The speed of electromagnetic radiation, such as light, is constant and is known as the speed of light in a vacuum, denoted by 'c.' This speed is approximately 299,792,458 meters per second (or about 186,282 miles per second).
The reason electromagnetic radiation travels at the speed of light is deeply rooted in the fundamental nature of the universe and is a consequence of the laws of physics as described by Einstein's theory of special relativity. Several key points can explain why electromagnetic radiation is limited to the speed of light:
Special Relativity: Einstein's theory of special relativity, formulated in 1905, shows that the speed of light in a vacuum is a universal constant and is the maximum speed at which information or energy can travel in the universe. According to this theory, as an object with mass approaches the speed of light, its mass increases, and it requires an infinite amount of energy to reach the speed of light. Since photons (particles of light) are massless, they can travel at the speed of light.
Lorentz Transformation: Special relativity also introduced the Lorentz transformation, which describes how time, space, and momentum change for objects moving close to the speed of light. As an object's velocity approaches 'c,' its time dilation and length contraction become significant, making it increasingly difficult for anything with mass to reach or exceed the speed of light.
Maxwell's Equations: James Clerk Maxwell's equations, formulated in the 19th century, describe the behavior of electromagnetic fields and waves, including light. These equations predict that electromagnetic waves travel at a speed equal to 1/sqrt(ε₀μ₀), where ε₀ is the vacuum permittivity and μ₀ is the vacuum permeability. These constants determine the speed of light in a vacuum, and thus, any electromagnetic radiation cannot travel faster or slower than 'c.'
In summary, the constancy of the speed of light is a fundamental property of our universe, deeply ingrained in the fabric of spacetime as described by special relativity and Maxwell's equations. Any attempt to accelerate an object with mass to the speed of light would require an infinite amount of energy, making it impossible to reach or exceed this speed. As for why electromagnetic radiation doesn't go slower, it's because the propagation speed is determined by the fundamental constants of nature, and electromagnetic waves simply travel at the speed dictated by these constants, namely the speed of light.