Hi Hilmar,
Here is something else that might help. I have heard several people state that it would be impossible for an object to travel at the speed of light, or beyond the speed of light; because, as the object accelerates towards the speed of light, the mass of the object tends toward infinite. As I understand relativistic mass, as the speed/velocity of matter accelerates, the matter gains mass. This definition of mass is rarely used by physicist today.
Here is a paper that explain the difference between relativistic mass and Newton more traditional mechanical definition of mass which has been converted into a more help geometric definition of mass. I hope I got that right, because it very confusing to me, other than it show how the mathematic of physics can change as our understanding increases or as the theory is applied to practical application.
http://www.weburbia.demon.co.uk/physics/mass.htmlRegards,
LelandJ