The Big Bang theory is the prevailing scientific model that describes the origin and evolution of the universe. According to this theory, the universe originated from a highly dense and hot state approximately 13.8 billion years ago. However, when it comes to understanding what happened before or after the Big Bang, our current scientific understanding reaches its limits. Here's why:
Before the Big Bang: The Big Bang theory does not provide a description of what happened before the initial singularity, which is the state of infinite density and temperature from which the universe emerged. The nature of time and physical laws as we know them breaks down at this singularity, making it currently impossible to make definitive statements about what preceded the Big Bang. Speculations and hypotheses exist, such as the concept of a cyclic universe or theories involving extra dimensions, but these are still speculative and lack empirical evidence.
After the Big Bang: Our scientific understanding of the universe becomes more reliable after the first few moments following the Big Bang. The subsequent expansion and evolution of the universe can be studied using observations, experiments, and mathematical models. However, our understanding becomes less precise as we approach the extremely early stages of the universe, often referred to as the Planck epoch. During this epoch, which occurred within a fraction of a second after the Big Bang, our current understanding of physics breaks down, and a quantum theory of gravity is needed to describe the universe accurately. Unfortunately, such a theory is yet to be fully developed.
In summary, the Big Bang theory provides our best understanding of the early moments and subsequent evolution of the universe. However, our knowledge about what occurred before the Big Bang or during the earliest stages of the universe remains limited. Scientific research and theoretical advancements are ongoing, aiming to expand our understanding of these fundamental questions, but definitive answers are yet to be found.