A year or so ago I read in some magazine that a reputable Japanese physicist was trying to take advantage of what he thinks may be a possible time-travel loophole in quantum physics. I can't remember where I read it (might have been Discover Magazine or Scientific American), and I don't even remember what the proposed quantum loophole is based on (!), but here is my take on the scenario as I do remember it.
I have built a time machine, but it can only receive messages from the future. My plan is I will turn it on at 12:00 noon Monday. The next day, at 12:00 noon Tuesday I will drop a message into the input saying, "It is now 12:00 noon Tuesday". What happens?
As soon as I turn the time machine on i get the first message, "It is now 12:00 noon Tuesday". Great, it works! ...But now I have an idea: one minute after I recieve the first message, I destroy the input part of the machine. It cannot be repaired in just 24 hours. As I stare at the broken part, I wonder what the consequences are of what I have done.
The paradox I'm trying to imply is, I get a message from myself from tomorrow, but when i break the input today after I recieve the message, tomorrow I'm unable to send the message. So, who is the me of tomorrow who sent the message that I've already recieved?
Another way of telling my story is: I turn the machine on Monday at noon, I recieve the message the future me sent Tuesday at noon, put it in my pocket, wait 24 hours, and Tuesday at noon I don't send the message. Again, who sent the message that I have in my pocket?
All this presupposes that the future already exists in some way. Many scientists of reputation think it does, Kurt Godel comes to mind as one. Space and time being inseperable as the spacetime continuum, if all space exists all time must exist also. If this is true, all possibilities would exist in this Time Dimension. All the choices we may make in the present moment already exist there as sets of possibilities, and when we choose A instead of B, both A and B are existant possibilities in Time, and in choosing we select one pre-existing timeline over another.