When you see the path of a controlled economy over time into the future as a stochastic process (the statisticians, according to a probability distribution subject), so therefore determined that future results of present decisions by this probability distribution.
It seems logical that if a decision maker's decisions would create reasonable statistical information about the future based, it would have to select a sample based on future data sets . Lay As can obtain this sample, however, virtually impossible (because the future is not known), makes it so, been many economic theorists simply the heroic assumption that the economy will be statistically described as an ergodic process. That is to say that random samples are drawn from available data sets from the past or the present, could be treated as logically equivalent samples from the datasets of the future.
Technically speaking: The realization of a stochastic process is defined as a data point of a multidimensional variables over a period of time or the time series values of recorded results. A stochastic process describes therefore a universe of such time series. Time statistics are based on statistical averages (mean, median, standard deviation, etc.), derived from a single realization over a period of calendar time. Spatial statistics on the other hand refer to statistical averages at a particular time of the universe of realizations, which are here on cross-sectoral (cross-sectional) or cross-sectional data are measured at the respective dates on each individual.
if and only if the stochastic process is ergodic, then for an infinite realization of the time statistics and spatial statistics . Coincide For finite realizations they coincide apart from random errors. In other words, time and spatial statistics tend to converge to it (with probability 1), insofar as increasing the number of observations. Consequence, if the axiom of ergodicity applies, are statistics that are obtained either from past or from cross-sectional data, statistically reliable estimates for spatial statistics at any future date.
The future is therefore never uncertain. For it can always be calculated from data available from the past or the present of the likelihood.
The axiom of ergodicity plays the logically equivalent role as the order axiom in the classical deterministic economy that is the assumption that at any time an economic entity knows all the future results of his decisions and he can arrange this logically correct according to its own preferences.
The terminology of ergodicity only in 1935 was explicitly designed by the Moscow mathematical school of probability theory and has been known until after 1945 in the West. She was therefore Keynes unknown.
Non Nevertheless, in the opinion of Paul Davidson shows the critique of Keynes on econometric methodology Tinbergen, Keynes implicitly that the applicability of the Ergodizitätsaxioms on the development of an economy denies. For Keynes, the future is uncertain, an entrepreneur can never be reliably calculated in advance whether an investment decision is rationally justified. It remains only to stay here to explain the so-called "animal spirits" of entrepreneurs, which Keynes had meant nothing more than "gut feeling" of the decision maker who can never know the future ahead, especially those not charged at the traditional methods of mathematics can.
It follows from this for the traditional economic theory, however, the fatal result that in theory is nonsense to expect that markets function could meet the efficient and optimal allocation of resources. This is even more so for the financial markets. According to Keynes, the main function of the same, the economic agents is to provide liquidity. Because liquidity in the diet is capitalism the mechanism of how the uncertainty can be addressed practically.
Source:
Paul Davidson: John Maynard Keynes. Palgrave Macmillan. ISBN 13-978-1-4039-92623-7. ISBN 10-4039-9623-7. P. 31ff.
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