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{{short description|Study of the fundamental properties of matter and energy}} | |||
{{Other uses}} | |||
{{distinguish|Physis}} | |||
{{pp-semi-indef}} | |||
{{pp-move-indef}} | |||
{{Use dmy dates|date=August 2019}} | |||
[[File:CollageFisica.jpg|upright=1.35|thumb|Various examples of [[Phenomenon|physical phenomena]]]] | |||
{{TopicTOC-Physics}} | |||
'''Physics''' is the [[natural science]] that studies [[matter]],{{efn|At the start of ''[[The Feynman Lectures on Physics]]'', [[Richard Feynman]] offers the [[Atomic theory|atomic hypothesis]] as the single most prolific scientific concept.<ref name="feynmanleightonsands1963-atomic">{{harvnb|Feynman|Leighton|Sands|1963|p=I-2}} "If, in some cataclysm, all [] scientific knowledge were to be destroyed [save] one sentence [...] what statement would contain the most information in the fewest words? I believe it is [...] that ''all things are made up of atoms – little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another'' ..."</ref> }} its [[Elementary particle|fundamental constituents]], its [[Motion (physics)|motion]] and behavior through [[Spacetime|space and time]], and the related entities of [[energy]] and [[force]].<ref name="maxwell1878-physicalscience">{{harvnb|Maxwell|1878|p=9}} "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular succession of events."</ref> Physics is one of the most fundamental [[science|scientific]] disciplines, with its main goal being to understand how the [[universe]] behaves.{{efn|The term "universe" is defined as everything that physically exists: the entirety of space and time, all forms of matter, energy and momentum, and the physical laws and constants that govern them. However, the term "universe" may also be used in slightly different contextual senses, denoting concepts such as the [[cosmos]] or the [[World (philosophy)|philosophical world]].}}<ref name="youngfreedman2014p1">{{harvnb |Young|Freedman|2014|p=1}} "Physics is one of the most fundamental of the sciences. Scientists of all disciplines use the ideas of physics, including chemists who study the structure of molecules, paleontologists who try to reconstruct how dinosaurs walked, and climatologists who study how human activities affect the atmosphere and oceans. Physics is also the foundation of all engineering and technology. No engineer could design a flat-screen TV, an interplanetary spacecraft, or even a better mousetrap without first understanding the basic laws of physics. (...) You will come to see physics as a towering achievement of the human intellect in its quest to understand our world and ourselves."</ref><ref name="youngfreedman2014p2">{{harvnb |Young|Freedman|2014|p=2}} "Physics is an experimental science. Physicists observe the phenomena of nature and try to find patterns that relate these phenomena."</ref><ref name="holzner2003-physics">{{harvnb|Holzner|2006|p=7}} "Physics is the study of your world and the world and universe around you."</ref> A scientist who specializes in the field of physics is called a [[physicist]]. | |||
[[ | Physics is one of the oldest [[academic discipline]]s and, through its inclusion of [[astronomy]], perhaps <em>the</em> oldest.<ref name="krupp2003">{{harvnb |Krupp|2003}}</ref> 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.{{efn|[[Francis Bacon]]'s 1620 ''[[Novum Organum]]'' was critical in the [[History of scientific method|development of scientific method]].<ref name="Cajori1917">{{harvnb |Cajori|1917|pp=48–49}}</ref>}} Physics intersects with many [[interdisciplinarity|interdisciplinary]] areas of research, such as [[biophysics]] and [[quantum chemistry]], and the boundaries of physics are not [[demarcation problem|rigidly defined]]. New ideas in physics often explain the fundamental mechanisms studied by other [[science]]s<ref name="youngfreedman2014p1" /> and suggest new avenues of research in these and other academic disciplines such as mathematics and [[philosophy]]. | ||
Advances in physics often enable advances in new [[technology|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]], [[computer]]s, [[domestic appliance]]s, and [[nuclear weapon]]s;<ref name="youngfreedman2014p1" /> advances in [[thermodynamics]] led to the development of [[industrialization]]; and advances in [[mechanics]] inspired the development of [[calculus]]. | |||
==History== | |||
{{Main|History of physics}} | |||
The word "physics" comes from {{lang-grc|φυσική (ἐπιστήμη)|physikḗ (epistḗmē)}}, meaning "knowledge of nature".<ref name="etymonline-physics">{{cite web |title=physics |website=[[Online Etymology Dictionary]] |url=http://www.etymonline.com/index.php?term=physics&allowed_in_frame=0|access-date=2016-11-01 |archive-url= https://web.archive.org/web/20161224191507/http://www.etymonline.com/index.php?term=physics&allowed_in_frame=0 |archive-date=24 December 2016 |url-status=live}}</ref><ref name="etymonline-physic">{{cite web |title=physic |website=[[Online Etymology Dictionary]] |url=http://www.etymonline.com/index.php?term=physic&allowed_in_frame=0 |access-date=2016-11-01 |archive-url= https://web.archive.org/web/20161224173651/http://www.etymonline.com/index.php?term=physic&allowed_in_frame=0 |archive-date=24 December 2016 |url-status=live}}</ref><ref name="LSJ">{{LSJ|fu/sis|φύσις}}, {{LSJ|fusiko/s|φυσική}}, {{LSJ|e)pisth/mh|ἐπιστήμη|ref}}</ref> | |||
=== Ancient astronomy === | === Ancient astronomy === | ||
Astronomy is the oldest [[natural science]]. | {{Main|History of astronomy}} | ||
[[File:Senenmut-Grab.JPG|thumb|right|Ancient [[Egyptian astronomy]] is evident in monuments like the [[Astronomical ceiling of Senemut Tomb|ceiling of Senemut's tomb]] from the [[Eighteenth Dynasty of Egypt]].]] | |||
[[Astronomy]] is one of the oldest [[natural science]]s. Early civilizations dating back before 3000 BCE, such as the [[Sumer]]ians, [[ancient Egypt]]ians, and the [[Indus Valley civilisation]], had a predictive knowledge and a basic awareness of the motions of the Sun, Moon, and stars. The stars and planets, believed to represent gods, were often worshipped. 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 circle]]s across the sky,<ref name="krupp2003"/> which however did not explain the positions of the [[planet]]s. | |||
According to [[Asger Aaboe]], the origins of [[Western world|Western]] astronomy can be found in [[Mesopotamia]], and all Western efforts in the [[exact science]]s are descended from late [[Babylonian astronomy]].<ref name ="aaboe1991">{{harvnb |Aaboe|1991}}</ref> [[Egyptian astronomy|Egyptian astronomers]] left monuments showing knowledge of the constellations and the motions of the celestial bodies,<ref name="clagett1995">{{harvnb |Clagett|1995}}</ref> while Greek poet [[Homer]] wrote of various celestial objects in his ''[[Iliad]]'' and ''[[Odyssey]]''; later [[Greek astronomy|Greek astronomers]] provided names, which are still used today, for most constellations visible from the [[Northern Hemisphere]].<ref name="thurston1994">{{harvnb |Thurston|1994}}</ref> | |||
=== Natural philosophy === | === Natural philosophy === | ||
Natural philosophy | {{main|Natural philosophy}} | ||
[[Natural philosophy]] has its origins in [[Greece]] during the [[Archaic Greece|Archaic period]] (650 BCE – 480 BCE), when [[Presocratics|pre-Socratic philosophers]] like [[Thales]] rejected [[Methodological naturalism|non-naturalistic]] explanations for natural phenomena and proclaimed that every event had a natural cause.<ref name="singer2008p35">{{harvnb |Singer|2008|p=35}}</ref> They proposed ideas verified by reason and observation, and many of their hypotheses proved successful in experiment;<ref name="lloyd1970pp108-109">{{harvnb |Lloyd|1970|pp=108–109}}</ref> for example, [[atomism]] was found to be correct approximately 2000 years after it was proposed by [[Leucippus]] and his pupil [[Democritus]].<ref name="about-atomism"> | |||
