Here's why:

* Gravitational Force: It's the force of attraction between any two objects with mass. It's the force that keeps us on the Earth, and the force that holds planets in their orbits. It's very weak at the scale of individual particles, but it's the dominant force over large distances.

* Electromagnetic Force: This force governs the interaction between electrically charged particles. It's responsible for light, electricity, magnetism, and chemical bonding. It's much stronger than gravity at short distances.

* Strong Nuclear Force: This force binds protons and neutrons together in the nucleus of an atom. It's the strongest of the four forces, but it only operates over extremely short distances (within the nucleus).

* Weak Nuclear Force: This force is responsible for radioactive decay. It's weaker than the strong force but stronger than the electromagnetic force. It's also a short-range force.

While gravity is the weakest force at the level of individual particles, it becomes the dominant force over vast distances due to the cumulative effect of mass. This is why gravity governs the motion of galaxies and the expansion of the universe.