Physics

This article is about the field of science. For other uses,see Physics (disambiguation).

Various examples of physical phenomena.Further information: Outline of physics

Physics (from Ancient Greek: φυσική (ἐπιστήμη)phusikḗ (epistḗmē) “knowledge of nature”, from φύσιςphúsis “nature”[1][2][3]) is the natural science that in-volves the study of matter[4] and its motion through spaceand time, along with related concepts such as energyand force.[5] More broadly, it is the general analysis ofnature, conducted in order to understand how the universebehaves.[lower-alpha 1][6][7]

Physics is one of the oldest academic disciplines, per-haps the oldest through its inclusion of astronomy.[8]Over the last two millennia, physics was a part of naturalphilosophy along with chemistry, certain branches ofmathematics, and biology, but during the scientific rev-olution in the 17th century, the natural sciences emergedas unique research programs in their own right.[lower-alpha 2]Physics intersects with many interdisciplinary areas of re-search, such as biophysics and quantum chemistry, andthe boundaries of physics are not rigidly defined. Newideas in physics often explain the fundamental mecha-nisms of other sciences[6] while opening new avenues ofresearch in areas such as mathematics and philosophy.Physics also makes significant contributions through ad-vances in new technologies that arise from theoreticalbreakthroughs. For example, advances in the understand-ing of electromagnetism or nuclear physics led directlyto the development of new products that have dramati-cally transformed modern-day society, such as television,computers, domestic appliances, and nuclear weapons;[6]

advances in thermodynamics led to the development ofindustrialization, and advances in mechanics inspired thedevelopment of calculus.

1 History

Main article: History of physics

1.1 Ancient astronomy

Main article: History of astronomyAstronomy is the oldest of the natural sciences. The ear-

Ancient Egyptian astronomy is evident in monuments like theceiling of Senemut’s tomb from the Eighteenth Dynasty of Egypt.

liest civilizations dating back to beyond 3000 BCE, suchas the Sumerians, ancient Egyptians, and the Indus ValleyCivilization, all had a predictive knowledge and a basicunderstanding of themotions of the Sun,Moon, and stars.The stars and planets were often a target of worship, be-lieved to represent their gods. While the explanations forthese phenomena were often unscientific and lacking inevidence, these early observations laid the foundation forlater astronomy.[8]

According to Asger Aaboe, the origins of Western as-tronomy can be found in Mesopotamia, and all West-ern efforts in the exact sciences are descended fromlate Babylonian astronomy.[9] Egyptian astronomers leftmonuments showing knowledge of the constellations andthe motions of the celestial bodies,[10] while Greek poetHomer wrote of various celestial objects in his Iliad andOdyssey; later Greek astronomers provided names, whichare still used today, for most constellations visible fromthe northern hemisphere.[11]

1

2 1 HISTORY

1.2 Natural philosophy

Main article: Natural philosophy

Natural philosophy has its origins in Greece during theArchaic period, (650 BC – 480 BC), when Pre-Socraticphilosophers like Thales rejected non-naturalistic expla-nations for natural phenomena and proclaimed that ev-ery event had a natural cause.[12] They proposed ideasverified by reason and observation, and many of theirhypotheses proved successful in experiment;[13] for ex-ample, atomism was found to be correct approximately2000 years after it was first proposed by Leucippus andhis pupil Democritus.[14]

1.3 Classical physics

Main article: Classical physicsPhysics became a separate science when early modern

Sir Isaac Newton (1643–1727), whose laws of motion anduniversal gravitation were major milestones in classical physics

Europeans used experimental and quantitative methodsto discover what are now considered to be the laws ofphysics.[15]

Major developments in this period include the replace-ment of the geocentric model of the solar system withthe helio-centric Copernican model, the laws governingthe motion of planetary bodies determined by JohannesKepler between 1609 and 1619, pioneering work ontelescopes and observational astronomy byGalileo Galilei

in the 16th and 17th Centuries, and Isaac Newton's dis-covery and unification of the laws of motion and universalgravitation that would come to bear his name.[16] New-ton also developed calculus,[lower-alpha 3] the mathematicalstudy of change, which provided newmathematical meth-ods for solving physical problems.[17]

The discovery of new laws in thermodynamics,chemistry, and electromagnetics resulted from greaterresearch efforts during the Industrial Revolution asenergy needs increased.[18] The laws comprising classicalphysics remain very widely used for objects on everydayscales travelling at non-relativistic speeds, since theyprovide a very close approximation in such situations,and theories such as quantum mechanics and the theoryof relativity simplify to their classical equivalents at suchscales. However, inaccuracies in classical mechanics forvery small objects and very high velocities led to thedevelopment of modern physics in the 20th century.

1.4 Modern physics

Main article: Modern physicsSee also: History of special relativity andHistory of quan-tum mechanicsModern physics began in the early 20th century with the

Albert Einstein (1879–1955), whose work on the photoelectriceffect and the theory of relativity led to a revolution in 20th cen-tury physics

work of Max Planck in quantum theory and Albert Ein-stein's theory of relativity. Both of these theories cameabout due to inaccuracies in classical mechanics in cer-tain situations. Classical mechanics predicted a varying

3

Max Planck (1858–1947), the originator of the theory ofquantum mechanics

speed of light, which could not be resolved with the con-stant speed predicted by Maxwell’s equations of electro-magnetism; this discrepancy was corrected by Einstein’stheory of special relativity, which replaced classical me-chanics for fast-moving bodies and allowed for a constantspeed of light.[19] Black body radiation provided anotherproblem for classical physics, which was corrected whenPlanck proposed that light comes in individual packetsknown as photons; this, along with the photoelectric ef-fect and a complete theory predicting discrete energy lev-els of electron orbitals, led to the theory of quantum me-chanics taking over from classical physics at very smallscales.[20]