{{cite web | |||
|last = Gill | |||
|first = N.S. | |||
|title = Atomism – Pre-Socratic Philosophy of Atomism | |||
|publisher = [[About.com|About Education]] | |||
|url = http://ancienthistory.about.com/od/presocraticphiloso/p/Atomism.htm | |||
|access-date = 1 April 2014 | |||
|url-status=live | |||
|archive-url = https://web.archive.org/web/20140710140657/http://ancienthistory.about.com/od/presocraticphiloso/p/Atomism.htm | |||
|archive-date = 10 July 2014 | |||
|df = dmy-all | |||
}}</ref> | |||
=== Medieval European and Islamic === | |||
{{main|European science in the Middle Ages|Physics in the medieval Islamic world}} | |||
The [[Western Roman Empire]] fell in the fifth century, and this resulted in a decline in intellectual pursuits in the western part of Europe. 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.{{sfn|Lindberg|1992|page=363}} | |||
In the sixth century, Isidore of Miletus created an important compilation of Archimedes' works that are copied in the [[Archimedes Palimpsest]]. | |||
[[File:Hazan.png|thumb|right|upright|[[Ibn al-Haytham]] (c. 965–c. 1040), ''Book of Optics'' Book I, [6.85], [6.86]. Book II, [3.80] describes his ''camera obscura'' experiments.{{sfn|Smith|2001|loc=Book I [6.85], [6.86], p. 379; Book II, [3.80], p. 453}}|alt=Ibn Al-Haytham (Alhazen) drawing]] | |||
In sixth-century Europe [[John Philoponus]], a Byzantine scholar, questioned [[Aristotle]]'s teaching of physics and noted its flaws. He introduced the [[theory of impetus]]. Aristotle's physics was not scrutinized until Philoponus appeared; unlike Aristotle, who based his physics on verbal argument, Philoponus relied on observation. On Aristotle's physics Philoponus wrote:<blockquote>But this is completely erroneous, and our view may be corroborated by actual observation more effectively than by any sort of verbal argument. For if you let fall from the same height two weights of which one is many times as heavy as the other, you will see that the ratio of the times required for the motion does not depend on the ratio of the weights, but that the difference in time is a very small one. And so, if the difference in the weights is not considerable, that is, of one is, let us say, double the other, there will be no difference, or else an imperceptible difference, in time, though the difference in weight is by no means negligible, with one body weighing twice as much as the other<ref>{{Cite web | url=http://homepages.wmich.edu/~mcgrew/philfall.htm | title=John Philoponus, Commentary on Aristotle's Physics | access-date=15 April 2018 | archive-url=https://web.archive.org/web/20160111105753/http://homepages.wmich.edu/~mcgrew/philfall.htm | archive-date=11 January 2016 | url-status=dead }}</ref></blockquote>Philoponus' criticism of Aristotelian principles of physics served as an inspiration for [[Galileo Galilei]] ten centuries later,<ref name="dialogTwoNewSciences">{{cite book |last=Galileo |date=1638 |title=[[Two New Sciences]] |quote=in order to better understand just how conclusive Aristotle’s demonstration is, we may, in my opinion, deny both of his assumptions. And as to the first, I greatly doubt that Aristotle ever tested by experiment whether it be true that two stones, one weighing ten times as much as the other, if allowed to fall, at the same instant, from a height of, say, 100 cubits, would so differ in speed that when the heavier had reached the ground, the other would not have fallen more than 10 cubits.<br/>Simp. - His language would seem to indicate that he had tried the experiment, because he says: We see the heavier; now the word see shows that he had made the experiment.<br/>Sagr. - But I, Simplicio, who have made the test can assure[107] you that a cannon ball weighing one or two hundred pounds, or even more, will not reach the ground by as much as a span ahead of a musket ball weighing only half a pound, provided both are dropped from a height of 200 cubits.}}</ref> during the [[Scientific Revolution]]. Galileo cited Philoponus substantially in his works when arguing that Aristotelian physics was flawed.{{sfn|Lindberg|1992|page=162}}<ref>{{Cite book | chapter-url=https://plato.stanford.edu/entries/philoponus/ | title=The Stanford Encyclopedia of Philosophy| chapter=John Philoponus| publisher=Metaphysics Research Lab, Stanford University| year=2018}}</ref> In the 1300s [[Jean Buridan]], a teacher in the faculty of arts at the University of Paris, developed the concept of impetus. It was a step toward the modern ideas of inertia and momentum.<ref>{{Cite book | chapter-url=https://plato.stanford.edu/entries/buridan/ | title=The Stanford Encyclopedia of Philosophy| chapter=John Buridan| publisher=Metaphysics Research Lab, Stanford University| year=2018}}</ref> | |||
[[Science in the medieval Islamic world|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]]. | |||
[[File:Pinhole-camera.svg|thumb|right|upright|The basic way a pinhole camera works]] | |||
The most notable innovations were in the field of optics and vision, which came from the works of many scientists like [[Ibn Sahl (mathematician)|Ibn Sahl]], [[Al-Kindi]], [[Ibn al-Haytham]], [[Kamāl al-Dīn al-Fārisī|Al-Farisi]] and [[Avicenna]]. The most notable work was ''[[Book of Optics|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. 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. Using dissections and the knowledge of previous scholars, he was able to begin to explain how light enters the eye. 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. His ''Treatise on Light'' explained the camera obscura, hundreds of years before the modern development of photography.<ref>{{harvnb |Howard|Rogers|1995|pp=6–7}}</ref> | |||
The seven-volume ''Book of Optics'' (''Kitab al-Manathir'') hugely influenced thinking across disciplines from the theory of visual [[perception]] to the nature of [[perspectivity|perspective]] in medieval art, in both the East and the West, for more than 600 years. 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. Indeed, the influence of Ibn al-Haytham's Optics ranks alongside that of Newton's work of the same title, published 700 years later. | |||
The translation of ''The Book of Optics'' had a huge impact on Europe. From it, later European scholars were able to build devices that replicated those Ibn al-Haytham had built, and understand the way light works. From this, important inventions such as eyeglasses, magnifying glasses, telescopes, and cameras were developed. | |||
=== Classical === | |||
{{main|Classical physics}} | |||
[[File:Justus Sustermans - Portrait of Galileo Galilei, 1636.jpg|thumb|right|upright|[[Galileo Galilei]] showed a modern appreciation for the proper relationship between mathematics, theoretical physics, and experimental physics.]] | |||
[[File:GodfreyKneller-IsaacNewton-1689.jpg|thumb|right|upright|Sir [[Isaac Newton]] (1643–1727), whose [[Newton's laws of motion|laws of motion]] and [[Newton's law of universal gravitation|universal gravitation]] were major milestones in classical physics]] | |||
Physics became a separate science when [[early modern Europe]]ans used experimental and quantitative methods to discover what are now considered to be the [[laws of physics]].<ref name="benchaim2004">{{harvnb |Ben-Chaim|2004}}</ref>{{Page needed|date=November 2016}} | |||
Major developments in this period include the replacement of the [[geocentric model]] of the [[Solar System]] with the heliocentric [[Copernican model]], the [[Kepler's laws|laws governing the motion of planetary bodies]] (determined by Kepler between 1609 and 1619), Galileo's pioneering work on [[telescope]]s and [[observational astronomy]] in the 16th and 17th Centuries, and Newton's discovery and unification of the [[Newton's laws of motion|laws of motion]] and [[Newton's law of universal gravitation|universal gravitation]] (that would come to bear his name).<ref>{{harvnb |Guicciardini|1999}}</ref> Newton also developed [[calculus]],{{efn|Calculus was independently developed at around the same time by [[Gottfried Wilhelm Leibniz]]; while Leibniz was the first to publish his work and develop much of the notation used for calculus today, Newton was the first to develop calculus and apply it to physical problems. See also [[Leibniz–Newton calculus controversy]]}} the mathematical study of change, which provided new mathematical methods for solving physical problems.<ref name="allen1997">{{harvnb |Allen|1997}}</ref> | |||
