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The first few hydrogen atom electron orbitals shown as cross-sections
with color-coded probability density.
Physics (from the Greek,
φύσις (phúsis),
"nature" and φυσικός (phusikós),
"natural"), the most fundamental natural science, is concerned with the
basic principles of the Universe. Physics deals with the elementary
constituents of the natural world (e.g. matter, energy, space, and
time)
and their interactions, as well as the
analysis of systems which are best understood in terms of these
principles. Physics is both an empirical
systematic study of Nature and the body of knowledge obtained as a
result of this process. The foremost task of the physicist
is to find patterns in the workings of the natural world and deduce
those elementary laws that govern the cosmos
in the most precise and simplest formulation.
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Introduction
Discoveries in physics find
applications throughout the
other natural sciences as they regard the basic
constituents of the Universe. Some of the phenomena studied in physics,
such as the phenomenon of conservation of energy, are common
to all material systems. These are often referred to as laws of
physics. Others, such as superconductivity,
stem from these laws, but are not laws themselves because they only
appear in some systems. Physics is often said to be the "fundamental
science" (chemistry is sometimes included), because each of the other
weaker sciences (biology, chemistry, geology, material science,
engineering, medicine
etc.) deals with particular types of material systems that obey the
laws of physics. For example, chemistry is the science of matter (such
as atoms
and molecules)
and the chemical substances that they form in
the bulk. The structure, reactivity, and properties of a chemical
compound are determined by the
properties of the underlying molecules, which can be described by areas
of physics such as quantum mechanics (called in this case quantum
chemistry), thermodynamics, and electromagnetism. Refer to
Branches of physics
Physics is closely related to
mathematics,
which provides the logical framework in which physical laws can be
precisely formulated and their predictions quantified. Physical
definitions, models
and theories
are invariably expressed using mathematical relations. A key difference
between physics and mathematics is that because physics is ultimately
concerned with descriptions of the material world, it tests its
theories
by observations (called experiments),
whereas mathematics is concerned with abstract logical patterns not
limited by those observed in the real world (because the real world is
limited in the number of dimensions and in many other ways it does not
have to correspond to richer mathematical structures). The distinction,
however, is not always clear-cut. There is a large area of research
intermediate between physics and mathematics, known as mathematical
physics.
Physics attempts to describe the
natural world by the
application of the scientific method. Natural philosophy,
its counterpart, is the study of the changing world by philosophy which
has been also called "physics" since classical times to at least up to
its separation from philosophy as a positive science
in the 19th century. Mixed questions, of which solutions can be
attempted through the applications of both disciplines (e.g. the
divisibility of the atom) can involve natural philosophy in physics the
science and vice versa.
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Etymology
The word Physics comes from
the Greek word φύσις
(phúsis) meaning "nature"
or from its adjectival form φυσικός
(phusikós) meaning "natural".
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Subdisciplines of Physics
Physicists
study a wide range of physical
phenomena, from quarks to black
holes, from individual atoms to the many-body systems of
superconductors.
The subject matter of
Physics is broadly classified into Pure Physics and Applied
Physics. Based on the chronological development of Physics, Pure
Physics is again classified into Classical Physics and Modern Physics.
Based on the method adopted
for study, Physics is classified into Theoretical physics and
Experimental physics.
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Classical Physics and Modern physics
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- Further information: Classical
physics, Quantum physics, Modern physics, Semiclassical
The deepest visible-light image of the Universe,
the Hubble Ultra Deep Field.
Classical physics generally covers the
developments of
physics up to
the end of 19th century. In the domain of classical physics, Nature
consists of a continuous distribution of matter
and energy
in space
and time.
By the end of the 19th century, however, a series of experimental and
theoretical developments provided evidence that some aspects of Nature
are non-continuous (e.g., discrete atomic energy levels), and that
space and time are interrelated (e.g., the constancy of the speed of
light). During a period of about twenty years, whose beginning is often
marked by the publication of two seminal papers by Albert Einstein in
1905, physicists discovered the theory of relativity and quantum
mechanics. The advances in
physics based on quantum physics and relativity during the last century
are collectively referred to as modern physics.
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Classical Physics
Classical physics has five distinct
branches such as Mechanics, Acoustics, Thermodynamics, Electrodynamics
and Optics.
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Mechanics
Mechanics deals with fundamental
concepts like matter, force, motion, energy, work, power, etc.
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Acoustics
Acoustics
is a branch of Physics that studies sound,
namely mechanical waves in gases, liquids,
and solids.
