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This article is about the field of science. Physics_sentence_0

For other uses, see Physics (disambiguation). Physics_sentence_1

Not to be confused with Physical science. Physics_sentence_2

Physics (from Ancient Greek: φυσική (ἐπιστήμη), romanized: physikḗ (epistḗmē), lit. Physics_sentence_3

'knowledge of nature', from φύσις phýsis 'nature') is the natural science that studies matter, its motion and behavior through space and time, and the related entities of energy and force. Physics_sentence_4

Physics is one of the most fundamental scientific disciplines, and its main goal is to understand how the universe behaves. Physics_sentence_5

Physics is one of the oldest academic disciplines and, through its inclusion of astronomy, perhaps the oldest. Physics_sentence_6

Over much of the past two millennia, physics, chemistry, biology, and certain branches of mathematics were a part of natural philosophy, but during the Scientific Revolution in the 17th century these natural sciences emerged as unique research endeavors in their own right. Physics_sentence_7

Physics intersects with many interdisciplinary areas of research, such as biophysics and quantum chemistry, and the boundaries of physics are not rigidly defined. Physics_sentence_8

New ideas in physics often explain the fundamental mechanisms studied by other sciences and suggest new avenues of research in academic disciplines such as mathematics and philosophy. Physics_sentence_9

Advances in physics often enable advances in new technologies. Physics_sentence_10

For example, advances in the understanding of electromagnetism, solid-state physics, and nuclear physics led directly to the development of new products that have dramatically transformed modern-day society, such as television, computers, domestic appliances, and nuclear weapons; advances in thermodynamics led to the development of industrialization; and advances in mechanics inspired the development of calculus. Physics_sentence_11

History Physics_section_0

Main article: History of physics Physics_sentence_12

Ancient astronomy Physics_section_1

Main article: History of astronomy Physics_sentence_13

Astronomy is one of the oldest natural sciences. Physics_sentence_14

Early civilizations dating back before 3000 BCE, such as the Sumerians, ancient Egyptians, and the Indus Valley Civilisation, had a predictive knowledge and a basic understanding of the motions of the Sun, Moon, and stars. Physics_sentence_15

The stars and planets, believed to represent gods, were often worshipped. Physics_sentence_16

While the explanations for the observed positions of the stars were often unscientific and lacking in evidence, these early observations laid the foundation for later astronomy, as the stars were found to traverse great circles across the sky, which however did not explain the positions of the planets. Physics_sentence_17

According to Asger Aaboe, the origins of Western astronomy can be found in Mesopotamia, and all Western efforts in the exact sciences are descended from late Babylonian astronomy. Physics_sentence_18

Egyptian astronomers left monuments showing knowledge of the constellations and the motions of the celestial bodies, while Greek poet Homer wrote of various celestial objects in his Iliad and Odyssey; later Greek astronomers provided names, which are still used today, for most constellations visible from the Northern Hemisphere. Physics_sentence_19

Natural philosophy Physics_section_2

Main article: Natural philosophy Physics_sentence_20

Natural philosophy has its origins in Greece during the Archaic period (650 BCE – 480 BCE), when pre-Socratic philosophers like Thales rejected non-naturalistic explanations for natural phenomena and proclaimed that every event had a natural cause. Physics_sentence_21

They proposed ideas verified by reason and observation, and many of their hypotheses proved successful in experiment; for example, atomism was found to be correct approximately 2000 years after it was proposed by Leucippus and his pupil Democritus. Physics_sentence_22

Physics in the medieval European and Islamic world Physics_section_3

Main articles: European science in the Middle Ages and Physics in the medieval Islamic world Physics_sentence_23

The Western Roman Empire fell in the fifth century, and this resulted in a decline in intellectual pursuits in the western part of Europe. Physics_sentence_24

By contrast, the Eastern Roman Empire (also known as the Byzantine Empire) resisted the attacks from the barbarians, and continued to advance various fields of learning, including physics. Physics_sentence_25

In the sixth century Isidore of Miletus created an important compilation of Archimedes' works that are copied in the Archimedes Palimpsest. Physics_sentence_26

In sixth century Europe John Philoponus, a Byzantine scholar, questioned Aristotle's teaching of physics and noted its flaws. Physics_sentence_27

He introduced the theory of impetus. Physics_sentence_28

Aristotle's physics was not scrutinized until Philoponus appeared; unlike Aristotle, who based his physics on verbal argument, Philoponus relied on observation. Physics_sentence_29

On Aristotle's physics Philoponus wrote: Physics_sentence_30

Philoponus' criticism of Aristotelian principles of physics served as an inspiration for Galileo Galilei ten centuries later, during the Scientific Revolution. Physics_sentence_31

