Electron Orbits and Nuclei 2- Rotation vs Orbital Motion

[Karrar]

1-is electron orbit about the nucleus ?
2-is there is different between rotation and orbit?


thanks in advance

 

[Civilized]

1-is electron orbit about the nucleus ?
2-is there is different between rotation and orbit?

1. No, in physics we don't say that "electrons orbit the nucleus." The word "orbit" implies following a path through space, and electrons don't do that in standard QM.

2. Yes, something can rotate even when no forces are applied (imagine throwing a stick in outer space and having it flip around and rotate as it travels away). Orbits require an external attractive force to make the thing which is orbiting stay bound to the thing it is orbiting around.

 

[mccoy1]

1. No, in physics we don't say that "electrons orbit the nucleus." The word "orbit" implies following a path through space, and electrons don't do that in standard QM.

2. Yes, something can rotate even when no forces are applied (imagine throwing a stick in outer space and having it flip around and rotate as it travels away). Orbits require an external attractive force to make the thing which is orbiting stay bound to the thing it is orbiting around.

Well if it doesn't orbit the nucleus,then how come electron has angular momentum?

 

[malawi_glenn]

Well if it doesn't orbit the nucleus,then how come electron has angular momentum?

Angular Momentum is due to rotational invariance of a system, so when we speak of angular momentum in QM (standard QM - Copenhagen interpretation) it reflects the shapes of the probability distribution functions.

 

[StandardsGuy]

1-is electron orbit about the nucleus ?

I was taught that they did, but that was a loooong time ago. Modern explanations are vague, but http://en.wikipedia.org/wiki/Atomic_orbital" is good "information".

 

[malawi_glenn]

I was taught that they did, but that was a loooong time ago. Modern explanations are vague, but http://en.wikipedia.org/wiki/Atomic_orbital" is good "information".

vague?

 

[Civilized]

Well if it doesn't orbit the nucleus,then how come electron has angular momentum?

You can read about the quantum mechanical treatment of the Hydrogen atom http://en.wikipedia.org/wiki/Hydrogen-like_atom"

If you already know QM, then you know that the Hamiltonian for an electron in a spherically symmetric potential commutes with the angular momentum operator, and so the stationary states of definite energy have definite angular momentum as well.

 

[Karrar]

3- what means Anglar moment then ? what thing that rotate to calculate it anglar monemt?
4- is electron rotate about it self(spin) ?

 

[malawi_glenn]

3- what means Anglar moment then ? what thing that rotate to calculate it anglar monemt?
4- is electron rotate about it self(spin) ?

I need appointment to disscus on line by mail these questions
posters email

3. I told you, in standard QM it means rotation symmetry (under SO(3))of the systems solutions (wavefunctions)

4. Is and Is.. it has intrinsic angular momentum but that is again in standard QM just a property of its wavefunction under a rotation group (SU(2) in this case)

much of this is covered in standard intro QM texts, I can give you some links to free pdf's if you want, it is not so efficient for us to give a full blown course here at the forum but rather discuss real specific issues.

Don't give your email here, the discussion will take place at the forum - what we write here is meant for others to read and be learned from so that we don't have to consider the same questions again again and again (compare with using a textbook)

 

[Karrar]

if you has the text.pdf supply me please

 

[Tac-Tics]

1-is electron orbit about the nucleus ?

Not in the same way that the Earth orbits the sun. It was believed before the 20th Century that electrons *did* orbit this way. We know now that these theories are incorrect, but they are still taught because they are easy to understand and are a useful stepping stone to the modern theory.

2-is there is different between rotation and orbit?

An orbit (or revolution) is when one object walks around another in an ellipse. A rotation is when an object spins around its own center. The Earth rotates, and because of it we have night and day. The Earth also revolves around the sun, and because of this, we have spring and winter.

3- what means Anglar moment then ? what thing that rotate to calculate it anglar monemt?

