Predestination must be true. So must free will.
Predestination refers to the concept that all events of history are predestined, usually in reference to divine predestination, but also in reference to the concept that the future is theoretically predictable and, thus, unalterable; that is, the idea that, given knowledge of everything in the universe, one could predict the future, because there is nothing in the universe that does not follow the laws of physics.
First note that predestination is a concept; an idea; a theory. Neither atheists nor creationists nor followers of most other major religions completely subscribe as a united block to predestination. Various counterarguments have been proposed from different points of view to prove predestination false. For our purposes, the main comparison to make is that between the Biblical argument of divine free will and the atheistic argument of quantum indeterminacy.
The Biblical argument is that of free will, which like predestination is a more general term than its Biblical use. In Biblical contexts free will refers to the concept, confirmed in Scripture, of humanity having free agency to change and affect its future. More generally, free will refers to all beings having free agency to change affect their futures.
Quantum indeterminacy is, like most things starting with ‘quantum’, a complex concept, but it boils down to the idea that, at a very basic levels, quarks, the components of atoms, are unpredictable. The idea is that, since to gather information about something you must observe it by bouncing rays of some sort off it, once the observed thing is small enough, it is impossible to gather all the information about it. This is borne out in reality; you can tell either where a quark is or tell its momentum, but not both at the same time, because to observe one quantity you inevitably alter the other. Thus one cannot have knowledge of everything in the universe, and therefore the universe cannot be predicted, and therefore predestination cannot be true, at least as we know it. Obviously this feels somewhat suspect, but under atheistic beliefs it holds true. The idea needs some altering under Biblical beliefs, though, because an omnipotent God would not need to alter a quark to observe it.
The counterargument I would offer is this: that we know that illogical things are a caveat of omnipotence (God can’t make a rock that he can’t lift, which is not a problem with his omnipotence but rather a necessary facet, just as he cannot make a square circle). It is possible that quark observation could be considered just as illogical as divinely un-liftable rocks, even if it doesn’t feel like it to humans for the simple reason that we have no practical experience or understanding of quantum indeterminacy. There is simply no real way for us to have a practical comprehension of most quantum things; they fall outside the wheelhouse of what our minds are trained to understand.
It is an inevitable counter-counterargument that the Bible contains examples of what many consider to be predestination (see Proverbs 16:9, Jeremiah 10:23, Acts 13:48). These are complex issues, and I would advise you to seek out all the arguments you can on the topic so as to gain a full understanding of it. Here, though, are a few articles that I commend to your study of free will: an argument that predestination is a man-made doctrine, an overview of predestination and free will, a list of Bible verses relevant to the topic, and an article about the prominent Richard Dawkins’ seemingly contradictory beliefs on the Bible, free will, and comfort against correctness. All these and more have their own light to shed on the fascinating topic of free will and predestination.
At the end of the day, though, this is a problem that nearly every religion, plus atheism, faces in one way or another. For instance, the solution of quantum indeterminacy may soon find threats as advances in the quantum field are made. I cannot make any claim to discovery of the silver bullet that will put the debate to rest once and for all, but rather would make you aware of the debate and lead you towards different solutions and problems, for your own perusal and conclusion-drawing.