It's Friday. File this one under Greg's completely random thoughts.
You can never predict and thus change your future. If you've seen the movie Paycheck, you may remember that Ben Affleck built a machine that could see into the future by bending light on an infinite curve or some other BS. Well, let's just imagine that there existed a type of Unified Theory Machine, which knew the exact position, composition, and all qualities of every atom in the universe. It would know the weather in Duluth. It would know the positions of all the RNA in your brain and what synapses were firing, and thus would know what you were thinking. And because it knew all this, it would be able to use the rules of physics to determine the exact quantum state of everything in five minutes, five hours, or five days. It would be able to calculate the next hundred years' worth of hurricaines and earthquakes, or tell you what your future grandson would dream about on New Years Eve of his 21st year.
Now the traditional sci-fi take on a machine like this is that you could use it to look into the future, and then take some action to change the future you saw. If you saw yourself get hit by a car on the way to work, you could simply decide not go to work that day. It sounds simple enough, but I think that this scenario is impossible.
If this machine truly worked, it would take all factors into account, and that would include your use of it. Thus, when it predicted events, it would take into its predictions the fact that you would come into posession of it, and that you would take actions to try to change the future. It would simply show you the result of those actions. So the only way that you would seemingly change the future is if the original prediction of the machine was flawed.