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The Impossibility of Rational Bubbles


  • Behzad T. Diba
  • Herschel I. Grossman


A rational bubble would involve a self-confirming belief that an asset price depends on information that includes variables or parameters that are not part of market fundamentals. The existing literature shows that, if market fundamentals are economically interesting, i.e., forward looking, any rational bubbles would be either explosive or implosive. Further arguments based on the existing literature show that utility maximizing behavior implies finite bounds on asset prices and, accordingly, precludes both explosive and implosive rational price expectations, except for the possible case of an implosion in the value of fiat money. These arguments rule out both positive and negative rational bubbles, except for the poissibility of rational inflationary bubbles.This paper extends the theoretical analysis of rational bubbles in two ways. First, it shows that, although a supply response of the current asset stock to the current asset price dampens fluctuations in market fundamentals, such a response would cause a rational bubble to explode or to implode even faster.Thus, the explosiveness or implosiveness of rational bubbles isnot an artifact of assuming that the asset stock evolves autonomously. Second, and more importantly, the present analysis considers the inception of rational bubbles and shows that, for anegative rational bubble -- such as a rational inflationary bubble -- to get started, a positive rational bubble also would have to have positive probability. Specifically, the expected initial absolute value of a potential negative rational bubble cannot exceed the expected, initial value of a potential positive rational bubble.This result dramatically expands the theoretical basis for precluding rational bubbles. Specifically, because utility maximization directly rules out rational deflationary bubbles, the inception of a rational inflationary bubbles is also precluded.

Suggested Citation

  • Behzad T. Diba & Herschel I. Grossman, 1985. "The Impossibility of Rational Bubbles," NBER Working Papers 1615, National Bureau of Economic Research, Inc.
  • Handle: RePEc:nbr:nberwo:1615
    Note: ME EFG

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    References listed on IDEAS

    1. Michael Mussa, 1984. "Rational Expectations Models with a Continuum of Convergent Solutions," NBER Technical Working Papers 0041, National Bureau of Economic Research, Inc.
    2. George Evans & Seppo Honkapohja, 1986. "A Complete Characterization of ARMA Solutions to Linear Rational Expectations Models," Review of Economic Studies, Oxford University Press, vol. 53(2), pages 227-239.
    3. Obstfeld, Maurice & Rogoff, Kenneth, 1983. "Speculative Hyperinflations in Maximizing Models: Can We Rule Them Out?," Journal of Political Economy, University of Chicago Press, vol. 91(4), pages 675-687, August.
    4. Gray, Jo Anna, 1984. "Dynamic Instability in Rational Expectations Models: An Attempt to Clarify," International Economic Review, Department of Economics, University of Pennsylvania and Osaka University Institute of Social and Economic Research Association, vol. 25(1), pages 93-122, February.
    5. Tirole, Jean, 1982. "On the Possibility of Speculation under Rational Expectations," Econometrica, Econometric Society, vol. 50(5), pages 1163-1181, September.
    6. Kingston, Geoffrey H., 1982. "The semi-log portfolio balance schedule is tenuous," Journal of Monetary Economics, Elsevier, vol. 9(3), pages 389-399.
    7. Flood, Robert P & Garber, Peter M, 1980. "Market Fundamentals versus Price-Level Bubbles: The First Tests," Journal of Political Economy, University of Chicago Press, vol. 88(4), pages 745-770, August.
    8. Azariadis, Costas, 1981. "Self-fulfilling prophecies," Journal of Economic Theory, Elsevier, vol. 25(3), pages 380-396, December.
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    Cited by:

    1. Behzad T. Diba & Herschel I. Grossman, 1985. "Rational Bubbles in Stock Prices?," NBER Working Papers 1779, National Bureau of Economic Research, Inc.
    2. FETINIUC, Valentina & IVAN, Luchian & GHERBOVEĊ˘, Sergiu, 2014. "Speculative Bubbles And Financial Crises," Journal of Financial and Monetary Economics, Centre of Financial and Monetary Research "Victor Slavescu", vol. 1(1), pages 153-162.
    3. Robert P. Flood & Robert J. Hodrick & Paul Kaplan, 1986. "An Evaluation of Recent Evidence on Stock Market Bubbles," NBER Working Papers 1971, National Bureau of Economic Research, Inc.
    4. Kowalski, Amanda E., 2015. "Estimating the tradeoff between risk protection and moral hazard with a nonlinear budget set model of health insurance," International Journal of Industrial Organization, Elsevier, vol. 43(C), pages 122-135.
    5. West, Kenneth D., 1987. "A standard monetary model and the variability of the deutschemark-dollar exchange rate," Journal of International Economics, Elsevier, vol. 23(1-2), pages 57-76, August.

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