The tunneling time problem and the consistent history approach to quantum mechanics

We review some of the well-known theories of tunneling time and introduce a new theory based on the consistent history approach to quantum mechanics (CHA). The CHA gives a striking result that a probability distribution of tunneling time is not definable. This forces us to reflect what is meaningful about tunneling time. Even in the absence of the probability distribution, the range of values of tunneling time is definable and well-known tunneling times are found to fall within the range for typical opaque barriers. By focusing our attention to the range, we would be able to develop constructive discussions about the tunneling time problem.