The discovery of new laws in [[thermodynamics]], [[chemistry]], and [[electromagnetics]] resulted from greater research efforts during the [[Industrial Revolution]] as energy needs increased.<ref name="schoolscience-industrialrevolution">{{cite web | |||
|title = The Industrial Revolution | |||
|publisher = Schoolscience.org, [[Institute of Physics]] | |||
|url = http://resources.schoolscience.co.uk/IoP/14-16/biogs/biogs5.html | |||
|access-date = 1 April 2014 | |||
|url-status=live | |||
|archive-url = https://web.archive.org/web/20140407083354/http://resources.schoolscience.co.uk/IoP/14-16/biogs/biogs5.html | |||
|archive-date = 7 April 2014 | |||
|df = dmy-all | |||
}}</ref> 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. However, inaccuracies in [[classical mechanics]] for very small objects and very high velocities led to the development of modern physics in the 20th century. | |||
=== Modern === | |||
{{main|Modern physics}} | |||
{{see also|History of special relativity|History of quantum mechanics}} | |||
[[File:Max Planck (Nobel 1918).jpg|thumb|right|upright|[[Max Planck]] (1858–1947), the originator of the theory of [[quantum mechanics]]]] | |||
[[File:Einstein1921 by F Schmutzer 2.jpg|thumb|right|upright|[[Albert Einstein]] (1879–1955), whose work on the [[photoelectric effect]] and the theory of relativity led to a revolution in 20th century physics]] | |||
[[Modern physics]] began in the early 20th century with the work of [[Max Planck]] in quantum theory and [[Albert Einstein]]'s theory of relativity. Both of these theories came about due to inaccuracies in classical mechanics in certain situations. [[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.<ref name="oconnorrobertson1996-relativity">{{harvnb |O'Connor|Robertson|1996a}}</ref> [[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 [[Atomic orbital|electron orbitals]], led to the theory of quantum mechanics taking over from classical physics at very small scales.<ref name="oconnorrobertson1996-quantum">{{harvnb |O'Connor|Robertson|1996b}}</ref> | |||
Quantum mechanics would come to be pioneered by [[Werner Heisenberg]], [[Erwin Schrödinger]] and [[Paul Dirac]].<ref name="oconnorrobertson1996-quantum"/> From this early work, and work in related fields, the [[Standard Model of particle physics]] was derived.<ref name="donut2001">{{cite web |website=[[DONUT]] |title=The Standard Model |publisher=[[Fermilab]] |date=29 June 2001 |url=http://www-donut.fnal.gov/web_pages/standardmodelpg/TheStandardModel.html |access-date=1 April 2014}}</ref> Following the discovery of a particle with properties consistent with the [[Higgs boson]] at [[CERN]] in 2012,<ref name="cho2012">{{harvnb |Cho|2012}}</ref> 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.<ref>{{cite magazine |last=Womersley |first=J. |url=http://www.symmetrymagazine.org/sites/default/files/legacy/pdfs/200502/beyond_the_standard_model.pdf |date=February 2005 |title=Beyond the Standard Model |magazine= Symmetry |volume=2 |issue=1 |pages=22–25 |archive-url=https://web.archive.org/web/20150924114111/http://www.symmetrymagazine.org/sites/default/files/legacy/pdfs/200502/beyond_the_standard_model.pdf |archive-date=24 September 2015 |url-status=live}}</ref> Areas of [[mathematics]] in general are important to this field, such as the study of [[probability amplitude|probabilities]] and [[Group theory#Physics|groups]]. | |||
==Philosophy== | |||
{{Main|Philosophy of physics}} | |||
In many ways, physics stems from [[ancient Greek philosophy]]. From Thales' first attempt to characterize 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 (Aristotle)|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 was known as natural philosophy until the late 18th century.{{efn|Noll notes that some universities still use this title.<ref>{{cite journal |last1=Noll |first1=Walter |title=On the Past and Future of Natural Philosophy |url=http://www.math.cmu.edu/~wn0g/noll/PFNP.pdf |journal=Journal of Elasticity |date=23 June 2006 |volume=84 |issue=1 |pages=1–11 |doi=10.1007/s10659-006-9068-y |s2cid=121957320 |url-status=live |archive-url=https://web.archive.org/web/20160418072444/http://www.math.cmu.edu/~wn0g/noll/PFNP.pdf |archive-date=18 April 2016}}</ref> }} | |||
By the 19th century, physics was realized as a discipline distinct from philosophy and the other sciences. Physics, as with the rest of science, relies on [[philosophy of science]] and its "scientific method" to advance our knowledge of the physical world.<ref name="rosenberg2006ch1">{{harvnb |Rosenberg|2006|loc=Chapter 1}}</ref> The scientific method employs ''[[A priori and a posteriori|a priori reasoning]]'' as well as ''[[Empirical evidence|a posteriori]]'' reasoning and the use of [[Bayesian inference]] to measure the validity of a given theory.<ref name="godfreysmith2003ch14">{{harvnb |Godfrey-Smith|2003|loc=Chapter 14: "Bayesianism and Modern Theories of Evidence"}}</ref> | |||
The development of physics has answered many questions of early philosophers, but has also raised new questions. 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 (philosophy)|naturalism]] and [[Philosophical realism|realism]].<ref name="godfreysmith2003ch15">{{harvnb |Godfrey-Smith|2003|loc=Chapter 15: "Empiricism, Naturalism, and Scientific Realism?"}}</ref> | |||
Many physicists have written about the philosophical implications of their work, for instance [[Pierre-Simon Laplace|Laplace]], who championed [[causal determinism]],<ref name="laplace1951">{{harvnb |Laplace|1951}}</ref> and Schrödinger, who wrote on quantum mechanics.<ref name="schroedinger1983">{{harvnb |Schrödinger|1983}}</ref><ref name="schroedinger1995">{{harvnb |Schrödinger|1995}}</ref> The mathematical physicist [[Roger Penrose]] had been called a [[Platonism|Platonist]] by [[Stephen Hawking]],<ref name="hawkingpenrose1996p4">{{harvnb|Hawking|Penrose|1996|p=4}} "I think that Roger is a Platonist at heart but he must answer for himself."</ref> a view Penrose discusses in his book, ''[[The Road to Reality]]''.<ref name="penrose2004">{{harvnb |Penrose|2004}}</ref> Hawking referred to himself as an "unashamed reductionist" and took issue with Penrose's views.<ref name="penroseshimonycartwrighthawking1997">{{harvnb |Penrose|Shimony|Cartwright|Hawking|1997}}</ref> | |||
==Core theories== | |||
{{further|Branches of physics|Outline of physics}} | |||
Though physics deals with a wide variety of systems, certain theories are used by all physicists. Each of these theories was experimentally tested numerous times and found to be an adequate approximation of nature. For instance, the theory of [[Classical physics|classical]] mechanics accurately describes the motion of objects, provided they are much larger than [[atom]]s and moving at much less than the speed of light. These theories continue to be areas of active research today. [[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). | |||
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. These include classical mechanics, quantum mechanics, thermodynamics and [[statistical mechanics]], [[electromagnetism]], and special relativity. | |||
===Classical=== | |||
{{Main|Classical physics}} | |||
