According to string theory, the origins of branes, as well as the universe itself, are still speculative and not fully understood. String theory is a theoretical framework that attempts to describe the fundamental nature of reality, including the nature of particles and forces, by modeling them as tiny vibrating strings.
In the context of branes, string theory suggests that our universe may be a three-dimensional brane embedded in a higher-dimensional space called the "bulk." The collision of two branes, as you mentioned, is one of the scenarios proposed within the framework of string theory. It is known as brane inflation or the ekpyrotic scenario.
However, the question of how the branes themselves were created in the first place is still an open question in string theory. String theorists are actively researching this topic, but definitive answers have not yet been found. The origins of the branes and the mechanisms that led to their creation remain speculative.
It's important to note that string theory is a highly complex and mathematically challenging theory, and many aspects of it are still under active investigation. As our understanding of the theory progresses, researchers hope to gain deeper insights into the origins of branes and the fundamental nature of the universe.