How can Big Bang happen without time?

Question

I had recently watched a video and he says big bang could have happen by the slow collision rather than a fast collision. But I know that there was no time before the big bang and fast and slow are measurements of speed which is distance/time. So how can we say fast or slow when there is no time?

Answer 1

One of ideas associated with string theory is the ekpyrotic universe. This starts with brane cosmology i.e. the idea that our universe is a four dimensional brane floating around in the ten dimensional string theory spacetime.

There will be many such brane worlds and the ekpyrotic idea is that a collision between two branes would appear just like the Big Bang inside the brane world. So if this idea is correct our Big Bang was just a collision with another brane world and wasn't the beginning of the universe. Time was running smoothly in the ten dimensional string spacetime before, during and after the collision.

For completeness we should note that the ekpyrotic universe is just one of many ideas in string theory for which no compelling evidence exists.