Various examples of physical phenomena
(from
Ancient Greek:
φύσις physis "nature") is a
natural science that involves the study of
matter[1] and its
motion through
spacetime, along with related concepts such as
energy and
force.
[2] More broadly, it is the general analysis of
nature, conducted in order to understand how the
universe behaves.
[3][4][5]
Physics is one of the oldest
academic disciplines, perhaps the oldest through its inclusion of
astronomy.
[6] Over the last two millennia, physics was a part of
natural philosophy along with
chemistry, certain branches of
mathematics, and
biology, but during the
Scientific Revolution in the 16th century, the
natural sciences emerged as unique research programs in their own right.
[7] Physics intersects with many
interdisciplinary areas of research, such as
biophysics and
quantum chemistry, and the boundaries of physics are not
rigidly defined. Indeed, new ideas in physics often explain the fundamental mechanisms of other sciences, while opening new avenues of research in areas such as mathematics and philosophy.
Physics also makes significant contributions through advances in new
technologies that arise from theoretical breakthroughs. For example, advances in the understanding of
electromagnetism or
nuclear physics led directly to the development of new products which have dramatically transformed modern-day society, such as
television,
computers,
domestic appliances, and
nuclear weapons; advances in
thermodynamics led to the development of
industrialization; and advances in
mechanics inspired the development of
calculus.
History
As noted below, the means used to understand the behavior of natural phenomena and their effects evolved from
philosophy, progressively replaced by
natural philosophy then
natural science, to eventually arrive at the modern conception of physics.
[citation needed]
Natural philosophy has its origins in Greece during the
Archaic period, (650 BCE – 480 BCE), when
Pre-Socratic philosophers like
Thales refused supernatural, religious or mythological explanations for natural phenomena and proclaimed that every event had a natural cause.
[8] They proposed ideas verified by reason and observation and many of their hypotheses proved successful in experiment,
[9] for example
atomism.
Natural science was developed in China, India and in Islamic caliphates, between the 4th and 10th century BCE.
Quantitative descriptions became popular among physicists and astronomers, for example
Archimedes in the domains of
mechanics,
statics and
hydrostatics. Experimental physics had its debuts with experimentation concerning statics by
medieval Muslim physicists like al-Biruni and
Alhazen.
[10][11]
Classical physics became a separate science when
early modern Europeans used these experimental and quantitative methods to discover what are now considered to be the
laws of physics.
[12][13] Kepler,
Galileo and more specifically
Newton discovered and unified the different laws of motion.
[14] During the industrial revolution, as energy needs increased, so did research, which led to the discovery of new laws in
thermodynamics,
chemistry and
electromagnetics.
Modern physics started with the works of
Einstein both in
relativity and
quantum physics.
[citation needed]
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 of a crystalline
firmament, and Aristotle's book
Physics, various Greek philosophers advanced their own theories of nature. Well into the 18th century, physics was known as
natural philosophy.
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 to give an adequate description of the scientific method.
[15] The scientific method employs
a priori reasoning as well as
a posteriori reasoning and the use of
Bayesian inference to measure the validity of a given theory.
[16]
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.
[17]
Many physicists have written about the philosophical implications of their work, for instance
Laplace, who championed
causal determinism,
[18] and
Erwin Schrödinger, who wrote on
quantum mechanics.
[19] The mathematical physicist
Roger Penrose has been called a
Platonist by
Stephen Hawking,
[20] a view Penrose discusses in his book,
The Road to Reality.
[21] Hawking refers to himself as an "unashamed reductionist" and takes issue with Penrose's views.
[22]
Core theories
Though physics deals with a wide variety of systems, certain theories are used by all physicists. Each of these theories were experimentally tested numerous times and found correct as an approximation of nature (within a certain domain of validity). For instance, the theory of
classical mechanics accurately describes the motion of objects, provided they are much larger than
atoms and moving at much less than the
speed of light. These theories continue to be areas of active research, and a remarkable aspect of classical mechanics known as
chaos was discovered in the 20th century, three centuries after the original formulation of classical mechanics by
Isaac Newton (1642–1727).
