Gravitation is a natural phenomenon by which all objects with mass attract each other, and is one of the fundamental forces of physics. A phenomenon (from Greek φαινόμενoν, pl φαινόμενα - phenomena) is any observable occurrence Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object In Physics, a fundamental interaction or fundamental force is a mechanism by which particles interact with each other and which cannot be explained in terms In everyday life, gravitation is most commonly thought of as the agency that gives objects weight. In the Physical sciences weight is a Measurement of the gravitational Force acting on an object It is responsible for keeping the Earth and the other planets in their orbits around the Sun; for keeping the Moon in its orbit around the Earth, for the formation of tides; for convection (by which hot fluids rise); for heating the interiors of forming stars and planets to very high temperatures; and for various other phenomena that we observe. In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star Characteristics A tide is a repeated cycle of sea level changes in the following stages Over several hours the water rises or advances up a beach in the flood Convection in the most general terms refers to the movement of molecules within Fluids (i Gravitation is also the reason for the very existence of the Earth, the Sun, and most macroscopic objects in the universe; without it, matter would not have coalesced into these large masses and life, as we know it, would not exist. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 The Sun (Sol is the Star at the center of the Solar System. The Universe is defined as everything that Physically Exists: the entirety of Space and Time, all forms of Matter, Energy Life is a state that distinguishes Organisms from non-living objects such as non-life and dead organisms being manifested by growth through Metabolism

Modern physics describes gravitation using the general theory of relativity, but the much simpler Newton's law of universal gravitation provides an excellent approximation in most cases. Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916 Newton 's law of universal Gravitation is a physical law describing the gravitational attraction between bodies with mass

The terms gravitation and gravity are mostly interchangeable in everyday use, but in scientific usage a distinction may be made. "Gravitation" is a general term describing the attractive influence that all objects with mass exert on each other, while "gravity" specifically refers to a force that is supposed in some theories (such as Newton's) to be the cause of this attraction. In Physics, a force is whatever can cause an object with Mass to Accelerate. By contrast, in general relativity gravitation is due to spacetime curvatures that cause inertially moving objects to accelerate towards each other. General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916 The vis insita or innate force of matter is a power of resisting by which every body as much as in it lies endeavors to preserve in its present state whether it be of rest or of moving

Gravitation keeps the planets in orbit about the Sun. (Not to scale)

## History of gravitational theory

### Early history

Efforts to understand gravity began in ancient times. In Physics, theories of gravitation postulate mechanisms of interaction governing the movements of bodies with mass Philosophers in ancient India explained the phenomenon from the 8th century BC. The term Indian philosophy (Sanskrit Darshanas) may refer to any of several traditions of philosophical thought that originated in the Indian subcontinent The History of science in early cultures refers to the study of Protoscience in Ancient history, prior to the development of Science in the Middle [1] According to Kanada, founder of the Vaisheshika school, "Weight causes falling; it is imperceptible and known by inference. Kanada ( Sanskrit: कणाद; also transliterated as Canada as well as other forms was a Hindu sage who founded the philosophical Vaisheshika, or Vaiśeṣika, (Sanskrit वैशॆषिक) is one of the six Hindu schools of Philosophy (orthodox Vedic systems Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object Inference is the act or process of deriving a Conclusion based solely on what one already knows "[2]

In the 4th century BC, the Greek philosopher Aristotle believed that there was no effect without a cause, and therefore no motion without a force. Ancient Greek philosophy focused on the role of Reason and Inquiry. Aristotle (Greek Aristotélēs) (384 BC – 322 BC was a Greek philosopher a student of Plato and teacher of Alexander the Great. A result is the final consequence of a Sequence of actions or events (broadly incidents and accidents expressed qualitatively or quantitatively being a loss injury disadvantage Causality (but not causation) denotes a necessary relationship between one event (called cause and another event (called effect) which is the direct consequence In Physics, motion means a constant change in the location of a body In Physics, a force is whatever can cause an object with Mass to Accelerate. He hypothesized that everything tried to move towards its proper place in the crystalline spheres of the heavens, and that physical bodies fell toward the center of the Earth in proportion to their weight. The celestial spheres or celestial orbs were the fundamental celestial entities of the cosmological celestial mechanics first invented by Eudoxus, and developed by Aristotle EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 In the Physical sciences weight is a Measurement of the gravitational Force acting on an object

