An ‘efficient’ market is defined as a market where there are large numbers of rational, profit ‘maximisers’ actively competing, with each trying to predict future market values of individual securities, and where important current information is almost freely available to all participants. In an efficient market, competition among the many intelligent participants leads to a situation where, at any point in time, actual prices of individual securities already reflect the effects of information based both on events that have already occurred and on events which, as of now, the market expects to take place in the future. In other words, in an efficient market at any point in time the actual price of a security will be a good estimate of its intrinsic value.
In its strongest form, the EMH says a market is efficient if all information relevant to the value of a share, whether or not generally available to existing or potential investors, is quickly and accurately reflected in the market price. For example, if the current market price is lower than the value justified by some piece of held information, the holders of that information will exploit the pricing anomaly by buying the shares. They will continue doing so until this excess demand for the shares has driven the price up to the level supported by their private information. At this point they will have no incentive to continue buying, so they will withdraw from the market and the price will stabilise at this new equilibrium level. This is called the of the EMH. It is the most satisfying and compelling form of EMH in a theoretical sense, but it suffers from one big drawback in practice. It is difficult to confirm empirically, as the necessary research would be unlikely to win the cooperation of the relevant section of the financial community – insider dealers.
If a market is semi-strong efficient, the current market price is the best available unbiased predictor of a fair price, having regard to all publicly available information about the risk and return of an investment. The study of public information (and not just past prices) cannot yield consistent excess returns. This is a somewhat more controversial conclusion than that of the weak-form EMH, because it means that analysis – the systematic study of companies, sectors and the economy at large – cannot produce consistently higher returns than are justified by the risks involved. Such a finding calls into question the relevance and value of a large sector of the financial services industry, namely investment research and analysis.
If a market is weak-form efficient, there is no correlation between successive prices, so that excess returns cannot consistently be achieved through the study of past price movements. This kind of study is called or analysis, because it is based on the study of past price patterns without regard to any further background information.
If a market is strong-form efficient, the current market price is the best available unbiased predictor of a fair price, having regard to all relevant information, whether the information is in the public domain or not. As we have seen, this implies that excess returns cannot consistently be achieved even by trading on inside information. This does prompt the interesting observation that must be the first to trade on the inside information and hence make an excess return. Attractive as this line of reasoning may be in theory, it is unfortunately well-nigh impossible to test it in practice with any degree of academic rigour.
The hypothesis further predicts that an astronomically short time later these civilizations would reorganize their solar system's planetary matter to achieve vastly greater STEM density, efficiency, and computational capability, a transition we may call a developmental singularity (Smart 2008).
For about ten years after publication of Fama's classic exposition in 1970, the Efficient Markets Hypothesis dominated the academic and business scene. A steady stream of studies and articles, both theoretical and empirical in approach, almost unanimously tended to back up the findings of EMH. As Jensen (1978) wrote: ‘There is no other proposition in economics which has more solid empirical evidence supporting it than the EMH.’
In a slightly less rigorous form, the EMH says a market is efficient if all relevant information is quickly reflected in the market price. This is called the form of the EMH. If the strong form is theoretically the most compelling, then the semi-strong form perhaps appeals most to our common sense. It says that the market will quickly digest the publication of relevant new information by moving the price to a new equilibrium level that reflects the change in supply and demand caused by the emergence of that information. What it may lack in intellectual rigour, the semi-strong form of EMH certainly gains in empirical strength, as it is less difficult to test than the strong form.
The transcension hypothesis proposes that a universal process of evolutionary development guides all sufficiently advanced civilizations into what may be called "inner space," a computationally optimal domain of increasingly dense, productive, miniaturized, and efficient scales of space, time, energy, and matter, and eventually, to a black-hole-like destination.
But far more important and relevant to science than determining whether intelligence-guided immunity exists is the determination of whether an extensive degree of universe-guided developmental immunity already exists in our current physics, as the transcension hypothesis claims.