In the course of time, physics as a science underwent great changes. From a subdivision of philosophy it gradually turned into an applied science and then, in the 20th century, into an extremely complicated, greatly specialized and somewhat closed science. For the majority of this time physics has been rather ambiguously limited, describing the movements of celestial bodies and other material objects that stand behind the construction of many mechanisms and so on. To be a physicist was to know something about all these fields. But in the 20th century and, especially, after the works of Albert Einstein, everything changed. Physics split into a number of very narrow and very specialized fields, sometimes with little connection between each other. The majority of scientists work in one and the same field their entire lives.