Everything maks perfect sense when we travel in to the future, but when someone start thinking about going back in time it become bit murky. Just to get an idea if you go back in time you can land in to a period that you were not born, how come that you exist before you born. These apparent contradiction called Time Travel Paradoxes.
As we mentioned earlier, the concept of journey into the past a little murky the second causal rears its head. Cause Causal loops, at least in this universe, which manages to hide even the best laid time to travel plans.
To begin with, if you traveled back in time 200 years, you would show up in a time before you were born. Think about that for a second. In the flow of time, the effect (you) exists before the cause (your birth).
To better understand what we are dealing with here, consider the famous grandfather paradox
Think about it. You have not been born yet. Nor has your father. If you kill your own grandfather in the past, he will never have a son. The son will never get you, and you will never happen to take that job as a time-traveling killer. You would not exist to pull the trigger, which counteracts the whole string of events. We call this an inconsistent causal loop.
On the other hand, we must consider the idea of a consistent causal loop.
Then there are the chosen model of time travel, which means distorted probability close to a paradoxical situation. What does this mean? Well, put yourself in the role of time-traveling killer again. This time travel model would make your grandfather near death certificate. You can pull the trigger, but the laser will operate. Maybe a bird will poop in just the right moment, but a few quantum fluctuation occurs to prevent a paradoxical situation from taking place.
But then there is another possibility: the future or the past you are traveling in, just be a parallel universe
Confused yet? Welcome to the world of time travel.