To know the mind of God
Or as Stephen Hawking actually put it
However, if we discover a complete theory, it should in time be understandable by everyone, not just by a few scientists. Then we shall all, philosophers, scientists and just ordinary people, be able to take part in the discussion of the question of why it is that we and the universe exist. If we find the answer to that, it would be the ultimate triumph of human reason — for then we should know the mind of God.
Hawking was attempting to combine our understanding of gravity and quantum mechanics, the two great theories that physics has given us in the last 100 years or so.
No small aspiration then.
But that is where we start off. We ask you to join us in the quest to know “the best that has been thought and said” in order that you can aspire to finish off the job that Hawking started. As Isaac Newton put it
If I have seen further it is by standing on the shoulders of Giants.