Revolutionary insights about the nature of light, time, and energy
As Einstein became better known in the scientific community, he began receiving requests to write about his new theory for journals and books. In 1912, he was asked to contribute several chapters on relativity to a book. The result is this 72-page manuscript. Because he did not save drafts of his 1905 papers, this manuscript is the earliest known description of relativity in Einstein's hand.
Pages from the 1912 Manuscript on the Special Theory of Relativity
Einstein first published his Special Theory of Relativity—which describes his revolutionary ideas about light, time and energy—in 1905. He revisited the theory in this 1912 manuscript when he was asked to write several book chapters. The outbreak of World War I in 1914 delayed publication, and when the project resumed, Einstein considered this manuscript outdated and it was never published.
Nevertheless, the manuscript represents an important stage in Einstein's work. The draft focuses on the Special Theory of Relativity, which applies to the "special" circumstance in which observers making measurements do not change speed, or accelerate. But this draft also hints at how Einstein developed his more comprehensive General Theory of Relativity. That theory, finalized in 1916, applies to all observers, even those undergoing acceleration, and is actually a theory of gravity.
Each page of the 1912 Manuscript on the Special Theory of Relativity reveals an exacting mind at work. Mathematical equations have been altered, words have been crossed out, and entire paragraphs have been rewritten.
When Einstein was asked to write these chapters, he decided to do more than simply summarize relativity. Instead, he derived from first principles the basic tenets of his influential theory about light, time and energy. In the process, he refined his ideas even further. For example, he adopted a novel four-dimensional mathematical system in this manuscript to explain portions of Special Relativity. Physicists refer to this four-dimensional system as "space-time"—the union of three-dimensional space with the fourth dimension of time.
Derivation of E=mc2 in the 1912 Manuscript on the Special Theory of Relativity
The 1912 Manuscript on the Special Theory of Relativity includes Einstein's most famous equation: E=mc2. In this draft, however, the equation, which demonstrates that mass is a form of energy, appears in a somewhat different form. Originally, Einstein used the variable "L" for energy (the "L" stood for Lagrangian, a general form of energy); later, he crossed out the "L" and changed it to "E."
The equation shown here also includes several extra terms. Technically, the short version of the equation, E=mc2, applies only when an object is at rest. The longer, more complete form of the equation included in this manuscript applies to moving masses as well.