I understand "They" are currently checking the microwave background for the signatures of "Black Holes" that are outside our universe. I may well have the wrong end of the stick!
I also know that the big bang theory is just that, one of many possibilities, just currently the most popular.
My uneducated idea is that distance, like the distance from one side of the universe to the other , can only be traversed at speed. In other words, you need time for light to travel across the universe.
I think time, or rather the passage of time is variable, and the rate of time is linked to the local density of matter.
The result is that as matter turns into energy, the universe becomes lighter, and as the universe expands, less dense, time speeds up, as it time speeds up light can travel from one side of the universe to the other practically instantly, hence the size of the universe in effectivly reduced to nothing. A natural result of the "Suns" turning matter in to energy.
Our sun, a small insignificant star in the scale of things, turns many thousands of tonnes of matter in to energy every second. If you take in to account all the stars in the universe, and the billions of years, then it's possible to imagine the universe getting lighter! (Less weight) time speeds up, the apparent distance across, vanishes, Bang! New start!