# Why there is a distance dependence in Coulomb's law if photons can travel to infinity?

Why there is a distance dependence in coulombs law if photons can travel to infinity? Why there is distance dependence at all?

• It is not clear why you think the distance dependence in Coulomb's law should have something to do with the maximum distance photons can travel. Coulomb's law is first and foremost a purely classical result of electromagnetism, where there are no photons. For its quantum derivation, see physics.stackexchange.com/q/142159/50583. – ACuriousMind Jul 28 '18 at 9:00
• @ACuriousMind, okay why force, provided by classic electric field decreases with distance? – user202572 Jul 28 '18 at 9:03

The simplified explanation is that photons spread out as they get further away from the source. And the strength of the electromagnetic force is roughly related to number of photons per unit cross-sectional area, not just the number of photons itself. So as the photons spread out and the area grows (as $r^2$), the strength of the force drops (as $1/r^2$).