http://www.sci.fi/~suntola/DU,%20Main/DU%20Main.htm

DU honours the basic quantities of physics: mass, time and distance. In the model the universe is the 3-dimensional hypersurface of a 4-dimensional sphere, with a zero total energy. The kinetic energy of expansion is balanced by gravitational attraction. From observations and arguments going back at least to Feynman, the rest mass *mc*^{2} is interpreted as the kinetic energy in the fourth, expanding dimension.

The above means that, in DU, the speed of light is not a constant. This is not actually a violation of GR, where the formal constancy of *c* is maintained by complicated changes in space and time coordinates; the experimental results are mostly identical. In DU the coordinate time is absolute, but the apparent time (as measured by clocks) changes with velocity and gravity.

The simplicity of DU is manifested in the small number of assumptions it makes, when compared to GR. In DU you can derive Mach's Principle (the origin of inertia) and the equation *F=ma*, for example.

Whether or not DU is approved, it should be noted that relativity is no longer valid in modern cosmology. Space has a preferred coordinate origin, the centre of expansion, and there is the notion of an absolute, universal time (cosmic time).