The fact that all electromagnetic waves move in space at the speed of light (c) is a fundamental principle in physics derived from Maxwell's equations and supported by experimental evidence. Maxwell's equations describe the behavior of electromagnetic waves and provide a mathematical framework to understand their propagation.
One of Maxwell's equations is the wave equation, which describes how electromagnetic waves propagate through space. When solving the wave equation, it is found that the speed of propagation, denoted by "v," is related to the electric permittivity (ε₀) and magnetic permeability (μ₀) of the medium:
v = 1/√(ε₀μ₀)
For free space (a vacuum), the electric permittivity (ε₀) and magnetic permeability (μ₀) have specific values. In the International System of Units (SI), these values are defined constants:
ε₀ ≈ 8.854 × 10^(-12) F/m (farads per meter) μ₀ ≈ 4π × 10^(-7) H/m (henries per meter)
When the values of ε₀ and μ₀ are substituted into the equation, the speed of propagation in a vacuum is calculated as:
v = 1/√(ε₀μ₀) = 1/√(8.854 × 10^(-12) × 4π × 10^(-7)) ≈ 299,792,458 m/s
The value obtained, approximately 299,792,458 meters per second, is defined as the speed of light (c) in a vacuum. This means that any electromagnetic wave traveling through a vacuum, regardless of its frequency or wavelength, will propagate at this constant speed.
Experimental evidence, including observations of electromagnetic radiation from various sources and measurements conducted in different contexts, consistently supports the conclusion that electromagnetic waves indeed move in space at the speed of light. The speed of light in a vacuum serves as a fundamental constant in physics and is denoted by "c."