Wow... I just made a really long post and deleted it. Writing it I realized something. Forward timetravel is possible (I hope anyone reading this already understands how it works). So, the same concept applied to backwards time travel would be impossible. The whole universe would have to slow down to a hault, then go in reverse. I doubt this would ever happen. The universe would collapse instead I believe. So the only logical answer is that backwards timetravel (using the same methods as forward timetravel(my concept of backwards time travel is to exceed the speed of light) would only affect the "traveler", reversing his stages of life until the point of non existence, or just kill him instatntly. Hey, why would you want to go backwards in time when you could stay in eternity forever (speed of light). So, when if comes to visiting the past, the only way I can think of is to pull the past and bring it to the future (use your imagination).