100 Years Later, Einstein's Theory Is The Basis of Modern Cosmology
Almost 100 years ago, on November 25, 1915, Albert Einstein presented to the Prussian Academy of Sciences the final version of his general theory of relativity, which also became the standard theory of gravity.
This event concluded a convoluted and dramatic intellectual odyssey that began almost a decade earlier, when Einstein realized the deep underlying connection between gravity and acceleration.
It continued through alternating phases of brilliant insights and successes, followed by erroneous sidetracks, misunderstanding and failures until the triumphal end when all the pieces of this complex puzzle came together.
A happy ending, no doubt, because it fulfilled the highest hopes Einstein had invested into this enterprise. Indeed, he had achieved a theory that was physically plausible and mathematically elegant.
In his Notes on the Origin of the General Theory of Relativity, in 1934, Einstein referred to this process saying: "In the light of knowledge attained, the happy achievement seems almost a matter of course and any intelligent student can grasp it without too much trouble. But the years of anxious searching in the dark, with their intense longing, their alterations of confidence and exhaustion, and the final emergence into the light... only those who have experienced it can understand that."
For many years after its completion, the general theory of relativity was regarded as obscure, intricate, and not really a part of mainstream physics. Only in the last four or five decades has it evolved into a pillar of modern physics and precision technology, and it has become central to the investigation of many problems at the forefront of physics.
The general theory of relativity predicts that time progresses slower in a stronger gravitational field than in a weaker one. This phenomenon has to be taken into account in calculating the distances between a GPS device and the satellites comprising the GPS system. Thus, whenever we use GPS to find our exact location on earth, we depend on general relativity.
General relativity today constitutes the basis of modern cosmology. It asserts that the expansion of our universe began with a singular event, the "big bang," that became, in later epochs, an accelerated expansion.
It predicts the existence of "black holes" and their peculiar properties. General relativity describes the synthesis of the elementary particles of physics and of chemical elements in the early epochs after the "big bang." It illuminates the processes of formation of galaxies in the universe in more recent times. The theory also predicts that violently accelerated matter, like that in an exploding star, will generate waves of gravity, propagating at the speed of light and causing the space they transverse to shrink and expand alternatively.
The detection of gravitational waves is one of the great challenges of astrophysical research. This process will open a new window on the universe and allow us to trace its evolution almost to its beginning.
All these capabilities and insights are due to Einstein's theory of general relativity. They give us a good reason to celebrate the centenary of this unique achievement.
After submitting the final version of his general theory of relativity in November 1915, Einstein wrote a comprehensive summary of the theory for the scientific community, which was published in March 1916. The handwritten manuscript of this article has been in the possession of the Hebrew University of Jerusalem since its opening on April 1, 1925, and is one of the university's most cherished treasures.
It was a gift to the university from Einstein's wife, Elsa, while he was on a visit in Argentina. When Einstein learned about it, he thanked her for doing him "this favor of love."
Einstein was a founder of the Hebrew University, a member of its Board of Governors and the Chairman of its Academic Committee. He bequeathed to the university all his papers, documents and personal correspondence. Today they constitute the Albert Einstein Archives at the Hebrew University.
The general relativity manuscript is one of many important manuscripts possessed by the Archives, all of which relate to inspiring chapters in the history of physics. They are being edited and explored by historians of science at the Einstein Papers Project at the California Institute of Technology and elsewhere. All the documents shed light on how science was done in the formative years of modern physics.
In 2013, the European Space Agency launched an Automated Transfer Vehicle (ATV- 4), named "Albert Einstein," carrying supplies and equipment to the International Space Station (ISS). The cargo of ATV-4 contained the first page of the general relativity manuscript, which astronaut Luca Parmitano signed on board the ISS.
It was a symbolic gesture acknowledging the importance of this document -- and what it represents in the history of mankind.
Hanoch Gutfreund has held the Andre Aisenstadt Chair in theoretical physics at the Hebrew University of Jerusalem since 1985. He is author, with Jurgen Renn of The Road to Relativity: The History and Meaning of Einstein's 'The Foundation of General Relativity' and author of Relativity: The Special and the General Theory, both published in 2015 by Princeton University Press.