Understanding Electron Spins: A High Schooler's Guide”

[Henrcr]

TL;DR

Curious about electron behavior

I know this is a rather weird question but I'm in high school studying physics and chemistry and a lot of the content is pretty basic for what I aim to learn. One topic that I was curious about was electron spins and how that works, because correct me if I'm wrong but aren't they waves of energy so how are they spinning. Thanks in advance for any help! :) (I didn't know whether to post this here or under science and maths textbooks so I apologise for the double post)

 

[PeterDonis]

Hi @Henrcr and welcome to PF!

The term "spin" as applied to quantum objects like electrons is not to be taken literally. They are not little spinning balls. However, they are not "waves of energy" either. They are quantum objects, and there is no intuitive picture that will accurately convey what they are.

However, electrons and other quantum objects do have an observable that has all of the important properties of what we call intrinsic angular momentum, or "spin", when we apply it to ordinary classical objects like spinning balls. So we call that observable "spin" to reflect that fact.

We can also use states of electrons and other quantum objects that have definite values of the spin observable as a "basis" (this is a technical term whose definition I won't go into here--if you study quantum mechanics in more detail at some point you will learn it) for describing all of the possible states of those quantum objects. So sometimes you will see descriptions of, for example, electrons in atoms that attribute a "spin" to them even though no measurement of the spin observable is being made; what "spin" is referring to here is the spin basis states.

 

[Henrcr]

So, and correct me if I'm understanding this incorrectly, electrons do not infact "spin". The term spin is just a term used to describe their behavior or a certain attribute of the electron itself, But the word "spin" is used to allow the attribute to be easier understood?

 

[PeterDonis]

electrons do not infact "spin".

That's too vague to have a yes or no answer. If you mean "electrons are not little spinning balls", that's true. But if you mean "electrons have no property that has anything in common with little spinning balls", that's false.

 

[Henrcr]

That's too vague to have a yes or no answer. If you mean "electrons are not little spinning balls", that's true. But if you mean "electrons have no property that has anything in common with little spinning balls", that's false.

I apologise for the confusion.
What I meant was that it's not the fact that electrons are "spinning" as a tennis ball would or another object that we use the general term for spinning but instead there are similar attributes to the given action so the word "spin" is used. If I'm still incorrect then may I ask as to why the word "spin" is used if the action of the election itself does not follow the same or similar action of spinning as most people know. Otherwise I think I have a grasp of the topic.

 

[Nugatory]

If I'm still incorrect then may I ask as to why the word "spin" is used if the action of the election itself does not follow the same or similar action of spinning as most people know.

It’s mostly historical accident.

At the end of the 19th century, physicists generally expected that subatomic particles would be objects like we’re already used to, except smaller. That was a natural enough starting assumption: they knew that the same laws of physics worked with planets, boulders, pebbles, grains of sand, dust motes so had no reason to expect anything different at smaller scales. Thus when they first encountered quantum phenomena, before it became clear that quantum objects really were different, they tried to describe them using the same words they’d been using to describe classical objects... and many of these words stuck.

“Spin” is just one of these historical accidents. You’ll find that in quantum mechanics the words “particle”, “observation”, “observer”, “measurement” all mean something different than you’d expect from the plain-language meaning.

 

[PeterDonis]

why the word "spin" is used

Because the property of electrons that we call "spin" has enough in common with the property of ordinary spinning balls that we call "spin" that the term "spin" was chosen to describe the former when physicists were first figuring out how quantum mechanics works. The fact that electrons are not spinning balls does not mean, as I said, that they have nothing at all in common with spinning balls.

The more technical term for "spin" is "intrinsic angular momentum" (notice that I used that term in post #2), which contributes to the total angular momentum of a system. The spin of electrons does that just as the spin of a spinning ball does.

 

[PeroK]

I apologise for the confusion.
What I meant was that it's not the fact that electrons are "spinning" as a tennis ball would or another object that we use the general term for spinning but instead there are similar attributes to the given action so the word "spin" is used. If I'm still incorrect then may I ask as to why the word "spin" is used if the action of the election itself does not follow the same or similar action of spinning as most people know. Otherwise I think I have a grasp of the topic.

Spin is sometimes called intrinsic angular momentum (AM), because it's a fixed amount of angular momentum that an electron always has.

If you compare this with a macroscopic object like the Earth. The Earth has orbital AM from its orbit round the Sun and spin AM from its rotation on its axis. But, the spin AM is really just the orbital AM of all the rocks and stuff that make up the Earth orbiting the Earth's axis. So, in fact, these two types of AM are essentially the same.

The electron's spin is however fundamentally different from orbital AM; which the electron may also have from its atomic orbital, for example. Most notably, the magnitude of its spin AM about any axis you care to measure is a fixed (quantised) amount. It never varies, except there are two possible directions.

The name has stuck because the properties of spin AM are analagous to a spinning charge. For example, in classical EM a spinning charge has a magnetic dipole moment. And, because of its intrinsic spin, an electron has a magentic dipole moment.

 

[Henrcr]

It’s mostly historical accident.

Ohh okay! Thank you that makes a lot more sense now!

 

[Henrcr]

The more technical term for "spin" is "intrinsic angular momentum" (notice that I used that term in post #2), which contributes to the total angular momentum of a system. The spin of electrons does that just as the spin of a spinning ball does.

Sorry it took me a little while to take in and grasp the concept but I think I get it now. I still have a lot to learn! Thank you for taking the time out of your day to help me out it is really appreciated.

 

[Henrcr]

If you compare this with a macroscopic object like the Earth. The Earth has orbital AM from its orbit round the Sun and spin AM from its rotation on its axis. But, the spin AM is really just the orbital AM of all the rocks and stuff that make up the Earth orbiting the Earth's axis. So, in fact, these two types of AM are essentially the same.

Thank you for breaking it down for me so it was easier to understand! I really appreciate your help and thank you for your time!

 

[PeterDonis]

Thank you for taking the time out of your day to help me out it is really appreciated.

You're welcome!