I apologize if this is a "stupid" question, but I have been trying to find information on this for weeks and it has been to no avail thus far. I know that there are two theories in regards to what came "before" the singularity; the cyclic universe and the "universe came from a vacuum fluctuation" theory. I understand the former relatively well, but I just do not understand the latter, and was wondering if someone could offer a hypothetical explanation. I understand that vacuums can be responsible for the temporary creation of particles. What I do not understand is how those particles could expand and become our current universe. Is the answer just "it has something to do with quantum gravity, which we do not understand," or is there a hypothetical situation in which the above could occur? If my conclusions are erroneous, please explain. Thank you so much.