# Physics - Classical And Modern Physics, Divisions Of Physics, Interrelationship Of Physics To Other Sciences, Physics And Philosophy

Science EncyclopediaScience & Philosophy: *Philosophy of Mind - Early Ideas* to *Planck length*

Physics is the science that deals with **matter** and **energy** and with the interaction between them. Physics, from which all other sciences derive their foundation, were the first attempts to provide rational explanations for the structure and workings of the Universe.

Even in the earliest civilizations, physics allowed a mechanism to understand and quantify nature.

An axiom among physicists—since the writings of Italian astronomer and physicist Galileo Galilei (1564–1642)—provides that the road to sure knowledge about the natural world is to carry out controlled observations (experiments) that will lead to measurable quantities. It is for this reason that experimental techniques, systems of measurements, and mathematical systems for expressing results lie at the core of research in physics.

In Ancient Greece, in a natural world largely explained by mystical and supernatural forces (i.e., 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 (582–500 B.C.) argued about the nature of numbers, Leucippus (c. 440 B.C.), Democritus (c. 420 B.C.), and Epicurus (342–270 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 (384–322 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 (ca. A.D 87–145) 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 (310–230 B.C.) proposed that the **earth** rotated around the **Sun** and Eratosthenes Of Cyrene (276–194 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 that 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 (1473–1543) reassertion of **heliocentric theory** sparked an intense interest in broad quantification of nature that eventually allowed German astronomer and mathematician Johannes Kepler (1571–1630) to develop laws of planetary **motion**. In addition to his fundamental astronomical discoveries, Galileo made concerted studies of the motion of bodies that subsequently inspired seventeenth century English physicist and mathematician Sir Isaac Newton's (1642–1727) 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 the **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 (1831–1879) 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 the 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 (1879–1955) 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 Maxwell Planck (1858–1947) 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 (1885–1962) 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 (1892–1987), Austrian physicist Erwin Schrödinger (1887–1961), German physicist Max Born (1882–1970), and English physicist P.A.M Dirac (1902–1984). 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.

The end of WWII gave formal birth to the atomic age. In one blinding flash, the Manhattan Project created the most terrifying of weapons that could—in a blinding flash—forever change course of history.

## Additional topics

- Physics - Middle Ages, Sixteenth And Seventeenth Centuries, Eighteenth Century, Nineteenth Century, Causes Of Motion: Medieval Understandings
- Physics - Classical And Modern Physics
- Physics - Divisions Of Physics
- Physics - Interrelationship Of Physics To Other Sciences
- Physics - Physics And Philosophy
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