In a series of articles he published a century ago, Albert Einstein changed the face of science. First article
Amit Hagar
Einstein, 1905. A turn of despair led to the theory of relativity
1905 was a good year for Albert Einstein. In April, the 26-year-old junior patent clerk finished his doctoral thesis at the Zurich Institute of Technology, and within six months, working in almost dazzling solitude and without continuous contact with the scientific community, he published four more articles, which changed the face of science beyond recognition. It is not for nothing that 1905 is called Einstein's "year of wonder" (Mirabilis Annus).
Einstein's greatness lies in part in the fact that he continued where other great scientists left off. Many of the physicists of his generation were dealing with the same issues at the time, but they did not want to change the rules of the game, and therefore remained behind, rooted in the physics of the 19th century. If until the beginning of the XNUMXth century scientists debated the very existence of atoms, believed in the continuity of the material world and the wave nature of light, and most of all, believed in the existence of the "ether" as an ethereal medium within which electromagnetic radiation moves and that space and time are separate and absolute, then the physics he became acquainted with The world in Einstein's groundbreaking essays was a new physics.
Einstein fully and uncompromisingly embraced the hypothesis regarding the existence of atoms and showed how it can be turned into an empirical hypothesis; He showed how fruitful is the hypothesis regarding the existence of discrete light particles that will later be called photons; And he removed with the wave of his hand that unobservable ethereal entity - the "ether" - thus changing the picture of space and time that has been an integral part of physics for hundreds of years.
To understand the background for writing Einstein's articles as well as why they are considered groundbreaking, it is worth listening to Einstein himself, who in 1919 coined a distinction that many today consider one of the most important methodological distinctions in theoretical physics.
Einstein distinguished between two types of physical theories: theories "of composition" and theories "of principle". Theories "of assembly", explained Einstein, are usually theories about the structure of matter. Based on some assumptions about the "building blocks" of the world, the physicist tries to put together models that describe more complex phenomena. The starting point from which "principle" theories start, on the other hand, is completely different. Here the physicist does not make any assumptions about the structure of matter or the "building blocks" of the world, but starts from a limited number of observational principles, and following them asks himself what the nature of the world is if these principles are muscles in it.
Einstein began his "miracle year", and in fact his entire academic career, precisely from the point of view of the assembly approach. To this approach belongs his doctoral thesis, written in April 1905, in which he proposed a new and original method for estimating the ratio of molecules and for calculating Avogadro's number - the number indicating the number of molecules present in a certain amount of substance. This paved the way for the transformation of the hypothesis regarding the existence of atoms into an empirical hypothesis.
About a month before submitting the thesis, Einstein published an article on the quantum hypothesis of light and the photoelectric effect. This article, the first of the four articles that Einstein sent that year to the respected scientific monthly "der physik Annalen", was one of the articles that broke the way for quantum theory, and it earned Einstein the Nobel Prize in 1921.
In another article, written in May 1905 and dealing (like his doctoral thesis) with the atomic hypothesis, which began to gain momentum among theoretical physicists at that time, Einstein mathematically analyzed "Brownian motion" - the random movement of microscopic particles floating in a liquid, which was observed already at the beginning of the 19th century . His calculations were another reinforcement of the fact of the existence of atoms, which the academic world was arguing about at the time.
In the last two articles of "The Year of the Miracle", published in June and September, Einstein abandoned the composition approach and turned to the principle approach. In both he sketched the main points of the special theory of relativity and one of its derivatives, which has long since become a cultural icon - the equation 
. The special theory of relativity starts from two observational principles - the principle of relativity and the principle of light - and deduces from them the structure of space and time. Based on these two principles, the special theory of relativity describes a world completely different from the one we are used to, a world where time and space are "welded" together into one entity called "space-time" and in which the answer to the question of whether two events occur at the same time is not fixed and unchanging, but depends at the respondent's speed of movement.
Historians of science debate to this day the question of what led Einstein to abandon the compositional approach and convert it to the principle approach. It is almost certain that Einstein noticed the fact that the more the scientist delves into the intricacies of the world of matter and tries to put together models for complex phenomena, the more his confidence in the truth of those models decreases, and indeed, the quantum hypothesis of light, which was the focus of the first article in "The Year of the Miracle", signaled to Einstein that the equations of the electromagnetic theory of James Clark Maxwell are probably not the end of the story, and the process for the exact identification of the "building blocks" of the material world is still long. From this point of view, the transition to the principle approach is a turn of despair - instead of continuing to make assumptions whose validity will remain unknown for a long time, perhaps it is better for the theoretical physicist to focus on indisputable phenomena and draw interesting conclusions from them about the structure of the world.
Today, fifty years after Einstein's death, his revolutionary conclusions continue to resonate powerfully, and that "wonder year", in which the world picture of the 19th century finally collapsed, will probably continue to serve as a major landmark in the history of science for many years to come.
Tomorrow: the quantum hypothesis of light
Dr. Hagar is a philosopher of physics, author of the book "Time and Randomness" (Mapa Publishing)