Brahmagupta, in the Brahmasphuta Siddhanta (AD 628), responded to critics of the heliocentric system of Aryabhata (AD 476–550) stating that "all heavy things are attracted towards the center of the earth" and that "all heavy things fall down to the earth by a law of nature, for it is the nature of the earth to attract and to keep things, as it is the nature of water to flow, that of fire to burn, and that of wind to set in motion. Brahmagupta ( (598–668 was an Indian mathematician and astronomer. The main work of Brahmagupta, Brahmasphuta-siddhanta (The Opening of the Universe, written in the year 628, contains some remarkably advanced ideas including In Astronomy, heliocentrism is the theory that the Sun is at the center of the Solar System. Āryabhaṭa ( Devanāgarī: आर्यभट (AD 476 &ndash 550 is the first in the line of great mathematician-astronomers from the classical age of Indian mathematics . . The earth is the only low thing, and seeds always return to it, in whatever direction you may throw them away, and never rise upwards from the earth. "[3][4]

In the 9th century, the eldest Banū Mūsā brother, Muhammad ibn Musa, in his Astral Motion and The Force of Attraction, hypothesized that there was a force of attraction between heavenly bodies,[5] foreshadowing Newton's law of universal gravitation. The Banū Mūsā brothers (بنو موسى "Sons of Mūsā" were three 9th century Persian Scholars of Baghdad, active in the House Newton 's law of universal Gravitation is a physical law describing the gravitational attraction between bodies with mass [6] In the 1000s, the Persian scientist Ibn al-Haytham (Alhacen), in the Mizan al-Hikmah, discussed the theory of attraction between masses, and it seems that he was aware of the magnitude of acceleration due to gravity. layout and formatting it should ensure no clashes with the top of the infobox TemplateInfobox Muslim scholars --> ( Arabic: ابو علی، حسن بن حسن بن هيثم Latinized Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object The magnitude of a mathematical object is its size a property by which it can be larger or smaller than other objects of the same kind in technical terms an Ordering [7] In 1121, Al-Khazini, in The Book of the Balance of Wisdom, differentiated between force, mass, and weight,[8] and discovered that gravity varies with the distance from the centre of the Earth,[9] though he believed that the weight of heavy bodies increase as they are farther from the centre of the Earth. Abd al-Rahman al-Khazini ( عبدالرحمن الخزيني) (flourished 1115–1130 was a Muslim scientist, physicist, astronomer, biologist In Physics, a force is whatever can cause an object with Mass to Accelerate. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object In the Physical sciences weight is a Measurement of the gravitational Force acting on an object [10] All these early attempts at trying to explain the force of gravity were philosophical in nature and it would be Isaac Newton that gave the first correct description of gravity. Sir Isaac Newton, FRS (ˈnjuːtən 4 January 1643 31 March 1727) Biography Early years See also Isaac Newton's early life and achievements Gravitation is a natural Phenomenon by which objects with Mass attract one another

### Scientific revolution

Modern work on gravitational theory began with the work of Galileo Galilei in the late 16th century and early 17th century. Galileo Galilei (15 February 1564 &ndash 8 January 1642 was a Tuscan ( Italian) Physicist, Mathematician, Astronomer, and Philosopher In his famous (though probably apocryphal) experiment dropping balls from the Tower of Pisa, and later with careful measurements of balls rolling down inclines, Galileo showed that gravitation accelerates all objects at the same rate. The Leaning Tower of Pisa (Torre pendente di Pisa or simply The Tower of Pisa (it La Torre di Pisa is the Campanile, or freestanding bell tower of the This article deals with the physical structure For related terms see Canal inclined plane, Cable railway, Funicular, or Fixed-wing This was a major departure from Aristotle's belief that heavier objects are accelerated faster. [11] (Galileo correctly postulated air resistance as the reason that lighter objects may fall more slowly in an atmosphere. ) Galileo's work set the stage for the formulation of Newton's theory of gravity.

