Jump to content

Kinetic energy of a nucleus


Dubbelosix
 Share

Recommended Posts

2 hours ago, Dubbelosix said:

I know fine well what it means, it was me who explained it was not a classical property of the electron in our current models. Maybe you should read the conversation properly. He was the one who mentioned the electron and then claimed the links I provided suggested he was correct and I was somehow wrong. 

 

Point is, and what is frustrating about this, is even when you [provide] the material, certain posters are still incapable of understanding its content and in what context.

That's just wrong - the electron is the only system subject to these ''non-internal degree's of freedom'' it is the only pointlike particle in existence since we cannot measure the radius (yet). We have attempted to measure the shape of electrons which suggests they are in fact spherical. 

Classically rotating systems always possess a kinetic energy associated to the rotation. This even applies to a nucleus. 

Right. But the quantum spin is not classic. Generally speaking when discussing subatomic particles doesn't "spin" refer to quantum spin, and not to any movement associated with kinetic energy?

Link to comment
Share on other sites

  • Replies 83
  • Created
  • Last Reply

Top Posters In This Topic

2 hours ago, Dubbelosix said:

That's just wrong - the electron is the only system subject to these ''non-internal degree's of freedom'' it is the only pointlike particle in existence

All elementary particles are point-like.

2 hours ago, Dubbelosix said:

We have attempted to measure the shape of electrons which suggests they are in fact spherical. 

What was measured was the electron dipole moment.

Link to comment
Share on other sites

4 hours ago, Dubbelosix said:

You never said such a thing, so you are saying you did not disagree with me?

 

Let's try again, did you not say

 

''The specific question that was asked was if the spin of a nucleus means it has KE. You said yes. I disagree.'' 

 

Since this is a direct quote, this is a no brainer. You disagree with something, so would be nice if you were not obtuse and get to the point. 

The nucleus is a quantum object, not a classical one.

On November 30, 2017 at 4:18 PM, Giorgio T. said:

Dear Dubbelosix and swansont,

Thanks for your replies,

You guys are obviously the experts. I am sorry but I have almost no knowledge in your field. Consider the question coming from and old fashioned “Natural Philosopher”.

I have a PhD in physics. I have no idea what Dubbelosix's bona-fides are.

On November 30, 2017 at 4:18 PM, Giorgio T. said:

Let me pose the question in a different way with a little thought experiment:

I have invented an inertial ray gun and I can aim it at things and control mass. I aim it at an old watch with a balance wheel and turn the inertial mass of the parts to one half - the watch goes twice as fast because the balance wheel loses mass and the spring stays the same.

What happens if I do the same with an atomic clock? Will it speed up?

Regards

Halving or doubling mass of an atomic clock would have no measurable effect on its rate. 

3 hours ago, Dubbelosix said:

I know fine well what it means, it was me who explained it was not a classical property of the electron in our current models. Maybe you should read the conversation properly. He was the one who mentioned the electron and then claimed the links I provided suggested he was correct and I was somehow wrong. 

Then tell me how much KE the proton in hydrogen has owing to its spin. Or any ground state nucleus. You pick.

3 hours ago, Dubbelosix said:

Point is, and what is frustrating about this, is even when you [provide] the material, certain posters are still incapable of understanding its content and in what context.

That's just wrong - the electron is the only system subject to these ''non-internal degree's of freedom'' it is the only pointlike particle in existence since we cannot measure the radius (yet). We have attempted to measure the shape of electrons which suggests they are in fact spherical. 

Classically rotating systems always possess a kinetic energy associated to the rotation. This even applies to a nucleus. 

So a nucleus is a classical rotating object, even though its spin is that of its constituent nucleons? Answer the question you avoided: if it has KE, where does the rotational (not spin) angular momentum go?

Link to comment
Share on other sites

1 hour ago, swansont said:

The nucleus is a quantum object, not a classical one.

 

 

Let's start here, first of all, you don't seem to understand what ''classical rotation'' means, as to what a quantum spin is. Though mathematically there is nothing different between the two, the former involves actual rotations in space, whereas the latter means '''instrinsic'' which means it is not a classical rotation, that means, it is not an actual rotation. Now, a nucleus certainly rotates - as it has internal dynamics ie. degrees of freedom.

 

Let's see if you can understand what it means now?

Because we cannot measure the electron, it is often taken to mean that it truly is fundamentally a pointlike object - but over the years it is not talked about enough, but there are problems which exist when thinking the electron has no internal structure/radius. A point like particle experiences a divergence problem in its self-energies. 

Link to comment
Share on other sites

17 minutes ago, Dubbelosix said:

 

Let's start here, first of all, you don't seem to understand what ''classical rotation'' means, as to what a quantum spin is. Though mathematically there is nothing different between the two, the former involves actual rotations in space, whereas the latter means '''instrinsic'' which means it is not a classical rotation, that means, it is not an actual rotation. Now, a nucleus certainly rotates - as it has internal dynamics ie. degrees of freedom.

