According to the prevailing scientific understanding, the universe has been expanding since the Big Bang, which is thought to have occurred approximately 13.8 billion years ago. This expansion suggests that the universe was indeed smaller in the past.
The concept of the expanding universe is supported by various lines of evidence, such as the observed redshift of distant galaxies, the cosmic microwave background radiation, and the abundance of light elements. These pieces of evidence collectively form the basis of the Big Bang theory.
In the early stages of the universe, shortly after the Big Bang, it is believed to have undergone a rapid period of expansion known as inflation. During this inflationary epoch, the universe expanded exponentially, causing it to become much larger and less dense. This period of rapid expansion smoothed out irregularities in the universe and laid the groundwork for the structures we observe today.
While the universe has been expanding over time, it's important to note that this expansion refers to the overall scale of the universe, rather than objects within it. On smaller scales, gravity can counteract the expansion and cause objects like galaxies and galaxy clusters to form and remain bound together.
In summary, the prevailing scientific consensus is that the universe has been expanding since the Big Bang, indicating that it was smaller and denser in the past.