Branches ofphysics include classicalmechanics;thermodynamics andstatistical mechanics;electromagnetism andphotonics; relativity;quantum mechanics,atomic physics, andmolecular physics;optics and acoustics; condensed matter physics; high-energy particle physics and nuclear physics; andchaos theory and cosmology; and interdisciplinary fields.
Classical mechanics is a model of thephysics offorces acting upon bodies; includes sub-fields to describe the behaviors ofsolids,gases, andfluids. It is often referred to as "Newtonian mechanics" afterIsaac Newton and hislaws of motion. It also includes the classical approach as given byHamiltonian andLagrange methods. It deals with the motion of particles and the general system of particles.
There are many branches of classical mechanics, such as:statics,dynamics,kinematics,continuum mechanics (which includesfluid mechanics),statistical mechanics, etc.
The first chapter ofThe Feynman Lectures on Physics is about theexistence of atoms, which Feynman considered to be the most compact statement of physics, from which science could easily result even if all other knowledge was lost.[1] By modeling matter as collections of hard spheres, it is possible to describe thekinetic theory of gases, upon which classical thermodynamics is based.
Thermodynamics studies the effects of changes intemperature,pressure, andvolume onphysical systems on themacroscopic scale, and the transfer of energy asheat.[2][3] Historically, thermodynamics developed out of the desire to increase theefficiency of earlysteam engines.[4]
The starting point for most thermodynamic considerations is thelaws of thermodynamics, which postulate thatenergy can be exchanged between physical systems as heat orwork.[5] They also postulate the existence of a quantity namedentropy, which can be defined for any system.[6] In thermodynamics, interactions between large ensembles of objects are studied and categorized. Central to this are the concepts ofsystem andsurroundings. A system is composed of particles, whose average motions define its properties, which in turn are related to one another throughequations of state. Properties can be combined to expressinternal energy andthermodynamic potentials, which are useful for determining conditions forequilibrium andspontaneous processes.
| Maxwell's equations ofelectromagnetism |
The study of the behaviours of electrons, electric media, magnets, magnetic fields, and general interactions of light.
The special theory of relativity enjoys a relationship with electromagnetism and mechanics; that is, theprinciple of relativity and theprinciple of stationary action in mechanics can be used to deriveMaxwell's equations,[7][8] andvice versa.
The theory of special relativity was proposed in 1905 byAlbert Einstein in his article "On the Electrodynamics of Moving Bodies". The title of the article refers to the fact that special relativity resolves an inconsistency betweenMaxwell's equations and classical mechanics. The theory is based ontwo postulates: (1) that the mathematical forms of thelaws of physics are invariant in allinertial systems; and (2) that thespeed of light invacuum is constant and independent of the source or observer. Reconciling the two postulates requires a unification ofspace andtime into the frame-dependent concept ofspacetime.
General relativity is thegeometrical theory ofgravitation published by Albert Einstein in 1915/16.[9][10] It unifies special relativity,Newton's law of universal gravitation, and the insight that gravitation can be described by thecurvature of space and time. In general relativity, the curvature of spacetime is produced by theenergy of matter and radiation.
Quantum mechanics is the branch of physics treatingatomic andsubatomic systems and their interaction based on the observation that all forms of energy are released in discrete units or bundles called "quanta". Remarkably, quantum theory typically permits onlyprobable orstatistical calculation of the observed features of subatomic particles, understood in terms ofwave functions. TheSchrödinger equation plays the role in quantum mechanics thatNewton's laws andconservation of energy serve in classical mechanics—i.e., it predicts the future behavior of adynamic system—and is awave equation that is used to solve for wavefunctions.
For example, the light, or electromagnetic radiation emitted or absorbed by an atom has only certainfrequencies (orwavelengths), as can be seen from theline spectrum associated with the chemical element represented by that atom. The quantum theory shows that those frequencies correspond to definite energies of the light quanta, orphotons, and result from the fact that theelectrons of the atom can have only certain allowed energy values, or levels; when an electron changes from one allowed level to another, a quantum of energy is emitted or absorbed whose frequency is directly proportional to the energy difference between the two levels. Thephotoelectric effect further confirmed the quantization of light.
In 1924,Louis de Broglie proposed that not only do light waves sometimes exhibit particle-like properties, but particles may also exhibit wave-like properties. Two different formulations of quantum mechanics were presented following de Broglie's suggestion. Thewave mechanics ofErwin Schrödinger (1926) involves the use of a mathematical entity, the wave function, which is related to the probability of finding a particle at a given point in space. Thematrix mechanics ofWerner Heisenberg (1925) makes no mention of wave functions or similar concepts but was shown to be mathematically equivalent to Schrödinger's theory. A particularly important discovery of the quantum theory is theuncertainty principle, enunciated by Heisenberg in 1927, which places an absolute theoretical limit on the accuracy of certain measurements; as a result, the assumption by earlier scientists that the physical state of a system could be measured exactly and used to predict future states had to be abandoned. Quantum mechanics was combined with the theory of relativity in the formulation ofPaul Dirac. Other developments includequantum statistics,quantum electrodynamics, concerned with interactions between charged particles and electromagnetic fields; and its generalization,quantum field theory.
String Theory
A possible candidate for the theory of everything, this theory combines the theory of general relativity and quantum mechanics to make a single theory. This theory can predict about properties of both small and big objects. This theory is currently under the developmental stage.
Optics is the study of light motions including reflection, refraction, diffraction, and interference.
Acoustics is the branch of physics involving the study of mechanical waves in different mediums.
The study of the physical properties of matter in a condensed phase.
Particle physics studies the nature of particles, whilenuclear physics studies theatomic nuclei.
Chaos theory represents a multidisciplinary area of study that encompasses both scientific inquiry and mathematics. It examines the essential models and deterministic principles governing dynamical systems that exhibit extreme sensitivity to initial conditions. Previously, these systems were believed to exist in a state of complete randomness and disorder. However, chaos theory posits that beneath the surface of apparent randomness in chaotic complex systems lie underlying patterns, interconnections, continuous feedback mechanisms, repetitions, self-similarity, fractals, and self-organization. The butterfly effect, a fundamental concept in chaos theory, illustrates how a minor alteration in one aspect of a nonlinear system can result in significant variations later on, highlighting a fragile dependence on initial circumstances. This phenomenon is often illustrated by the metaphor that a butterfly flapping its wings in Brazil could potentially influence or avert a tornado in Texas by altering the conditions in its environment.
Cosmology studies how the universe came to be, and its eventual fate. It is studied byphysicists andastrophysicists. It also studies about fictional universes people made, how the universes came to be, and their eventual fate and destruction.
To the interdisciplinary fields, which define partially sciences of their own, belong e.g. the
The table below lists the core theories along with many of the concepts they employ.
{{cite book}}:ISBN / Date incompatibility (help). Feynman begins with theatomic hypothesis, as his most compact statement of all scientific knowledge: "If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generations ..., what statement would contain the most information in the fewest words? I believe it is ... thatall things are made up of atoms – little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another. ..." vol.I p. I–2{{cite book}}:ISBN / Date incompatibility (help)[clarification needed]