In fact, quantum physics is not arbitrary at all. Perhaps I didn't understand your article, but even in QP, you have a tendency. I guess you're considering brownian motionand Liouville theory instead QP, then the statement might be right, but still in debate, because you want to specify short-term trading. If you're investing in one minute, then the tendency cannot be predicted with the last step, but it can be determined by the past few minutes, so it is not arbitrary at all. In one minute trading, you're using Laplace statistics, 50% upward, 50 percent, however, the point is you need to use simply bayesian data and use the last minutes to forecast the movement. Based on that, you can assemble profitable models.
Your analogy using QP is rather wrong then, since you do not have a wave function to your EUR/USD value assembled. If you are able to construct it, then trust me, you'll be the best trader , even if it's random!