I think that's the understanding of gravity for sizes of an atom and larger, which fall under the theory of relativity. In relativity, gravity is not a force; spacetime is a fabric that is bent by the presence of matter. For things smaller than an atoms, the leading theory is quantum mechanics. Quantum mechanics hasn't definitely explained gravity. One of the leading subtheories to quantum mechanics uses a hypothetical particle called a graviton to communicate gravity. No one has been able to unite the two leading theories in physics (relativity and quantum mechanics) with any experimental success. In the meantime, we just treat (a) things smaller than atom and (b) everything larger as two different worlds.