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Physics is  the most basic of the [[natural sciences]].  Physics deals with the fundamental constituents of matter and their interactions, as well as how matter is organized on all possible length and time scales. Physics aims to provide unified descriptions of the behavior of matter and energy, from fundamental principles as much as possible, while describing a wide-variety of phenoma. Physics has considerable overlap with other sciences and engineering fields, most notably biology, chemistry, mathematics, electrical engineering and materials science
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[[Physicist]]s study a wide range of physical phenomena, from [[quark]]s to galaxies, from individual [[atoms]] to macroscopic biological systems.
'''Physics''' (from the Greek ''physikos,'' nature) is the [[science]] of nature at its most fundamental form, and is the foundation of the [[natural sciences]]. From [[quark]]s to galaxies, from individual [[Atom_(science)|atoms]] to macroscopic biological systems, [[physicist]]s study a wide range of physical phenomena.


== Key Areas of Physics ==
Over the course of time, physical phenomena have been grouped together under specific branches. While it is widely believed that the whole of physics can be considered within a single unified theory, including all phenomena both at the level of [[quantum mechanics]] and on a scale as wide as the [[universe]], this has not yet been proven.
This is made clear especially by the fact that the current models developed by the different branches of physics give contradictory solutions to the same problem when they are combined. For example, the unification of [[general relativity]] and quantum mechanics has so far proven impossible due to creation of infinite values when looking at some properties of systems of subatomic particles. <!-- I am 90% sure this is an example but I am glad an expert will be checking it ~~~~ -->
<!-- an example would be nice, but I don't pretend to understand why relativistic QM hits problems. ~~~ -->
Nevertheless, these are considered as problems "to be solved". The central branches of physics are:


== Physics and Other disciplines ==
* [[Classical mechanics]] is a model of the physics of [[force]]s acting upon bodies, and the motion of those bodies. As opposed to quantum mechanics, classical mechanics is deterministic. Classical mechanics is usually regarded as a limit of quantum mechanics, although this has not been proven in general. Classical mechanics can be divided into two parts:
 
::Newtonian, after Isaac Newton and his laws of motion. This can be more generally formulated in Lagrangian mechanics, after Joseph-Louis Lagrange.
Physics finds applications throughout the other [[natural science]]s as they regard the basic principles of nature.  Physics is often said to be the "fundamental science", because the other sciences deal with material systems that obey the laws of physics. For example, chemistry is the science of matter (such as [[atom]]s and [[molecule]]s) and the [[chemical substance]]s that they form in the bulk. The structure, reactivity, and properties of a [[chemical compound]] are determined by the properties of the underlying molecules, which can be described by areas of physics such as [[quantum mechanics]] ( in the applied subfiled of[[quantum chemistry]]), [[thermodynamics]], and [[electromagnetism]].
::Relativistic, due to [[Albert Einstein]] and his [[theory of relativity]]. This includes both special and general relativity, and addresses regimes in which Newtonian mechanics is no longer valid: when relative speeds of object are comparable to the speed of light, and for motion occurring near very massive objects.
 
Physics is closely related to  [[mathematics]], which provides the logical framework in which physical laws can be precisely formulated and their predictions quantified. Physical [[definitions]], [[model theory | models]] and [[theory | theories]] are invariably expressed using mathematical relations. A key difference between physics and mathematics is that because physics is ultimately concerned with descriptions of the material world, it tests its [[theories]] by [[observation]]s (called [[experiment]]s), whereas mathematics does not have such requirements. The distinction, however, is not always clear-cut. This large area of research intermediate between physics and mathematics is known as [[mathematical physics]].
 
Physics is also closely related to [[engineering]] and [[technology]]. For instance, [[electrical engineering]] is the study of the practical application of [[electromagnetism]]. [[Statics]], a subfield of [[mechanics]], is responsible for the building of [[bridge]]s. Further, [[physicist]]s, or practitioners of physics, [[invention | invent]] and design processes and [[tool | device]]s, such as the [[transistor]], whether in [[basic research | basic]] or [[applied research]]. [[Experiment | Experimental]] physicists design and perform experiments with [[particle accelerator]]s, [[nuclear reactor]]s, [[telescope]]s, [[barometer]]s, [[synchrotron]]s, [[cyclotron]]s, [[spectrometer]]s, [[laser]]s, and other equipment.
 
== Central theories ==
 
While physics deals with a wide variety of systems, there are certain theories that are basis for physics. Each of these theories has been  experimentally tested numerous times and found correct as an approximation of nature (within a certain domain of validity).  These theories continue to be areas of active research; for instance, a remarkable aspect of classical mechanics known as [[chaos theory | chaos]] was discovered in the 20th century, three centuries after the original formulation of classical mechanics by [[Isaac Newton]] ([[1642]]–[[1727]]). These "central theories" are important tools for research into more specialized topics, and any physicist, regardless of his or her specialization, is expected to be literate in them.
 
