Although white holes have no been spotted, how can we actually say that they do not exists? Think about this:
The universe was once a singularity before the big bang. So, how did this singular object just appear magically from nothing, then go on to create atoms, and the universal expansion and all the laws of physics. Sounds a little odd. Now we know that Blackholes exists. My personal theory is: What if blackholes bend spacetime so much that it seperates the singularity into a different demension and causes another "big bang" in another universe?