Space and time — answers to frequently asked questions
Despite the fact that the laws of mathematics allow for a variety of types of spaces, up to the XX century, the properties of physical space were assumed to be the simplest possible, those which Euclid described back in the III century BC. The time flow was considered regardless of movements in three-dimensional space. By the beginning of the century, there were experimental evidence of independence of light speed from the velocity of an observer, and attempts were made to explain that by introducing additional physical principles. Meanwhile, Albert Einstein explained the constancy of light speed by the connection between the passage of time and the velocity of the observer. This meant that the rapid effects must be considered in four-dimensional space-time. Ten years later, he developed a theory of gravity, which indicated that space-time becomes curved in the presence of massive objects. Soon the theory of gravity became the basis for opening of the space expansion of the universe by Lemaitre and Hubble.