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. Classical mechanics is concerned with bodies acted on by [[force]]s and bodies in [[motion (physics)|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 [[Analytical dynamics|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]], [[Fluid dynamics|hydrodynamics]], [[aerodynamics]], and [[pneumatics]]. Acoustics is the study of how sound is produced, controlled, transmitted and received.<ref name="britannica-acoustics">{{cite encyclopedia |title=acoustics |url=http://www.britannica.com/EBchecked/topic/4044/acoustics |encyclopedia=[[Encyclopædia Britannica]] |access-date=14 June 2013 |url-status=live |archive-url=https://web.archive.org/web/20130618235952/http://www.britannica.com/EBchecked/topic/4044/acoustics |archive-date=18 June 2013 }}</ref> 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,<ref>{{cite web |url=http://www.bioacoustics.info/ |title=Bioacoustics – the International Journal of Animal Sound and its Recording |publisher=Taylor & Francis |access-date=31 July 2012 |url-status=live |archive-url=https://web.archive.org/web/20120905120546/http://www.bioacoustics.info/ |archive-date=5 September 2012 }}</ref> and [[electroacoustics]], the manipulation of audible sound waves using electronics.<ref>{{cite web |publisher=[[Acoustical Society of America]] |title=Acoustics and You (A Career in Acoustics?) |url=http://asaweb.devcloud.acquia-sites.com/education_outreach/careers_in_acoustics |archive-url=https://web.archive.org/web/20150904010934/http://asaweb.devcloud.acquia-sites.com/education_outreach/careers_in_acoustics |url-status=dead |archive-date=4 September 2015 |access-date=21 May 2013 }}</ref> | |||
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. [[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 century; an [[electric current]] gives rise to a [[magnetic field]], and a changing magnetic field induces an electric current. [[Electrostatics]] deals with [[electric charge]]s at rest, [[Classical electromagnetism|electrodynamics]] with moving charges, and [[magnetostatics]] with magnetic poles at rest. | |||
===Modern=== | |||
{{Main|Modern physics}} | |||
{{Modern Physics}} | |||
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. For example, [[Atomic physics|atomic]] and [[nuclear physics]] study matter on the smallest scale at which [[chemical element]]s can be identified. The [[Particle physics|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 accelerator]]s. On this scale, ordinary, commonsensical notions of space, time, matter, and energy are no longer valid.<ref>{{harvnb |Tipler|Llewellyn|2003|pp=269, 477, 561}}</ref> | |||
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. 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. 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 relativity|general theory of relativity]] with motion and its connection with [[gravitation]]. Both quantum theory and the theory of relativity find applications in all areas of modern physics.<ref>{{harvnb |Tipler|Llewellyn|2003|pp=1–4, 115, 185–187}}</ref> | |||
==== Fundamental concepts in modern physics ==== | |||
* [[Causality (physics)|Causality]] | |||
* [[Principle of covariance|Covariance]] | |||
* [[Action (physics)|Action]] | |||
* [[Physical field]] | |||
* [[symmetry (physics)|Symmetry]] | |||
* [[Physical interaction]] | |||
* [[Statistical ensemble]] | |||
* [[Quantum]] | |||
* [[Wave]] | |||
* [[Particle]] | |||
===Difference=== | |||
[[File:Modernphysicsfields.svg|thumb|upright=1.5|left|The basic domains of physics]] | |||
While physics aims to discover universal laws, its theories lie in explicit domains of applicability. | |||
[[File:Solvay conference 1927.jpg|thumb|right|[[Solvay Conference]] of 1927, with prominent physicists such as [[Albert Einstein]], [[Werner Heisenberg]], [[Max Planck]], [[Hendrik Lorentz]], [[Niels Bohr]], [[Marie Curie]], [[Erwin Schrödinger]] and [[Paul Dirac]]]] | |||
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 predictions provided by classical mechanics. 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. Planck, 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. | |||
==Relation to other fields== | |||
[[File:Pahoeoe fountain original.jpg|thumb|This [[parabola]]-shaped [[lava flow]] illustrates the application of mathematics in physics—in this case, Galileo's [[law of falling bodies]].]] | |||
[[File:Physics and other sciences.png|thumb|upright=0.5|left|Mathematics and ontology are used in physics. Physics is used in chemistry and cosmology.]] | |||
===Prerequisites=== | |||
Mathematics provides a compact and exact language used to describe the order in nature. This was noted and advocated by [[Pythagoras]],<ref name="dijksterhuis1986">{{harvnb|Dijksterhuis|1986}}</ref> [[Plato]],<ref name="mastin2010-plato">{{harvnb|Mastin|2010}} "Although usually remembered today as a philosopher, Plato was also one of ancient Greece's most important patrons of mathematics. Inspired by Pythagoras, he founded his Academy in Athens in 387 BC, where he stressed mathematics as a way of understanding more about reality. In particular, he was convinced that geometry was the key to unlocking the secrets of the universe. The sign above the Academy entrance read: 'Let no-one ignorant of geometry enter here.'"</ref> Galileo,<ref name="toraldodifrancia1976p10-galileo">{{harvnb|Toraldo Di Francia|1976|p=10}} 'Philosophy is written in that great book which ever lies before our eyes. I mean the universe, but we cannot understand it if we do not first learn the language and grasp the symbols in which it is written. This book is written in the mathematical language, and the symbols are triangles, circles, and other geometrical figures, without whose help it is humanly impossible to comprehend a single word of it, and without which one wanders in vain through a dark labyrinth.' – Galileo (1623), ''[[The Assayer]]''"</ref> and Newton. | |||
Physics uses mathematics<ref name="applicationsofmathematics">{{cite web |url=http://www.math.niu.edu/~rusin/known-math/index/tour_sci.html |title=Applications of Mathematics to the Sciences |date=25 January 2000 |access-date=30 January 2012 |archive-url=https://web.archive.org/web/20150510112012/http://www.math.niu.edu/~rusin/known-math/index/tour_sci.html |archive-date=2015-05-10 |url-status=dead}}</ref> to organise and formulate experimental results. From those results, [[analytic solution|precise]] or [[simulation#Computer simulation|estimated]] solutions are obtained, or quantitative results, from which new predictions can be made and experimentally confirmed or negated. The results from physics experiments are numerical data, with their [[units of measure]] and estimates of the errors in the measurements. Technologies based on mathematics, like [[scientific computing|computation]] have made [[computational physics]] an active area of research. | |||
[[File:Mathematical Physics and other sciences.png|thumb|The distinction between mathematics and physics is clear-cut, but not always obvious, especially in mathematical physics.]] | |||
[[Ontology]] is a prerequisite for physics, but not for mathematics. It means physics is ultimately concerned with descriptions of the real world, while mathematics is concerned with abstract patterns, even beyond the real world. Thus physics statements are synthetic, while mathematical statements are analytic. Mathematics contains hypotheses, while physics contains theories. Mathematics statements have to be only logically true, while predictions of physics statements must match observed and experimental data. | |||