### Newton's theory of gravitation

In 1687, English mathematician Sir Isaac Newton published Principia, which hypothesizes the inverse-square law of universal gravitation. Newton 's law of universal Gravitation is a physical law describing the gravitational attraction between bodies with mass Sir Isaac Newton, FRS (ˈnjuːtən 4 January 1643 31 March 1727) Biography Early years See also Isaac Newton's early life and achievements The Philosophiæ Naturalis Principia Mathematica ( Latin: "mathematical principles of natural philosophy" often Principia In Physics, an inverse-square law is any Physical law stating that some physical Quantity or strength is inversely proportional In his own words, “I deduced that the forces which keep the planets in their orbs must be reciprocally as the squares of their distances from the centers about which they revolve; and thereby compared the force requisite to keep the Moon in her orb with the force of gravity at the surface of the Earth; and found them answer pretty nearly. ”

Newton's theory enjoyed its greatest success when it was used to predict the existence of Neptune based on motions of Uranus that could not be accounted by the actions of the other planets. Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. Calculations by John Couch Adams and Urbain Le Verrier both predicted the general position of the planet, and Le Verrier's calculations are what led Johann Gottfried Galle to the discovery of Neptune. John Couch Adams ( June 5 1819 &ndash January 21, 1892) was a British Mathematician and Astronomer Urbain Jean Joseph Le Verrier ( March 11, 1811 &ndash September 23, 1877) was a French Mathematician who specialized in Celestial Johann Gottfried Galle ( June 9, 1812 &ndash July 10, 1910) was a German Astronomer at the Berlin Observatory

Ironically, it was another discrepancy in a planet's orbit that helped to point out flaws in Newton's theory. By the end of the 19th century, it was known that the orbit of Mercury could not be accounted for entirely under Newton's theory, but all searches for another perturbing body (such as a planet orbiting the Sun even closer than Mercury) had been fruitless. The Sun (Sol is the Star at the center of the Solar System. The issue was resolved in 1915 by Albert Einstein's new General Theory of Relativity, which accounted for the discrepancy in Mercury's orbit. Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916

Although Newton's theory has been superseded, most modern non-relativistic gravitational calculations are still made using Newton's theory because it is a much simpler theory to work with than General Relativity, and gives sufficiently accurate results for most applications. General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916

### General relativity

In general relativity, the effects of gravitation are ascribed to spacetime curvature instead of a force. General relativity (GR is a Theory of Gravitation that was developed by Albert Einstein between 1907 and 1915 General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916 SpaceTime is a patent-pending three dimensional graphical user interface that allows end users to search their content such as Google Google Images Yahoo! YouTube eBay Amazon and RSS In Mathematics, curvature refers to any of a number of loosely related concepts in different areas of geometry The starting point for general relativity is the equivalence principle, which equates free fall with inertial motion. The equivalence principle The issue that this creates is that free-falling objects can accelerate with respect to each other. In Newtonian physics, no such acceleration can occur unless at least one of the objects is being operated on by a force (and therefore is not moving inertially). Classical mechanics is used for describing the motion of Macroscopic objects from Projectiles to parts of Machinery, as well as Astronomical objects

To deal with this difficulty, Einstein proposed that spacetime is curved by matter, and that free-falling objects are moving along locally straight paths in curved spacetime. (This type of path is called a geodesic. In General relativity, Geodesics generalize the notion of "straight lines" to curved Spacetime. ) More specifically, Einstein discovered the field equations of general relativity, which relate the presence of matter and the curvature of spacetime and are named after him. A field equation is an equation in a Physical theory that describes how a Fundamental force (or a combination of such forces interacts with Matter The Einstein field equations are a set of 10 simultaneous, non-linear, differential equations. The Einstein field equations ( EFE) or Einstein's equations are a set of ten equations in Einstein 's theory of General relativity in which the In Mathematics simultaneous equations are a set of Equations containing multiple variables This article describes the use of the term nonlinearity in mathematics A differential equation is a mathematical Equation for an unknown function of one or several variables that relates the values of the The solutions of the field equations are the components of the metric tensor of spacetime. This article discusses metrics in General relativity, for a discussion of metrics in general see Metric tensor. A metric tensor describes a geometry of spacetime. The geodesic paths for a spacetime are calculated from the metric tensor.

