# What is Tunnelling: Definition and 50 Discussions

A tunnelling shield is a protective structure used during the excavation of large, man-made tunnels. When excavating through ground that is soft, liquid, or otherwise unstable, there is a potential health and safety hazard to workers and the project itself from falling materials or a cave-in. A tunnelling shield can be used as a temporary support structure. It is usually in place for the short-term from when the tunnel section is excavated until it can be lined with a permanent support structure. The permanent structure may be made up of, depending on the period, bricks, concrete, cast iron, or steel. Although modern shields are commonly cylindrical, the first "shield", designed by Marc Isambard Brunel, was actually a large, rectangular, scaffold-like iron structure with three levels and twelve sections per level, with a solid load-bearing top surface. The structure protected the men from cave-ins as they laboured within it, digging the tunnel out in front of the shield.

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1. ### I Decoherence and Quantum tunnelling

A macroscopic object has the order of Avogadro’s number of particles. That’s over 10^23. So the probability of all of them tunneling, at the same time, is on the order of that original small probability, to the 10^23 power. And then on top of that, you have to factor in the chances of it...
2. ### I Potential step and tunneling effect

We know that thanks to the tunnel effect, in the case of a finite potential step (V) and considering a stationary state, when a plane wave with energy E < V encounter the step the probabability that the wave-particle coming from -∞ (where potential is V=0) will be ≠ 0, in particular the wave...
3. ### I Can Quantum Tunneling Occur Through a Material Barrier?

A lot of popular level explanations introduce the idea of tunneling by saying that "in principle" a person in one room can "find themselves" in the next room, i.e. one can tunnel through a wall Of course, the presenter then hastens to clarify that this is so unlikely that we would have to wait...
4. ### B White dwarf quantum tunnelling

I just finished watching the video "The Last Light Before Eternal Darkness – White Dwarfs & Black Dwarfs" At 5:17 he mentioned quantum tunneling will take up a timespan so long that calling it forever is ok. But nothing takes forever,so,how long will it actually take? ps:I later realized...
5. ### Understanding solar cell band diagram

Hi everyone, I have been studying the physics of solar cells for a long time. The only thing that I can not completely understand is the physical operation of solar cell based on band diagram. Can anyone briefly explain the movements of carriers from one electrode to the another based on band...
6. ### I Why isn't tunnelling considered proof of hidden variables?

When I hear that mass of a particle has managed to hop through a solid barrier ..it tells me that the mass was a variable and not physical at the time.
7. ### Time Dilation & Tunnelling Probability in Double Potential Wells

Assume you have a 2 particles sitting inside a double potential well. Each particle occupies one side of the well and given enough time the particles may both be found on the same side or swap sides (tunnelling). Assume that the well is inside a gravitational field. It is positioned in such a...
8. ### Square Hill Barrier, weird question wording

Homework Statement Consider a square hill barrier produced by a 10V potential. Incident upon this barrier is a steady stream of 5eV electrons. (a) If half the electrons are transmitted, how thick is the barrier? (Please derive the transmission probability rather than merely quoting it.)...
9. ### Need help modelling Quantum Tunnelling Composites

Hi all, This is my first post on PF so forgive any rookie errors. I'm a 17 year old British student. I have just finished a month long placement at Newcastle University researching my chosen topic of quantum tunnelling. The placement itself was very disappointing and I had no interaction with...
10. ### Quantum tunnelling - what is real?

Is it correct that that the wavefunction of a particle is well defined in the classically forbidden region? This would seem to suggest that there would be a chance of finding it there. But I think that is not allowed. Have any experiments actually discovered particles in the barrier or do they...
11. ### Nanoparticle dragged off a layer and tunnelling to a STM tip, equation

Here we have a STM tip placing a potential V across a monolayer with a single electron on it. | STM (scanning tunneling microscope) Tip | | |...
12. ### Is tunnelling from nothing a transition?

Sorry for my abysmal level of ignorance, but I'm not understanding why quantum tunneling from nothing is considered a possible starting point for a multiverse, when the permanence of our pocket universe within the multiverse is also considered to be threatened by a phase transition if its vacuum...
13. ### Quantum Tunnelling: Where Does Energy Go?

