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Quantum Tunneling

Dustin Kesselberg

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Nov 30, 2004
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I am trying to understand exactly how quantum tunneling works and I don't know if I have an idea or not. Can someone tell me if this is right?

Quantum tunneling is a phenomenon when a particle is able to 'tunnel' through a solid object because it's wave function has a slight probability of appearing behind that specific object. For example. If an electron is on one side of a wall and then it's "wave function" is has a slight probability of appearing on the other side of the wall then as the particle moves toward the wall there is a slight probability the particle can appear on the other side of the wall.


I made a flash file to demonstrate how I imagine it to give you a better idea of what I'm saying. (To see the file just click the link and type in the security code and wait for it to download).

Edited by tim: 
Sigh. Porn link.

(Dustin, please check your PMs.) On checking the link was not to porn but to the animation, however the upload/download site that Dustin used was certainly "NSFW". I've attached the animation file to this post.
Replying to this modbox in thread will be off topic  Posted By: Darat



Someone tell me if I have it right or not or what I might be missing.

Thanks.
 
Last edited by a moderator:
Ok first of all, the idea that there is such a thing as a solid object on the quantum scale is just wrong. This happens in situations like the nucleus of an atom, and it can tunnel out of it. So do not think at all about solid objects.

What it is about is potentials, when something tunnels it goes from being on one side of a potential to the other and lacks enough energy to classically be able to cross such a potential.

This has been explained as being related to uncertainties and such, and I have done basic calculations about it. But it has nothing to do with solid objects, as on this scale nothing is solid.

this web site has some real animations of tunneling. The important thing to remember is that there is no absolute position for a particle so it can have some probability it reflected from the potential(generally higher) and some probability it tunneled across the potential.
 
ponderingturtle said:
What it is about is potentials, when something tunnels it goes from being on one side of a potential to the other and lacks enough energy to classically be able to cross such a potential.
Click to expand...

If a large object did this, what law of physics would it be violating? Would it be the 1st law of thermodynamics?
 
ma1ic3 said:
If a large object did this, what law of physics would it be violating? Would it be the 1st law of thermodynamics?
Click to expand...

The simple answer is that Quantum scale concepts do not apply to the "macro"* scale. (cf Schrodinger's cat)

Evaluation of the wave function of a particle "trapped" by a potential greater than the kenetic energy of the particle produces a probablity distribution of where the particle may be found (e.g. the electron shells/orbitals of atoms). The weird thing is for certain situations, the probablity function extends beyond the potenial barrier if there exists a lower potential on the "other side" of the potential barrier. The PD will have a zero chance that the particle can be found within the region of higher potential, but non-zero outside of it and on both sides, but with a much lower probablity of the side of the barrier your were not "expecting" to be able to find the particle.

If you were to deal with a macro object on a quantum scale, what you would see is that the probablity functions of all of the particles in the object overlap and reinforce to effectively place the object in the location you observe it and nowhere else - the "tails" of the distribution are so infinitesimally (sp?) small that you would have to wait for a very, very, very large multiple of the life of the universe, watching over the entire universe to maybe see this occur once.

* I'm not sure how large a collcetion of particles is required to be at the "macro" scale.
 
Doubtless, we'll have some crackpot now claiming to have invented a quantum tunnelling teleportation machine. Having used a Scanning Tunnelling Microscope in electronic component engineering, I'm happy enough with reality. The machine was a real revelation after the somewhat more basic Scanning Electron Microscope I used before.
 
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