Vincent Causse wrote: Chaos is what we call, the states of things or actions that we do not understand.
Nothing says a rule-goverend system the rules of which we perfectly understand cannot
also be chaotic, though. That's not what chaos means. Take your own example of gravity. We have only strictly deterministic theories of gravity so far, but even if we take them seriously at that they are still perfectly capable of governing chaotic systems. If one can specify exactly the mass density and mass flow density of a gravitationally closed system, one can predict and retrodict all of its history exactly. That is what makes it deterministic, all right. However, if the system is
any different than its description, then not only will it eventually deviate noticeably from either the prediction or the retrodiction, but in fact that deviation in the past and future surpasses at one point or another any arbitrarily large limit.
This is chaos. It has nothing to do with whether or not we understand the system on a fundamental level. Even toy systems that live only in an ideal world of spherical cows, designed from the ground up to obey well-defined and perfectly understood rules, can still easily be chaotic in that two trajectories arbitrarily close in one phase space location are arbitrarily far apart in another. So just because something is chaotic and we recognize it as such doesn't mean we don't understand it, even down to its most fundamental level.
