Do Electrons Orbit the Nucleus Like Planets?

[Pollywoggy]

Today, I had an argument with my physics teacher about the movement of electrons around the nucleus. I have read way more quantum mechanics than any normal high school student and my teacher is trained as an engineer, not a physicist, but I am not sure if I'm right.

His argument was something like the following:
Electrons move around the nucleus much like planets around the sun. They move in an elliptical orbit. The centrifugal force is what keeps them from crashing into the nucleus.

I think it is possible that your teacher has been out of school for a very long time and he or she does not keep up with developments in the field.

 

[blechman]

I think it is possible that your teacher has been out of school for a very long time and he or she does not keep up with developments in the field.

He'd have to be out the the field a LONG time to not be up to date about how the Bohr model isn't correct! This is 1926 we're talking about!

 

[GDogg]

He'd have to be out the the field a LONG time to not be up to date about how the Bohr model isn't correct! This is 1926 we're talking about!

More like 1897 before the Larmor formula. That's not even the Bohr model. In his teacher's model the electron would radiate and lose energy as it orbits the nucleus. No centrifugal force would be able to keep it from crashing. That guy shouldn't be a physics teacher.

 

[jtbell]

In the USA, there are unfortunately many high school physics teachers who don't have a degree in physics, not even a bachelor's degree. Many of them were hired primarily to teach other subjects, and teach physics as a secondary duty. Most high schools don't offer enough physics courses that they can have a teacher who teaches only physics.

Many high school physics teachers probably have had only the freshman-level college/university "general physics" course, which has maybe a couple of weeks on relativity and quantum physics at the end of the course when everybody is exhausted and just looking forward to the end of the semester!

 

[Pollywoggy]

In the USA, there are unfortunately many high school physics teachers who don't have a degree in physics, not even a bachelor's degree. Many of them were hired primarily to teach other subjects, teach physics as a secondary duty. Most high schools don't offer enough physics courses that they can have a teacher who teaches only physics.

Many high school physics teachers probably have had only the freshman-level college/university "general physics" course, which has maybe a couple of weeks on relativity and quantum physics at the end of the course when everybody is exhausted and just looking forward to the end of the semester!

When I was in high school, one physical education instructor joked that we might see him teaching biology, a subject he knew little about. It's the same at community colleges in California, that a teacher can teach any subject, though this is not actually done at community colleges.

Realistically, I don't think we can expect someone who has a degree in physics to be working as a physics teacher in a high school. I don't think it matters if their degree is in English or physical education, so long as they know the subjects they are teaching.

 

[mendocino]

Can you tell me is there anything wrong with these two arguments using uncertainty principle?
If yes, what's wrong with it?

a) "We cannot know the precise position of an electron inside the bubble chamber because of the uncertainty principle, It is therefore impossible to establish electron path in it" and this argument
b) "We cannot know the precise position of an electron around the nucleus because of the uncertainty principle (note my name). It is therefore impossible to establish the electron as orbiting (elliptically) the nucleus.

 

[Peter Morgan]

How about "there's no such thing as a particle"? That's early in the chain of reasoning. Of course there is a line of isolated thermodynamic transitions from the metastable bubble chamber state to the bubble state, but does that mean that there is a single particle that caused that transition? It doesn't have to. Yes, there is something that causes the bubble chamber to make a transition from no tracks to one track, whatever the radiation source is, but it is the bubble chamber itself that makes the appearance of a track possible. No bubble chamber=no tracks.
The same argument applies to your a) and to your b). There is no particle, so there's no path. Thinking about QM and QFT in terms of <i>no</i> particles is a head-bending way to go --- but that's why it's intellectually productive.

 

[BoTemp]

Halfway

Your teacher is correct that the centrifugal force keeps the electron away from the nucleus...sort of. When you work out the orbits of planets, you get a 1/r^3 centrifugal term coming from the angular momentum. Something similar happens with an electron around a nucleus.

However, a planet can be well approximated as a particle with a definite location. An electron, at that level, is more like a spread out wave packet. In fact, if you look at the lowest state of a hydrogen atom, the wavefunction actually has a maximum at the origin! It's essentially exp(-r/ab), ab = Bohr radius. However, the centrifugal force keeps it from just sitting there.

 

[eep]

On the bubble chamber: the bubbles are *much* larger than the electron, hence the exact position of the electron is still unknown. In Heisenberg's autobiography "Physics and Beyond" he speaks about how he calculated the path of an electron in a bubble chamber still respects the uncertainty principle. The complaint at the time was something along "How do we not know the position of an electron in an atom, yet can see it moving through a bubble chamber?"