1. Propagation of Light: The most obvious indication is the propagation of light. We see objects because light waves travel from them to our eyes. This travel takes time, as evidenced by the delay in seeing events happening at a distance, like lightning strikes.
2. Doppler Effect: When a source of electromagnetic radiation is moving relative to an observer, the observed frequency changes. This is known as the Doppler effect. For instance, an ambulance siren sounds higher pitched as it approaches and lower pitched as it moves away. This frequency shift only occurs because the waves are traveling.
3. Interference and Diffraction: Electromagnetic waves exhibit interference and diffraction patterns. This means they can interact with each other, adding and subtracting in a predictable way, and bend around obstacles. These phenomena demonstrate the wave-like nature of light and its ability to move and interact with its surroundings.
4. Polarization: Electromagnetic waves are polarized, meaning their electric field oscillates in a specific direction. This polarization can be manipulated and used to filter and control the light. The fact that polarization can be changed indicates that the wave is moving and changing direction.
5. Measurement of Speed: The speed of electromagnetic waves has been precisely measured and is constant in a vacuum (the speed of light, c). This constant speed further confirms that these waves are traveling through space.
6. Mathematical Models: Electromagnetic waves are described by Maxwell's equations, which are a set of fundamental laws that govern the behavior of electric and magnetic fields. These equations predict the wave-like behavior and propagation of electromagnetic radiation.
7. Experimental Evidence: Numerous experiments, like Young's Double Slit experiment, demonstrate the wave nature of light and the ability of electromagnetic waves to travel and interact with matter.
In summary, the combination of these observations and theoretical frameworks provides strong evidence that electromagnetic waves travel and move through space.
