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Line 1: − + − + − + − + + + − Thermodynamics/Statistical Mechanics+ − E&M+ + − waves/light/sound+ + − ==Modern Physics==+ − Planck's quantum hypothesis, relativity, quantum mechanics − Greeks, Aristotle, etc. − + − Galileo, Brahe, Kepler, Newton, etc.+ − Perhaps Lagrange, Hamilton here as well? (though they came later)+ + + + + + + + + + + + + + + + + + + + + + + − + − Ampere, Faraday, Maxwell − ===Development of Thermodynamics and Statistical Mechanics===+ − Thompson, Joule, Boltzmann − ===Development of Quantum Mechanics===+ − Planck, Einstein, Bohr, Schrodinger, Heisenberg, Born, Dirac, Fermi − ===Physics Today===+ − Particles, dark matter, dark energy+ + + +
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'''Physics''' is the branch of [[physical science]] that traditionally deals with [[matter]], [[energy]], [[force]], and [[motion]]. These concepts can be applied to virtually any area of the physical sciences; therefore, physics is often considered to be the most fundamental branch of science. Indeed, according to [[reductionism|reductionist]] thought, other branches of science are specialized subdivisions of physics.
'''Physics''' is the branch of [[physical science]] that traditionally deals with [[matter]], [[energy]], [[force]], and [[motion]]. These concepts can be applied to virtually any area of the physical sciences; therefore, physics is often considered to be the most fundamental branch of science. Indeed, according to [[reductionism|reductionist]] thought, all other branches of science are specialized subdivisions of physics.
Physics is generally subdivided into two major categories: [[Classical Physics]] and [[Modern Physics]].
Physics can be broadly divided into two major categories: [[Classical Physics]] and [[Modern Physics]].
==Classical Physics==
==Classical Physics==
Classical physics generally describes the aspects of physics that were well-understood by the end of the 19th century (i.e., before the advent of [[quantum mechanics]]). It includes the study of [[mechanics]], [[thermodynamics]], and [[electricity and magnetism]].
Classical physics generally encompasses all areas of physics that were well-understood by the end of the 19th century (i.e., before the events that led to the advent of quantum mechanics). It is applicable to problems on an "everyday" scale; that is, situations in which energies are large enough to permit one to neglect quantum effects, but small enough to neglect relativistic effects. Areas of study within classical physics include
Mechanics deals with the action of forces on bodies, and encompasses [[statics]], the study of forces on objects at rest, and [[dynamics]], the study of forces on moving bodies. The major contributors to mechanics were [[Galileo Galilei]], [[Isaac Newton]], [[Joseph Louis Lagrange]], and [[William Rowan Hamilton]].
*[[Mechanics]], the study of forces acting on bodies
*[[Thermodynamics]], the study of heat and entropy
*[[Electricity and magnetism]], the study of electric and magnetic phenomena
Most kinds of [[wave]] behavior are also considered to lie within the classical domain. Therefore, the studies of [[sound]] (which may be considered a subset of mechanics) and the wavelike nature of [[light]] (a subset of electricity and magnetism) are classical pursuits.
==Modern Physics==
Modern physics generally includes areas of study within physics that surfaced after 1900, the year in which [[Max Planck]] proposed a "quantum hypothesis" to explain the properties of light emitted by [[blackbody|hot, dark objects]]. The two major aspects of modern physics are
*[[Relativity]], a form of mechanics that is applicable in very high-energy situations
*[[Quantum mechanics]], a probabilistic description of the behavior of matter and energy at tiny length and energy scales
Modern physics was distinguished from classical physics mainly because these two ideas were so radically different from the classical viewpoint that they produced a [[paradigm shift]] in the way that physicists interpret the natural world.
==History==
==History==
===Physics in Antiquity===
===Physics in Antiquity===
===Development of Classical Mechanics===
The ancient [[Greeks]] thought of the material [[universe]] as being composed four different [[elements]]--[[earth]], [[air]], [[fire]], and [[water]]. Motion and interactions between objects were explained by the concept of "like desires like." For example, a rock fell back to the ground after being tossed in the air because it was composed mostly of earth; naturally, it desired to be near the earth's surface, which also consisted mostly of earth. Furthermore, [[Aristotle]] held that the natural state of objects was to be at rest. Hence, an object rolled along the ground stopped because its motion was contrary to its natural (motionless) state. The planet Earth was considered to be the center of the universe, so all motion was measured relative to it.
The ideas of the Greeks formed a [[paradigm]] that lasted for over 1500 years, making it one of the most successful scientific theories ever in terms of length of time spent as the dominant viewpoint.
===The Scientific Revolution===
As [[scientific method|scientific methodology]] became further developed, the Aristotelian view came under scrutiny. By the 16th century, force and motion had become topics of interest among scientists of the day. [[Galileo Galilei]] performed a series of experiments involving rolling balls down inclined planes, and [[Johannes Kepler]] found [[Kepler's laws|mathematical relations]] governing the motion of the [[planets]]. [[Isaac Newton]] was able to explain the results of Galileo and Kepler through the use of three succinct [[Newton's laws of motion|laws of motion]] and an expression that accounted for [[gravity|gravitational]] force. Newton also made important contributions to the field of [[optics]] and suggested that light consisted of tiny corpuscles (particles).
