Mariana Cook’s book, “Faces of Science,” portrays 77 scientists who have made many of the most important discoveries of our time. Each photograph is accompanied by a personal essay written by the scientists. The portraits in this online series are accompanied by excerpts from those essays. For more information, please visit Mariana Cook’s website: www.cookstudio.com.
Almost all of my career as a theoretical physicist has been devoted to the study of string theory. This is a type of relativistic quantum theory based on fundamental objects that are tiny loops (called strings) rather than points, as is the case in more conventional quantum theories. String theory arose in the late 1960s as a candidate theory of the strong nuclear force. This is a force that holds neutrons and protons together inside the nucleus of an atom. However, in the early 1970s a very successful alternative theory of the strong nuclear force, called quantum chromodynamics (or QCD), was developed. As a result, most physicists stopped working on string theory. However, I was so enthralled by the mathematical beauty of string theory that I continued to work on it. This persistence paid off when in 1974, the late French physicist Joël Scherk and I proposed to change the goal of string theory to one that is much more ambitious: the construction of a unified quantum theory containing gravity and all other fundamental forces.
An important ingredient of string theory is a type of symmetry, called supersymmetry, which relates those particles responsible for stable matter (fermions) to those that transmit forces (bosons). As a result, the subject has been dubbed superstring theory. If successful, superstring theory should account for the properties of all the elementary particles as well as the physics that controls the origin and evolution of the universe. The basic idea is that the elementary particles correspond to different motions of the fundamental string. Surprisingly, the mathematical consistency of such a theory requires the existence of gravity. As Einstein taught us, gravity is determined by the geometry of space and time. In the case of string theory, it turns out that in addition to the three familiar dimensions of space, six or seven extra spatial dimensions are required for mathematical consistency. They should form a tiny space (attached to every point in ordinary space) that is too small to have been observed. The details of the geometry of the extra dimensions play an important role in determining the physics that is observed.
What is the relevance of this work to lay people? In my opinion, most important is the satisfaction that comes from knowing that humankind is making great strides toward unraveling the deepest mysteries of the physical universe. Isn’t that enough?