* [[Quantum mechanics]] is the branch of physics treating [[atom | atomi]]c and [[subatomic]] systems and their interaction with [[radiation]] in terms of observable quantities. It is based on the observation that all forms of energy are released in discrete units or bundles called ''[[quantum | quanta]]''. Quantum theory typically permits only [[probability | probable]] or [[statistics | statistical]] calculation of the observed features of subatomic particles, understood in terms of [[wave function]]s. Quantum mechanics itself has several levels of approximation.
 
* [[Classical mechanics]] is a model of the physics of [[force]]s acting upon bodies. As opposed to quantum mechanics, classical mechanics is deterministic. Classical mechanics is usually regarded as a limit of quantum mechanics, although this has not been proven in general. Classical mechanics can be divided into two parts: Newtonian, after Newton and his laws of motion, and relativistic, due to Einstein and his [[theory of relativity]].


* [[Electromagnetism]], or electromagnetic theory, is the physics of the [[electromagnetic field]]: a [[field (physics) | field]], encompassing all of [[space]], which exerts a [[force]] on those [[Elementary particle | particle]]s that possess the property of [[electric charge]], and is in turn affected by the presence and motion of such particles. Electromagnetism encompasses various real-world ''electromagnetic phenomena''.
* [[Quantum mechanics]] is the branch of physics treating [[Atom_(science) | atomic]] and subatomic systems and their interaction with [[radiation]] in terms of observable quantities. It is based on the observation that all forms of [[Energy_(science)|energy]] are released in discrete units or bundles called ''quanta''. Quantum theory typically permits only [[probability | probable]] or [[statistics | statistical]] calculation of the observed features of particles, understood in terms of [[wave function]]s. Quantum mechanics itself has several levels of approximation.


* [[Statistical mechanics]] and [[Thermodynamics]] are the branches of physics that deals with [[heat]], [[work]] and [[entropy]]. Thermodynamics is particularly concerned macroscopic energy and the effects of [[temperature]], [[pressure]], [[volume]], [[action (physics) | mechanical action]], and [[work]]. , Statistical mechanic  is the branch of physics that analyzes [[macroscopic]] [[thermodynamic system | systems]] by applying [[statistics | statistical principles]] to their microscopic constituents and, thus, connects the macroscopic viewpoint of thermodynamics with the atomic nature of matter descriped by either classical physics or quantum mechanics
* [[Electromagnetism]], or electromagnetic theory, is the physics of the electromagnetic field: a field, encompassing all of [[space (physics)|space]], which exerts a [[force]] on those [[Elementary particle | particle]]s that possess the property of [[electric charge]], and is in turn affected by the presence and motion of such particles. Electromagnetism encompasses various real-world ''electromagnetic phenomena''. Electromagnetism, as taught in a typical undergraduate college physics curriculum, can be divided into several areas:
:: Electrostatics, the study of charged objects, the forces between them, and electric fields and potentials for charged objects at rest.
:: Magnetism, the study of forces between moving charged objects, the magnetic field, and electromagnetic induction.
:: Electric circuits, the study of electric potential difference and electric currents for various arrangements of circuit components.
:: Optics and electromagnetic waves, the study of how time-varying electromagnetic fields propagate through space.


*  Statistical mechanics and [[Thermodynamics]] are the branches of physics that deal with [[heat]], [[work]] and [[entropy (thermodynamics)|entropy]]. Thermodynamics is particularly concerned with macroscopic [[Energy_(science)|energy]] and the effects of [[temperature]], [[pressure]], [[Volume (science)|volume]], [[action (physics)|mechanical action]], and [[work]].  Statistical mechanics is the branch of physics that analyzes macroscopic [[thermodynamic system | systems]] by applying [[statistics | statistical principles]] to their microscopic constituents and, thus, connects the macroscopic viewpoint of thermodynamics with the atomic nature of matter described by either classical physics or quantum mechanics.


==Research and fields within physics ==
==Research and fields within physics ==
Physics can be subdivided in a variety of different manners; for teaching, for historical purposes, or  for research purposes. Contemporary research in physics is divided into many distinct subfields. An incomplete listing includes:


Physics can be subdivided in a variety of different manners; for teaching, for historical purposes, or  for research purposes.
* [[Condensed matter physics]] is the study of the condensed phases of matter, [[Solid (state of matter)|solid]] and [[liquid]], and how the properties of matter in these phases arise from the properties and mutual interactions of the constituent [[Atom_(science)|atoms]]. More physicists study condensed matter physics than any other field.
 