Quantum mechanics would come to be pioneeredby Werner Heisenberg, Erwin Schrödinger and PaulDirac.[20] From this early work, and work in relatedfields, the Standard Model of particle physics wasderived.[21] Following the discovery of a particle withproperties consistent with the Higgs boson at CERN in2012,[22] all fundamental particles predicted by the stan-dard model, and no others, appear to exist; however,physics beyond the Standard Model, with theories suchas supersymmetry, is an active area of research.[23]

2 Philosophy

Main article: Philosophy of physics

In many ways, physics stems from ancient Greek philos-ophy. From Thales' first attempt to characterize mat-ter, to Democritus' deduction that matter ought to re-duce to an invariant state, the Ptolemaic astronomy ofa crystalline firmament, and Aristotle’s book Physics (anearly book on physics, which attempted to analyze anddefine motion from a philosophical point of view), var-ious Greek philosophers advanced their own theories ofnature. Physics was known as natural philosophy until thelate 18th century.[24]

By the 19th century, physics was realized as a disci-pline distinct from philosophy and the other sciences.Physics, as with the rest of science, relies on philosophyof science to give an adequate description of the scien-tific method.[25] The scientific method employs a priorireasoning as well as a posteriori reasoning and the useof Bayesian inference to measure the validity of a giventheory.[26]

The development of physics has answeredmany questionsof early philosophers, but has also raised new questions.Study of the philosophical issues surrounding physics, thephilosophy of physics, involves issues such as the natureof space and time, determinism, and metaphysical out-looks such as empiricism, naturalism and realism.[27]

Many physicists have written about the philosophical im-plications of their work, for instance Laplace, who cham-pioned causal determinism,[28] and Erwin Schrödinger,who wrote on quantum mechanics.[29][30] The mathemat-ical physicist Roger Penrose has been called a Platonistby Stephen Hawking,[31] a view Penrose discusses in hisbook, The Road to Reality.[32] Hawking refers to himselfas an “unashamed reductionist” and takes issue with Pen-rose’s views.[33]

3 Core theories

Further information: Branches of physics, Outline ofphysics

Though physics deals with a wide variety of systems, cer-tain theories are used by all physicists. Each of thesetheories were experimentally tested numerous times andfound correct as an approximation of nature (within acertain domain of validity). For instance, the theory ofclassical mechanics accurately describes the motion ofobjects, provided they are much larger than atoms andmoving at much less than the speed of light. These the-ories continue to be areas of active research, and a re-markable aspect of classical mechanics known as chaoswas discovered in the 20th century, three centuries after

4 3 CORE THEORIES

the original formulation of classical mechanics by IsaacNewton (1642–1727).These central theories are important tools for researchinto more specialised topics, and any physicist, regard-less of their specialisation, is expected to be literatein them. These include classical mechanics, quantummechanics, thermodynamics and statistical mechanics,electromagnetism, and special relativity.

3.1 Classical physics

Main article: Classical physicsClassical physics includes the traditional branches

Classical physics implemented in an acoustic engineering modelof sound reflecting from an acoustic diffuser

and topics that were recognised and well-developedbefore the beginning of the 20th century—classicalmechanics, acoustics, optics, thermodynamics, andelectromagnetism. Classical mechanics is concernedwith bodies acted on by forces and bodies in motionand may be divided into statics (study of the forceson a body or bodies not subject to an accelera-tion), kinematics (study of motion without regard toits causes), and dynamics (study of motion and theforces that affect it); mechanics may also be divided

into solid mechanics and fluid mechanics (known to-gether as continuummechanics), the latter including suchbranches as hydrostatics, hydrodynamics, aerodynamics,and pneumatics. Acoustics is the study of how sound isproduced, controlled, transmitted and received.[34] Im-portant modern branches of acoustics include ultrasonics,the study of sound waves of very high frequency beyondthe range of human hearing; bioacoustics the physics ofanimal calls and hearing,[35] and electroacoustics, the ma-nipulation of audible sound waves using electronics.[36]Optics, the study of light, is concerned not only withvisible light but also with infrared and ultraviolet radia-tion, which exhibit all of the phenomena of visible lightexcept visibility, e.g., reflection, refraction, interference,diffraction, dispersion, and polarization of light. Heatis a form of energy, the internal energy possessed bythe particles of which a substance is composed; ther-modynamics deals with the relationships between heatand other forms of energy. Electricity and magnetismhave been studied as a single branch of physics sincethe intimate connection between them was discovered inthe early 19th century; an electric current gives rise toa magnetic field, and a changing magnetic field inducesan electric current. Electrostatics deals with electriccharges at rest, electrodynamics withmoving charges, andmagnetostatics with magnetic poles at rest.

3.2 Modern physics

Main article: Modern physicsClassical physics is generally concerned with matter and

Solvay Conference of 1927, with prominent physicists suchas Albert Einstein, Werner Heisenberg, Max Planck, HendrikLorentz, Niels Bohr, Marie Curie, Erwin Schrödinger and PaulDirac.

energy on the normal scale of observation, while much ofmodern physics is concerned with the behavior of matterand energy under extreme conditions or on a very large orvery small scale. For example, atomic and nuclear physicsstudies matter on the smallest scale at which chemicalelements can be identified. The physics of elementaryparticles is on an even smaller scale since it is concerned

5

with the most basic units of matter; this branch of physicsis also known as high-energy physics because of the ex-tremely high energies necessary to produce many typesof particles in large particle accelerators. On this scale,ordinary, commonsense notions of space, time, matter,and energy are no longer valid.The two chief theories of modern physics present a dif-ferent picture of the concepts of space, time, and matterfrom that presented by classical physics. Quantum the-ory is concerned with the discrete, rather than continu-ous, nature of many phenomena at the atomic and sub-atomic level and with the complementary aspects of par-ticles and waves in the description of such phenomena.The theory of relativity is concerned with the descriptionof phenomena that take place in a frame of reference thatis inmotion with respect to an observer; the special theoryof relativity is concerned with relative uniform motion ina straight line and the general theory of relativity withaccelerated motion and its connection with gravitation.Both quantum theory and the theory of relativity find ap-plications in all areas of modern physics.

