Einstein needed to be able to predict a result that hadn’t been observed yet. Only in this way could he definitively show the superiority of his theory over Newton’s. Think of it this way: Suppose you have been talking to two investment advisers, Fred and Barney. Fred shows you his calculations that predicted yesterday what the stock market did today. Barney shows you his calculations today that predict what the market will do tomorrow. Tomorrow the market performs exactly as Barney predicted. Whom do you believe? Fred could have manipulated his theory to match today’s results because he knew the result before he gave you his prediction. But Barney couldn’t have known what the market would do today except through his theory.
Einstein had long pondered the relationship between light and gravity. Since the General Theory of Relativity defines gravity as a warp in the fabric of spacetime and light travels through spacetime, under Einstein’s theory light should be affected by a massive body such as the sun. Einstein theorized that light from a star behind the sun would be bent, resulting in an apparent shift in its position. The problem was, you can’t see any stars when the sun is shining. Einstein realized that during a total solar eclipse stars are visible in the daytime sky so he looked for an opportunity and an astronomer (remember, Einstein was a theoretical physicist — he didn’t actually conduct experiments) to observe stars during a solar eclipse. He found both a partner in Arthur Eddington and an opportunity in the Southern Hemisphere in 1919. Eddington and one team went to the island of Principe off West Africa and another team went to Brazil, hoping that if clouds obscured the eclipse in one location, the other location would be clear.
In the end both teams were successful in observing the eclipse and taking what photographs needed to be taken. After developing the plates, making measurements and calculating margins of error, Einstein’s predictions were within the margin of error while the results predicted by Newton’s laws were far too low. Both Eddington and Einstein became virtual rock stars in science. Eddington became inextricably connected to general relativity. At one point someone said to him that he was one of three people in the world who understood the General Theory of Relativity. Eddington was silent for several seconds and finally the person urged him not to be so modest. “On the contrary,” Eddington replied, “I am trying to think who the third person is.”
The vindication of Einstein’s theory required a paradigm shift, a complete and sudden alteration in the way science viewed the universe. Science usually moves incrementally, in small changes. It isn’t often that Saul becomes Paul on the road to Damascus. When a paradigm shift such as this occurs it usually isn’t generally accepted. Older scientists who have devoted their professional lives to a particular view of things are reluctant to change and often it requires a dying off of the older generation before a new theory is completely accepted. Such was the case with the General Theory of Relativity. Yet his theories have been proven correct. Einstein was once asked by a student how he would have felt if the universe had ultimately turned out to be different than his theory predicted. With tongue firmly in cheek he replied, “Then I would feel sorry for the Good Lord. The theory is correct anyway.”