The spatial dimensions of the universe are Euclidean. In other words, the axes are orthogonal (i.e. 90 degrees) to each other. Also, the three angles of all triangles always sum to 180 degrees.

Lecture 2 – The Principle of Relativity has been added to the Home Page. This lecture discusses the historical views of the nature of the universe, the development of the Principle of Relativity, and early views of light including the Doppler Effect and redshift. This lecture provides background which helps to explain the assumptions Einstein used in his Theory of Relativity. Length: 55:59

Spacetime Spacetime is a four-dimensional system that is composed of three spatial dimensions and a temporal time dimension. Einstein used the concept of spacetime in…