All types of electromagnetic waves, including radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays, move with a constant speed denoted by "c," which is approximately equal to 299,792,458 meters per second in a vacuum. This speed is commonly referred to as the speed of light.
The fundamental reason why electromagnetic waves travel at this specific speed is rooted in the underlying properties of space and time. It is a consequence of the relationship between electric and magnetic fields, as described by Maxwell's equations, which are a set of fundamental equations governing electromagnetism.
Maxwell's equations mathematically describe how electric charges and currents generate electric and magnetic fields and how these fields interact with each other. When Maxwell's equations are solved, they predict the existence of electromagnetic waves and their propagation characteristics.
In the solutions to Maxwell's equations, a fundamental constant emerges: the reciprocal of the product of the permeability of free space (μ₀) and the permittivity of free space (ε₀). This constant is numerically equal to the square of the speed of light:
1 / √(μ₀ ε₀) = c
The permeability of free space relates to the behavior of magnetic fields, while the permittivity of free space relates to the behavior of electric fields. The reciprocal of their product gives rise to the speed of light. Therefore, the constant speed at which electromagnetic waves propagate in a vacuum is a fundamental property of the electric and magnetic fields and the medium in which they propagate.
This constant speed of light applies to all electromagnetic waves because they all arise from the same underlying physical principles. Regardless of the wavelength or frequency of the electromagnetic wave, they all exhibit this universal speed when traveling through a vacuum. In other materials or mediums, electromagnetic waves may travel at slightly different speeds, but in a vacuum, their speed remains constant at c.