you have the ability, but i'm not going to come up with any downsides to it, because it already has some pretty stuffty downsides. everybody you ever knew and loved will die, everything and everywhere you ever knew will one day meet it's demise, and you'll watch the world end, and eventually you'll just be floating around in the infinite darkness. unable to die. forever alone with just your thoughts.
i want the ability to go back and relive my favorite memories/days, kinda like the "replay mission" feature from GTA 5.