Electron crash into Proton

1. Jan 10, 2009

feynmann

Why doesn’t the Electron crash into the proton??
We know in an H atom the e- is attracted to the + charge of the proton.
And it wants to get down to the "0 level" orbit.
But what makes that level zero – or why does e- stop going down?
Is there another force that counteracts the force of charge trying to pull them together?

Note: the intent of this thread is potential descriptions of why the electron does not crash into a proton. NOT how QM defines it or that QM can claim that no one can describe it. But how people do try to describe it. So explaining why an idea doesn't work should also be described in Non-QM terms. Everybody already knows that uncertainty and the math of QM does work, we do not need to be reminded.

Last edited: Jan 10, 2009
2. Jan 10, 2009

cam875

3. Jan 10, 2009

feynmann

It's irrelevant

4. Jan 10, 2009

malawi_glenn

Yes QM explains this very well, why do you want another answer/explanation?

5. Jan 10, 2009

feynmann

I think what QM tells us is to "shut up and calculate", but does not really "explain" it
If you know the answer, why don't you spell it out for us?

6. Jan 10, 2009

malawi_glenn

then you are perhaps more interested in the philosiphical viewpoint?

Quantum is the best way (well quantum electrodynamics is) to describe the hydrogen atom and its observables.

What explanation are you looking for? (or are there several other

It is like answering the question why does the stone fall to the ground if I realse it from a height? "The law of gravity tells that there is a force acting on the body and make it accelerate down til it hits the ground"

Quantum mechanics tells you that you alot of things, that the potential of the proton (hydrogen nucleus) and the electron is an operator and one should find the eigenvalues and eigenstates to that operator.

Quantum mechanics is not just "shut up and calculate", what that quote is saying (R. Feynman ironically) is that one should leave the intutive (newtonian, macroscopic) way to look at physics and instead stay to the formalism and axioms of QM and see what u get.

"What is REALLY" going on, and why, is a philosophical question.

You are demanding that quantum phenomenon should be explained in NON QM terms, is that a plausible demand you think?

7. Jan 10, 2009

Dmitry67

Most aspects Newton mechanics is obvious for our brain because it is pre-wired in our muscles: we know how to jump, how to catch objects, we understand spacial/time relationships.

but QM is not pre-installed in our brain.

In order to understand 4,10,11,26-dimensional spaces, non-euclidean geometries and QM you need to have more imagination.

Anyway, what do you mean by "really explain"?

8. Jan 10, 2009

Staff: Mentor

From the Physics Forums FAQ in the General Physics forum:

https://www.physicsforums.com/showpost.php?p=862093&postcount=2 [Broken]

I'll also point out that in a sense, electrons do "crash into the nucleus" because the wave functions for most orbitals are non-zero at the origin (the nucleus). In some isotopes, this causes the nucleus to decay into another one via a process called (surprise!) electron capture.

Last edited by a moderator: May 3, 2017
9. Jan 10, 2009

malawi_glenn

well yes, but i think he was after why the electron don't fall deeper into the potential well of the proton than 13.6 eV. :)

10. Jan 10, 2009

feynmann

Yes, at least Feynman think it's plausible demand. He gave his answer in his famous Lecture on Physics volume 3, page 5 of chapter 2, hope you have a copy

I like Feynman's idea that if you can not explain something to a layman so that he can understand it, you don't understand it yourself.

Last edited: Jan 10, 2009
11. Jan 11, 2009

granpa

you do realize that the electron doesnt actually 'orbit' the nucleus. right?

12. Jan 11, 2009

malawi_glenn

it is a difference in explaining things in layman terms and "non-QM" terms. Maybe you like the idea since you are not a physicsits yourself? ;-)

Anyway, it is philosophical problem since our daily life language is developed over thousands of years to describe daily life phenomenon. It will be like a blind man demanding someone who can see to describe colors.

And well, feynmans answer is basically telling you one way to see it. But he uses QM terms, he invokes the uncertainty principle.

And if this is the correct way of answering the question why the electron is not bounded harder to the proton, I would doubt. The uncertainty principle is used often in layman explanations, but one does not really uses that principle at all when deriving binding energies etc. So by just be given an answer that can be understood, does not mean that the answer is correct.

13. Jan 11, 2009

ZapperZ

Staff Emeritus
Why don't you try it yourself? Try explaining, say, classical E&M for a bunch of layman and see if you can get them not only to "understand" it, but understand it in the SAME way.

I've been involved in public outreach for the work that I do for many years. No matter how hard one tries, a person can only "understand" something based on the level of knowledge that he/she already has. And since everyone has different knowledge and experiences, this means that practically everyone understands things differently, even if given the SAME set of information! Try it if you don't believe me.

