the Great War. In Europe, modern architecture departed from the decorated styles of the Victorian era. Streamlined forms inspired by machines became commonplace, enabled by developments in building materials and technologies. Before World War II, many European architects moved to the United States, where modern architecture continued to develop. The automobile increased the mobility of people in the Western countries in the early-to-mid-century, and in many other places by the end of the 20th century. City design throughout most of the West became focused on transport via car. Sport The popularity of sport increased considerably—both as an activity for all, and as entertainment, particularly on television. The modern Olympic Games, first held in 1896, grew to include tens of thousands of athletes in dozens of sports. The FIFA World Cup was first held in 1930, and was held every four years after World War II. Science Mathematics Multiple new fields of mathematics were developed in the 20th century. In the first part of the 20th century, measure theory, functional analysis, and topology were established, and significant developments were made in fields such as abstract algebra and probability. The development of set theory and formal logic led to Gödel's incompleteness theorems. Later in the 20th century, the development of computers led to the establishment of a theory of computation. Computationally-intense results include the study of fractals and a proof of the four color theorem in 1976. Physics New areas of physics, like special relativity, general relativity, and quantum mechanics, were developed during the first half of the century. In the process, the internal structure of atoms came to be clearly understood, followed by the discovery of elementary particles. It was found that all the known forces can be traced to only four fundamental interactions. It was discovered further that two forces, electromagnetism and weak interaction, can be merged in the electroweak interaction, leaving only three different fundamental interactions. Discovery of nuclear reactions, in particular nuclear fusion, finally revealed the source of solar energy. Radiocarbon dating was invented, and became a powerful technique for determining the age of prehistoric animals and plants as well as historical objects. Astronomy A much better understanding of the evolution of the universe was achieved, its age (about 13.8 billion years) was determined, and the Big Bang theory on its origin was proposed and generally accepted. The age of the Solar System, including Earth, was determined, and