Physics (Encyclopedia of Science)
Physics is the science that deals with matter and energy and with the interaction between them. Perhaps you would like to determine how best to aim a rifle in order to hit a target with a bullet. Or you want to know how to build a ship out of steel and make sure that it will float. Or you plan to design a house that can be heated just with sunlight. Physics can be used in answering any of these questions.
Physics is one of the oldest of the sciences. It is usually said to have begun with the work of Italian scientist Galileo Galilei (1564642) in the first half of the seventeenth century. Galileo laid down a number of basic rules as to how information about the natural world should be collected. For example, the only way to obtain certain knowledge about the natural world, he said, is to carry out controlled observations (experiments) that will lead to measurable quantities. The fact that physics today is based on careful experimentation, measurements, and systems of mathematical analysis reflects the basic teachings of Galileo.
Classical and modern physics
The field of physics is commonly subdivided into two large categories: classical and modern physics. The dividing line between these two subdivisions can be drawn in the early 1900s. During that period, a number of revolutionary new concepts about the nature of matter were proposed. Included...
(The entire section is 1055 words.)
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Physics (Encyclopedia of Science and Religion)
Physics is the branch of scientific investigation that focuses its attention on fundamental concepts, patterns, and relationships involving matter, energy, space, and time. Other natural sciences, such as chemistry, biology, geology, and astronomy, also deal with these categories in their investigation of material systems like atoms, molecules, life processes, organisms, planets, stars, and galaxies, but physics is concerned with the most basic and universal principles that apply to all of these diverse systems.
It is sometimes convenient to divide physics into several different arenas of concern, such as mechanics (the study of motion), electromagnetism and optics, thermodynamics, quantum physics, atomic physics, nuclear physics, particle physics, and relativity (the study of space, time, and gravity).
Classical mechanics is the study of motion in the manner established by Isaac Newton in the seventeenth century. Among its major contributions is a fruitful method for describing the cause-effect relationship for motion in a quantifiable manner. A force, like the familiar push or pull, functions as the cause of acceleration (any change in the speed or direction of motion), which is its effect. Another major contribution of Newton was his concept and description of the force of gravity that is experienced and exerted by every object possessing the quality of mass. The gravitational force that causes apples to fall earthward is also the kind of kind of force that steers the moon in its orbit around the Earth and the planets in their orbits around the sun.
Electromagnetism encompasses all phenomena in which electric and magnetic fields play a role. In classical physics, fields may be thought of as qualities of space that lead objects with certain properties to experience a force. Any object possessing the property of electric charge, for example, will experience a force in the presence of an electric field. Electromagnetic radiation (light, X-rays, radio waves) may be understood as variations in electric and magnetic fields that travel at the characteristic speed of three hundred thousand meters per second through space.
Thermodynamics is concerned with the manner in which energy, especially heat energy, affects the state of a system and its interaction with its environment. Energy, often characterized as the capacity to do work, appears in a diversity of forms and may be changed in either form or location as a consequence of some physical process. In all processes, however, the sum of the energy possessed by a system and its environment remains constant. This principle, called the First Law of Thermodynamics, or the conservation of energy, is thought to apply without exception to all physical phenomena.
Quantum theory describes the structure and behavior of systems like atoms, atomic nuclei, and molecules. Extremely small structures behave in a manner different from the predictions of classical mechanics. The quantities of energy possessed by a system or exchanged between systems, for instance, is restricted to certain values only. Furthermore, the outcome of many processes is open to diverse options, each outcome having a calculable probability of occurrence.
Relativity theory provides a framework for speaking of the interactive relationships among space, time, mass, and gravity. Special Relativity describes the way in which the experience of time and space are interrelated, while General Relativity focuses its attention on the interrelationships among mass, space, gravity, and motion.
See also COSMOLOGY, PHYSICAL ASPECTS
Asimov, Isaac. Understanding Physics. New York: Barnes and Noble Books, 1988.
Kuhn, Karl. Basic Physics: A Self-teaching Guide, 2nd edition. New York: Wiley, 1996.
