Astrophysics (index)about

Gravity

(theory that mass attracts)

In physics, Gravity is the name given to a force that attracts masses together generally according to the product of their masses and the reciprocal of the square of the intervening distance (Law of Gravitation). It was theorized by Isaac Newton who observed the force drawing objects toward Earth and that drawing planets toward the Sun and Moons toward planets could all be explained by a single law, according to his estimates of feasible masses of the Sun, planets, and moons. Newton posited it as universal, i.e., that in other situations masses would affect each other according to the same law, its effect between everyday objects being negligible because of their relatively tiny mass.

Albert Einstein recast the theory as space itself being sucked into each mass (General Relativity, GR), calibrating his formula to virtually match Newton's excepting extreme circumstances, but with some consequences, such as Electromagnetic Radiation passing near a massive object being affected just as a passing object would be. The term Newtonian Gravity is used when it is necessary to distinguish it from GR.

These theories are phenomenally successful: for example, their reliability and precision has made space navigation as we know it possible, and the theorized bending of light has been observed. Yet they have failed to explain some observations:

  • Stars in galaxies do not orbit the galaxy in accordance to gravitational theory, given the apparent masses of the galaxies' constituent stars and clouds.
  • Gravity would make the universe accelerate inwardly (or given its current expansion, would make that expansion decelerate), but observations suggest it is doing the opposite.

Scientists have sufficient faith in gravitational theory that they cite it to assert galaxies must include matter that has yet to be seen (Dark Matter), and that there must be an as-yet-unexplained outward force at work in the universe (Dark Energy). Alternately, attempts have been made to further refine gravitational theory to explain these observations (Modified Newtonian Dynamics and DGP Gravity).


(physics,relativity)
http://en.wikipedia.org/wiki/Gravity

Referenced by:
Accretion
Accretion Disk
Advection
Alcock-Paczyński Effect
Atmosphere
Atmospheric Tide
Baryon Acoustic Oscillations (BAO)
Binary Star
Binding Energy
Birkhoff's Theorem
Black Hole (BH)
CASTRO
Cold Dark Matter (CDM)
Chandrasekhar Limit
Computational Astrophysics
Conic Section
Corotation Torque
Cosmological Constant (Λ)
Coulomb's Law
Critical Density (ρc)
Curvature
Darcy Velocity Field
Dark Flow
Dark Matter
Dark Matter Annihilation
Dark Matter Halo
DGP Gravity
Doppler Shift
Effelsberg 100-m Radio Telescope
Einstein-de Sitter Model
Electron Degeneracy
Electroweak
Extra-Solar Planet
Star Formation Feedback
Free-Fall Time
Galactic Halo
Galaxy Cluster (CL)
Geodesic
Giant Molecular Cloud (GMC)
General Relativity (GR)
Gravitational Collapse
Gravitational Constant
Gravitational Instability Model
Gravitational Lensing
Gravitational Potential
Gravity Sounding
Gravity Wave
Gravitational Wave (GW)
Hale Telescope
Helium Rain
Homologous Collapse
Hydrodynamic Equations
Hydrostatic Equilibrium
Internal Gravity Wave
Inverse Square Law
Isothermal Core
J2
Jeans Length
JUICE
Juno
Kepler's Laws
Kelvin-Helmholtz Mechanism
Lagrangian Point
Lambda-CDM model (ΛCDM)
Lane-Emden Equation
Libration
Liquid Mirror Telescope
Mass Function
Maximum Iron Fraction
Maxwell-Boltzmann Distribution
Mirror Support Cell
Mixing Length Theory
Modified Newtonian Dynamics (MOND)
Multi-messenger Astronomy
Multipole Expansion
N-Body Problem
Neutron Star
Orbital Resonance
Orbital Speed
Planetesimal
Potential Energy (PE)
Power Law
Precession
Psyche
Redshift (z)
Reduced Mass
Relativity
Roche Limit
Solar and Heliospheric Observatory (SOHO)
Stellar Cluster
Stellar Core
Stellar Mass Determination
Stellar Structure
Strong-Field Gravity
Strong Force
Surface Gravity
Symmetry Breaking
Tidal Force
Time Dilation
Timescale (t)
Time Standard
Titan
Virial Parameter
Virial Theorem
Wormhole

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