At a lonely border post high on the Himalayan frontier, Ramaswamy Balasubramanian peered through his binoculars at the People’s Liberation Army soldiers stationed in Tibet—who were peering through their scopes back at him. Tensions between India and China had been high for several years since 1962, when the two countries traded shots across their disputed border. The PLA soldiers, knowing they were being watched, taunted Balasubramanian and his fellow Indian soldiers by shaking, defiantly, high in the air, their pocket-sized, bright-red copies of Quotations from Chairman Mao—better known in the West as “Mao’s Little Red Book.”

Balasubramanian, then a conscript studying physics in his spare time, soon grew tired of these taunts. So one day, he came to his observation post prepared with a suitable rejoinder. As soon as the PLA soldiers started waving Mao’s Little Red Book in the air again, he and two fellow Indian soldiers picked up and held aloft the three big, bright-red volumes of The Feynman Lectures on Physics.

One day I received a letter from Mr. Balasubramanian. His was among hundreds of letters I have received over the years that describe the lasting impact Richard Feynman has had on people’s lives. After recounting the “red-books” incident on the Sino-Indian frontier, he wrote: “Now, twenty years later, whose red books are still being read?”

Indeed. Today, more than forty years after they were delivered, The Feynman Lectures on Physics are still being read—and still inspire—even in Tibet, I suspect.

A special case in point: several years ago I met Michael Gottlieb at a party where the host was displaying on a computer screen the harmonic overtones of a live Tuvan throat-singer—the kind of event that makes living in San Francisco such fun. Gottlieb had studied math and was very interested in physics, so I suggested he read The Feynman Lectures on Physics—and about a year later, he devoted six months of his life to reading The Lectures very carefully from beginning to end. As Gottlieb describes in his introduction, this led, eventually, to the book you are reading now, as well as to a new, “Definitive Edition” of The Feynman Lectures on Physics.

Thus I am pleased that people interested in physics all over the world can now study, with the addition of this supplemental volume, a more correct and complete edition of The Feynman Lectures on Physics—a monumental work that will continue to inform and inspire students for decades to come, whether in midtown Manhattan or high in the Himalayas.