Final answer:
With an infinite speed of light, astronomers could not observe the universe's past, as the delay in light's travel time allows us to see distant galaxies as they were long ago. The finite light speed operates as a cosmic time machine, vital for studying the universe's evolution, which would be lost at infinite speed.
Step-by-step explanation:
If the speed of light were infinite, astronomers would lose the ability to look back at galaxies as they appeared long ago. This is because the finite speed of light allows us to view celestial objects as they were in the past; the light that reaches us only after traversing vast cosmic distances carries information from the time it was emitted. For example, when we look at the Andromeda galaxy, which is 2 million light years away, we are seeing light that left it 2 million years ago. If light traveled instantaneously, we would see every astronomical object as it exists in the current moment, losing the ability to use the universe as a cosmic time machine.
Large telescopes and sensitive detectors have been instrumental in studying galaxies billions of light years away, examining how galaxies formed and evolved over time. This relies on the light from these galaxies taking billions of years to reach Earth, effectively allowing astronomers to observe these galaxies at various stages of their formation.
Unfortunately, with an infinite light speed, we would not be able to reconstruct the history of the cosmos nor observe the evolution of the universe over time, eliminating one of the fundamental methods with which we currently understand cosmological development and test hypotheses about the Big Bang and universe's history.