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Line 24: − 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.+ − + Line 36:
Line 36: + − + − − 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. − + Line 59:
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→Modern Physics
==Modern Physics==
==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
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 [[black body|hot, dark objects]]. The two major aspects of modern physics are
*[[Relativity]], a form of mechanics that is applicable in very high-energy situations
*[[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
*[[Quantum mechanics]], a probabilistic description of the discrete 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.
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.
===Physics in Antiquity===
===Physics in Antiquity===
Ancient [[Greek]] scholars, such as [[Democritus]] and [[Aristotle]], 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 a "natural state" for each element. Bodies tended to move towards their natural state, and remained motionless when they attained it. For example, a rock fell to the ground after being tossed in the air because it was composed mostly of earth; as such, it moved toward its natural state at the center of the Earth as much as it was able. The Greeks also made advances in [[astronomy]]; [[Ptolemy]] developed a geocentric (Earth-centered) model of the solar system.
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 ideas of the Greeks formed a [[paradigm]] that lasted for over 1000 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===
===The Scientific Revolution===
===Further Development of Classical Physics===
===Further Development of Classical Physics===
Newtonian mechanics was expanded by several other scientists, notably [[Pierre-Simon Laplace]] and [[Joseph Louis Lagrange]]. The motions of
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.
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]].
Thermodynamics also came of age during roughly the same era. Advances by [[James Joule]], [[Sadi Carnot]], and [[Lord Kelvin]], among many others, led to a better understanding of heat and entropy, and the formulation of the laws of thermodynamics. Later, attempts to relate the behavior of particles on the atomic and molecular level to the properties of large aggregates of such particles led to the development of [[statistical mechanics]].
===The Modern Era===
===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.
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 [[black body|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.
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.
*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.
*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.
*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.
*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 [[string 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.
*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.