Henry Semat Professor of Theoretical Physics at the Graduate Center of the City University of New York.

His books:
Parallel Worlds (February 14, 2006).
Beyond Einstein (September 1, 1995).
Hyperspace (February 1, 1995).
Physics of the Impossible (March 11, 2008).

Physics of the Impossible is first book that he explain the about UFO. But not included Crop Circle.
He said in this book, current people in this planet is stage 0. Next existence is stage 1 (like people in Star Trek ), next is stage 2, next is stage 3, next is stage 4. Technology difference between stage 0 and stage 1 is like ant and people.

Many years a go I attended conference by Michio Kaku and John Mack in New York. It was interesting combination. But that time Michio Kaku never talk the about UFO.