Photons travel at the speed of light because they have no mass. According to Einstein's theory of relativity, objects with mass cannot reach the speed of light because it would require an infinite amount of energy. Since photons have no mass, they are able to travel at the speed of light.
The speed of light has been measured and confirmed using various methods, such as the Michelson-Morley experiment and the measurement of the speed of light in a vacuum. These experiments have consistently shown that the speed of light is approximately 299,792,458 meters per second, which is the same speed at which photons travel.
According to the theory of relativity, nothing can travel faster than the speed of light. This is because as an object approaches the speed of light, its mass increases and it requires more energy to accelerate it further. Therefore, it is impossible for any object with mass to reach or exceed the speed of light.
The speed of light is considered a universal constant and is used as a fundamental component in the equations of special relativity. One of the consequences of this is time dilation, where time appears to pass slower for objects moving at high speeds. This means that as an object approaches the speed of light, time slows down for that object.
There are no known exceptions to this rule. Photons have been observed traveling at the speed of light in all experiments and observations. However, there are theories, such as the string theory, that propose the existence of particles called "tachyons" which could potentially travel faster than the speed of light. However, this is currently only a theoretical concept and has not been proven or observed.