I understand that you keep avoiding my question and request for experimental evidence

Quote

Let's see if you can understand what it means now?

Because we cannot measure the electron, it is often taken to mean that it truly is fundamentally a pointlike object - but over the years it is not talked about enough, but there are problems which exist when thinking the electron has no internal structure/radius. A point like particle experiences a divergence problem in its self-energies. 

Then answer my question about this KE, and the angular momentum that must be associated with it.

Link to comment
Share on other sites

I didn't avoid anything. Did I or did I not provide you reading material pertinent to the discussion?

 

It's you who is avoiding what was given to you. You want a demonstration, I don't have one to give you at the moment, but I have provided plenty material which supports my claim. It's not something new to me, I knew there was a rotational energy associated to the nucleus, in fact, anything that has a measurable radius has internal degree's of freedom and the idiom ''intrinsic spin'' is silly. It's just a spin, around an axis. 

It's you refusing to engage in a meaningful discussion. You are still failing to admit you objected to my assertions and then tried to say you weren't objecting to anything.

Link to comment
Share on other sites

8 hours ago, Dubbelosix said:

 It's you refusing to engage in a meaningful discussion. You are still failing to admit you objected to my assertions and then tried to say you weren't objecting to anything.

I do object to your assertions. I have not changed that at all. (This includes your assertion that I have ever applied this to anything classical, which the nucleus is not)

Quote

I didn't avoid anything. Did I or did I not provide you reading material pertinent to the discussion?

Anything about classical systems is not pertinent

 

Quote

anything that has a measurable radius has internal degree's of freedom

A hydrogen atoms has a measurable radius, and yet the orbital angular momentum of the ground state electron is zero. Same for helium. (true of any s-state electrons)

Link to comment
Share on other sites

You have a problem with terminology, or me?

 

Classical rotation is just that, a classical rotation in space. Intrinsic means something else. If you are so profoundly confused by the use of spin in this context, I don't think science is your area.

And regardless, I have also said the mathematics of classical spin and that associated to quantum mechanics, has no formal difference.

6 hours ago, swansont said:

A hydrogen atoms has a measurable radius, and yet the orbital angular momentum of the ground state electron is zero. Same for helium. (true of any s-state electrons)

 

 

So? You still don't seem to be getting the point, the point is the electron is the only pointlike system (as far as we can tell in existence). It's a total hit and miss with you.

8 hours ago, Strange said:

Then why is it quantised and determined by the number of nucleons and how they pair-up?

What is quantized exactly?

 

strange

Are you also aware there is no formal difference between the mathematics that describes classical spin and the ''intrinsic case'' only appropriate for electrons?

There are some serious issues, all extending from classical physics, relativity and quantum concerning pointlike systems. They are a problem in physics because they are actually a closely related to the divergence problems of relativity.

 

In classical physics, a pointlike system will possess infinite energies.

For a pointlike system in relativity, the curvature tensor vanishes, implying a zero radius and a singularity in the curvature.

Finally, pointlike systems do not make sense in phase space - early on, it was found a point particle is smeared in the phase space so points are physically meaningless, according to Von Neumann. 

Edited by Dubbelosix
Link to comment
Share on other sites

13 minutes ago, Strange said:

The spin of a nucleus. Therefore not classical. 

Yeah, right. 

 

If the nucleus makes real rotations in space (which it does) then the spin is classical. Are you having problems with terminology as well?

Note though, it depends on whether the nucleus is perfectly spherically symmetric. 

http://www.scholarpedia.org/article/Shape_deformations_in_atomic_nuclei

I think I have realised both your problems.

 

Just because an atom is a microscopic object, does not mean it cannot classically rotate. Classical rotation, as opposed to an intrinsic case (like we might expect for an electron) is still subject to nuclei of atoms, and to atoms themselves, even to diatomic molecules. 

Link to comment
Share on other sites

2 hours ago, Dubbelosix said:

So? You still don't seem to be getting the point, the point is the electron is the only pointlike system (as far as we can tell in existence). It's a total hit and miss with you.

A hydrogen atom is not. It has a size, and therefore (according to you) should have rotational KE. How can the angular momentum be zero?

 

Link to comment
Share on other sites

2 minutes ago, swansont said:

A hydrogen atom is not. It has a size, and therefore (according to you) should have rotational KE. How can the angular momentum be zero?

 

What do you mean, how can the angular momentum be zero? It's angular momentum is not zero, if my memory serves. 

Link to comment
Share on other sites

58 minutes ago, Dubbelosix said:

Just because an atom is a microscopic object, does not mean it cannot classically rotate. Classical rotation, as opposed to an intrinsic case (like we might expect for an electron) is still subject to nuclei of atoms, and to atoms themselves, even to diatomic molecules. 

Nobody is denying that a microscopic can rotate. But the topic here is limited to a system of some nucleus, with nucleons that have spin, and your contention that this means there is rotational KE.

please stop changing the topic.