Contemporary research in physics is divided into several subfields.  The following is based on the units the members of the American Physical Society organize themselves into in order of size. Although many physicists are members of multiple units


* [[Condensed matter physics]] is the study of the condensed phases;  [[solid]]s and [[liquid]]s, and how the properties of these phase arise from the properties and mutual interactions of the constituent [[atoms]].  
*[[Particle physics]], also known as "high-energy physics". This branch is concerned with the properties of subatomic particles much smaller than [[Atom_(science)|atoms]], including the [[elementary particle]]s from which all other units of matter are constructed.


* [[Particles and fields |particle physics]], also known as "high-energy physics". This branch is concerned with the properties of subatomic particles much smaller than [[atoms]], including the [[elementary particle]]s from which all other units of matter are constructed.
*[[Astrophysics]] attempts to explain the physical workings of celestial objects and phenomena.


* [[Atomic, molecular, and optical physics]] (AMO physics) which deals with the behavior of individual [[atoms]] and molecules, and including the ways in which they absorb and emit [[light]]. Molecular physics is sometimes considered a branch of chemical physics. Laser science may be considered a subfield of AMO or as a separate field.
* [[Atomic, molecular, and optical physics]] (AMO physics) deals with the behavior of individual [[Atom_(science)|atoms]] and molecules, including the ways in which they absorb and emit [[light]]. Molecular physics is sometimes also considered a branch of chemical physics. Laser science may be considered a subfield of AMO or as a separate field.


* [[Fluid dynamics ]] concerns itself with the study of the moving fluids; liquids or gases.
* [[Nuclear physics]] is the study of atomic nuclei. A [[nucleus]] is comprised of [[proton]]s and (usually) [[neutron]]s, and makes up about 99.97% of a typical atom's total mass.


* [[Plasma physics]] deals with the behavior of the [[plasma]] state of matter
* Materials physics is the study of various physical properties of materials. Classifications of physical properties include, but are not limited to, thermal, electronic, magnetic, optical, and mechanical.


* [[Nuclear physics]]
*Computational physics deals with numerically (as opposed to analytically) solving the equations that govern physical systems.


* [[Materials physics ]]
A number of fields of physics overlap strongly with other sciences: [[Biophysics]], [[Physical chemistry]] and [[Geophysics]] overlap  considerably with [[biology]], [[chemistry]] and [[geography]], but the focus is on the application of physics and physical techniques to problems within the other field.
 
* [[Computational physics]]
 
*[[Astrophysics ]]
 
*[[Biological physics]] or biophysics. Many members of this field are actually biologists and chemists who are members of other societies. As evidenced by the size of the Biophysical Society, ~7000 members when compared to the biological physics unit of the APS , ~1800 members.
 
*[[Chemical physics]]


=== Classical and quantum  physics ===
=== Classical and quantum  physics ===
{{further | [[Classical physics]], [[Quantum physics]], [[Modern physics]], [[Semiclassical]]}}
{{further | [[Classical physics]], [[Quantum physics]], [[Modern physics]], [[Semiclassical]]}}


Another overall classification of physicial theories is classical vs. quantum. All theories should ultimately become quantum, but classical theories are often both sufficiently valid and accurate so as to avoid the need for quantum theories. Additionally, for some classical theories, e.g., relativity, quantum analogs have yet to be fully determine.
The distinction between classical and quantum theories is important in physics. Classical theories are generally valid despite not considering the quantum nature of things, but are ultimately an approximation to a deeper quantized truth; this approximation typically breaks down at extreme scales, particularly the subatomic. Some fundamental classical theories, such as [[Theory of relativity | relativity]] do not yet have full analogous quantum theories.
 
Quantum physics refers to those theories which follow the postulates of quantum mechanics. To this effect, all results that are not quantized are called ''classical'': this includes the [[Theory of relativity | special and general theories of relativity]]. Simply because a result is classical does not mean that it was discovered before the advent of quantum mechanics.  


Both classical and quantum physics are active areas of research. However, there exist problems in physics in which classical and quantum aspects must be combined to attain some approximation or limit that may acquire several forms as the passage from classical to quantum mechanics is often difficult — such problems are termed ''semiclassical''.
Both classical and quantum physics are active areas of research. However, there exist problems in physics in which classical and quantum aspects must be combined to attain some approximation or limit that may acquire several forms as the passage from classical to quantum mechanics is often difficult — such problems are termed ''semiclassical''.


=== Theoretical and experimental physics ===
=== Theoretical and experimental physics ===
 
Most individual physicists specialize in either theoretical physics or experimental physics. There have been a few exceptions, such as  great [[Italy | Italian]] physicist [[Enrico Fermi]] (1901–1954), who made fundamental contributions to both theory and experimentation.
Most individual physicists specialize in either [[theoretical physics]] or [[experimental physics]]. There have been few exceptions, such as  great [[Italy | Italian]] physicist [[Enrico Fermi]] ([[1901]]–[[1954]]), who made fundamental contributions to both theory and experimentation.