Angular momentum is a property of a physical system. It has two different, but historically related meanings.

The first is classical angular momentum. A system with angular momentum rotates or revolves about an axis, and can be calculated by the position and velocities of all the masses involved. It is conserved. Because of this, things that rotate or revolve tend to continue rotating or revolving.

4- is electron rotate about it self(spin) ?

The second meaning of angular momentum is a quantum phenomenon. It is called spin. It gets its name because it produces effects similar to what would happen if an electron rotated ("spun") around its own axis. However, this is just an analogy, and shouldn't be taken literally. It is treated as a quantum property and we usually only experience its effects in indirect ways (such as permanent magnets).

A very intriguing idea behind angular momentum is that its units: \frac{kg m^2}{s} are the same units as action, an extremely important quantity in physics. Action is what you get when you add up the kinetic energy minus the potential energy of a system at every instant of time. When the universe chooses a path that a particle takes, it always chooses the path which costs the least amount of action. This is called the Principle of Least Action, and among many, many other things, it explains why and how light bends when it goes between air and water.

 

[malawi_glenn]

if you has the text.pdf supply me please

please edit your post and remove your e-mail, it is against the rules to post it here.

https://www.physicsforums.com/showthread.php?t=220904

https://www.physicsforums.com/showthread.php?t=220901

 

[Karrar]

5- why electron not lost its energy and fall in nucleus ? i.e what source of energy for electron movement make it stand near nucleus?

 

[Tac-Tics]

5- why electron not lost its energy and fall in nucleus ? i.e what source of energy for electron movement make it stand near nucleus?

There is no need for a "source" of energy to hold the electron in place. An electron around a nucleus is a stable system. It doesn't consume energy, nor does it produce it.

The reason the electron doesn't fall into the nucleus is because it's magic. If it did fall in, the universe would blow up. But we see a universe that hasn't blown up, so we know it doesn't fall in.

More precisely, it's because of the nature of quantum mechanics. A rough argument of why this happens goes like this. The uncertainty principle says there is a lower limit to how well defined a particle's momentum and position can be. If you know where a particle is, it's momentum becomes almost random. If you know a particle's momentum, it's location is almost random.

If we try squeezing an electron to the size of the nucleus, we know its position very well. By the uncertainty principle, it's momentum becomes randomized. Very soon afterwards, it will end up (by simple chance) with a very high momentum, allowing it to break free of the electric field.

 

[ZapperZ]

5- why electron not lost its energy and fall in nucleus ? i.e what source of energy for electron movement make it stand near nucleus?

You may have a problem with understanding the responses being posted on here, at least based on how you are writing your questions.

Please start by reading the FAQ thread in the General Physics forum. Some of the posts there may have already addressed a few of your questions.

Zz.

 

[mccoy1]

Angular Momentum is due to rotational invariance of a system, so when we speak of angular momentum in QM (standard QM - Copenhagen interpretation) it reflects the shapes of the probability distribution functions.

Hi malawi_glenn,
Yes I understand that, but what business do electrons get upto really inside the atom? The n(quantum number) fits itself around the nucleus of the atom and there the electrons oscillate,rotate etc, right? If so, do they oscillate at fixed points or around the nucleus as they move?
Cheers

 

[jtbell]

what business do electrons get upto really inside the atom?

There is no generally accepted answer to this question. The mathematics of QM allows us to calculate the probabilities of getting various values for physical quantities when we measure/observe them, but it does not address the question of what is "really going on" when we don't measure/observe them. This is the subject of interpretations of QM, about which people argue vigorously (in this forum and elsewhere). We cannot as yet distinguish between these interpretations experimentally, even in principle, as far as I can tell.

 

[DaveC426913]

More precisely, it's because of the nature of quantum mechanics. A rough argument of why this happens goes like this. The uncertainty principle says there is a lower limit to how well defined a particle's momentum and position can be. If you know where a particle is, it's momentum becomes almost random. If you know a particle's momentum, it's location is almost random.

