Taqyon
sage
Reged: 06/17/08
Posts: 201
Loc: Cape Town, South Africa
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Silly question time again.
I was just listing to a podcast about the end of the universe and it struck me that the hydrogen atoms that we breathe and drink evey day, has been around since the beginning - over 13 billion years. During all this time, each atom has an electron spinning frantically around the nucleus non-stop. What drives this bugger? Why doesnt it slow down? Will it ever slow down? Did I fall alseep in high school physics?
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Hein du Plessis
8" Skywatcher Collapsible Dobsonian
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Dane B
super member
Reged: 02/23/08
Posts: 120
Loc: Seattle, Wa
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That's not a silly question at all!
I once asked a physical chemist a similar question - "what prevents an electron from falling into the nucleus". Because I had only minimal education in quantum mechanics he couldn't give me a direct answer, but what I took away from the conversation is that the question is flawed. While we can measure properties of the electron and get either a position or a velocity or an uncertain combination of both, the wavefunction that actually describes the properties of the electron do not yield specific locations or velocities and so it is incorrect to think of an electron as moving along a definite path.
Perhaps it is incorrect to think of the electron as moving at all. It exists in a superposition of states, and upon measuring we get information about one of those states, but that doesn't describe the electron in general.
Hopefully someone here can provide a more definitive answer...
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Meade DS-2130AT w/ GOTO
Nikon 12x50AEs
Without judgement what would we do? We would be forced to look at ourselves...
-Death
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Taqyon
sage
Reged: 06/17/08
Posts: 201
Loc: Cape Town, South Africa
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Thanks, wow.
I can see why Einstein didn't want to have anything to do with this 
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Hein du Plessis
8" Skywatcher Collapsible Dobsonian
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Joad
Wordsmith
Reged: 03/22/05
Posts: 11749
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Yes, there are all of these displays, especially in science and technology museums, showing a nice Rutherford atom with electrons whirling around nuclei in what look like tidy little solar systems. This image is imprinted in our minds. And it is wrong. Whatever is the actual atomic situation, I think, cannot be represented in any visual form.
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llanitedave
Humble Megalomaniac
Reged: 09/26/05
Posts: 9655
Loc: Amargosa Valley, NV, USA
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There is, however, the case that a neutron can decay into a proton and an electron (plus an anti-neutrino), and during the creation of a neutron star, electrons can be squeezed into protons to create neutrons.
So the question about what keeps electrons and protons apart isn't really meaningless.
And that question, I believe, is one of those that led to research into nuclear forces.
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Homebuilt 10" dob, old Coulter mirror.
16" Royce conical mirror: Construction on S.O.E. (Sauron's Other Eye) has officially begun!
Edited by llanitedave (07/11/08 11:53 PM)
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stefsaber
Post Laureate
Reged: 06/24/06
Posts: 4459
Loc: Rainy Florida
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Quote:
Yes, there are all of these displays, especially in science and technology museums, showing a nice Rutherford atom with electrons whirling around nuclei in what look like tidy little solar systems. This image is imprinted in our minds. And it is wrong. Whatever is the actual atomic situation, I think, cannot be represented in any visual form.
Indeed, after the Rutherford model numerous other scientists came along and modified the model of the atom. There is no specific straight forth planetary orbit for an electron circling an atom, instead just an electron orbit planetary cloud. Basically a region of probability where the electron can orbit. Based on the type of atom, monoatomic, polyatomic and the complexity of its geometric structure you get various electron clouds overlapping, and combining via different energy levels to create a complex structure.
So we can't really provide a precise visual image of the atom, but vaguely an estimation...
Electron Cloud...
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-Stefan
"It’s not the fall that kills you; it’s the sudden stop at the end." -Douglas Adams
Current Scopes: "Gator" William Optics 66SD---Black Swan William Optics Megrez 80 II ED Triplet---Zhumell 10" Dob
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Fort Myers, FL
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Dane B
super member
Reged: 02/23/08
Posts: 120
Loc: Seattle, Wa
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Quote:
So we can't really provide a precise visual image of the atom, but vaguely an estimation...
Electron Cloud...
For clarification, that is just one probability cloud for one to two electrons of a particular energy level (it is the d-z^2 orbital). The different colors correspond to different signs (positive/negative) of the wavefunction.
The electron(s) of this energy level are found to be within the volume of this orbital 90% of the time. As you can tell from the shapes of some of the more complicated orbitals, any consistent "orbit" you could imagine for an electron would have to be very convoluted to result in the electron being within the orbital's volume 90% of the time. The electron would have to constantly change speed and direction (ie accelerate). Because electrons have a mass, as tiny as it is, it takes energy to accelerate.