3.3 Difference between classical and mod-ern physics

Far larger than

Far less than Comparable to

Near or less than

The basic domains of physics

While physics aims to discover universal laws, its theorieslie in explicit domains of applicability. Loosely speaking,the laws of classical physics accurately describe systemswhose important length scales are greater than the atomicscale and whose motions are much slower than the speedof light. Outside of this domain, observations do notmatch their predictions. Albert Einstein contributed theframework of special relativity, which replaced notionsof absolute time and space with spacetime and allowedan accurate description of systems whose componentshave speeds approaching the speed of light. Max Planck,Erwin Schrödinger, and others introduced quantum me-chanics, a probabilistic notion of particles and interac-tions that allowed an accurate description of atomic andsubatomic scales. Later, quantum field theory unifiedquantum mechanics and special relativity. General rel-ativity allowed for a dynamical, curved spacetime, withwhich highly massive systems and the large-scale struc-ture of the universe can be well-described. General rela-tivity has not yet been unified with the other fundamental

descriptions; several candidate theories of quantum grav-ity are being developed.

4 Relation to other fields

This parabola-shaped lava flow illustrates the application ofmathematics in physics—in this case, Galileo's law of fallingbodies.

4.1 Prerequisites

Mathematics is the language used for compact descrip-tion of the order in nature, especially the laws ofphysics. This was noted and advocated by Pythagoras,[37]Plato,[38] Galileo,[39] and Newton.Physics theories use mathematics[40] to obtain order andprovide precise formulas, precise or estimated solutions,quantitative results and predictions. Experiment re-sults in physics are numerical measurements. Technolo-gies based on mathematics, like computation have madecomputational physics an active area of research.Ontology is a prerequisite for physics, but not for math-ematics. It means physics is ultimately concerned withdescriptions of the real world, while mathematics is con-cerned with abstract patterns, even beyond the real world.Thus physics statements are synthetic, while mathemat-ical statements are analytic. Mathematics contains hy-potheses, while physics contains theories. Mathematicsstatements have to be only logically true, while predic-tions of physics statements must match observed and ex-perimental data.The distinction is clear-cut, but not always obvious.For example, mathematical physics is the application ofmathematics in physics. Its methods are mathematical,but its subject is physical.[41] The problems in this fieldstart with a "mathematical model of a physical situation"and a “mathematical description of a physical law”. Ev-ery mathematical statement used for solution has a hard-to-find physical meaning. The final mathematical solu-tion has an easier-to-find meaning, because it is what thesolver is looking for.

6 5 RESEARCH

Physics is a branch of fundamental science, not practicalscience.[42] Physics is also called “the fundamental sci-ence” because the subject of study of all branches ofnatural science like chemistry, astronomy, geology andbiology are constrained by laws of physics,[43] similarto how chemistry is often called the central science be-cause of its role in linking the physical sciences. Forexample, chemistry studies properties, structures, andreactions of matter (chemistry’s focus on the atomic scaledistinguishes it from physics). Structures are formed be-cause particles exert electrical forces on each other, prop-erties include physical characteristics of given substances,and reactions are bound by laws of physics, like conser-vation of energy, mass and charge.Physics is applied in industries like engineering andmedicine.

4.2 Application and influence

Main article: Applied physicsApplied physics is a general term for physics researchwhich is intended for a particular use. An applied physicscurriculum usually contains a few classes in an applieddiscipline, like geology or electrical engineering. It usu-ally differs from engineering in that an applied physicistmay not be designing something in particular, but ratheris using physics or conducting physics research with theaim of developing new technologies or solving a problem.The approach is similar to that of applied mathemat-ics. Applied physicists can also be interested in the useof physics for scientific research. For instance, peopleworking on accelerator physics might seek to build betterparticle detectors for research in theoretical physics.Physics is used heavily in engineering. For example,statics, a subfield of mechanics, is used in the buildingof bridges and other static structures. The understandingand use of acoustics results in sound control and betterconcert halls; similarly, the use of optics creates betteroptical devices. An understanding of physics makes formore realistic flight simulators, video games, and movies,and is often critical in forensic investigations.With the standard consensus that the laws of physicsare universal and do not change with time, physics canbe used to study things that would ordinarily be miredin uncertainty. For example, in the study of the ori-gin of the earth, one can reasonably model earth’s mass,temperature, and rate of rotation, as a function of time al-lowing one to extrapolate forward and backward in timeand so predict prior and future conditions. It also allowsfor simulations in engineering which drastically speed upthe development of a new technology.But there is also considerable interdisciplinarity in thephysicist’s methods, so many other important fields areinfluenced by physics (e.g., the fields of econophysics andsociophysics).

