If everything is pre-destined then it means that we have no free will, but I don't believe that things could be pre-destined, I believe that we take each day as it comes and we could all suddenly do something spontaneous that would change the world.
It's like ripples in water. If you create one small ripple it will continue to grow, and if you create several they will react with each other and change.
Using the example of The Matrix, within it everything is spontaneous, people are controlled to a certain extent but as long as they stay within certain boundaries then they are OK. It is the small percent of people who think differently that want to change the world, that want to get out and be free. They are the ones that show how unpredictable we can be, and even within the matrix the oracle can apparently see the future, but can't see everything, as there is no certainty, nothing is fixed, nothing is stable.
I think that the theory Adrian mentioned is good about every variable createing a new universe, like in the film Sliding Doors, which shows how one little thing can change the course of your entire life.
I suppose no-one will ever know though.
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