Note I'm not talking about Mathematical Physics. This is a Physical concept not a Mathematical concept. Speed of light is less than 300000000m/s. Physically, 300000001 (+1) m/s does not exist, but mathematically, this isn't impossible. So Physics is limited by our universe, but Mathematics is only limited by our imagination. Some ago I read Einstein said in its Relativity that Geometry(, Mathematics) can be considered as a branch of Physics. But, if as I said, Mathematics is less limited than Physics, how can it be considered as a branch of Physics? Then, how is Mathematics limited? Well, first of all, if Physics it's limited by our universe while Mathematics isn't, its perfectly possible the existence of other universes that can have different rules of physics (the speed of light may be higher or lower), because they don't break any rule of mathematics. Then the limit of Mathematics; Mathematics is limited by our imagination, Is our imagination limited? Well, as Mathematics is created by the human mind, it must have a limit. Universes with different physical or mathematical rules? To organize this, it may be sets of universes: In each set are universes with different rules of physics but with the same mathematical logic. Each set has a different mathematical logic (please correct me if Mathematics isn't really limited by anything anything anything). So, as Mathematics and Physics are separating (many people think they are the same thing!), I'm asking about a branch that connects physics and mathematics: Mathematics that are limited by physics, by our universe. This is a concept of Einstein's Geometry, Geometry limited by the rules of our universe (but in fact, Geometry is only limited by our universe), but as Einstein thought, it isn't the whole Geometry branch, it's only the Geometry limited by our universe. In this concept, a speed of 300000001 (+1) m/s does not exits. So, does this branch have a name? Abstract: Einstein's Geometry.