Time

Yep - did it yesterday.

We're all traveling through time

I did it tomorrow.

I don't think that's quite what the OP meant. He was clearly thinking of time travel in the H.G. Wells or Doctor Who sense.

In the spirt of the question as he actually meant it, I would answer that time travel is extremely unlikely to be possible.

One thing though. If time travel is possible, so is faster than light travel (and vice versa). And an engine that achieves one of those, can also be rigged to achieve the other.

But like I said, extremely unlikely to be possible.

I was given a time out of mind your manners.