Physics

Physics (from the Greek, φυσικός (phusikos), "natural", and φύσις (phusis), "nature") is the science of the natural world in the broadest sense, dealing with matter and energy and the fundamental forces of nature that govern the interactions between particles; it was called natural philosophy until the late 19th century. Physicists study a wide range of physical phenomena spanning all length scales, from the sub-nuclear particles of which all ordinary matter is made (particle physics) to the material Universe as a whole (cosmology).

Overview of physics research

Classical physics

Classical physics includes the traditional branches and topics that were recognized and fairly well developed before the beginning of the 20th century? mechanics, sound, light, heat, and electricity and magnetism.

Related Topics:
20th century - Mechanics - Sound - Light - Heat - Electricity and magnetism

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• Mechanics is concerned with bodies acted on by forces and bodies in motion and may be divided into statics (study of the forces on a body or bodies at rest), kinematics (study of motion without regard to its causes), and dynamics (study of motion and the forces that affect it); mechanics may also be divided into solid mechanics and fluid mechanics, the latter including such branches as hydrostatics, hydrodynamics, aerodynamics, and pneumatics.
• Acoustics, the study of sound, is often considered a branch of mechanics because sound is due to the motions of the particles of air or other medium through which sound waves can travel and thus can be explained in terms of the laws of mechanics. Among the important modern branches of acoustics is ultrasonics, the study of sound waves of very high frequency, beyond the range of human hearing.
• Optics, the study of light, is concerned not only with visible light but also with infrared and ultraviolet radiation, which exhibit all of the phenomena of visible light except visibility, e.g., reflection, refraction, interference, diffraction, dispersion (see electromagnetic spectrum), and polarization of light.
• Heat is a form of energy, the internal energy possessed by the particles of which a substance is composed; thermodynamics deals with the relationships between heat and other forms of energy.
• Electricity and magnetism have been studied as a single branch of physics since the intimate connection between them was discovered in the early 19th cent.; an electric current gives rise to a magnetic field and a changing magnetic field induces an electric current. Electrostatics deals with electric charges at rest, electrodynamics with moving charges, and magnetostatics with magnetic poles at rest. http://www.encyclopedia.com/html/section/physics-ent_ClassicalPhysics.asp

Modern physics

Most of classical physics is concerned with matter and energy on the normal scale of observation; by contrast, much of modern physics (i.e., the changes in the physicist's world view wrought by the revolutionary theories early in the 20th cent.) is concerned with the behavior of matter and energy under extreme conditions (e.g., at luminal or near-luminal speeds) or on the very large or very small scale. For example, atomic and nuclear physics studies matter on the smallest scale at which chemical elements can be identified. The physics of elementary particles is on an even smaller scale, being concerned with the most basic units of matter; this branch of physics is also known as high-energy physics because of the extremely high energies necessary to produce many types of particles in large particle accelerators . On this scale, ordinary, commonsense notions of space, time, matter, and energy are no longer valid.

Related Topics:
20th cent. - Atomic - Nuclear physics - Chemical element - Physics of elementary particles - Particle accelerator

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The two chief theories of modern physics present a different picture of the concepts of space, time, and matter from that presented by classical physics. The quantum theory is concerned with the discrete, rather than continuous, nature of many phenomena at the atomic and subatomic level, and with the complementary aspects of particles and waves in the description of such phenomena. The theory of relativity is concerned with the description of phenomena that take place in a frame of reference that is in motion with respect to an observer; the special theory of relativity is concerned with relative uniform motion in flat spacetime and objects moving at or near the speed of light and the general theory of relativity with relative accelerated motion in curved spacetime and its connection with gravitation. Both the quantum theory and the theory of relativity find applications in all areas of modern physics. http://www.encyclopedia.com/html/section/physics-ent_ModernPhysics.asp

Related Topics:
Quantum theory - Theory of relativity - Special theory of relativity - Flat spacetime - Speed of light - General theory of relativity - Curved spacetime - Gravitation

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Theoretical and experimental physics

The culture of physics research differs from the other sciences in the separation of theory and experiment. Since the 20th century, most individual physicists have specialized in either theoretical physics or experimental physics, and in the twentieth century, very few physicists have been successful in both forms of research 1.