5 Research

5.1 Scientific method

Physicists use the scientific method to test the validity ofa physical theory, using a methodical approach to com-pare the implications of the theory in question with theassociated conclusions drawn from experiments and ob-servations conducted to test it. Experiments and obser-vations are collected and compared with the predictionsand hypotheses made by a theory, thus aiding in the de-termination or the validity/invalidity of the theory.A scientific law is a concise verbal or mathematical state-ment of a relation which expresses a fundamental prin-ciple of some theory, such as Newton’s law of universalgravitation.[44]

5.2 Theory and experiment

Main articles: Theoretical physics and ExperimentalphysicsTheorists seek to develop mathematical models thatboth agree with existing experiments and successfullypredict future experimental results, while experimen-talists devise and perform experiments to test theoreti-cal predictions and explore new phenomena. Althoughtheory and experiment are developed separately, theyare strongly dependent upon each other. Progress inphysics frequently comes about when experimentalistsmake a discovery that existing theories cannot explain,or when new theories generate experimentally testablepredictions, which inspire new experiments.Physicists who work at the interplay of theory andexperiment are called phenomenologists. Phenomenolo-gists look at the complex phenomena observed in exper-iment and work to relate them to fundamental theory.Theoretical physics has historically taken inspirationfrom philosophy; electromagnetism was unified thisway.[lower-alpha 4] Beyond the known universe, the fieldof theoretical physics also deals with hypotheticalissues,[lower-alpha 5] such as parallel universes, a multiverse,and higher dimensions. Theorists invoke these ideas inhopes of solving particular problems with existing theo-ries. They then explore the consequences of these ideasand work toward making testable predictions.Experimental physics expands, and is expanded by,engineering and technology. Experimental physicists in-volved in basic research design and perform experimentswith equipment such as particle accelerators and lasers,whereas those involved in applied research often work inindustry developing technologies such as magnetic reso-nance imaging (MRI) and transistors. Feynman has notedthat experimentalists may seek areas which are not well-explored by theorists.[45]

5.4 Research fields 7

5.3 Scope and aims

Physics covers a wide range of phenomena, fromelementary particles (such as quarks, neutrinos, and elec-trons) to the largest superclusters of galaxies. Included inthese phenomena are the most basic objects composingall other things. Therefore physics is sometimes calledthe "fundamental science".[43] Physics aims to describethe various phenomena that occur in nature in terms ofsimpler phenomena. Thus, physics aims to both connectthe things observable to humans to root causes, and thenconnect these causes together.For example, the ancient Chinese observed that certainrocks (lodestone) were attracted to one another by someinvisible force. This effect was later called magnetism,and was first rigorously studied in the 17th century. Alittle earlier than the Chinese, the ancient Greeks knewof other objects such as amber, that when rubbed withfur would cause a similar invisible attraction between thetwo. This was also first studied rigorously in the 17th cen-tury, and came to be called electricity. Thus, physics hadcome to understand two observations of nature in termsof some root cause (electricity and magnetism). How-ever, further work in the 19th century revealed that thesetwo forces were just two different aspects of one force—electromagnetism. This process of “unifying” forces con-tinues today, and electromagnetism and the weak nu-clear force are now considered to be two aspects of theelectroweak interaction. Physics hopes to find an ulti-mate reason (Theory of Everything) for why nature is asit is (see section Current research below for more infor-mation).

5.4 Research fields

Contemporary research in physics can be broadly dividedinto condensed matter physics; atomic, molecular, andoptical physics; particle physics; astrophysics; geophysicsand biophysics. Some physics departments also supportphysics education research and physics outreach.Since the 20th century, the individual fields of physicshave become increasingly specialized, and today mostphysicists work in a single field for their entire careers.“Universalists” such as Albert Einstein (1879–1955) andLev Landau (1908–1968), who worked in multiple fieldsof physics, are now very rare.[lower-alpha 6]

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

5.4.1 Condensed matter

Main article: Condensed matter physicsCondensedmatter physics is the field of physics that dealswith the macroscopic physical properties of matter.[46] Inparticular, it is concerned with the “condensed” phasesthat appear whenever the number of particles in a system

is extremely large and the interactions between them arestrong.[47]

The most familiar examples of condensed phases aresolids and liquids, which arise from the bonding by way ofthe electromagnetic force between atoms.[48]More exoticcondensed phases include the superfluid[49] and the Bose–Einstein condensate[50] found in certain atomic systems atvery low temperature, the superconducting phase exhib-ited by conduction electrons in certain materials,[51] andthe ferromagnetic and antiferromagnetic phases of spinson atomic lattices.[52]

Condensed matter physics is the largest field of contem-porary physics. Historically, condensed matter physicsgrew out of solid-state physics, which is now consideredone of its main subfields.[53] The term condensed matterphysics was apparently coined by Philip Anderson whenhe renamed his research group—previously solid-statetheory—in 1967.[54] In 1978, the Division of Solid StatePhysics of the American Physical Society was renamedas the Division of Condensed Matter Physics.[53] Con-densed matter physics has a large overlap with chemistry,materials science, nanotechnology and engineering.[47]

5.4.2 Atomic, molecular, and optical physics

Main article: Atomic, molecular, and optical physics

Atomic, molecular, and optical physics (AMO) is thestudy of matter–matter and light–matter interactions onthe scale of single atoms and molecules. The three areasare grouped together because of their interrelationships,the similarity of methods used, and the commonality oftheir relevant energy scales. All three areas include bothclassical, semi-classical and quantum treatments; they cantreat their subject from a microscopic view (in contrast toa macroscopic view).Atomic physics studies the electron shells of atoms. Cur-rent research focuses on activities in quantum control,cooling and trapping of atoms and ions,[55][56][57] low-temperature collision dynamics and the effects of elec-tron correlation on structure and dynamics. Atomicphysics is influenced by the nucleus (see, e.g., hyperfinesplitting), but intra-nuclear phenomena such as fission andfusion are considered part of high-energy physics.Molecular physics focuses on multi-atomic structures andtheir internal and external interactions with matter andlight. Optical physics is distinct from optics in that ittends to focus not on the control of classical light fieldsby macroscopic objects but on the fundamental proper-ties of optical fields and their interactions with matter inthe microscopic realm.

