Question

Which fundamental force acts over the longest distance?

Answer 1

Both electromagnetism and gravity have infinite range. But gravity is more likely to actually be seen over great distances.

Explanation:

Start with the fact that there are four fundamental forces. The strong nuclear force and the weak nuclear force are, as the names imply, active only within atomic nuclei; they have ranges only about as long as the extent of an atomic nucleus.

That leaves electromagnetism and gravity. There are both long-range, able to act over indefinitely large distances. But on a large scale, positive and negative charges tend to cancel out their electromagnetic fields, whereas all masses add more and more to the gravitational field with no cancellation.

So -- electromagnetism and gravity are equally long-range, but gravity is more likely to be seen over great distances.