Halliday, David; Resnick, Robert; and Walker, Jearl. Fundamentals of Physics, 6th edition. New York: Wiley, 2000.
Feynman, Richard P.; Leighton, Robert B.; and Sands, Matthew L. The Feynman Lectures on Physics. Boston: Addison-Wesley, 1994.
HOWARD J. VAN TILL
Physics (World of Earth Science)
Physics and astronomy, from which all other sciences derive their foundation, are attempts to provide a rational explanation for the structure and workings of the Universe. The creation of the earliest civilizations and of mankind's religious beliefs was profoundly influenced by the movements of the Sun, Moon, and stars across the sky. As our most ancient ancestors instinctively sought to fashion tools through which they gained mechanical advantage beyond the strength of their limbs, they also sought to understand the mechanisms and patterns of the natural world. From this quest for understanding evolved the science of physics. Although these ancient civilizations were not mathematically sophisticated by contemporary standards, their early attempts at physics set mankind on the road toward the quantification of nature.
In Ancient Greece, in a natural world largely explained by the whim of gods, the earliest scientists and philosophers of record dared to offer explanations of the natural world based on their observations and reasoning. Pythagoras (58200 B.C.) argued about the nature of numbers, Leucippus (c. 440 B.C.), Democritus (c. 420 B.C.), and Epicurus (34270 B.C.) asserted matter was composed of extremely small particles called atoms.
Many of the most cherished arguments of ancient science ultimately proved erroneous. For example, in Aristotle's (38422 B.C.) physics, for example, a moving body of any mass had to be in contact with a "mover," and for all things there had to be a "prime mover." Errant models of the universe made by Ptolemy (c.A.D.10070) were destined to dominate the Western intellectual tradition for more than a millennium. Midst these misguided concepts, however, were brilliant insights into natural phenomena. More then 1700 years before the Copernican revolution, Aristarchus of Samos (31030 B.C.) proposed that the earth rotated around the Sun and Eratosthenes Of Cyrene (27694 B.C.), while working at
the great library at Alexandria, deduced a reasonable estimate of the circumference of the earth.
Until the collapse of the Western Roman civilization there were constant refinements to physical concepts of matter and form. Yet, for all its glory and technological achievements, the science of ancient Greece and Rome was essentially nothing more than a branch of philosophy. Experimentation would wait almost another two thousand years for injecting its vigor into science. Although there were technological advances and more progress in civilization than commonly credited, during the Dark and Medieval Ages in Europe science slumbered. In other parts of the world, however, Arab scientists preserved the classical arguments as they developed accurate astronomical instruments and compiled new works on mathematics and optics.
At the start of the Renaissance in Western Europe, the invention of the printing press and a rediscovery of classical mathematics provided a foundation for the rise of empiricism during the subsequent Scientific Revolution. Early in the sixteenth century, Polish astronomer Nicolaus Copernicus's (1473543) reassertion of heliocentric theory sparked an intense interest in broad quantification of nature that eventually allowed German astronomer and mathematician Johannes Kepler (1571630) to develop laws of planetary motion. In addition to his fundamental astronomical discoveries, Italian astronomer and physicist Galileo Galilei (1564642) made concerted studies of the motion of bodies that subsequently inspired seventeenth century English physicist and mathematician Sir Isaac Newton's (1642727) development of the laws of motion and gravitation in his influential 1687 work, Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy).
Following the Principia, scientists embraced empiricism during an Age of Enlightenment. Practical advances spurred by the beginning of an industrial revolution resulted in technological advances and increasingly sophisticated instrumentation that allowed scientists to make exquisite and delicate calculations regarding physical phenomena. Concurrent advances in mathematics, allowed development of sophisticated and quantifiable models of nature. More tantalizingly for physicists, many of these mathematical insights ultimately pointed toward a physical reality not necessarily limited to three dimensions and not necessarily absolute in time and space.
Nineteenth century experimentation culminated in the formulation of Scottish physicist James Clerk Maxwell's (1831879) unification of concepts regarding electricity, magnetism, and light in his four famous equations describing electromagnetic waves.