8 6 CURRENT RESEARCH

5.4.3 High-energy physics (particle physics) and nu-clear physics

Main articles: Particle physics and Nuclear physicsParticle physics is the study of the elementary con-stituents of matter and energy and the interactions be-tween them.[58] In addition, particle physicists design anddevelop the high energy accelerators,[59] detectors,[60] andcomputer programs[61] necessary for this research. Thefield is also called “high-energy physics” because many el-ementary particles do not occur naturally but are createdonly during high-energy collisions of other particles.[62]

Currently, the interactions of elementary particles andfields are described by the Standard Model.[63] Themodel accounts for the 12 known particles of matter(quarks and leptons) that interact via the strong, weak,and electromagnetic fundamental forces.[63] Dynamicsare described in terms of matter particles exchanginggauge bosons (gluons, W and Z bosons, and photons,respectively).[64] The Standard Model also predicts a par-ticle known as the Higgs boson.[63] In July 2012 CERN,the European laboratory for particle physics, announcedthe detection of a particle consistent with the Higgsboson,[65] an integral part of a Higgs mechanism.Nuclear physics is the field of physics that studies theconstituents and interactions of atomic nuclei. Themost commonly known applications of nuclear physicsare nuclear power generation and nuclear weaponstechnology, but the research has provided applicationin many fields, including those in nuclear medicineand magnetic resonance imaging, ion implantation inmaterials engineering, and radiocarbon dating in geologyand archaeology.

5.4.4 Astrophysics

Main articles: Astrophysics and Physical cosmologyAstrophysics and astronomy are the application of thetheories and methods of physics to the study of stellarstructure, stellar evolution, the origin of the solar system,and related problems of cosmology. Because astrophysicsis a broad subject, astrophysicists typically apply manydisciplines of physics, including mechanics, electromag-netism, statistical mechanics, thermodynamics, quantummechanics, relativity, nuclear and particle physics, andatomic and molecular physics.The discovery by Karl Jansky in 1931 that radio sig-nals were emitted by celestial bodies initiated the scienceof radio astronomy. Most recently, the frontiers of as-tronomy have been expanded by space exploration. Per-turbations and interference from the earth’s atmospheremake space-based observations necessary for infrared,ultraviolet, gamma-ray, and X-ray astronomy.Physical cosmology is the study of the formation andevolution of the universe on its largest scales. AlbertEinstein’s theory of relativity plays a central role in all

modern cosmological theories. In the early 20th cen-tury, Hubble's discovery that the universe is expanding,as shown by the Hubble diagram, prompted rival expla-nations known as the steady state universe and the BigBang.The Big Bang was confirmed by the success of Big Bangnucleosynthesis and the discovery of the cosmic mi-crowave background in 1964. The Big Bang model restson two theoretical pillars: Albert Einstein’s general rela-tivity and the cosmological principle. Cosmologists haverecently established the ΛCDM model of the evolutionof the universe, which includes cosmic inflation, dark en-ergy, and dark matter.Numerous possibilities and discoveries are anticipated toemerge from new data from the Fermi Gamma-ray SpaceTelescope over the upcoming decade and vastly revise orclarify existing models of the universe.[66][67] In partic-ular, the potential for a tremendous discovery surround-ing dark matter is possible over the next several years.[68]Fermi will search for evidence that dark matter is com-posed of weakly interacting massive particles, comple-menting similar experiments with the Large Hadron Col-lider and other underground detectors.IBEX is already yielding new astrophysical discoveries:“No one knows what is creating the ENA (energetic neu-tral atoms) ribbon” along the termination shock of thesolar wind, “but everyone agrees that it means the text-book picture of the heliosphere — in which the solarsystem’s enveloping pocket filled with the solar wind’scharged particles is plowing through the onrushing 'galac-tic wind' of the interstellar medium in the shape of acomet — is wrong.”[69]

6 Current research

Further information: List of unsolved problems in physicsResearch in physics is continually progressing on a largenumber of fronts.In condensed matter physics, an important unsolved theo-retical problem is that of high-temperature superconduc-tivity. Many condensed matter experiments are aiming tofabricate workable spintronics and quantum computers.In particle physics, the first pieces of experimental evi-dence for physics beyond the Standard Model have be-gun to appear. Foremost among these are indicationsthat neutrinos have non-zero mass. These experimen-tal results appear to have solved the long-standing solarneutrino problem, and the physics of massive neutrinosremains an area of active theoretical and experimentalresearch. Particle accelerators have begun probing en-ergy scales in the TeV range, in which experimental-ists are hoping to find evidence for the Higgs boson andsupersymmetric particles.[70]

Theoretical attempts to unify quantum mechanics and

9

general relativity into a single theory of quantum grav-ity, a program ongoing for over half a century, have notyet been decisively resolved. The current leading candi-dates are M-theory, superstring theory and loop quantumgravity.Many astronomical and cosmological phenomena haveyet to be satisfactorily explained, including the existenceof ultra-high energy cosmic rays, the baryon asymmetry,the acceleration of the universe and the anomalous rota-tion rates of galaxies.Although much progress has been made in high-energy, quantum, and astronomical physics, many ev-eryday phenomena involving complexity,[71] chaos,[72] orturbulence[73] are still poorly understood. Complex prob-lems that seem like they could be solved by a clever appli-cation of dynamics and mechanics remain unsolved; ex-amples include the formation of sandpiles, nodes in trick-ling water, the shape of water droplets, mechanisms ofsurface tension catastrophes, and self-sorting in shakenheterogeneous collections.[74]

These complex phenomena have received growing at-tention since the 1970s for several reasons, includingthe availability of modern mathematical methods andcomputers, which enabled complex systems to be mod-eled in new ways. Complex physics has become part ofincreasingly interdisciplinary research, as exemplified bythe study of turbulence in aerodynamics and the observa-tion of pattern formation in biological systems. In 1932,Horace Lamb said:[75]

I am an old man now, and when I die andgo to heaven there are two matters on whichI hope for enlightenment. One is quantumelectrodynamics, and the other is the turbulentmotion of fluids. And about the former I amrather optimistic.—Horace Lamb, Annual Reviews in FluidMechanics

7 See also

8 Notes[1] The term 'universe' is defined as everything that physi-

cally exists: the entirety of space and time, all forms ofmatter, energy and momentum, and the physical laws andconstants that govern them. However, the term 'universe'may also be used in slightly different contextual senses,denoting concepts such as the cosmos or the philosophicalworld.

