Hi, I'm writing a sci-fiction story and have a question I believe is probably somewhat simple. What I am looking for is the smallest measurement of time in the universe that could be considered a constant value. I have no background in physics or anything so while I do consider myself a fan of science, what I would assume might be constants might be completely wrong so I need to ask. Would the the shortest half-life of something be a constant? or the time of an electron orbit around an atom? What would take the shortest amount of time, and be constant, no matter where you were in the universe? Or do the laws of physics say that time is different depending on gravity, thereby making it impossible for there to be a constant? Thanks for any help.