Physics is the
natural science that studies
matter, its
fundamental constituents, its
motion and behavior through
space and time, and the related entities of
energy and
force.
[ "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular succession of events."] Physics is one of the most fundamental
scientific disciplines, with its main goal being to understand how the
universe
The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the univers ...
behaves.
[ "Physics is one of the most fundamental of the sciences. Scientists of all disciplines use the ideas of physics, including chemists who study the structure of molecules, paleontologists who try to reconstruct how dinosaurs walked, and climatologists who study how human activities affect the atmosphere and oceans. Physics is also the foundation of all engineering and technology. No engineer could design a flat-screen TV, an interplanetary spacecraft, or even a better mousetrap without first understanding the basic laws of physics. (...) You will come to see physics as a towering achievement of the human intellect in its quest to understand our world and ourselves."][ "Physics is an experimental science. Physicists observe the phenomena of nature and try to find patterns that relate these phenomena."][ "Physics is the study of your world and the world and universe around you."] A
scientist who specializes in the field of physics is called a
physicist.
Physics is one of the oldest
academic discipline
An academy (Attic Greek: Ἀκαδήμεια; Koine Greek Ἀκαδημία) is an institution of secondary education, secondary or tertiary education, tertiary higher education, higher learning (and generally also research or honorary membershi ...
s and, through its inclusion of
astronomy
Astronomy () is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, g ...
, perhaps ''the'' oldest.
Over much of the past two millennia, physics,
chemistry
Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, proper ...
,
biology, and certain branches of
mathematics
Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics ...
were a part of
natural philosophy, but during the
Scientific Revolution in the 17th century these natural sciences emerged as unique research endeavors in their own right. Physics intersects with many
interdisciplinary areas of research, such as
biophysics and
quantum chemistry, and the boundaries of physics are not
rigidly defined. New ideas in physics often explain the fundamental mechanisms studied by other
sciences
and suggest new avenues of research in these and other academic disciplines such as mathematics and
philosophy
Philosophy (from , ) is the systematized study of general and fundamental questions, such as those about existence, reason, knowledge, values, mind, and language. Such questions are often posed as problems to be studied or resolved. ...
.
Advances in physics often enable advances in new
technologies. For example, advances in the understanding of
electromagnetism,
solid-state physics, and
nuclear physics led directly to the development of new products that have dramatically transformed modern-day society, such as
television
Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertising, ...
,
computer
A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations ( computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These prog ...
s,
domestic appliances, and
nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions ( thermonuclear bomb), producing a nuclear explosion. Both bomb ...
s;
advances in
thermodynamics led to the development of
industrialization; and advances in
mechanics inspired the development of
calculus
Calculus, originally called infinitesimal calculus or "the calculus of infinitesimals", is the mathematics, mathematical study of continuous change, in the same way that geometry is the study of shape, and algebra is the study of generalizati ...
.
History
The word "physics" comes from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), meaning "knowledge of nature".
[, , ]
Ancient astronomy
Astronomy
Astronomy () is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, g ...
is one of the oldest
natural sciences. Early civilizations dating back before 3000 BCE, such as the
Sumerians,
ancient Egyptians, and the
Indus Valley Civilisation, had a predictive knowledge and a basic awareness of the motions of the Sun, Moon, and stars. The stars and planets, believed to represent gods, were often worshipped. While the explanations for the observed positions of the stars were often unscientific and lacking in evidence, these early observations laid the foundation for later astronomy, as the stars were found to traverse
great circles across the sky,
which could not explain the positions of the
planets.
According to
Asger Aaboe
Asger Hartvig Aaboe (26 April 1922 – 19 January 2007) was a historian of the exact sciences and of mathematics who is known for his contributions to the history of ancient Babylonian astronomy. In his studies of Babylonian astronomy, he went b ...
, the origins of
Western astronomy can be found in
Mesopotamia, and all Western efforts in the
exact sciences are descended from late
Babylonian astronomy.
Egyptian astronomers
Egyptian describes something of, from, or related to Egypt.
Egyptian or Egyptians may refer to:
Nations and ethnic groups
* Egyptians, a national group in North Africa
** Egyptian culture, a complex and stable culture with thousands of years of ...
left monuments showing knowledge of the constellations and the motions of the celestial bodies,
while Greek poet
Homer wrote of various celestial objects in his ''
Iliad'' and ''
Odyssey''; later
Greek astronomers provided names, which are still used today, for most constellations visible from the
Northern Hemisphere.
Natural philosophy
Natural philosophy has its origins in
Greece
Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders wi ...
during the
Archaic period (650 BCE – 480 BCE), when
pre-Socratic philosophers
Pre-Socratic philosophy, also known as early Greek philosophy, is ancient Greek philosophy before Socrates. Pre-Socratic philosophers were mostly interested in cosmology, the beginning and the substance of the universe, but the inquiries of th ...
like
Thales rejected
non-naturalistic explanations for natural phenomena and proclaimed that every event had a natural cause.
They proposed ideas verified by reason and observation, and many of their hypotheses proved successful in experiment;
for example,
atomism was found to be correct approximately 2000 years after it was proposed by
Leucippus and his pupil
Democritus.
[
]
Medieval European and Islamic
The
Western Roman Empire fell in the fifth century, and this resulted in a decline in intellectual pursuits in the western part of Europe. By contrast, the
Eastern Roman Empire (also known as the
Byzantine Empire) resisted the attacks from the barbarians, and continued to advance various fields of learning, including physics.