As a result of the success of Newton's laws, the Aristotelian paradigm was rejected. It was replaced by a "clockwork universe" viewpoint, in which (theoretically) all future events could be predicted with arbitrary precision, given enough information about the present.
===Further Development of Classical Physics===
As Newton's laws became the dominant tool in physical science, they began to be applied to phenomena other than gravitational interactions. During the first half of the 19th century, several laws governing electricity and magnetism were discovered. In the mid-1860s, [[James Clerk Maxwell]] unified these individual laws into a single set of [[Maxwell's equations|equations]]. Maxwell was able to derive a [[wave equation]] from his new set of equations, and found that the speed of the waves predicted by the equation was close to the measured [[speed of light]]. [[Thomas Young]] had [[double-slit experiment|demonstrated]] in 1801 that light had wavelike properties, but Maxwell's result provided the new insight that light waves were oscillating electric and magnetic fields.
Thermodynamics also came of age during the same era, leading to a better understanding of heat and entropy. A description of heat transfer by considering the motion of individual molecules was problematic due to the sheer number of particles in a typical gas, but [[Ludwig Boltzmann]], and others, developed a statistical framework for describing such problems that became known as [[statistical mechanics]].
The success of these and other advances solidified the classical Newtonian paradigm of a deterministic universe. Although the idea of an Earth-centered universe had been discarded, a "true" absolute reference frame was thought to exist, from which all motion all motion could be measured relative to.
===The Modern Era===
By the close of the 19th century, the study of physics was widely thought to be essentially complete, with the exception of only a few "loose ends"--minor unsolved problems to be dealt with. As a solution to the so-called [[ultraviolet catastrophe]] problem, which involved light emission from [[blackbody|hot, dark objects]], Max Planck proposed in 1900 that the sources of light could be represented by small individual oscillators. Planck referred to the individual oscillators as ''quanta''. At the time, Planck did not regard his finding as revolutionary; he thought that he was merely "fudging" the mathematics to arrive at a better solution. However, in 1905, [[Albert Einstein]] published a solution to the [[photoelectric effect]] problem: light could be thought of as being composed of very small, discrete packets (quanta), as opposed to the classical representation of light as a collection of waves. The discoveries of Planck and Einstein ushered in an entirely new era in physics. By the end of the 1930s, quantum mechanics--the name given to the new theory that applied to matter and energy on atomic scales--was well-established. Other physicists began applying the theory to more specific aspects of physics, resulting in quantum mechanical descriptions of electricity and magnetism, the [[weak force|weak]] and [[strong force|strong]] atomic forces, [[condensed matter]] physics, and many other areas.
In another 1905 publication, Einstein announced his discovery of what became known as the [[special relativity|special theory of relativity]], which revolutionized the way physicists thought about [[space]] and [[time]]. Einstein later extended the concept to non-inertial [[reference frames]], which resulted in the [[general relativity|general theory of relativity]], an improved description of [[gravity|gravitational]] interactions, which was published in 1915.
The development of quantum mechanics and relativity induced a shift from the Newtonian "clockwork universe" paradigm. According to quantum mechanics, the fundamental laws of the universe are not deterministic, but probabilistic; one can't predict events with certainty, but can only find the [[probability]] of an event taking place. According to relativity, the universe has no preferred reference frame, and there is no such thing as absolute space and absolute time.
===Development of Electricity and Magnetism===
===Contemporary Physics===
Like all other modern sciences, areas of interest in contemporary physics encompass an enormous variety of general and specialized subjects. Today's professional physicists can generally be categorized into two types: theoretical physicists, who are trained extensively in [[mathematics]] and work to develop or enhance physical theories; and experimental physicists, who obtain and analyze data in laboratory or laboratory-like settings. Theorists and experimentalists often collaborate in attempts to reconcile theoretical predictions with experimental results. Both types of physicists conduct research on a plethora of unsolved problems.
In terms of fundamental universal laws, there are several unsolved problems. Some are listed below.
*The [[Standard Model]] of particle physics is known to be incomplete; particle physicists are working to predict and discover unknown constituents of matter
*Evidence suggests that the matter in the universe that humans can currently detect directly is only a fraction of the matter that actually exists. Attempts to discover the nature of the as-yet-undetectable [[dark matter]] are underway.
*The universe is known to be expanding at an accelerated rate. Such acceleration requires energy, but the form and source of this [[dark energy]] is not well-understood.
*Quantum mechanics has not yet successfully been applied to the gravitational interaction. At huge energy scales, where both quantum mechanics and general relativity are required to describe the system, the known laws of physics break down. Attempts to discover a quantum theory of gravity have led to [[superstring theory]] and [[m-theory]], but to date neither have permitted the design of a technologically feasible experiment to verify them.
*General relativity predicts the existence of gravitational waves, but none have been conclusively detected. Due to the weakness of the gravitational interaction, extremely sensitive detectors are required. The [[LIGO]] project is an example of current efforts to detect such waves.