3. The Nature of Light
What is light? Light is a special force, why do you say so, because photons do not have mass, electric charge and magnetic charge, and the speed of propagation is the speed of light (its speed is the same as the speed of propagation of electrostatic force, magnetic force and gravitational force, so it shall be said that the propagation speed of force is the speed of light), and its effect is to cause entity particles to move (for example, we feel warm when the sunlight is on our body), so if light is not force, what else is it? So light is a kind of force, and a single photon is the fundamental unit of light, and a ray is made up of a huge number of photons moving in the same direction. But light is the only unidirectional force, which is very different from the other three omnidirectional forces (electrostatic force, magnetic force, and gravitational force). Moreover, when photon interacts with particle, it is also very different from the other three omnidirectional forces. The propagation direction and magnitude of omnidirectional forces will not be affected when they encounter particles. In other words, the interaction of omnidirectional forces with particles only tells the particles how to move, without changing the forces, as if there is no particle. As a unidirectional force, the photon will change its propagation direction after encountering the particle, but the magnitude of the force it carries will remain the same. When a particle encounters a photon, it will also receive the force carried by the photon and change its motion.