Thus, we would NOT expect the speed to increase without limit as barrier thickness is increased. In other words, if the tunneling time has a maximum, the speed of the particle must increase without limit as the barrier thickness is increased.īut the question asks, "What if there was no maximum tunneling time?" In that case, the tunneling time CAN increase indefinitely as barrier thickness is increased. After that maximum tunneling time has been reached, we could theoretically double the thickness of the barrier and, since the tunneling time cannot increase any further, the speed of the particle must be doubled. As the barrier thickness (the distance traveled by the particle) is increased, the time it takes the particle to cross the barrier also increases, but only up to a certain point. The passage implies that if tunneling time reached no maximum in increasing with barrier thickness, thenĪ) Tunneling speed would increase with barrier thicknessī) Tunneling speed would decline with barrier thicknessĬ) Tunneling speed would vary with barrer thicknessĭ) Tunneling speed would not be expected to increase without limitĮ) Successful tunneling would occur even less frequently than it doesĪccording to the passage, the time it takes for the particle to tunnel will increase until the tunneling time reaches a certain maximum. According to measurements performed by Raymond Chiao and colleagues, for example, photons can pass through an optical filter at 1.7 times the speed of light. Several recent experiments have supported this hypothesis that tunneling particles sometimes reach superluminal speed. This would imply that once maximum tunneling time is reached, tunneling speed will increase without limit as barrier thickness increases. Their grounds were calculations that suggested that the time it takes a particle to tunnel through a barrier increases with the thickness of the barrier until tunneling time reaches a maximum beyond that maximum, tunneling time stays the same regardless of barrier thickness. Though the extreme rapidity of quantum tunneling was noted as early as 1932, not until 1955 was it hypothesized-by Wigner and Eisenbud-that tunneling particles sometimes travel faster than light. Quantum theory says that there is a distinct, albeit small, probability that such a particle will tunnel its way through a barrier the probability declines exponentially as the thickness of the barrier increases. Yet subatomic particles perform the equivalent feat. If you throw a ball at a wall, you expect it to bounce back, not to pass straight through it. Most attempts by physicists to send particles faster than the speed of light involve a remarkable phenomenon called quantum tunneling, in which particles travel through solid barriers that appear to be impenetrable.
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