Homework Statement The waves amplitude appears to decrease as it tunnels through the barrier. If we think of the amplitude as energy like in a sound wave etc, where does this energy go? The Attempt at a Solution I think it has something to do with the fact that for a matter wave the...
14. ### Probability for Quantum tunnelling

Homework Statement A particle with the energy E < V_{0} (V_{0} > 0) moves in the potential V(x) = 0, x<0 ; V(x)= V_{0}, 0<x<d and V(x)= 0, x>d. Measure the probability that the particle will tunnel through the barrier by calculating the absolute value of the ratio squared...
15. ### Scanning Tunnelling Microscope

Homework Statement The tip of a scanning tunnelling microscope is placed 1.0 nm away from a conducting surface and a potential of dV = 0.03 V is applied to the surface relative to the tip. When the tip is moved laterally to a new position on the surface the tunnelling current increases by...
16. ### Tunnelling and special relativity

I have an undergraduate minor in astrophysics from a long time ago and have been brushing up to teach my kids, so I'm not an expert or even a great student of these things, but something I thought I'd log in and ask here: If special relativity stands for the premise that there is no preferred...
17. ### Quantum tunnelling and black holes

Just a quick question, that I'm not completely clear about; Quantum tunnelling allows particles to overcome barriers that they classically shouldn't be able to overcome, my question is simply, do/can particles escape a black hole after passing the event horizon due to tunnelling? If not, why...
18. ### Exponental Tunnelling Factor (Electron Microscope)

I'm reading a little bit about electron microscopes. It states, "the exponential tunnelling factor is proportional to the square root of the mass. So, the lower mass means lower exponential decay of the wavefunction". Would anyone be able to let me know what this exponential tunnelling...
19. ### Solving for L in Tunneling Probability Equation

I'm in the process of studying for my final and I just can't solve this problem: The work function (energy needed to remove an electron) of gold is 5.1 eV. Two pieces of gold (at the same potential) are separated by a distance L. For what value of L will the transmission probability for an...
20. ### How Does Quantum Tunneling Affect Particle Reflection?

Homework Statement A beam of particles of energy E is incident from the left on a rectangular step of infinite width and height U0, situated at the origin, with E > U0, as shown in the diagram. http://img39.imageshack.us/img39/5918/problemda.jpg (a) Write down the Schrodinger equation for...
21. ### Radioactivity - quantum tunnelling

Can anyone link to a synthetic and understandable explanation of radioactivity through basic quantum mechanics? It does not need to be a comprehensive explanation at all, examples or partial explanations are fine. Online class notes are welcome but so are books suggestions. Thanks in advance
22. ### Transmission coefficient, quantum tunnelling

I have been trying to calculate the transmission coefficient for a quantum tunelling case, but I seem to get the coefficient value more than 1. How is that possible? The equation i used is based on the wikipedia page (I am unable to link because I am underpost). Also typically what are...
23. ### What types of particles have a higher probability of tunnelling?

Hi, This is a really basic question that I was hoping to get a simple answer for. What types of particles tunnel the most effectively? Do high energy electrons tunnel more effectively than if they were at low energy?
24. ### Scanning tunnelling microscope - Whats the piezoscanner for?

What does the piezoelectric scanner do? Does it record the electric current tunnelled by the tip or is it just used to move the tip in response to electric currents?
25. ### Energy of First Tunnelling Resonance

Homework Statement COnsider electrons tunnelling through a 10eV barrier over a distance 0.001mm. Find E_{1}. (The energy of the first tunnelling resonance.) Homework Equations I have an equation for the tunnelling probability...
26. ### Quantum tunnelling outside the light cone?

Zee's QFT in a Nutshell makes a short comment in the first chapter about the possibility of particles tunnelling outside their light cone - is there some probability that a particle could do this? I know the neutrino thing has been debunked as a faulty cable, but did not see this offered as an...
27. ### Quantum tunnelling w/ macroscopic objects

does not occur because the probabilities are of the magnitude of exp[ -1 / h ], give or take a few decimal places, correct? i.e. 1 / some number with > 10^30 zeros after it (trying to explain this simply to my daughter)
28. ### Quantum Tunnelling - Transmission Probability

Homework Statement It's not really a given problem, it's more of a section of my lecturing I truly just don't understand. I'm given that the probability of transmission (T) is the ratio of the intensities of the transmitted wave and the incident wave. However, a bunch of math gives also that...
29. ### Is this a reasonable analogy for quantum tunnelling?

Hi, I wanted to explain quantum tunnelling to people with no scientific background - I've come up with the following analogy, but I'm only a physics undergrad and I'm not sure if it's a good enough analogy. I can do the maths behind tunnelling but it's just the concept I'm trying to get across...
30. ### Tunneling probability and higher order terms in WKB method

Hi All, I have a question regarding the WKB method for computing tunnelling through barriers. I understand the method and the ability to arrive at a solution as given in the first part (summary) of the first page here: http://www.physics.udel.edu/~msafrono/425/Lecture%2018.pdf Is it...
31. ### Some problems about Quantum tunnelling

In quantum tunnelling,as I understood,when a particle reaches the boundry of a potential barrier,it is possible,that the particle passes the barrier and it is performed like disappearing before the barrier and appearing after it.If the latter is the case,so there should be a motin which is...
32. ### Quantum Tunnelling Technologies

Hey guys what are some technologies that use Quantum Tunneling? I've been looking on Google and i havnt had much luck! I just need a point in the right direction so links to websites and such would be greatly appreciated! BTW when searching google i found Quantum Tunnelling Composites which...
33. ### A question about quantum tunnelling

I understand quantum tunnelling while thought as the one happening in fusion.But could someone explain the process when we're talking about a particle passing through a physical barrier not just a potential barrier? thanks
34. ### Can Quantum Tunnelling Explain the Physicist's Ice Cream Parlor Strategy?

