It is said that there is no such thing as gravity. Mass/energy curves spacetime and a body follows this curvature so gravity is basically the geometry of spacetime. If there is no force of gravity why does a mass move at all along the curvature of spacetime and what determines which way it will move. E.G. If I drop an apple, if there is no gravitation attraction to the earth why does it move towards the earth, why doesn't it move upwards instead?
Gravity is a force. It is exerted by curvature of space, which in turn, is caused by mass of earth. So, it is roundabout way of saying that earth exerts a force on the apple. This is per GR which so far, is the most accurate way for quantitative description of the force/phenomena.
It causes acceleration, it requires another force to counter it, it imparts momentum, and kinetic energy, it follows inverse square law, similar to electromagnetic force .. It has all the characteristics of a force.
Curvature of space describes how the action/force at a distance is realized. It does not say that the action/force does not exist.
If you drop an apple it does not accelerate. Weird, huh, but fundamental. To elaborate, if I was in the apple's frame of reference I would feel no acceleration. But normally there I am standing on the ground by the apple, and I do feel acceleration. But I'm not speeding up. In fact I experience a force resisting the natural motion that free objects will take in a gravity well.
Anyway in the way I described above you can intuitively feel the truth - that gravity is different from other forces.
All the answers are perfect. I am telling the same in a simpler version. The idea is, consider mass as a deformation, or for convenience, conceptually, a drawing in space-time. Seeing it from a particle physics level, the drawings consist of certain jigzo puzzle like pieces(again conceptually). They cannot be altered or deformed but, together a few such pieces make the drawing. The fundamental particles are these jigzos. When fundamental particles get into a structure, with stability, the nucleus, the atom and everything, they form the matter that we see. Now, to explain gravity, it will be too complex to think in this particle sense. But, since the deformation doesn't really have a definite frame of reference, we can treat gravity like we do to isometric factors. We can see the earth as a big piece of mass, that is a big drawing in space time. But, these drawings or deformations have a tendency to get back to nothing. This cause a force to decrease the deformation. Two such deformations, as they get closer, the sum of their deformations will get lesser. In order to attain such a partial stability by reducing deformations, masses tend to come closer. Call it gravity, if interested. Thank you.
protected by Qmechanic♦ Feb 5 '17 at 12:08
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