But the wavefunction producing the orbital/probability cloud does not require an input of energy to remain constant with time. That is why I don't think of the electron as moving, because any motion of an electron which stays within an orbital 90% of the time would be accelerated motion, which requires an energy input that the mathematics do not call for.
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Meade DS-2130AT w/ GOTO
Nikon 12x50AEs
Without judgement what would we do? We would be forced to look at ourselves...
-Death
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stefsaber
Post Laureate
Reged: 06/24/06
Posts: 4459
Loc: Rainy Florida
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Exactly, thanks for adding that bit...was in a bit of a rush this morning 
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-Stefan
"It’s not the fall that kills you; it’s the sudden stop at the end." -Douglas Adams
Current Scopes: "Gator" William Optics 66SD---Black Swan William Optics Megrez 80 II ED Triplet---Zhumell 10" Dob
-Sirius Mount---Canon Rebel XT-
Past Scopes: ETX 90---Vixen ED80Sf
Fort Myers, FL
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jupiterzkool
Pooh-Bah
Reged: 05/08/06
Posts: 1183
Loc: Pasadena, CA
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By coincidence, I saw this on another forum. The hydrogen atom on the iPhone.
-S
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Scott G. Edgington, Planetary Scientist
Cassini-Huygens: Mission to Saturn & Titan
Yes, Asia, John Wetton Fan
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UWastronomer
sage
Reged: 06/28/05
Posts: 268
Loc: Sammamish, WA
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Another interesting related topic:
Scientists have been pushing the limits in trying to make the shortest pulse of light possible. They think that it may be possible, with good fortune, that a pulse of light can be made which is shorter in duration than the predicted orbit times of electrons in certain atoms (probably larger ones with longer orbital times, not hydrogen), and take a "picture" of sorts to see if an electron or proton has a definite position with time. They'd probably get a blur, and it wouldn't really be an image in the conventional sense. They think they can get one pulse down to the orbital time of one electron around a hydrogen nucleus. It was a funny unit of time, like 22 yoctoseconds, don't count on my being completely correct. From what I remember, the shortest pulse was about two wavelengths, of whatever wavelength of light they were working with. Hopefully it wasn't shortwave. I imagine it was of a visible wavelength or less. Might be something interesting to look up.
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StarMax 127 + clock drive
12x45 binocs
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stefsaber
Post Laureate
Reged: 06/24/06
Posts: 4459
Loc: Rainy Florida
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Interesting indeed...one of the early 1900's scientists claimed is impossible to know both the direction and speed of an electron (Heisenberg Uncertainty Principle if memory serves me correctly) Though with increasing technological techniques and inventions the impossible barrier is quote often broken.
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-Stefan
"It’s not the fall that kills you; it’s the sudden stop at the end." -Douglas Adams
Current Scopes: "Gator" William Optics 66SD---Black Swan William Optics Megrez 80 II ED Triplet---Zhumell 10" Dob
-Sirius Mount---Canon Rebel XT-
Past Scopes: ETX 90---Vixen ED80Sf
Fort Myers, FL
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HiggsBoson
professor emeritus
Reged: 02/21/07
Posts: 708
Loc: Kal-li-fornia
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Quote:
I was just listing to a podcast about the end of the universe and it struck me that the hydrogen atoms that we breathe and drink evey day, has been around since the beginning - over 13 billion years. During all this time, each atom has an electron spinning frantically around the nucleus non-stop. What drives this bugger? Why doesnt it slow down? Will it ever slow down? Did I fall alseep in high school physics?
While you may have fallen asleep during high school physics this does not account for your confusion. It is likely that you were taught that the electron spins around the nucleus. Please consider the simplest case of the single electron in a hydrogen atom. Please do so because it is the only case that I understand.
This case, called the ground state of the hydrogen atom, the electron has no angular momentum. For clarity I will not refer to the quantum mechanical property of the electron called ‘spin’(1). This ground state is modeled by a wave function which is motionless relative to the nucleus. This should be confusing because they do teach that orbiting version in high school. This is how I learned it in high school.
In my first quantum class the first meeting started with an apology for all the lies that we had been taught up to this point. The lecturer said ‘ now I will tell you the truth’. Please leave your intuition at the door when you come to this class because you will not be using it here.
