Question

How light travel without any external force

Answer 1

Basically, traveling at incredible speeds 299 792 458 m/s and at different wavelengths, depending on its energy. It also behaves as both a wave and a particle, able to propagate through mediums as well as space. It has no mass, but can still be absorbed, reflected, or refracted if it comes in contact with a medium. And in the end, the only thing that can truly slow down or arrest the speed of light is gravity

the force on a charged particle which might be travelling near the speed of light relativistic form of the Lorentz force