Galileo cited Philoponus substantially in his works when arguing that Aristotelian physics was flawed. Physics_sentence_32

In the 1300s Jean Buridan, a teacher in the faculty of arts at the University of Paris, developed the concept of impetus. Physics_sentence_33

It was a step toward the modern ideas of inertia and momentum. Physics_sentence_34

Islamic scholarship inherited Aristotelian physics from the Greeks and during the Islamic Golden Age developed it further, especially placing emphasis on observation and a priori reasoning, developing early forms of the scientific method. Physics_sentence_35

The most notable innovations were in the field of optics and vision, which came from the works of many scientists like Ibn Sahl, Al-Kindi, Ibn al-Haytham, Al-Farisi and Avicenna. Physics_sentence_36

The most notable work was The Book of Optics (also known as Kitāb al-Manāẓir), written by Ibn al-Haytham, in which he conclusively disproved the ancient Greek idea about vision, but also came up with a new theory. Physics_sentence_37

In the book, he presented a study of the phenomenon of the camera obscura (his thousand-year-old version of the pinhole camera) and delved further into the way the eye itself works. Physics_sentence_38

Using dissections and the knowledge of previous scholars, he was able to begin to explain how light enters the eye. Physics_sentence_39

He asserted that the light ray is focused, but the actual explanation of how light projected to the back of the eye had to wait until 1604. Physics_sentence_40

His Treatise on Light explained the camera obscura, hundreds of years before the modern development of photography. Physics_sentence_41

The seven-volume Book of Optics (Kitab al-Manathir) hugely influenced thinking across disciplines from the theory of visual perception to the nature of perspective in medieval art, in both the East and the West, for more than 600 years. Physics_sentence_42

Many later European scholars and fellow polymaths, from Robert Grosseteste and Leonardo da Vinci to René Descartes, Johannes Kepler and Isaac Newton, were in his debt. Physics_sentence_43

Indeed, the influence of Ibn al-Haytham's Optics ranks alongside that of Newton's work of the same title, published 700 years later. Physics_sentence_44

The translation of The Book of Optics had a huge impact on Europe. Physics_sentence_45

From it, later European scholars were able to build devices that replicated those Ibn al-Haytham had built, and understand the way light works. Physics_sentence_46

From this, such important things as eyeglasses, magnifying glasses, telescopes, and cameras were developed. Physics_sentence_47

Classical physics Physics_section_4

Main article: Classical physics Physics_sentence_48

Physics became a separate science when early modern Europeans used experimental and quantitative methods to discover what are now considered to be the laws of physics. Physics_sentence_49

Major developments in this period include the replacement of the geocentric model of the Solar System with the heliocentric Copernican model, the laws governing the motion of planetary bodies determined by Kepler between 1609 and 1619, pioneering work on telescopes and observational astronomy by Galileo in the 16th and 17th Centuries, and Newton's discovery and unification of the laws of motion and universal gravitation that would come to bear his name. Physics_sentence_50

Newton also developed calculus, the mathematical study of change, which provided new mathematical methods for solving physical problems. Physics_sentence_51

The discovery of new laws in thermodynamics, chemistry, and electromagnetics resulted from greater research efforts during the Industrial Revolution as energy needs increased. Physics_sentence_52

The laws comprising classical physics remain very widely used for objects on everyday scales travelling at non-relativistic speeds, since they provide a very close approximation in such situations, and theories such as quantum mechanics and the theory of relativity simplify to their classical equivalents at such scales. Physics_sentence_53

However, inaccuracies in classical mechanics for very small objects and very high velocities led to the development of modern physics in the 20th century. Physics_sentence_54

Modern physics Physics_section_5

Main article: Modern physics Physics_sentence_55

See also: History of special relativity and History of quantum mechanics Physics_sentence_56

Modern physics began in the early 20th century with the work of Max Planck in quantum theory and Albert Einstein's theory of relativity. Physics_sentence_57

Both of these theories came about due to inaccuracies in classical mechanics in certain situations. Physics_sentence_58

Classical mechanics predicted a varying speed of light, which could not be resolved with the constant speed predicted by Maxwell's equations of electromagnetism; this discrepancy was corrected by Einstein's theory of special relativity, which replaced classical mechanics for fast-moving bodies and allowed for a constant speed of light. Physics_sentence_59

Black-body radiation provided another problem for classical physics, which was corrected when Planck proposed that the excitation of material oscillators is possible only in discrete steps proportional to their frequency; this, along with the photoelectric effect and a complete theory predicting discrete energy levels of electron orbitals, led to the theory of quantum mechanics taking over from classical physics at very small scales. Physics_sentence_60