Related Topics:
Theory - Experiment - 20th century - Theoretical physics - Experimental physics - 1

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In contrast, almost all the successful theorists in biology and chemistry have also been experimentalists.

Related Topics:
Biology - Chemistry

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Roughly speaking, theorists seek to develop theories that can describe and interpret existing experimental results and successfully predict future results, while experimentalists devise and perform experiments to explore new phenomena and test theoretical predictions. Although theory and experiment are developed separately, they are strongly dependent on each other. Progress in physics frequently comes about when experimentalists make a discovery that existing theories cannot account for, necessitating the formulation of new theories. Likewise, ideas arising from theory often inspire new experiments. In the absence of experiment, theoretical research can go in the wrong direction; this is one of the criticisms that has been leveled against M-theory, a popular theory in high-energy physics for which no practical experimental test has ever been devised.

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Central theories

While physics deals with a wide variety of systems, there are certain theories that are used by all physicists. Each of these theories is believed to be basically correct, within a certain domain of validity. For instance, the theory of classical mechanics accurately describes the motion of objects, provided they are much larger than atoms and moving at much less than the speed of light. These theories continue to be areas of active research; for instance, a remarkable aspect of classical mechanics known as chaos was discovered in the 20th century, three centuries after the original formulation of classical mechanics by Isaac Newton. These "central theories" are important tools for research into more specialized topics, and any student of physics, regardless of his or her specialization, is expected to be well-versed in them.

Related Topics:
Classical mechanics - Atom - Speed of light - Chaos - Isaac Newton

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Major fields of physics

Contemporary research in physics is divided into several distinct fields that study different aspects of the material world 2. Condensed matter physics, by most estimates the largest single field of physics, is concerned with how the properties of bulk matter, such as the ordinary solids and liquids we encounter in everyday life, arise from the properties and mutual interactions of the constituent atoms. The field of atomic, molecular, and optical physics deals with the behavior of individual atoms and molecules, and in particular the ways in which they absorb and emit light. The field of particle physics, also known as "high-energy physics", is concerned with the properties of submicroscopic particles much smaller than atoms, including the elementary particles from which all other units of matter are constructed. Finally, the field of astrophysics applies the laws of physics to explain astronomical phenomena, ranging from the Sun and the other objects in the solar system to the universe as a whole.

Related Topics:
2 - Condensed matter physics - Solid - Liquid - Atom - Atomic, molecular, and optical physics - Light - Particle physics - Elementary particle - Astrophysics - Astronomical - Sun - Solar system

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Related fields

There are many areas of research that mix physics with other disciplines. For example, the wide-ranging field of biophysics is devoted to the role that physical principles play in biological systems and the field of quantum chemistry studies how the theory of quantum mechanics gives rise to the chemical behavior of atoms and molecules. Some of these fields are listed below.

Related Topics:
Biophysics - Quantum chemistry

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Acoustics - Astronomy - Agrophysics - Biophysics - Chemical physics - Computational physics - Econophysics - Electronics - Engineering - Geophysics - Materials science - Mathematical physics - Medical physics - Physical chemistry - Physics of computation - Quantum chemistry - Quantum information science - Vehicle dynamics

Related Topics:
Acoustics - Astronomy - Agrophysics - Biophysics - Chemical physics - Computational physics - Econophysics - Electronics - Engineering - Geophysics - Materials science - Mathematical physics - Medical physics - Physical chemistry - Physics of computation - Quantum chemistry - Quantum information science - Vehicle dynamics

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Fringe theories

Cold fusion - Dynamic theory of gravity - Luminiferous aether - Steady state theory - Wave Structure Matter

Related Topics:
Cold fusion - Dynamic theory of gravity - Luminiferous aether - Steady state theory - Wave Structure Matter

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