The idea that our universe was a black hole before the Big Bang is a hypothesis put forth by some physicists, but it remains highly speculative and is not currently supported by strong evidence or widely accepted in the scientific community. It is important to approach this notion with caution and recognize it as a speculative idea rather than an established fact.
The concept you are referring to is known as the "black hole cosmology" or the "black hole universe hypothesis." It suggests that our universe originated from the collapse of a previous universe into a black hole, which then underwent a bounce or a transition into the expanding state we observe today.
This hypothesis arises from attempts to reconcile the principles of general relativity (describing gravity) with quantum mechanics (describing the behavior of particles on a microscopic scale) in the context of cosmology. However, developing a consistent and complete theory that unifies these two frameworks, known as quantum gravity, remains an ongoing challenge in physics.
While the black hole universe hypothesis is an intriguing idea, it is important to note that it is still speculative and lacks empirical confirmation. Our understanding of the early moments of the universe, particularly the period before the Big Bang, remains an active area of research and exploration. Scientists continue to study and develop various models and theories to explain the origins and evolution of the universe.