The Big Bang theory is the prevailing scientific model for the origin and early development of the universe. According to this theory, the universe began as an extremely hot and dense singularity, a point of infinite temperature and density. However, our understanding of the exact moment of the Big Bang is limited due to the extreme conditions and the lack of a complete theory of quantum gravity.
As we extrapolate back in time, the laws of physics as we currently understand them break down near the singularity. At such high energies and densities, the effects of quantum mechanics and general relativity become intertwined, and a unified theory that combines these two frameworks, known as a theory of quantum gravity, is needed to describe the initial moments of the universe.
While we don't yet have a complete theory of quantum gravity, scientists have made significant progress in developing models and hypotheses to explain the early universe. One such model is called cosmic inflation, which proposes that the universe underwent an exponential expansion in a fraction of a second after the Big Bang. Inflation can help explain some observed features of the universe, such as its overall homogeneity and isotropy.
Regarding the cause of the initial singularity, the answer is not yet known. The singularity represents a point where our current understanding of physics breaks down, and classical concepts like cause and effect may not apply. It's an area of active research and remains a subject of speculation and exploration for physicists and cosmologists.
In summary, the exact moment of the Big Bang and the cause of the initial singularity are still open questions in our understanding of the universe. Ongoing scientific investigations and future advancements in theoretical physics may bring us closer to a more complete understanding of these fundamental aspects of our cosmos.