When physicists assert that light can travel through empty space, they’re referring to the existence of non-trivial vacuum solutions to Maxwell’s equations. A vacuum solution implies that all sources are zero. In the context of Maxwell’s equations, this means both charge density and current density are zero. Furthermore, these specific solutions also satisfy the wave equation, and waves are often described as “traveling.”
The statement “there exist non-trivial vacuum solutions to Maxwell’s equations which are also solutions to the wave equation” is not easily digestible for most people. Hence, the simplified statement, “light can travel through empty space,” serves as a concise and effective way to convey this idea, albeit with some loss of technical accuracy. It’s an acceptable non-technical explanation, intended to be understood without excessive scrutiny.
Some might find the description of light as the field itself perplexing, even sounding like doublespeak. However, this is indeed the correct way to understand it. The notion that light travels through the electromagnetic field can be misleading. When we say a plane travels through the air, we acknowledge a clear distinction between the plane and the air. They are separate entities, with one physically situated within the other. This relationship doesn’t accurately represent the connection between light and the electromagnetic field.
Light is a particular kind of solution to Maxwell’s equations, which define electromagnetic fields. More specifically, light is a vacuum solution characterized by traveling waves (potentially with wavelengths specifically in the optical spectrum). Therefore, light is an electromagnetic field, and there’s no fundamental difference between them. Saying light travels through the electromagnetic field is more akin to saying wind travels through air rather than a plane traveling through air. While not entirely incorrect, it’s an unconventional way of phrasing it.
In essence, light doesn’t travel through empty space as if it were a separate entity traversing a medium. Instead, light is a manifestation of the electromagnetic field, a self-sustaining disturbance that propagates according to the laws of physics, even in the absence of matter.