=== Physics | The distinction is clear-cut, but not always obvious. For example, [[mathematical physics]] is the application of mathematics in physics. Its methods are mathematical, but its subject is physical.<ref name="jmp-def">{{cite web | url=https://www.researchgate.net/journal/0022-2488_Journal_of_Mathematical_Physics | title=Journal of Mathematical Physics | access-date=31 March 2014 | quote=[Journal of Mathematical Physics] purpose is the publication of papers in mathematical physics — that is, the application of mathematics to problems in physics and the development of mathematical methods suitable for such applications and for the formulation of physical theories. | url-status=live | archive-url=https://web.archive.org/web/20140818231853/http://www.researchgate.net/journal/0022-2488_Journal_of_Mathematical_Physics | archive-date=18 August 2014 | df=dmy-all }}</ref> The problems in this field start with a "[[Boundary condition|mathematical model of a physical situation]]" (system) and a "mathematical description of a physical law" that will be applied to that system. Every mathematical statement used for solving has a hard-to-find physical meaning. The final mathematical solution has an easier-to-find meaning, because it is what the solver is looking for.{{clarify|date=August 2015}} | ||
[ | |||
Pure physics is a branch of [[fundamental science]] (also called basic science). 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.<ref name="feynmanleightonsands1963v1ch3">{{harvnb|Feynman|Leighton|Sands|1963|loc=Chapter 3: "The Relation of Physics to Other Sciences"}}; see also [[reductionism]] and [[special sciences]]</ref> Similarly, chemistry is often called [[the central science]] because of its role in linking the physical sciences. For example, chemistry studies properties, structures, and [[chemical reaction|reactions]] of matter (chemistry's focus on the molecular and atomic scale [[Difference between chemistry and physics|distinguishes it from physics]]). 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]], [[Conservation of mass|mass]], and [[charge conservation|charge]]. Physics is applied in industries like engineering and medicine. | |||
===Application and influence=== | |||
{{Main|Applied physics}} | |||
[[File:Prediction of sound scattering from Schroeder Diffuser.jpg|thumb|upright|left|Classical physics implemented in an [[acoustic engineering]] model of sound reflecting from an acoustic diffuser]] | |||
[[File:Archimedes-screw one-screw-threads with-ball 3D-view animated small.gif|thumb|upright|[[Archimedes' screw]], a [[simple machine]] for lifting]] | |||
[[File:Military laser experiment.jpg|thumb|Experiment using a [[laser]]]] | |||
[[Applied physics]] is a general term for physics research, which is intended for a particular use. An applied physics curriculum usually contains a few classes in an applied discipline, like geology or electrical engineering. 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. | |||
The approach is similar to that of [[applied mathematics]]. Applied physicists use physics in scientific research. For instance, people working on [[accelerator physics]] might seek to build better [[particle detector]]s for research in theoretical physics. | |||
Physics is used heavily in engineering. For example, statics, a subfield of [[mechanics]], is used in the building of [[bridge]]s and other static structures. The understanding and use of acoustics results in sound control and better concert halls; similarly, the use of optics creates better optical devices. An understanding of physics makes for more realistic [[flight simulator]]s, [[video game]]s, and movies, and is often critical in [[forensic]] investigations. | |||
With the [[Uniformitarianism (science)|standard consensus]] that the [[Scientific law|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]]. For example, in the [[History of Earth#Origin of the Earth's core and first atmosphere|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. It also allows for simulations in engineering that drastically speed up the development of a new technology. | |||
But there is also considerable [[interdisciplinarity]], so many other important fields are influenced by physics (e.g., the fields of [[econophysics]] and [[sociophysics]]). | |||
==Research== | |||
== | ===Scientific method=== | ||
Physicists use the scientific method to test the validity of a [[physical theory]]. By using a methodical approach to compare the implications of a theory with the conclusions drawn from its related [[experiment]]s and observations, physicists are better able to test the validity of a theory in a logical, unbiased, and repeatable way. To that end, experiments are performed and observations are made in order to determine the validity or invalidity of the theory.<ref>{{cite journal |last1=Ellis |first1=G. |last2=Silk |first2=J. |title=Scientific method: Defend the integrity of physics |journal=Nature |date=16 December 2014 |volume=516 |issue=7531 |pages=321–323 |doi=10.1038/516321a |bibcode=2014Natur.516..321E |pmid=25519115 |doi-access=free }}</ref> | |||
== | 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.<ref name="honderich1995pp474-476">{{harvnb |Honderich|1995|pp=474–476}}</ref> | ||
===Theory and experiment=== | |||
{{Main|Theoretical physics|Experimental physics}} | |||
[[File:Bruce McCandless II during EVA in 1984.jpg|thumb|right|The [[astronaut]] and [[Earth]] are both in [[free fall]].]] | |||
[[File:Lightning in Arlington.jpg|thumb|right|[[Lightning]] is an [[electric current]].]] | |||
Theorists seek to develop [[mathematical model]]s that both agree with existing experiments and successfully predict future experimental results, while [[Experimentalism|experimentalists]] devise and perform experiments to test theoretical predictions and explore new phenomena. Although [[theory]] and experiment are developed separately, they strongly affect and depend upon each other. 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 [[prediction]]s, which inspire the development of new experiments (and often related equipment).<ref>{{cite web |date=June 2015 |title=Has theoretical physics moved too far away from experiments? Is the field entering a crisis and, if so, what should we do about it? |url=https://www.perimeterinstitute.ca/research/conferences/convergence/roundtable-discussion-questions/has-theoretical-physics-moved-too |publisher=[[Perimeter Institute for Theoretical Physics]] |archive-url=https://web.archive.org/web/20160421064320/http://www.perimeterinstitute.ca/research/conferences/convergence/roundtable-discussion-questions/has-theoretical-physics-moved-too |archive-date=21 April 2016 }}</ref> | |||
[[Physicist]]s who work at the interplay of theory and experiment are called [[Phenomenology (particle physics)|phenomenologists]], who study complex phenomena observed in experiment and work to relate them to a [[Theory of everything|fundamental theory]].<ref>{{cite web |title=Phenomenology |url=https://www.mpp.mpg.de/english/research/theory/phenomenologie/index.html |publisher=[[Max Planck Institute for Physics]] |access-date=22 October 2016 |archive-url=https://web.archive.org/web/20160307105406/https://www.mpp.mpg.de/english/research/theory/phenomenologie/index.html |archive-date=7 March 2016 }}</ref> | |||
Theoretical physics has historically taken inspiration from philosophy; electromagnetism was unified this way.{{efn|See, for example, the influence of [[Immanuel Kant|Kant]] and [[Johann Wilhelm Ritter|Ritter]] on [[Hans Christian Ørsted|Ørsted]].}} Beyond the known universe, the field of theoretical physics also deals with hypothetical issues,{{efn|Concepts which are denoted ''hypothetical'' can change with time. For example, the [[atom]] of nineteenth-century physics was denigrated by some, including [[Ernst Mach]]'s critique of [[Ludwig Boltzmann]]'s formulation of [[statistical mechanics]]. By the end of World War II, the atom was no longer deemed hypothetical.}} such as [[Many-worlds interpretation|parallel universes]], a [[multiverse]], and [[higher dimension]]s. 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. | |||
