This paper investigates the nature and the presence of bubbles in financial markets. Are bubbles consistent with rationality? If they are, do they, like Ponzi games, require the presence of new players forever? Do they imply impossible events in finite time, such as negative prices? Do they need...

Should managers, when making investment decisions, follow the signals given by the stock market even if those do not coincide with their own assessments of fundamental value? This paper reviews the theoretical arguments and examines the empirical evidence, constructing and using a new US time...