Greetings, I was hoping to find some help with a question that I have. I'm an amateur writter and I'm currently developing a short story based on time travel. To that end I was hopingt o find some advice on a specific area. I'm looking for a method to explain how the "machine" could target a specific point in time. My own thoughts led me to the idea of finding something that exists as a constant in the universe but is always changing (that's the only way I can think to explain it). So not being that scientifically minded, I thought I'd seek help here. If anyone has ideas or thoughts they could point me to I'd be greatful. Thank you.