How could a final theory help us understand the origin and fate of the universe?
When the universe was three minutes old, there were nuclear reactions that produced the lightest chemical elements, with which the stars began their lifetime. We can follow the story back a little further than that, to perhaps the first second. When you try to push the story back much beyond that, you get the conditions where the density of energy is so high that you can no longer ignore the quantum nature of gravity. And we don’t have a quantum theory of gravity that is mathematically consistent. So that in itself is a barrier. We can’t look back in time beyond a certain moment. As far as the future is concerned, the universe is expanding and getting colder, and is easier to describe as time passes. But there are some big questions that we don’t know. For instance, recent observations indicate that the expansion of the Universe is accelerating, and this is related to an energy density in empty space which has a negative pressure and creates an accelerated expansion of the Universe rat
