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).

History

Main article: History of physics. See also Famous physicists and Nobel Prize in Physics.

Related Topics:
History of physics - Famous physicists - Nobel Prize in Physics

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Since antiquity, people have tried to understand the behavior of matter: why unsupported objects drop to the ground, why different materials have different properties, and so forth. Also a mystery was the character of the universe, such as the form of the Earth and the behavior of celestial objects such as the Sun and the Moon. Several theories were proposed, most of which were wrong. These theories were largely couched in philosophical terms, and never verified by systematic experimental testing as is popular today. There were exceptions and there are anachronisms: for example, the Greek thinker Archimedes derived many correct quantitative descriptions of mechanics and hydrostatics.

Related Topics:
Matter - Materials - Universe - Earth - Sun - Moon - Philosophical - Anachronism - Greek - Archimedes - Mechanics - Hydrostatics

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The works of Ptolemy (Astronomy) and Aristotle were also found to not always match everyday observations.

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Ptolemy - Aristotle

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The willingness to question previously held truths and search for new answers resulted in a period of major scientific advancements, now known as the Scientific Revolution. Its origins can be found in the European re-discovery of Aristotle in the twelfth and thirteenth centuries. This period culminated with the publication of the Philosophiae Naturalis Principia Mathematica in 1687 by Isaac Newton (dates disputed).

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Scientific Revolution - Philosophiae Naturalis Principia Mathematica - 1687 - Isaac Newton

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The Scientific Revolution is held by most historians (e.g., Howard Margolis) to have begun in 1543, when there was brought to the Polish astronomer Nicolaus Copernicus the first printed copy of the book De Revolutionibus he had written about a dozen years earlier. The thesis of this book is that the Earth moves around the Sun.

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1543 - Polish - Nicolaus Copernicus - De Revolutionibus

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Other significant scientific advances were made during this time by Galileo Galilei, Christiaan Huygens, Johannes Kepler, and Blaise Pascal.

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Galileo Galilei - Christiaan Huygens - Johannes Kepler - Blaise Pascal

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During the early 17th century, Galileo pioneered the use of experimentation to validate physical theories, which is the key idea in the scientific method. Galileo formulated and successfully tested several results in dynamics, in particular the Law of Inertia. In 1687, Newton published the Principia Mathematica, detailing two comprehensive and successful physical theories: Newton's laws of motion, from which arise classical mechanics; and Newton's Law of Gravitation, which describes the fundamental force of gravity. Both theories agreed well with experiment. The Principia also included several theories in fluid dynamics. Classical mechanics was extended by Leonhard Euler, Joseph-Louis de Lagrange, William Rowan Hamilton, and others, who produced new results and new formulations of the theory. The law of universal gravitation initiated the field of astrophysics, which describes astronomical phenomena using physical theories.

Related Topics:
17th century - Galileo - Scientific method - Dynamics - Inertia - 1687 - Newton - Principia Mathematica - Newton's laws of motion - Classical mechanics - Newton's Law of Gravitation - Fundamental force - Fluid dynamics - Leonhard Euler - Joseph-Louis de Lagrange - William Rowan Hamilton - Astrophysics - Astronomical

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After Newton defined classical mechanics, the next great field of inquiry within physics was the nature of electricity. Observations in the 17th and 18th century by scientists such as Robert Boyle, Stephen Gray, and Benjamin Franklin created a foundation for later work. These observations also established our basic understanding of electrical charge and current.

Related Topics:
Classical mechanics - Electricity - 17th - 18th century - Robert Boyle - Stephen Gray - Benjamin Franklin - Current

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In 1821, Michael Faraday integrated the study of magnetism with the study of electricity. This was done by demonstrating that a moving magnet induced an electric current in a conductor. Faraday also formulated a physical conception of electromagnetic fields. James Clerk Maxwell built upon this conception, in 1864, with an interlinked set of 20 equations that explained the interactions between electric and magnetic field. These 20 equations were later reduced, using vector calculus, to a set of four equations by Oliver Heaviside.