In the sixth century,
Isidore of Miletus created an important compilation of
Archimedes' works that are copied in the
Archimedes Palimpsest.
In sixth-century Europe
John Philoponus, a Byzantine scholar, questioned
Aristotle
Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of ...
's teaching of physics and noted its flaws. He introduced the
theory of impetus. Aristotle's physics was not scrutinized until Philoponus appeared; unlike Aristotle, who based his physics on verbal argument, Philoponus relied on observation. On Aristotle's physics Philoponus wrote:
But this is completely erroneous, and our view may be corroborated by actual observation more effectively than by any sort of verbal argument. For if you let fall from the same height two weights of which one is many times as heavy as the other, you will see that the ratio of the times required for the motion does not depend on the ratio of the weights, but that the difference in time is a very small one. And so, if the difference in the weights is not considerable, that is, of one is, let us say, double the other, there will be no difference, or else an imperceptible difference, in time, though the difference in weight is by no means negligible, with one body weighing twice as much as the other
Philoponus' criticism of Aristotelian principles of physics served as an inspiration for
Galileo Galilei
Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He ...
ten centuries later,
during the
Scientific Revolution. Galileo cited Philoponus substantially in his works when arguing that Aristotelian physics was flawed. In the 1300s
Jean Buridan, a teacher in the faculty of arts at the
University of Paris, developed the concept of impetus. It was a step toward the modern ideas of inertia and momentum.
Islamic scholarship inherited
Aristotelian physics from the Greeks and during the
Islamic Golden Age developed it further, especially placing emphasis on observation and ''
a priori
("from the earlier") and ("from the later") are Latin phrases used in philosophy to distinguish types of knowledge, justification, or argument by their reliance on empirical evidence or experience. knowledge is independent from current ex ...
'' reasoning, developing early forms of the
scientific method.
Although
Aristotle’s principles of physics was criticized, it is important to identify his the evidence he based his views off of. When thinking of the history of science and math, it is notable to acknowledge the contributions made by older scientists. Aristotle’s science was the backbone of the science we learn in schools today. Aristotle published many biological works including ''
The Parts of Animals,'' in which he discusses both biological science and natural science as well. It is also integral to mention the role Aristotle had in the progression of physics and metaphysics and how his beliefs and findings are still being taught in science classes to this day. The explanations that Aristotle gives for his findings are also very simple. When thinking of the elements, Aristotle believed that each element (earth, fire, water, air
had its own natural place Meaning that because of the density of these elements, they will revert back to their own specific place in the atmosphere. So, because of their weights, fire would be at the very top, air right underneath fire, then water, then lastly earth. He also stated that when a small amount of one element enters the natural place of another, the less abundant element will automatically go into its own natural place. For example, if there is a fire on the ground, if you pay attention, the flames go straight up into the air as an attempt to go back into its natural place where it belongs. Aristotle called his
metaphysics “first philosophy” and characterized it as the study of “being as being”.
Aristotle defined the paradigm of motion as a being or entity encompassing different areas in the same body.
Meaning that if a person is at a certain location (A) they can move to a new location (B) and still take up the same amount of space. This is involved with Aristotle’s belief that motion is a continuum. In terms of matter, Aristotle believed that the change in category (ex. place) and quality (ex. color) of an object is defined as “alteration”. But, a change in substance is a change in matter. This is also very close to our idea of matter today.
He also devised his own laws of motion that include 1) heavier objects will fall faster, the speed being proportional to the weight and 2) the speed of the object that is falling depends inversely on the density object it is falling through (ex. density of air).
He also stated that, when it comes to violent motion (motion of an object when a force is applied to it by a second object) that the speed that object moves, will only be as fast or strong as the measure of force applied to it.
This is also seen in the rules of velocity and force that is taught in physics classes today. These rules are not necessarily what we see in our physics today but, they are very similar. It is evident that these rules were the backbone for other scientists to come revise and edit his beliefs.
The most notable innovations were in the field of
optics and vision, which came from the works of many scientists like
Ibn Sahl,
Al-Kindi,
Ibn al-Haytham,
Al-Farisi and
Avicenna. The most notable work was ''
The Book of Optics'' (also known as Kitāb al-Manāẓir), written by Ibn al-Haytham, in which he conclusively disproved the ancient Greek idea about vision and came up with a new theory. In the book, he presented a study of the phenomenon of the
camera obscura (his thousand-year-old version of the
pinhole camera) and delved further into the way the
eye itself works. Using dissections and the knowledge of previous scholars, he was able to begin to explain how light enters the eye. He asserted that the light ray is focused, but the actual explanation of how light projected to the back of the eye had to wait until 1604. His ''Treatise on Light'' explained the camera obscura, hundreds of years before the modern development of photography.
The seven-volume ''Book of Optics'' (''Kitab al-Manathir'') hugely influenced thinking across disciplines from the theory of visual
perception to the nature of
perspective in medieval art, in both the East and the West, for more than 600 years. Many later European scholars and fellow polymaths, from
Robert Grosseteste and
Leonardo da Vinci to
René Descartes
René Descartes ( or ; ; Latinized: Renatus Cartesius; 31 March 1596 – 11 February 1650) was a French philosopher, scientist, and mathematician, widely considered a seminal figure in the emergence of modern philosophy and science. Ma ...
