## Space and time — answers to FAQ

Despite the fact that the laws of mathematics allow for a variety of types of space, up to the 20th century, the properties of physical space were assumed to be the simplest possible , those Euclid described back in the century III BC for a three-dimensional space. Not to mention that time flow was considered regardless of motion. By the beginning of the 20th century, there appeared experimental evidence of independence of the light speed from a velocity of an observer. Then attempts were made to explain that by introducing additional physical principles like compression of moving solids. Meanwhile, Albert Einstein explained the constancy of the light speed by the dependence of time passed on the velocity of the observer. This meant that rapid effects must be considered in four-dimensional space-time. Ten years later, he developed a theory of gravity, which claimed that space-time becomes curved in the vicinity of massive objects. Soon the theory of gravity has become the basis for dynamical description of the universe done by Alexander Friedman (1922) and the experimental discovery of the universe expansion by Edwin Hubble (1929).