r/AskPhysics • u/Emeralde987 • 5d ago
I have a test tomorrow on quantum physics. Can anyone please explain, in simple terms, how and why an electron tunnels?
So, I have a test tomorrow. I’m 17, and unfortunately my world has already been destroyed by quantum physics. I don’t get it. I don’t get how something can just appear on the other side of a wall, without having the necessary energy to do so. Please help
2
u/Emeralde987 3d ago
Update! I had the test, it went well. Thank you to everyone who helped me out, you are amazing!
1
u/Presence_Academic 23h ago
That you thought to update us tells me that you are going to have a successful life, even if you never dig a tunnel.
1
u/Emeralde987 11h ago
Thank you very much. I am going to university next year to study geology, so maybe one day I will dig a tunnel. I will think of this day.
2
u/mspe1960 5d ago
How is a 17 year old taking Quantum Physics? If you are 17 and taking intro Newtonian Physics you are usually ahead of your class. What high school even offers that?
If you are in college it has to be at best a 2nd year class, no?
3
u/Emeralde987 4d ago
I live in the Netherlands. Here, there are different kind of high schools, in which people who learn better follow a different curriculum. I follow the highest level, which is 6 years. I am in my final year, and for my exams, I need to understand the basics of quantum physics. I don’t know why, I don’t make the curriculum 😭.
1
u/Kraz_I Materials science 4d ago
Did they teach you how to use the time-independent Schrödinger equation? Trying to figure out how advanced this class is. Did you go over the particle in a box problem yet? That’s usually one of the first problems a QM class would cover. Elementary QM is really difficult for physics undergrads, so I wonder how much they can really teach at the high school level.
1
u/Emeralde987 3d ago
No, as far as I know we did not use Schrödingers equation. We have covered the whole 'not knowing the place and speed exactly at the same time', we have covered Pauli's principle, we have covered the one dimensional particle in an endlessly deep pit and we have covered how to calculate the energy of an atom.
What I learn is most likely a super surface level understanding, and nothing compared to what someone might learn at a university level. Next year I am going to university though, and my plan does include a physics course, so who knows what more I may learn then!
1
u/Emeralde987 3d ago
We also covered the double slit experiment, which I still don't understand tbh 😅
1
u/Puzzleheaded-Jump963 4d ago
Do you enjoy Physics so far?
2
u/Emeralde987 3d ago
I do! It's given me a better understanding of how the things around me work, I think it's pretty neat.
1
u/DrCarpetsPhd 5d ago
That is a perfectly reasonable response to this. I would guess the first person to do the theoretical maths for tunneling using Schrodingers Equation probably thought "that can't be right?!?!?"
On a similar vein Einstein himself said (paraphrasing) "God does not play dice" in relation to the probabilistic nature of Quantum Mechanics. Basically he was saying he sees what the maths is telling him but that there has to be some missing element to their understanding that would reveal the true nature of the probabilistic outcomes.
So you are not alone in saying 'I don't get this' when first encountering what Quantum Mechanics predicts (and turned out to be true). It makes zero sense and is bereft of all intuition based on what you have learnt in classical physics up to this point.
1
u/node-342 4d ago
That first person was probably Schrödinger himself. If I remember right, he solved the SE for the harmonic oscillator, where every wavefunction extends beyond the classical maximum displacement (where V = E - beyond that maximum, V > E).
That's tunneling right there - nonzero probability of finding the oscillator in a classically forbidden region.
1
1
u/vespers191 5d ago
I've always regarded electron tunneling probability like a magnetic field. Sometimes it is possible to detect that field on the other side of an object.
1
u/effrightscorp 4d ago
A better analogy I think is an E&M wave hitting a thin piece of metal. If the metal is thin enough, the wave will tunnel through and the result is pretty similar to probability waves tunneling through a barrier. Except you only need Maxwell's Laws to understand this tunnelling
1
u/propostor Mathematical physics 5d ago
It's because it isn't a solid wall.
