What IF: time travel

People say you cant go back in time because if you can then we would see space travelers traveling back in time to visit us. Well... what if.. WHAT IF: we didn't travel back to the past because we didn't want to change the past which would later change the future. So in the future the scientists mke an agreement that they'll never travel into the past because they do not want to disturb anything.

You're assuming a mass/energy imbalance. That isn't always the case. We could send something, theoretically, back in time into a preconstructed "shell" of the same mass of what we're hoping to send back. The physical form in the current timeline could jump in and out of existence in an infinitely small timeframe while existing in the past timeline for a much longer timeframe.