Theory What the Force of Gravity is

It might that the space-time, at the particles' level, be curved too by mass and that the gravity be there too of a Einsteinian nature, with those space-time's 'micro-curvatures' mixing up with the electro-magnetism or the strong force. The subsequent developement of the structured matter would just make the Einsteinian curvature more apparent. Backwards toward the Big Bang, that would bring the idea that, when the gravity splits from the other forces, few after the end of the Planck time, that occurs, simply, because the quantum fluctuation of the scalar field already is, by nature, creating, although void, some space-time. That transition from the void energy to the very first bricks of the particles thus logically comes with the gravity as the void turns into 'some thing', that some thing being the Einstein space-time, where matter is curving the latter! The very first particles likely keep being laced with the strong, electromagnetic, and weak forces however. The inflation thus should mostly be the conflicting cohabitation of particles of that type. Quantum gravity might be probabilistic, a kind of relativistic gravity wrapped upon itself, beyond the Planck time and dimension and forming some kinds of pockets inside the primordial soup
Dark matter, on the other hand, might well have something to do with such primeval particles as the dark energy might only be due to dark matter winning over the 'usual' matter. Einstein thus might have had the good intuition with his idea of the cosmological constant

Early scientists, for long, held for the wrong idea which has been taught by the Greek, 300's B.C. philosopher and scientist Aristotle, that the lighter objects were falling slower than the heavier ones. The idea was accepted until proved scientifically false by the Italian scientist Galileo, by the 1600's, who demonstrated than any object, independently of what its mass is, is falling at the same rate, due to gravity. The famed vision, by the English astronomer and scientist Isaac Newton, of a apple fallig down Earth from a tree, led him to understand that the force of gravity was a far-reaching one. In his work, in 1687, called 'Philosophiae naturalis principia mathematica' or the 'Mathematical Principles of Natural Philosophy', he computed the strength of the force of gravity, showing it was decreasing as far one gets distant from its source -any celestial body, for example. The mathematical expression of that is Newton's law of gravitation, which says that the gravitational force between two objects is directly proportional to the masses of those. The larger both masses are, the larger the force. Newton's law too is stating that the gravitational force between two objects is oppositely proportional to the distance between the two objects squared (which is the formula: F=m1xm2/d2). He further established the theory according which it's gravity which holds the planets around the Sun, keeping them is such a free fall, just the equivalent of the fall of an object on Earth! The acceleration of an object toward the ground caused by gravity alone, near the surface of Earth, is called 'normal gravity,' or 1G. This acceleration is equal to 32.2 ft/sec2 (9.8 m/sec2). Objects inside a space capsule, or the ISS, for exemple, appear to float in a state called 'zero gravity' (0G), or more accurately microgravity (1x10-6 G.)

The next step into the understanding of the force of gravity was in the early 1900's when Einstein came to a new vision of how all that was working. The General theory of Relativity, in 1915, came like the new explanation of space, time, and the force of gravity. According to Einstein, time and space are just one entity, known like 'space-time', a combination of time, and the three, usual, dimensions of space (the length, the width, and the height). Einstein further estimated that mass and energy can curve that space-time. In such a renewed view of the solar system, the reason why Earth is orbiting around the Sun, or Moon is orbiting around the Earth, resides into that the body -the Sun, or the Earth- at the center of the system, is curvating its space-time environment -about the same way a ball of lead laid down unto an elastic fabric of sort would yield a entonnoir-shaped curvature. The result of that shape of space-time around, for example, the Sun or the Earth, just makes that any object, with a certain speed, caught into that entonnoir just keeps orbiting around the central body! Einstein, thus, was just augmenting, dramatically however, the concept laid by Newton of why the planets were orbiting the Sun, or any celestial object another one. The subtility just was the trick of the curved space-time, as Newton just saw the force of gravity like a physical force, like any other, of a immaterial nature. The other major step performed by Einstein's Relativity is the 'principle of equivalence', which says that the effects of gravity are just similar to those of acceleration. Acceleration is another physical force which is felt by an object when its motion's speed is changed. Einstein demonstrated how a ball let fallen inside a spaceship which felt no acceleration would just hover, as, inside a spaceship in a phase of acceleration -and level- the ball would fall -and fall behind hand. That falling motion which would draw the ball down, and behind, is in that specific case due to acceleration, as, on any celestial body, for example, it's due (at least as far as the falling motion only is concerned) to gravity only. The General Relativity, too, with its new concept of the gravity due to the curvature of the space-time, led scientist to observe that the lights rays and radio waves are just bended too by any objet with a mass. The bending of the light of stars as seen perspectively behind the Sun was experimentally evidenced during a total solar eclipse in 1919. The bending of the radio waves were mostly observed when the interplanetary space exploration began, with radio signals of spacecraft shifted when received from behind the Sun, in the solar system

The most recent years in physics, at last, seem to be renewing, or, at least, increasing the views of Einstein. The concept of the 'dark matter' that stock of matter in the Universe which is part of the Universe's mass budget, or the one of the 'dark energy', which is a force, of unknown origin yet, see accelerating the expansion of the Universe since 7 billion years. The dark matter, on one hand, is just using gravity only in its relation with the rest of the matter in the Universe, as the dark energy seems of an anti-gravitational nature, both such discoveries and researches putting back the question of the force of gravity on the saddle