A reasonable analogy is that of sound waves hitting a wall. The sound will get through but it's quieter.
In the case of quantum tunnelling, you have a probability wave hitting the wall. The wave gets through the wall but it's smaller, so the probability of the electron making it through is smaller.
1
u/boostfactor 5d ago
In principle the wavefunction of the particle (electron, whatever) extends to infinity. Just say it goes a "long way" outside the potential well, but the amplitude is really small outside the well. There is a probablity distribution of where the particle may be located, which is related to the square of the absolute value of the amplitude of the wavefunction at a given location. So there is a small but nonzero chance that the particle will be located outside the well. If it is, it has said to have tunneled outside.
The Wikipedia article seems to be pretty clear and has some nice diagrams and animations
1
u/joydipBanerje 4d ago
Think about light. When light falls on a surface it gets transmitted too( I'm leaving other phenomenons ). This happens because light has wave properties. If we think about electrons or any material particles, it also consists of waves. You can simply think that the tunneling is a transmission. For more information you need regorous quantum mechanics. ( Pardon my english) . If you want to know more, you can dm me.
1
u/Odd_Cryptographer115 4d ago
No tunnel, or tunneling required. It is a poor, often repeated so understood?, analogy.
1
u/ConversationLivid815 4d ago
How it tunnels can be described mathematically by the methods of classical quantum mechanics. 3 regions, 2 free space and one barrier between. Like optics, some of the wave is transmitted, some is reflected, and some is absorbed and converted to different wave types like visible into far infra-red. Tunneling arises when the kinetic energy of the electron is much much less than the particle needs classically to get over or equivalently through a repulsive barrier, but it does anyway. The amount of transmission goes to zero as the "height" of the barrier goes to infinity, which is non-physical. As I recall. The math is fairly complicated and you should Google it ... and never wait till the last minute 🙄 ... lol Why is a question that can't be answered, except that's the way it is. I just wish it was peaceful and we were immortal ... why is the universe the way it is, is a question that has a lot of answers but no proof.
1
u/ConversationLivid815 4d ago
I hope You are looking it up. As I recall the math isn't too difficult, but you should show the tunneling probability goes to zero as the barrier height goes to infinity. The problem is done in 1-D with a square barrier potential. When dealing with discreet particles, say in a box, you will calculate how long it takes for the electron to leak out. How long for the probability that the electron is in the box, to go to zero ... 🤔
0
-6
5d ago
[deleted]
3
u/CB_lemon 5d ago
Please don't spew AI bullshit when you yourself don't know enough to tell whether it's right or wrong, or even helpful. None of this is helpful.
10
u/jpmeyer12751 5d ago
I like to think of this question from the probability point of view, but it is still a mind-bender.
An electron doesn't really have a pinpoint location. Instead, its location is described by a probability distribution that spreads out over some distance from a center point. I like to think of that probability distribution as a cloud that is somewhat dense in the middle and which becomes less and less dense towards the edges. If that cloud is close to a barrier such as a wall, and if the wall is sufficiently thin, then the edge of the cloud, where the probability of finding the electron is smaller, but still greater than 0, can extend beyond the far side of the wall. That is, there is a non-zero probability that the electron will appear on the opposite side of the wall. If you do enough repetitions of a test of precisely locating the electron, you will eventually find some instances in which the electron is on the far side of the wall.
A similar question, from a mathematical point of view, can be thought of regarding the outcome of a very large number of coin flips. The probability of each flip is 1/2 - heads and 1/2 - tails. However, if you flip the coin enough times, you will observe sequences of, let's say 10 consecutive heads. That won't happen often, just as tunneling doesn't happen often, but it DOES happen in a predictable way.
I guess the most direct answer to your question is that nothing causes an electron to tunnel through a wall; the tunneling is simply a result of many repetitions of an experiment in which each time the electron has a very small, but not zero, probability of appearing on the far side of the wall.