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Various examples of physical phenomena

Physics (from Ancient Greek: φυσική (ἐπιστήμη), romanizedphysikḗ (epistḗmē), lit.'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 is one of the most fundamental scientific disciplines, and its main goal is to understand how the universe behaves.

Physics is one of the oldest academic disciplines and, through its inclusion of astronomy, perhaps the oldest. 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 intersects with many interdisciplinary areas of research, such as biophysics and quantum chemistry, and the boundaries of physics are not rigidly defined. 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.

Advances in physics often enable advances in new technologies. 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. ( Full article...)

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Portrait by Jakob Emanuel Handmann (1753)

Leonhard Euler ( /ˈɔɪlər/ OY-lər; German: [ˈɔʏlɐ] ( About this sound listen); 15 April 1707 – 18 September 1783) was a Swiss mathematician, physicist, astronomer, geographer, logician and engineer who made important and influential discoveries in many branches of mathematics, such as infinitesimal calculus and graph theory, while also making pioneering contributions to several branches such as topology and analytic number theory. He also introduced much of the modern mathematical terminology and notation, particularly for mathematical analysis, such as the notion of a mathematical function. He is also known for his work in mechanics, fluid dynamics, optics, astronomy and music theory.

Euler is held to be one of the greatest mathematicians in history. A 1988 Mathematical Intelligencer poll ranked 3 of his results in the top 5 most beautiful equations ever (his iconic identity was ranked number one). A statement attributed to Pierre-Simon Laplace expresses Euler's influence on mathematics: "Read Euler, read Euler, he is the master of us all." He is also widely considered to be the most prolific, as his collected works fill 92 volumes, more than anyone else in the field. He spent most of his adult life in Saint Petersburg, Russia, and in Berlin, then the capital of Prussia. ( Full article...)
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Albert Einstein's official portrait after receiving the 1921 Nobel Prize in Physics

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Difference between classical and modern physics

The basic domains of physics

While physics aims to discover universal laws, its theories lie in explicit domains of applicability. 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. Outside of this domain, observations do not match their predictions. Albert 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. Max Planck, Erwin Schrödinger, and others introduced quantum mechanics, a probabilistic notion of particles and interactions that allowed an accurate description of atomic and subatomic scales. Later, quantum field theory unified quantum mechanics and special relativity. 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. General relativity has not yet been unified with the other fundamental descriptions; several candidate theories of quantum gravity are being developed.

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Schematic representation of the Dirac delta function by a line surmounted by an arrow. The height of the arrow is usually meant to specify the value of any multiplicative constant, which will give the area under the function. The other convention is to write the area next to the arrowhead.

In mathematics, the Dirac delta function (δ function) is a generalized function or distribution introduced by physicist Paul Dirac. It is called a function, although it is not a function on the level you would expect, that is, it is not a function RC, but a function on the space of test functions. It is used to model the density of an idealized point mass or point charge as a function equal to zero everywhere except for zero and whose integral over the entire real line is equal to one. As there is no function that has these properties, the computations made by theoretical physicists appeared to mathematicians as nonsense until the introduction of distributions by Laurent Schwartz to formalize and validate the computations. As a distribution, the Dirac delta function is a linear functional that maps every function to its value at zero. The Kronecker delta function, which is usually defined on a discrete domain and takes values 0 and 1, is a discrete analog of the Dirac delta function.

In engineering and signal processing, the delta function, also known as the unit impulse symbol, may be regarded through its Laplace transform, as coming from the boundary values of a complex analytic function of a complex variable. The formal rules obeyed by this function are part of the operational calculus, a standard tool kit of physics and engineering. In many applications, the Dirac delta is regarded as a kind of limit (a weak limit) of a sequence of functions having a tall spike at the origin (in theory of distributions, this is a true limit). The approximating functions of the sequence are thus "approximate" or "nascent" delta functions. ( Full article...)

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Fundamentals: Concepts in physics | Constants | Physical quantities | Units of measure | Mass | Length | Time | Space | Energy | Matter | Force | Gravity | Electricity | Magnetism | Waves

Basic physics: Mechanics | Electromagnetism | Statistical mechanics | Thermodynamics | Quantum mechanics | Theory of relativity | Optics | Acoustics

Specific fields: Acoustics | Astrophysics | Atomic physics | Molecular physics | Optical physics | Computational physics | Condensed matter physics | Nuclear physics | Particle physics | Plasma physics

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Background: Physicists | History of physics | Philosophy of physics | Physics education | Physics journals | Physics organizations

Other: Physics in fiction | Pseudophysics | Physics lists | Physics software | Physics stubs

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Physics topics

Classical physics traditionally includes the fields of mechanics, optics, electricity, magnetism, acoustics and thermodynamics. The term Modern physics is normally used for fields which rely heavily on quantum theory, including quantum mechanics, atomic physics, nuclear physics, particle physics and condensed matter physics. General and special relativity are usually considered to be part of modern physics as well.

Fundamental Concepts Classical Physics Modern Physics Cross Discipline Topics
Continuum Solid Mechanics Fluid Mechanics Geophysics
Motion Classical Mechanics Analytical mechanics Mathematical Physics
Kinetics Kinematics Kinematic chain Robotics
Matter Classical states Modern states Nanotechnology
Energy Chemical Physics Plasma Physics Materials Science
Cold Cryophysics Cryogenics Superconductivity
Heat Heat transfer Transport Phenomena Combustion
Entropy Thermodynamics Statistical mechanics Phase transitions
Particle Particulates Particle physics Particle accelerator
Antiparticle Antimatter Annihilation physics Gamma ray
Waves Oscillation Quantum oscillation Vibration
Gravity Gravitation Gravitational wave Celestial mechanics
Vacuum Pressure physics Vacuum state physics Quantum fluctuation
Random Statistics Stochastic process Brownian motion
Spacetime Special Relativity General Relativity Black holes
Quanta Quantum mechanics Quantum field theory Quantum computing
Radiation Radioactivity Radioactive decay Cosmic ray
Light Optics Quantum optics Photonics
Electrons Solid State Condensed Matter Symmetry breaking
Electricity Electrical circuit Electronics Integrated circuit
Electromagnetism Electrodynamics Quantum Electrodynamics Chemical Bonds
Strong interaction Nuclear Physics Quantum Chromodynamics Quark model
Weak interaction Atomic Physics Electroweak theory Radioactivity
Standard Model Fundamental interaction Grand Unified Theory Higgs boson
Information Information science Quantum information Holographic principle
Life Biophysics Quantum Biology Astrobiology
Conscience Neurophysics Quantum mind Quantum brain dynamics
Cosmos Astrophysics Cosmology Observable universe
Cosmogony Big Bang Mathematical universe Multiverse
Chaos Chaos theory Quantum chaos Perturbation theory
Complexity Dynamical system Complex system Emergence
Quantization Canonical quantization Loop quantum gravity Spin foam
Unification Quantum gravity String theory Theory of Everything

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