Notable solutions of the Einstein field equations include:

• The Schwarzschild solution, which describes spacetime surrounding a spherically symmetric non-rotating uncharged massive object. In Einstein's theory of General relativity, the Schwarzschild solution (or the Schwarzschild vacuum) describes the Gravitational field outside This article is about rotations in three-dimensional Euclidean space A rotation is a movement of an object in a circular motion A two- Dimensional object rotates around a center (or point) of rotation For compact enough objects, this solution generated a black hole with a central singularity. A black hole is a theoretical region of space in which the Gravitational field is so powerful that nothing not even Electromagnetic radiation (e A gravitational singularity (sometimes spacetime singularity) is approximately a place where quantities which are used to measure the Gravitational field become For radial distances from the center which are much greater than the Schwarzschild radius, the accelerations predicted by the Schwarzschild solution are practically identical to those predicted by Newton's theory of gravity. The Schwarzschild radius (sometimes historically referred to as the gravitational radius) is a characteristic Radius associated with every Mass.
• The Reissner-Nordström solution, in which the central object has an electrical charge. In Physics and Astronomy, the Reissner-Nordström metric is a solution to the Einstein field equations in empty space which corresponds to the gravitational For charges with a geometrized length which are less than the geometrized length of the mass of the object, this solution produces black holes with two event horizons. A geometrized unit system or geometric unit system is a system of Natural units in which the base physical units are chosen so that the Speed of light In General relativity, an event horizon is a boundary in Spacetime, an area surrounding a Black hole or a Wormhole, inside which events cannot
• The Kerr solution for rotating massive objects. In General relativity, the Kerr metric (or Kerr vacuum) describes the geometry of Spacetime around a rotating massive body This solution also produces black holes with multiple event horizons.
• The Kerr-Newman solution for charged, rotating massive objects. The Kerr-Newman metric is a solution of Einstein's General relativity field equation that describes the spacetime geometry in the region surrounding a charged This solution also produces black holes with multiple event horizons.
• The cosmological Robertson-Walker solution, which predicts the expansion of the universe. Physical cosmology, as a branch of Astronomy, is the study of the large-scale structure of the Universe and is concerned with fundamental questions about its The Universe is defined as everything that Physically Exists: the entirety of Space and Time, all forms of Matter, Energy

General relativity has enjoyed much success because of how its predictions of phenomena which are not called for by the theory of gravity have been regularly confirmed. For example:

• General relativity accounts for the anomalous perihelion precession of Mercury. At its introduction in 1915 the general theory of relativity did not have a solid empirical foundation
• The prediction that time runs slower at lower potentials has been confirmed by the Pound-Rebka experiment, the Hafele-Keating experiment, and the GPS. The Pound-Rebka experiment is a well known experiment to test Albert Einstein 's theory of General relativity. The Hafele–Keating experiment was a test of the Theory of relativity. Basic concept of GPS operation A GPS receiver calculates its position by carefully timing the signals sent by the constellation of GPS Satellites high above the Earth
• The prediction of the deflection of light was first confirmed by Arthur Eddington in 1919, and has more recently been strongly confirmed through the use of a quasar which passes behind the Sun as seen from the Earth. Sir Arthur Stanley Eddington, OM (28 December 1882 – 22 November 1944 was an English Astrophysicist of the early 20th century A quasar (contraction of QUASi-stellAR radio source) is an extremely powerful and distant Active galactic nucleus. The Sun (Sol is the Star at the center of the Solar System. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 See also gravitational lensing. A gravitational lens is formed when the light from a very distant bright source (such as a Quasar) is "bent" around a massive object (such as a cluster of
• The time delay of light passing close to a massive object was first identified by Irwin Shapiro in 1964 in interplanetary spacecraft signals. The Shapiro time delay effect or gravitational time delay effect is one of the four classic solar system Tests of general relativity. Irwin I Shapiro is an American Astrophysicist. Since 1982 he has been a Professor at Harvard University.
• Gravitational radiation has been indirectly confirmed through studies of binary pulsars. In Physics, a gravitational wave is a Fluctuation in the Curvature of Spacetime which propagates as a wave, traveling outward from Pulsars are highly magnetized rotating Neutron stars that emit a beam of Electromagnetic radiation in the form of radio waves
• The expansion of the universe (predicted by Alexander Friedmann) was confirmed by Edwin Hubble in 1929. Alexander Alexandrovich Friedman or Friedmann (Александр Александрович Фридман ( June 16 1888, Saint Petersburg, Imperial Edwin Powell Hubble ( November 20, 1889 – September 28, 1953) was an American astronomer.

