This month the world is celebrating the 100th anniversary of Albert Einstein’s theory of general relativity, which shaped our concepts of space, time and gravity, and spurred generations of scientists to contemplate new ideas about the universe. The anniversary was celebrated on Nov. 5-6 at a conference co-hosted by Princeton University and the Institute for Advanced Study in the town of Princeton.

The conference was sponsored by Institute Trustee Eric Schmidt, who graduated from Princeton in 1976 and is executive chairman of Alphabet Inc., and his wife, Wendy.

One of Princeton’s most notable residents, Einstein was a faculty member at the Institute for Advanced Study (IAS) from 1933 until his death in 1955. IAS is an independent research institution located about one mile from Princeton University. During construction of the institute, from 1933 to 1939, Einstein’s office was located in Fine Hall (now Jones Hall) on the University campus.

Relativity at 100 Einstein portrait

Albert Einstein was a faculty member at the Institute for Advanced Study from 1933 until his death in 1955 and had an office on the University campus from 1933 to 1939. (Image courtesy of Münchner Stadtmuseum, Sammlung Fotografie, Archiv Landshoff)

Einstein’s theory of general relativity, set down in a series of lectures in Berlin in late 1915, predicted many features of the universe — including black holes and gravitational waves — for which we now have experimental evidence.

The theory also predicted some things that have not yet been discovered, like wormholes and travel back in time. In additions to relvations about the universe, the theory has enabled technologies in our everyday lives, like the accurate GPS systems in smartphones.

“Einstein’s theory of general relativity completely changed our view of the universe,” said Lyman Page, the James S. McDonnell Distinguished University Professor in Physics and chair of Department of Physics. “It had a huge impact on researchers in physics, astrophysical sciences and mathematics, here at Princeton and around the world.”

Robbert Dijkgraaf, director of IAS and the Leon Levy Professor, called Einstein’s theory of general relativity “the largest intellectual achievement in the last few centuries.”

“The fact that this celebration is happening in Princeton is important for two reasons,” Dijkgraaf said about the conference. “Princeton was the home of Einstein for a long time, and it was also the home of the revival of interest [in the 1950s and 1960s] in the study of general relativity.”

A theory of how gravity works

At the time Einstein developed his theory, people already knew from the work of Sir Isaac Newton more than 200 hundred years earlier that massive objects, such as stars, attract smaller objects, such as stars and planets, through the force of gravity. While Newton’s laws enabled highly accurate predictions of planetary orbits, they didn’t explain how the attractive force of gravity comes about.

Einstein’s theory of general relativity takes care of that, according to David Spergel, the Charles A. Young Professor of Astronomy on the Class of 1897 Foundation and chair of the Department of Astrophysical Sciences. “It essentially describes how gravity works.”

Einstein’s theory showed that massive objects cause distortions in the fabric of the universe. Imagine that the universe is a large bedsheet held on all four corners so that the sheet is taut but can still deform, and that on the sheet sits our sun, represented by a bowling ball. The mass of the sun deforms the fabric of the universe the way a bowling bowl causes a depression on the sheet. A marble placed on the sheet would begin a circular trajectory around the bowling ball, just as the planets orbit the sun.

Through an elegant set of mathematical “field equations,” Einstein explained that gravity is the curving of this fabric, which is made of the three dimensions of space and the fourth dimension of time. He also showed that just as space-time is curved by matter such as stars, this matter is also influenced by the curvature of space-time. One of the first predictions to come out of the theory was that light passing by a star would be bent due to the star’s gravitational pull. Just a few years later in 1919, scientists observed this effect during a solar eclipse. The confirmation of this key prediction of his theory catapulted Einstein to international fame.

Over the next decades, a few scientists and mathematicians studied Einstein’s equations and made interesting discoveries. For example, the physicist Karl Schwarzschild, who was the father of Princeton professor Martin Schwarzschild, found that the theory predicted points of extreme gravity that Princeton faculty member John Archibald Wheeler later renamed “black holes.”

For the most part, however, the development of general relativity languished as the physics community became focused on the theory of quantum mechanics.

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by Catherine Zandonella, Office of the Dean for Research