The question of what happened before the Big Bang is still an open and active area of scientific inquiry. However, it's important to note that our current understanding of the laws of physics breaks down at the moment of the Big Bang itself, making it challenging to provide a definitive explanation for what occurred before that point.
The Big Bang theory describes the rapid expansion of the universe from a highly dense and hot state. It provides a detailed framework for understanding the evolution of the universe from an extremely early time onward, supported by various lines of evidence, such as the cosmic microwave background radiation and the observed redshift of distant galaxies.
However, the nature of the universe before the Big Bang is still a subject of speculation and ongoing research. Some physicists propose that the universe emerged from a singularity, a point of infinite density and temperature, while others suggest the possibility of a cyclic or multiverse model. These ideas are explored within the framework of theoretical physics, such as quantum cosmology and string theory, but they are still under development and lack empirical confirmation.
It's worth noting that our current scientific methods and tools have limitations when it comes to probing the conditions before the Big Bang. The extreme energies and densities associated with that epoch require a comprehensive understanding of quantum gravity, which is an area where our current theories, like general relativity and quantum mechanics, are not yet fully reconciled.
In summary, while scientists continue to investigate the nature of the pre-Big Bang universe, our understanding is limited due to the lack of a complete theory of quantum gravity and the difficulty of making observations or gathering empirical evidence from that era.