Physics
Quantum Physics
Quantum physics is the branch of physics that deals with the behavior of particles at the atomic and subatomic levels. It describes the fundamental nature of energy and matter, incorporating principles such as wave-particle duality, superposition, and entanglement. Quantum physics has led to groundbreaking technologies like quantum computing and has revolutionized our understanding of the universe at its most fundamental level.
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12 Key excerpts on "Quantum Physics"
eBook - PDFThe Sciences
An Integrated Approach
- James Trefil, Robert M. Hazen(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
Quantum mechanics, then, is the branch of science that is devoted to the study of the motion of objects that come in small bundles, or quanta. We have already seen that material inside the atom comes in little bundles—tiny pieces of matter we call electrons travel in orbits around another little bundle of matter we call the nucleus. In the language of physicists, the atom’s matter is said to be quantized. Electrical charge is also quantized—electrons have a charge of exactly −1 fundamental unit of charge, and protons have a +1 charge. We’ve seen that photons emitted by an atom can have only certain values of energy, so that energy levels in the atom and emitted energy are quantized. In fact, inside the atom, in the world of the submicroscopically small, everything comes in quantized bundles. Our everyday world isn’t like this at all. Although we’ve been told since childhood that the objects around us are made up of atoms, for all intents and purposes we experience matter as if it were smooth, continuous, and infinitely divisible. Indeed, for almost any phenomenon in the physical world, the idea of matter existing in continuous form works as well as anyone would want. The quantum world is foreign to our senses. All of the intuition that we have built up about the way the world operates—all of the “gut feelings” we have about the universe— comes from our experiences with large-scale objects made up of apparently continuous material. If it should turn out (as it does) that the world of the quantum does not match our intuition, we should not be surprised. We have never dealt with this kind of world, so we have no particular reason, based on observations or experience, to believe that it should behave one way or the other. Digital Pictures It’s 9:30 a.m. as you pull into the oceanside parking lot. You’ve made great time and are eager to hit the beach.
eBook - PDF- Md Nazoor Khan, Simanchala Panigrahi(Authors)
- 2017(Publication Date)
- Cambridge University Press(Publisher)
7 Elementary Concepts of Quantum Physics 7.1 Introduction It is correctly told that mathematics is the queen of all sciences; in the same spirit, Quantum Physics or quantum mechanics may be called the king of all sciences. Our knowledge in any field of science is incomplete as long as we remain unacquainted with Quantum Physics. The concepts of Quantum Physics form the basis for our present understanding of physical phenomena on an atomic and microscopic scale. The concepts of Quantum Physics can be applied to most fields of science and engineering starting from biology to quantum computers to cosmology. Within engineering, important subjects of practical significance include semiconductor transistors, lasers, quantum optics, and molecular devices where Quantum Physics plays the most vital role. As technology advances, quantum concepts give birth to an increasing number of new electronic and opto-electronic devices. Their fabrications and functions can only be understood by using Quantum Physics. Within the next few years, fundamentally quantum devices such as single-electron memory cells and photonic signal processing systems may be available commercially. As nano-and atomic-scale devices become easier to manufacture, these sophisticated manufacturing units will require an increasing number of individuals with sound knowledge of Quantum Physics. Therefore, all universities in the world have included Quantum Physics as a subject in their technical course curricula. Quantum Physics is no longer a theoretical subject with mathematical complexities but an engineering subject! 7.2 Need for Quantum Physics Two time-tested proverbs are, ‘Failure is the pillar of success' and 'Necessity is the mother of invention’. Classical physics based on Newtonian laws, thermodynamical laws and 550 Principles of Engineering Physics 1 classical laws of electromagnetism explained successfully the macroscopic world.
