What sudden change of material reality caused the abrupt fall of the A value? None. The reality still there, exactly equal, blindly indifferent, but the abstract a value had fallen dramatically. Behind change in abstract reality, represented by the dramatic curves of the Down Jones and the Nasdaq came changes in the material realm, first with the contraction of the consumption, then the decrease in the production of goods and finally with the expulsion of the workers. Graphs of Wall Street measure superstition that relates the abstract world of the values and the material world of goods and services. It is not a simple expression of the State of the latter, but the measurement of the nervous pulse of investors moving in this abstract world which strategically is called the real world, the world of pragmatic men.
It is no coincidence, because the social myths always refer to a phenomenon with names that contradict it, deny it or silencing it. One of the oldest laws of Economics, the law of supply and demand, relates the value of something with the material world. This material world is composed of goods (supply) and needs (demand). This law still unites the material world and the symbolic world of a narrow way. Example: during the escalation of the price of oil in the first half of 2008, the explanation and the possible reason for the phenomenon derived from this law. The increase in industrial consumption of China and India justify the price of a barrel of oil at $145. Leave aside the factor of speculation and manipulation of prices by the big oil companies. In any way the law of supply and demand continued linking closely the price/value of a product to a given material reality. Then we said that such escalation could only be a bubble, since it was difficult to imagine a demand increased proportional to the tripling of the price of oil in so few months.