,
Johannes Kepler and
Isaac Newton, were in his debt. Indeed, the influence of Ibn al-Haytham's Optics ranks alongside that of Newton's work of the same title, published 700 years later.
The translation of ''The Book of Optics'' had a huge impact on Europe. From it, later European scholars were able to build devices that replicated those Ibn al-Haytham had built and understand the way light works. From this, important inventions such as eyeglasses, magnifying glasses, telescopes, and cameras were developed.
Classical
Physics became a separate science when
early modern Europeans used experimental and quantitative methods to discover what are now considered to be the
laws of physics.
Major developments in this period include the replacement of the
geocentric model of the
Solar System with the heliocentric
Copernican model
Copernican heliocentrism is the astronomical model developed by Nicolaus Copernicus and published in 1543. This model positioned the Sun at the center of the Universe, motionless, with Earth and the other planets orbiting around it in circula ...
, the
laws governing the motion of planetary bodies (determined by Kepler between 1609 and 1619), Galileo's pioneering work on
telescopes and
observational astronomy in the 16th and 17th Centuries, and
Isaac Newton's discovery and unification of the
laws of motion and
universal gravitation (that would come to bear his name). Newton also developed
calculus
Calculus, originally called infinitesimal calculus or "the calculus of infinitesimals", is the mathematics, mathematical study of continuous change, in the same way that geometry is the study of shape, and algebra is the study of generalizati ...
, the mathematical study of continuous change, which provided new mathematical methods for solving physical problems.
The discovery of new laws in
thermodynamics,
chemistry
Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, proper ...
, and
electromagnetics resulted from research efforts during the
Industrial Revolution as energy needs increased.
The laws comprising classical physics remain very widely used for objects on everyday scales travelling at non-relativistic speeds, since they provide a very close approximation in such situations, and theories such as
quantum mechanics and the
theory of relativity simplify to their classical equivalents at such scales. Inaccuracies in
classical mechanics for very small objects and very high velocities led to the development of modern physics in the 20th century.
Modern
Modern physics began in the early 20th century with the work of
Max Planck in quantum theory and
Albert Einstein's theory of relativity. Both of these theories came about due to inaccuracies in classical mechanics in certain situations.
Classical mechanics predicted that the
speed of light depends on the motion of the observer, which could not be resolved with the constant speed predicted by
Maxwell's equations of electromagnetism. This discrepancy was corrected by Einstein's theory of
special relativity, which replaced classical mechanics for fast-moving bodies and allowed for a constant speed of light.
Black-body radiation provided another problem for classical physics, which was corrected when Planck proposed that the excitation of material oscillators is possible only in discrete steps proportional to their frequency. This, along with the
photoelectric effect and a complete theory predicting discrete
energy levels of
electron orbitals, led to the theory of quantum mechanics improving on classical physics at very small scales.
Quantum mechanics would come to be pioneered by
Werner Heisenberg,
Erwin Schrödinger and
Paul Dirac.
From this early work, and work in related fields, the
Standard Model of particle physics was derived.
Following the discovery of a particle with properties consistent with the
Higgs boson at
CERN in 2012,
all
fundamental particles
In particle physics, an elementary particle or fundamental particle is a subatomic particle that is not composed of other particles. Particles currently thought to be elementary include electrons, the fundamental fermions (quarks, leptons, anti ...
predicted by the standard model, and no others, appear to exist; however,
physics beyond the Standard Model, with theories such as
supersymmetry, is an active area of research. Areas of
mathematics
Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics ...
in general are important to this field, such as the study of
probabilities and
groups
A group is a number of persons or things that are located, gathered, or classed together.
Groups of people
* Cultural group, a group whose members share the same cultural identity
* Ethnic group, a group whose members share the same ethnic ide ...
.
Philosophy
In many ways, physics stems from
ancient Greek philosophy. From
Thales' first attempt to characterize matter, to
Democritus' deduction that matter ought to reduce to an invariant state the
Ptolemaic astronomy
In astronomy, the geocentric model (also known as geocentrism, often exemplified specifically by the Ptolemaic system) is a superseded description of the Universe with Earth at the center. Under most geocentric models, the Sun, Moon, stars, ...
of a crystalline
firmament, and Aristotle's book ''
Physics'' (an early book on physics, which attempted to analyze and define motion from a philosophical point of view), various Greek philosophers advanced their own theories of nature. Physics was known as natural philosophy until the late 18th century.
By the 19th century, physics was realized as a discipline distinct from philosophy and the other sciences. Physics, as with the rest of science, relies on
philosophy of science and its "
scientific method" to advance our knowledge of the physical world.
The scientific method employs ''
a priori reasoning'' as well as ''
a posteriori
("from the earlier") and ("from the later") are Latin phrases used in philosophy to distinguish types of knowledge, justification, or argument by their reliance on empirical evidence or experience. knowledge is independent from current ex ...
'' reasoning and the use of
Bayesian inference to measure the validity of a given theory.
The development of physics has answered many questions of early philosophers but has also raised new questions. Study of the philosophical issues surrounding physics, the
philosophy of physics, involves issues such as the nature of
space and
time,
determinism, and
metaphysical outlooks such as
empiricism,
naturalism and
realism
Realism, Realistic, or Realists may refer to:
In the arts
*Realism (arts), the general attempt to depict subjects truthfully in different forms of the arts
Arts movements related to realism include:
* Classical Realism
*Literary realism, a mov ...
.
Many physicists have written about the philosophical implications of their work, for instance
Laplace, who championed
causal determinism,
and
Erwin Schrödinger, who wrote on quantum mechanics.
