Time. I don’t believe in it. It’s not a real thing, it’s a convenient construct for our everyday lives.  Think of a theoretical point in space. Where is time? There is none.  Now add a second point, and by moving them relative to each other, time, or the concept of time is born.  Whether it’s about your hour hand on your watch moving relative to the Earths movement around the sun, or any movement in relationship to any other, its not some all-pervading fluid called time. I don’t think traveling back “in time” could ever happen, because that would mean returning every atom in the universe back where it was and as it was — it gets a little complex — especially if you (like Fry on Futurama) fall for your gramma.