== | Experimental physics expands, and is expanded by, engineering and [[technology]]. Experimental physicists who are involved in [[basic research]], design and perform experiments with equipment such as particle accelerators and [[laser]]s, whereas those involved in [[applied research]] often work in industry, developing technologies such as [[magnetic resonance imaging]] (MRI) and [[transistor]]s. [[Richard Feynman|Feynman]] has noted that experimentalists may seek areas that have not been explored well by theorists.<ref name="feynman1965p157-experiment">{{harvnb|Feynman|1965|p=157}} "In fact experimenters have a certain individual character. They ... very often do their experiments in a region in which people know the theorist has not made any guesses."</ref> | ||
== | ===Scope and aims=== | ||
[[File:Acceleration components.JPG|thumb|left|Physics involves modeling the natural world with theory, usually quantitative. Here, the path of a particle is modeled with the mathematics of [[calculus]] to explain its behavior: the purview of the branch of physics known as [[mechanics]].]] | |||
Physics covers a wide range of [[phenomenon|phenomena]], from [[elementary particle]]s (such as quarks, neutrinos, and electrons) to the largest [[supercluster]]s of galaxies. Included in these phenomena are the most basic objects composing all other things. Therefore, physics is sometimes called the "fundamental science".<ref name="feynmanleightonsands1963v1ch3" /> Physics aims to describe the various phenomena that occur in nature in terms of simpler phenomena. Thus, physics aims to both connect the things observable to humans to root causes, and then connect these causes together. | |||
For example, the [[History of China|ancient Chinese]] observed that certain rocks ([[lodestone]] and [[magnetite]]) were attracted to one another by an invisible force. This effect was later called magnetism, which was first rigorously studied in the 17th century. But even before the Chinese discovered magnetism, the [[Ancient Greece|ancient Greeks]] knew of other objects such as [[amber]], that when rubbed with fur would cause a similar invisible attraction between the two.<ref name=stewart>{{cite book |last=Stewart |first=J. |year=2001 |title=Intermediate Electromagnetic Theory |page=50 |publisher=World Scientific |isbn=978-981-02-4471-2}}</ref> This was also first studied rigorously in the 17th century and came to be called electricity. Thus, physics had come to understand two observations of nature in terms of some root cause (electricity and magnetism). However, further work in the 19th century revealed that these two forces were just two different aspects of one force—electromagnetism. 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 hopes to find an ultimate reason (theory of everything) for why nature is as it is (see section ''[[#Current research|Current research]]'' below for more information).<ref>{{cite book |last=Weinberg |first=S. |year=1993 |title=Dreams of a Final Theory: The Search for the Fundamental Laws of Nature |publisher=Hutchinson Radius |isbn=978-0-09-177395-3}}</ref> | |||
=== | ===Research fields=== | ||
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. Some physics departments also support [[physics education research]] and [[physics outreach]].<ref>{{cite web |last=Redish |first=E. |title=Science and Physics Education Homepages |url=https://www.physics.umd.edu/perg/homepages.htm |publisher=University of Maryland Physics Education Research Group |url-status=live |archive-url=https://web.archive.org/web/20160728005227/http://www.physics.umd.edu/perg/homepages.htm |archive-date=28 July 2016 }}</ref> | |||
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. "Universalists" such as Einstein (1879–1955) and [[Lev Landau]] (1908–1968), who worked in multiple fields of physics, are now very rare.{{efn|Yet, universalism is encouraged in the culture of physics. For example, the [[World Wide Web]], which was innovated at [[CERN]] by [[Tim Berners-Lee]], was created in service to the computer infrastructure of CERN, and was/is intended for use by physicists worldwide. The same might be said for [[arXiv.org]]}} | |||
The major fields of physics, along with their subfields and the theories and concepts they employ, are shown in the following table. | |||
{{Subfields of physics}} | |||
=== | ====Nuclear and particle==== | ||
[[ | {{Main|Particle physics|Nuclear physics}} | ||
[[File:CMS Higgs-event.jpg|thumb|A simulated event in the CMS detector of the [[Large Hadron Collider]], featuring a possible appearance of the [[Higgs boson]].]] | |||
=== | Particle physics is the study of the elementary constituents of [[matter]] and energy and the [[Fundamental interaction|interactions]] between them.<ref name="aps-dpf">{{cite web|title=Division of Particles & Fields |url=http://www.aps.org/units/dpf/index.cfm |publisher=American Physical Society |access-date=18 October 2012 |url-status=dead |archive-url=https://web.archive.org/web/20160829105655/http://www.aps.org/units/dpf/index.cfm |archive-date=29 August 2016 }}</ref> In addition, particle physicists design and develop the high-energy accelerators,<ref name="halpern2010">{{harvnb|Halpern|2010}}</ref> detectors,<ref name="grupen1999">{{harvnb|Grupen|1999}}</ref> and [[Computational particle physics|computer programs]]<ref name="walsh2012">{{harvnb|Walsh|2012}}</ref> necessary for this research. The field is also called "high-energy physics" because many elementary particles do not occur naturally but are created only during high-energy [[collision]]s of other particles.<ref name="iop-hepp">{{cite web|title=High Energy Particle Physics Group|url=http://www.iop.org/activity/groups/subject/hepp/index.html|publisher=Institute of Physics|access-date=18 October 2012}}</ref> | ||
Currently, the interactions of elementary particles and [[Field (physics)|fields]] are described by the [[Standard Model]].<ref name="oerter2006">{{harvnb|Oerter|2006}}</ref> The model accounts for the 12 known particles of matter ([[quark]]s and [[lepton]]s) that interact via the [[strong nuclear force|strong]], weak, and electromagnetic [[fundamental force]]s.<ref name="oerter2006" /> Dynamics are described in terms of matter particles exchanging [[gauge boson]]s ([[gluon]]s, [[W and Z bosons]], and [[photon]]s, respectively).<ref name="gribbin1998">{{harvnb|Gribbin|Gribbin|Gribbin|1998}}</ref> The Standard Model also predicts a particle known as the Higgs boson.<ref name="oerter2006" /> In July 2012 CERN, the European laboratory for particle physics, announced the detection of a particle consistent with the Higgs boson,<ref name="eonr-higgs">{{cite web |title=CERN experiments observe particle consistent with long-sought Higgs boson |url=http://press-archived.web.cern.ch/press-archived/PressReleases/Releases2012/PR17.12E.html |publisher=[[CERN]] |access-date=18 October 2012 |date=4 July 2012 |url-status=dead |archive-url=https://web.archive.org/web/20121114084952/http://press-archived.web.cern.ch/press-archived/PressReleases/Releases2012/PR17.12E.html |archive-date=14 November 2012 }}</ref> an integral part of the [[Higgs mechanism]]. | |||
Nuclear physics is the field of physics that studies the constituents and interactions of [[atomic nuclei]]. 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]]. | |||
====Atomic, molecular, and optical==== | |||
{{Main|Atomic, molecular, and optical physics}} | |||
Atomic, [[Molecule|molecular]], and optical physics (AMO) is the study of matter–matter and light–matter interactions on the scale of single atoms and molecules. The three areas are grouped together because of their interrelationships, the similarity of methods used, and the commonality of their relevant energy scales. All three areas include both classical, semi-classical and [[quantum physics|quantum]] treatments; they can treat their subject from a microscopic view (in contrast to a macroscopic view). | |||
