ELI5 Time Travel

Time travel is something that I find very interesting; however, it's also something I don't hear a lot about. I was curious to those that are knowledgeable in this area. From what I understand of time travel, theoretically, it is possible to go into the past; however, doing so creates a parallel universe similar to our own, but the time traveler goes back in time to the period of their per-determined choosing. This is why such things as the "grand father's paradox" can never happen because the traveler can never return from the universe from which they came from. In short, is this still the current theory, or is there now new evidence pointing to a different idea?