In the early 1970s, David J. Gross exposed the hidden structure of the atomic nucleus. He helped to reinvent string theory in the 1980s. In 2004, he shared the Nobel Prize in Physics. And today he struggles mightily to describe the basic forces of nature at the Planck scale (billions of times smaller than a proton), where, string theorists hope, the equations of gravity and quantum mechanics mesh.

Gross, H. David Politzer and Frank Wilczek were awarded the Nobel for discovering asymptotic freedom, more colloquially known as the strong force that binds the components of the atomic nucleus, the protons and neutrons. Forty years ago, their counterintuitive calculations plugged an important gap in the Standard Model of physics, which describes the 61 known elementary particles. This theoretical work revitalized the nearly moribund quantum field theory and gave birth to QCD (quantum chromodynamics), the theory of the strong interactions.

These days, Gross enjoys challenging young physicists as they chalk equations at the Kavli Institute for Theoretical Physics, the think tank funded by the National Science Foundation that he ran from 1997 until stepping down last year. He is eager for younger scientists to surpass his achievements, to break the impasse of under-determination that currently troubles particle physics, whereby competing theories predict the same physical results and may therefore be immune to experimental verification within the lifetime of the universe.

Gross characterizes theoretical physics as rife with esoteric speculations, a strange superposition of practical robustness and theoretical confusion. He has problems with the popularizing of “multiverses” and “landscapes” of infinite worlds, which are held up as emblematic of physical reality. Sometimes, he says, science is just plain stuck until new data, or a revolutionary idea, busts the status quo. But he is optimistic: Experience tells him that objects that once could not be directly observed, such as quarks and gluons, can be proven to exist. Someday, perhaps the same will be true for the ideas of strings and branes and the holographic boundaries that foreshadow the future of physics.