Atomic physics studies the [[electron shell]]s of atoms. Current research focuses on activities in quantum control, cooling and trapping of atoms and ions,<ref>{{cite web |title=Atomic, Molecular, and Optical Physics |website=MIT Department of Physics |url=http://web.mit.edu/physics/research/abcp/areas.html#amo |access-date=21 February 2014 |archive-url= https://web.archive.org/web/20140227043906/http://web.mit.edu/physics/research/abcp/areas.html#amo |archive-date=27 February 2014 |url-status=live }}</ref><ref>{{cite web |title=Korea University, Physics AMO Group |url=http://physics.korea.ac.kr/research/research_amo.php |access-date=21 February 2014 |archive-url=https://web.archive.org/web/20140301112653/http://physics.korea.ac.kr/research/research_amo.php |archive-date=1 March 2014 |url-status=dead }}</ref><ref>{{cite web |title=Aarhus Universitet, AMO Group |url=http://phys.au.dk/forskning/forskningsomraader/amo/ |access-date=21 February 2014 |url-status=live |archive-url=https://web.archive.org/web/20140307062146/http://phys.au.dk/forskning/forskningsomraader/amo/ |archive-date=7 March 2014 }}</ref> low-temperature collision dynamics and the effects of electron correlation on structure and dynamics. Atomic physics is influenced by the [[Atomic nucleus|nucleus]] (see [[hyperfine splitting]]), but intra-nuclear phenomena such as [[nuclear fission|fission]] and [[nuclear fusion|fusion]] are considered part of nuclear physics. | |||
[[Molecular physics]] focuses on multi-atomic structures and their internal and external interactions with matter and light. [[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 field]]s and their interactions with matter in the microscopic realm. | |||
== | ====Condensed matter==== | ||
{{Main|Condensed matter physics}} | |||
[[File:Bose Einstein condensate.png|right|thumb|upright=1.25|Velocity-distribution data of a gas of [[rubidium]] atoms, confirming the discovery of a new phase of matter, the [[Bose–Einstein condensate]]]] | |||
== | Condensed matter physics is the field of physics that deals with the macroscopic physical properties of matter.<ref name="taylorheinonen2002">{{harvnb|Taylor|Heinonen|2002}}</ref><ref>{{Cite book |last1=Girvin |first1=Steven M. |url= https://books.google.com/books?id=2ESIDwAAQBAJ |title=Modern Condensed Matter Physics|last2=Yang|first2=Kun|date=2019-02-28|publisher=Cambridge University Press |isbn=978-1-108-57347-4|language=en}}</ref> In particular, it is concerned with the "condensed" [[phase (matter)|phases]] that appear whenever the number of particles in a system is extremely large and the interactions between them are strong.<ref name=cohen2008>{{harvnb|Cohen|2008}}</ref> | ||
{{ | |||
== | The most familiar examples of condensed phases are [[Solid-state physics|solids]] and [[liquid]]s, which arise from the bonding by way of the [[electromagnetic force]] between atoms.<ref name="moore2011">{{harvnb |Moore|2011|pp=255–258}}</ref> More exotic condensed phases include the [[superfluid]]<ref name="leggett1999">{{harvnb |Leggett|1999}}</ref> and the [[Bose–Einstein condensate]]<ref name="levy2001">{{harvnb |Levy|2001}}</ref> found in certain atomic systems at very low temperature, the [[superconductivity|superconducting]] phase exhibited by [[conduction electron]]s in certain materials,<ref name=stajiccoontzosborne2011>{{harvnb |Stajic|Coontz|Osborne|2011}}</ref> and the [[ferromagnet]]ic and [[antiferromagnet]]ic phases of [[spin (physics)|spins]] on [[crystal lattice|atomic lattices]].<ref name="mattis2006">{{harvnb|Mattis|2006}}</ref> | ||
{{ | Condensed matter physics is the largest field of contemporary physics. Historically, condensed matter physics grew out of solid-state physics, which is now considered one of its main subfields.<ref name="aps-dcmp">{{cite web |url=http://www.aps.org/units/dcmp/history.cfm |title=History of Condensed Matter Physics |publisher=[[American Physical Society]] |access-date=31 March 2014 |url-status=live |archive-url=https://web.archive.org/web/20110912081611/http://www.aps.org/units/dcmp/history.cfm |archive-date=12 September 2011 }}</ref> The term ''condensed matter physics'' was apparently coined by [[Philip Warren Anderson|Philip Anderson]] when he renamed his research group—previously ''solid-state theory''—in 1967.<ref name="princeton-anderson">{{cite web |title=Philip Anderson |url=http://www.princeton.edu/physics/people/display_person.xml?netid=pwa&display=faculty |publisher=Princeton University, Department of Physics |access-date=15 October 2012 |url-status=live |archive-url=https://web.archive.org/web/20111008123438/http://www.princeton.edu/physics/people/display_person.xml?netid=pwa&display=faculty |archive-date=8 October 2011 }}</ref> In 1978, the Division of Solid State Physics of the [[American Physical Society]] was renamed as the Division of Condensed Matter Physics.<ref name="aps-dcmp" /> Condensed matter physics has a large overlap with chemistry, [[materials science]], [[nanotechnology]] and engineering.<ref name="cohen2008" /> | ||
* [https:// | ====Astrophysics==== | ||
{{Main|Astrophysics|Physical cosmology}} | |||
[[File:Hubble ultra deep field high rez edit1.jpg|thumb|left|The deepest visible-light image of the [[universe]], the [[Hubble Ultra-Deep Field]]]] | |||
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 [[Physical cosmology|cosmology]]. 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.<ref>{{cite web |url=http://manoa.hawaii.edu/astronomy/bs-in-astrophysics/ |title=BS in Astrophysics |publisher=University of Hawaii at Manoa |access-date=14 October 2016 |archive-url=https://web.archive.org/web/20160404195943/http://manoa.hawaii.edu/astronomy/bs-in-astrophysics/ |archive-date=4 April 2016 }}</ref> | |||
The discovery by [[Karl Jansky]] in 1931 that radio signals were emitted by celestial bodies initiated the science of [[radio astronomy]]. Most recently, the frontiers of astronomy have been expanded by space exploration. Perturbations and interference from the earth's atmosphere make space-based observations necessary for [[infrared astronomy|infrared]], [[ultraviolet astronomy|ultraviolet]], [[gamma-ray astronomy|gamma-ray]], and [[X-ray astronomy]]. | |||
Physical cosmology is the study of the formation and evolution of the universe on its largest scales. Albert Einstein's theory of relativity plays a central role in all modern cosmological theories. In the early 20th century, [[Edwin Hubble|Hubble]]'s discovery that the universe is expanding, as shown by the [[Hubble diagram]], prompted rival explanations known as the [[steady-state model|steady state]] universe and the [[Big Bang]]. | |||
The Big Bang was confirmed by the success of [[Big Bang nucleosynthesis]] and the discovery of the [[cosmic microwave background]] in 1964. The Big Bang model rests on two theoretical pillars: Albert Einstein's general relativity and the [[cosmological principle]]. Cosmologists have recently established the [[Lambda-CDM model|ΛCDM model]] of the evolution of the universe, which includes [[cosmic inflation]], [[dark energy]], and [[dark matter]]. | |||
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.<ref name="nasa-glast">{{cite web |url=http://www.nasa.gov/mission_pages/GLAST/main/questions_answers.html |title=NASA – Q&A on the GLAST Mission |access-date=29 April 2009 |website=Nasa: Fermi Gamma-ray Space Telescope |publisher=[[NASA]] |date=28 August 2008 |url-status=live |archive-url=https://web.archive.org/web/20090425121001/http://www.nasa.gov/mission_pages/GLAST/main/questions_answers.html |archive-date=25 April 2009 }}</ref><ref>See also [http://www.nasa.gov/mission_pages/GLAST/science/index.html Nasa – Fermi Science] {{webarchive|url=https://web.archive.org/web/20100403041501/http://www.nasa.gov/mission_pages/GLAST/science/index.html |date=3 April 2010 }} and [http://www.nasa.gov/mission_pages/GLAST/science/unidentified_sources.html NASA – Scientists Predict Major Discoveries for GLAST] {{webarchive|url=https://web.archive.org/web/20090302071338/http://www.nasa.gov/mission_pages/GLAST/science/unidentified_sources.html |date=2 March 2009 }}.</ref> In particular, the potential for a tremendous discovery surrounding dark matter is possible over the next several years.<ref name="nasa-glast-darkmatter">{{cite web |url=http://www.nasa.gov/mission_pages/GLAST/science/dark_matter.html |title=Dark Matter |publisher=[[NASA]] |date=28 August 2008 |access-date=30 January 2012 |url-status=live |archive-url=https://web.archive.org/web/20120113060142/http://www.nasa.gov/mission_pages/GLAST/science/dark_matter.html |archive-date=13 January 2012 }}</ref> 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. | |||