Quantum mechanics would come to be pioneered by Werner Heisenberg, Erwin Schrödinger and Paul Dirac. Physics_sentence_61

From this early work, and work in related fields, the Standard Model of particle physics was derived. Physics_sentence_62

Following the discovery of a particle with properties consistent with the Higgs boson at CERN in 2012, all fundamental particles predicted by the standard model, and no others, appear to exist; however, physics beyond the Standard Model, with theories such as supersymmetry, is an active area of research. Physics_sentence_63

Areas of mathematics in general are important to this field, such as the study of probabilities and groups. Physics_sentence_64

Philosophy Physics_section_6

Main article: Philosophy of physics Physics_sentence_65

In many ways, physics stems from ancient Greek philosophy. Physics_sentence_66

From Thales' first attempt to characterise matter, to Democritus' deduction that matter ought to reduce to an invariant state, the Ptolemaic astronomy of a crystalline firmament, and Aristotle's book Physics (an early book on physics, which attempted to analyze and define motion from a philosophical point of view), various Greek philosophers advanced their own theories of nature. Physics_sentence_67

Physics was known as natural philosophy until the late 18th century. Physics_sentence_68

By the 19th century, physics was realised as a discipline distinct from philosophy and the other sciences. Physics_sentence_69

Physics, as with the rest of science, relies on philosophy of science and its "scientific method" to advance our knowledge of the physical world. Physics_sentence_70

The scientific method employs a priori reasoning as well as a posteriori reasoning and the use of Bayesian inference to measure the validity of a given theory. Physics_sentence_71

The development of physics has answered many questions of early philosophers, but has also raised new questions. Physics_sentence_72

Study of the philosophical issues surrounding physics, the philosophy of physics, involves issues such as the nature of space and time, determinism, and metaphysical outlooks such as empiricism, naturalism and realism. Physics_sentence_73

Many physicists have written about the philosophical implications of their work, for instance Laplace, who championed causal determinism, and Schrödinger, who wrote on quantum mechanics. Physics_sentence_74

The mathematical physicist Roger Penrose had been called a Platonist by Stephen Hawking, a view Penrose discusses in his book, The Road to Reality. Physics_sentence_75

Hawking referred to himself as an "unashamed reductionist" and took issue with Penrose's views. Physics_sentence_76

Core theories Physics_section_7

Further information: Branches of physics and Outline of physics Physics_sentence_77

Though physics deals with a wide variety of systems, certain theories are used by all physicists. Physics_sentence_78

Each of these theories were experimentally tested numerous times and found to be an adequate approximation of nature. Physics_sentence_79

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. Physics_sentence_80

These theories continue to be areas of active research today. Physics_sentence_81

Chaos theory, a remarkable aspect of classical mechanics was discovered in the 20th century, three centuries after the original formulation of classical mechanics by Newton (1642–1727). Physics_sentence_82

These central theories are important tools for research into more specialised topics, and any physicist, regardless of their specialisation, is expected to be literate in them. Physics_sentence_83

These include classical mechanics, quantum mechanics, thermodynamics and statistical mechanics, electromagnetism, and special relativity. Physics_sentence_84

Classical physics Physics_section_8

Main article: Classical physics Physics_sentence_85

Classical physics includes the traditional branches and topics that were recognised and well-developed before the beginning of the 20th century—classical mechanics, acoustics, optics, thermodynamics, and electromagnetism. Physics_sentence_86

Classical 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 not subject to an acceleration), 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 (known together as continuum mechanics), the latter include such branches as hydrostatics, hydrodynamics, aerodynamics, and pneumatics. Physics_sentence_87

Acoustics is the study of how sound is produced, controlled, transmitted and received. Physics_sentence_88

Important modern branches of acoustics include ultrasonics, the study of sound waves of very high frequency beyond the range of human hearing; bioacoustics, the physics of animal calls and hearing, and electroacoustics, the manipulation of audible sound waves using electronics. Physics_sentence_89

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, and polarization of light. Physics_sentence_90

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. Physics_sentence_91

Electricity and magnetism have been studied as a single branch of physics since the intimate connection between them was discovered in the early 19th century; an electric current gives rise to a magnetic field, and a changing magnetic field induces an electric current. Physics_sentence_92

Electrostatics deals with electric charges at rest, electrodynamics with moving charges, and magnetostatics with magnetic poles at rest. Physics_sentence_93

Modern physics Physics_section_9

Main article: Modern physics Physics_sentence_94

Classical physics is generally concerned with matter and energy on the normal scale of observation, while much of modern physics is concerned with the behavior of matter and energy under extreme conditions or on a very large or very small scale. Physics_sentence_95