Related Topics:
1821 - Michael Faraday - Magnetism - Magnet - Electric current - Conductor - Electromagnetic field - James Clerk Maxwell - 1864 - Electric - Magnetic field - Vector calculus - Four equations - Oliver Heaviside

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In addition to other electromagnetic phenomena, Maxwell's equations also can be used to describe light. Confirmation of this observation was made with the 1888 discovery of radio by Heinrich Hertz and in 1895 when Wilhelm Roentgen detected X rays. The ability to describe light in electromagnetic terms helped serve as a springboard for Albert Einstein's publication of his theory of special relativity. This theory combined classical mechanics with Maxwell's equations.

Related Topics:
Light - 1888 - Radio - Heinrich Hertz - 1895 - Wilhelm Roentgen - X rays - Albert Einstein - Special relativity

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The theory of special relativity unifies space and time into a single entity, spacetime. Relativity prescribes a different transformation between reference frames than classical mechanics; this necessitated the development of relativistic mechanics as a replacement for classical mechanics. In the regime of low (relative) velocities, the two theories agree. Einstein built further on the special theory by including gravity into his calculations, and published his theory of general relativity in 1915.

Related Topics:
Special relativity - Spacetime - Reference frames - Gravity - General relativity - 1915

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One part of the theory of general relativity is Einstein's field equation. This describes how the stress-energy tensor creates curvature of spacetime and forms the basis of general relativity. Further work on Einstein's field equation produced results which predicted the Big Bang{{fn|3}},{{fn|4}} black holes, and the expanding universe. Einstein believed in a static universe and tried (and failed) to fix his equation to allow for this. However, by 1929 Edwin Hubble argued that astronomical observations demonstrate that the universe is expanding.

Related Topics:
Einstein's field equation - Spacetime - Big Bang - Black hole - Expanding universe - 1929 - Edwin Hubble

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From the 18th century onwards, thermodynamics was developed by Boyle, Young, and many others. In 1733, Bernoulli used statistical arguments with classical mechanics to derive thermodynamic results, initiating the field of statistical mechanics. In 1798, Thompson demonstrated the conversion of mechanical work into heat, and in 1847 Joule stated the law of conservation of energy, in the form of heat as well as mechanical energy. Ludwig Boltzmann, in the 19th century, is responsible for the modern form of statistical mechanics.

Related Topics:
18th century - Thermodynamics - Boyle - Young - 1733 - Bernoulli - Statistical mechanics - 1798 - Thompson - 1847 - Joule - Energy - Ludwig Boltzmann

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In 1895, Roentgen discovered X-rays, which turned out to be high-frequency electromagnetic radiation. Radioactivity was discovered in 1896 by Henri Becquerel, and further studied by Marie Curie, Pierre Curie, and others. This initiated the field of nuclear physics.

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1895 - Roentgen - X-ray - Radioactivity - 1896 - Henri Becquerel - Marie Curie - Pierre Curie - Nuclear physics

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In 1897, Joseph J. Thomson discovered the electron, the elementary particle which carries electrical current in circuits. In 1904, he proposed the first model of the atom, known as the plum pudding model. (The existence of the atom had been proposed in 1808 by John Dalton.)

Related Topics:
1897 - Joseph J. Thomson - Electron - Circuits - 1904 - Atom - Plum pudding model - 1808 - John Dalton

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These discoveries revealed that the assumption of many physicists that atoms were the basic unit of matter was flawed, and prompted further study into the structure of atoms.

Related Topics:
Matter - Atom

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In 1911, Rutherford deduced from scattering experiments the existence of a compact atomic nucleus, with positively charged constituents dubbed protons. Neutrons, the neutral nuclear constituents, were discovered in 1932 by Chadwick. The equivalence of mass and energy (Einstein, 1905) was spectacularly demonstrated during World War II, as research was conducted by each side into nuclear physics, for the purpose of creating a nuclear bomb. The German effort, led by Heisenberg, did not succeed, but the Allied Manhattan Project reached its goal. In America, a team led by Fermi achieved the first man-made nuclear chain reaction in 1942, and in 1945 the world's first nuclear explosive was detonated at Trinity site, near Alamogordo, New Mexico.

Related Topics:
1911 - Rutherford - Scattering experiments - Proton - Neutrons - 1932 - Chadwick - World War II - Nuclear physics - Nuclear bomb - Manhattan Project - Fermi - Nuclear chain reaction - 1942 - 1945 - Trinity site - Alamogordo - New Mexico

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In 1900, Max Planck published his explanation of blackbody radiation. This equation assumed that radiators are quantized in nature, which proved to be the opening argument in the edifice that would become quantum mechanics.