Roughly speaking, theorists seek to develop theories, through mathematical and computational models, that can both describe and interpret existing experimental results and successfully predict future results, while experimentalists devise and perform experiments to explore new phenomena and test theoretical predictions. Although theory and experiment can be developed separately, they are strongly dependent on each other. Progress in physics frequently comes about when experimentalists make a discovery that existing theories cannot account for, necessitating the formulation of new theories, or when theorists make predictions that experimentalists test.
Roughly speaking, theorists seek to develop theories, through mathematical and computational models, that can both describe and interpret existing experimental results and successfully predict future results, while experimentalists devise and perform experiments to explore new phenomena and test theoretical predictions. Although theory and experiment can be developed separately, they are strongly dependent on each other. Progress in physics frequently comes about when experimentalists make a discovery that existing theories cannot account for, necessitating the formulation of new theories, or when theorists make predictions that experimentalists test.


== Physics and Other disciplines ==
Physics finds applications throughout the other [[natural science]]s as they regard the basic principles of nature.  Physics is often said to be the "fundamental science", because the other sciences deal with material systems that obey the laws of physics. For example, chemistry is the science of matter (such as [[Atom_(science)|atom]]s and [[molecule]]s) and the chemical substances that they form in the bulk. The structure, reactivity, and properties of a [[chemical compound]] are determined by the properties of the underlying molecules, which can be described by areas of physics such as [[quantum mechanics]] (in the applied subfield of [[quantum chemistry]]), [[thermodynamics]], and [[electromagnetism]].


Physics is closely related to  [[mathematics]], which provides the logical framework in which physical laws can be precisely formulated and their predictions quantified. Physical [[definitions]], [[model theory | models]] and [[theory | theories]] are invariably expressed using mathematical relations. A key difference between physics and mathematics is that because physics is ultimately concerned with descriptions of the material world, it tests its [[theories]] by [[observation]]s (called [[experiment]]s), whereas mathematics does not have such requirements. The distinction, however, is not always clear-cut. This large area of research intermediate between physics and mathematics is known as [[mathematical physics]].
Physics is also closely related to [[engineering]] and [[technology]]. For instance, [[electrical engineering]] is the study of the practical application of [[electromagnetism]]. Statics, a subfield of [[mechanics]], is responsible for the building of [[Bridge (civil engineering)|bridge]]s. Further, [[physicist]]s, or practitioners of physics, invent and design processes and [[tool | device]]s, such as the [[Electronic switch#Transistor|transistor]], whether in [[basic research | basic]] or [[applied research]]. [[Experiment | Experimental]] physicists design and perform experiments with [[particle accelerator]]s, [[nuclear reactor]]s, [[telescope]]s, barometers, synchrotrons, cyclotrons, spectrometers, [[laser]]s, and other equipment.


== Current research directions ==
== Current research directions ==
{{main | Unsolved problems in physics}}
Research in physics is progressing constantly on a large number of fronts, and is likely to do so for the foreseeable future.
Research in physics is progressing constantly on a large number of fronts, and is likely to do so for the foreseeable future.
A sampling of a few current directions include.
Some current directions include:


In condensed matter physics, the biggest unsolved theoretical problem is the explanation for [[high-temperature superconductivity]]. Strong efforts, largely experimental, are being put into making workable [[spintronics]] and [[quantum computer]]s.
In [[condensed matter physics]], the biggest unsolved theoretical problem is the explanation for [[superconductivity|high-temperature superconductivity]]. Strong efforts, largely experimental, are being put into making workable [[spintronics]] and [[quantum computer]]s.


In particle physics, the first pieces of experimental evidence for physics beyond the [[Standard Model]] have begun to appear. Foremost amongst these are indications that [[neutrino]]s have non-zero [[mass]]. These experimental results appear to have solved the long-standing [[solar neutrino problem]] in solar physics. The physics of massive neutrinos is currently an area of active theoretical and experimental research. In the next several years, [[particle accelerator]]s will begin probing energy scales in the [[TeV]] range, in which experimentalists are hoping to find evidence for the [[Higgs boson]] and [[supersymmetry | supersymmetric particles]].
In [[particle physics]], the first pieces of experimental evidence for physics beyond the [[Standard Model]] have begun to appear. Foremost amongst these are indications that [[neutrino]]s have non-zero [[mass]]. These experimental results appear to have solved the long-standing solar neutrino problem in solar physics. The physics of massive neutrinos is currently an area of active theoretical and experimental research. In the next several years, [[particle accelerator]]s will begin probing [[Energy_(science)|energy]] scales in the [[TeV]] range, in which experimentalists are hoping to find evidence for the [[Higgs boson]] and [[supersymmetry|supersymmetric particles]].