For example, atomic and nuclear physics studies matter on the smallest scale at which chemical elements can be identified. Physics_sentence_96

The physics of elementary particles is on an even smaller scale since it is 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 particle accelerators. Physics_sentence_97

On this scale, ordinary, commonsensical notions of space, time, matter, and energy are no longer valid. Physics_sentence_98

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. Physics_sentence_99

Classical mechanics approximates nature as continuous, while quantum theory is concerned with the discrete 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. Physics_sentence_100

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 motion in the absence of gravitational fields and the general theory of relativity with motion and its connection with gravitation. Physics_sentence_101

Both quantum theory and the theory of relativity find applications in all areas of modern physics. Physics_sentence_102

Difference between classical and modern physics Physics_section_10

While physics aims to discover universal laws, its theories lie in explicit domains of applicability. Physics_sentence_103

Loosely speaking, the laws of classical physics accurately describe systems whose important length scales are greater than the atomic scale and whose motions are much slower than the speed of light. Physics_sentence_104

Outside of this domain, observations do not match predictions provided by classical mechanics. Physics_sentence_105

Einstein contributed the framework of special relativity, which replaced notions of absolute time and space with spacetime and allowed an accurate description of systems whose components have speeds approaching the speed of light. Physics_sentence_106

Planck, Schrödinger, and others introduced quantum mechanics, a probabilistic notion of particles and interactions that allowed an accurate description of atomic and subatomic scales. Physics_sentence_107

Later, quantum field theory unified quantum mechanics and special relativity. Physics_sentence_108

General relativity allowed for a dynamical, curved spacetime, with which highly massive systems and the large-scale structure of the universe can be well-described. Physics_sentence_109

General relativity has not yet been unified with the other fundamental descriptions; several candidate theories of quantum gravity are being developed. Physics_sentence_110

Relation to other fields Physics_section_11

Prerequisites Physics_section_12

Mathematics provides a compact and exact language used to describe the order in nature. Physics_sentence_111

This was noted and advocated by Pythagoras, Plato, Galileo, and Newton. Physics_sentence_112

Physics uses mathematics to organise and formulate experimental results. Physics_sentence_113

From those results, precise or estimated solutions are obtained, quantitative results from which new predictions can be made and experimentally confirmed or negated. Physics_sentence_114

The results from physics experiments are numerical data, with their units of measure and estimates of the errors in the measurements. Physics_sentence_115

Technologies based on mathematics, like computation have made computational physics an active area of research. Physics_sentence_116

Ontology is a prerequisite for physics, but not for mathematics. Physics_sentence_117

It means physics is ultimately concerned with descriptions of the real world, while mathematics is concerned with abstract patterns, even beyond the real world. Physics_sentence_118

Thus physics statements are synthetic, while mathematical statements are analytic. Physics_sentence_119

Mathematics contains hypotheses, while physics contains theories. Physics_sentence_120

Mathematics statements have to be only logically true, while predictions of physics statements must match observed and experimental data. Physics_sentence_121

The distinction is clear-cut, but not always obvious. Physics_sentence_122

For example, mathematical physics is the application of mathematics in physics. Physics_sentence_123

Its methods are mathematical, but its subject is physical. Physics_sentence_124

The problems in this field start with a "mathematical model of a physical situation" (system) and a "mathematical description of a physical law" that will be applied to that system. Physics_sentence_125

Every mathematical statement used for solving has a hard-to-find physical meaning. Physics_sentence_126

The final mathematical solution has an easier-to-find meaning, because it is what the solver is looking for. Physics_sentence_127

Pure physics is a branch of fundamental science (also called basic science. Physics_sentence_128

Physics is also called "the fundamental science" because all branches of natural science like chemistry, astronomy, geology, and biology are constrained by laws of physics. Physics_sentence_129

Similarly, chemistry is often called the central science because of its role in linking the physical sciences. Physics_sentence_130

For example, chemistry studies properties, structures, and reactions of matter (chemistry's focus on the molecular and atomic scale distinguishes it from physics). Physics_sentence_131

Structures are formed because particles exert electrical forces on each other, properties include physical characteristics of given substances, and reactions are bound by laws of physics, like conservation of energy, mass, and charge. Physics_sentence_132

Physics is applied in industries like engineering and medicine. Physics_sentence_133

Application and influence Physics_section_13

Main article: Applied physics Physics_sentence_134

Applied physics is a general term for physics research which is intended for a particular use. Physics_sentence_135

An applied physics curriculum usually contains a few classes in an applied discipline, like geology or electrical engineering. Physics_sentence_136