The mathematical physicist
Roger Penrose has been called a
Platonist by
Stephen Hawking,
[ "I think that Roger is a Platonist at heart but he must answer for himself."] a view Penrose discusses in his book, ''
The Road to Reality''.
Hawking referred to himself as an "unashamed reductionist" and took issue with Penrose's views.
Core theories
Though physics deals with a wide variety of systems, certain theories are used by all physicists. Each of these theories was experimentally tested numerous times and found to be an adequate approximation of nature. For instance, the theory of
classical mechanics accurately describes the motion of objects, provided they are much larger than
atoms and moving at a speed much less than the speed of light. These theories continue to be areas of active research today.
Chaos theory, a remarkable aspect of classical mechanics, was discovered in the 20th century, three centuries after the original formulation of classical mechanics by Newton (1642–1727).
These central theories are important tools for research into more specialized topics, and any physicist, regardless of their specialization, is expected to be literate in them. These include classical mechanics, quantum mechanics, thermodynamics and
statistical mechanics,
electromagnetism, and special relativity.
Classical
Classical physics includes the traditional branches and topics that were recognized and well-developed before the beginning of the 20th century—classical mechanics,
acoustics,
optics, thermodynamics, and electromagnetism. Classical mechanics is concerned with bodies acted on by
forces and bodies in
motion and may be divided into
statics (study of the forces on a body or bodies not subject to an acceleration),
kinematics (study of motion without regard to its causes), and
dynamics (study of motion and the forces that affect it); mechanics may also be divided into
solid mechanics and
fluid mechanics (known together as
continuum mechanics), the latter include such branches as
hydrostatics,
hydrodynamics,
aerodynamics, and
pneumatics. Acoustics is the study of how sound is produced, controlled, transmitted and received.
Important modern branches of acoustics include
ultrasonics, the study of sound waves of very high frequency beyond the range of human hearing;
bioacoustics, the physics of animal calls and hearing, and
electroacoustics, the manipulation of audible sound waves using electronics.
Optics, the study of
light, is concerned not only with
visible light but also with
infrared and
ultraviolet radiation, which exhibit all of the phenomena of visible light except visibility, e.g., reflection, refraction, interference, diffraction, dispersion, and polarization of light.
Heat is a form of
energy, the internal energy possessed by the particles of which a substance is composed; thermodynamics deals with the relationships between heat and other forms of energy.
Electricity and
magnetism have been studied as a single branch of physics since the intimate connection between them was discovered in the early 19th century; an
electric current gives rise to a
magnetic field, and a changing magnetic field induces an electric current.
Electrostatics deals with
electric charges at rest,
electrodynamics with moving charges, and
magnetostatics with magnetic poles at rest.
Modern
Classical physics is generally concerned with matter and energy on the normal scale of observation, while much of modern physics is concerned with the behavior of matter and energy under extreme conditions or on a very large or very small scale. For example,
atomic and
nuclear physics study matter on the smallest scale at which
chemical elements can be identified. The
physics of elementary particles is on an even smaller scale since it is concerned with the most basic units of matter; this branch of physics is also known as high-energy physics because of the extremely high energies necessary to produce many types of particles in
particle accelerators. On this scale, ordinary, commonsensical notions of space, time, matter, and energy are no longer valid.
The two chief theories of modern physics present a different picture of the concepts of space, time, and matter from that presented by classical physics. Classical mechanics approximates nature as continuous, while quantum theory is concerned with the discrete nature of many phenomena at the atomic and subatomic level and with the complementary aspects of particles and waves in the description of such phenomena. The theory of relativity is concerned with the description of phenomena that take place in a
frame of reference that is in motion with respect to an observer; the special theory of relativity is concerned with motion in the absence of gravitational fields and the
general theory of relativity with motion and its connection with
gravitation. Both quantum theory and the theory of relativity find applications in many areas of modern physics.
Fundamental concepts in modern physics
*
Causality
*
Covariance
*
Action
*
Physical field
*
Symmetry
*
Physical interaction
*
Statistical ensemble
*
Quantum
*
Wave
*
Particle
Difference
While physics aims to discover universal laws, its theories lie in explicit domains of applicability.
Loosely speaking, the laws of classical physics accurately describe systems whose important length scales are greater than the atomic scale and whose motions are much slower than the speed of light. Outside of this domain, observations do not match predictions provided by classical mechanics. Einstein contributed the framework of special relativity, which replaced notions of
absolute time and space
Absolute space and time is a concept in physics and philosophy about the properties of the universe. In physics, absolute space and time may be a preferred frame.
Before Newton
A version of the concept of absolute space (in the sense of a preferr ...
with
spacetime and allowed an accurate description of systems whose components have speeds approaching the speed of light. Planck, Schrödinger, and others introduced quantum mechanics, a probabilistic notion of particles and interactions that allowed an accurate description of atomic and subatomic scales. Later,
quantum field theory unified quantum mechanics and special relativity. General relativity allowed for a dynamical, curved spacetime, with which highly massive systems and the large-scale structure of the universe can be well-described. General relativity has not yet been unified with the other fundamental descriptions; several candidate theories of
quantum gravity are being developed.
