Final answer:
While the electromagnetic force is far stronger than gravity at the level of subatomic particles, gravity dominates on a large scale because most objects are electrically neutral, causing electromagnetic forces to cancel out, unlike the always attractive gravity.
Step-by-step explanation:
The electromagnetic force is indeed much stronger than gravitational force on a small scale, such as between subatomic particles. For instance, the electrostatic force between two protons is vastly greater than the gravitational force they exert on each other. This disparity is because the electromagnetic force varies with the charge of the interacting particles and can be both attractive and repulsive. In contrast, gravity is always attractive and its force depends on the mass of the objects involved.
However, on large scales, gravity tends to dominate because most objects in the universe are electrically neutral, meaning their overall charge is balanced. Thus, the attractive and repulsive electromagnetic forces cancel each other out, whereas gravitational force, being always attractive, does not cancel and thus accumulates over large distances and masses. The large-scale structures of the universe, such as galaxies and clusters of galaxies, are held together by gravity for this reason, despite the comparative weakness of gravity on a per-particle basis.