The vacuum is central to physicists' best theories of subatomic particles, gravitation, and cosmology. Nothingness provides the reference point with which to compare new particle creation and annihilation. Cosmologists use empty universes to study the causal structure of spacetime. Paradoxically, our best physical theories of particles, gravity, and spacetime are theories of nothingness. Stranger still, the physicists' vacuum is a hive of activity. Quantum fluctuations fill empty space wit...

Sidney Coleman (1937–2007) was a renowned theoretical physicist, who taught for more than forty years at Harvard University. He contributed critical work on quantum field theory, high-energy particle physics, and cosmology. He was also a remarkably effective teacher who introduced generations of physicists to quantum field theory, mentoring several leading members in the field. His sense of humor and wit became legendary. This selection of his previously unpublished correspondence illumina...