Relation to other fields
Prerequisites
Mathematics provides a compact and exact language used to describe the order in nature. This was noted and advocated by
Pythagoras,
Plato,
[ "Although usually remembered today as a philosopher, Plato was also one of ancient Greece's most important patrons of mathematics. Inspired by Pythagoras, he founded his Academy in Athens in 387 BC, where he stressed mathematics as a way of understanding more about reality. In particular, he was convinced that geometry was the key to unlocking the secrets of the universe. The sign above the Academy entrance read: 'Let no-one ignorant of geometry enter here.'"] Galileo,
[ 'Philosophy is written in that great book which ever lies before our eyes. I mean the universe, but we cannot understand it if we do not first learn the language and grasp the symbols in which it is written. This book is written in the mathematical language, and the symbols are triangles, circles, and other geometrical figures, without whose help it is humanly impossible to comprehend a single word of it, and without which one wanders in vain through a dark labyrinth.' – Galileo (1623), '']The Assayer
''The Assayer'' ( it, Il Saggiatore) was a book published in Rome by Galileo Galilei in October 1623 and is generally considered to be one of the pioneering works of the scientific method, first broaching the idea that the book of nature is t ...
''" and Newton.
Physics uses mathematics
to organise and formulate experimental results. From those results,
precise
Precision, precise or precisely may refer to:
Science, and technology, and mathematics Mathematics and computing (general)
* Accuracy and precision, measurement deviation from true value and its scatter
* Significant figures, the number of digit ...
or
estimated
Estimation (or estimating) is the process of finding an estimate or approximation, which is a value that is usable for some purpose even if input data may be incomplete, uncertain, or unstable. The value is nonetheless usable because it is der ...
solutions are obtained, or quantitative results, from which new predictions can be made and experimentally confirmed or negated. The results from physics experiments are numerical data, with their
units of measure and estimates of the errors in the measurements. Technologies based on mathematics, like
computation have made
computational physics an active area of research.
Ontology
In metaphysics, ontology is the philosophy, philosophical study of being, as well as related concepts such as existence, Becoming (philosophy), becoming, and reality.
Ontology addresses questions like how entities are grouped into Category ...
is a prerequisite for physics, but not for mathematics. It means physics is ultimately concerned with descriptions of the real world, while mathematics is concerned with abstract patterns, even beyond the real world. Thus physics statements are synthetic, while mathematical statements are analytic. Mathematics contains hypotheses, while physics contains theories. Mathematics statements have to be only logically true, while predictions of physics statements must match observed and experimental data.
The distinction is clear-cut, but not always obvious. For example,
mathematical physics is the application of mathematics in physics. Its methods are mathematical, but its subject is physical.
The problems in this field start with a "
mathematical model of a physical situation" (system) and a "mathematical description of a physical law" that will be applied to that system. Every mathematical statement used for solving has a hard-to-find physical meaning. The final mathematical solution has an easier-to-find meaning, because it is what the solver is looking for.
Pure physics is a branch of
fundamental science (also called basic science). Physics is also called "''the'' fundamental science" because all branches of natural science like chemistry, astronomy, geology, and biology are constrained by laws of physics.
[The Feynman Lectures on Physics Vol. I Ch. 3: The Relation of Physics to Other Sciences](_blank)
see also reductionism and special sciences Similarly, chemistry is often called
the central science
Chemistry is often called the central science because of its role in connecting the physical sciences, which include chemistry, with the life sciences and applied sciences such as medicine and engineering. The nature of this relationship is one ...
because of its role in linking the physical sciences. For example, chemistry studies properties, structures, and
reactions
Reaction may refer to a process or to a response to an action, event, or exposure:
Physics and chemistry
*Chemical reaction
*Nuclear reaction
* Reaction (physics), as defined by Newton's third law
*Chain reaction (disambiguation).
Biology and m ...
of matter (chemistry's focus on the molecular and atomic scale
distinguishes it from physics). Structures are formed because particles exert electrical forces on each other, properties include physical characteristics of given substances, and reactions are bound by laws of physics, like
conservation of energy,
mass, and
charge. Physics is applied in industries like engineering and medicine.
Application and influence
Applied physics
Applied physics is the application of physics to solve scientific or engineering problems. It is usually considered to be a bridge or a connection between physics and engineering.
"Applied" is distinguished from "pure" by a subtle combination ...
is a general term for physics research, which is intended for a particular use. An applied physics curriculum usually contains a few classes in an applied discipline, like geology or electrical engineering. It usually differs from
engineering
Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad range of more speciali ...
in that an applied physicist may not be designing something in particular, but rather is using physics or conducting physics research with the aim of developing new technologies or solving a problem.
The approach is similar to that of
applied mathematics. Applied physicists use physics in scientific research. For instance, people working on
accelerator physics might seek to build better
particle detectors for research in theoretical physics.
Physics is used heavily in engineering. For example, statics, a subfield of
mechanics, is used in the building of
bridges and other static structures. The understanding and use of acoustics results in sound control and better concert halls; similarly, the use of optics creates better optical devices. An understanding of physics makes for more realistic
flight simulators,
video games, and movies, and is often critical in
forensic investigations.
With the
standard consensus that the
laws of physics are universal and do not change with time, physics can be used to study things that would ordinarily be mired in
uncertainty. For example, in the
study of the origin of the earth, one can reasonably model earth's mass, temperature, and rate of rotation, as a function of time allowing one to extrapolate forward or backward in time and so predict future or prior events. It also allows for simulations in engineering that drastically speed up the development of a new technology.
But there is also considerable
interdisciplinarity, so many other important fields are influenced by physics (e.g., the fields of
econophysics and
sociophysics).
