I'm sure you have heard about, read about it book and even seen it in movies. Well I am hear to give you a basic overview, it is very complicated once you really look into it. I'm hear to shed light onto this for all of you. (All with out the use of a flux capacitor or a Delorean.)
I'm going to talk about the types into the future or into the past. Lets start with the future. In some ways this is on display everyday. The clocks on the GPS satellites need to be adjusted due to fact that when you are moving
time moves slower thus you age slower. In theory, you could send someone out into orbit for say 20 years, he would only age 20 year when family member and friends on earth would age 30 or 40 years. And the faster you move the slower time would move but you would run into the problem that the faster you move the more massive you become.
Something I think that cool about time travel into the past is in some ways we see it all the time too, ever night to be exact. When you look at a star, your not seeing how it looks now, you seeing how it look 100, 200, even 1000 years ago. Now don't be worried, I know you though it would be slightly more interesting and let me try my best to make it so. Einstein's law of causality does kind of put a damper on the idea that you could step in a machine and just go back due to, in simple terms, cause and effect. Everything happens causing something else and something else to happen and we can't upset that. Now don't give up your dreams just yet. some physicist do theorize that if we could push past light speed time could flow backwards.
Well there it is in a few minutes, time travel. Now to fully understand the science and theory behind it you would need to read a book and be much smarter than me. It is something very cool to think about. Stephen Hawking as talked about the idea of time traveling tourist if you want to look into that. But to save you the time. But if someone knocks on your door claiming to be your great-great-great-great-great-great-great-great-great-great-great-great-great-great-great grandson, maybe you should listen.