Theoretical attempts to unify [[quantum mechanics]] and [[general relativity]] into a single theory of [[quantum gravity]], a program ongoing for over half a century, have not yet borne fruit. The current leading candidates are [[M-theory]], [[superstring theory]] and [[loop quantum gravity]].
Theoretical attempts to unify [[quantum mechanics]] and [[general relativity]] into a single theory of [[quantum gravity]], a program ongoing for over half a century, have not yet borne fruit. The current leading candidates are [[M-theory]], [[superstring theory]] and [[loop quantum gravity]].


Many [[astronomy | astronomical]] and [[physical cosmology | cosmological]] phenomena have yet to be satisfactorily explained, including the existence of [[GZK paradox | ultra-high energy cosmic rays]], the [[baryon asymmetry]], the [[accelerating universe | acceleration of the universe]] and the [[galaxy rotation problem | anomalous rotation rates of galaxies]].
Many [[astronomy | astronomical]] and [[physical cosmology | cosmological]] phenomena have yet to be satisfactorily explained, including the existence of GZK paradox | ultra-high energy cosmic rays, the [[baryon asymmetry]], the [[accelerating universe | acceleration of the universe]] and the [[galaxy rotation problem | anomalous rotation rates of galaxies]].
 
Although much progress has been made in high-energy, [[quantum]], and astronomical physics, many everyday phenomena, involving [[complex systems | complexity]], [[chaos]], or [[turbulence]] are still poorly understood. Complex problems that seem like they could be solved by a clever application of dynamics and mechanics, such as the formation of sandpiles, nodes in trickling [[water]], the shape of water [[droplet]]s, mechanisms of [[surface tension]] [[catastrophe theory | catastrophes]], or self-sorting in shaken heterogeneous collections are unsolved. These complex phenomena have received growing attention since the 1970s for several reasons, not least of which has been the availability of modern [[mathematics | mathematical]] methods and [[computers]] which enabled [[complex systems]] to be modeled in new ways. The [[interdisciplinary]] [[relevance]] of complex physics has also increased, as exemplified by the study of [[turbulence]] in [[aerodynamics]] or the [[observation]] of [[pattern]] [[formation]] in [[biology | biological]] systems.
 
Two rapidly-growing applied fields to which physics makes contributions are biophysics, or biological physics, and nanotechnology.
 
== See also ==
* [[History of physics]]
* [[Classical physics]]
* [[Unsolved problems in physics]]
* [[Philosophy of physics]]
 
 
 
== Further reading ==
 
=== Popular reading ===
 
* {{cite book | author=[[Stephen Hawking | Hawking, Stephen]] | title=[[A Brief History of Time]] | publisher=Bantam | year=1988 | id=ISBN 0-553-10953-7}}
 
* {{cite book | author=[[Richard Feynman | Feynman, Richard]] | title=Character of Physical Law | publisher=Random House | year=1994 | id=ISBN 0-679-60127-9}}
 
* {{cite book | author=[[Brian Greene | Greene, Brian]] | title=[[The Elegant Universe | The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory]] | publisher=Vintage | year=2000 | id=ISBN 0-375-70811-1}}
 
=== University-level textbooks ===
 
==== Introductory ====
 
* {{cite book | author=Feynman, Richard; Leighton, Robert; Sands, Matthew | title=[[The Feynman Lectures on Physics | Feynman Lectures on Physics]] | publisher=Addison-Wesley | year=1989 | id=ISBN 0-201-51003-0}}
 
* {{cite book | author=Hewitt, Paul | title=Conceptual Physics with Practicing Physics Workbook (9th ed.) | publisher=Addison Wesley | year=2001 | id=ISBN 0-321-05202-1}}
 
* {{cite book | author=Serway, Raymond A.; Jewett, John W. | title=Physics for Scientists and Engineers (6th ed.) | publisher=Brooks/Cole | year=2004 | id=ISBN 0-534-40842-7}}
 
==== Undergraduate ====
 
 
* {{cite book | author=Thornton, Stephen T.; Marion, Jerry B. | title=Classical Dynamics of Particles and Systems (5th ed.) | publisher=Brooks Cole | year=2003 | id=ISBN 0-534-40896-6}}
 
* {{cite book | author=Griffiths, David J. | authorlink = David Griffiths | title=Introduction to Electrodynamics (3rd ed.) | publisher=Prentice Hall | year=1998 | id=ISBN 0-13-805326-X}}
 
* {{cite book | author=Hecht, Eugene | title=Optics (4th ed.) | publisher=Pearson Education | year=2001 | id=ISBN 0-8053-8566-5}}
 
* {{cite book | author=Kroemer, Herbert; Kittel, Charles | title=Thermal Physics (2nd ed.) | publisher=W. H. Freeman Company | year=1980 | id=ISBN 0-7167-1088-9}}
 
* {{cite book | author=Griffiths, David J. | authorlink = David Griffiths |  title=Introduction to Quantum Mechanics (2nd ed.) | publisher=Prentice Hall | year=2004 | id=ISBN 0-13-805326-X}}
 
