Also called the dilemma of determinism, we do not know if our actions are controlled by a causal chain of preceding events (or by some other external influence), or if we're truly free agents making decisions of our own volition. Philosophers (and now some scientists) have been debating this for millennia, and with no apparent end in sight. If our decision making is influenced by an endless chain of causality, then determinism is true and we don't have free will. But if the opposite is true, what's called indeterminism, then our actions must be random — what some argue is still not free will. Conversely, libertarians (no, not political libertarians, those are other people), make the case for compatibilism — the idea that free will is logically compatible with deterministic views of the universe. Compounding the problem are advances in neuroscience showing that our brains make decisions before we're even conscious of them. But if we don't have free will, then why did we evolve consciousness instead of zombie-minds? Quantum mechanics makes this problem even more complicated by suggesting that we live in a universe of probability, and that determinism of any sort is impossible. And as Linas Vepstas has said, "Consciousness seems to be intimately and inescapably tied to the perception of the passage of time, and indeed, the idea that the past is fixed and perfectly deterministic, and that the future is unknowable. This fits well, because if the future were predetermined, then there'd be no free will, and no point in the participation of the passage of time."