Explanation why dosen't the electron fall into the nucleus?

[QuantumClue]

Since the nucleus of an atom is +charged and the electron is -charged, why doesn't at least one electron fall into the nucleus?

One explanation, I have heard prof. Hawking recite is that an electron cannot settle at the nuclei of atoms because that would give an electron a well-defined position. So the electron does not spiral to the nucleus because it is forbidden by the Uncertainty Principle.

 

[JayAaroBe]

Could you address the bolded part of my post?

I've read all the threads relating to this question but my mind is just having trouble with the concept. Let's take the simplest case: a hydrogen atom with one proton and one electron. They have opposite charges and attract. If I think of each as a particle, then my mind wonders why wouldn't the two particles attract each other and come together and collide.

The only way I can make sense of it is as follows, and tell me if this is an okay way to think of it: the electron is not a particle, but rather a spherical cloud of charge. In this case, I think of it the electron not as a single point but rather as the atmosphere around a planet and the planet itself as the proton (I know the sizes are not to scale). This is the only way I can think of it that makes any sense to me and answers the question of why an electron is not pulled into the nucleus (the proton).

 

[dextercioby]

One explanation, I have heard prof. Hawking recite is that an electron cannot settle at the nuclei of atoms because that would give an electron a well-defined position. So the electron does not spiral to the nucleus because it is forbidden by the Uncertainty Principle.

I think the author of such a statement has a deformed view of the notions involved in the so-called uncertainty principles. He should definitely do more reading.

 

[JayAaroBe]

Could you address the bolded part of my post?

I've read all the threads relating to this question but my mind is just having trouble with the concept. Let's take the simplest case: a hydrogen atom with one proton and one electron. They have opposite charges and attract. If I think of each as a particle, then my mind wonders why wouldn't the two particles attract each other and come together and collide.

The only way I can make sense of it is as follows, and tell me if this is an okay way to think of it: the electron is not a particle, but rather a spherical cloud of charge. In this case, I think of it the electron not as a single point but rather as the atmosphere around a planet and the planet itself as the proton (I know the sizes are not to scale). This is the only way I can think of it that makes any sense to me and answers the question of why an electron is not pulled into the nucleus (the proton).

 

[Chopin]

Could you address the bolded part of my post?

Please do not cross-post--asking your question in one post is sufficient.

You are correct--the electron can be interpreted as a cloud that surrounds the nucleus. The laws of quantum mechanics control how dense the cloud pulls in around the nucleus. Or, if there are multiple nuclei, the cloud will surround them both in a pattern determined by the positioning of the charges. This is the basis for chemical bonds.

 

[JayAaroBe]

Thank you!

 

[QuantumClue]

I think the author of such a statement has a deformed view of the notions involved in the so-called uncertainty principles. He should definitely do more reading.

No I think it is quite accurate.

Post 21, the user also says something similar.

 

[QuantumClue]

I think the author of such a statement has a deformed view of the notions involved in the so-called uncertainty principles. He should definitely do more reading.

Also, it enters the understanding of a Fermi pressure. http://en.wikipedia.org/wiki/Electron_degeneracy_pressure so the uncertainty principle plays a large part in this understanding. Saying an electron cannot fall into the nucleus of atoms is akin to saying an electron must occupy every bit of space it can within the atom.

 

[eaglelake]

Re: why doesn't the electron fall into the nucleus!?

I just posted this elsewhere, but it also fits here.

This is what happens when we insist on using classical physics to describe a quantum system! Classically, an electron-proton system has no equilibrium state – the electron will spiral into the nucleus while radiating away its orbital energy. There is no such thing as a “classical atom”. There are only “quantum atoms”. And, quantum mechanics is about probabilities. It does not describe the motion of the particles involved. In fact, the electron and the proton are entangled in a way that has no classical analog. We must think of the atom as a single entity. The electron and proton are not separate objects that have independent identities . I know this is not what most of you want to hear, but there is no “electron moving around a nucleus”!

