I consider myself a bit of a movie buff. I love movies and love watching them with someone who doesn't mind picking them apart and discussing the intricacies of the story line. The possibility of a great debate is probably most present in time travel movies.
In other movies, going back and killing off an ancestor would have no effect on you. You would have altered the future from that moment, but since you already exist, you would continue to do so. This would not change even if you traveled back to the future again.
In some movies, a change in the past will effect the previous future. In others, what has happened has already happened and cannot be changed. In yet other movies, making a change in the past, creates a parallel timeline with the newly instituted changes.
So, when looking for these movie mistakes, one must be careful to only look at the time travel rules that have been established by that particular movie. For instance, in the recent movie Looper, there is a man from the future who is now in the present who must be caught and killed. The gangsters have caught the younger version of this man.
According to the rules of the movie, if they killed the younger version, then the older version would cease to exist. However, they cannot do that because it would cause a problem with time continuity. The future actions of the younger man still need to happen. They need to capture the older man and then kill him.
This all makes sense until they start using their method to draw the older man back to them. First, they carve an address into the body of the younger man knowing that it will leave scars. The older man, seeing them on his own body, knows where they want him to go. Then they start cutting off parts of the younger man's body. The older version of him, suddenly missing a few fingers, knows they will continue to do this if he doesn't go to the address. As he is racing across town to get there, other parts begin to disappear off his body.
This is where the mistake comes in. Obviously, they're going to kill him when he reaches the address. However, the radical amputations that the younger version has suffered would drastically alter the future actions he would take, which is specifically why they said they couldn't kill him. Someone didn't think this through.
It does seem that in most time travel movies, the idea of messing up the space-time continuum is something to be concerned about. If time travel ever does become possible, I wonder if that would actually be something that we'd have to be concerned with.
Let's assume that time travel has become possible and we could do it safely. Let's also assume that it hasn't been government regulated as always seems to be the case in the movies. If this were the case, I see all sorts of commercial possibilities.
Let's forget about the ideas of going back in time to do things like buy stock in Apple, secure thousands of acres where Manhattan or Los Angeles will one day be, stop Nickelback from forming, buy Mickey Mantle baseball cards, or warn your younger self to take care of those Star Wars figurines. I am more interested in the implications for the average working man.
Travel agencies with access to time travel technology would make a fortune. Someone wanting to book a tropical getaway is always taking a gamble on what the weather will be like. We all know someone who paid thousands to go to an exotic beach somewhere and it rained through their entire vacation. However, a travel agency that could send you to any point in time could send you to your destination on a week guaranteed to have excellent weather based on past weather records. They could also make money sending people to experience first hand historical events of their choosing.
Pizza places would never have late deliveries again. A person calling in would give all the usual information they give now, but would also be asked when they would like their pizza delivered. The time would be stamped on the ticket and as soon as it was done, the driver would zap himself to the moment in time it was requested and would knock on the door of the customer. Customers could even make a call and ask for it to be delivered right now. As soon as they hung up, they would get a knock on their door. In the event of a mistake on the pizza, the company would fix it and then send the delivery out to arrive seconds before the first one. This would stop the bad one from ever being delivered and the customer would never even know there had been a problem.
This could even be used by families to salvage a bad night. Let's say one of the kids runs through the kitchen as dinner is being placed on the table causing it to be spilled all over the floor. Dinner is now ruined. They could call the time travel pizza delivery to have pizza delivered at the beginning of the night and avoid the entire scene.
Fathers would never have to miss the birth of their children. No one would ever miss their flights and packages would always be delivered in time for the holidays.
A world with time travel would be awesome. As soon as it becomes possible, I'm opening a pizza place. I'll make a fortune.