It's possible. But if you think about it, they would never tell us. That would be extremely dangerous. People could go back in time for tests and get the right answers, undo things that they know don't work out.
From what I have read,if a machine could be made to take you back in time,it could only go back to when the machine was made...going forward in time is a more plausible theory,if you could travel faster than the time curve.
I once read an article in a science magazine and they did experiments with black holes and found that time travel IS POSSIBLE, it's just finding the resources to make it happen. You should look it up, it's an interesting article. I believe I read it in a How It Works Magazine, their website is: www.Howitworksdaily.com! Good Luck!