So, what does quantum mechanics tell us about the hydrogen atom? It tells us the possible values to expect IF WE MEASURE the energy, for example, and it tells us the probability of obtaining each energy value. Notice that we do not know the atom’s energy, but only the value we might get as a result of an energy measurement. This is because the atom is further entangled with the energy measuring device: the atom is non-separable from the rest of the experimental apparatus. The bottom line is this – we only know that we have an experimental apparatus involving hydrogen atoms that measures the energy.

It is very difficult to discuss such things because we are using the language of classical physics to describe non-classical events. This is an unavoidable dilemma that physicists are forced to live with!

 

[Zakk]

Could you address the bolded part of my post?

...The photo electric cell which is used in most supermarket / airport auotmatic doors uses the electron as a particle...this shows us that electron is not a cloud but a real particle which can trigger and rebound

Also see Thomas Youngs Double Slit experiment which is now more than 100 years old with no clear answer which proves electron as a particle and not as a cloud.

 

[ZapperZ]

...The photo electric cell which is used in most supermarket / airport auotmatic doors uses the electron as a particle...this shows us that electron is not a cloud but a real particle which can trigger and rebound

Also see Thomas Youngs Double Slit experiment which is now more than 100 years old with no clear answer which proves electron as a particle and not as a cloud.

But this is highly misleading because it depends on the situation. When you have free electrons shooting at something, they certainly can be considered as classical particles because they are far apart and with negligible wavefunction overlap. We model their dynamics with classical description. But in situation such as atomic potential, molecular bonding, plane-wave states in superconductors, etc., such "particle" picture is meaningless.

Furthermore, I also don't see how the double slit experiment "proves electron as a particle". A particle does not "interfere with itself" through both slits, since that is essentially what the phenomenon is describing (single-particle interference). This may not show that it is a "cloud", but it certainly doesn't prove that it is a particle.

Zz.

 

[harrylin]

Re: why doesn't the electron fall into the nucleus!?

I just posted this elsewhere, but it also fits here.

This is what happens when we insist on using classical physics to describe a quantum system! Classically, an electron-proton system has no equilibrium state – the electron will spiral into the nucleus while radiating away its orbital energy. There is no such thing as a “classical atom”. There are only “quantum atoms”. And, quantum mechanics is about probabilities. It does not describe the motion of the particles involved. In fact, the electron and the proton are entangled in a way that has no classical analog. We must think of the atom as a single entity. The electron and proton are not separate objects that have independent identities . I know this is not what most of you want to hear, but there is no “electron moving around a nucleus”!

So, what does quantum mechanics tell us about the hydrogen atom? It tells us the possible values to expect IF WE MEASURE the energy, for example, and it tells us the probability of obtaining each energy value. Notice that we do not know the atom’s energy, but only the value we might get as a result of an energy measurement. This is because the atom is further entangled with the energy measuring device: the atom is non-separable from the rest of the experimental apparatus. The bottom line is this – we only know that we have an experimental apparatus involving hydrogen atoms that measures the energy.

It is very difficult to discuss such things because we are using the language of classical physics to describe non-classical events. This is an unavoidable dilemma that physicists are forced to live with!

How can you know that it's unavoidable? Some authors come a long way with classical concepts. Since it's less popular, the progress is very slow but here's an example:

http://en.wikipedia.org/wiki/Free-fall_atomic_model

A weak point of that particular model is that it doesn't explain (I think) why the bound electron doesn't radiate. I have seen plausible explanations for that in other theories, such as that an electron in steady state around the nucleus may be regarded as a self-enclosed wave; with a smeared out electron the charge distribution is static (sorry I don't have a reference at hand).

Now just find a way to glue such theories together.

 

[alxm]

How can you know that it's unavoidable? Some authors come a long way with classical concepts. Since it's less popular, the progress is very slow but here's an example:

That's not a example of anything. Wikipedia has lots of pages devoted to crackpot theories, many created by the crackpots themselves. A brief look at that article's history shows that it was created and almost etirely edited by a single person, possibly Gryziński himself, whose Wikipedia contributions consist almost exclusively of having created and edited that page, and one on Gryzińsky. Every article cited is by that guy. The fact that the article points out there are "many peer-reviewed articles", as if peer-review was some kind of guarantee of correctness, is a crackpot warning flag in-itself.

