Ancient Greek Understanding

     Recent observations of galactic rotation curves fail to correspond with the predicted orbital speeds generated by our current Keplerian model.  This inconsistency of prediction matching actual observation has led astronomers to conjecture that there must exist a great deal of unidentified mass in the universe.  This missing mass is currently estimated to make up approximately 90 percent of the total mass of the universe (Hawley, 392).  This mass is collectively known as "dark matter" and presently there exist several different candidates to explain its composition.  As of this time, there has not been any strong consensus on which, if any, of these models is correct.  Just as the mystery of how the universe is structured and how the laws governing its motion currently perplex scientists of today, so too did such questions trouble and bewilder cultures of other times and geography.  One of the most prominent and notable of such cultures is that of ancient Greece.  Those notions of universal motion presented by Aristotle held great influence over this culture and seem particularly interesting to contrast with modern theories.  This paper will attempt to evaluate how some of Aristotle's theories might have been applied to the observed galactic rotation curve data and the potential consequences/outcome of that interpretation.

     It should be noted that the ancient Greek world was seen as being defined in terms of four basic elements of which all Earthly matter belonged.  These mediums consisted of the elements earth, water, air, and fire (Hawley, 25).  An object placed in an inappropriate medium would be propelled by that medium to its natural state.  This was used to explain the natural order and laws that governed the Earthly realm.  A bubble for instance, would float to the surface of water to obtain its natural state of air while a rock would sink to the bottom of the pond as earth's natural state is lower than that of water.  So too was every object said to be a composite of these elements.  This was the standard explanation for why pigeons were able to fly; they were composed of nearly equal parts air and earth.  The heavens, seen as infinite and unchanging, were thought to be made of a stuff more perfect than the Earth, and so were said to exist in a fifth medium, aether.  The natural motion of aether was said to be that of a circle rather than that of a straight line, as is observed on Earth (Dicks, 199).  All objects existing in this aether were said to be at rest but attached to a type of ring which was eternally rotating (Heath, 76).

     The Greek notion of movement dictated that any moving object constantly be in contact with the force moving it to maintain its motion (Hope, 176-7).  For the rings upon which the heavens were attached to constantly be in motion, there had to be a constant force driving them.  This pushing force which drove the heavens is sometimes referred to as the prime mover (Dicks, 214).  Each planet was said to have a lesser mover, propelled by the prime mover, which accounted for varying orbital speeds and why the planets so obviously appeared to move in relation to the heavens.  Given that all astronomy up to this point in history was done naked eye, it seems reasonable to expect that should more the stars have shown signs of moving, they too could be attributed lesser movers in order to account for their motion.

     It is perhaps due to the fact that the ancient Greeks used only naked eye astronomy that so many of their models were based more on conjecture than on large scale observation.  It would seem possible that should the Greeks be told of the dark matter problem, they could create an infinite number of lesser movers to account for, what seems to modern day astronomy, inconsistent orbital speeds.  The effectiveness of a model with a different force for each moving body however, quickly loses its ability to be a useful tool for predicting movements of any body at all.  It would seem that the Greeks would then be stuck in the position of making a generalized set of laws to predict the movement of heavenly bodies which would leave them in the mire which modern astronomy is now stuck.

BACK TO DARK MATTER HOME PAGE