If gravity had not ‘switched on’ after the Big Bang time might not RZ IRUZDUGV
The direction of time is associated with order changing to disorder – the direction in which castles crumble, eggs break and so on. Ultimately, therefore, the ‘arrow of time’ must be due to the Big Bang being in a highly ordered state, which is very unlikely. Actually, early on, when matter from the Big Bang fireball was smeared smoothly across space, the Universe was disordered. However, when the Universe was 380,000 years old, gravity was able to gather matter together for the first time. In a gravitating system, clumped is the most likely state. The smeared-out Universe was therefore suddenly thrown into a very unlikely state – precisely the requirement to create our forward direction of time.