A Brief History of Time is quite old. Hawking, among others, finds it difficult to express esoteric theory in terms everyone gets on the first read-through. Saying that the Big Bang was the beginning of time, means time as we measure it. For us, this universe, this reality, this time-line, there was nothing before it began. (Not that I comprehend any of it.)

There is not, as yet, a workable unified theory. That's why the current study of quantum gravity is so important. If we can understand how gravity functions on the very large and the very small scale, we're one step closer to seeing what's really around us.

If black holes don't exist, what's that big dark thing sucking up stars at the center of our galaxy?