Editing Mechanics (section)

=== Quantum ===
{{main|Quantum mechanics}}
The following are categorized as being part of quantum mechanics:
* [[Schrödinger equation|Schrödinger wave mechanics]], used to describe the movements of the wavefunction of a single particle.
* [[Matrix mechanics]] is an alternative formulation that allows considering systems with a finite-dimensional state space.
* [[Quantum statistical mechanics]] generalizes ordinary quantum mechanics to consider systems in an unknown state; often used to derive [[thermodynamics|thermodynamic]] properties.
* [[Particle physics]], the motion, structure, and behavior of fundamental particles
* [[Nuclear physics]], the motion, structure, and reactions of nuclei
* [[Condensed matter physics]], quantum gases, solids, liquids, etc.

Historically, [[classical mechanics]] had been around for nearly a quarter millennium before quantum mechanics developed. Classical mechanics originated with [[Isaac Newton]]'s [[Newton's laws of motion|laws of motion]] in [[Philosophiæ Naturalis Principia Mathematica]], developed over the seventeenth century. Quantum mechanics developed later, over the nineteenth century, precipitated by [[Planck postulate|Planck's postulate]] and Albert Einstein's explanation of the [[photoelectric effect]]. Both fields are commonly held to constitute the most certain knowledge that exists about physical nature.

Classical mechanics has especially often been viewed as a model for other so-called [[exact science]]s. Essential in this respect is the extensive use of [[mathematics]] in theories, as well as the decisive role played by [[experiment]] in generating and testing them.

Quantum mechanics is of a bigger scope, as it encompasses classical mechanics as a sub-discipline which applies under certain restricted circumstances. According to the [[correspondence principle]], there is no contradiction or conflict between the two subjects, each simply pertains to specific situations. The correspondence principle states that the behavior of systems described by quantum theories reproduces classical physics in the limit of large [[quantum numbers]], i.e. if quantum mechanics is applied to large systems (for e.g. a baseball), the result would almost be the same if classical mechanics had been applied. Quantum mechanics has superseded classical mechanics at the foundation level and is indispensable for the explanation and prediction of processes at the molecular, atomic, and sub-atomic level. However, for macroscopic processes classical mechanics is able to solve problems which are unmanageably difficult (mainly due to computational limits) in quantum mechanics and hence remains useful and well used.
Modern descriptions of such behavior begin with a careful definition of such quantities as displacement (distance moved), time, velocity, acceleration, mass, and force. Until about 400 years ago, however, motion was explained from a very different point of view. For example, following the ideas of Greek philosopher and scientist Aristotle, scientists reasoned that a cannonball falls down because its natural position is in the Earth; the Sun, the Moon, and the stars travel in circles around the Earth because it is the nature of heavenly objects to travel in perfect circles.

Often cited as father to modern science, [[Galileo]] brought together the ideas of other great thinkers of his time and began to calculate motion in terms of distance travelled from some starting position and the time that it took. He showed that the speed of falling objects increases steadily during the time of their fall. This acceleration is the same for heavy objects as for light ones, provided air friction (air resistance) is discounted. The English mathematician and physicist [[Isaac Newton]] improved this analysis by defining force and mass and relating these to acceleration. For objects traveling at speeds close to the speed of light, Newton's laws were superseded by [[Albert Einstein]]'s [[Special relativity|theory of relativity]]. [A sentence illustrating the computational complication of Einstein's theory of relativity.] For atomic and subatomic particles, Newton's laws were superseded by [[Quantum mechanics|quantum theory]]. For everyday phenomena, however, Newton's three laws of motion remain the cornerstone of dynamics, which is the study of what causes motion.