Do Electrons Orbit the Nucleus Like Planets?

[blechman]

I agree, I think that everybody should do more math and labs, but money and good programs are needed. If I wasn't so darn interested in research, I would want to teach high school physics. I guess I'll have to settle for university teaching. Either way, if ever I get a PH.D, I hope I'll be able to find the time to go into high school physics classes and talk to students. Frankly, I still do not know what a physicist REALLY does.

Heheh - what a wonderfully cavalier attitude toward "hav[ing] to settle for university teaching"! I'm sorry to say that such jobs are not easy to come by.

I would just like to point out: whatever you may think of my physics teacher, he really is a great guy, a great teacher and is very intelligent and accessible.

Yeah, I suppose I've said some nasty things about this nameless teacher based on what you've told us. Rest assured that it's nothing personal, but a symptom of the pandemic facing science education in North America (and the world). I"m happy you guys get along.

 

[Bork]

Well, I know of many (extremely good!) physicists who enjoy looking at balls and springs, and maybe they are madmen, but they're also some of the greatest physicists I know!

What I meant is that if high school kids are getting the impression physicists make careers out of clanking balls together on their desks and stuff like that, they're way off. Anyone who makes a career out of studying that stuff better be doing it in serious detail, down to the atomic level thermodynamic fluctuations, and hopefully they'd have some sort of industrial application in mind.

Anyhow, I don't see how a career in ball clanking would be any crazier than a career of telling hordes dressed in their Sunday best just who and what it is that "God" wants them to hate. That's just how it appears to the average Joe. Such is the state of backwardness in about 99.5% of the world.

But I do agree with you that science ed could do with some impovements: make sure teachers have MS in science (or at least a BS); offer and encourage continuing ed courses and make science teachers participate; offer plenty of career encouragement opportunities to students so they can see what's out there in science; I can go on and on...

But it is very hard to design a good class this early. You cannot really teach modern physics to high-schoolers - it's just not feasible unless it's a special school. And once again, even if you are really into "modern" physics, you still have to master the mechanics stuff - in the end of the day, that's what physics is all about!

Let me also say that it's not just the actual mechanics that must be taught: it's how to think! Physics (as I always say to my PreMed students) is the one real science subject where you learn how to THINK, as opposed to just memorizing and regurgitating. And this is a life-long skill. That is what high-school physics classes should be aimed at. If students are really interested in learning physics, they will learn all they need to learn in college. But it is so VERY important for the Joe Slobs of the high school who will never see a physics class again to learn how to think logically about the world around them. This may be the only opportunity they get. And that is what the high-school-level science class must try to cater to; the future Physics Professors will do fine.

Well, there is the occasional flicker of original thinking in medicine/biology on the abstract level. Think discoveries like the helical structure of DNA, or how hormones interact with cells; a lot of times there's scattered evidence and you need to construct a theoretical model to explain what's going on and guide the way forward. Nevertheless, this kind of thinking is the bread and butter of physics, whereas a lot of medicine is just "this is the way animals are wired. Brain goes here, tail goes there, and voila we have life!" Ok not quite so simple, but pure memorization/regurgitation directly from the data.

I remember when I was a freshman at science frosh, and I'm standing around having a beer and chatting with the fellow newbies I just met 6 hours ago. I was explaining what I wanted to do, and some butthead biology guy puts in his gab about how he doesn't think math is creative. Oh, has there ever been such creativity as one finds in math, in any other discipline? The sheer ignorance just offended me to the bone... I wanted to call the guy out right there and explain to him that he barely even knew what math was, but instead I was diplomatic about it, and he continued to act like a bonehead. I say roughly 50% chance the guy got pushed into an arts major after 1 year of pre-science math, but I didn't see him around much after a few months so who knows.

 

[blechman]

What I meant is that if high school kids are getting the impression physicists make careers out of clanking balls together on their desks and stuff like that, they're way off. Anyone who makes a career out of studying that stuff better be doing it in serious detail, down to the atomic level thermodynamic fluctuations, and hopefully they'd have some sort of industrial application in mind.

fair enough.

 

[Flatland]

high school science teachers never know what they are talking about. My high school astronomy teacher once told me that the universe had a center. HA!

 

[DaveC426913]

high school science teachers never know what they are talking about. My high school astronomy teacher once told me that the universe had a center. HA!

Ah yes, there's no humour like Astronomy humour.

