[Sarah Raphaella Rodgers]

Sarah Raphaella Rodgers asked the Naked Scientists:
   
I'm a 16 year old Chemistry student. My Chemistry class has been focusing on the periodic table recently. I know that protons are positively charged, neutrons are neutral, electrons are  negatively charged and that atoms are mostly empty space. I also know for magnets opposites attract.

So why don't electrons stick to protons instead of flying around the nucleus? Magnets do it, so why can't atoms?

What do you think?

[Mr. Scientist]

It has to do with the uncertainty principle. Because the electron cannot have a defined position in the nuclei of atoms means that it must occupy every other space within the atom in a wave of possibilities. If the electron was positioned with great certainty within the nuclei of atoms, their momenta becomes infinitely uncertaint. But instead, they seem to have energy-orbits inside of atoms which determine the chemical struture of the universe. Another interesting thing to note is that electrons could not be in the center of atoms, because if they where, matter would drastically sink in size.

We already know of nature objects which undergo this process, and they go by the name of neutron stars. In classical mechanics, electrons couple so strongly with protons that they should collapse all the time; and would in classical physics mean that every nucleus of every atom would gobble up the electrons in about 100 microseconds.

[Vern]

When I was 16 people like Einstein and Schrodinger were reassuring us that we need not worry; the Copenhagen interpretation and Quantum Theory were too weird to make any real difference. Now we are a half century into Physics becoming Quantum theory to the exclusion of reality even. Causality was abandoned because Quantum theory can't survive if we insist upon it.

There is a cause for quantum phenomena just as there is a cause for uncertainty.  Philosopher David Hume trashed causality with his view that no matter the times we observe an event and its precursor we can never be certain that such an event will follow a future precursor of the same nature. Philosopher Emanual Kant insisted that there is a cause for every event, however; it is just that we may never know that cause with certainty.

Edit: The cause of all quantum phenomena is that the electric and magnetic amplitude that space can support is a finite value; all photons peak at this value. Max Planck observed this. But because we did not demand causality, we imagined the Quantum nature of the universe without even considering its cause.

Uncertainty has been boiled down to the statement that it is impossible to know both the position and the momentum of anything absolutely. The more you know about the position of something, the less you can know about its momentum.

Books have been written about the implications of this. The link describes the cause of uncertainty. The quote below is the meat of it.

Edit: I should point out that the causes mentioned are my speculation; you won't find them in physics books. []

The electromagnetic fields that comprise a photon are in a state of constant change. This change drives the central point of a photon forward through space. We measure the photon's path to be that of the central point, but the fields exist spatially around the photon at an amplitude that is greatest close to the point and diminishes as the square of distance away from the point.
When this photon nears its target, churning electrons belonging to atoms in the target begin to sense the photon's approach. Some electromagnetic fields in the electrons will be in good phase relation with the approaching photon. Among this huge jumble of moving electrons, some will be more inclined to absorb the photon's fields than others. Those most inclined will probably not be dead centre in the photon's path.

[Vern]

So why don't electrons stick to protons instead of flying around the nucleus? Magnets do it, so why can't atoms?

The present state of physical science does not allow "why" questions. Any answer will have to be speculative. I have an answer to the question that works well for me.

There has never been found any substance of an electron that is smaller than its electromagnetic radius. This radius is much larger than a proton. So if observations are correct, and electrons only exist at their electromagnetic radius, they would consist of a hollow shell about 12 times larger than a proton. The electron would engulf the proton and form a dynamic dance with the proton's charges.

This is speculative, but it explains the observations.

[Homely Physicist]

It has to do with the uncertainty principle.

I'm afraid not. It's actually a result of two physical phenomena.


1) Pauli exclusion principle

This states that two fermions must be distinguishable i.e. you can always tell them apart. In practice, this means they must have at least one different quantum number. This restricts electrons into their shell structure. For example, consider hydrogen. The first shell (s- shell) has quantum numbers (1,1,1) and (1,1,-1). This is why two electrons, at most, can occupy the s- shell. These number combinations are easily derivable by solving the Schrodinger wave equation for hydrogen.


2) Entropy

Processes in physics tend to increase the entropy of the universe. Energy likes to go from ordered states to disordered (like how a ball wants to roll down a slope). A proton and an electron is more energetically favourable than a neutron. The decay of neutrons this way is known as beta decay. In order to 'squash' together a proton and an electron into a neutron you need to supply a large amount of energy, as well as overcome the electron degeneracy force (as you're probably going to try it with a large collection of atoms rather than waiting millions of years for a single electron to pair up). This occurs inside neutron stars.

[Vern]

Principles do not cause things; principles merely describe the happenings. We tend to think of principles and theories as causes; they can not be causes; their use is in describing the happenings. [] I'm just trying to keep folks honest.

[Mr. Scientist]

It has to do with the uncertainty principle.

I'm afraid not. It's actually a result of two physical phenomena.


1) Pauli exclusion principle

This states that two fermions must be distinguishable i.e. you can always tell them apart. In practice, this means they must have at least one different quantum number. This restricts electrons into their shell structure. For example, consider hydrogen. The first shell (s- shell) has quantum numbers (1,1,1) and (1,1,-1). This is why two electrons, at most, can occupy the s- shell. These number combinations are easily derivable by solving the Schrodinger wave equation for hydrogen.


