Gravity is a fundamental force of nature that arises due to the presence of mass or energy. It acts on all objects, whether they are composite objects made up of atoms or individual atoms themselves.
In classical physics, gravity is described by Newton's law of universal gravitation, which states that any two objects with mass attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
At the microscopic level, the gravitational force between individual atoms or particles is extremely weak compared to other fundamental forces, such as the electromagnetic force. The reason for this is that gravity is much weaker in strength compared to the other forces. For example, the electromagnetic force between two electrons is about 10^40 times stronger than the gravitational force between them.
However, when large numbers of atoms or particles come together to form composite objects like planets, stars, or galaxies, the cumulative effect of gravity becomes significant and dominates on larger scales. The gravitational force between these composite objects determines their motion, shape, and interaction on cosmological scales.
It is important to note that our understanding of gravity is based on Einstein's theory of general relativity, which describes gravity as the curvature of spacetime caused by mass and energy. In this theory, the concept of individual atoms is not directly relevant; rather, it is the distribution of mass and energy in spacetime that determines the gravitational effects.
So, while gravity acts on all objects, whether composite or individual atoms, its effects become more apparent and significant on larger scales where the cumulative mass and energy have a substantial impact on the curvature of spacetime.