How can we know? Noted science writer on what cosmic background radiation tells us before the Big Bang. http://dld.bz/fgngC
Pre-Big Bang inflation is important to historians because we want to know before, during, and after past events. That's how our minds work. Yes, Einstein theory is that time cannot exist outside of universe. No space-time continuum. The present knowledge of pre-Big Bang inflation is vital to history and a game-changer to science.
Also, here's my Herodotus page, the first universal historian. http://dld.bz/eaTpb The Landmark edition is the best Herodotus available imo.