Question

What led to the idea that the Universe started out in a big bang?

1.
The observation of the cosmic microwave background

2.
The earliest galaxies observed by the Hubble Space Telescope

3.
Using the Type 1A supernovae in the measurements of the expansion of the universe

4.
The observed expansion of the universe

Answer 1

A. The observation of the cosmic microwave background led to the idea that the Universe started out in a big bang.

Step-by-step explanation:

The cosmic microwave background (CMB) is radiation left over from the Big Bang. It is the oldest light in the Universe and provides a snapshot of the Universe at a very early time. The CMB was discovered in 1964 by Arno Penzias and Robert Wilson, and its existence supports the Big Bang theory. The CMB is nearly uniform in all directions, with small variations that correspond to the density fluctuations in the early Universe that gave rise to the formation of galaxies and other structures. The CMB is one of the strongest pieces of evidence for the Big Bang theory and led to its widespread acceptance among scientists.