The statement that "expansion of space can exceed the speed of light" is a bit misleading. In the context of the expansion of the universe, it is not accurate to say that objects are moving away from each other at speeds faster than the speed of light. Instead, the expansion of space itself causes the distances between objects to increase.
The concept of objects moving faster than light is related to the theory of relativity, which governs the behavior of objects within space and time. According to the theory of relativity, nothing can travel through space faster than the speed of light. However, the expansion of space is a different phenomenon, and it does not violate this principle.
Regarding distance units, light years are commonly used to describe astronomical distances because they provide a convenient measure of the vast distances involved. A light year is defined as the distance that light travels in one year, which is approximately 9.46 trillion kilometers or 5.88 trillion miles. It is important to note that a light year is a measure of distance, not of time.
Since the expansion of space affects the distances between objects, it does not render the concept of light years non-standard or variable. Light years remain a useful and relevant unit of measurement for describing the vast distances in the universe. They provide a practical way to express distances on astronomical scales, allowing us to comprehend the enormous spans involved in interstellar and intergalactic distances.
It's worth mentioning that cosmologists and astronomers may use other distance measures or cosmological parameters, such as comoving distance or the Hubble constant, in their calculations when studying the dynamics of the expanding universe. However, light years remain widely understood and utilized for communicating astronomical distances to the general public.