When visible light travels through empty space without encountering any objects, it continues to propagate in a straight line until it interacts with something else, such as a planet, star, or interstellar medium.
In the vast emptiness of space, light can travel immense distances without being significantly affected. It moves at a constant speed of approximately 299,792,458 meters per second in a vacuum. As long as there are no obstructions or absorption along its path, light can travel indefinitely.
However, it's important to note that space is not completely empty. There are various particles and gases scattered throughout, albeit at very low densities. These particles can scatter and slightly affect the path of light, leading to phenomena like cosmic dust scattering or interstellar reddening. Additionally, the expansion of the universe causes a phenomenon called cosmological redshift, which stretches the wavelengths of light from distant sources, shifting them toward longer wavelengths (lower energy).
In summary, when visible light travels through empty space without encountering objects, it continues to propagate in a straight line until it interacts with other matter or is affected by cosmic phenomena.