eBook - PDF- Nelson Bolívar(Author)
- 2020(Publication Date)
- Arcler Press(Publisher)
Fundamentals of Physics 3 i.e., the so-called thermal death of the universe (Reimann and Hänggi, 2002; Schmid and Zieģelmann, 2017). Quantum mechanics is a whole new world of physics which introduces us to non-traditional laws of physics. It seems that quantum mechanics provides to us a universal opinion in which: • There exists a loss of certainty and an unremovable, unavoidable randomness encompasses the physical world. Albert Einstein was extremely dissatisfied with this quantum physical concept, as stated in his well-known saying: “God does not play dice with the universe.” It is also predicted that the method of performing an observation may disturb the focused subject in an irrepressibly random way (even if there is no physical contact of the object with the outside world). • All the physical systems seem to behave as if they are performing a variety of mutually exclusive tasks simultaneously. For example, an electron bombarded at a wall having two holes in it can seem to act as if it passes through both of the holes simultaneously (Popper, 1950; Kofler and Brukner, 2007). • Broadly disjointed physical systems can act as if they are somehow entangled by a ‘spooky action at a distance.’ In this way, these physical systems are interconnected in mysterious ways that seem to defy either the rules of special relativity or the laws of probability (Brandt and Physics, 1973; Boyer, 1984). The third property of quantum mechanics mentioned above leads us to the deduction that there are some facets of the contemporary physical world which are hard to be termed objectively ‘real’ (Averill and Keating, 1981; Schulze et al., 2000). In short, all of the above three points clearly defy our classical standpoint of the world. 1.2. CLASSICAL PHYSICS Before the introduction of quantum mechanics for understanding the affairs of the physical world, it is worthwhile to comprehend the classical laws of physics.
- Chary Rangacharyulu, Emmanuel Haven(Authors)
- 2010(Publication Date)
- World Scientific(Publisher)
The same holds true for the laser and the light-emitting diode, which jointly provide the basis for optical communication networks (the backbone of the telecommunications industry) and optical data storage (in the form of CDs and DVDs, for example), and many other 204 technologies. Yet more quantum technology (such as quantum computers and quantum cryptography) is waiting in the wings, promising to transform our lives still further. The empirical successes of quantum theory leave little doubt that the mathematical rules of quantum theory—the quantum formalism — accurately capture fundamental features of the workings of the physical world. Since their formulation over 80 years ago, there have been very strong indications that these rules describe a physical reality that cannot be encompassed within the view of reality that underpins classical physics. However, the precise nature of the implications of the quantum formalism for our understanding of the material world remains obscure. 2. Classical Physics and the Nature of a Physical Theory To understand better the nature of the problem and its importance, it is helpful to begin by considering classical physics. Underlying classical physics is a definite conception of the nature of reality, which traces back to the pioneering work of such figures as Descartes, Galileo, and Newton in the seventeenth century. The essential idea is that the totality of all that exists in the phenomenal world (namely that aspect of the world registered by our senses or instrumental extensions thereof such as microscopes or telescopes) is matter moving on the fixed stage of space in step with a universal time in precise accord with mathematical, deterministic laws of motion.
The description of particles in terms of a wave defies our com- monsense. Situations in which a photon or an electron seems to “know” how an appa- ratus will be arranged before the arranging is done seem wrong and unnatural. Many people, scientists and nonsci- entists alike, find the conclusions of quan- tum mechanics to be quite unsettling. The American physicist Richard Feynman stressed this point when he said, “I can safely say that nobody understands quan- tum mechanics. . . . Do not keep saying to yourself, ‘But how can it be like that?’ . . . Nobody knows how it can be like that.” In spite of this rather disturbing situ- ation, the success of quantum mechanics provides ample evidence that there is a cor- rect way to describe an atomic-scale system. If you ignore this fact, you can get into a lot of trouble. Newtonian notions like position and velocity just aren’t appropri- ate for the quantum world, which must be described from the beginning in terms of waves and probabilities. Quantum mechan- ics thus becomes a way of predicting how subatomic objects change in time. If you know the state of an electron now, you can use quantum mechanics to predict the state of that electron in the future. This process is identical to the application of Newton’s laws of motion in the macroscopic world. The only difference is that in the quantum world, the “state” of the system is a probability. In the view of most working scientists, quantum mechanics is a marvelous tool that allows us to do all sorts of experiments and build all manner of new and important pieces of equipment. The fact that we can’t visualize the quantum world in familiar terms seems a small price to pay for all the benefits we receive. TECHNOLOGY Quantum Computing Computers have become a common tool in everyday life—you probably use one rou- tinely in your schoolwork.