If we try squeezing an electron to the size of the nucleus, we know its position very well. By the uncertainty principle, it's momentum becomes randomized. Very soon afterwards, it will end up (by simple chance) with a very high momentum, allowing it to break free of the electric field.

I have never heard of HUP being applied as the reason electrons do not physically interact with the nucleus. This may be my oversight. I'd like to ask for independent clarification.

 

[mccoy1]

5- why electron not lost its energy and fall in nucleus ? i.e what source of energy for electron movement make it stand near nucleus?

In other word,it's like asking why atom doesn't collapse.okay according to intro chemistry,when you have say 5 electrons atom,no more than two electrons can share a 'spot',so the filling will be 1s^2 2s^2 2p^1.lowest energy orbitals get filled first and the next electrons move to the next orbitals(i.e no one electron sitting on top of other electron).I guess this makes the atom 'stable'.I may be wrong!

 

[sokrates]

vague?

Yes. Modern interpretations are vague when it comes to these issues. (angular momentum, electron "movement" in atom etc.)

Using buzzwords or writing down the mathematical theory doesn't make it clear.

 

[sokrates]

There is no generally accepted answer to this question. The mathematics of QM allows us to calculate the probabilities of getting various values for physical quantities when we measure/observe them, but it does not address the question of what is "really going on" when we don't measure/observe them. This is the subject of interpretations of QM, about which people argue vigorously (in this forum and elsewhere). We cannot as yet distinguish between these interpretations experimentally, even in principle, as far as I can tell.

Great post. Enlightening and insightful. Had I seen this, I wouldn't have posted my previous one.

 

[DaveC426913]

Yes. Modern interpretations are vague when it comes to these issues. (angular momentum, electron "movement" in atom etc.)

Using buzzwords or writing down the mathematical theory doesn't make it clear.

These things are not vague; they are exactly the opposite of vague.

You're up against something that needs a set of definitions beyond day-to-day language. In order to discuss these things meaningfully, you need to learn the language.

How do you suppose you would discuss the details of an integrated circuit with someone who thought that voltage and resistance were "buzzwords"?

 

[sokrates]

These things are not vague; they are exactly the opposite of vague.

You're up against something that needs a set of definitions beyond day-to-day language. In order to discuss these things meaningfully, you need to learn the language.

How do you suppose you would discuss the details of an integrated circuit with someone who thought that voltage and resistance were "buzzwords"?

No. That's what some brilliant people around here want to believe. They want to believe that QM is well-understood and Copenhagen is the way to go, although much of the interpretation is still vague. Worse yet, the understanding and the MACHINERY can change depending on the interpretation.

Voltage and Resistance can be physically defined in day-to-day language, I'll give you one if you want a layman explanation. And that's what makes Voltage and Resistance CLEAR - that they can be expressed simply.

Using rotational invariance to explain electron's angular momentum and pretending (or naively believing) that mathematics of it is the reason behind the physics is misleading.
and incorrect.

 

[diazona]

Using rotational invariance to explain electron's angular momentum and pretending (or naively believing) that mathematics of it is the reason behind the physics is misleading.
and incorrect.

Sure, that is arguably true. But nobody is pretending that.

 

[DaveC426913]

They want to believe that QM is well-understood and Copenhagen is the way to go, although much of the interpretation is still vague. Worse yet, the understanding and the MACHINERY can change depending on the interpretation.

You claimed, or at least implied, that terms such as 'angular momentum' are buzzwords. They're not. I was arguing your complaint of unclear terminology, not unclear theories.

Voltage and Resistance can be physically defined in day-to-day language, I'll give you one if you want a layman explanation. And that's what makes Voltage and Resistance CLEAR - that they can be expressed simply.