* {{cite book | author=Tipler, Paul; Llewellyn, Ralph | title=Modern Physics (4th ed.) | publisher=W. H. Freeman | year=2002 | id=ISBN 0-7167-4345-0}}
 
* {{cite book | author=Griffiths, David J. | authorlink = David Griffiths |  title=Introduction to Elementary Particles | publisher=Wiley, John & Sons, Inc | year=1987 | id=ISBN 0-471-60386-4}}
 
==== Graduate ====
 
* {{cite book | author=Landau, L. D.; Lifshitz, E. M. | title=Course of Theoretical Physics | publisher=Butterworth-Heinemann | year=1976 | id=ISBN 0-7506-2896-0}}
 
* {{cite book | author=Morse, Philip; Feshbach, Herman | title=Methods of Theoretical Physics | publisher=Feshbach Publishing | year=2005 | id=ISBN 0-9762021-2-3}}
 
* {{cite book | author=Arfken, George B.; Weber, Hans J. | title=Mathematical Methods for Physicists (5th ed.) | publisher=Academic Press | year=2000 | id=ISBN 0-12-059825-6}}
 
* {{cite book | author=Goldstein, Herbert | title=Classical Mechanics | publisher=Addison Wesley | year=2002 | id=ISBN 0-201-65702-3}}
 
* {{cite book | author=Jackson, John D. | title=Classical Electrodynamics (3rd ed.) | publisher=Wiley | year=1998 | id=ISBN 0-471-30932-X}}
 
* {{cite book | author=[[Lev Landau | Landau, L. D.]]; Lifshitz, E. M. | title=Mechanics and Electrodynamics, Vol. 1 | publisher=Franklin Book Company, Inc | year=1972 | id=ISBN 0-08-016739-X}}
 
* {{cite book | author=Huang, Kerson | title=Statistical Mechanics | publisher=Wiley, John & Sons, Inc | year=1990 | id=ISBN 0-471-81518-7}}
 
* {{cite book | author=Merzbacher, Eugen | title=Quantum Mechanics | publisher=Wiley, John & Sons, Inc | year=1998 | id=ISBN 0-471-88702-1}}
 
* {{cite book | author=Peskin, Michael E.; Schroeder, Daniel V. | title=Introduction to Quantum Field Theory | publisher=Perseus Publishing | year=1994 | id=ISBN 0-201-50397-2}}
 
* {{cite book | author=[[Kip Thorne | Thorne, Kip S.]]; Misner, Charles W.; Wheeler, John Archibald | title=Gravitation | publisher=W.H. Freeman | year=1973 | id=ISBN 0-7167-0344-0}}
 
* {{cite book | author=Wald, Robert M. | title=General Relativity | publisher=University of Chicago Press | year=1984 | id=ISBN 0-226-87033-2}}
 
* {{cite book | author=[[Steven Weinberg | Weinberg, Steven]] | title=Gravitation and Cosmology: Principles and Applications of the General Theory of Relativity | publisher=John Wiley & Sons | year=1972 | id=ISBN 0-471-92567-5}}
 
==== History ====
 
* {{cite book | author=Cropper, William H. | title=Great Physicists: The Life and Times of Leading Physicists from Galileo to Hawking | publisher=Oxford University Press | year=2004 | id=ISBN 0-19-517324-4}}
 
* {{cite book | author=[[George Gamow | Gamow, George]] | title=The Great Physicists from Galileo to Einstein | publisher=Dover Publications | year=1988 | id=ISBN 0-486-25767-3}}
 
* {{cite book | author=Heilbron, John L. | title=The Oxford Guide to the History of Physics and Astronomy | publisher=Oxford University Press | year=2005 | id=ISBN 0-19-517198-5}}
 
* {{cite book | author=Weaver, Jefferson H. (editor) | title=The World of Physics | publisher=Simon and Schuster | year=1987 | id=ISBN 0-671-49931-9}} A selection of 56 articles, written by physicists. Commentaries and notes by [[Lloyd Motz]] and Dale McAdoo.
 
== External links ==
 
; General
 
 
* [http://math.ucr.edu/home/baez/physics/ Usenet Physics FAQ]. A [[FAQ]] compiled by sci.physics and other physics newsgroups.
* [http://www.nobel.se/physics Website of the Nobel Prize in Physics].
* [http://www.physicstoday.org Physics Today] - Your daily physics news and research source
 
 
; Organizations
 
* [http://www.aip.org/index.html AIP.org] Website of the [[American Institute of Physics]]
* [http://www.iop.org IOP.org] Website of the [[Institute of Physics]]
* [http://www.aps.org APS.org] Website of the [[American Physical Society]]
* [http://www.spsnational.org SPS National] Website of the [[Society of Physics Students]]
 


{{Physics-footer}}
Although much progress has been made in high-energy, quantum, and astronomical physics, many everyday phenomena, involving complexity, chaos, or turbulence are still poorly understood. Complex problems that seem like they could be solved by a clever application of dynamics and mechanics, such as the formation of sand piles, nodes in trickling [[water]], the shape of water droplets, mechanisms of [[surface tension]] catastrophes, or self-sorting in shaken heterogeneous collections are unsolved. These complex phenomena have received growing attention since the 1970s for several reasons, not least of which has been the availability of modern [[mathematics | mathematical]] methods and [[computers]] which enabled complex systems to be modeled in new ways. The interdisciplinary relevance of complex physics has also increased, as exemplified by the study of turbulence in aerodynamics or the observation of pattern [[formation]] in [[biology | biological]] systems.