[2] Francis Bacon's 1620 Novum Organum was critical in thedevelopment of scientific method.

[3] Calculus was independently developed at around the sametime by GottfriedWilhelm Leibniz; while Leibniz was the

first to publish his work, and developed much of the no-tation used for calculus today, Newton was the first to de-velop calculus and apply it to physical problems. See alsoLeibniz–Newton calculus controversy

[4] See, for example, the influence of Kant and Ritter onOersted.

[5] Concepts which are denoted hypothetical can change withtime. For example, the atom of nineteenth century physicswas denigrated by some, including Ernst Mach's critiqueof Ludwig Boltzmann's formulation of statistical mechan-ics. By the end of World War II, the atom was no longerdeemed hypothetical.

[6] Yet, universalism is encouraged in the culture of physics.For example, the World Wide Web, which was innovatedat CERN by Tim Berners-Lee, was created in service tothe computer infrastructure of CERN, andwas/is intendedfor use by physicists worldwide. The same might be saidfor arXiv.org

9 References[1] “physics”. Online Etymology Dictionary.

[2] “physic”. Online Etymology Dictionary.

[3] φύσις, φυσική, ἐπιστήμη. Liddell, Henry George; Scott,Robert; A Greek–English Lexicon at the Perseus Project

[4] At the start of The Feynman Lectures on Physics, RichardFeynman offers the atomic hypothesis as the single mostprolific scientific concept: “If, in some cataclysm, all []scientific knowledge were to be destroyed [save] one sen-tence [...] what statement would contain the most infor-mation in the fewest words? I believe it is [...] that allthings are made up of atoms – little particles that movearound in perpetual motion, attracting each other whenthey are a little distance apart, but repelling upon be-ing squeezed into one another ...” (Feynman, Leighton &Sands 1963, p. I-2)

[5] “Physical science is that department of knowledge whichrelates to the order of nature, or, in other words, to theregular succession of events.” (Maxwell 1878, p. 9)

[6] Young & Freedman 2014, p. 9

[7] “Physics is the study of your world and the world and uni-verse around you.” (Holzner 2006, p. 7)

[8] Krupp 2003

[9] Aaboe 1991

[10] Clagett 1995

[11] Thurston 1994

[12] Singer 2008, p. 35

[13] Lloyd 1970, pp. 108–109

[14] Gill, N.S. “Atomism - Pre-Socratic Philosophy of Atom-ism”. Ancient/Classical History. About.com. Retrieved2014-04-01.

10 9 REFERENCES

[15] Ben-Chaim 2004

[16] Guicciardini 1999

[17] Allen 1997

[18] “The Industrial Revolution”. Schoolscience.org, Instituteof Physics. Retrieved 2014-04-01.

[19] O'Connor & Robertson 1996a

[20] O'Connor & Robertson 1996b

[21] DONUT 2001

[22] Cho 2012

[23] See, for example, John Womersley, Beyond the standardmodel

[24] Noll notes that some universities still use this title —Walter Noll (23 Jun 2006), “On the Past and Future ofNatural Philosophy” Journal of Elasticity July 2006, 84(1)pp 1-11

[25] Rosenberg 2006, Chapter 1

[26] Godfrey-Smith 2003, Chapter 14: “Bayesianism andModern Theories of Evidence”

[27] Godfrey-Smith 2003, Chapter 15: “Empiricism, Natural-ism, and Scientific Realism?"

[28] Laplace 1951

[29] Schrödinger 1983

[30] Schrödinger 1995

[31] “I think that Roger is a Platonist at heart but he must an-swer for himself.” (Hawking & Penrose 1996, p. 4)

[32] Penrose 2004

[33] Penrose et al. 1997

[34] “acoustics”. Encyclopædia Britannica. Retrieved 14 June2013.

[35] “Bioacoustics – the International Journal of Animal Soundand its Recording”. Taylor & Francis. Retrieved 31 July2012.

[36] Acoustical Society of America. “Acoustics and You (ACareer in Acoustics?)". Retrieved 21 May 2013.

[37] Dijksterhuis 1986

[38] “Although usually remembered today as a philosopher,Plato was also one of ancient Greece’s most important pa-trons of mathematics. Inspired by Pythagoras, he foundedhis Academy in Athens in 387 BC, where he stressedmathematics as a way of understanding more about re-ality. In particular, he was convinced that geometry wasthe key to unlocking the secrets of the universe. The signabove the Academy entrance read: 'Let no-one ignorantof geometry enter here.'" (Mastin 2010)

[39] “Philosophy is written in that great book which ever liesbefore our eyes. I mean the universe, but we cannot un-derstand it if we do not first learn the language and graspthe symbols in which it is written. This book is written inthe mathematical language, and the symbols are triangles,circles and other geometrical figures, without whose helpit is humanly impossible to comprehend a single word ofit, and without which one wanders in vain through a darklabyrinth.” – Galileo (1623), The Assayer, as quoted inToraldo Di Francia 1976, p. 10

[40] “Applications of Mathematics to the Sciences”.Math.niu.edu. 25 January 2000. Retrieved 30 January2012.

[41] “Journal of Mathematical Physics”. ResearchGate. Re-trieved 31 March 2014. mathematical physics — thatis, the application of mathematics to problems in physicsand the development of mathematical methods suitablefor such applications and for the formulation of physicaltheories.

