Physics is the science that tries to understand, model, and explain the natural phenomena of the universe. It corresponds to the study of the world which surrounds us in all its forms, laws of its variation and evolution.
System modeling can leave out or include chemical and biological processes. Physics develops experimentally verifiable representations of the world in a given domain of definition. It thus produces several readings of the world, each being considered precise only to a certain point.
Physics as conceptualized by Isaac Newton, now called classical physics, stumbled upon the explanation of natural phenomena such as the black body radiation (ultraviolet catastrophe) or anomalies of the orbit of the planet Mercury, which posed a real problem to physicists. Attempts to understand and model new phenomena at the end of the nineteenth century thoroughly revised the Newtonian model to give rise to two new sets of physical theories. Some would say that there are three sets of established physical theories, each valid in its own field of application:
- Classical physics (the world of solid, liquid and gaseous media), which is still relevant, applies to the construction of roads, bridges and airplanes, for example. It uses the ancient notions of time, space, matter and energy as defined by Isaac Newton;
- Quantum physics (microscopic world of particles and fields) which applies, for example, to the technology used for the production of electronic components (tunnel diode for example) or lasers. It is based on new definitions of energy and matter but retains the old notions of time and space of classical physics, the latter two being contradicted by general relativity. Quantum physics has never been faulted to date;
- General relativity (macroscopic world of planets, black holes and gravity) that applies, for example, to the development and processing of information necessary for the operation of GPS systems. It is based on new definitions of time and space but retains the old notions of energy and matter of classical physics, the latter two being contradicted by quantum physics. General relativity has never been faulted to date.
Others believe that each branch of physics is important in its own right, without necessarily including itself in one of these sets. Moreover, it turns out that there is no current physical situation where these last two theories apply at the same time. Relativity applies to the macroscopic world and quantum physics to the microscopic world. The current problem of research in fundamental physics is therefore to try to unify these last two theories.
The old divisions in force at the end of the 19th century: mechanics, caloric, acoustics, optics, electricity, magnetism are supplemented or replaced by:
- the size of structural elements in the center of modeling: elementary particles, atomic nuclei, atoms, molecules, macromolecules or polymers, grains of matter …
- the characters of the interactions at the origin of the phases or states of matter: plasma, supercritical fluid, gas, liquid, solid.
Classical physics is based on theories prior to relativity and quanta. It applies when:
- either the speed is much less than the speed of light in the void;
- either the discontinuity of the energy levels is impossible to highlight.
Physics is born with the repeated experiences of Galileo who accepts, beyond the principles and conventions derived from mathematical schemes, only measurable and reproducible results by experience. The method chosen makes it possible to confirm or refute hypotheses based on a given theory. It describes in a quantitative way and models the fundamental beings present in the universe, trying to describe the movement by the forces that exercise themselves and their effects. She develops theories using the mathematical tool to describe and predict the evolution of systems.
Terminology
The term “physics” comes from the Greek η φυσικη (ê physikê) adopted in the Greco-Roman world, meaning “knowledge of nature”. The physika or Greco-Roman physica is etymologically what relates to the nature or precisely the harmonious and cyclical knowledge on the nature denominated φυσις. In a general and ancient sense, physics refers to the knowledge of nature that is perpetuated by remaining essentially the same with the return of seasons or living generations. The work Physica by Aristotle (384-322) uses this terminology.
The ancient term is perpetuated by the tradition of ancient philosophy. According to Plato, physics is one of the three parts of the teaching of philosophy, alongside ethics and logic. According to his pupil Aristotle, philosophy is divided into theoretical philosophy, practical philosophy and poetic philosophy; Physics is one of the three parts of theoretical philosophy, alongside mathematics and theology. Aristotle writes a book on physics. What escapes the triple categorization and can not be cataloged in physics is devolved to metaphysics, that is to say what goes beyond physics.
At the end of the quattrocento or fifteenth century, it appears as an adjective. It designates “that which relates to nature” but the substantive affirms itself as a science of natural things. The adjective remains of rare use before the seventeenth century. The physical word then refers to “knowledge about natural causes”, his study brings the expression “natural philosophy” according to an academic corpus guarded by Isaac Newton, author of the mathematical principles of natural philosophy. This is the meaning of René Descartes and his pupils Jacques Rohault and Régis. It corresponds then to natural sciences or even to natural philosophy.
Chairs of natural philosophy are established in some universities, notably in the United Kingdom (Oxford, Edinburgh, etc.). In Paris, for example, there is a chair of natural philosophy at the college of Clermont, occupied notably by Ignace Gaston Pardies. Maxwell occupies for a time a similar pulpit at Edinburgh, where teaching remains an indigestible catch-all.
In the eighteenth century, physics clearly designates experimental science.
The ancient meaning of this physics is no longer suitable for the actual exact sciences of physics, chemistry and biology, the latter being the latest direct heir to the natural sciences.
Translated from Wikipedia
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