I personally don't believe that it is possible to time travel to the past. However if it ever does become possible to do so then surely any effects cause by such time travel have lead us to this moment, me typing this and you reading it. Is my statement correct? Our past cannot be changed from what it is, therefore any conceivable time travel to the past in the coming years has been done and dusted before this moment in time, yes?
So you go back, kill your Grandfather, your Grandmother remarries, you eventually get born. Do you then go back and kill all of your Grandmother's suitors until she's too old to have kids, thereby negating your own existence anyway?
Will/would/could/has someone/anyone explain/ed how someone/anyone would/could/would've/could of conceivably do/did/done something/anything sometime/anytime somewhere/anywhere before they have/n't already been conceived . . . yet?