I think the bottom line is our understanding of time, space, etc. is all limited by our observations. Based on what we observe we came with a model that differantiates time and space, and yet at the same time allows us to use the time-space 4 vector. 150 years ago no one would have considered arguments that we are making today, limited by one's experiences, and the whole idea that time space is a function of one's velocity was pretty unorthodox. 200 years before that, you would most likely be burned for such reasoning. I really wonder how well we will understand the subject in another 100-150 years. Perhaps at that point our ancestors will read arguments on blogs like this and laugh at how primitive our thought pattern was...