What is quantum physics? This post covers the first chapter of Michael Raymer's book; Quantum physics - What everyone needs to know. You can buy the book on Amazon or listen to all chapters on Audible. I have both.
"Quantum Physics is the study of matter and energy, the basic constituents of the physical world in the quantum realm. The quantum realm encompasses those aspects of nature that cannot be explained using classical physics. By classical physics, we physicists mean the theory of nature, devised from the 1600s Onward by Isaac Newton and others, who built their theories based on the behavior of familiar objects such as rocks, planets, oceans, clouds, wheels, gears, pulleys, clocks, and steam engines.
Because of the mechanical nature of many of these things, the theory of classical physics is also called the classical mechanics. The theory was expanded during the 1800s to encompass electricity and magnetism, which are more difficult to visualize. But in those days, they were also explained in more or less mechanical terms, using the basic concepts of classical physics. Thus, the classical physics theory of nature was concerned largely with so called particles, discrete bits of matter moving through time and space, and force fields, influences that established forces between objects that are not in direct physical contact. For example, electric and magnetic fields established forces between electrically charged object and lead to phenomenon such as radio signals and light waves that exist over regions much larger than the size of single particles.
Initially, around 1900, when scientists were first figuring out the makeup and structure of atoms, and they naturally perceived that electrons, protons and neutrons, had to be particles, and that their behaviors would be well described by classical mechanics, or they imagined electrons as being like tiny planets orbiting a larger atomic nucleus playing the sun's role, but to their shock when they ran the calculations using Newton's theory of classical mechanics and those of electromagnetism. And they found that the predictions of the theory were completely wrong when compared with the results of real world experiments. This historic situation drove an intellectual revolution between 1911- 25 which in many ways had as great an effect on humanity, as did for example, the French and American political revolutions.
Just more than a century earlier, classical mechanics was supplemented by the far more powerful theory called quantum mechanics, or simply quantum theory, I say supplemented rather than overthrown. Because classical mechanics is still an extremely useful theory, which yields highly accurate predictions for a phenomenon the human size scale. We don't need to use quantum mechanics, although we could to describe the motions of planes, trains and automobiles, for example, but we do need quantum mechanics to gain an understanding of the working of electrons and other atomic scale phenomenon. The challenge for us is that quantum mechanics is a highly abstract theory, making it hard to fathom its true meaning. The good news is that a straightforward use of the quantum theory yield extraordinarily accurate predictions for every phenomenon to which it has been applied. For example, using the ideas of quantum theory, physicists were able to understand how electrons travel through pieces of semiconductor crystals that now make up most of today's electronic devices. Without such an understanding, engineers could never have invented modern computers which now power the internet, and thus the information society. The big questions this small book attempts to answer are, what aspects and behaviors of atomic scale objects and force fields related to them cannot be described using classical physics? How are we to understand these behaviors using quantum theory? And to what good uses can this knowledge be applied? The latter question leads us to explore some very interesting and recent applications of quantum physics and a new field of research and development called quantum technology.
How does quantum physics affect everyday life and understanding of quantum physics enabled the invention of many familiar technologies? The laser the light emitting diode LED the transistor semiconductor based electronics including computers and smartphones, high capacity magnetic disk drives for computer data storage, all electronic memory used in flash drives and laptop computers, and liquid crystal displays LCDs that are used in nearly all information technology devices. A less familiar invention that emerged recently from quantum physics research is highly secure data encryption This invention is all the more important now with recent revelations about the difficulty of protecting information, and the degree to which interceptions of data traffic on the internet are attempted by unintended persons or agencies. modern electronics, including computers and smartphones rely on the quantum physics of electrons. Lasers, which appear in a wide range of technology and consumer product, create light using the quantum nature of photons. You might wonder what are electrons and photons? And how do they behave?
How do physicists explain the seemingly strange behaviors of electrons and photons? Using quantum theory? What does the word quantum really mean? One might also be curious about the many news reports touting this or that breakthrough in so called quantum computing or quantum technology. What can quantum technology do for us that classical technology can't? Could new breakthroughs lead to creating the technology of the future? Answers to these questions are explored in this book?
What is a physics theory? And what is the program of physics? A physics theory is a way of reasoning made up of a set of well substantiated concepts or principles that we use to construct models, which are conceptual representations of natural phenomena. A good physics theory captures or encapsulates many features and behaviors of some broad class of physical systems. It compresses a general description of a large portion of nature into concise statements or principles, almost always such a compressed description as expressed using mathematics. From this viewpoint, physics is a human endeavor to construct mathematical models of the physical world. To be considered an established scientific theory, it must first survive rigorous experimental testing, during which researchers try to find situations in which it might fail. If a physics theory passes all the tests to which it is subject, then it may be thought to be correct, and then it can be used reliably to create models of particular situations. But note that scientists can never really prove a theory is absolutely correct. Only that it works in all cases tested so far, there was always the chance that theory can be superseded by a better more complete theory. On the other hand, it is possible to disprove a theory if experimental observations go directly against it. The physics theories can do more than simply predict what will happen in a given situation. Ideally, they explained through their many interlinked details, how a phenomenon happens, and in some sense, why it happened. But to be honest, when pushed to the limits of our fundamental knowledge of nature, currently, the only answer that physics can offer for why is that's the way it is, we have learned the way it is by experimentation.
