The question of what existed before the Big Bang, or what caused the Big Bang itself, remains a topic of active scientific research and philosophical speculation. The current understanding of the Big Bang theory provides a description of the universe's evolution from an extremely dense and hot state, but it does not provide a complete explanation of its ultimate origin.
According to the prevailing cosmological model, the universe as we know it began with the Big Bang. However, the concept of "before" the Big Bang is difficult to grasp because the standard framework of space and time as we understand them breaks down near the singularity—the point of infinite density and temperature at the start of the universe.
The prevailing view among cosmologists is that our current understanding of space, time, and the laws of physics breaks down at the singularity. Therefore, it is challenging to determine what, if anything, existed prior to the Big Bang or how the universe emerged from that singularity. Some theories, such as certain models of quantum cosmology and string theory, attempt to provide speculative explanations for the origin of the universe or propose alternative cosmological scenarios. However, these ideas are still being explored and remain subject to further investigation and refinement.
It's important to note that the term "appear out of nowhere" or "instant" may not accurately describe the actual process of the universe's origin. Our intuition and everyday experiences may not directly apply to the extreme conditions near the singularity. The fundamental nature of the universe and the events leading up to the Big Bang are still open questions that scientists are actively pursuing through theoretical investigations and observational experiments, such as studying the cosmic microwave background radiation and the behavior of particles in particle accelerators.