2) Entropy

Processes in physics tend to increase the entropy of the universe. Energy likes to go from ordered states to disordered (like how a ball wants to roll down a slope). A proton and an electron is more energetically favourable than a neutron. The decay of neutrons this way is known as beta decay. In order to 'squash' together a proton and an electron into a neutron you need to supply a large amount of energy, as well as overcome the electron degeneracy force (as you're probably going to try it with a large collection of atoms rather than waiting millions of years for a single electron to pair up). This occurs inside neutron stars.

I am sure Hawking himself said the Uncertainty Principle had something to do with it.

Either way you're wrong, the pauli explusion principle has nothing to do with electrons falling into the nuclei of atoms. It's a process which eliminates one fermion energy level to another. This happens everywhere, not only inside an atom. And entropy also has nothing to do with it.

[Mr. Scientist]

Just in case you would like an example of the exclusionary principle ordinary in nature, it even happens when two electrons come close to each other in space. It's closely related to the wave function, which is actually one main reason why the electron does not fall into the nuclei of atoms; specifically because they are not located to any particular region of space, which would induce a collapse of their superpositioned states. They are ''arranged'' within their superpositioning because of energy levels. But the exclusion principle is not the prime cause of either the wave function or the fundemental reason why particles do not fall into the nuclei of atoms.

[Mr. Scientist]

I knew i was right. I came across this convo on the net:

If these particles are attracted to one another, shouldn't electrons be pulled into the nucleus? I gather the reasoning is because of the strong force? If thats the case i need to understand this "strong force" better..

Mizzuno

This question is actually addressed in the Feynmann lectures, which are linked to in the physics napster thread in the General Physics forum. The answer is:

What keeps the electrons from simply falling in? [The uncertainty principle]: If they were in the nucleus, we would know their position precisely, which would require them to have a very large, but uncertain, momentum, i.e., a very large kinetic energy. This would cause them to break away from the nucleus. They make a compromise: they leave themselves a little room for this uncertainty and then jiggle with a certain amount of minimum motion in accordance with this rule.

It wasn't really the answer I was expecting. I was previously under the impression that the uncertainty relations were only an expression of our own limitation as subjective observers of a subatomic event, but apparently they are actually an expression of a fundamental principle governing the behavior of small particles. If you're curious, the relation used here is:

\Delta x \Delta \rho \geq \frac{h}{2\pi}

Where
x = the position of the particle,
\rho = the momentum of the particle, and
h = Planck's constant
[\i][\b]

[Vern]

If you like to think that Quantum theory represents reality you have to invent excuses. Quarks can not exist outside nuclei, for example. Electrons dance to the uncertainty tune, etc. To me it is much easier just to accept reality as it presents itself.

[Mr. Scientist]

But it seems that we hve experimental evidence for these conclusions. If anything, i think reality has shaped physics for the larger part, not so much intentionally the other the way.

[Vern]

But it seems that we hve experimental evidence for these conclusions.

But we really don't. I started looking for experimental evidence for wave function collapse years ago. I'm still looking. None found. We have a habit of reporting our conclusions as experimental results. Sometimes it is hard to find the actual results that led the experimenters to their reported conclusions.

In every case where I have searched out the actual experiment the evidence was not there. The POS thought experiment Einstein and company proposed is still valid.

[Mr. Scientist]

We can measure decoherence, which is the gradual collapse of the wave function in wave-states of matter. We may not be able to directly observe the transformation because in doing so we disturb the p-field ''probability-field''. But, we know the collapse must occur as an actual transition from having matter acts as waves and then suddenly not.

[Vern]

But, we know the collapse must occur as an actual transition from having matter acts as waves and then suddenly not.

But this is what we don't know; this is the idea in contention. Does the observed state happen at the time of observation as in wave function collapse, or does the observed state happen at the time of creation of the particles, as in the POS experiment?

[Mr. Scientist]

But there is very little else that can happen. Given the intantaneous change from wave to particle-nature means that there is little room other than to say there is a sudden collapse. All models have agreed with observation.

[Vern]

We don't know that there is an instantaneous transition from wave to particle. We know that there is an instantaneous transition of a previously unknown state to a known state at the time of observation. We have not yet figured out how to know the state of the previously unknown state. 

In the simple case of a photon striking a target, my speculative model has changing fields driving two points of maxima of the fields. Interaction always occurs very close to the points of maxima; the fields determine the trajectory.

Edit: Bolded text was edited for clarification.

[Mr. Scientist]

Though, we have what we need to know about this state, and that is it acts in every way like a particle when its not being observed.

[Vern]

I can't argue with the success of Quantum theory. It is the only theory I know that demands a change in reality when reality does not agree with it. []

[Mr. Scientist]

I meant a wave by the way in the passage above - oops.

[Vern]

I don't mean to be contrary. [] I just need to explore every possibility that might offer experimental evidence that my vision of a photon is not reality. As far as I can determine the double slit experiment supports the vision. If I did not have the photon defined so that it must produce the observed results by cause and effect, I might fantasize some magical wave-particle duality.

The anatomy of a photon: A photon consists of two half cycles of electric and magnetic fields that drive points of maxima through space. The fields exist in a spatial area around the points. The changing amplitude of the fields drive the points and determine their path through space. Photon interaction happens at the points of maxima. So any observation will see the points. Edit: It is not my definition; it is Maxwell's definition.

What perplexes me is that folks don't seem to understand that. Is it that I just can't put the right words together?

Here's a schematic of the vision. It looks just like those that were in the text books when I studied electronics and nuclear instrumentation back in the 50's.