[42] American Association for the Advancement of Science,Science. 1917. Page 645

[43] Feynman, Leighton & Sands 1963, Chapter 3: “The Rela-tion of Physics to Other Sciences"; see also reductionismand special sciences

[44] Honderich 1995, pp. 474–476

[45] “In fact experimenters have a certain individual charac-ter. They ... very often do their experiments in a re-gion in which people know the theorist has not made anyguesses.” (Feynman 1965, p. 157)

[46] Taylor & Heinonen 2002

[47] Cohen 2008

[48] Moore 2011, pp. 255–258

[49] Leggett 1999

[50] Levy 2001

[51] Stajic, Coontz & Osborne 2011

[52] Mattis 2006

[53] “History of Condensed Matter Physics”. American Phys-ical Society. Retrieved 31 March 2014.

[54] “Philip Anderson”. Physics Faculty. Princeton University.Retrieved 15 October 2012.

[55] For example, AMO research groups at “MIT AMOGroup”. Retrieved 21 February 2014.

[56] “Korea University, Physics AMO Group”. Retrieved 21February 2014.

[57] “Aarhus Universitet, AMO Group”. Retrieved 21 Febru-ary 2014.

[58] “Division of Particles & Fields”. American Physical So-ciety. Retrieved 18 October 2012.

[59] Halpern 2010

11

[60] Grupen 1999

[61] Walsh 2012

[62] “High Energy Particle Physics Group”. Institute ofPhysics. Retrieved 18 October 2012.

[63] Oerter 2006

[64] Gribbin, Gribbin & Gribbin 1998

[65] “CERN experiments observe particle consistent withlong-sought Higgs boson”. European Organization forNuclear Research. 4 July 2012. Retrieved 18 October2012.

[66] “NASA – Q&A on the GLAST Mission”. Nasa: FermiGamma-ray Space Telescope. NASA. 28 August 2008.Retrieved 29 April 2009.

[67] See also Nasa – Fermi Science and NASA – ScientistsPredict Major Discoveries for GLAST.

[68] “Dark Matter”. Nasa.gov. 28 August 2008. Retrieved 30January 2012.

[69] Kerr 2009

[70] DØ Collaboration 2007 finds a mass of 5.774 GeV for theΞ−

b

[71] National Research Council & Committee on Technologyfor Future Naval Forces 1997, p. 161

[72] Kellert 1993, p. 32

[73] Burchard 2002, p. 2

[74] See the work of Ilya Prigogine, on 'systems far from equi-librium', and others, e.g., Heinrich M. Jaeger, Andrea J.Liu (24 Sep 2010) “Far-From-Equilibrium Physics: AnOverview” http://arxiv.org/abs/1009.4874

[75] Goldstein 1969

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13

11 External links

General

• Encyclopedia of Physics at Scholarpedia

• de Haas, Paul, Historic Papers in Physics (20th Cen-tury) at the Wayback Machine (archived August 26,2009)

• PhysicsCentral – Web portal run by the AmericanPhysical Society

• Physics.org – Web portal run by the Institute ofPhysics

• The Skeptic’s Guide to Physics

• Usenet Physics FAQ – A FAQ compiled bysci.physics and other physics newsgroups

• Website of the Nobel Prize in physics

• World of Physics An online encyclopedic dictionaryof physics

• Nature: Physics

• Physics announced 17 July 2008 by the AmericanPhysical Society

• Physics/Publications at DMOZ

• Physicsworld.com – News website from Institute ofPhysics Publishing

• Physics Central – includes articles on astronomy,particle physics, and mathematics.

• The Vega Science Trust – science videos, includingphysics

• Video: Physics “Lightning” Tour with Justin Mor-gan

• 52-part video course: The Mechanical Uni-verse...and Beyond Note: also available at 01 – In-troduction at Google Videos

• HyperPhysics website –HyperPhysics, a physics andastronomy mind-map from Georgia State University

Organizations

• AIP.org – Website of the American Institute ofPhysics

• APS.org – Website of the American Physical Soci-ety

• IOP.org – Website of the Institute of Physics

• PlanetPhysics.org

• Royal Society – Although not exclusively a physicsinstitution, it has a strong history of physics

• SPS National – Website of the Society of PhysicsStudents

14 11 EXTERNAL LINKS

Mathematics and ontology are used in physics. Physics is used inchemistry and cosmology.

The distinction between mathematics and physics is clear-cut, butnot always obvious, especially in mathematical physics.

Archimedes’ screw, a simple machine for lifting

The application of physical laws in lifting liquids

15

The astronaut and Earth are both in free-fall

Lightning is an electric current

Physics involves modeling the natural world with theory, usuallyquantitative. Here, the path of a particle is modeled with themathematics of calculus to explain its behavior: the purview ofthe branch of physics known as mechanics.

Velocity-distribution data of a gas of rubidium atoms, confirm-ing the discovery of a new phase of matter, the Bose–Einsteincondensate

A simulated event in the CMS detector of the Large Hadron Col-lider, featuring a possible appearance of the Higgs boson.

16 11 EXTERNAL LINKS

The deepest visible-light image of the universe, the Hubble UltraDeep Field

Feynman diagram signed by R.P. Feynman

A typical event described by physics: a magnet levitating above asuperconductor demonstrates the Meissner effect.