"He's so dumb he thinks the ultraviolet catastrophe actually happened!"

 

[mendocino]

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.

My response was:
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.

I don't think "We cannot know the precise position of an electron around the nucleus because of the uncertainty principle". After all, how come we do see the tracks of electron in pictures of bubble chamber

I think what uncertainty principle say is this:
If you know the precise position of an electron, then the uncertainty of momentum will be very large or infinity

 

[blechman]

I don't think "We cannot know the precise position of an electron around the nucleus because of the uncertainty principle". After all, how come we do see the tracks of electron in pictures of bubble chamber

Except we don't know the precise position of the electron in a bubble chamber: all we see is the macrscopic bubbles left behind from the ionization of the medium by the passing electron - that's a VERY imprecise position measurement!

 

[mendocino]

Except we don't know the precise position of the electron in a bubble chamber: all we see is the macrscopic bubbles left behind from the ionization of the medium by the passing electron - that's a VERY imprecise position measurement!

Those tracks are good enough for particle physicists to figure out what particle it is.
We don't need to know where it is with 100% accuracy or 99.999999999999%

 

[blechman]

Those tracks are good enough for particle physicists to figure out what particle it is.
We don't need to know where it is with 100% accuracy or 99.999999999999%

absolutely, but put your comment in context: the question was about the position of the electron inside a hydrogen atom. Bubble-chamber resolution does not resolve this!

 

[staf9]

Apparently one can still win a Nobel prize with such a picture...

proof:

http://www.nobel-prize.org/EN/Peace/images/iaea.jpg



Regards, Hans.

Well, I don't know if

would look more aesthetic to the general public

EDIT: I'm really bad with MS paint!

 

[mendocino]

absolutely, but put your comment in context: the question was about the position of the electron inside a hydrogen atom. Bubble-chamber resolution does not resolve this!

But we can say "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/track in it", can't we?

-----------------------------------------------------------------------
>>My response was:
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.

 

[blechman]

But we can say "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/track in it", can't we?

I'm confused by this. We never MEASURE the position of the electron inside a bubble chamber! The electron flies through, and as it goes it creates a track of bubbles behind it. When we see the bubbles, the electron is long-gone! I don't understand what the HUP has to do with bubble chambers!

It is true (I am thinking at first glance) that there is a (theoretically) nonvanishing probability that the electron was not "in the track" left in the chamber. But this probability is exponentially small, and is essentially zero.

Compare this to the problem at hand: the question was about how an electron behaves inside a hydrogen atom. Now the electron is confined to a microscopic distance (roughly 1 angstrom) and the HUP can give you information about the size of the spread in radial momentum (as far as we're concerned, all you need is that it's non-zero and macroscopic compared to all other scales in the problem such as binding energy, etc). This fact alone tells you that the electrons cannot be thought of as living on circular (or elliptic) orbits. That's all that was said. I don't see anything wrong with this argument.

 

[mendocino]

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.

My response was:
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.

THAT'S NOT A VALID ANSWER: it's like to say "this is so, because so it is".

 

[Peter Morgan]

It surely is difficult enough to teach QM in universities because of the conceptual issues that inevitably arise. The most common answer that is ultimately given is to shut up and calculate, the only alternative being to disappear into the wormhole of "interpretation of QM". At the school level, the question of what all this mathematics means is surely even worse, because most high school kids are not enamored enough of mathematics of itself to be willing or able to accept that they should just do the math.
Special relativity is similar, though not in such an extreme manner, in that there is no widely accepted intuitively obvious reason why we should replace the Galilean group that seems entirely natural from our everyday experience with the Lorentz group. We just do it, pursue the math, and out comes answers that are empirically correct.
For many teachers, these philosophical issues are the kiss of death. Much of their teaching is the passing on of authoritative knowledge, from which the teacher derives authority, whether their teaching of it is terrible or not.
Conclusion: get an almost universally accepted interpretation of quantum theory to look more-or-less sensible to an average 16 year old, and to take teachers less than five years of research in the academic literature to figure it out for themselves, then teachers will have the time and inclination to throw the math at their high-school classes. This teacher appears to have tried to understand quantum theory but has (from this account, without him entering his own defence) failed ... why are we throwing stones?

 

[mendocino]

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.

My response was:
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.

The problem with this kind of argument is that the uncertainty principle won't apply to just one single variable(position), it's uncertainty about a pair of variables (position and momentum) that are complementary to each other

 

[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?"