I am going to talk about something technical but fun. No such thing? Yes, there is. It's called Science fiction!
In science fiction exists this thing called Causal Loop or Causality Loop. I will explain this slowly and simply, even at the risk of sounding patronizing. :)
In regular, non-sci-fi life, there is something called cause and effect. For example, you walked to office and hence reached the office. Someone buys a car, and then they can drive in that car. Two lovers have a fight and as a result they break up. These things are simple and straightforward. Jake talked back to his wife and had to sleep on the couch. It's easy to see what is the cause and what is the effect.
In a causal loop, these lines are blurred. Causal Loops, so far as I know, can only be caused by time travel. At least the ones I have seen are. In a causal loop,it's hard to say which event is the cause and which one the effect. Both are both actually. If you have heard the question, "which came first, the egg or the chicken?", then you have heard of a causal loop.
Let's take a fun example. Have you seen the movie The Terminator? The first part I mean. Do you understand the story?
When I saw this movie the very first time, on a rented VCR with a bunch of my friends, I don't think any of us understood more than 50% of the story. We were just happy to see the "hot" scene in addition to all the fast-paced action and shooting by our friend Arnie the Terminator. So,let's recoup the story for all of us in simple terms.
-A defense firm Cyberdyne creates a computer network called Skynet.
-Skynet is an artificially intelligent network and becomes autonomous.
-As Skynet tries to take over the Earth and kill all humans...
-One man, John Connor leads the resistance against it.
-Skynet sends a killer robot, a Terminator, to the past to kill John Connor's mother Sarah Connor so that John connor is never born.
-The humans, at the same time, send a human, Kyle Reese, back to the same time, to protect Sarah Connor
-While Kyle Reese is running around with Sarah Connor, trying to keep her safe from the Terminator robot, the two have sex, Kyle and Sarah, not Sarah and Robot, ok?
-From that copulation is born John Connor...
-Who later leads the charge against the machines and...
-Sends Kyle Reese back to the past to save his mother who....
See what I mean? If John had never sent Kyle back, John would never have been born and so on. It's a circle. cause becomes effect and vice versa.
It's also called the Predestination Paradox. You can read more on the topic on Wikipedia.
http://en.wikipedia.org/wiki/Predestination_paradox
