Historical clue formulations

• This is the way the world began, per 51-Across — 2021-05-19
• Beginning of the universe — 2019-02-11
• Beginning of time? — 2013-09-28
• Theory of the universe, or a hint to the starts of 17-Across and 7-, 10-, 35- and 40-Down — 2008-01-07
• Cosmic explosion — 2004-12-06
• Start of everything — 1999-03-06