Nice try. The fact that something cannot be expressed simply does not invalidate it. It is a matter of the listener's level of competence in the subject. Good luck explaining how a computer works to a caveman - in a form he finds acceptable - while using only his own vocabulary. To understand QM, you need to understand the math.

No. That's what some brilliant people around here want to believe.

Yeah, that attitude will go far... "I don't understand all this. Obviously, I'm smarter than the rest of you delusional ones..."

 

[sokrates]

My argument was not about whether the theory was well-defined it was about whether the terminology was well-defined. You claimed, or at least implied, that terms such as 'angular momentum' are buzzwords. They're not.

No, I never implied terms "such as '''angular momentum''' are buzzwords" or not. I specifically criticized a specific post that attempted to explain the angular momentum of an electron with rotational invariance (which is not wrong) to a person who required physical intuition and visualization. If you had read what I wrote carefully, you'd have easily caught that. But since you are too busy posting and trying so hard to 'bust', I can see why...

To understand QM, you need to understand the math.

You don't understand QM, you write some equations and formulate the theory. Understanding and calculating are two different things. But I have a feeling that you feel better when you think you understand QM...

Yeah, that attitude will go far... "I don't understand all this. Obviously, I'm smarter than the rest of you delusional ones..."

It definitely goes further than yours. At least, I know what I don't understand about QM and I don't satisfy myself with half-baked
intuition gained from deep, solid mathematics. This is why, contrary to popular belief, great deal of research is being conducted to "understand" about things, you think, are clearly "established".

This is what distinguishes mediocre physicists from the precious few... Physics is about INTUITION and IDEAS, not just some extremely complicated mathematical construct.

 

[DaveC426913]

No, I never implied terms "such as '''angular momentum''' are buzzwords" or not.

You may not have intended to, but this is pretty implicative:

Modern interpretations are vague when it comes to these issues. (angular momentum, electron "movement" in atom etc.)

Using buzzwords or writing down the mathematical theory doesn't make it clear.

I specifically criticized a specific post that attempted to explain the angular momentum of an electron with rotational invariance (which is not wrong). If you had read what I wrote carefully, you'd have caught that!

I read what you wrote. I caught it. I take issue with the implication.

Here is your opportunity to clarify your use of the term "buzzword".

 

[DaveC426913]

I'll give you a moment to finish retro-editing your posts...

 

[sokrates]

I'll give you a moment to finish retro-editing your posts...

I respect your "eager" wait for new material to debunk!

Coming, almost ready...

 

[DaveC426913]

I respect your "eager" wait for new material to debunk!

Coming, almost ready...

Debunking? I'm not debunking anything. I'm taking issue with unsupported claims.

And I'm talking about editing posts that have already been in the discussion stream.

 

[sokrates]

Debunking? I'm not debunking anything. I'm taking issue with unsupported claims.

And I'm talking about editing posts that have already been in the discussion stream.

That's the definition of debunking, considering that you are trying to take the issues with humor.

You just edited your post as well. But that's OK... There's a reason why the edit button is there, and I don't sit here all day to instantly reply to posts ,this is not instant messaging.
You should wait a while before you take the post into the stream (your reply rate averages on seconds) if you don't want to see edited replies.

My claims are not unsupported. You just don't understand them. Because you don't read them carefully. Because you post too fast. Then you complain about the whole process.

 

[DaveC426913]

My claims are not unsupported. You just don't understand them. Because you don't read them carefully. Because you post too fast. Then you complain about the whole process.

Nonsense. I read everything. I got what you were saying. I got that you were attacking the earlier argument. That does not change my objection.

 

[humanino]

Understanding and calculating are two different things.

QM has never been falsified, so discussing your emotions belongs to the philosophy forum, please.

 

[Phrak]

If this were universally enforced, all discussion of multiple world theories, and the Copenhagen interpretations, and notions concerning elements of physical reality would be moved from the quantum mechanics folder to philosophy, where they would die in the sesquipedalian world where conculsions are never meant to be found.