Two rapidly-growing applied fields to which physics makes contributions are [[biophysics]] and [[nanotechnology]].


{{Natural sciences-footer}}
== Attribution ==
{{WPAttribution}}


[[Category:CZ Live]]
== References ==[[Category:Suggestion Bot Tag]]

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This editable Main Article is under development and subject to a disclaimer.

Physics (from the Greek physikos, nature) is the science of nature at its most fundamental form, and is the foundation of the natural sciences. From quarks to galaxies, from individual atoms to macroscopic biological systems, physicists study a wide range of physical phenomena.

Key Areas of Physics

Over the course of time, physical phenomena have been grouped together under specific branches. While it is widely believed that the whole of physics can be considered within a single unified theory, including all phenomena both at the level of quantum mechanics and on a scale as wide as the universe, this has not yet been proven. This is made clear especially by the fact that the current models developed by the different branches of physics give contradictory solutions to the same problem when they are combined. For example, the unification of general relativity and quantum mechanics has so far proven impossible due to creation of infinite values when looking at some properties of systems of subatomic particles. Nevertheless, these are considered as problems "to be solved". The central branches of physics are:

  • Classical mechanics is a model of the physics of forces acting upon bodies, and the motion of those bodies. As opposed to quantum mechanics, classical mechanics is deterministic. Classical mechanics is usually regarded as a limit of quantum mechanics, although this has not been proven in general. Classical mechanics can be divided into two parts:
Newtonian, after Isaac Newton and his laws of motion. This can be more generally formulated in Lagrangian mechanics, after Joseph-Louis Lagrange.
Relativistic, due to Albert Einstein and his theory of relativity. This includes both special and general relativity, and addresses regimes in which Newtonian mechanics is no longer valid: when relative speeds of object are comparable to the speed of light, and for motion occurring near very massive objects.
  • Quantum mechanics is the branch of physics treating atomic and subatomic systems and their interaction with radiation in terms of observable quantities. It is based on the observation that all forms of energy are released in discrete units or bundles called quanta. Quantum theory typically permits only probable or statistical calculation of the observed features of particles, understood in terms of wave functions. Quantum mechanics itself has several levels of approximation.
  • Electromagnetism, or electromagnetic theory, is the physics of the electromagnetic field: a field, encompassing all of space, which exerts a force on those particles that possess the property of electric charge, and is in turn affected by the presence and motion of such particles. Electromagnetism encompasses various real-world electromagnetic phenomena. Electromagnetism, as taught in a typical undergraduate college physics curriculum, can be divided into several areas:
Electrostatics, the study of charged objects, the forces between them, and electric fields and potentials for charged objects at rest.
Magnetism, the study of forces between moving charged objects, the magnetic field, and electromagnetic induction.
Electric circuits, the study of electric potential difference and electric currents for various arrangements of circuit components.
Optics and electromagnetic waves, the study of how time-varying electromagnetic fields propagate through space.

Research and fields within physics

Physics can be subdivided in a variety of different manners; for teaching, for historical purposes, or for research purposes. Contemporary research in physics is divided into many distinct subfields. An incomplete listing includes:

  • Condensed matter physics is the study of the condensed phases of matter, solid and liquid, and how the properties of matter in these phases arise from the properties and mutual interactions of the constituent atoms. More physicists study condensed matter physics than any other field.
  • Particle physics, also known as "high-energy physics". This branch is concerned with the properties of subatomic particles much smaller than atoms, including the elementary particles from which all other units of matter are constructed.
  • Astrophysics attempts to explain the physical workings of celestial objects and phenomena.
  • Atomic, molecular, and optical physics (AMO physics) deals with the behavior of individual atoms and molecules, including the ways in which they absorb and emit light. Molecular physics is sometimes also considered a branch of chemical physics. Laser science may be considered a subfield of AMO or as a separate field.
  • Materials physics is the study of various physical properties of materials. Classifications of physical properties include, but are not limited to, thermal, electronic, magnetic, optical, and mechanical.
  • Computational physics deals with numerically (as opposed to analytically) solving the equations that govern physical systems.

A number of fields of physics overlap strongly with other sciences: Biophysics, Physical chemistry and Geophysics overlap considerably with biology, chemistry and geography, but the focus is on the application of physics and physical techniques to problems within the other field.

