Is time travel possible?

[cyberninja45]

 Keeping in trend with vgchartz these days simple question is time travel possible? To me if time travel is possible why have we never encountered time travellers, what is stopping them from coming back into the past (our present).   This leaves me to conclude three logical scenarios.

1. Scientist got it wrong and time travel is impossible.

2. Time travel is possible and there are time travellers ,they just keep themselves hidden.

3. The world soon ends so time travel is never invented.

Is there something I am not understaning that someone would like to explain.

Note when I say explain I mean in your own words ,providing links and large quote trees does not show your knowledge on a topic.