It usually differs from engineering in that an applied physicist may not be designing something in particular, but rather is using physics or conducting physics research with the aim of developing new technologies or solving a problem. Physics_sentence_137

The approach is similar to that of applied mathematics. Physics_sentence_138

Applied physicists use physics in scientific research. Physics_sentence_139

For instance, people working on accelerator physics might seek to build better particle detectors for research in theoretical physics. Physics_sentence_140

Physics is used heavily in engineering. Physics_sentence_141

For example, statics, a subfield of mechanics, is used in the building of bridges and other static structures. Physics_sentence_142

The understanding and use of acoustics results in sound control and better concert halls; similarly, the use of optics creates better optical devices. Physics_sentence_143

An understanding of physics makes for more realistic flight simulators, video games, and movies, and is often critical in forensic investigations. Physics_sentence_144

With the standard consensus that the laws of physics are universal and do not change with time, physics can be used to study things that would ordinarily be mired in uncertainty. Physics_sentence_145

For example, in the study of the origin of the earth, one can reasonably model earth's mass, temperature, and rate of rotation, as a function of time allowing one to extrapolate forward or backward in time and so predict future or prior events. Physics_sentence_146

It also allows for simulations in engineering that drastically speed up the development of a new technology. Physics_sentence_147

But there is also considerable interdisciplinarity, so many other important fields are influenced by physics (e.g., the fields of econophysics and sociophysics). Physics_sentence_148

Research Physics_section_14

Scientific method Physics_section_15

Physicists use the scientific method to test the validity of a physical theory. Physics_sentence_149

By using a methodical approach to compare the implications of a theory with the conclusions drawn from its related experiments and observations, physicists are better able to test the validity of a theory in a logical, unbiased, and repeatable way. Physics_sentence_150

To that end, experiments are performed and observations are made in order to determine the validity or invalidity of the theory. Physics_sentence_151

A scientific law is a concise verbal or mathematical statement of a relation that expresses a fundamental principle of some theory, such as Newton's law of universal gravitation. Physics_sentence_152

Theory and experiment Physics_section_16

Main articles: Theoretical physics and Experimental physics Physics_sentence_153

Theorists seek to develop mathematical models that both agree with existing experiments and successfully predict future experimental results, while experimentalists devise and perform experiments to test theoretical predictions and explore new phenomena. Physics_sentence_154

Although theory and experiment are developed separately, they strongly affect and depend upon each other. Physics_sentence_155

Progress in physics frequently comes about when experimental results defy explanation by existing theories, prompting intense focus on applicable modelling, and when new theories generate experimentally testable predictions, which inspire the development of new experiments (and often related equipment). Physics_sentence_156

Physicists who work at the interplay of theory and experiment are called phenomenologists, who study complex phenomena observed in experiment and work to relate them to a fundamental theory. Physics_sentence_157

Theoretical physics has historically taken inspiration from philosophy; electromagnetism was unified this way. Physics_sentence_158

Beyond the known universe, the field of theoretical physics also deals with hypothetical issues, such as parallel universes, a multiverse, and higher dimensions. Physics_sentence_159

Theorists invoke these ideas in hopes of solving particular problems with existing theories; they then explore the consequences of these ideas and work toward making testable predictions. Physics_sentence_160

Experimental physics expands, and is expanded by, engineering and technology. Physics_sentence_161

Experimental physicists who are involved in basic research, design and perform experiments with equipment such as particle accelerators and lasers, whereas those involved in applied research often work in industry, developing technologies such as magnetic resonance imaging (MRI) and transistors. Physics_sentence_162

Feynman has noted that experimentalists may seek areas that have not been explored well by theorists. Physics_sentence_163

Scope and aims Physics_section_17

Physics covers a wide range of phenomena, from elementary particles (such as quarks, neutrinos, and electrons) to the largest superclusters of galaxies. Physics_sentence_164

Included in these phenomena are the most basic objects composing all other things. Physics_sentence_165

Therefore, physics is sometimes called the "fundamental science". Physics_sentence_166

Physics aims to describe the various phenomena that occur in nature in terms of simpler phenomena. Physics_sentence_167

Thus, physics aims to both connect the things observable to humans to root causes, and then connect these causes together. Physics_sentence_168

For example, the ancient Chinese observed that certain rocks (lodestone and magnetite) were attracted to one another by an invisible force. Physics_sentence_169

This effect was later called magnetism, which was first rigorously studied in the 17th century. Physics_sentence_170

But even before the Chinese discovered magnetism, the ancient Greeks knew of other objects such as amber, that when rubbed with fur would cause a similar invisible attraction between the two. Physics_sentence_171