[[IBEX]] is already yielding new [[astrophysical]] discoveries: "No one knows what is creating the [[energetic neutral atom|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."<ref name="kerr2009">{{harvnb|Kerr|2009}}</ref> | |||
===Current research=== | |||
{{further|List of unsolved problems in physics}} | |||
[[File:Feynman'sDiagram.JPG|thumb|right|[[Feynman diagram]] signed by [[R. P. Feynman]].]] | |||
[[File:Meissner effect p1390048.jpg|thumb|right|A typical phenomenon described by physics: a [[magnet]] levitating above a [[superconductor]] demonstrates the [[Meissner effect]].]] | |||
Research in physics is continually progressing on a large number of fronts. | |||
In condensed matter physics, an important unsolved theoretical problem is that of [[high-temperature superconductivity]].<ref name=Legg2006>{{cite journal |last1=Leggett |first1=A.J. |year=2006 |title=What DO we know about high ''T''<sub>c</sub>? |url=http://leopard.physics.ucdavis.edu/rts/p242/nphys254.pdf |journal=[[Nature Physics]] |volume=2 |issue=3 |pages=134–136 |bibcode=2006NatPh...2..134L |doi=10.1038/nphys254 |s2cid=122055331 |url-status=dead |archive-url=https://web.archive.org/web/20100610183622/http://leopard.physics.ucdavis.edu/rts/p242/nphys254.pdf |archive-date=10 June 2010 }}</ref> Many condensed matter experiments are aiming to fabricate workable [[spintronics]] and [[quantum computer]]s.<ref name=cohen2008/><ref>{{Cite journal |last1=Wolf |first1=S.A. |last2=Chtchelkanova |first2=A.Y. |last3=Treger |first3=D.M. |title=Spintronics—A retrospective and perspective |journal=[[IBM Journal of Research and Development]] |volume=50 |pages=101–110 |year=2006 |doi=10.1147/rd.501.0101|s2cid=41178069 |url=http://pdfs.semanticscholar.org/10b1/d4e488fabf429cb0630d96687548aa14158f.pdf |archive-url=https://web.archive.org/web/20200924021923/http://pdfs.semanticscholar.org/10b1/d4e488fabf429cb0630d96687548aa14158f.pdf |url-status=dead |archive-date=2020-09-24 }}</ref> | |||
In particle physics, the first pieces of experimental evidence for physics beyond the Standard Model have begun to appear. Foremost among these are indications that [[neutrino]]s have non-zero [[mass]]. 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. 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. Research on the nature of the major mysteries of dark matter and dark energy is also currently ongoing.<ref>{{cite journal |last1=Gibney |first1=E. |year=2015 |title=LHC 2.0: A new view of the Universe |journal=[[Nature (journal)|Nature]] |volume=519 |issue=7542 |pages=142–143 |doi=10.1038/519142a |bibcode=2015Natur.519..142G |pmid=25762263 |doi-access=free }}</ref> | |||
Although much progress has been made in high-energy, [[quantum]], and astronomical physics, many everyday phenomena involving [[complex system|complexity]],<ref name="nrc1997v9p161">{{harvnb|National Research Council|Committee on Technology for Future Naval Forces|1997|p=161}}</ref> chaos,<ref name="kellert1993p32">{{harvnb|Kellert|1993|p=32}}</ref> or [[turbulence]]<ref name="eames-quoting-feynman">{{cite journal |last1=Eames |first1=I. |last2=Flor |first2=J.B. |year=2011 |title=New developments in understanding interfacial processes in turbulent flows |journal=[[Philosophical Transactions of the Royal Society A]] |volume=369 |issue=1937 |pages=702–705 |bibcode=2011RSPTA.369..702E |doi=10.1098/rsta.2010.0332 |pmid=21242127 |quote=Richard Feynman said that 'Turbulence is the most important unsolved problem of classical physics' |doi-access=free }}</ref> are still poorly understood. 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]] [[catastrophe theory|catastrophes]], and self-sorting in shaken heterogeneous collections.{{efn |See the work of [[Ilya Prigogine]], on 'systems far from equilibrium', and others.}}<ref>{{Cite book |author1=National Research Council |chapter=What happens far from equilibrium and why |chapter-url= https://www.nap.edu/read/11967/chapter/7 |title=Condensed-Matter and Materials Physics: the science of the world around us |year=2007 |pages=91–110 |doi=10.17226/11967 |isbn=978-0-309-10969-7 |url-status=live |archive-url= https://web.archive.org/web/20161104001321/https://www.nap.edu/read/11967/chapter/7 |archive-date=4 November 2016}}<br/>– {{cite arXiv |last1=Jaeger |first1=Heinrich M. |last2=Liu |first2=Andrea J. |year=2010 |title=Far-From-Equilibrium Physics: An Overview |class=cond-mat.soft |eprint=1009.4874}}</ref> | |||
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. 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. In the 1932 ''Annual Review of Fluid Mechanics'', [[Horace Lamb]] said:<ref name="goldstein1969">{{harvnb|Goldstein|1969}}</ref> | |||
{{bquote|I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former I am rather optimistic.}} | |||
==See also== | |||
{{Portal|Physics}} | |||
{{cols|colwidth=20em}} | |||
*[[List of important publications in physics]] | |||
*[[List of physicists]] | |||
*[[Lists of physics equations]] | |||
*[[Relationship between mathematics and physics]] | |||
*[[Earth science]] | |||
*[[Neurophysics]] | |||
*[[Psychophysics]] | |||
*[[Science tourism]] | |||
{{colend}} | |||
==Notes== | |||
{{notelist}} | |||
==References== | |||
{{Reflist}} | |||
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|archive-date=29 July 2016 | |||
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|year=2014 | |||
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|title=Sears and Zemansky's University Physics with Modern Physics Technology Update | |||
|publisher=Pearson Education | |||
|isbn=978-1-292-02063-1 | |||
|title-link=University Physics | |||
}} | |||
{{Refend}} | |||
==External links== | |||
{{Wiktionary|physics}} | |||
{{Wikibooks|Physics}} | |||
{{Wikisource portal|Physics}} | |||
* [http://www.physicscentral.com/ PhysicsCentral] – Web portal run by the [http://www.aps.org/ American Physical Society] | |||
* [http://www.physics.org/ Physics.org] – Web portal run by the [http://www.iop.org/ Institute of Physics] | |||
* [http://math.ucr.edu/home/baez/physics/ Usenet Physics FAQ] – FAQ compiled by sci.physics and other physics newsgroups | |||
* [http://nobelprize.org/nobel_prizes/physics/ Website of the Nobel Prize in physics] – Award for outstanding contributions to the subject | |||
* [http://scienceworld.wolfram.com/physics/ World of Physics] – Online encyclopedic dictionary of physics | |||
* [http://www.nature.com/naturephysics ''Nature Physics''] – Academic journal | |||
* [http://physics.aps.org/ Physics] – Online magazine by the [[American Physical Society]] | |||
* {{curlie|/Science/Physics/Publications/|Physics/Publications}} – Directory of physics related media | |||
* [http://www.vega.org.uk/ The Vega Science Trust] – Science videos, including physics | |||
* [http://hyperphysics.phy-astr.gsu.edu/Hbase/hframe.html HyperPhysics website] – Physics and astronomy mind-map from [[Georgia State University]] | |||
* [https://ocw.mit.edu/courses/physics/ PHYSICS at MIT OCW] – Online course material from [[Massachusetts Institute of Technology]] | |||
{{Fundamental interactions}} | |||
{{Branches of physics}} | |||
{{Natural science}} | |||
{{Authority control}} | |||
[[Category:Physics| ]] | [[Category:Physics| ]] | ||