If the Big Bang didn't happen and the universe has always existed, it would have significant implications for our understanding of the origin and evolution of the cosmos. The Big Bang theory is currently the prevailing model that describes the early stages of the universe's development.
The Big Bang theory suggests that the universe originated from a singularity—an extremely hot and dense point—approximately 13.8 billion years ago. From this initial state, the universe rapidly expanded and has been evolving ever since. This theory is supported by various lines of observational evidence, such as the cosmic microwave background radiation and the observed redshift of galaxies.
If the universe has always existed without a beginning, it would challenge the idea of a singularity and a definitive starting point. It would imply that the universe has been in existence for an infinite amount of time, with no particular origin event. This notion goes against the current understanding of the universe's history.
However, it is essential to note that our knowledge and understanding of the universe are based on scientific theories and observations. If a different model were proposed that could explain the existence of the universe without a Big Bang, it would require significant evidence and testing to be considered scientifically valid.
One alternative idea to the Big Bang is the concept of an oscillating universe, where the universe undergoes cycles of expansion and contraction indefinitely. This model suggests that the universe expands to a certain point, then contracts back into a singularity before expanding again in a never-ending cycle. However, this hypothesis also requires further investigation and observational evidence.
In summary, if the Big Bang didn't occur and the universe always existed, it would challenge our current understanding of cosmology and require new models and evidence to explain the origin and evolution of the universe. Scientific investigation and advancements would be necessary to explore and validate alternative theories or explanations.