Research
Scientific method
Physicists use the scientific method to test the validity of a
physical theory. By using a methodical approach to compare the implications of a theory with the conclusions drawn from its related
experiments and observations, physicists are better able to test the validity of a theory in a logical, unbiased, and repeatable way. To that end, experiments are performed and observations are made in order to determine the validity or invalidity of the theory.
A scientific law is a concise verbal or mathematical statement of a relation that expresses a fundamental principle of some theory, such as Newton's law of universal gravitation.
Theory and experiment
Theorists seek to develop
mathematical models that both agree with existing experiments and successfully predict future experimental results, while
experimentalists devise and perform experiments to test theoretical predictions and explore new phenomena. Although
theory and experiment are developed separately, they strongly affect and depend upon each other. Progress in physics frequently comes about when experimental results defy explanation by existing theories, prompting intense focus on applicable modelling, and when new theories generate experimentally testable
predictions, which inspire the development of new experiments (and often related equipment).
Physicists who work at the interplay of theory and experiment are called
phenomenologists, who study complex phenomena observed in experiment and work to relate them to a
fundamental theory.
Theoretical physics has historically taken inspiration from philosophy; electromagnetism was unified this way. Beyond the known universe, the field of theoretical physics also deals with hypothetical issues, such as
parallel universes, a
multiverse, and
higher dimensions. Theorists invoke these ideas in hopes of solving particular problems with existing theories; they then explore the consequences of these ideas and work toward making testable predictions.
Experimental physics expands, and is expanded by, engineering and
technology
Technology is the application of knowledge to reach practical goals in a specifiable and reproducible way. The word ''technology'' may also mean the product of such an endeavor. The use of technology is widely prevalent in medicine, scien ...
. Experimental physicists who are involved in
basic research design and perform experiments with equipment such as particle accelerators and
lasers, whereas those involved in
applied research often work in industry, developing technologies such as
magnetic resonance imaging (MRI) and
transistors.
Feynman has noted that experimentalists may seek areas that have not been explored well by theorists.
[ "In fact experimenters have a certain individual character. They ... very often do their experiments in a region in which people know the theorist has not made any guesses."]
Scope and aims
Physics covers a wide range of
phenomena, from
elementary particles (such as quarks, neutrinos, and electrons) to the largest
supercluster
A supercluster is a large group of smaller galaxy clusters or galaxy groups; they are among the largest known structures in the universe. The Milky Way is part of the Local Group galaxy group (which contains more than 54 galaxies), which in t ...
s of galaxies. Included in these phenomena are the most basic objects composing all other things. Therefore, physics is sometimes called the "fundamental science".
Physics aims to describe the various phenomena that occur in nature in terms of simpler phenomena. Thus, physics aims to both connect the things observable to humans to root causes, and then connect these causes together.
For example, the
ancient Chinese observed that certain rocks (
lodestone and
magnetite) were attracted to one another by an invisible force. This effect was later called magnetism, which was first rigorously studied in the 17th century. But even before the Chinese discovered magnetism, the
ancient Greeks knew of other objects such as
amber, that when rubbed with fur would cause a similar invisible attraction between the two.
This was also first studied rigorously in the 17th century and came to be called electricity. Thus, physics had come to understand two observations of nature in terms of some root cause (electricity and magnetism). However, further work in the 19th century revealed that these two forces were just two different aspects of one force—electromagnetism. This process of "unifying" forces continues today, and electromagnetism and the
weak nuclear force
In nuclear physics and particle physics, the weak interaction, which is also often called the weak force or weak nuclear force, is one of the four known fundamental interactions, with the others being electromagnetism, the strong interacti ...
are now considered to be two aspects of the
electroweak interaction. Physics hopes to find an ultimate reason (theory of everything) for why nature is as it is (see section ''
Current research'' below for more information).
Research fields
Contemporary research in physics can be broadly divided into nuclear and particle physics;
condensed matter physics;
atomic, molecular, and optical physics;
astrophysics; and applied physics. Some physics departments also support
physics education research
Physics education research (PER) is a form of discipline-based education research specifically related to the study of the teaching and learning of physics, often with the aim of improving the effectiveness of student learning. Approximatel ...
and
physics outreach.
Since the 20th century, the individual fields of physics have become increasingly specialised, and today most physicists work in a single field for their entire careers. "Universalists" such as Einstein (1879–1955) and
Lev Landau (1908–1968), who worked in multiple fields of physics, are now very rare.
The major fields of physics, along with their subfields and the theories and concepts they employ, are shown in the following table.
Nuclear and particle
Particle physics is the study of the elementary constituents of
matter and energy and the
interactions
Interaction is action that occurs between two or more objects, with broad use in philosophy and the sciences. It may refer to:
Science
* Interaction hypothesis, a theory of second language acquisition
* Interaction (statistics)
* Interactions ...
between them.
In addition, particle physicists design and develop the high-energy accelerators,
detectors,
and
computer programs
A computer program is a sequence or set of instructions in a programming language for a computer to execute. Computer programs are one component of software, which also includes documentation and other intangible components.
A computer prog ...
necessary for this research. The field is also called "high-energy physics" because many elementary particles do not occur naturally but are created only during high-energy
collisions of other particles.
Currently, the interactions of elementary particles and
fields are described by the
Standard Model.