eBook - PDF- Ian D. Lawrie(Author)
- 2012(Publication Date)
- CRC Press(Publisher)
While the mathemati- cal developments that constitute quantum mechanics have been outstandingly successful in describing all manner of observed properties of matter, it is fair to say that the conceptual basis of the theory is still somewhat obscure. I my- self do not properly understand what it is that quantum theory tells us about the nature of the physical world, and by saying this I mean to imply that I do not think anybody else understands it either, though there are respectable scientists who write with confidence on the subject. This need not worry us unduly. There does exist a canon of generally accepted phrases which, if we do not examine them too critically, provide a reliable means of extracting from the mathematics well defined predictions for the outcome of any experiment we can perform (apart, that is, from the difficulty of solving the mathemat- ical equations, which can be very great). I shall generally use these without comment, and readers must choose for themselves whether or not to accept them at face value. This chapter deals with non-relativistic quantum mechanics, and I am go- ing to assume that readers are already familiar with the more elementary 141 142 A Unified Grand Tour of Theoretical Physics aspects of the subject. The following section outlines the reasons why clas- sical mechanics has proved inadequate and reviews the elementary ideas of wave mechanics. Although the chapter is essentially self-contained, readers who have not met this material before are urged to consult a textbook on quantum mechanics for a fuller account. The remaining sections develop the mathematical theory in somewhat more general terms, and this provides a point of departure for the quantum field theories to be studied in later chap- ters. 5.0 Wave Mechanics The observations which led to the quantum theory are often summarized by the notion of particle–wave duality.
eBook - PDFA Basic Theory of Everything
A Fundamental Theoretical Framework for Science and Philosophy
- Atle Ottesen Søvik(Author)
- 2022(Publication Date)
- De Gruyter(Publisher)
13 Understanding Quantum Mechanics Quantum mechanics gives us some fundamental insights into how the world works that a theory of the world should be able to integrate. It is the purpose of this chapter to do so, and we shall see that it fits well into what is said in the rest of the book. Quantum mechanics is often made more mysterious than it has to be. There are certainly some strange findings and some new ways of thinking about how nature works, but there are also good ways of understanding it and many exag- gerations being made in presentations of quantum mechanics. There are some strange phenomena in nature that are predicted by the formalism of quantum mechanics, but it is very controversial what this tells us about the world. The phenomena and how to understand the formalism give us a list of standard problems that a good theory of quantum mechanics should explain. In this chapter I will list some problems first (Section 13.1), which also will serve to introduce quantum mechanics, then I will present a good way of think- ing about these problems (Section 13.2). This presentation of problems and sol- utions leans heavily on the book Quantum Theory by Tim Maudlin, which is by far the best book I have read on quantum mechanics (Maudlin, 2019).²⁵⁸ My own presentation is a simplified and non-technical/non-mathematical version of the real issues involved for the sake of readability, so for details one should consult Maudlin’s book (a little taste of the mathematics is given in an excursus in the end). In Section 13.3 I will discuss some remaining problems and suggest how they should be solved. This will show where my thinking differs from Maudlin. There are two excursuses in the end, first one for those who would like a lit- tle taste of the formalism of quantum mechanics (13.4), then one excursus spec- ulating over why we have the often seemingly strange laws of nature that we do (13.5).
