Gravity does act between all objects with mass, but its strength is directly proportional to the product of the masses and inversely proportional to the square of the distance between them. In daily life, most objects we encounter have relatively small masses compared to celestial bodies like the Earth. The gravitational force between two everyday objects, say between a book and a pen, is minuscule and practically undetectable. In contrast, Earth, with its enormous mass, exerts a gravitational force that is strong enough to be very noticeable, keeping everything anchored to its surface.

If the value of the gravitational constant, G, were to increase significantly, it would enhance the gravitational force between all objects with mass. Celestial bodies would experience stronger attractions, leading to changes in orbital motions of planets, stars, and galaxies. On Earth, everything would weigh more due to the increased gravitational force. This could lead to numerous catastrophic events, including potential planetary collisions and even the collapse of stars. Furthermore, the delicate balance of forces within atoms could be disrupted, affecting fundamental processes at the microscopic level.

The gravitational constant, G, was first measured by Henry Cavendish in 1797-98 using a torsion balance experiment. He used a horizontal bar suspended from a thin wire, with small lead spheres attached to each end. Large lead spheres were placed close to the smaller ones, and the gravitational attraction between them caused the bar to twist, rotating the wire. By measuring this twist and knowing the properties of the wire and the masses involved, Cavendish could determine the gravitational force between the masses and thus calculate the value of G. His experiment was incredibly precise for his time, and his value was very close to the currently accepted value.

The inverse-square law, given by F = G (m1 * m2) / r², implies that as the distance between two masses increases, the gravitational force decreases rapidly. This ensures that planets farther from the Sun experience a weaker gravitational force than those closer to it. If gravity didn't decrease with the square of the distance, planets farther from the Sun might not have been captured into stable orbits. The law ensures that planets, regardless of their distance from the Sun, are in balance between the gravitational pull of the Sun and their inertial tendency to move in a straight line, resulting in stable, elliptical orbits.

Gravity, despite being the weakest force, has two distinct characteristics that make it the dominant force at astronomical scales. Firstly, it has an infinite range, which means that no matter how far two masses are from each other, they'll always exert a gravitational force on one another. Secondly, it is always attractive and cumulative, unlike electromagnetism where positive and negative charges can cancel each other out. Hence, on a cosmic scale, where you have massive bodies like planets, stars, and galaxies, the gravitational force becomes substantial, determining the motion and interaction of these celestial entities.