Just now, Dubbelosix said:

What do you mean, how can the angular momentum be zero? It's angular momentum is not zero, if my memory serves. 

What is the angular momentum of the s state of hydrogen? 

Link to comment
Share on other sites

1 minute ago, swansont said:

Nobody is denying that a microscopic can rotate. But the topic here is limited to a system of some nucleus, with nucleons that have spin, and your contention that this means there is rotational KE.

please stop changing the topic.

I'm not changing the subject. You are ignoring everything that is being said to you, in obvious ways. You are fixated on me being wrong some how, when all the material I have provided you says otherwise. You are actually wasting my time. 

Link to comment
Share on other sites

Is he?

". Because it is not a classical properties, we cannot write spin in terms of position and momentum operator. The spin is dened in an abstract spin space (not the usual phase space)."

https://www.google.ca/url?sa=t&source=web&rct=j&url=https://ocw.mit.edu/courses/nuclear-engineering/22-02-introduction-to-applied-nuclear-physics-spring-2012/lecture-notes/MIT22_02S12_lec_ch4.pdf&ved=0ahUKEwj-2-GonezXAhUBRWMKHT4oDkkQFgguMAU&usg=AOvVaw1TBY59gANm3pXNerkxKdLY

 

Edited by Mordred
Link to comment
Share on other sites

It is intrinsic to the spin space itself,  when something is intrinsic it is intrinsic to the state space itself. Swansont did allude to that earlier.

On 30/11/2017 at 4:00 AM, swansont said:

 

Spin does not indicate motion. It's intrinsic angular momentum.

To wit

Edited by Mordred
Link to comment
Share on other sites

18 hours ago, Dubbelosix said:

I'm not changing the subject. You are ignoring everything that is being said to you, in obvious ways. You are fixated on me being wrong some how, when all the material I have provided you says otherwise.

You are wrong. All of the physics experts who have weighed in disagree with you. Pointing out that you are wrong, and that what you've posted that you claim supports you is irrelevant, is not ignoring what is being said.

18 hours ago, Dubbelosix said:

You are actually wasting my time. 

And you're not wasting mine?

Can you answer the question or not? How do you account for the angular momentum that must accompany the alleged rotational KE ?

 

Since you won't pick a nucleus, I will. He-3. It has a spin of 1/2, owing to the protons being spin up and spin down (as per the Pauli exclusion principle). A neutron has a spin of 1/2. If it has rotational KE, where is the associated angular momentum? (or, if it has this spin, how can it also have rotational KE?)

 

Link to comment
Share on other sites

Previous experts?

 

Name them. No one here is an expert in my opinion. And I think you will find the evidence I provided is overwhelmingly in my favour, I find your behaviour, strange concerning this. 

Your question was ''show me how the electron had a spin.'' I explained this was a red herring. You then went on to talk about protons, and other objects which are not pointlike.

 

Intrinsic spin was suggested to be required because a point cannot rotate classically. The electron is the only pointlike particle in existence, as far as we can tell. Atoms do rotate classically, and the nucleus rotates classically - there is no need for intrinsic processes, that's just woo woo.

Link to comment
Share on other sites

Sorry, I didn't mean anything against you Mordred. You weren't exactly part of this discussion till now.

I don't change my opinions on Swansont. Sorry if it causes offence, I've felt pretty offended by the constant hounding of a moderator.

Link to comment
Share on other sites

12 minutes ago, Mordred said:

 

Prove both myself and Swansont wrong. It should be a trivial matter if your correct

For me it always was a non-trivial matter with electrons  But then Swansont knew that anyway because he has enough guile to mention it as a type of academic trap. 

3 minutes ago, Strange said:

I think swansont's position as a moderators is irrelevant. He is arguing from his position as a working physicist.

His position as a moderator means something to me. Second, if he is arguing as a ''working physicist,'' good for him. This kind of appeal of authority still doesn't make him right.

Edited by Dubbelosix
Link to comment
Share on other sites

I don't see any trap he asked a valid question. Particles are not spinning balls the angular momentum term is an aspect of how to model the linear and angular vector symmetry relations under rotations.

The point like characteristic is defined by the Compton wavelength

Edited by Mordred
Link to comment
Share on other sites

5 minutes ago, Mordred said:

I don't see any trap he asked a valid question. Particles are not spinning balls the angular momentum term

That's a very big assumption you are making here, you are generalizing one rule for pointlike systems to objects in space which are clearly not pointlike. 

 

Do you know why points cannot spin? It's because they have to rotate 720 degrees just to get back to their original orientation. Clearly, when you have a system which is not pointlike, there is no need to assume ''instinsic spin'' in fact, spin is a non--problem for those kinds of objects. Atoms really do spin. You can't generalize a rule for pointlike fermions to all classes of particles and extended objects in spacetime. 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share


×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.