Theory of Relativity: its experimental verification

In 1905 Alfred Einstein published an article whose content is what we now call the theory of special relativity. That was a mature topic that other researchers were close to. But between 1907 and 1915 he made a very personal reflection that led him to replace the Newtonian image of gravitation, considered as the attraction between two massive bodies, with a completely revolutionary conception. Time had already been incorporated as a “fourth dimension” forming what is called “space-time.” In his publications of 1915 and 1916 he enunciates a new theory called general relativity in which gravitation appears as an effect of the curvature of space-time produced by matter and energy. But in science the validity of a theory has to be confirmed experimentally.

A. Einstein was well aware that the elliptical orbit of the planet Mercury changes orientation every year and takes 244,000 years to rotate 360º. Applying Newton’s theory, the time to wait is 225,000 years. This discrepancy is 43 degree seconds per century. As you can see, it is a very small discrepancy if we take into account that it is half a second per year. Can you imagine the precision of measurement that the astronomers of 1859 already had? Einstein, applying his theory of General Relativity, obtains a theoretical result for the precession of Mercury that coincides with the experimental one. This is not to say that Newton’s Theory is false. He needed the gravitational increase supplied by the energy. Therefore, like any other theory, it is valid within its range of application.

A spectacular prediction that appears in general relativity was the following: Gravitational fields deflect light rays (photons) that pass close enough to them. It is the same effect that occurs when an outer comet passes close to the sun. It experiences a curvature and goes back into outer space. Also, the higher the speed of the object, the smaller the deflection. To observe this effect, in 1919 an expedition was made to the southern hemisphere to measure the deviation of a light ray that, coming from a distant star, passed very close to the sun. That is why a total eclipse is necessary, so that the sun is completely covered. If the theory was correct, the deviation of the light beam should be 50 thousandths of a degree. The result found confirmed the theoretical prediction. However, there were voices that questioned the analysis of the precision of the observation, despite the fact that those who did it had estimated a 10% experimental uncertainty. It is true that the experimental corrections are complex. By not giving much importance to the result on Mercury and due to the existence of doubts regarding the verification of the deviation of light, he caused that the proposals, for 5 years, for the Nobel Prize were not taken into account. Prize that was awarded in 1921, not for general relativity, but for the photoelectric effect. In the second half of the 20th century, with the increased precision of radio astronomy, the deviation of light was undoubtedly proven and effects similar to those of Mercury on other celestial bodies were explained. Also, let’s not forget that GPS accuracy is due to general relativity.