These central theories are important tools for research into more specialized topics, and any physicist, regardless of his or her specialization, is expected to be literate in them. These include
classical mechanics,
quantum mechanics,
thermodynamics and
statistical mechanics,
electromagnetism, and
special relativity.
Fundamental physics
The basic domains of physics
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 their predictions.
Albert Einstein contributed the framework of
special relativity, which replaced notions of
absolute time and space with
spacetime and allowed an accurate description of systems whose components have speeds approaching the speed of light.
Max Planck,
Erwin 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 candidates theories of
quantum gravity are being developed.
Relation to other fields
Mathematics and Ontology are used in Physics. Physics is used in Chemistry and Cosmology.
Prerequisites
Mathematics is the language used for compact description of the order in nature, especially the laws of Physics. This was noted and advocated by Pythagoras,
[23] Plato,
[24] Galileo,
[25] and Newton.
Physics theories use Mathematics
[26] to obtain order and provide precise formulas,
precise or
estimated solutions, quantitative results and predictions. Experiment results in physics are numerical measurements. Technologies based on Mathematics, like
computation have made
computational physics an active area of research.
The distinction between Mathematics and Physics is clear-cut, but not always obvious, especially in Mathematical Physics.
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 Math statements are analytic. Mathematics contains hypothesis, 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.
[27] The problems in this field start with a "
Math model of a Physical situation" and a "Math description of a Physical law". Every math statement used for solution 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.
Physics is a branch of
fundamental science, not
practical science.
[28] Physics is also called "the fundamental science" because the subject of study of all branches of
natural science like Chemistry, Astronomy, Geology and Biology are constrained by laws of physics.
[29] For example, Chemistry studies properties, structures, and
reactions of matter (chemistry's focus on the 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
application in lifting liquids
is a general term for physics research which is intended for a particular
use. An applied physics curriculum usually contains a few classes in an applied discipline, like geology or electrical engineering. It usually differs from
engineering in that an applied physicist may not be designing something in particular, but rather is using physics or conducting physics research with the aim of developing new technologies or solving a problem.
The approach is similar to that of
applied mathematics. Applied physicists can also be interested in the use of physics for 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 structures. The understanding and use of
acoustics results in 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, over
time. It also allows for simulations in engineering which drastically speed up the development of a new technology.
But there is also considerable
interdisciplinarity in the physicist's methods and so many other important fields are influenced by physics, e.g. the fields of
econophysics and sociophysics.
Research
Scientific method
Physicists use a
scientific method to test the validity of a
physical theory, using a methodical approach to compare the implications of the theory in question with the associated conclusions drawn from
experiments and observations conducted to test it. Experiments and observations are collected and compared with the predictions and hypotheses made by a theory, thus aiding in the determination or the validity/invalidity of the theory.
Theories which are very well supported by data and have never failed any competent empirical test are often called
scientific laws, or natural laws. Of course, all theories, including those called scientific laws, can always be replaced by more accurate, generalized statements if a disagreement of theory with observed data is ever found.
[30]
Theory and experiment
Theorists seek to develop
mathematical models that both agree with existing experiments and successfully predict future results, while experimentalists devise and perform experiments to test theoretical predictions and explore new phenomena. Although theory and experiment are developed separately, they are strongly dependent upon each other. Progress in physics frequently comes about when experimentalists make a discovery that existing theories cannot explain, or when new theories generate experimentally testable predictions, which inspire new experiments.
Physicists who work at the interplay of theory and experiment are called
phenomenologists. Phenomenologists look at the complex phenomena observed in experiment and work to relate them to fundamental theory.
Theoretical physics has historically taken inspiration from philosophy;
electromagnetism was unified this way.
[31] Beyond the known universe, the field of theoretical physics also deals with hypothetical issues,
[32] 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 informs, and is informed by,
engineering and
technology. Experimental physicists 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 which are not well explored by theorists.
