If I design a trading model, I might want to know the [model's half life][1]. Unfortunately, it doesn't seem possible to predict alpha longevity without a [meta-model of the market][2]. Intuitively, such a meta-model does not exist, but has that ever been proven? This sounds like a Russell's paradox or Gödel's incompleteness theorems for the financial markets.

  [1]: http://quant.stackexchange.com/questions/147/what-are-the-key-risks-to-the-quantitative-strategy-development-process/150#150
  [2]: http://quant.stackexchange.com/questions/175/is-there-a-way-to-estimate-predict-the-half-life-of-a-quantitative-trading-syst/177#177