Classical and quantum physics

Further information: Classical physics, Quantum physics, Modern physics, Semiclassical

The distinction between classical and quantum theories is important in physics. Classical theories are generally valid despite not considering the quantum nature of things, but are ultimately an approximation to a deeper quantized truth; this approximation typically breaks down at extreme scales, particularly the subatomic. Some fundamental classical theories, such as relativity do not yet have full analogous quantum theories.

Both classical and quantum physics are active areas of research. However, there exist problems in physics in which classical and quantum aspects must be combined to attain some approximation or limit that may acquire several forms as the passage from classical to quantum mechanics is often difficult — such problems are termed semiclassical.

Theoretical and experimental physics

Most individual physicists specialize in either theoretical physics or experimental physics. There have been a few exceptions, such as great Italian physicist Enrico Fermi (1901–1954), who made fundamental contributions to both theory and experimentation.

Roughly speaking, theorists seek to develop theories, through mathematical and computational models, that can both describe and interpret existing experimental results and successfully predict future results, while experimentalists devise and perform experiments to explore new phenomena and test theoretical predictions. Although theory and experiment can be developed separately, they are strongly dependent on each other. Progress in physics frequently comes about when experimentalists make a discovery that existing theories cannot account for, necessitating the formulation of new theories, or when theorists make predictions that experimentalists test.

Physics and Other disciplines

Physics finds applications throughout the other natural sciences as they regard the basic principles of nature. Physics is often said to be the "fundamental science", because the other sciences deal with material systems that obey the laws of physics. For example, chemistry is the science of matter (such as atoms and molecules) and the chemical substances that they form in the bulk. The structure, reactivity, and properties of a chemical compound are determined by the properties of the underlying molecules, which can be described by areas of physics such as quantum mechanics (in the applied subfield of quantum chemistry), thermodynamics, and electromagnetism.

Physics is closely related to mathematics, which provides the logical framework in which physical laws can be precisely formulated and their predictions quantified. Physical definitions, models and theories are invariably expressed using mathematical relations. A key difference between physics and mathematics is that because physics is ultimately concerned with descriptions of the material world, it tests its theories by observations (called experiments), whereas mathematics does not have such requirements. The distinction, however, is not always clear-cut. This large area of research intermediate between physics and mathematics is known as mathematical physics.

Physics is also closely related to engineering and technology. For instance, electrical engineering is the study of the practical application of electromagnetism. Statics, a subfield of mechanics, is responsible for the building of bridges. Further, physicists, or practitioners of physics, invent and design processes and devices, such as the transistor, whether in basic or applied research. Experimental physicists design and perform experiments with particle accelerators, nuclear reactors, telescopes, barometers, synchrotrons, cyclotrons, spectrometers, lasers, and other equipment.

Current research directions

Research in physics is progressing constantly on a large number of fronts, and is likely to do so for the foreseeable future. Some current directions include:

In condensed matter physics, the biggest unsolved theoretical problem is the explanation for high-temperature superconductivity. Strong efforts, largely experimental, are being put into making workable spintronics and quantum computers.

In particle physics, the first pieces of experimental evidence for physics beyond the Standard Model have begun to appear. Foremost amongst these are indications that neutrinos have non-zero mass. These experimental results appear to have solved the long-standing solar neutrino problem in solar physics. The physics of massive neutrinos is currently an area of active theoretical and experimental research. In the next several years, particle accelerators will begin probing energy scales in the TeV range, in which experimentalists are hoping to find evidence for the Higgs boson and supersymmetric particles.

Theoretical attempts to unify quantum mechanics and general relativity into a single theory of quantum gravity, a program ongoing for over half a century, have not yet borne fruit. The current leading candidates are M-theory, superstring theory and loop quantum gravity.

Many astronomical and cosmological phenomena have yet to be satisfactorily explained, including the existence of GZK paradox | ultra-high energy cosmic rays, the baryon asymmetry, the acceleration of the universe and the anomalous rotation rates of galaxies.

Although much progress has been made in high-energy, quantum, and astronomical physics, many everyday phenomena, involving complexity, chaos, or turbulence are still poorly understood. Complex problems that seem like they could be solved by a clever application of dynamics and mechanics, such as the formation of sand piles, nodes in trickling water, the shape of water droplets, mechanisms of surface tension catastrophes, or self-sorting in shaken heterogeneous collections are unsolved. These complex phenomena have received growing attention since the 1970s for several reasons, not least of which has been the availability of modern mathematical methods and computers which enabled complex systems to be modeled in new ways. The interdisciplinary relevance of complex physics has also increased, as exemplified by the study of turbulence in aerodynamics or the observation of pattern formation in biological systems.

Two rapidly-growing applied fields to which physics makes contributions are biophysics and nanotechnology.

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== References ==

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