The Big Bang theory is the prevailing scientific explanation for the origins and evolution of the universe based on extensive observational evidence and theoretical modeling. It is supported by a wide range of observations, including the cosmic microwave background radiation, the abundance of light elements, the large-scale structure of the universe, and the redshift of distant galaxies.
While the Big Bang theory describes the expansion and evolution of the universe, it doesn't attempt to explain the ultimate cause or what existed before the Big Bang. The theory focuses on the early stages of the universe, starting from a hot, dense, and extremely small singularity.
The concept of causality, which is the relationship between cause and effect, is deeply ingrained in our everyday experience and within the framework of classical physics. However, the behavior of the universe at its earliest moments, including the singularity itself, falls within the realm of extreme conditions where our current understanding of physics, including causality, may break down. The laws of physics, as we know them, may not fully apply to such extreme conditions, and we would need a more complete theory that unifies quantum mechanics and general relativity to address these questions.
Regarding the existence of space and time before the Big Bang, the prevailing view among cosmologists is that the concept of time as we know it breaks down at the singularity. The singularity represents a point of infinite density and temperature where the laws of physics, as we currently understand them, are unable to describe the conditions. Therefore, it is challenging to make definitive statements about what existed before the Big Bang or if the concept of "before" even applies in that context.
It's important to note that the Big Bang theory is continually refined and investigated through ongoing research, and scientists are actively working to explore the fundamental nature of the early universe. While there are still many open questions, the Big Bang theory remains the most widely supported explanation for the origin and evolution of the universe based on the available evidence.