The model accounts for the 12 known particles of matter (
quarks and
leptons) that interact via the
strong
Strong may refer to:
Education
* The Strong, an educational institution in Rochester, New York, United States
* Strong Hall (Lawrence, Kansas), an administrative hall of the University of Kansas
* Strong School, New Haven, Connecticut, United S ...
, weak, and electromagnetic
fundamental forces.
Dynamics are described in terms of matter particles exchanging
gauge bosons (
gluons,
W and Z bosons, and
photons, respectively).
The Standard Model also predicts a particle known as the Higgs boson.
In July 2012 CERN, the European laboratory for particle physics, announced the detection of a particle consistent with the Higgs boson,
an integral part of the
Higgs mechanism
In the Standard Model of particle physics, the Higgs mechanism is essential to explain the generation mechanism of the property " mass" for gauge bosons. Without the Higgs mechanism, all bosons (one of the two classes of particles, the other b ...
.
Nuclear physics is the field of physics that studies the constituents and interactions of
atomic nuclei. The most commonly known applications of nuclear physics are
nuclear power generation and
nuclear weapons technology, but the research has provided application in many fields, including those in
nuclear medicine and magnetic resonance imaging,
ion implantation in
materials engineering, and
radiocarbon dating in
geology and
archaeology
Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landsc ...
.
Atomic, molecular, and optical
Atomic,
molecular, and optical physics (AMO) is the study of matter–matter and light–matter interactions on the scale of single atoms and molecules. The three areas are grouped together because of their interrelationships, the similarity of methods used, and the commonality of their relevant energy scales. All three areas include both classical, semi-classical and
quantum treatments; they can treat their subject from a microscopic view (in contrast to a macroscopic view).
Atomic physics studies the
electron shells of atoms. Current research focuses on activities in quantum control, cooling and trapping of atoms and ions, low-temperature collision dynamics and the effects of electron correlation on structure and dynamics. Atomic physics is influenced by the
nucleus
Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to:
* Atomic nucleus, the very dense central region of an atom
*Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA
Nucl ...
(see
hyperfine splitting
In atomic physics, hyperfine structure is defined by small shifts in otherwise degenerate energy levels and the resulting splittings in those energy levels of atoms, molecules, and ions, due to electromagnetic multipole interaction between the ...
), but intra-nuclear phenomena such as
fission and
fusion are considered part of nuclear physics.
Molecular physics focuses on multi-atomic structures and their internal and external interactions with matter and light.
Optical physics is distinct from optics in that it tends to focus not on the control of classical light fields by macroscopic objects but on the fundamental properties of
optical fields and their interactions with matter in the microscopic realm.
Condensed matter
Condensed matter physics is the field of physics that deals with the macroscopic physical properties of matter.
In particular, it is concerned with the "condensed"
phases that appear whenever the number of particles in a system is extremely large and the interactions between them are strong.
The most familiar examples of condensed phases are
solids and
liquids, which arise from the bonding by way of the
electromagnetic force between atoms.
More exotic condensed phases include the
superfluid and the
Bose–Einstein condensate found in certain atomic systems at very low temperature, the
superconducting phase exhibited by
conduction electron
In solid-state physics, the valence band and conduction band are the bands closest to the Fermi level, and thus determine the electrical conductivity of the solid. In nonmetals, the valence band is the highest range of electron energies in wh ...
s in certain materials,
and the
ferromagnetic and
antiferromagnet
In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules, usually related to the spins of electrons, align in a regular pattern with neighboring spins (on different sublattices) pointing in opposite directions. ...
ic phases of
spins
The spins (as in having "the spins")Diane Marie Leiva. ''The Florida State University College of Education''Women's Voices on College Drinking: The First-Year College Experience"/ref> is an adverse reaction of intoxication that causes a state of v ...
on
atomic lattices.
Condensed matter physics is the largest field of contemporary physics. Historically, condensed matter physics grew out of solid-state physics, which is now considered one of its main subfields.
The term ''condensed matter physics'' was apparently coined by
Philip Anderson when he renamed his research group—previously ''solid-state theory''—in 1967.
In 1978, the Division of Solid State Physics of the
American Physical Society was renamed as the Division of Condensed Matter Physics.
Condensed matter physics has a large overlap with chemistry,
materials science,
nanotechnology and engineering.
Astrophysics
Astrophysics and astronomy are the application of the theories and methods of physics to the study of
stellar structure,
stellar evolution, the origin of the Solar System, and related problems of
cosmology. Because astrophysics is a broad subject, astrophysicists typically apply many disciplines of physics, including mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics.
The discovery by
Karl Jansky
Karl Guthe Jansky (October 22, 1905 – February 14, 1950) was an American physicist and radio engineer who in April 1933 first announced his discovery of radio waves emanating from the Milky Way in the constellation Sagittarius. He is considered ...
in 1931 that radio signals were emitted by celestial bodies initiated the science of
radio astronomy. Most recently, the frontiers of astronomy have been expanded by space exploration. Perturbations and interference from the earth's atmosphere make space-based observations necessary for
infrared,
ultraviolet,
gamma-ray, and
X-ray astronomy.
Physical cosmology is the study of the formation and evolution of the universe on its largest scales. Albert Einstein's theory of relativity plays a central role in all modern cosmological theories. In the early 20th century,
Hubble's discovery that the universe is expanding, as shown by the
Hubble diagram
Hubble's law, also known as the Hubble–Lemaître law, is the observation in physical cosmology that galaxies are moving away from Earth at speeds proportional to their distance. In other words, the farther they are, the faster they are moving a ...
