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The most basic basic answer one could give is that gravity is caused by mass. This is essentially the answer that would have been given in Newton's era.
In 1916 Einstein published his Theory of General Relativity which quickly became (and still is) the best model for gravitation that we have. In Einstein's theory mass and energy are the same thing (consider his famous equation E = mc^2), therefore you might say that gravity is caused by energy (and all mass is energy).
Einstein's theory also offers a geometric picture of gravity; gravity consists of warps and curves in spacetime (caused by the presence of energy) which alter the paths of particles and give the 'illusion' of gravity.
The most in-depth answer currently available is that gravity is caused by the local Poincare invariance of the Laws of Nature. This basically means that you are free to use any coordinate system at any point in space and time and that the laws of nature are the same everywhere. This requirement automatically leads to Einstein's gravity. This is a result from quantum field theory. (Incidentally you can get the other forces of nature, such as the electromagnetic force from similar symmetry considerations).
What else can I help you with?
What is the Gravity in horse jumping?
You come up, you come down.
Where does the gravity of a planet come from?
Its mass
Where does the gravity that holds the planets in their orbits come from?
The gravity that keeps the planets in orbit is the sun's gravity, which is a product of the sun's mass.
How come the moon orbits the earth?
gravity
How come balloons have air but they do not bounce?
gravity
Where does force of a avalanche come from?
The force is gravity.
What causes gravity to come to earth?
the mass of the earth exerts gravity on all objects around it
What is a gravity knife?
The blade of a gravity knife is contained within the handle of the knife. It requires a spinning motion or gravity for the blade to come out of the handle.
Where did gravity come from. What did Gravity come from. and When did Gravity come into being?
Of those three questions, the only one that makes any sense is the last one. Gravity doesn't come from a place (the "Where" part) or a thing (the "What" part). Gravity is strongly suspected to have come into existence at the time of the Big Bang, along with the other three fundamental forces. If the Theory of Everything people are right, at extremely high energies the forces combine; gravity would probably have been the first to separate out, at about one Planck time after the Big Bang (a "Planck time" is about 5 x 10-44 seconds).
Why does your boyfriends sperm come straight out of you after sex?
gravity
How come an object can never be weightless?
gravity and mass...
When did the Samsung gravity 2 come out?
it came out in 2008
