What did radio telescopes do in the big bang theory?

Answer 1

Perhaps the most important contribution of radio astronomy to the Big Bang theory was to finally put to rest its only real rival, the Steady State theory.

Steady State theory required the Universe to be eternally similar to the way it is today, with the known expansion of the Universe compensated for by a continual creation of matter in intergalactic space.

However, in 1965, Arno Penzias and Robert Wilson, working with a Bell Labs horn antenna at Holmdel, New Jersey, (and looking for quite something else entirely) discovered a uniform microwave hiss coming from all over the sky. This turned out to match a prediction by George Gamow and others that the Big Bang should leave just such a remnant noise filling the Universe.

The Steady State theory had no explanation for the existence of this noise (now termed the cosmic microwave background), while the Big Bang theory not only demanded it but rather closely predicted its temperature.

Answer 2

Radio telescopes help study the cosmic microwave background radiation, which is a remnant of the Big Bang. By observing this radiation with radio telescopes, scientists can gather insights into the early universe, its evolution, and the formation of structures in the cosmos.