History of Physics
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 cosmos. The creation of the earliest civilizations and of mankind's religious beliefs were 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 argued about the nature of numbers, Leucippus (c. 440 B.C.), Democritus, and Epicurus (341-270 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 physics 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 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 than 1,700 years before the Copernican revolution, Aristarchus of Samos (310-230 B.C.) proposed that Earth rotated around the Sun and Eratosthenes of Cyrene, while working at the great library at Alexandria, deduced a reasonable estimate of the circumference of 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 2,000 years for injecting its vigor into science. 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 Nicholas Copernicus's reassertion of heliocentric theory sparked an intense interest in broad quantification of nature that eventually allowed German astronomer and mathematician Johannes Kepler to develop laws of planetary motion. In addition to his fundamental astronomical discoveries, Italian astronomer and physicist Galileo made concerted studies of the motion of bodies that subsequently inspired seventeenth-century English physicist and mathematician Sir Isaac Newton's development of the laws of motion and gravitation in his influential 1687 work, Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy).
Following 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 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 universe--both 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 theory of special relativity, German American physicist Albert Einstein provided an explanation for seemingly conflicting and counterintuitive 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 Max Planck proposed that atoms absorb or emit electromagnetic radiation in discrete units of energy termed quanta. Although Plank's quantum concept seemed counterintuitive 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 quests to find the most elemental and fundamental particles of nature. In 1913, Danish physicist Niels Bohr 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 French physicist Louis Victor de Broglie, Austrian physicist Erwin Schrödinger, German physicist Max Born, and English physicist Paul Dirac. More than simple refinements of the Bohr model, however, these scientists made fundamental advances in defining the properties of matter--especially 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 World War II gave birth to the atomic age. In one blinding flash, the Manhattan Project created the most terrifying of weapons that could--in an instant--forever change course of history for all peoples of Earth.
The insights of relativity theory and quantum theory also stretched the methodology of science. No longer would science be mainly an 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 of causes and effects. Instead, physical phenomena were described as the result of fundamentally statistical, unreadable, indeterminist (unpredictable) processes.
The development of quantum theory, especially the delineation of Planck's constant and the articulation of the Heisenberg 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) that carried with it an understanding of nucleosynthesis (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.
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