Quantum Tunneling

[Stratego]

My understanding of quantum physics is limited to the few weeks I took back in Freshmen year of college, so pardon the simplicity in my thinking. My question is how do we know that in the phenomenon we describe as quantum tunneling, that it's actually the same particle that we observe?

 

The way it was describe to me was to imagine throwing a ball at a wall. Most of the time, the ball will bounce back, but in the quantum level there is a small chance that the ball will pass through the wall and appear on the other side.

 

Could it be that the particle just got absorbed by the "wall" and the "wall" just spit out something that looks like the particle? (Here's where I bring in another aspect of physics where I have little knowledge of) If E=mc^2, could it be that when the particle hits the wall it gets converted into energy, then the energy causes the "wall" to be destabilized, and as it re-stabilizes part of the energy gets converted back to mass, and it just happens to look like the particle that you shot and happens to be on the other side?

 

Basically what I'm asking is equivalent to explaining the phenomenon as throwing a brick at a wall, and having the energy knock out a piece of the wall that looks like that brick.

[swansont]

There are situations where this might be true — that the particle could simply be replaced by another one that is identical, and you wouldn't be able to tell. One issue with that is that not all identical particles behave the same way — bosons (integral spin particles) act differently than fermions (half-integral spin particles) so there are complications with this model. If it were a matter of energy conversion, you would expect to get different particles some of the time, as we see in actual collisions. Another problem with the scenario is that the "wall" is often not made up of the same thing as the "ball". Charged particles, e.g. electrons, tunnel through barriers that are electric fields, not electrons. So the brick knocking out a brick scenario can't hold.

 

The accepted model is quantum mechanics, which has a very good track record. In that model, tunneling involves the same particle.

[DrRocket]

The accepted model is quantum mechanics, which has a very good track record. In that model, tunneling involves the same particle.

 

With the caveat that by "the same particle" one means a particle with the same quantum state. All such particles are, of course, perfectly identical. So whether the particles actually pierces the potential barrier or somehow an identical particles is created on the other side is immaterial.

 

The point here, for the neophyte (and Swansont is not a neophyte) is that the quantum world is not some simple analog of the macroscopic world and the words we use and the stories we tell to understand it in classical terms are not completely accurate. That electron is not a little marble.

 

This is one example why debates on "interpretations of quantum mechanics" (the words and stories) often get bogged down and one really should pay attention to the mathematics and the predictions that one can actually measure.

[michel123456]

My understanding of quantum physics is limited to the few weeks I took back in Freshmen year of college, so pardon the simplicity in my thinking. My question is how do we know that in the phenomenon we describe as quantum tunneling, that it's actually the same particle that we observe?

 

The way it was describe to me was to imagine throwing a ball at a wall. Most of the time, the ball will bounce back, but in the quantum level there is a small chance that the ball will pass through the wall and appear on the other side.

 

Could it be that the particle just got absorbed by the "wall" and the "wall" just spit out something that looks like the particle? (Here's where I bring in another aspect of physics where I have little knowledge of) If E=mc^2, could it be that when the particle hits the wall it gets converted into energy, then the energy causes the "wall" to be destabilized, and as it re-stabilizes part of the energy gets converted back to mass, and it just happens to look like the particle that you shot and happens to be on the other side?

 

Basically what I'm asking is equivalent to explaining the phenomenon as throwing a brick at a wall, and having the energy knock out a piece of the wall that looks like that brick.

 

Like Newton's craddle?