During the first half of the twentieth century, these insights found full expression in the advancement of quantum and relativity theory. Scientists, mathematicians, and philosophers united to examine and explain the innermost workings of the universeoth on the scale of the very small subatomic world and on the grandest of cosmic scales.
By the dawn of the twentieth century more than two centuries had elapsed since Newton's Principia set forth the foundations of classical physics. In 1905, in one grand and sweeping Special Theory of Relativity, German-American physicist Albert Einstein (1879955) provided an explanation for seemingly conflicting and counter-intuitive experimental determinations of the constancy of the speed of light, length contraction, time dilation, and mass enlargements. A scant decade later, Einstein once again revolutionized concepts of space, time and gravity with his General Theory of Relativity.
Prior to Einstein's revelations, German physicist Maxwell Planck (1858947) proposed that atoms absorb or emit electromagnetic radiation in discrete units of energy termed quanta. Although Planck's quantum concept seemed counter-intuitive to well-established Newtonian physics, quantum mechanics accurately described the relationships between energy and matter on atomic and subatomic scale and provided a unifying basis to explain the properties of the elements.
Concepts regarding the stability of matter also proved ripe for revolution. Far from the initial assumption of the indivisibility of atoms, advancements in the discovery and understanding of radioactivity culminated in renewed quest to find the most elemental and fundamental particles of nature. In 1913, Danish physicist Niels Bohr (1885962) published a model of the hydrogen atom that, by incorporating quantum theory, dramatically improved existing classical Copernican-like atomic models. The quantum leaps of electrons between orbits proposed by the Bohr model accounted for Planck's observations and also explained many important properties of the photoelectric effect described by Einstein.
More mathematically complex atomic models were to follow based on the work of the French physicist Louis Victor de Broglie (1892987), Austrian physicist Erwin Schrödinger (1887961), German physicist Max Born (1882970) and English physicist P.A.M Dirac (1902984). More than simple refinements of the Bohr model, however, these scientists made fundamental advances in defining the properties of matterspecially the wave nature of subatomic particles. By 1950, the articulation of the elementary constituents of atoms grew dramatically in numbers and complexity and matter itself was ultimately to be understood as a synthesis of wave and particle properties.
Against a maddeningly complex backdrop of politics and fanaticism that resulted in two World Wars within the first half of the twentieth century, science knowledge and skill became more than a strategic advantage. The deliberate misuse of science scattered poisonous gases across World War I battlefields at the same time that advances in physical science (e.g., x-ray diagnostics) provided new ways to save lives. The dark abyss of WWII gave birth to the atomic age. In one blinding flash, the Manhattan Project created the most terrifying of weapons that couldn an blinding flashorever change the course of history for all peoples of the earth.
The insights of relativity theory and quantum theory also stretched the methodology of science. No longer would science be mainly exercise in inductively applying the results of experimental data. Experimentation, instead of being only a genesis for theory, became a testing ground to test the apparent truths unveiled by increasingly mathematical models of the universe. Moreover, with the formulation of quantum mechanics, physical phenomena could no longer be explained in terms of deterministic causality, that is, as a result of at least a theoretically measurable chain causes and effects. Instead, physical phenomena were described as the result of fundamentally statistical, unreadable, indeterminant (unpredictable) processes.
The development of quantum theory, especially the delineation of Planck's constant and the articulation of the Heisenburg uncertainty principle carried profound philosophical implications regarding limits on knowledge. Modern cosmological theory (i.e., theories regarding the nature and formation of the universe) provided insight into the evolutionary stages of stars (e.g., neutron stars, pulsars, black holes, etc.) that carried with it an understanding of nucleosythesis (the formation of elements) that forever linked mankind to the lives of the very stars that had once sparked the intellectual journey towards an understanding of nature based upon physical laws.
With specific regard to geology, the twentieth century development of geophysics and advances in sensing technology made possible the revolutionary development of plate tectonic theory.
See also Earth Science; History of exploration I (Ancient and classical); History of exploration II (Age of exploration); History of exploration III (Modern era); History of geo-science: Women in the history of geoscience; History of manned space exploration