A weak point of that particular model is that it doesn't explain (I think) why the bound electron doesn't radiate. I have seen plausible explanations for that in other theories, such as that an electron in steady state around the nucleus may be regarded as a self-enclosed wave; with a smeared out electron the charge distribution is static (sorry I don't have a reference at hand).

Now just find a way to glue such theories together.

We have a theory that already explains how electrons act in an atomic system, and why they do not radiate in their ground state, and what their ground state is, and every other property. It's called quantum theory, and it's one of the most successful scientific theories of all time.

There does not exist any known discrepancies between quantum theory and experiment for any atomic or molecular property. There are dozens of papers http://www.chemfeeds.com/allphys.php" making quantum-mechanical predictions of atomic and molecular systems, from spectroscopy to chemistry, and that's been the situation for 80 years now.

So why do we need to 'glue theories together', when we have an entirely consistent, working theory?

 

[Zakk]

But this is highly misleading because it depends on the situation. When you have free electrons shooting at something, they certainly can be considered as classical particles because they are far apart and with negligible wavefunction overlap. We model their dynamics with classical description. But in situation such as atomic potential, molecular bonding, plane-wave states in superconductors, etc., such "particle" picture is meaningless.

Furthermore, I also don't see how the double slit experiment "proves electron as a particle". A particle does not "interfere with itself" through both slits, since that is essentially what the phenomenon is describing (single-particle interference). This may not show that it is a "cloud", but it certainly doesn't prove that it is a particle.

Zz.

SINGLE PARTICLE INTERFERENCE... exactly ...thats what it is also proving that electrons are particles too. The experiment was designed to prove it either it is a wave or a particle..but it actually proved that it is both...and more...it proved something unthinkable..single particle interference..

Though Thomas Young's experiment was done with photons it is very much applicable to electrons as well.

 

[ZapperZ]

SINGLE PARTICLE INTERFERENCE... exactly ...thats what it is also proving that electrons are particles too. The experiment was designed to prove it either it is a wave or a particle..but it actually proved that it is both...and more...it proved something unthinkable..single particle interference..

Though Thomas Young's experiment was done with photons it is very much applicable to electrons as well.

But what "particle" do you know can "interfere" with itself, meaning in that double slit experiment, it went through BOTH slits simultaneously?

This is not the behavior of a "particle" in the classical sense. We only call it a particle because it comes either in clumps of energy or obeys a "which way" experiment. But look at the bonding-antibonding phenomenon in chemistry. Explain that in terms of the particle picture.

Zz.

 

[harrylin]

That's not a example of anything. [..] crackpot [..]

I gave a direct link to a publication lists of a theory that I saw recently discussed on sci.physics.research... but perhaps I should have given a link to that instead, here it is:

http://groups.google.com/group/sci.physics.research/msg/ddcfc9c2f7e86cef

Note that publications in Physical review etc. are certainly not a "crackpot warning flag"!

So why do we need to 'glue theories together', when we have an entirely consistent, working theory?

Nobody says that you need to do that. Eagellake spoke of "an unavoidable dilemma that physicists are forced to live with", and I merely illustrated why that doesn't seem necessary at all.

 

[Zakk]

But what "particle" do you know can "interfere" with itself, meaning in that double slit experiment, it went through BOTH slits simultaneously?

This is not the behavior of a "particle" in the classical sense. We only call it a particle because it comes either in clumps of energy or obeys a "which way" experiment. But look at the bonding-antibonding phenomenon in chemistry. Explain that in terms of the particle picture.

Zz.

But is there any proof of chemical bonding within the atom between its nucleas and the electrons..

So far the atom is projected to contain 99% empty space and the 1% of the energy is chasing all around the atom at unimaginable speed giving it a solid appearance. (Eg: Like a rotor blade moving at a high speed gives the appearance of a solid plate)

Yes I agree that we need to leave the classical view of particles...but only when we try to understand the particle in relation to the universe... And adopt a view such as string theory by adding in new dimensions to reality. But this only suggests the entaglement of a particle inextricably within its universe ...then everything is just a wave. Thanks for the suggestion on the bonding phenomenon...Will check it out.

