Thursday, March 19, 2009

Belated St. Patrick's Day Post

A problem from David J. Griffiths' Introduction to Quantum Mechanics

p. 339 Problem 8.17 About how long would it take for a can of beer at room temperature to topple over spontaneously, as a result of quantum tunneling? Hint: Treat it as a uniform cylinder of mass m, radius R, and length h. As the can tips, let x be the height of the center above its equilibrium position (h/2). The potential energy is mgx, and it topples when x reaches the critical value of x0 = {R2 + (h/2)2}1/2 -h/2. Calculate the tunneling probability for E=0. Use the thermal energy ((1/2)mv2 = (1/2)kBT) to estimate the velocity. Put in reasonable numbers, and give your final answer in years.

The final answer may be found in R.E. Crandall, Scientific American, February 1997, p. 74

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