Final answer:
Light traveling between two galaxies travels a longer distance due to cosmic expansion and experiences a cosmological redshift, as the wavelength of light is stretched by the expansion of space.
Step-by-step explanation:
The expansion of the universe due to the Big Bang affects everything within it, including light. As a result, light that is emitted by distant galaxies and travels through space experiences a phenomenon known as cosmological redshift. Due to the expansion, the wavelength of light is stretched, and thus, the light appears redder, which is a shift to lower energy wavelengths. If we consider light traveling from one galaxy to another, we can deduce that the light actually travels a longer distance than the distance between the galaxies when the light was first emitted. This is because as space expands, the light waves themselves are also stretched. Hence, the correct answer is that the light (b) travels a longer distance than the distance between galaxies when the light was first emitted and (d) experiences a cosmic redshift—not a cosmic blue shift—due to the same expansion of space.