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1900 - Max Planck - Blackbody radiation - Quantized - Quantum mechanics

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Beginning in 1900, Planck, Einstein, Niels Bohr, and others developed quantum theories to explain various anomalous experimental results by introducing discrete energy levels. In 1925, Heisenberg and 1926, Schrödinger and Paul Dirac formulated quantum mechanics, which explained the preceding heuristic quantum theories. In quantum mechanics, the outcomes of physical measurements are inherently probabilistic; the theory describes the calculation of these probabilities. It successfully describes the behavior of matter at small distance scales. During the 1920s Erwin Schrödinger, Werner Heisenberg, and Max Born were able to formulate a consistent picture of the chemical behavior of matter, a complete theory of the electronic structure of the atom, as a byproduct of the quantum theory.

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1900 - Planck - Niels Bohr - Quantum - 1925 - Heisenberg - 1926 - Schrödinger - Paul Dirac - Quantum mechanics - Probabilistic - 1920s - Max Born

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Quantum field theory was formulated in order to extend quantum mechanics to be consistent with special relativity. It was devised in the late 1940s with work by Richard Feynman, Julian Schwinger, Sin-Itiro Tomonaga, and Freeman Dyson. They formulated the theory of quantum electrodynamics, which describes the electromagnetic interaction, and successfully explained the Lamb shift. Quantum field theory provided the framework for modern particle physics, which studies fundamental forces and elementary particles.

Related Topics:
Quantum field theory - 1940s - Richard Feynman - Julian Schwinger - Sin-Itiro Tomonaga - Freeman Dyson - Quantum electrodynamics - Lamb shift - Particle physics - Fundamental force

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Chen Ning Yang and Tsung-Dao Lee, in the 1950s, discovered an unexpected asymmetry in the decay of a subatomic particle{{fn|5}}. In 1954, Yang and Robert Mills then developed a class of gauge theories{{fn|6}},{{fn|7}} which provided the framework for understanding the nuclear forces. The theory for the strong nuclear force was first proposed by Murray Gell-Mann. The electroweak force, the unification of the weak nuclear force with electromagnetism, was proposed by Sheldon Lee Glashow, Abdus Salam and Steven Weinberg and confirmed in 1964 by James Watson Cronin and Val Fitch. This led to the so-called Standard Model of particle physics in the 1970s, which successfully describes all the elementary particles observed to date.

Related Topics:
Chen Ning Yang - Tsung-Dao Lee - 1950s - Asymmetry - Subatomic particle - 1954 - Robert Mills - Gauge theories - Strong nuclear force - Murray Gell-Mann - Electroweak force - Weak nuclear force - Sheldon Lee Glashow - Abdus Salam - Steven Weinberg - 1964 - James Watson Cronin - Val Fitch - Standard Model - 1970s

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Quantum mechanics also provided the theoretical tools for condensed matter physics, whose largest branch is solid state physics. It studies the physical behavior of solids and liquids, including phenomena such as crystal structures, semiconductivity, and superconductivity. The pioneers of condensed matter physics include Bloch, who created a quantum mechanical description of the behavior of electrons in crystal structures in 1928. The transistor was developed by physicists John Bardeen, Walter Houser Brattain and William Bradford Shockley in 1947 at Bell Telephone Laboratories.

Related Topics:
Condensed matter physics - Solid state physics - Crystal structure - Semiconductivity - Superconductivity - Bloch - 1928 - John Bardeen - Walter Houser Brattain - William Bradford Shockley - 1947 - Bell Telephone Laboratories

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The two themes of the 20th century, general relativity and quantum mechanics, appear inconsistent with each other. General relativity describes the universe on the scale of planets and solar systems while quantum mechanics operates on sub-atomic scales. This challenge is being attacked by string theory, which treats spacetime as composed, not of points, but of one-dimensional objects, strings. Strings have properties like a common string (e.g., tension and vibration). The theories yield promising, but not yet testable results. The search for experimental verification of string theory is in progress.

Related Topics:
20th century - Universe - Planet - Solar system - String theory - Spacetime - Strings - Tension - Vibration

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The United Nations have declared the year 2005, the centenary of Einstein's annus mirabilis, as the World Year of Physics.

Related Topics:
2005 - Annus mirabilis - World Year of Physics

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