17

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18 12 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

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12.2 Images 19

12.2 Images• File:Acceleration_components.JPG Source: http://upload.wikimedia.org/wikipedia/commons/e/e4/Acceleration_components.JPG Li-cense: CC BY-SA 3.0 Contributors: Own work Original artist: Brews ohare

• File:Archimedes-screw_one-screw-threads_with-ball_3D-view_animated_small.gif Source: http://upload.wikimedia.org/wikipedia/commons/2/22/Archimedes-screw_one-screw-threads_with-ball_3D-view_animated_small.gif License: CC BY-SA 2.5 Con-tributors: File:Archimedes-screw_one-screw-threads_with-ball_3D-view_animated.gif created by Silberwolf Original artist: Silberwolf(size changed by: Jahobr)

• File:Astronaut-EVA.jpg Source: http://upload.wikimedia.org/wikipedia/commons/8/88/Astronaut-EVA.jpg License: Public domainContributors: http://grin.hq.nasa.gov/ABSTRACTS/GPN-2000-001156.html Original artist: NASA

• File:Bose_Einstein_condensate.png Source: http://upload.wikimedia.org/wikipedia/commons/a/af/Bose_Einstein_condensate.png Li-cense: Public domain Contributors: NIST Image Original artist: NIST/JILA/CU-Boulder

• File:CMS_Higgs-event.jpg Source: http://upload.wikimedia.org/wikipedia/commons/1/1c/CMS_Higgs-event.jpg License: CC BY-SA3.0 Contributors: http://cdsweb.cern.ch/record/628469 Original artist: Lucas Taylor

• File:CollageFisica.jpg Source: http://upload.wikimedia.org/wikipedia/commons/9/9a/CollageFisica.jpg License: Public domain Contrib-utors:Fastfission, United States Department of Energy, public domainOriginal artist: Aushulz

• File:Einstein1921_by_F_Schmutzer_2.jpg Source: http://upload.wikimedia.org/wikipedia/commons/a/af/Einstein1921_by_F_Schmutzer_2.jpg License: Public domain Contributors: http://www.bhm.ch/de/news_04a.cfm?bid=4&jahr=2006 Original artist:Ferdinand Schmutzer

• File:Feynman’{}sDiagram.JPG Source: http://upload.wikimedia.org/wikipedia/commons/3/3b/Feynman%27sDiagram.JPG License:CC BY-SA 2.5 Contributors: Transferred from en.wikipedia; transferred to Commons by User:Shizhao using CommonsHelper. Origi-nal artist: Original uploader was Ancheta Wis at en.wikipedia

• File:GodfreyKneller-IsaacNewton-1689.jpg Source: http://upload.wikimedia.org/wikipedia/commons/3/39/GodfreyKneller-IsaacNewton-1689.jpg License: Public domain Contributors: http://www.newton.cam.ac.uk/art/portrait.html Orig-inal artist: Sir Godfrey Kneller

• File:Hubble_ultra_deep_field_high_rez_edit1.jpg Source: http://upload.wikimedia.org/wikipedia/commons/0/0d/Hubble_ultra_deep_field_high_rez_edit1.jpg License: Public domain Contributors: http://hubblesite.org/newscenter/archive/releases/2004/07/image/a/warn/ Original artist: NASA and the European Space Agency. Edited by Noodle snacks

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• File:Ilc_9yr_moll4096.png Source: http://upload.wikimedia.org/wikipedia/commons/3/3c/Ilc_9yr_moll4096.png License: Public do-main Contributors: http://map.gsfc.nasa.gov/media/121238/ilc_9yr_moll4096.png Original artist: NASA / WMAP Science Team

• File:Lightning_in_Arlington.jpg Source: http://upload.wikimedia.org/wikipedia/commons/6/69/Lightning_in_Arlington.jpg License:CC-BY-SA-3.0 Contributors: Digital photo taken by User:Postdlf Original artist: Postdlf

• File:Mathematical_Physics_and_other_sciences.png Source: http://upload.wikimedia.org/wikipedia/commons/d/d8/Mathematical_Physics_and_other_sciences.png License: CC BY-SA 3.0 Contributors: Own work Original artist: Saeed.Veradi

• File:Max_Planck_(Nobel_1918).jpg Source: http://upload.wikimedia.org/wikipedia/commons/4/42/Max_Planck_%28Nobel_1918%29.jpg License: Public domain Contributors: http://nobelprize.org/nobel_prizes/physics/laureates/1918/planck-bio.htmlOriginal artist: ABLagrelius & Westphal. The American Institute of Physics also credits the photo [1] to AB Lagrelius & Westphal, which is the Swedishcompany used by the Nobel Foundation for most photos of its book series Les Prix Nobel.

• File:Meissner_effect_p1390048.jpg Source: http://upload.wikimedia.org/wikipedia/commons/5/55/Meissner_effect_p1390048.jpg Li-cense: CC-BY-SA-3.0 Contributors: self photo Original artist: Mai-Linh Doan

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• File:Pahoeoe_fountain_original.jpg Source: http://upload.wikimedia.org/wikipedia/commons/0/01/Pahoeoe_fountain_original.jpg Li-cense: Public domain Contributors: http://pubs.usgs.gov/dds/dds-80/ Original artist: Jim D. Griggs, HVO (USGS) staff photographer[1][2]

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• File:Prediction_of_sound_scattering_from_Schroeder_Diffuser.jpg Source: http://upload.wikimedia.org/wikipedia/commons/b/bc/Prediction_of_sound_scattering_from_Schroeder_Diffuser.jpg License: CC BY-SA 3.0 Contributors: Own work Original artist: TrevorCox

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• File:Stylised_Lithium_Atom.svg Source: http://upload.wikimedia.org/wikipedia/commons/e/e1/Stylised_Lithium_Atom.svg License:CC-BY-SA-3.0 Contributors: based off of Image:Stylised Lithium Atom.png by Halfdan. Original artist: SVG by Indolences. Recoloringand ironing out some glitches done by Rainer Klute.

20 12 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

• File:Wikibooks-logo-en-noslogan.svg Source: http://upload.wikimedia.org/wikipedia/commons/d/df/Wikibooks-logo-en-noslogan.svg License: CC BY-SA 3.0 Contributors: Own work Original artist: User:Bastique, User:Ramac et al.

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