No they don't. They believe that time travel is like a loop on a toy race car track. You loop being the invention of time travel. You can never go backwards because of the loop, however you can always go forwards of backwards, but only up to the loop. This would explain why we've never seen time travellers.

Have you ever seen Interstellar? It's a great movie I would suggest watching it. It explains a lot about space and is very interesting.