1.21 Giga whats?!!!

We were having a discussion on time travel. The thing is, can we really say that time is relative? Are we in a position to truly come to these conclusions? And what really is the conventional wisdom about time and it's correlation to physical elements (light, atoms, space, gravity). After all time is an intangible concept, an idea. The passage of which is not truly felt, but imagined. So good at imagining the passage of time we have become, because, we practice. Everyday we think about what amount of time has come to pass and the time that will pass from now to a future event. We're always asking what time it is. And we schedule everything according to a set time. I do not have to go into detail about how the earth rotates around the sun every 365 1/4 days and winter and summer and calanders and such. -Yes, these things, these physical changes (which happen on a definite routine set at regular intervals) have shaped our concept of time and helped us to set schedules and seasons and such.
So we imagine the passage of time because we are used to seeing these changes every day, every year. The argument I want to make however, is that just because these changes happen at a different rate in different spots of the universe doesn't mean that time can somehow be altered. Can one really move forward in time? That would mean violating the principles of cause and effect. I don't know... Just a thought... I could be totally wrong.