So don't give me this tired argument that if one can't explain it to a layman, one hasn't understood it. You have no clue on what you are saying, besides the fact that you haven't defined what is meant by "understand". If you pay that much attention to Feynman and you accept his words as "gospel", then his "shut up and calculate" should have sufficed and you shouldn't be asking any anymore. How come that part didn't take?

If this thread degenerates into philosophical issues, it will be moved to that forum where you'll get very little legitimate physics. Is this what you wish?

Zz.

Last edited: Jan 11, 2009
14. Jan 11, 2009

Staff Emeritus
ZapperZ, I agree. Often this is used in a way very close to, "I am not going to put any effort into understanding this, and if I still don't understand it, it's your fault!"

"Feynmann", quantum mechanics was invented to explain exactly the question you are asking. Asking for a non-QM answer is like saying "explain why a sliding object eventually stops without using friction."

15. Jan 11, 2009

edguy99

To ask the question more specifically, consider an electon and proton relatively at rest (both with kinetic energy of less then .1 evolts) and approx. 1 angstom apart. Where is the electron after a few attoseconds?

16. Jan 11, 2009

ZapperZ

Staff Emeritus
I have no idea, because you might as well come up with other implausible scenario.

Why is this implausible? Because how does one get two things (a proton and an electron) to be at precisely not only a particular location, but also to be AT REST as the initial conditions. By simply knowing that, you've already altered any kind of situation that you want to simulate, especially for an atom, i.e. this will probably not become an electron being captured by a proton to become a hydrogen atom.

Zz.

17. Jan 11, 2009

edguy99

The problem is specified not with an AT REST electron, but a slow electron and "approximate" locations not exact locations. All I am trying to do here, is see how accurate the electron can be tracked and/or simulated and the 2 compared. Clearly there are times when people track electrons in a traditional sense. How far can that envelope be pushed both in simulations and in real life?

18. Jan 11, 2009

Staff Emeritus
I wouldn't say "implasuible". I would say "impossible".

Placing an electron within a window of 0.1 A and with an energy less than 0.1 eV violates Heisenberg uncertainty. You can't ask QM how a state evolves if that state isn't possible to begin with.

19. Jan 11, 2009

ZapperZ

Staff Emeritus
This is what you originally wrote:

We can "track" single electrons. That's what we do in cloud chambers and other particle detectors. What we can't do is place those two at the location that you want under the conditions that you want.

If you want to solve this classically without regards to reality, then knock yourself out. That's a simple problem in classical E&M. But to do that quantum mechanically under such condition, I don't see that happening.

Zz.

20. Jan 11, 2009

granpa

the electron cant be placed at that position but what about the electron cloud?

21. Jan 12, 2009

edguy99

Thank you for your insight. Whats your feeling on a window of 0.5 A if the energy is less then 0.1 eV?

22. Jan 12, 2009

edguy99

I assume you understand the silly solution I get in classical E&M tracking a slow moving electron 1 Angstrom away from a proton for a few attoseconds (it gains enormous amounts of energy - way over 13.6ev, and shots out somewhere and ends up very far away, clearly not what happens in hydrogen gas).

I would like to say, if you assume that the electron does not continue to gain energy once inside the first orbital radius (I use 53 picometers), you get a nice oscillating electron with a period of 340 attoseconds that never goes more then 1 angstrom away from the proton. If, in addition, you shot off 10.2evolts worth of energy, you end up with an electron with less then 3.4evolts worth of kinetic energy completely trapped inside the orbital.

23. Jan 12, 2009

Staff Emeritus
It's not about "feelings". It's about calculations. Heisenberg uncertainty makes a very specific prediction: $\Delta x \Delta p \geq \hbar/2$. 0.5 A and 0.1 eV also violates this.

If you want to know if any other pair of $\Delta x$ and $\Delta p$ work, you can calculate them yourself. Note that a lower bound on E corresponds to a lower bound on p.

You shouldn't be too surprised that $\Delta x$ of order an Angstrom works out to $\Delta E$ of order 10 eV.

24. Jan 12, 2009

ZapperZ

Staff Emeritus
... and all of this is meaningful in what way? What useful information do you get out of this that has any resemblance to reality?

For your information, I could come up with a gazillion toy-model that would blow you away. Want to see my toy-model that initiates a vacuum breakdown? It is as useful as yours.

Zz.

25. Jan 12, 2009

nuby

Couple questions..

1). It is the coulombs force that keeps the electron near the proton, but is there is an equal "outward" force(?) from nucleous that makes the (ground state) electron cloud want to stay within a certain range, and be sphere shaped (on average).

2.) Would it make sense to explain an electron proton relationship as like a "gaseous planet", where the gas is the electron, and the most dense area in the center is the proton, and the outer most dense area(s) within the atmosphere is where the electron is supposed to be?