Light travels through space until it is either absorbed by matter or scattered by particles. In a vacuum or in regions of extremely low density, light can travel great distances without significant interaction. However, even in these cases, there are factors that can cause light to be "lost" or become undetectable.
One factor is the expansion of the universe itself. As the universe expands, the wavelengths of light traveling through space also stretch, causing a phenomenon called cosmological redshift. This means that light waves get stretched to longer wavelengths, shifting toward the red end of the electromagnetic spectrum. In extreme cases, such as with very distant galaxies, this redshift can be so severe that the light is shifted out of the visible spectrum into infrared or radio wavelengths, making it undetectable to our eyes.
Additionally, light can be absorbed or scattered by various particles or objects it encounters along its path. For example, interstellar dust and gas can absorb or scatter light, reducing its intensity or altering its direction. In the vastness of space, light can encounter numerous such obstacles, which can eventually diminish its intensity over long distances.
However, it's important to note that light itself does not simply "fade" over time in the sense of losing energy or diminishing to nothing. Light is composed of individual particles called photons that carry a fixed amount of energy. As long as photons are not absorbed or scattered, they will continue to travel indefinitely.
So while light can be subject to absorption, scattering, or redshifting, its energy is conserved, and it can continue to propagate through space unless it encounters something that interrupts its path.