eBook - PDF- Bernard Dugué(Author)
- 2018(Publication Date)
- Wiley-ISTE(Publisher)
Thus, quantum description in terms of complex waves corresponds to an element of the physical world under exceptional conditions. In a totally different context, quantum entanglement has equally pushed the horizon of knowledge. In a device containing two intertwined “elements”, a measurement on one of them makes it possible to obtain information about the second one. In other words, global information is contained in the part (see Chapter 3). As a result, these considerations open a dialogue with nature: in fact, what is matter from the quantum point of view? Having elaborated this question in other papers, I suggest some elements of response by refocusing on the notion of information, which will be a common thread in this work. Primordial quantum matter “produces” or “contains” information that can be communicated to the experimenter by means of a technological interface. Therefore, following the previous example, the information content is provided by a wave function that looks like this: √1 / 3 | ψ-red> + √2 / 3 | ψ- blue>. The information communicated corresponds to one of the observables, red or blue. In other words, it is quantum gum that sticks and is introduced into the technological device. It is in a similar 6 Time, Emergences and Communications fashion that hidden impressionist matter projects a few tiny drops of paint, if we look close enough. By nature, Quantum Physics is a dynamic. However, it is a dynamic of communications, not of mechanics with forces and is arranged in a geometrical extent, like that of Newton or Lagrange. 1.2. Quantum states or how nature communicates with physicists Let us start with a general idea that is applicable to every physical experience; two notions are always present: state and measurement. In a sense, a state is like a “dynamic and kinematic inventory”. With variables and equations that determine dynamics and kinematics, that is, the arrangement of forces and the movement of particles.
- Tian Yu Cao(Author)
- 2019(Publication Date)
- Cambridge University Press(Publisher)
We must refrain from determining the amount of momentum that passes into the instrument in order to apply the space-time point of view” (Bohr, 1928). 124 The Rise of Quantum Theory 7 The Formation of the Conceptual Foundations of Quantum Field Theory Quantum field theory (QFT) can be analyzed in terms of its mathematical structure, its conceptual scheme, or its basic ontology. The analysis can be done logically or historically. In this chapter, only the genesis of the conceptual foundations of QFT relevant to its basic ontology will be treated carefully; no detailed discussion of its mathematical structures or its epistemological underpinnings will be given. Some conceptual problems, such as those related to probability and measurement, will be discussed, but only because of their relevance to the basic ontology of QFT, rather than their intrinsic philosophical interest. The content of this chapter involves the formation and interpretation, in a roughly chronological order, of the concepts of the wave function, quantization (of energy or of the electromagnetic field), quantum field, the vacuum, interactions between fields, and renormalization. The first two topics will be discussed in relation to the discovery of the quantum field and its various representations, which was the starting point of the concep- tual development of QFT. As to interactions, which were the origin of field theories (classical as well as quantum) and the main subject of this volume, in addition to a brief treatment given here, further discussions will be given in Part III. 7.1 The Tortuous Route to the Quantum Field Quantum field theory is not a quantum theory applied to classical fields. Rather, it is a theory of quantum fields. Quantum fields belong to a new natural kind, categorically different from the old natural kind of classical fields. The recognition of quantum fields as such was achieved through a complicated constructive process rife with confusions and misinterpretations.
eBook - PDF- P R Wallace(Author)
- 1991(Publication Date)
- World Scientific(Publisher)
Angular de Brogile waves. particle. In these statements, the words causality, observation, observer, reality, phenomena and particle are not used in their conventional sense, so that the images conveyed by them may be misleading and give a false impression of the significance of the quantum theory. Even the word uncertainty (as in uncertainty principle) has misleading connotations. It is unfortunate that some philosophers, as well as some physicists (including Einstein himself), (a) 2 wavelengths (c) 4 wavelengths (b) 3 wavelengths (d) 6 wavelengths 346 Phyeici: Imagination 8 Reality to say nothing of popularizers of science who wish to titillate the reader with the supposed paradoxical character of Quantum Physics, do not take greater pains to be precise in the use of these terms. We shall subsequently deal with these questions, but for the moment, we will confine our attention to wave-particle duality. A useful starting point in the discussion is to affirm, as Feyn-man is so fond of doing, that nature behaves in a quantum fashion. This fashion is quite strange to us, because it manifests itself on the level of the elementary components of matter. We have not been en-dowed, being, relatively speaking, macroscopic creatures made up of astronomically large quantities of these components, with sen-sory organs to perceive how matter behaves on this microscopic scale. We can only surmise, from macroscopic observation, what is going on at the level of atoms, molecules and the like. But our lan-guage is based on our experience, so we only have our macroscopic images to describe the microscopic world. In short, we carry deep within us prejudices based on our observation of the world at the human scale. The images, in fact, are all deeply rooted in the world of physics as observed at that scale. This is, in essence, Newtonian physics. But the new physics is — as in the case of relativity — very novel, outside our direct experience and the language and images rooted in it.