 

[ZapperZ]

But is there any proof of chemical bonding within the atom between its nucleas and the electrons..

What does that have anything to do with the point I'm making? Look at the bonding-antibond state for a molecule and tell me that you can explain that using your scenario.

So far the atom is projected to contain 99% empty space and the 1% of the energy is chasing all around the atom at unimaginable speed giving it a solid appearance. (Eg: Like a rotor blade moving at a high speed gives the appearance of a solid plate)

So a photon moves so fast, it goes through both path in a Kennedy-Thorndyke setup? And this is more "appealing" to your common sense?

Yes I agree that we need to leave the classical view of particles...but only when we try to understand the particle in relation to the universe... And adopt a view such as string theory by adding in new dimensions to reality. But this only suggests the entaglement of a particle inextricably within its universe ...then everything is just a wave. Thanks for the suggestion on the bonding phenomenon...Will check it out.

You seem to be arguing things not on the basis of physical phenomenon or evidence, but based on TASTES. At some point, you need to make that realization.

Zz.

 

[Drakkith]

So far the atom is projected to contain 99% empty space and the 1% of the energy is chasing all around the atom at unimaginable speed giving it a solid appearance. (Eg: Like a rotor blade moving at a high speed gives the appearance of a solid plate)

This is an incorrect view of what's going on. The electrons aren't simply wizzing around so fast they make the atom LOOK solid, the electrons are actually all over their orbitals at the same time. The force is everywhere at once, with certain probabilities of finding the electron at a certain point when we measure it. Even in a chemical bond where the electrons are being shared between atoms they are still everywhere at once. It's a very difficult concept to grasp.

 

[Zakk]

This is an incorrect view of what's going on. The electrons aren't simply wizzing around so fast they make the atom LOOK solid, the electrons are actually all over their orbitals at the same time. The force is everywhere at once, with certain probabilities of finding the electron at a certain point when we measure it. Even in a chemical bond where the electrons are being shared between atoms they are still everywhere at once. It's a very difficult concept to grasp.

I know that this is the suggestion of HUP and EPR experiments etc.. that they are all present at the same time everywhere.

But this is against common sense. It is possible that we do not have adequate devices/techniques to measure such minute particles traveling at such high speeds. Even the smallest of interference with the system distorts the system. So as of now we can only measure either their location or the velocity of the particle.

So is it our Inability to measure or is it really uncertain ?

Added to this due to other experiments such as the Schroedinger's cat experiment have thrown in enough complications such as probability theory and wave functions into this that now we have a situation of logically accepting existence of many universes which is again outside the realm of our common sense and experience.

Our common sense/experience agrees with classical physics and Newtonion concepts even after 100 years after the birth of quantum mechanics.

If we accept the theory of Electrons being present at the same time at different places..then our experience of Time as a measure of chronological sequence of action is wrong.

So the entire idea is against our experience of reality.

How do we explain this ?

 

[ZapperZ]

I know that this is the suggestion of HUP and EPR experiments etc.. that they are all present at the same time everywhere.

But this is against common sense. It is possible that we do not have adequate devices/techniques to measure such minute particles traveling at such high speeds. Even the smallest of interference with the system distorts the system. So as of now we can only measure either their location or the velocity of the particle.

The problem here is that it has already been shown that what we call "common sense" isn't correct all the time! In fact, one can argue that common sense is nothing more than an accumulation of knowledge! So the use of common sense as the criteria for something to be correct is not valid.

Again, there are many experiments and phenomena in which such superposition has been confirmed and verified. The measurement of the coherence gap in the Delft/Stony Brook experiments that I've mentioned repeatedly is a clear example.

This thread has no degenerated beyond just asking about why electrons don't fall into the nucleus, but rather about quantum superposition. Topics on quantum superposition and Schrodinger Cat-type experiments have been exhaustively discussed in here. A quick browse or search of such threads might get people unaware of it up to speed.