, prompted rival explanations known as the
steady state universe and the
Big Bang.
The Big Bang was confirmed by the success of
Big Bang nucleosynthesis and the discovery of the
cosmic microwave background in 1964. The Big Bang model rests on two theoretical pillars: Albert Einstein's general relativity and the
cosmological principle
In modern physical cosmology, the cosmological principle is the notion that the spatial distribution of matter in the universe is homogeneous and isotropic when viewed on a large enough scale, since the forces are expected to act uniformly throu ...
. Cosmologists have recently established the
ΛCDM model
The ΛCDM (Lambda cold dark matter) or Lambda-CDM model is a parameterization of the Big Bang cosmological model in which the universe contains three major components: first, a cosmological constant denoted by Lambda (Greek Λ) associated with d ...
of the evolution of the universe, which includes
cosmic inflation,
dark energy, and
dark matter
Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not ...
.
Numerous possibilities and discoveries are anticipated to emerge from new data from the
Fermi Gamma-ray Space Telescope over the upcoming decade and vastly revise or clarify existing models of the universe.
In particular, the potential for a tremendous discovery surrounding dark matter is possible over the next several years.
Fermi will search for evidence that dark matter is composed of
weakly interacting massive particles, complementing similar experiments with the
Large Hadron Collider and other underground detectors.
IBEX
An ibex (plural ibex, ibexes or ibices) is any of several species of wild goat (genus ''Capra''), distinguished by the male's large recurved horns, which are transversely ridged in front. Ibex are found in Eurasia, North Africa and East Africa ...
is already yielding new
astrophysical discoveries: "No one knows what is creating the
ENA (energetic neutral atoms) ribbon" along the
termination shock
The heliosphere is the magnetosphere, astrosphere and outermost atmospheric layer of the Sun. It takes the shape of a vast, bubble-like region of space. In plasma physics terms, it is the cavity formed by the Sun in the surrounding interstell ...
of the
solar wind, "but everyone agrees that it means the textbook picture of the
heliosphere—in which the Solar System's enveloping pocket filled with the solar wind's charged particles is plowing through the onrushing 'galactic wind' of the interstellar medium in the shape of a comet—is wrong."
Current research
Research in physics is continually progressing on a large number of fronts.
In condensed matter physics, an important unsolved theoretical problem is that of
high-temperature superconductivity.
Many condensed matter experiments are aiming to fabricate workable
spintronics
Spintronics (a portmanteau meaning spin transport electronics), also known as spin electronics, is the study of the intrinsic spin of the electron and its associated magnetic moment, in addition to its fundamental electronic charge, in solid- ...
and
quantum computers.
[
In particle physics, the first pieces of experimental evidence for physics beyond the Standard Model have begun to appear. Foremost among these are indications that neutrinos have non-zero mass. These experimental results appear to have solved the long-standing ]solar neutrino problem
The solar neutrino problem concerned a large discrepancy between the flux of solar neutrinos as predicted from the Sun's luminosity and as measured directly. The discrepancy was first observed in the mid-1960s and was resolved around 2002.
The fl ...
, and the physics of massive neutrinos remains an area of active theoretical and experimental research. The Large Hadron Collider has already found the Higgs boson, but future research aims to prove or disprove the supersymmetry, which extends the Standard Model of particle physics. Research on the nature of the major mysteries of dark matter and dark energy is also currently ongoing.
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 remain unsolved; examples include the formation of sandpiles, nodes in trickling water, the shape of water droplets, mechanisms of surface tension catastrophes, and self-sorting in shaken heterogeneous collections.
–
These complex phenomena have received growing attention since the 1970s for several reasons, including the availability of modern mathematical methods and computers, which enabled complex systems to be modeled in new ways. Complex physics has become part of increasingly interdisciplinary research, as exemplified by the study of turbulence in aerodynamics and the observation of pattern formation
The science of pattern formation deals with the visible, ( statistically) orderly outcomes of self-organization and the common principles behind similar patterns in nature.
In developmental biology, pattern formation refers to the generation of ...
in biological systems. In the 1932 ''Annual Review of Fluid Mechanics'', Horace Lamb said:
See also
* List of important publications in physics
*List of physicists
Following is a list of physicists who are notable for their achievements.
A
* Jules Aarons – United States (1921–2016)
*Ernst Karl Abbe – Germany (1840–1905)
*Derek Abbott – Australia (born 1960)
* Hasan Abdullayev – Azerbaijan De ...
* Lists of physics equations
* Relationship between mathematics and physics
* Earth science
* Neurophysics
* Psychophysics
*Science tourism
Science tourism is a travel topic grouping scientific attractions. It covers interests in visiting and exploring scientific landmarks, including museums, laboratories, observatories and universities. It also includes visits to see events of ...
Notes
References
Sources
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External links
Physics at Quanta Magazine
Usenet Physics FAQ
– FAQ compiled by sci.physics and other physics newsgroups
Website of the Nobel Prize in physics
– Award for outstanding contributions to the subject
World of Physics
– Online encyclopedic dictionary of physics
''Nature Physics''
– Academic journal
Physics
– Online magazine by the American Physical Society
* – Directory of physics related media
The Vega Science Trust
– Science videos, including physics
– Physics and astronomy mind-map from Georgia State University
Physics at MIT OpenCourseWare
– Online course material from Massachusetts Institute of Technology
The Feynman Lectures on Physics
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