Physics
Particles
Particles are tiny units of matter that make up the universe. They can be classified as either elementary particles, which are the building blocks of matter, or composite particles, which are made up of smaller particles. In physics, the study of particles helps to understand the fundamental forces and interactions in the universe.
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6 Key excerpts on "Particles"
eBook - PDF- André Rubbia(Author)
- 2022(Publication Date)
- Cambridge University Press(Publisher)
1 Introduction and Notation A particle (from the Latin particula, little part) is a minute portion of matter. 1.1 Subatomic Particles When we first observe the Universe, it might appear to us as a very complex object. One of the primary goals of the philosophy of Nature (or simply Physics) is to “reduce” (“simplify”) this picture in order to find out what the most fundamental constituents of matter (i.e., the atoms from the Greek word indivisible ) are and to understand the basic forces by which they interact in the otherwise void space, along the line of thinking of Demokritos 1 who wrote “Nothing exists except atoms and empty space.” In this context, subatomic Particles are physical objects smaller than atoms. In particle physics, Particles are objects that are localized in space and that are characterized by intrinsic properties. As we will see later, the set of intrinsic properties used to classify Particles is chosen from those which behave in a well-defined way under the action of a transformation. As a matter of fact, we would expect some of these properties not to change at all under particular transformation. For instance, we expect some of its properties to be independent of the velocity of the particle or the direction in which it is traveling. This procedure of classification was actually initiated by Eugene Wigner 2 in his seminal paper of 1939 [1]. We will come back to this later. Elementary Particles are Particles which, according to current theories, are not made of other Particles, or we should rather say, whose substructure, if any, is unknown. They are thus considered as point-like objects. Composite Particles, on the other hand, are composed of other Particles, in general of elementary Particles, and are thus extended in space. All subatomic Particles are classified according to their properties and given common names such as electrons, muons, taus, protons, neutrons, neutrinos, etc.
eBook - PDF- Stephen Thornton, Andrew Rex, Carol Hood, , Stephen Thornton, Stephen Thornton, Andrew Rex, Carol Hood(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
C H A P T E R 521 14 Particle Physics If I could remember the names of all these Particles, I’d be a botanist. Enrico Fermi I have done a terrible thing: I have postulated a particle that cannot be detected. Wolfgang Pauli (after postulating the existence of the neutrino) We began our study of subatomic physics in Chapter 12. We investigated the nucleus in Chapters 12 and 13. Now we want to delve deeper, because finding answers to some of the basic questions about nature is a foremost goal of science: What are the basic building blocks of matter? What is inside the nucleus? What are the forces that hold matter together? How did the universe begin? Will the universe end, and if so, how and when? We use the ideas, concepts, and laws of physics to try to answer most of these questions here and save the last two ques- tions for the two remaining chapters. The ancient Greek philosophers, among them Aristotle, supposed things were made of earth, fire, wind, and water. Democritus derived the word atom from the Greek word atomos, which refers to an object that cannot be further cut into pieces. So the atom was meant to be the smallest indivisible unit of matter. In this book we have shown that matter is made of molecules and atoms, and electromagnetic forces are responsible for holding atoms together. At a smaller level, an atom is made of electrons and a nucleus. The electromagnetic force is responsible for attracting the electrons to the nucleus, and the strong (nuclear) force is responsible for keeping neutrons and protons together in the nucleus. The definition of elementary particle has changed over the years. In particle physics, we refer to an elementary particle as having no known substructure.
eBook - PDF- Nelson Boli´var(Author)
- 2023(Publication Date)
- Arcler Press(Publisher)
ELEMENTARY PARTICLE PHYSICS 4 CONTENTS 4.1. Introduction ...................................................................................... 88 4.2. Particles and AntiParticles ................................................................. 88 4.3. The Four Forces of Nature ................................................................. 93 4.4. Quarks.............................................................................................. 94 4.5. The Electromagnetic Force .............................................................. 100 4.6. The Electroweak Force .................................................................... 103 4.7. The Gravitational Force and Quantum Gravity ................................ 109 References ............................................................................................. 114 CHAPTER Developments in Modern Physics 88 4.1. INTRODUCTION Humanity has long sought simplicity in the natural world. The ancient Greeks attempted to characterize the whole physical universe in terms of air, earth, fire, and water. To characterize the physical universe of time, matter, and space, these were substituted with the basic standards of mass, length, time, and charge. We saw that time and space are structure in the same foot, a representation of a single amount of time and space and that energy and matter are convertible, to the point where energy may be considered one of the basic quantities. We also discovered that energy is finite, thus matter must likewise be finite (Budker and Skrinskiĭ, 1978; Glashow, 1980). What is the lowest possible unit of matter? In other words, what are the basic or elemental components of matter? What forces are at work on such basic Particles? Is it feasible to unite such natural forces into a single integrated force that accounts for all observable interactions? In this chapter, we will try to address such questions (Gatti and Manfredi, 1986; Passon et al., 2018).
