The problem is you killed your grandfather that conceived your father. Not some other timelines' grandfathers that might have conceived other versions of your father. And why not going back into the past, does not mean simply going back to your past, according to your unique timeline? So you killed, in your timeline, someone who conceived you, you should cease to exist because you are your past, isn't it? If you don't come from your past, where do you come from?

No, we are talking about hypothetically speaking, not refering to how that would be possible.

As you can see in "Back to the future" movies, it assumes that if you change your history, you will be transported to an alternate future.

From my explanation, that would not be called "time travel", only "space travel".

Which infers that we can't change our pass.  Unless it is predestined. But predestined is a silly concept because, that would mean that we will not be able to control our own actions.

Therefore I conclude that, time travelling to the pass is impossible.
I'm looking for proof like these for time dilation. Can you provide some references on this problem on satelites/GPS? Not refering to Astronaut's time in space, as their biology would be effected by more than just time.

  hum... yep.. I guess it won't be time travel, I guess it's like how scientist are tracing the history of the universe from radiation let off from the pass.

We are definately just an observer.

There is theory, however. That even if you killed whoever conceived you, you will still exist.

The theory suggests that time does not really move in a straight line like an arrow. It moves likes a river, in different sets of streams. At times, the river can split into different directions, resulting in different timelines, or else known as the explaination for parallel universes. This theory is probably oming from an everyday human experiences. Have you remebered how certain minutes actually "felt" as if it is longer than other days? Theory suggests that the river sometimes forms a small vortex, trapping any matter into a temporary time stop, hence you hear things like, "That is the longest ONE minute I ever have".

Theories, anyways. But it sure gave a way out for time paradoxes.