This was also first studied rigorously in the 17th century and came to be called electricity. Physics_sentence_172

Thus, physics had come to understand two observations of nature in terms of some root cause (electricity and magnetism). Physics_sentence_173

However, further work in the 19th century revealed that these two forces were just two different aspects of one force—electromagnetism. Physics_sentence_174

This process of "unifying" forces continues today, and electromagnetism and the weak nuclear force are now considered to be two aspects of the electroweak interaction. Physics_sentence_175

Physics hopes to find an ultimate reason (theory of everything) for why nature is as it is (see section Current research below for more information). Physics_sentence_176

Research fields Physics_section_18

Contemporary research in physics can be broadly divided into nuclear and particle physics; condensed matter physics; atomic, molecular, and optical physics; astrophysics; and applied physics. Physics_sentence_177

Some physics departments also support physics education research and physics outreach. Physics_sentence_178

Since the 20th century, the individual fields of physics have become increasingly specialised, and today most physicists work in a single field for their entire careers. Physics_sentence_179

"Universalists" such as Einstein (1879–1955) and Lev Landau (1908–1968), who worked in multiple fields of physics, are now very rare. Physics_sentence_180

The major fields of physics, along with their subfields and the theories and concepts they employ, are shown in the following table. Physics_sentence_181


FieldPhysics_header_cell_0_0_0 SubfieldsPhysics_header_cell_0_0_1 Major theoriesPhysics_header_cell_0_0_2 ConceptsPhysics_header_cell_0_0_3
Nuclear and particle physicsPhysics_cell_0_1_0 Nuclear physics, Nuclear astrophysics, Particle physics, Astroparticle physics, Particle physics phenomenologyPhysics_cell_0_1_1 Standard Model, Quantum field theory, Quantum electrodynamics, Quantum chromodynamics, Electroweak theory, Effective field theory, Lattice field theory, Lattice gauge theory, Gauge theory, Supersymmetry, Grand Unified Theory, Superstring theory, M-theoryPhysics_cell_0_1_2 Fundamental force (gravitational, electromagnetic, weak, strong), Elementary particle, Spin, Antimatter, Spontaneous symmetry breaking, Neutrino oscillation, Seesaw mechanism, Brane, String, Quantum gravity, Theory of everything, Vacuum energyPhysics_cell_0_1_3
Atomic, molecular, and optical physicsPhysics_cell_0_2_0 Atomic physics, Molecular physics, Atomic and molecular astrophysics, Chemical physics, Optics, PhotonicsPhysics_cell_0_2_1 Quantum optics, Quantum chemistry, Quantum information sciencePhysics_cell_0_2_2 Photon, Atom, Molecule, Diffraction, Electromagnetic radiation, Laser, Polarization (waves), Spectral line, Casimir effectPhysics_cell_0_2_3
Condensed matter physicsPhysics_cell_0_3_0 Solid-state physics, High-pressure physics, Low-temperature physics, Surface physics, Nanoscale and mesoscopic physics, Polymer physicsPhysics_cell_0_3_1 BCS theory, Bloch's theorem, Density functional theory, Fermi gas, Fermi liquid theory, Many-body theory, Statistical mechanicsPhysics_cell_0_3_2 Phases (gas, liquid, solid), Bose–Einstein condensate, Electrical conduction, Phonon, Magnetism, Self-organization, Semiconductor, superconductor, superfluidity, Spin,Physics_cell_0_3_3
AstrophysicsPhysics_cell_0_4_0 Astronomy, Astrometry, Cosmology, Gravitation physics, High-energy astrophysics, Planetary astrophysics, Plasma physics, Solar physics, Space physics, Stellar astrophysicsPhysics_cell_0_4_1 Big Bang, Cosmic inflation, General relativity, Newton's law of universal gravitation, Lambda-CDM model, MagnetohydrodynamicsPhysics_cell_0_4_2 Black hole, Cosmic background radiation, Cosmic string, Cosmos, Dark energy, Dark matter, Galaxy, Gravity, Gravitational radiation, Gravitational singularity, Planet, Solar System, Star, Supernova, UniversePhysics_cell_0_4_3
Applied physicsPhysics_cell_0_5_0 Accelerator physics, Acoustics, Agrophysics, Atmospheric physics, Biophysics, Chemical physics, Communication physics, Econophysics, Engineering physics, Fluid dynamics, Geophysics, Laser physics, Materials physics, Medical physics, Nanotechnology, Optics, Optoelectronics, Photonics, Photovoltaics, Physical chemistry, Physical oceanography, Physics of computation, Plasma physics, Solid-state devices, Quantum chemistry, Quantum electronics, Quantum information science, Vehicle dynamicsPhysics_cell_0_5_1

