basically it’s a theory that would explain why the universe is here, it states that all of the universe was completed enclosed in a singularity, then BOOM! it exploded, into the universe, slowly but surely gases like hydrogen and oxygen compacted to make the sun, the sun dies in a supernova which makes more suns, so now rocks ice and strange clouds exist, which makes earth, so that’s the big brain theory, it’s got evidence to, considering the universe expands, it makes sense why, an ignition followed by explosion would make sense as to why the universe expands, also there are hotspots of the Big Bang, so ye, i believe it