In 1916 Albert Einstein published his theory of General Relativity, which is used in modern cosmology. Our universe expands - 13.7 billion years ago this expansion started with the creation of the universe, the Big Bang. Quarks and electrons were created, later the protons and neutrons were formed as bound states of quarks. Finally the atomic nuclei and the atoms appeared, forming the observed matter in our universe. But more than 80 % of the matter is dark matter, which is observed by its gravity. Thus far details about the dark matter are not known.