eBook - PDF- Gary N. Felder, Kenny M. Felder(Authors)
- 2022(Publication Date)
- Cambridge University Press(Publisher)
13 Particle Physics Following Chadwick’s discovery of the neutron in 1932, it might have seemed that all forms of matter could be explained as different combinations of fewer than 100 elements, and those elements in turn could be explained as different combinations of protons, neutrons, and electrons. Add photons to the list, and you pretty much had the universe summed up. This is the kind of model physicists like: complicated behavior arising from a few simple building blocks. If there was a moment of such confidence, it didn’t last long. Carl Anderson identified a positively charged electron in 1932 (dubbed a “positron” by the Physical Review), and over the next few decades hundreds of new Particles were discovered. When Nobel Laureate Isidor Rabi was informed of a particle essentially identical to the electron but with larger mass (now called a “muon”), he responded: “Who ordered that?” Enrico Fermi supposedly quipped: “If I could remember the names of all these Particles, I would have been a botanist.” In the 1960s, Murray Gell-Mann found a way out. He proposed that most of the apparently fundamental Particles were made from more basic building blocks that he called “quarks.” In the 1970s a small group of fundamental Particles, including Gell-Mann’s quarks, were formalized into the “standard model of particle physics”, which is still used today. That model accounts for all the Particles we have ever observed, and for three of the four known fundamental forces of nature. The first two sections of this chapter survey the overwhelming “zoo” of Particles that emerged over decades of experiments, and the standard model that brought order to the chaos. If you want a general overview of particle physics, you could stop after those two sections. The third section fills in some of the experimental evidence that uncovered so many Particles.
eBook - PDF- Lincoln Wolfenstein, Joao P. Silva(Authors)
- 2010(Publication Date)
- CRC Press(Publisher)
11 2 C H A P T E R Waves That Are Particles; Particles That Are Waves A major revolution in our understanding of nature took place in the early twentieth century; we learned that light can have particle-like properties and that Particles can have wave-like properties. This is deeply ingrained into the standard model of particle physics. 2.1 Particles VERSUS WAVES This book tells the exhilarating recent history of the search for the funda-mental building blocks of all things and their interactions. When physi-cists mention “point Particles,” they may not be talking about fundamental Particles at all. Point Particles might have some internal structure, but they are so named because, whatever their internal structure might be, it has no bearing on the phenomenon under study. For example, consider a rigid ball sliding down an inclined plane without rolling and without friction. If this experiment is performed in a vacuum (that is, with all the air sucked out), the velocity that the ball has after it slides for 1 in. can be calculated ignoring what the ball is made of. It is even independent of the ball’s mass; it depends exclusively on the slope of the inclined plane. There is an interesting way to describe how this happens. When the ball is placed in a high position, we say that it has the potential to gain speed and we ascribe to it some potential energy. As it accelerates down the 12 ◾ Exploring Fundamental Particles inclined plane, we say that it transforms this potential energy into kinetic energy, from the Greek word kinesis , which means motion. That is, the potential energy the ball had because it was placed in a high position is transformed into the kinetic energy associated with its speed as it moves down the plane. 1 Another interesting quantity is the momentum of this particle. Momentum is an arrow (so-called vector) that has a size equal to the prod-uct of mass with velocity, and it has the direction of the particle’s movement.
eBook - PDFInterpreting Bodies
Classical and Quantum Objects in Modern Physics
- Elena Castellani(Author)
- 2020(Publication Date)
- Princeton University Press(Publisher)
PART THREE OBJECTS AND MEASUREMENT 12 What Is an Elementary Particle? Erwin Schr¨ odinger Increasing knowledge has in some ways made us not more certain but less certain of the nature of matter. Whereas Dalton and his school had a clear picture of the existence of atomic Particles as real and indestruc-tible solid Particles, modern wave mechanics implies very clearly that, in fact, they are not identifiable individuals at all. Although Daltonian con-ceptions provide convenient terms in which to describe the properties of matter, their original significance has undergone very important changes during the last thirty years. 1. A Particle Is Not an Individual Atomism in its latest form is called quantum mechanics. It has ex-tended its range to comprise, besides ordinary matter, all kinds of ra-diation, including light—in brief, all forms of energy, ordinary matter being one of them. In the present form of the theory the “atoms” are electrons, protons, photons, mesons, etc. The generic name is elemen-tary particle, or merely particle. The term atom has very wisely been retained for chemical atoms, though it has become a misnomer. This essay deals with the elementary particle, more particularly with a certain feature that this concept has acquired—or rather lost—in quan-tum mechanics. I mean this: that the elementary particle is not an indi-vidual; it cannot be identifled, it lacks “sameness.” The fact is known to every physicist, but is rarely given any prominence in surveys readable by nonspecialists. In technical language it is covered by saying that the par-ticles “obey” a newfangled statistics, either Einstein-Bose or Fermi-Dirac statistics. The implication, far from obvious, is that the unsuspected ep-ithet “this” is not quite properly applicable to, say, an electron, except with caution, in a restricted sense, and sometimes not at all. My objec-tive here is to explain this point and to give it the thought it deserves.
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