I'm not going to sit here and say that time travel exists, rather I an going to say why we shouldn't figure out how to time travel. All comments are welcome!
Let's pretend for a minute that someone invented time travel;
"Look! I've done it! I've finally figured out Time Travel!" Jonathan shouts, setting back the day to his grandmother died. He never got to say goodbye. When he gets there, everyone is surrounding her. He tells her he's from the future. Nothing happens, but she dies happy. Later, back in his own time, he thinks; "Hey! I can go back and time and stop World War Two from ever happening!" So he gets his nice shot-gun and sets the time back to 1932, and shoots Hitler before he has a chance to do anything.
Okay, what will now happen to him, he didn't just change something little, he changed something drastic. Yes, he stopped alot of people suffering, but we had quite a number of social advancements at that time. If that wouldn't have happened, we might not have been as aware of the damages of prejustice. That was also a time when people of different races were forced out of there country and went in to others, and people of many different races might not even exist. It's the same for other events, big and small, we don't fully know the consiquinses of our actions, expesually in Time Travel, we might end up entering an entirely different reality, just for changing the slightest thing.