[33]
Scope and aims
Physics involves modeling the natural world with theory, usually quantitative. Here, the path of a particle is modeled with the mathematics of
calculus to explain its behavior: the purview of the branch of physics known as
mechanics.
Physics covers a wide range of
phenomena, from
elementary particles (such as quarks, neutrinos and electrons) to the largest
superclusters of galaxies. Included in these phenomena are the most basic objects composing all other things. Therefore physics is sometimes called the "
fundamental science".
[29] 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) were attracted to one another by some invisible force. This effect was later called
magnetism, and was first rigorously studied in the 17th century. A little earlier than the Chinese, 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 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
condensed matter physics;
atomic, molecular, and optical physics;
particle physics;
astrophysics;
geophysics and
biophysics. Some physics departments also support research in
Physics education.
Since the twentieth century, the individual fields of physics have become increasingly
specialized, and today most physicists work in a single field for their entire careers. "Universalists" such as
Albert Einstein (1879–1955) and
Lev Landau (1908–1968), who worked in multiple fields of physics, are now very rare.
[34]
Table of the major fields of physics, along with their subfields and the theories they employ[show]
| Field | Subfields | Major theories | Concepts |
|---|
| Astrophysics | Astronomy, Astrometry, Cosmology, Gravitation physics, High-energy astrophysics, Planetary astrophysics, Plasma physics, Solar Physics, Space physics, Stellar astrophysics | Big Bang, Cosmic inflation, General relativity, Newton's law of universal gravitation, Lambda-CDM model, Magnetohydrodynamics | Black hole, Cosmic background radiation, Cosmic string, Cosmos, Dark energy, Dark matter, Galaxy, Gravity, Gravitational radiation, Gravitational singularity, Planet, Solar system, Star, Supernova, Universe |
| Atomic, molecular, and optical physics | Atomic physics, Molecular physics, Atomic and Molecular astrophysics, Chemical physics, Optics, Photonics | Quantum optics, Quantum chemistry, Quantum information science | Photon, Atom, Molecule, Diffraction, Electromagnetic radiation, Laser, Polarization (waves), Spectral line, Casimir effect |
| Particle physics | Nuclear physics, Nuclear astrophysics, Particle astrophysics, Particle physics phenomenology | Standard Model, Quantum field theory, Quantum electrodynamics, Quantum chromodynamics, Electroweak theory, Effective field theory, Lattice field theory, Lattice gauge theory, Gauge theory, Supersymmetry, Grand unification theory, Superstring theory, M-theory | Fundamental force (gravitational, electromagnetic, weak, strong), Elementary particle, Spin, Antimatter, Spontaneous symmetry breaking, Neutrino oscillation, Seesaw mechanism, Brane, String, Quantum gravity, Theory of everything, Vacuum energy |
| Condensed matter physics | Solid state physics, High pressure physics, Low-temperature physics, Surface Physics, Nanoscale and Mesoscopic physics, Polymer physics | BCS theory, Bloch wave, Density functional theory, Fermi gas, Fermi liquid, Many-body theory, Statistical Mechanics | Phases (gas, liquid, solid), Bose-Einstein condensate, Electrical conduction, Phonon, Magnetism, Self-organization, Semiconductor, superconductor, superfluid, Spin, |
| Applied Physics | Accelerator physics, Acoustics, Agrophysics, Biophysics, Chemical Physics, Communication Physics, Econophysics, Engineering physics, Fluid dynamics, Geophysics, Laser Physics, Materials physics, Medical physics, Nanotechnology, Optics, Optoelectronics, Photonics, Photovoltaics, Physical chemistry, Physics of computation, Plasma physics, Solid-state devices, Quantum chemistry, Quantum electronics, Quantum information science, Vehicle dynamics |
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 constituents in a system is extremely large and the interactions between the constituents are strong.
The most familiar examples of condensed phases are
solids and
liquids, which arise from the bonding and
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 electrons in certain materials, and the
ferromagnetic and
antiferromagnetic phases of
spins on
atomic lattices.
Condensed matter physics is by far 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 at the
American Physical Society was renamed as the Division of Condensed Matter Physics.
