The Big Bang theory is one theory for the origin of the Universe - Edexcel - GCSE Physics - Question 10 - 2021 - Paper 1

To determine which option provides evidence that the Universe had a beginning, we must consider the implications of each discovery:

• A: The discovery of other galaxies: While discovering other galaxies expands our understanding of the Universe, it does not specifically indicate a beginning.
• B: The discovery of the moons of Jupiter: This discovery is related to our solar system and does not provide evidence of the Universe's beginning.
• C: The discovery of planets orbiting distant stars: Similar to other galaxies, this discovery indicates the vastness of the Universe but lacks evidence of a starting point.
• D: The discovery of cosmic microwave background (CMB) radiation: This is key evidence supporting the Big Bang theory, as it represents the afterglow of the initial explosion, providing a direct link to the Universe's beginning.

Thus, the correct answer is D: the discovery of cosmic microwave background (CMB) radiation.