The most accurate description of the electron is a math model which predicts the probability of an observation. One may adopt the position that it’s shape is the shape of the electron or one may adopt the position that the electron does not have a shape. If one considers a surface of constant probability it will look like the shapes that they showed you in high school. Few high school teachers actually understand those drawings. If one chooses to take the shape of the function to be the shape of the electron then it has spherical symmetry, is centered on the nucleus and the peak of the function is in good agreement with the classical electron radius from the orbital picture.
You did not miss anything during your nap.
1) Spin in quantum is easer to think about if one considers it a type of polarization.
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Michael
ATM: 6" F/9 Newtonian Travel Scope
ATM: 12.5" F/4.5 Real Soon Now...
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Dane B
super member
Reged: 02/23/08
Posts: 120
Loc: Seattle, Wa
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Quote:
Another interesting related topic:
Scientists have been pushing the limits in trying to make the shortest pulse of light possible. They think that it may be possible, with good fortune, that a pulse of light can be made which is shorter in duration than the predicted orbit times of electrons in certain atoms (probably larger ones with longer orbital times, not hydrogen), and take a "picture" of sorts to see if an electron or proton has a definite position with time. They'd probably get a blur, and it wouldn't really be an image in the conventional sense. They think they can get one pulse down to the orbital time of one electron around a hydrogen nucleus. It was a funny unit of time, like 22 yoctoseconds, don't count on my being completely correct. From what I remember, the shortest pulse was about two wavelengths, of whatever wavelength of light they were working with. Hopefully it wasn't shortwave. I imagine it was of a visible wavelength or less. Might be something interesting to look up.
I thought up almost the exact same experiment just yesterday! In addition to their goal of seeing if one could track the electron, I would be interested in seeing if the electron could be located in two "distant" parts of the orbital within such a short time interval that the electron would have had to travel faster than light to actually move from one part of the orbital to the other.
A positive finding would be a pretty strong piece of evidence for the "the orbital is the electron" crowd.
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Meade DS-2130AT w/ GOTO
Nikon 12x50AEs
Without judgement what would we do? We would be forced to look at ourselves...
-Death
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HiggsBoson
professor emeritus
Reged: 02/21/07
Posts: 708
Loc: Kal-li-fornia
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Rather than comment on the experiment I will suggest that I do not understand the experiment.
Consider that the shortest pulse possible would consist of a single photon. One could not make a pulse shorter than that! If an electron is ‘orbiting’ a nucleus of an atom and you release your photon there are only two possible outcomes:
The photon does not interact with the electron. The photon would exit the experiment without returning to the imager and you have nothing in your photography.
The second case is where the photon interacts with the electron, knocking it into a higher energy state. The photon is gone and you still do not know where the electron ‘was’ in its orbit at the time of interaction with the photon. In this case it is possible for the electron to drop back to the same ‘orbit’ and omit a new photon. There is a possibility that the new photon will emit in a direction that allows it to encounter the imaging system. I submit that the location of the new photon in your image will tell you nothing about where the electron was in its ‘orbit’ at the time of interaction with the first photon.
I would rather believe that these guys actually do know what they are doing and that we may have insufficient detail in this forum to evaluate their efforts.
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Michael
ATM: 6" F/9 Newtonian Travel Scope
ATM: 12.5" F/4.5 Real Soon Now...
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Taqyon
sage
Reged: 06/17/08
Posts: 201
Loc: Cape Town, South Africa
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Wow, the complexity only increases.
"Please leave your intuition at the door.." Well put indeed! I love to work out theories that might fit observations, but common sense it seems does not apply on electrons.
I need at least 2 more lives to study what I really want;)
So, since there is no change of direction, and therefore no energy spent, the internals of an atom will be fixed forever it appears.
Thanks guys, you opened a window for me.
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Hein du Plessis
8" Skywatcher Collapsible Dobsonian
Celestron NexImage Webcam
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Edited by Taqyon (07/13/08 11:45 AM)
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Dane B
super member
Reged: 02/23/08
Posts: 120
Loc: Seattle, Wa
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Quote:
Rather than comment on the experiment I will suggest that I do not understand the experiment.
Consider that the shortest pulse possible would consist of a single photon. One could not make a pulse shorter than that!
I don't know about a short pulse; what I was thinking of was successively pinpointing the location of the electron repeatedly in as short a time as possible.
The position of an electron can be pinpointed with little uncertainty, as long as we accept a high uncertainty with regard to the electron's velocity.