 

[DaveC426913]

If this were universally enforced, all discussion of multiple world theories, and the Copenhagen interpretations, and notions concerning elements of physical reality would be moved from the quantum mechanics folder to philosophy, where they would die in the sesquipedalian world where conculsions are never meant to be found.

humanino didn't post the full quote. His rebuke makes more sense with it:

Understanding and calculating are two different things. But I have a feeling that you feel better when you think you understand QM...

 

[sokrates]

humanino didn't post the full quote. His rebuke makes more sense with it:

1) His rebuke doesn't make sense at all (but I can see why otherwise you'd be happy) - because he's simply proposing to put all the interpretational discussions to philosophy board (as pointed out) which, with all due respect, is not up to anyone who dislikes the course of a debate.

Despite the resistance, the research on the interpretation of QM is still evolving, slowly but surely.

2) Adding that second line, made *so much more* sense... Thank you for the clarification.

 

[Phrak]

Yeah, well, I did read the post by sokrates.

I do appreciate an escalating argument between the two of you as well as the next guy, but if anyone isn't uncomfortable with the structure of quantum mechanics they've either gained immunity through repetition, or don't understand it.

 

[humanino]

he's simply proposing to put all the interpretational discussions to philosophy board

I really think discussions of the interpretation of QM have nothing to do here. If you apply the same well-defined set of rules, you'll obtain the same results. It is a matter of philosophy to decide whether you want to go for this or that interpretation. I did not say I was not interested in interpretation. I claim that you should be able to do the calculations first, and you can discuss that here. Once you are able to do decent calculations, you may discuss interpretations. There is enough technical material in QM to keep this part of the forum quiet and rigorous. I suggest you read serious books about the interpretation of QM if you want to attract people who really understand the issues.

 

[DaveC426913]

His rebuke doesn't make sense at all...

Adding that second line, made *so much more* sense... Thank you for the clarification.

It pointed out that you were talking about your (and other people's) feelings.

 

[sokrates]

I really think discussions of the interpretation of QM have nothing to do here. If you apply the same well-defined set of rules, you'll obtain the same results. It is a matter of philosophy to decide whether you want to go for this or that interpretation. I did not say I was not interested in interpretation. I claim that you should be able to do the calculations first, and you can discuss that here. Once you are able to do decent calculations, you may discuss interpretations. There is enough technical material in QM to keep this part of the forum quiet and rigorous. I suggest you read serious books about the interpretation of QM if you want to attract people who really understand the issues.

I don't agree. "Being able to do the calculations" cannot be a measure at all. I like this requirement a lot... So how do I know whether I am "allowed" to discuss the interpretations? Maybe you could upload some qualification tests and we could try to solve the exercises...

I am a Ph.D student, I am able to do the calculations , but I cannot at all condone the snobbish physicist view: Only people good at math can discuss the interpretations.

Really?

You are right on the spot. BECAUSE we don't know the answers yet,, we don't want laymen to come here and ask : "OK what is the electron doing inside the atom?" That's annoying. But sending people (no, thanks I have read enough on the subject) to books because we don't know simple answers is just hypocrisy... As if they would REALLY find the answers in the books... The answers are NOT in the books, if they were in the books, we'd be able to tell them the answers - rather than bash them due to their lack of mathematical knowledge when they come up with innocent questions.

We could say, we don't know the answer to that. And people in this thread did that. That's perfectly okay! And that's arguably the answer. It's much more exciting and fascinating than pointing out some graduate level theorem.

-----------------
@DaveC: I'm really not interested about getting into a discussion about your "feelings" - since this is Physics Forums (rather than Loveshack) so I'll leave it here, I proved my points.

Whenever you want to follow up intellectually, I'll be here.

 

[StandardsGuy]

This is what distinguishes mediocre physicists from the precious few... Physics is about INTUITION and IDEAS, not just some extremely complicated mathematical construct.

