The expansion of space, as described by the theory of cosmic inflation or the current accelerated expansion of the universe, does indeed suggest that certain regions of space can appear to recede from each other at speeds exceeding the speed of light. This phenomenon is known as the metric expansion of space.
However, it's important to note that the expansion of space itself does not violate the principle of special relativity, which states that information cannot be transmitted faster than the speed of light. The expansion of space is not the same as an object moving through space at a velocity exceeding the speed of light. Instead, it refers to the stretching of space itself, causing the distances between galaxies or other objects to increase.
The concept of "light years" as a unit of distance remains a useful and commonly used measure for astronomical distances. A light year represents the distance that light travels in one year, and it provides a convenient scale for discussing astronomical distances within our observable universe.
While the expansion of space can affect the comoving distances between objects over cosmic timescales, it doesn't alter the local dynamics within systems bound by gravity, such as our solar system or galaxies. In these systems, the gravitational forces dominate, and objects within them are not subject to the same expansion.
For discussing cosmological distances affected by the metric expansion of space, cosmologists often use alternative distance measures like comoving distance, proper distance, or redshift. These measures take into account the changing scale of the universe due to its expansion and provide a more accurate description of the distances between cosmological objects.
So, while the concept of "light years" remains a valuable and practical unit for everyday astronomical discussions, cosmologists have developed alternative distance measures to accurately describe the changing scale of the universe due to its expansion.