As someone who once styled themselves as a theoretical mathematician, I was happily surprised and somewhat embarrassed to have learned the title of this blog post from this book. The concept had never occurred to me before.
The problem with a Universe of infinite age is that you can't reach any given point in time. That is, if time goes back infinitely through endless repetitions of Big Bangs and Collapses, you can't get to the November 30, 2014 and watch Southampton blow a perfect chance to at least draw with Manchester City after Man City went down to ten men because of a stupid challenge by Mangala near the box.
Where was I? Oh yes. Time.
Since time is sequential with one second following another, in order to reach the moment when Frank Lampard scores in ridiculous fashion for City, you need to cover the time between when you started counting and when the ball went into the back of the net. If you go back in time 90 minutes, the game hasn't started, but we know those 90 minutes have taken place. You can go back to the year 1066 and we know that time has happened. You can go back to any time you like and we know that time has gone by.
If the Universe was inifinitely old, no matter how far you went back, there would be moments older than that. Since time is sequential, those moments must have taken place. If that were the case, you could never wait long enough to get to Frank Lampard's goal. The current moment in time could never occur.
Ergo, the Universe had a beginning.
Way cool, no?