[35] Condensed matter physics has a large overlap with
chemistry,
materials science,
nanotechnology and
engineering.
Atomic, molecular, and optical physics
Atomic,
molecular, and
optical physics (AMO) is the study of
matter-matter and
light-matter interactions on the scale of single
atoms or structures containing a few atoms. The three areas are grouped together because of their interrelationships, the similarity of methods used, and the commonality of the
energy scales that are relevant. All three areas include both
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, the collective behavior of atoms in weakly interacting gases (Bose–Einstein Condensates and dilute Fermi degenerate systems), precision measurements of fundamental constants, and the effects of electron correlation on structure and dynamics. Atomic physics is influenced by the
nucleus (see, e.g.,
hyperfine splitting), but intra-nuclear phenomenon such as
fission and
fusion are considered part of
high energy 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.
High energy physics (particle physics)
Particle physics is the study of the
elementary constituents of
matter and
energy, and the
interactions between them. It may also be called "high energy physics", because many elementary particles do not occur naturally, but are created only during high energy
collisions of other particles, as can be detected in
particle accelerators.
Currently, the interactions of elementary particles are described by the
Standard Model. The model accounts for the 12 known particles of matter (
quarks and
leptons) that interact via the
strong,
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, the existence of which has not yet been verified; as of 2010
[update], searches for it are underway in the
Tevatron at
Fermilab and in the
Large Hadron Collider at
CERN.
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 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 was expanding, as shown by the
Hubble diagram, 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. Cosmologists have recently established the
ΛCDM model of the evolution of the universe, which includes
cosmic inflation,
dark energy and
dark matter.
Numerous possibilities and discoveries are anticipated to emerge from new data from the
Fermi Gamma-ray Space Telescope over the upcoming decade and vastly revise or clarify existing models of the
Universe.
[36][37] In particular, the potential for a tremendous discovery surrounding
dark matter is possible over the next several years.
[38] Fermi will search for evidence that dark matter is composed of
weakly interacting massive particles, complementing similar experiments with the
Large Hadron Collider and other underground detectors.
IBEX is already yielding new
astrophysical discoveries: "No one knows what is creating the
ENA (energetic neutral atoms) ribbon" along the
termination shock of the
solar wind, "but everyone agrees that it means the textbook picture of the
heliosphere — in which the solar system's enveloping pocket filled with the solar wind's charged particles is plowing through the onrushing 'galactic wind' of the interstellar medium in the shape of a comet — is wrong."
[39]
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 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, and the physics of massive neutrinos remains an area of active theoretical and experimental research.
Particle accelerators have begun probing energy scales in the
TeV range, in which experimentalists are hoping to find evidence for the
Higgs boson and
supersymmetric particles.
[40]
Theoretical attempts to unify
quantum mechanics and
general relativity into a single theory of
quantum gravity, a program ongoing for over half a century, have not yet been decisively resolved. The current leading candidates are
M-theory,
superstring theory and
loop quantum gravity.
Many
astronomical and
cosmological phenomena have yet to be satisfactorily explained, including the existence of
ultra-high energy cosmic rays, the
baryon asymmetry, the
acceleration of the universe and the
anomalous rotation rates of galaxies.
Although much progress has been made in high-energy,
quantum, and astronomical physics, many everyday phenomena involving
complexity,
chaos, or
turbulence are still poorly understood.
[citation needed] 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.
[citation needed]
These complex phenomena have received growing attention since the 1970s for several reasons, including the availability of modern
mathematical methods and
computers, which enabled
complex systems to be modeled in new ways. Complex physics has become part of increasingly
interdisciplinary research, as exemplified by the study of
turbulence in
aerodynamics and the observation of
pattern formation in
biological systems. In 1932,
Horace Lamb said:
[41]
Louis Pasteur's portrait in his later years.
The physicist Albert Einstein is one of the most well known scientists of the 20th century.
Theoretical physicist Stephen Hawking is known for his contributions to the fields of cosmology and quantum gravity
.jpg)
