JTP and I have had this discussion before... many times over the years. We've agreed (at least in my view) to disagree re: "... At very small levels you get massive quatities of particles popping in and out of existance all the time..." And the disagreement centers on the phrase "popping in and out of existance..." I maintain (with a modicum of scientific backing) that the particles are only "popping in and out" of observation, not existance.
Fact is, we have fairly good mathmatics (albeit, at the quantum level) backing the "Big Bang" back to Planck Time... the smallest amount of time (or distance) that can be persuasively shown to have existed. Planck Time equates to 10^-43 seconds or the time it takes a proton to travel Planck Length (1.6 x 10-35 m).
Granted, bog-standard (love that thoroughly British phrase) physics appears to break down at Planck time, but by interpolation on must consider that the remaining micro-micro seconds "before" Planck time must equate to original comming into existance...
from nothing.
At any rate, even more perplexing is the "Inflationary Phase"... but that's another subject.
You may wish to cnsider also, that the geometry of the known universe is most likely flat like a sheet of paper.. not, as most surmise, a globe shape...