On the sitcom 'The Big Bang Theory', one of the jokes goes: "A physicist walks into an ice cream parlor and orders an ice cream for himself and one for the empty seat next to him. He does this for weeks until the owner asks him what he's doing. The physicist says, "well, I'm a physicist, and...
35. ### What does Wikkepedia mean when they talk about Quantum tunnelling

This is what it says on Wikipedia : Quantum tunneling refers to the quantum mechanical phenomenon where a particle tunnels through a barrier that it classically could not surmount because its total mechanical energy is lower than the potential energy of the barrier. But I would like to...
36. ### Atoms tunnelling through a metal surface

Hey guys.i have heard it has been experimentally proved that even atoms can tunnel through a metal surface.I tried searching all over the web but just could not get any references on that.So,is that true?if somebody know where i can read more about that experimental proof,please point it out...
37. ### Transmission coefficient (quantum tunnelling)

Homework Statement What is transmission probability (T), when the incident particle energy (E) is equal to the energy of the barrier (U)? Homework Equations Equations to transmission and reflection probabilities. http://i950.photobucket.com/albums/ad348/gs5720/img099.png?t=1278212132...
38. ### Basic Infinite Potential Well, Tunnelling, etc.

I have an exam later today, and I would really apreciate it if someone could check my work or at least point out flaws in my process here. Thanks! Homework Statement At x=0, a proton with a kinetic energy of 10 eV is traveling in the x direction (potential energy = 0). At x=1nm, it...
39. ### Quantum tunnelling for a finite-square potential parrier

Homework Statement At x=0, a proton with a kinetic energy of 10 eV is traveling in the x direction (potential energy = 0). At x = 1nm, it encounters a potential barrier of height 12 eV and width .2nm. The potential returns to 0 at x = 1.2nm. Give the amount of the particle on both sides...

Or not?
41. ### Time delay for evanescent wave to spread (photon tunnelling)

Nimtz and Stahlhofen claim that their recent tunnelling experiment proves that tunnelling time for light between double prisms is zero. In Herbert Winful's response to this (http://arxiv.org/ftp/arxiv/papers/0709/0709.2736.pdf) he explains that the evanescent wave formed in the gap only has real...
42. ### Energy of a Tunnelling Particle

I'm just making sure... after a particle tunnels through a potential barrier, assuming that there are no forces acting on the particle, like friction, etc. which dissipates energy, the particle should have the same energy as it did before it tunneled through, right?
43. ### Scanning Tunnelling Microscope (STM)

''The Scanning Tunnelling Microscope probes the density of states of a material''... What does this actually mean?
44. ### Fermi Question - quantum tunnelling of a person

Homework Statement The probability of a person quantum mechanically tunnelling through a wall Homework Equations The Attempt at a Solution I'm not too sure how to approach this problem, I calculated the de Broglie wavelength of the person (mass = 60kg, velocity = 30 m/s; These values are...
45. ### Quick Potential Barrier tunnelling question

I am dealing with the classic problem of a potential barrier of finite width, with a particle tunneling through, in the case of E < V. I am to calculate the transmission/reflection coefficients, and we first start off with the wavefunctions for the three regions. Before the barrier, we...
46. ### Probability of quantum tunnelling

I'm continuing to read Jim Al-Khalili's book Quantum: A Guide for the Perplexed. I'm on page 190; today I just read a few paragraphs and page 176 about quantum tunnelling. My question is this: what does it take to say that an electron, for example, has successfully and definitely tunnelled...
47. ### Fowler Nordheim Tunnelling -

Hi, I wanted to know how the pre-exponential and exponential terms of the standard Fowler Nordheim Tunnelling is calculated to a certain value. So can anyone give the calculations of these two terms? The FN Expression is given as J = A.F^2.exp(-B/F) Where J = Current Density, A =...
48. ### Quantum Tunnelling and Spacetime

Does relativistic quantum mechanics make use of 4 dimensional Minkowskian geometry? Or does it just use special relativity formulated in 3 space dimensions and 1 time dimension? And if quantum mechanics can apply to Minkowskian spacetime, then can something tunnel through time?
49. ### A Poll about Quantum Tunnelling

In the quantum tunnelling process, where an electron tunnels though the potential barrier, we known this to be true by always seeing the electron we test for. We have always found what we were looking for and therefore have NEVER considered or thought about any other vallid or acceptable...
50. ### Quantum Tunneling Explained: How Does it Work?

Could some please explain me how quantum tunneling works?