Time travel is possible through books. How else can you experience what it was like to fight in the Civil War, cross the ocean with the Mayflower, or sign the Constitution?
One of my favorite people is John Adams. I have traveled with him to France and watched him help found our country. I have seen his parenting style and read over his shoulder as he read letters from his loving wife. All of this was made possible through books. I have been inspired by this awesome man, and his life. He wasn't perfect, but for me that makes him more endearing. (I certainly didn't learn all these things from a class at school. I learned little more than his name and the fact that he was a Founding Father there.)
I think this aspect of reading is why so many books have time travel in them. Avid readers don't have to suspend reality too much to believe in time travel. After all, they experience it for themselves almost every time they open a book.