I applaud this sentence. There is too much math with too little logic and common sense.

 

[humanino]

If you think you have studied the maths enough, I do not question it. I point out that before asking the physical meaning, the physical content of an equation, one should be able to define and manipulate the concepts at the very least. If you need help with an equation, how to define or manipulate the terms, the place is here. Yet my ultimate stance on the interpretation, once we have discussed something, I suspect will remain that it does not belong here anymore, unless you have a proposal to distinguish interpretations (but that does not qualify for merely "interpretation" anymore it seems to me...)

Note that I do not want the discussion to close either. If you start adding material making it interesting, it will survive for sure, with or without me BTW. Please feel free to add beef to it. Define a situation, give us a matrix element, construct a complete orthonormal basis, tell us how you think your operator is represented, question the role of gravity in the reduction/collapse/measurement... something. There are very interesting technical papers published for decades.

 

[DaveC426913]

@DaveC: I'm really not interested about getting into a discussion about your "feelings"

What is with you??

You said "I have a feeling that you feel better when you think you understand QM..." You are talking about feelings. Your own and those of an ambiguous "you". You have been asked to take this kind of talk somewhere else.



Now that that's straightened out, I'm still interested in what "buzzwords" you think QM is filled with. That post never did emerge.

 

[humanino]

If you think you have studied the maths enough, I do not question it.

Please note that angular momentum is kindergarden still. It does not present any serious difficulty in terms of interpretation at all.

 

[jtbell]

Physics is about INTUITION and IDEAS,

...which lead to quantifiable predictions that can be tested through experiment...

not just some extremely complicated mathematical construct.

 

[sokrates]

Please note that angular momentum is kindergarden still. It does not present any serious difficulty in terms of interpretation at all.

Read my posts in their context (not in their deliberately distorted form quoted by DaveC), I was talking about electron inside an atom, how do we think about the rotation of an electron, how does it relate to angular momentum and so forth...

 

[sokrates]

What is with you??
Now that that's straightened out, I'm still interested in what "buzzwords" you think QM is filled with. That post never did emerge.

Sigh... I really don't have time for this. It did emerge really well. My point is delivered to the people who read my posts. Go back and read them a few more times before "contributing" another dozen posts and you'll get it. Thanks

 

[humanino]

I was talking about electron inside an atom, how do we think about the rotation of an electron, how does it relate to angular momentum and so forth...

Do you realize that there is absolutely no difficulty with that ? Have you ever read any serious book saying there is a fundamental problem with that ? There is a tower of wavefunctions for the electrons which we can calculate to daunting accuracy. The only theoretical issue with the angular momentum of the constituents was remaining 10 years ago with the partons inside hadrons, in a highly relativistic fully quantum situation. Today we understand this in terms of Wigner functions, we can define the energy momentum tensor for those states, and this is merely an experimental problem with model-dependent (but consistent) results already.

 

[Phrak]

Please note that angular momentum is kindergarden still. It does not present any serious difficulty in terms of interpretation at all.

Does a particle have absolute angular momentum or angular momentum in relation to another particle?

 

[Civilized]

Sokrates, I read your posts, and I disagree with your statements about mathematical understanding. First of all, mathematical understanding is not to be confused with calculations. Anyone can "shut up and calculate" without understanding QM mathematically. The working knowledge of QM that they teach in grad school (e.g. Sakurai, Shrednicki, etc) shows you how to calculate, but does not show you much of the mathematial understanding behind QM. The mathematical understanding explains why QM is the way it is, why it works, by developing Classical Mechanics and Classical Statistical Mechanics in a sufficiently abstract setting so that QM is seen as a natural generalization. Physics books describe quantization in terms of poissoin brackets - > i*hbar*commutators. Mathematical understanding shows us why this is the case.

Classical intuition is not that mathematically appealing to me. Quantum intuition is much more mathematically rich I think.