So what is the program of physics? That is, what are physicists striving to achieve? Why do humans want to develop mathematical models of the physical world? There are two main reasons curiosity and utility. All physics discoveries, although most are driven initially by curiosity have the potential for useful application. In some cases, the time lag is longer than another's. For example, the physics discoveries leading to the transistor led immediately to useful micro circuitry, which began the current computer revolution. On the other hand, Einstein's discovery of the general theory of relativity in 1915, was not applied practically until about 80 years later, when that theory was built into the global positioning system, GPS, which has revolutionized many aspects of our lives.
Why do we use the word model when referring to physics? This question gets to the heart of the purpose and role of science. Long ago, philosophers believed that natural philosophy as they then called science could reveal the true nature of things in the world. In modern times, a different viewpoint generally prevails. A common view of science now is that it provides conceptual models of the behavior of the world, rather than revealing its true underlying nature. What it really is. In science, a model is a mental or conceptual construct used to represent what goes on in the real world. The model is designed to perform in such a way that we can predict how the item being modeled actually performs. The such models are usually described mathematically. An example of a model is a computer program that climate scientists use to make their best predictions of the effect of adding carbon dioxide to Earth's atmosphere. It is important to distinguish between a conceptual model and the system the model represents. By analogy a toy train might be an excellent model of a real train, but no one would confuse the toy model for the real thing. Quantum physics is an attempt to model nature at its most fundamental level. But we should not confuse the quantum physics model that is the collection of concepts and mathematical representations with the real thing. Nature. This kind of thinking if taken too seriously can lead to fairytale physics. In the words of science author, Jim Packard. Quantum physics had a lot to do with a historical change to the viewpoint that science provides conceptual models only. Because we cannot see or even infer what electrons really are.
We are forced to work at a more remove more abstract level when talking about nature at the quantum level. And because all things are made of quantum stuff, many scientists believe the same insight holds ultimately for everything. Why was 2015 and especially good year for quantum physics? As I worked on writing this book, three groups of scientists announced successful experiments verifying for the first time that classical physics theory cannot explain observed measurements on a pair of separated objects that were prepared to have correlated properties. Physicists in Delft Netherlands Boulder, Colorado, United States, and Vienna, Austria carried out measurements on distant but correlated objects that put an end once and for all, to the classical worldview called Local realism. This worldview is based on the assumptions that physical objects carry with them definite properties or instructions for how to respond to a measurement being performed on them, and that physical influences acting on any object cannot travel faster than the speed of light. In the classical worldview, to objects can have correlated properties.
For example, two balls can be prepared to have the same color although the actual color is unknown. The balls colors are fixed before they are observed. And if one balls color is observed to the others is known immediately as well. Experiment experiments meant to test local realism are called Bell tests. After John Bell, who first proposed such experiment, local realism as an assumed basis for physical theory has now been proved false by such experiments. This remarkable conclusion is based on the fact that outcomes on too distant object can yield random outcomes with no fixed preordained values, yet can at the same time display remarkably well ordered coordination between the distant outcomes. This result flies in the face of common sense ideas of how the world works. Again, in the classical view, results of observations may appear to be random, but they are fixed before the measurement is actually carried out. On the other hand, quantum theory is perfectly capable of modeling and in a sense, explaining these experiments without appealing to the concept of fixed preordained measurement outcomes. This means that quantum theory is inconsistent with local realism, as was first proved theoretically by John Bell during the 1960s. These facts seem to have deep philosophical implications about the nature of reality. It remains a mystery how such strong correlations can occur at all, when the outcomes of distant experiments cannot be thought of as revealing predetermined values of the quantities being measured. chapters of this book are devoted to explaining the bell test experiments, and how so called quantum entanglement explains the results.