eBook - PDF"Thermodynamic" Universe, The: Exploring The Limits Of Physics
Exploring the Limits of Physics
- B G Sidharth(Author)
- 2008(Publication Date)
- World Scientific(Publisher)
One of these ideas was the wave particle duality. Another was Heisenberg’s Uncertainty Principle: surprisingly it would not be possible to measure simultaneously and accurately the position and momentum of a particle. This was related to wave particle duality itself. Yet another was that of the collapse of the wave function in which process causality becomes a casual-ity. To put it simply, if the wave function is a super position of the eigen states of an observable, then a measurement of the observable yields one of the eigen values no doubt, but it is not possible to predict which one. Due to the act of observation, the wave function instantly collapses to any one of its eigen states in an acausal manner. To put it another way, the wave function obeys the causal Schrodinger equation, for example, till the instant of observation at which point, causality ceases. Indeed, we saw that this was true within the Compton scale itself. Another important counter intuitive feature of Quantum Mechanics is that of non locality. In fact Einstein with Podolsky and Rosen put forward in 1935 his arguments for the incompleteness of Quantum Mechanics on this score [24 , 25]. This has later come to be known as the EPR paradox. To put it in a simple way, without sacrificing the essential concepts, let us consider two elementary particles, for example two protons kept together somehow. They are then released and move in opposite directions. When the first proton reaches the point A its momentum is measured and turns out to be say, ~ p . At that instant we can immediately conclude, without any further measurement that the momentum of the second proton which is at 18 The “Thermodynamic” Universe the point B is -~ p . This follows from the Conservation of Linear Momen-tum, and is perfectly acceptable in Classical Physics, in which the particles possess a definite momentum at each instant.
eBook - PDFFundamental Principles of Modern Theoretical Physics
International Series of Monographs in Natural Philosophy
- R. H. Furth, D. Ter Haar(Authors)
- 2013(Publication Date)
- Pergamon(Publisher)
We are therefore led to believe that an individual photon can either penetrate through the boundary or be reflected by it, and as all photons are identical, it must be the result of chance whether the one or the other event happens. This idea is, by the way, remarkably close to the notions of Newton's particle theory of light, accord-ing to which the light particles should be subject to fits of easy reflection and easy penetration of boundaries. A similar dual nature is exhibited in the movement of material particles because, according to De Broglie's theory, this movement can also be described as a propagation of De Broglie waves. Here, again a unique relationship between the direction and speed of the particle movement, on the one hand, and the direction and velocity of the corresponding wave is established by the equations (2.2.18), but the position of the particle is not determined at all. In 1926 Born therefore suggested the statistical interpretation of the quan-tum mechanical wave function , now almost generally accepted. According to this Iy i1 2 is the probability density for finding a particle at some specified point in space at any particular time, again provided that the normalization condition (3.2.3) is satisfied. This, of course, constitutes a break with the classical law of causation, as already indicated in the introduction, because in contrast to the situation in classical mechanics, the solution of the wave equation (3.1.6) does not determine the position r of the particle as a func-tion of time but only allows the probabilities for the various values of r to be calculated. However, as will be explained later in detail in section 7.1, the observable quantities, which play the role of the classical parameters of physical systems, are in quantum mechanics represented by operators whose expectation values for sets of very many observations are defined in terms of the wave function.
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