### Gravity and quantum mechanics

Main articles: Graviton and Quantum gravity

Several decades after the discovery of general relativity it was realized that general relativity is incompatible with quantum mechanics. In Physics, the graviton is a hypothetical Elementary particle, a Boson to be exact that mediates the force of Gravity in the framework Quantum gravity is the field of Theoretical physics attempting to unify Quantum mechanics, which describes three of the fundamental forces of nature Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons [12] It is possible to describe gravity in the framework of quantum field theory like the other fundamental forces, with the attractive force of gravity arises due to exchange of virtual gravitons, in the same way as the electromagnetic force arises from exchange of virtual photons. In quantum field theory (QFT the forces between particles are mediated by other particles In Physics, a fundamental interaction or fundamental force is a mechanism by which particles interact with each other and which cannot be explained in terms In Physics, a virtual particle is a particle that exists for a limited time and space introducing uncertainty in their energy and momentum due to the Heisenberg Uncertainty In Physics, the graviton is a hypothetical Elementary particle, a Boson to be exact that mediates the force of Gravity in the framework In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena [13][14] This reproduces general relativity in the classical limit. The classical limit is the ability of a physical theory to approximate or "recover" Classical mechanics when considered over special values of its parameters However, this approach fails at short distances of the order of the Planck length,[15] where a more complete theory of quantum gravity (or a new approach to quantum mechanics) is required. The Planck length, denoted by \scriptstyle\ell_P \, is the unit of Length approximately 1 Quantum gravity is the field of Theoretical physics attempting to unify Quantum mechanics, which describes three of the fundamental forces of nature Many believe the complete theory to be string theory,[16] or more currently M Theory. String theory is a still-developing scientific approach to Theoretical physics, whose original building blocks are one-dimensional extended objects called strings In Theoretical physics, M-theory is a new limit of String theory in which 11 dimensions of Spacetime may be identified

## Specifics

### Earth's gravity

Main article: Earth's gravity

Every planetary body (including the Earth) is surrounded by its own gravitational field, which exerts an attractive force on all objects. Earth's gravity, denoted by g, refers to the Gravitational attraction that the Earth exerts on objects on or near its surface Assuming a spherically symmetrical planet (a reasonable approximation), the strength of this field at any given point is proportional to the planetary body's mass and inversely proportional to the square of the distance from the center of the body.

The strength of the gravitational field is numerically equal to the acceleration of objects under its influence, and its value at the Earth's surface, denoted g, is approximately expressed below as the standard average. Standard gravity, usually denoted by g 0 or g n is the nominal acceleration due to gravity at the Earth's surface at sea level

$g = 9.8 \frac{m}{s^2} = 32.2 \frac{ft}{s^2}$

This means that, ignoring air resistance, an object falling freely near the earth's surface increases its velocity with $9.8\tfrac{m}{s}$ ($32.2\tfrac{ft}{s}$ or 22 mph) for each second of its descent. Thus, an object starting from rest will attain a velocity of $9.8\tfrac{m}{s}$ ($32.2\tfrac{ft}{s}$) after one second, $19.6\tfrac{m}{s}$ ($64\tfrac{ft}{s}$) after two seconds, and so on, adding $9.8\tfrac{m}{s}$ to each resulting velocity. According to Newton's 3rd Law, the Earth itself experiences an equal and opposite force to that acting on the falling object, meaning that the Earth also accelerates towards the object. However, because the mass of the Earth is huge, the acceleration of the Earth by this same force is negligible, when measured relative to the system's center of mass.

### Equations for a falling body

Ball falling freely under gravity. See text for description.

The kinematical and dynamical equations describing the trajectories of falling bodies are considerably simpler if the gravitational force is assumed constant. Under normal earth-bound conditions when objects move owing to a constant Gravitational Force a set of dynamical equations describe the resultant Trajectories This assumption is reasonable for objects falling to Earth over the relatively short vertical distances of our everyday experience, but does not hold over larger distances, such as spacecraft trajectories, since the acceleration due to Earth's gravity is much smaller at large distances. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001

Under an assumption of constant gravity, Newton’s law of gravitation simplifies to F = mg, where m is the mass of the body and g is a constant vector with an average magnitude of 9. Newton 's law of universal Gravitation is a physical law describing the gravitational attraction between bodies with mass Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object 81 m/s². The acceleration due to gravity is equal to this g. An initially-stationary object which is allowed to fall freely under gravity drops a distance which is proportional to the square of the elapsed time. The image on the right, spanning half a second, was captured with a stroboscopic flash at 20 flashes per second. During the first 1/20th of a second the ball drops one unit of distance (here, a unit is about 12 mm); by 2/20ths it has dropped at total of 4 units; by 3/20ths, 9 units and so on.