Nuclear and particle physics Physics_section_19

Main articles: Particle physics and Nuclear physics Physics_sentence_182

Particle physics is the study of the elementary constituents of matter and energy and the interactions between them. Physics_sentence_183

In addition, particle physicists design and develop the high-energy accelerators, detectors, and computer programs necessary for this research. Physics_sentence_184

The field is also called "high-energy physics" because many elementary particles do not occur naturally but are created only during high-energy collisions of other particles. Physics_sentence_185

Currently, the interactions of elementary particles and fields are described by the Standard Model. Physics_sentence_186

The model accounts for the 12 known particles of matter (quarks and leptons) that interact via the strong, weak, and electromagnetic fundamental forces. Physics_sentence_187

Dynamics are described in terms of matter particles exchanging gauge bosons (gluons, W and Z bosons, and photons, respectively). Physics_sentence_188

The Standard Model also predicts a particle known as the Higgs boson. Physics_sentence_189

In July 2012 CERN, the European laboratory for particle physics, announced the detection of a particle consistent with the Higgs boson, an integral part of a Higgs mechanism. Physics_sentence_190

Nuclear physics is the field of physics that studies the constituents and interactions of atomic nuclei. Physics_sentence_191

The most commonly known applications of nuclear physics are nuclear power generation and nuclear weapons technology, but the research has provided application in many fields, including those in nuclear medicine and magnetic resonance imaging, ion implantation in materials engineering, and radiocarbon dating in geology and archaeology. Physics_sentence_192

Atomic, molecular, and optical physics Physics_section_20

Main article: Atomic, molecular, and optical physics Physics_sentence_193

Atomic, molecular, and optical physics (AMO) is the study of matter–matter and light–matter interactions on the scale of single atoms and molecules. Physics_sentence_194

The three areas are grouped together because of their interrelationships, the similarity of methods used, and the commonality of their relevant energy scales. Physics_sentence_195

All three areas include both classical, semi-classical and quantum treatments; they can treat their subject from a microscopic view (in contrast to a macroscopic view). Physics_sentence_196

Atomic physics studies the electron shells of atoms. Physics_sentence_197

Current research focuses on activities in quantum control, cooling and trapping of atoms and ions, low-temperature collision dynamics and the effects of electron correlation on structure and dynamics. Physics_sentence_198

Atomic physics is influenced by the nucleus (see hyperfine splitting), but intra-nuclear phenomena such as fission and fusion are considered part of nuclear physics. Physics_sentence_199

Molecular physics focuses on multi-atomic structures and their internal and external interactions with matter and light. Physics_sentence_200

Optical physics is distinct from optics in that it tends to focus not on the control of classical light fields by macroscopic objects but on the fundamental properties of optical fields and their interactions with matter in the microscopic realm. Physics_sentence_201

Condensed matter physics Physics_section_21

Main article: Condensed matter physics Physics_sentence_202

Condensed matter physics is the field of physics that deals with the macroscopic physical properties of matter. Physics_sentence_203

In particular, it is concerned with the "condensed" phases that appear whenever the number of particles in a system is extremely large and the interactions between them are strong. Physics_sentence_204

The most familiar examples of condensed phases are solids and liquids, which arise from the bonding by way of the electromagnetic force between atoms. Physics_sentence_205

More exotic condensed phases include the superfluid and the Bose–Einstein condensate found in certain atomic systems at very low temperature, the superconducting phase exhibited by conduction electrons in certain materials, and the ferromagnetic and antiferromagnetic phases of spins on atomic lattices. Physics_sentence_206

Condensed matter physics is the largest field of contemporary physics. Physics_sentence_207

Historically, condensed matter physics grew out of solid-state physics, which is now considered one of its main subfields. Physics_sentence_208

The term condensed matter physics was apparently coined by Philip Anderson when he renamed his research group—previously solid-state theory—in 1967. Physics_sentence_209

In 1978, the Division of Solid State Physics of the American Physical Society was renamed as the Division of Condensed Matter Physics. Physics_sentence_210

Condensed matter physics has a large overlap with chemistry, materials science, nanotechnology and engineering. Physics_sentence_211

Astrophysics Physics_section_22

Main articles: Astrophysics and Physical cosmology Physics_sentence_212

Astrophysics and astronomy are the application of the theories and methods of physics to the study of stellar structure, stellar evolution, the origin of the Solar System, and related problems of cosmology. Physics_sentence_213

