When I started to get interested in Relativity (mostly SR) the one thing that kept me confused (most likely the same for everyone else) was the definition of time. And through some thought I came up with some questions. Without matter does time exist? (not getting into the debate of whether a photon has mass) My understanding is that time is a measurement of an event. An event is a physical change of mass i.e. change in position (oscillation) or change in size (growth). So does time exist in a vacume? And if my previous statements of time are true, at absolute zero will time stop? This leads me too my second thought. I have been told that mass (and time) are elementary measurements, but mass is the amount of matter, which is the amount of stuff something is made of. A quark is stuff. And lets say a quark has a shape of a perfect cube. Then a quark has a volume of L*W*H. And since a quark is the (currently) the most elementary particle with no empty space in its cube shape. The volume is the mass. Therefore the mass is a relavent measure of distances. So why isn't mass defined as a calculation of distances. And why isn't time defined as a measurment of the change in mass. -Tim FYI, Anything or everything I stated above could be idiotic, uniformed, ignorant, benight, stupid, very stupid, or just wrong. These are just the random thoughts that taunt me as I try to understand 13 billion years in one lifetime.