A first thought

Some people believe that the universe follow a strict line of parameters. That it works just like a machine, but on a larger scale. This is called Determinism. Lets say that's the case. That would mean that all outcome are already decided since the birth of the universe.
Then if you knew every single little detail you could measure what would happen in the future.
The problem then is this:

If you see yourself walking on a sidewalk in the future, can you decide not to? If you can't then you have no free will and we're all just machines. If you can, then does that mean the future you measured were false? If it was false, then the measurement must have been wrong which means it's not a fixed future. If it's not a fixed future, then the outcome can't already be decided. If the outcome is not decided then there must be something more than just a matematic that rules what happens in the universe.

I haven't decided what to believe in this. I'm all for science and I don't believe in God, but maybe the truth is somewhere in between.