Which fundamental force dominates over the longest distances in the universe?

Gravity is the only one of the four fundamental forces that acts significantly over astronomical distances. It never cancels itself out the way electric forces often do in bulk matter, so it becomes the controlling force for planets, stars and galaxies. On cosmic scales, gravity is responsible for the formation of solar systems, the orbits of planets and the clustering of galaxies. Although it is the weakest force at the particle level, its cumulative effect on large masses makes it dominant in astronomy. General relativity, published by Albert Einstein in 1915, is the modern theory of gravity.