Zz.

 

[A. Neumaier]

This is an incorrect view of what's going on. The electrons aren't simply wizzing around so fast they make the atom LOOK solid, the electrons are actually all over their orbitals at the same time. The force is everywhere at once, with certain probabilities of finding the electron at a certain point when we measure it. Even in a chemical bond where the electrons are being shared between atoms they are still everywhere at once. It's a very difficult concept to grasp.

I know that this is the suggestion of HUP and EPR experiments etc.. that they are all present at the same time everywhere.

But this is against common sense. It is possible that we do not have adequate devices/techniques to measure such minute particles traveling at such high speeds. Even the smallest of interference with the system distorts the system. So as of now we can only measure either their location or the velocity of the particle.

So is it our Inability to measure or is it really uncertain ?

The charge density in a molecule is fully predictable. Nothing is uncertain, except for the presence of a tiny bullet called electron.

Common sense is restored to a large extent by not thinking of the electron as a tiny bullet but as a spread out substance forming the electron field. See the entry ''Does an atom mostly consist of empty space?'' in Chapter A6 of my theoretical physics FAQ at http://arnold-neumaier.at/physfaq/physics-faq.html#touch

 

[alxm]

I'm not sure 'common sense' ever really dictated that an electron in a molecule 'should' behave as an individual particle with a specific position/location/'orbit'. At least if 'common sense' means believing experiment. There's nothing in chemistry that indicates that electrons would behave that way. Every physical and chemical theory which tried to describe them that way, from the Bohr model to the "Cubical Atom" was a failure. The only reason you'd ever try, really, was in order to reconcile atoms with classical physics - not 'common sense'. And we now know that's not possible.

The fact that electrons in a molecule do behave quantum-mechanically and form superpositions is in fact so elementary to chemical behavior, that its effects were known to chemists well before quantum mechanics. When Kekulé in 1882 theorized that electrons 'oscillate' (in modern terminology: resonate) between single and double bonds in the benzene molecule, he was in effect describing a quantum-mechanical superposition of electrons, well before the existence of atoms or even electrons had been commonly accepted.

Thanks to QM, the distinction between chemistry and physics no longer exists, so I think it's a bit unfortunate that we continue to perpetuate it when it comes to writing the history of QM. It's a bit like writing the history of genetics by starting with Crick and Watson and ignoring the insights of Darwin and Mendel. Darwin didn't know what DNA was, Kekulé didn't know what electrons were. But the fact that they managed to draw the correct conclusions without an underlying theory only makes their insights more impressive.

 

[Drakkith]

Exactly Alxm. Thinking of an electron as a little solid particle is wholly incorrect. It has been repeatedly observed by experiments and by math that pretty much all matter is wavelike. It "acts" like a particle only in the sense that an electron is a WHOLE object in itself. Just like a photon acts like a particle in the same way.

 

[zenith8]

Exactly Alxm. Thinking of an electron as a little solid particle is wholly incorrect. It has been repeatedly observed by experiments and by math that pretty much all matter is wavelike.

You might think that, but surely if you read PF with any regularity you must know by now that the whole thing can be 'explained' by thinking of the electron as a solid little particle with an accompanying wave which pushes it around (i.e. wave-particle duality => two things rather than one). This is the viewpoint of the de Broglie-Bohm theory, where QM is just a dynamical theory - the statistical mechanics of particles moving along non-classical trajectories - rather than a probability calculus for the results of measurements.

Within that model, it is simply obvious why the electron doesn't fall into the nucleus: the electron is held in a web of opposing forces (electromagnetic and quantum). Under the right circumstances (a stationary state with zero angular momentum such as the ground state of the hydrogen atom) the electron can even be stationary.

Debating which of these views is 'true' is a thoroughly pointless exercise (since one can never answer such a question for certain, even if experiments might well later prove capable of distinguishing between them). Pretending that QM has 'proven' that matter consists entirely of waves is simply incorrect ; the particle(s)+wave idea is a perfectly legitimate way of viewing the atom. But since the de Broglie-Bohm theory provides a visualizable picture and a simple conceptual explanation for essentially any quantum phenomena, you ought to at least ask yourself how the phenomena is represented in deBB before asking conceptual questions of this nature, since it is in general the only variant of QM capable of answering them.