A physicist
who works in the field of acoustics is an acoustician.
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Thermodynamics
Thermodynamics is the science of Heat.
It
deals with heat and temperature.
Macroscopic systems are generally analysed by applying statistical
principles to their microscopic constituents. The statistical tools
used to describe thermodynamic system constitute what is called
Statistical mechanics,
an auxiliary branch of Thermodynamics. The statistical distribution
used in classical thermodynamics is the Maxwell-Boltzmann distribution.
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Electromagnetics
Electromagnetics deals with
Electricity,
Magnetism, Electromagnetism, Electromagnetic waves etc. The
classical electromagnetics was developed over the course of the 19th
century, most prominently by James Clerk Maxwell.
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Optics
Optics
is that branch of physics which describes
the behavior and properties of light and
the interaction of light with matter.
Classical optics is generally divided into two: Ray Optics and Wave
Optics.
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Modern Physics
Since relativity and quantum mechanics
provide the most
complete
known description of fundamental interactions, and because the changes
brought by these two frameworks to the physicist's world view were
revolutionary, the term modern physics is used to describe
physics which relies on these two theories. Colloquially, modern
physics can be described as the physics of extremes: from systems at
the extremely small (atoms, nuclei, fundamental particles) to the
extremely large (the Universe) and of the extremely fast (relativity).
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Relativistic Mechanics
Relativistic mechanics deals with
Einstein's
Special theory of relativity and General theory of relativity.
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Quantum Mechanics
Quantum mechanics
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Quantum Thermodynamics
Quantum thermodynamics is the study
of heat
and work dynamics in quantum systems. Approximately, quantum
thermodynamics attempts to combine thermodynamics and quantum mechanics
into a coherent whole. A central objective in quantum thermodynamics is
the quantitative and qualitative determination of the laws of
thermodynamics at the quantum level in which uncertainty and
probability begin to take effect. In quantum thermodynamics, the
statistical distributions used are Bose-Einstein Statistics and
Fermi-Dirac Statistics.
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Quantum Electrodynamics
Quantum electrodynamics
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Quantum Optics
Quantum optics (Modern Optics)
is a
branch of Modern physics, dealing with the
application of quantum mechanical principles to
phenomena involving light and its interactions with matter.
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Applied Physics
Applied physics is physics that is
intended for a particular technological or practical use, as for
example in engineering, as opposed to basic research. This approach is
similar to
that of applied mathematics.
Applied physics is rooted in the fundamental truths and basic concepts
of the physical sciences but is concerned with the utilization of
scientific principles in practical devices and systems, and in the
application of physics in other areas of science. "Applied" is
distinguished from "pure" by a subtle combination of factors such as
the motivation and attitude of researchers and the nature of the
relationship to the technology or science that may be affected by the
work. [1]
Branches of Applied Physics |
Agrophysics, Biophysics,
Chemical Physics, Communication Physics, Econophysics, Engineering
physics, Fluid dynamics, Geophysics, Medical physics, Nanotechnology,
Optoelectronics, Photovoltaics, Physical chemistry, Physics of
computation, Quantum chemistry, Quantum information science, Vehicle
dynamics |
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Theoretical physics and experimental
physics
The culture of physics research
differs from the other
sciences in the separation of theory
and experiment. Since the 20th
century, most individual physicists have specialized in either
theoretical physics or experimental physics. The great Italian
physicist Enrico Fermi (1901—1954), who
made fundamental contributions to both theory and experimentation in
nuclear physics, was a notable exception.
In contrast, almost all the successful theorists in biology
and chemistry
(e.g. American quantum chemist and biochemist Linus
Pauling) have also been
experimentalists, though this is changing as of late.
Roughly speaking, theorists seek to
develop through abstractions and mathematical models
theories that can both describe and interpret existing experimental
results and successfully predict future results, while experimentalists
devise and perform experiments to explore new phenomena and test
theoretical predictions. Although theory and experiment are developed
separately, they are strongly dependent on each other. However,
theoretical research in physics may further be considered to draw from
mathematical physics and computational physics
in addition to experimentation. Progress in physics frequently comes
about when experimentalists make a discovery that existing theories
cannot account for, necessitating the formulation of new theories.
Likewise, ideas arising from theory often inspire new experiments. In
the absence of experiment, theoretical research can go in the wrong
direction; this is one of the criticisms that has been leveled against
M-theory,
a popular theory in high-energy physics for which no practical
experimental test has ever been devised.
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