theoretically if the past had in fact have been altered then us as the wider largely ignorant community would be unaware of this. Im sure this has already been established, though if people were constantly altering minor events, or even major events that subsequently alter certain dates it would just appear normal to us. For the reason how can we be certain that it is not occurring? With current knowledge it would not seem possible as travelling at the speed of light would destroy us.. But is the universe so rigidly structured that there is no leway for alterations? is everything preordained? Perhaps transdimensional theories are more plausible than travel in our specific version of reality.. Interested to hear of peoples thoughts on fate...