Because astrophysics is a broad subject, astrophysicists typically apply many disciplines of physics, including mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics. Physics_sentence_214

The discovery by Karl Jansky in 1931 that radio signals were emitted by celestial bodies initiated the science of radio astronomy. Physics_sentence_215

Most recently, the frontiers of astronomy have been expanded by space exploration. Physics_sentence_216

Perturbations and interference from the earth's atmosphere make space-based observations necessary for infrared, ultraviolet, gamma-ray, and X-ray astronomy. Physics_sentence_217

Physical cosmology is the study of the formation and evolution of the universe on its largest scales. Physics_sentence_218

Albert Einstein's theory of relativity plays a central role in all modern cosmological theories. Physics_sentence_219

In the early 20th century, Hubble's discovery that the universe is expanding, as shown by the Hubble diagram, prompted rival explanations known as the steady state universe and the Big Bang. Physics_sentence_220

The Big Bang was confirmed by the success of Big Bang nucleosynthesis and the discovery of the cosmic microwave background in 1964. Physics_sentence_221

The Big Bang model rests on two theoretical pillars: Albert Einstein's general relativity and the cosmological principle. Physics_sentence_222

Cosmologists have recently established the ΛCDM model of the evolution of the universe, which includes cosmic inflation, dark energy, and dark matter. Physics_sentence_223

Numerous possibilities and discoveries are anticipated to emerge from new data from the Fermi Gamma-ray Space Telescope over the upcoming decade and vastly revise or clarify existing models of the universe. Physics_sentence_224

In particular, the potential for a tremendous discovery surrounding dark matter is possible over the next several years. Physics_sentence_225

Fermi will search for evidence that dark matter is composed of weakly interacting massive particles, complementing similar experiments with the Large Hadron Collider and other underground detectors. Physics_sentence_226

IBEX is already yielding new astrophysical discoveries: "No one knows what is creating the ENA (energetic neutral atoms) ribbon" along the termination shock of the solar wind, "but everyone agrees that it means the textbook picture of the heliosphere—in which the Solar System's enveloping pocket filled with the solar wind's charged particles is plowing through the onrushing 'galactic wind' of the interstellar medium in the shape of a comet—is wrong." Physics_sentence_227

Current research Physics_section_23

Further information: List of unsolved problems in physics Physics_sentence_228

Research in physics is continually progressing on a large number of fronts. Physics_sentence_229

In condensed matter physics, an important unsolved theoretical problem is that of high-temperature superconductivity. Physics_sentence_230

Many condensed matter experiments are aiming to fabricate workable spintronics and quantum computers. Physics_sentence_231

In particle physics, the first pieces of experimental evidence for physics beyond the Standard Model have begun to appear. Physics_sentence_232

Foremost among these are indications that neutrinos have non-zero mass. Physics_sentence_233

These experimental results appear to have solved the long-standing solar neutrino problem, and the physics of massive neutrinos remains an area of active theoretical and experimental research. Physics_sentence_234

The Large Hadron Collider has already found the Higgs boson, but future research aims to prove or disprove the supersymmetry, which extends the Standard Model of particle physics. Physics_sentence_235

Research on the nature of the major mysteries of dark matter and dark energy is also currently ongoing. Physics_sentence_236

Theoretical attempts to unify quantum mechanics and general relativity into a single theory of quantum gravity, a program ongoing for over half a century, have not yet been decisively resolved. Physics_sentence_237

The current leading candidates are M-theory, superstring theory and loop quantum gravity. Physics_sentence_238

Many astronomical and cosmological phenomena have yet to be satisfactorily explained, including the origin of ultra-high-energy cosmic rays, the baryon asymmetry, the accelerating expansion of the universe and the anomalous rotation rates of galaxies. Physics_sentence_239

Although much progress has been made in high-energy, quantum, and astronomical physics, many everyday phenomena involving complexity, chaos, or turbulence are still poorly understood. Physics_sentence_240

Complex problems that seem like they could be solved by a clever application of dynamics and mechanics remain unsolved; examples include the formation of sandpiles, nodes in trickling water, the shape of water droplets, mechanisms of surface tension catastrophes, and self-sorting in shaken heterogeneous collections. Physics_sentence_241

These complex phenomena have received growing attention since the 1970s for several reasons, including the availability of modern mathematical methods and computers, which enabled complex systems to be modeled in new ways. Physics_sentence_242

Complex physics has become part of increasingly interdisciplinary research, as exemplified by the study of turbulence in aerodynamics and the observation of pattern formation in biological systems. Physics_sentence_243

In the 1932 Annual Review of Fluid Mechanics, Horace Lamb said: Physics_sentence_244

See also Physics_section_24

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