I just found this on slashdot:

http://news.bbc.co.uk/2/hi/science/nature/4097258.stm

Now, from the books that I have read, it seems that you would have a chance (albeit incredably small) at killing your father/grandfather. Something along the multitude of 1 in a 1 [with a billion billion billion zeros after it]. This article seems to disprove what Stevn Hawkings (among several Theoretical Physists have stated.

Although there is a chance, it is impossible. Anyone who has read some recent theoretical physics ? Mine is kinda out of date