Why are some objects well described by classical physics models whereas others require a quantum physics description. There are two main reasons smallness and coherence, each of which is summarized briefly here. The smallness can refer to different aspects of objects, smallness of size or smallness of energy content. If the object is roughly the size of an atom about 10 to the negative 10th power meters, then it almost certainly cannot be modeled accurately using classical mechanics, and it must be described by the more accurate quantum theory. But interestingly, the opposite is not necessarily true. objects as large as a millimeter, about a 20th of an inch have been observed in experiments displaying behaviors that indicate a quantum nature, smallness or lowness of energy content. Good for example, refer to a tiny electric current in a metal wire, a superconductor at a temperature only slightly greater than absolute have zero and negative 273 degrees Celsius or negative 459 degrees Fahrenheit. A low temperature means small or low energy, or it could refer to a feeble flash of light containing only a tiny fraction, say 10 to the negative 21st power of the energy emitted by a 100 watt bulb in one second. Such a flash of light is said to contain just one photon of light, which refers to the smallest discrete amount of energy that light of a certain color can carry. A discrete amount of energy such as this is also called a light Quantum. The plural of quantum is quanta. Therefore, for example, a burst of light with a large amount of energy is said to contain many quanta. This discreteness of the energy carried in light, which we explore in more detail later, is the origin of the name quantum physics. In principle, a single quantum entity, such as a photon could extend across a very large volume, for example, many kilometers although such a photon would be large in size, it would be very small or low in energy content, and so the quantum theory would still apply to it. The second general reason an object may require a quantum description is quantum coherence. quantum coherence is a subtle concept, and it cannot be understood properly until after one understands how the state of an object is described using quantum theory. To give you a flavor of what is to come in later chapters, quantum objects can behave in ways that appear random although there is no obvious underlying physical cause of this randomness. For the case of an electron quantum coherence enters the theory in how it accounts for the different possibilities that may exist before the electrons location is observed. In a sense, the usual rules of logical thinking such as saying, it is located here or it is not located here, do not apply to quantum objects. Instead, it is said both possibilities must be superimposed in our thinking and not considered separately. quantum coherence makes such a superposition of possibilities physically realizable, as explained in later chapters. What are the elementary entities that make up the physical universe? This is a big question, and answering it has been the aim of physics research for centuries.
The simplest answer is that nearly all matter we can observe directly with our simple human senses, is made up of atoms, which are comprised of electrons, protons and neutrons. As stated previously, electrons are thought to be elementary constituents of matter, in the sense that they are not made of yet smaller constituents. Notice I'm not using the word particle here to avoid any misleading impressions that word might convey. On the other hand, protons and neutrons are comprised of smaller elementary constituents called quarks, which have the curious property that they cannot exist on their own outside of the groupings of quarks that make up objects such as protons or neutrons. Their existence is known for experiments began during the 1960s, in which fast moving electrons were aimed at protons, and the pattern of the deflected electrons indicated that protons have an internal substructure. A detailed model based on quantum physics was developed in which each proton or neutron is composed of three quarks of specific times. The model also made concrete predictions about further experiments, all of which had been verified, so we have good reason to believe the quark model is correct. Another important entity is the electromagnetic field, which refers to the combination of the electric fields and magnetic fields that surround electrically charged objects or magnets. These fields of influence not only transmit static electric forces and magnetic forces, they also make up radio waves and light waves. As mentioned earlier, light and radio waves carry energy, energy is defined most simply as the capability to cause motion. For example, a radio wave impinging on a radio antenna causes electrons in the metal of the antenna to move the motion of which can be detected and amplified to drive audio speakers. These phenomena are well described by classical mechanics. At the quantum level light can be viewed as being comprised of photons, which can be thought of very roughly as particle like entities that carry the energy in a radio wave or light beam. The photons are elementary, in that they are not comprised of constituents. It turns out that for a photon there is no clear concept of a precise position or location. concept we associate With particles, yet, as we will find out, they do behave in certain ways that we expect particles to behave. At the same time we know that light has some wave like behavior, so photons must also somehow carry wavelike behaviors. Therefore, a photon is neither a particle nor a wave in the classical sense. This verbal dance I'm doing to try to describe photons illustrates the difficulty of saying what a photon really is, and the difficulty of visualizing accurately how a photon behaves. Physicists have gotten used to this ambiguity and have no trouble deploying the mathematical machinery that we use to predict the outcomes of events involving photons. Yet even physicists have a hard time picturing in a simple way how all this really happened. For some, like me, this puzzlement makes quantum physics all the more intriguing and fascinating. But there are other kinds of particle like entities with exotic names such as me zones, muons, positrons and neutrinos. And there are fields other than the electromagnetic field, for example, the strong force, which is a field responsible for holding protons and neutrons together in an atomic nucleus. A rather exhaustive theoretical model, based on quantum physics, and called the Standard Model of particle physics encompasses all the known entities mentioned here, plus others I won't mention. This model, which is mathematical and highly abstract, predicts successfully essentially all the known processes involving all the identified elementary entities in nature. The capstone, the discovery that supports the Standard Model most strongly was the detection of the Higgs boson in 2012. The invention of the standard model and its experimental confirmation are together and exceptional achievement for humanity. There are still large unknowns in the universe, so called dark matter and dark energy, the existence of which astronomers infer from analysis of the motions of distant galaxies. In fact, it is estimated that about 95% of the universe is comprised of these as yet unknown entities. When they are identified, it is expected the standard model will need to be updated. "
End Part one of Chapter 1. I suggest to buy the book. It is an excellent Read. Look it up on Amazon.com
Transcribed by https://otter.ai
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