particles of matter called quarks. Scientists theorize that leptons and quarks are held together by yet another type of fundamental particles called bosons. All three types of fundamental particlesleptons, quarks, and bosonsare described below. The following Figure 1.1 shows the variety of particles of each type. There are six types of quarks. In ordinary matter, virtually all quarks are of the types called up and down quarks. All quarks have mass, and they have an electric charge of either +2/3 or -1/3. For example, up quarks have a charge of +2/3, and down quarks have a charge of -1/3. Quarks also have a different type of charge, called color charge, although it has nothing to do with the colors that we see. Quarks are never found alone but instead always occur in groups of two or three quarks. There are also six types of leptons, including electrons. Leptons have an electric charge of either -1 or 0. Electrons, for example, have a charge of -1. Leptons have mass, although the mass of electrons is extremely small. There are four known types of bosons, which are force-carrying particles. Each of these bosons carries a different fundamental force between interacting particles. In addition, there is a particle which may exist, called the "Higgs Boson", which gives objects the masses they have. Some types of bosons have mass; others are massless. Bosons have an electric charge of +1, -1, or 0. Q: Protons consist of three quarks: two up quarks and one down quark. Neutrons also consist of three quarks: two down quarks and one up quark. Based on this information, what is the total electric charge of a proton? Of a neutron? A: These combinations of quarks give protons a total electric charge of +1 (2/3 + 2/3 - 1/3 = 1) and neutrons a total electric charge of 0 (2/3 - 1/3 - 1/3 = 0). The interactions of matter particles are subject to four fundamental forces: gravity, electromagnetic force, weak nuclear force, and strong nuclear force. All of these forces are thought to be transmitted by bosons, the force- carrying fundamental particles. The different types of bosons and the forces they carry are shown in Table 1.2. Consider the examples of gluons, the bosons that carry the strong nuclear force. A continuous exchange of gluons between quarks binds them
Question: fundamental particles that make up protons and neutrons are known as
quarks.