Under the same constant gravity assumptions, the potential energy, Ep, of a body at height h is given by Ep = mgh (or Ep = Wh, with W meaning weight). Potential energy can be thought of as Energy stored within a physical system This expression is valid only over small distances h from the surface of the Earth. Similarly, the expression $h = \tfrac{v^2}{2g}$ for the maximum height reached by a vertically projected body with velocity v is useful for small heights and small initial velocities only. In case of large initial velocities we have to use the principle of conservation of energy to find the maximum height reached. This same expression can be solved for v to determine the velocity of an object dropped from a height h immediately before hitting the ground, $v=\sqrt{2gh}$, assuming negligible air resistance.

### Gravity and astronomy

The discovery and application of Newton's law of gravity accounts for the detailed information we have about the planets in our solar system, the mass of the Sun, the distance to stars, quasars and even the theory of dark matter. In Astronomy, the discovery and application of Newton's law of gravity accounted for the detailed information we have about the planets in our solar system the mass of the sun A quasar (contraction of QUASi-stellAR radio source) is an extremely powerful and distant Active galactic nucleus. In Physics and cosmology, dark matter is hypothetical Matter that does not interact with the electromagnetic force but whose presence can be inferred from Although we have not traveled to all the planets nor to the Sun, we know their masses. These masses are obtained by applying the laws of gravity to the measured characteristics of the orbit. In space an object maintains its orbit because of the force of gravity acting upon it. In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star Planets orbit stars, stars orbit galactic centers, galaxies orbit a center of mass in clusters, and clusters orbit in superclusters. The Galactic Center is the rotational center of the Milky Way Galaxy. A galaxy is a massive gravitationally bound system consisting of Stars an Interstellar medium of gas and dust, and Dark matter Superclusters are large groupings of smaller galaxy groups and clusters, and are among the largest structures of the Cosmos. The force of gravity is proportional to the mass of an object and inversely proportional to the square of the distance between the objects.

Main article: Gravitational wave

In general relativity, gravitational radiation is generated in situations where the curvature of spacetime is oscillating, such as is the case with co-orbiting objects. In Physics, a gravitational wave is a Fluctuation in the Curvature of Spacetime which propagates as a wave, traveling outward from SpaceTime is a patent-pending three dimensional graphical user interface that allows end users to search their content such as Google Google Images Yahoo! YouTube eBay Amazon and RSS The gravitational radiation emitted by the solar system is far too small to measure. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. However, gravitational radiation has been indirectly observed as an energy loss over time in binary pulsar systems such as PSR 1913+16. It is believed that neutron star mergers and black hole formation may create detectable amounts of gravitational radiation. A neutron star is a type of remnant that can result from the Gravitational collapse of a massive Star during a Type II, Type Ib or Type A black hole is a theoretical region of space in which the Gravitational field is so powerful that nothing not even Electromagnetic radiation (e Gravitational radiation observatories such as LIGO have been created to study the problem. For the Latvian holiday Ligo see Jāņi. LIGO stands for Laser Interferometer Gravitational-Wave Observatory. No confirmed detections have been made of this hypothetical radiation, but as the science behind LIGO is refined and as the instruments themselves are endowed with greater sensitivity over the next decade, this may change.

## Anomalies and discrepancies

There are some observations that are not adequately accounted for, which may point to the need for better theories of gravity or perhaps be explained in other ways.

• Stars on the outskirts of galaxies are moving faster than they should. Also galaxies within galaxy clusters are moving faster than they should. Dark Matter and MOND have both been proposed as explanations. In Physics and cosmology, dark matter is hypothetical Matter that does not interact with the electromagnetic force but whose presence can be inferred from In Physics, Modified Newtonian dynamics ( MOND) is a theory that proposes a modification of Newton's Second Law of Dynamics (F = ma to explain
• The expansion of the universe seems to be speeding up. The metric expansion of space is the averaged increase of metric (i Dark Energy has been proposed to explain this. In Physical cosmology, dark energy is a hypothetical exotic form of Energy that permeates all of space and tends to increase the rate of expansion of the universe A recent alternative explanation is that the geometry of space is not homogeneous (due to clusters of galaxies) and that when the data is reinterpreted to take this into account, the expansion is not speeding up after all. [17]
• The Pioneer spacecraft seem to be slowing down in a way which has yet to be explained. The Pioneer anomaly or Pioneer effect is the observed deviation from expectations of the trajectories of various Unmanned spacecraft visiting the Outer [18]
• Various spacecraft have experienced greater accelerations during slingshot maneuvers than expected. The flyby anomaly is an unexpected energy increase during Earth flybys of satellites
• An apparent frame dragging effect has been measured by Martin Tajmar and others which exceeds that predicted by General Relativity by many orders of magnitude. Albert Einstein 's theory of General relativity predicts that rotating bodies drag Spacetime around themselves in a phenomenon referred to as frame-dragging Martin Tajmar is a research scientist and project manager in the Space Propulsion group at Austrian Research Center (ARC Seibersdorf.

