An economic bubble (sometimes referred to as a speculative bubble, a market bubble, a price bubble, a financial bubble, a speculative mania or a balloon) is trade in an asset at a price or price range that strongly deviates from the corresponding asset's intrinsic value. It could also be described as a situation in which asset prices appear to be based on implausible or inconsistent views about the future.Because it is often difficult to observe intrinsic values in real-life markets, bubbles are often conclusively identified only in retrospect, when a sudden drop in prices appears. Such a drop is known as a crash or a bubble burst. Both the boom and the burst phases of the bubble are examples of a positive feedback mechanism, in contrast to the negative feedback mechanism that determines the equilibrium price under normal market circumstances. Prices in an economic bubble can fluctuate erratically, and become impossible to predict from supply and demand alone.While some economists deny that bubbles occur, the cause of bubbles remains disputed by those who are convinced that asset prices often deviate strongly from intrinsic values. Many explanations have been suggested, and research has recently shown that bubbles may appear even without uncertainty, speculation, or bounded rationality. In such cases, the bubbles may be argued to be rational, where investors at every point fully compensated for the possibility that the bubble might collapse by higher returns. These approaches require that the timing of the bubble collapse can only be forecast probabilistically and the bubble process is often modelled using a Markov switching model. It has also been suggested that bubbles might ultimately be caused by processes of price coordination or emerging social norms.