The concept of the Big Bang refers to the beginning of the observable universe as we know it. According to the prevailing scientific theory, the Big Bang occurred approximately 13.8 billion years ago and marked the origin of space, time, and matter. However, it is important to clarify some points regarding your question:
The Previous Universe: The Big Bang theory does not provide a direct explanation or evidence regarding the existence of a previous universe before the Big Bang. The theory describes the expansion of the universe from an extremely hot and dense state, but it does not encompass or provide information about any hypothetical universe that may have existed before it.
Existence of Galaxies and Planets: The early stages of the universe after the Big Bang were characterized by the rapid expansion and cooling of matter. Over time, as the universe expanded and cooled further, it allowed for the formation of galaxies, stars, and eventually planets. However, the specific processes and timeline of galaxy and planet formation are still active areas of scientific research and study.
In summary, while the Big Bang theory describes the beginning of the observable universe and the subsequent development of galaxies and planets over billions of years, it does not provide information about any previous universe or its composition. Our current understanding of the universe's history is based on observations, mathematical models, and scientific theories that continue to evolve as new evidence and discoveries emerge.