Mathematical and Physical Sciences
Authored theories of the origin of the universe that have revolutionized cosmology. Helped establish the concept of inflation-wherein the universe began with a rapid expansion of space in a vacuum-like state. Proposed other versions, such as chaotic inflation, a theory that suggests that our universe is one of many inflationary universes (bubbles) sprouting from an eternal cosmic tree. With Kallosh, proposed that dark energy, the theoretical phenomenon reminiscent of Einstein's cosmological constant, which is presently stretching spacetime at an increasing rate, might become negative. As a result, the universe (our bubble) might begin collapsing in 10 to 100 billion years and end in a big crunch. The multiverse of other bubbles would persist forever. Member, National Academy of Sciences.