When we talk about time travel we really need to be more clear and say that we are talking about going faster, because time is really all about speed. Time doesn't exist as we think of it. We're only noting the passage of time and calling that observance passage. It's all about distances and speed.

Its like if you weant back in time and talked to a Roman and were wearing jeans and a northface, you would come back here and there could be giant butterflies controlling humans. Thats a little extreme. But it makes sense that every little thing you do has an effect on the world.

We cannot do anything to change the past, because, changing one event in the past (even just watching), will make a leak in the main chain of power distribution, and it will swallow everything. Think about it like a black hole (but it is not a black hole, it is worse).

The only way to know the past history, is by tracking the traces and reading the written knowledge.

But seeing the future is a different story. Because, seeing it does not change anything in the future because nothing of the future had ever happened yet. It is just a vision drove by current chain of power distribution, and caused by some supernatural being. And I think it is a high evidence of contact with a supernatural being.