 

[Drakkith]

Zenith, I don't limit my knowledge of this to just the PF forums. I said what I said because that is exactly how I understand it to be.

You might think that, but surely if you read PF with any regularity you must know by now that the whole thing can be 'explained' by thinking of the electron as a solid little particle with an accompanying wave which pushes it around (i.e. wave-particle duality => two things rather than one).

Yes, I have heard of this before. However most of my reading has pointed to matter NOT being a particle with an associated wave. However I will say that my knowledge is FAR from complete on the matter.

 

[zenith8]

Zenith, I don't limit my knowledge of this to just the PF forums. I said what I said because that is exactly how I understand it to be.

Sure, and you're wrong. The experimental evidence does not unequivocally support your view, as you claim. Just sayin'..

Yes, I have heard of this before. However most of my reading has pointed to matter NOT being a particle with an associated wave. However I will say that my knowledge is FAR from complete on the matter.

Evidently..

 

[Drakkith]

Sure, and you're wrong. The experimental evidence does not unequivocally support your view, as you claim. Just sayin'..


Evidently..

Thats fine. I actually just read the following on wikipedia's article on Wave-Particle Duality. Its a quote from L. Ballentine, Quantum Mechanics, A Modern Development, p. 4

When first discovered, particle diffraction was a source of great puzzlement. Are "particles" really "waves?" In the early experiments, the diffraction patterns were detected holistically by means of a photographic plate, which could not detect individual particles. As a result, the notion grew that particle and wave properties were mutually incompatible, or complementary, in the sense that different measurement apparatuses would be required to observe them. That idea, however, was only an unfortunate generalization from a technological limitation. Today it is possible to detect the arrival of individual electrons, and to see the diffraction pattern emerge as a statistical pattern made up of many small spots (Tonomura et al., 1989). Evidently, quantum particles are indeed particles, but whose behaviour is very different from classical physics would have us to expect.

Interesting...

 

[zenith8]

Thats fine. I actually just read the following on wikipedia's article on Wave-Particle Duality. Its a quote from L. Ballentine, Quantum Mechanics, A Modern Development, p. 4

Interesting...

Indeed. Prof. Ballentine is the world's most prominent exponent of the ensemble interpretation of quantum mechanics which, the first time you hear it, sounds eminently sensible. But the only thing that makes it different from Copenhagen is the (never explicitly mentioned) fact that it involves hidden variables. However, he does not specify what they are, or what they do, or whether when you measure stuff you are actually measuring properties of these hidden variables or not.

If you feel comfortable doing so, you might enjoy the following toy explanation of what I was going on about in my previous post (a popular lecture from Cambridge that I witnessed a year or so ago):

http://www.tcm.phy.cam.ac.uk/~mdt26/PWT/towler_pilot_waves.pdf"

I'd be interested to know what you think (the title page contains a series of stills of a video of the two-slit experiment that Ballentine was talking about..).

 

[Drakkith]

Indeed. Prof. Ballentine is the world's most prominent exponent of the ensemble interpretation of quantum mechanics which, the first time you hear it, sounds eminently sensible. But the only thing that makes it different from Copenhagen is the (never explicitly mentioned) fact that it involves hidden variables. However, he does not specify what they are, or what they do, or whether when you measure stuff you are actually measuring properties of these hidden variables or not.

If you feel comfortable doing so, you might enjoy the following toy explanation of what I was going on about in my previous post (a popular lecture from Cambridge that I witnessed a year or so ago):

http://www.tcm.phy.cam.ac.uk/~mdt26/PWT/towler_pilot_waves.pdf"

I'd be interested to know what you think (the title page contains a series of stills of a video of the two-slit experiment that Ballentine was talking about..).

Unfortunently I can't understand any of the math and equations behind all that, but if its true then that's pretty remarkable. Great read, thanks for linking it.