## Alternative theories

### Historical alternative theories

• Aristotelian theory of gravity
• Le Sage's theory of gravitation (1784) also called LeSage gravity, proposed by Georges-Louis Le Sage, based on a fluid-based explanation where a light gas fills the entire universe. Alternatives to general relativity are physical theories that attempt to describe the phenomena of Gravitation in competition to Einstein's theory of General The Greek Philosopher Aristotle ( 384 BC – 322 BC) developed many theories on the nature of Physics that are completely different Le Sage's theory of gravitation is the most common name for the kinetic theory of gravity originally proposed by Nicolas Fatio de Duillier in 1690 and later by Georges-Louis Georges-Louis Le Sage (* June 13, 1724 in Geneva, † November 9 1803 in Geneva) was a Physicist and is most
• Nordström's theory of gravitation (1912, 1913), an early competitor of general relativity. In Theoretical physics, Nordström's theory of gravitation was a predecessor of General relativity.
• Whitehead's theory of gravitation (1922), another early competitor of general relativity. In Theoretical physics, Whitehead's theory of gravitation was introduced by the distinguished mathematician and philosopher Alfred North Whitehead in 1922

### Recent alternative theories

• Brans-Dicke theory of gravity (1961)
• Induced gravity (1967), a proposal by Andrei Sakharov according to which general relativity might arise from quantum field theories of matter. In Theoretical physics, the Brans-Dicke theory of gravitation (sometimes called the Jordan-Brans-Dicke theory) is a theoretical framework to explain Gravitation Induced gravity (or Emergent gravity) is an idea in Quantum gravity that space-time background emerges asa Mean field approximation of underlying microscopic Andrei Dmitrievich Sakharov (Андре́й Дми́триевич Са́харов (May 21 1921 – December 14 1989 was an eminent Soviet nuclear Physicist General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916 In quantum field theory (QFT the forces between particles are mediated by other particles
• Rosen bi-metric theory of gravity
• In the modified Newtonian dynamics (MOND) (1981), Mordehai Milgrom proposes a modification of Newton's Second Law of motion for small accelerations. In Physics, Modified Newtonian dynamics ( MOND) is a theory that proposes a modification of Newton's Second Law of Dynamics (F = ma to explain Mordehai Milgrom is an Israeli Physicist and Professor in the department of Condensed Matter Physics at the Weizmann Institute in Newton's laws of motion are three Physical laws which provide relationships between the Forces acting on a body and the motion of the
• The new and highly controversial Process Physics theory attempts to address gravity
• The self-creation cosmology theory of gravity (1982) by G. Self-creation cosmology (SCC theories are gravitational theories in which the Mass of the Universe is created out of its self-contained gravitational and scalar fields A. Barber in which the Brans-Dicke theory is modified to allow mass creation. In Theoretical physics, the Brans-Dicke theory of gravitation (sometimes called the Jordan-Brans-Dicke theory) is a theoretical framework to explain Gravitation
• Nonsymmetric gravitational theory (NGT) (1994) by John Moffat
• Tensor-vector-scalar gravity (TeVeS) (2004), a relativistic modification of MOND by Jacob Bekenstein

