A few hundred years back, it was thought that earth is flat. When the realization came that earth is spherical, a question came up- why the objects on the bottom side of the spherical earth do not fall off? Answer for this was given by Newton, when he suggested that earth is pulling everything towards itself, and he called the pulling force as gravitational force, thus gravity came to be known. But how the gravity is created and why heavy masses pull each other was not clarified by him.
Einstein went a step further and theorized that heavy masses pull each other due to curvature of space-time. But he did not give reasoning as to why heavy mass curves space-time and creates gravity? He said, ‘Gravity curves space-time and curvature of space-time is gravity’. This statement is similar to the statement ‘Hen produced egg, and egg developed into hen’. Thus, the reasoning of gravity being curvature of space-time is ambiguous, and therefore, even after Einstein’s General Theory of Relativity, it could not be known how gravity is created?
Here is a possible answer to this question.
As we know that matter can disintegrate into energy as per Einstein’s famous equation E= mc2, if we assume that a planet having gravity disintegrates into energy, then what will happen to its gravity? Gravity of the planet will disappear. Considering the reverse case, when energy converts to matter, and creates a planet, gravity should appear.
So, there is a possibility that gravity came into existence when energy (or dark energy) of the space converted into matter.