TOP TEN UNSOLVED PROBLEMS IN PHYSICS

Why is any of this important? In presenting his own list of mysteries, Hilbert put it this way: “It is by the solution of problems that the investigator tests the temper of his steel; he finds new methods and new outlooks, and gains a wider and freer horizon.” And in physics, the horizon is no less than a theory that finally makes sense of the universe.

via TOP TEN UNSOLVED PROBLEMS IN PHYSICS.