Quantum Tunnels

 Natalie Wolchover believes that No sooner had the radical equations of quantum mechanics been discovered than physicists identified one of the strangest phenomena the theory allows.

“Quantum tunneling” shows how profoundly particles such as electrons differ from bigger things. Throw a ball at the wall and it bounces backward; let it roll to the bottom of a valley and it stays there. But a particle will occasionally hop through the wall. It has a chance of “slipping through the mountain and escaping from the valley,” as two physicists wrote in Nature in 1928, in one of the earliest descriptions of tunneling.

Physicists quickly saw that particles’ ability to tunnel through barriers solved many mysteries. It explained various chemical bonds and radioactive decays and how hydrogen nuclei in the sun are able to overcome their mutual repulsion and fuse, producing sunlight.

But physicists became curious — mildly at first, then morbidly so. How long, they wondered, does it take for a particle to tunnel through a barrier?

The trouble was that the answer didn’t make sense.

The first tentative calculation of tunneling time appeared in print in 1932. Even earlier stabs might have been made in private, but “when you get an answer you can’t make sense of, you don’t publish it,” noted Aephraim Steinberg, a physicist at the University of Toronto.

It wasn’t until 1962 that a semiconductor engineer at Texas Instruments named Thomas Hartman wrote a paper that explicitly embraced the shocking implications of the math.

Hartman found that a barrier seemed to act as a shortcut. When a particle tunnels, the trip takes less time than if the barrier weren’t there. Even more astonishing, he calculated that thickening a barrier hardly increases the time it takes for a particle to tunnel across it. This means that with a sufficiently thick barrier, particles could hop from one side to the other faster than light traveling the same distance through empty space.

In short, quantum tunneling seemed to allow faster-than-light travel, a supposed physical impossibility.  Read More