## Notes

• Note 1: Proposition 75, Theorem 35: p. In Theoretical physics, the nonsymmetric gravitational theory (NGT of John Moffat is a classical theory of Gravitation which tries to explain the mystery Tensor-Vector-Scalar gravity (TeVeS is a proposed relativistic theory which purports to explain Galactic rotation curves without invoking Dark matter. Jacob David Bekenstein (born May 1, 1947) is a Physicist who has contributed to the foundation of Black hole thermodynamics and to other aspects Anti-gravity is the idea of creating a place or object that is free from the force of Gravity. Artificial gravity is a simulation of gravity in Outer space or Free-fall. In Physics, escape velocity is the speed where the Kinetic energy of an object is equal to the magnitude of its Gravitational potential energy General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916 g-force (also G-force, g-load) is a measurement of an object's Acceleration expressed in g s A gravitational field is a model used within Physics to explain how gravity exists in the universe In Physics, a gravitational wave is a Fluctuation in the Curvature of Spacetime which propagates as a wave, traveling outward from The Gravitational Binding energy of an object consisting of loose material held together by gravity alone is the amount of Energy required to pull all The Gravity Research Foundation, established in 1948 by businessman Roger Babson (founder of Babson College) was an organization designed to find ways to implement In Physics, Gauss' law for gravity, also known as Gauss' flux theorem for gravity, is a law of physics which is essentially equivalent to Newton's law of universal The Jovian-Plutonian gravitational effect, a hoax phenomenon stated to cause a noticeable short-term reduction in gravity on Earth, was an invention for In Astronomy, Kepler's Laws of Planetary Motion are three mathematical laws that describe the motion of Planets in the Solar System. Newton's laws of motion are three Physical laws which provide relationships between the Forces acting on a body and the motion of the The n -body problem is the problem of finding given the initial positions masses and velocities of n bodies their subsequent motions as determined by The Pioneer anomaly or Pioneer effect is the observed deviation from expectations of the trajectories of various Unmanned spacecraft visiting the Outer Scalar theories of gravitation are field theories of Gravitation in which the gravitational field is described using a scalar field, which is required to satisfy some In the context of Classical theories of gravitation, the speed of gravity refers to the Speed at which a Gravitational field propagates Small body orbiting a central body Under Standard assumptions in astrodynamics we have m where m \ is the mass Standard gravity, usually denoted by g 0 or g n is the nominal acceleration due to gravity at the Earth's surface at sea level In the Physical sciences weight is a Measurement of the gravitational Force acting on an object Weightlessness is a phenomenon experienced by people during Free-fall. In Orbital mechanics and Aerospace engineering, a gravitational slingshot, gravity assist or swing-by is the use of the relative movement and 956 - I. Bernard Cohen and Anne Whitman, translators: Isaac Newton, The Principia: Mathematical Principles of Natural Philosophy. Preceded by A Guide to Newton's Principia, by I. Bernard Cohen. University of California Press 1999 ISBN 0-520-08816-6 ISBN 0-520-08817-4
• Note 2: Max Born (1924), Einstein's Theory of Relativity (The 1962 Dover edition, page 348 lists a table documenting the observed and calculated values for the precession of the perihelion of Mercury, Venus, and Earth. Max Born (11 December 1882 &ndash 5 January 1970 was a German Physicist and Mathematician who was instrumental in the development of Quantum )

## References

1. ^ Dick Teresi (2002), Lost Discoveries: The Ancient Roots of Modern Science - from the Babylonians to the Maya, Simon & Schuster, New York, ISBN 0-684-83718-8:

"Two hundred years before Pythagoras, philosophers in northern India had understood that gravitation held the solar system together, and that therefore the sun, the most massive object, had to be at its centre. "Pythagoras of Samos" redirects here For the Samian statuary of the same name see Pythagoras (sculptor. "

2. ^ S. Kak (2003). Subhash Kak (सुभाष काक Subhāṣ Kāk) (born March 26, 1947 in Srinagar, Kashmir) is an Indian American Indian Physics: Outline of Early History, p. 22. arXiv. The arXiv ( pronounced " Archive " as if the "X" were the Greek letter Chi, χ is an Archive for electronic Louisiana State University. Louisiana State University and Agricultural and Mechanical College, generally known as Louisiana State University or LSU, is a public, Coeducational
3. ^ Brahmagupta (628 AD). Brahmagupta ( (598–668 was an Indian mathematician and astronomer. Brahmasphuta Siddhanta ("The Opening of the Universe"). The main work of Brahmagupta, Brahmasphuta-siddhanta (The Opening of the Universe, written in the year 628, contains some remarkably advanced ideas including
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17. ^ [1] Dark energy may just be a cosmic illusion New Scientist
18. ^ [2] Wanted: Einstein Jr, Mar 6th 2008 The Economist
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