Steven Gray wrote:
"DARTH VADER" wrote in
oups.com:

What exactly is electron tunelling?

In classical physics, if a particle has energy A and it needs energy B to
get past a barrier, and A is less than B, then the particle simply won't
get past the barrier. This is true even if A is "close" to B or if the
energy needed after the particle gets past the barrier is equal to or less
than A.

In quantum mechanics, there is a probability that the particle will pass
the barrier even if A is less than B. The closer A is to B, and the
shorter the time that the particle needs the higher energy to pass, the
higher the probability is that the particle will get past. The effect is
called tunneling.

You can't say the particle goes through anything unless you apply
position measurements on it - when you do, you will find it follows the
classical predictions. That it "seems" to have "non-zero probability of
going through" arises from the inability to KNOW how it is moving
during the period that it is not being measured. If you don't look at
the particles then don't say it DID something, if you look then you can
say.

Just because you can observe a particle beyond the barrier does not
mean that it "went through" that barrier. It could've easily gone up
then done a few loops, then a few zig-zags, then gone back a bit, then
gone around the barrier and right into the detector. In fact there are
infinite paths if may have taken - the probability of each is the
absolute square of amplitude with Lagrangian time integral complex
phase. After you detect it you can start to deduce the classical path
it must necessarily have taken to have gotten there.



--
Steve Gray