You are right that the very act of measuring the position of the electron changes the position and energy of the electron, but I disagree with your conclusion that this means we cannot know where the electron was. I don't know how physicists determine the location of a quantum particle, but the uncertainty principle allows for the position to be determined with precision in exchange for knowing very little about the velocity.
If such an experiment were to show the electron following a path it wouldn't be a "natural" path like the one an electron follows when left alone, but it would still provide valuable information. And it would be especially interesting if the electron was located at two different points within such a short time period light would not have had time to span that distance.
Also, by changing the wavelength/frequency of the photons being used to probe the electron you also change the energy the photon carries. This energy can be calibrated to promote the electron into a particular orbital. If a highly unstable orbital is chosen the electron will immediately emit a photon and return to a more stable orbital. If the orbitals are chosen correctly it may be possible to have the electron drop into a more stable orbital so quickly that the photons never catch it in the excited state, and only yield information about the photon in one particular orbital.
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Meade DS-2130AT w/ GOTO
Nikon 12x50AEs
Without judgement what would we do? We would be forced to look at ourselves...
-Death
Edited by Dane B (07/14/08 06:14 AM)
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HiggsBoson
professor emeritus
Reged: 02/21/07
Posts: 708
Loc: Kal-li-fornia
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Hello Dave
Your quest to locate the position of an electron presupposes that an electron has a position. The only electrons that exhibit particle properties are those who have high energy such as an electron beam in a video tube. At lower energies such as the ground state of the hydrogen atom, one can not localize it's position to one side or the other of the atom because there is no evidence that it orbits at all. It's wave function is centered on the nucleus and is non-zero every where in the universe.
Yes, this is non-intuitive. The wave function describes the probability of an observation. An observation does not allow the electron to be undisturbed. In the situation you describe you wish to take a photograph of an electron. If the photon hit’s the electron, the electron will go to a different energy state. If the electron emits a photon later it can not tell you about the position of the electron prior to the high energy state.
An incomplete list of non-intuitive ideas from Quantum Mechanics:
- There is no such thing as a beam of light. Light consist of quanta that may not be subdivided.
- Electrons are not little balls that can cast a shadow in a beam of light.
- Electrons can have smaller wavelength than visible photons. This is why we use electrons for illumination in microscopes and can ‘see’ smaller things. Using visible photons to locate electrons is like using a Am football 10 yard chain set to measure the width of a needle. http://en.wikipedia.org/wiki/Electron_Microscope
If one shrunk a nikon coolpic camera and attempted to photograph an electron one would first observe that electrons are invisible. With no light on you would not see them. When the flash fires a burst of photons come out. If all of the photons miss the electron you would see nothing. You would think that your flash did not work because all of the photons moved away from you and did not return. If one photon interacts with an electron, it would move to a different energy state. You and your camera would still see nothing.
This situation is enshrined in the Feynman diagrams. It shows in infinite variation that when an electron meets a photon, both are changed.
Please do not feel that there is something preventing you from understanding this. This area is one of the reasons that physics has the reputation it has. Just hearing the results without the theory behind it does not facilitate understanding.
Quote:
As I explained in the first lecture, the way we have to describe Nature is generally incomprehensible to us.
Richard Feynman from his book QED where he was explaining the interaction between photons and electrons.
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Michael
ATM: 6" F/9 Newtonian Travel Scope
ATM: 12.5" F/4.5 Real Soon Now...
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Taqyon
sage
Reged: 06/17/08
Posts: 201
Loc: Cape Town, South Africa
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Michael
I think even I understand it.
Are we sure there is such a thing as a photon? Could it just be the wave of light energizing the electron and if energized sufficiently, it in turn will cause a tiny wave itself releasing its energy and returning to its ground state.
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Hein du Plessis
8" Skywatcher Collapsible Dobsonian
Celestron NexImage Webcam
7mm SWA 58° Plössl
My Jupiter|My Company
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HiggsBoson
professor emeritus
Reged: 02/21/07
Posts: 708
Loc: Kal-li-fornia
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Why would we doubt the existence of the photon? We see! We attempt to understand our ability to see and this drove us to quanta of light. The photoelectric effect suggest quanta rather than some other arrangement.
The photon is the thing that interacts with the electron and other charged particles. In other words to say that something is charged is to say it interacts with photons.
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Michael
ATM: 6" F/9 Newtonian Travel Scope
ATM: 12.5" F/4.5 Real Soon Now...
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Pess
Carpal Tunnel
Reged: 09/12/07
Posts: 1646
Loc: Toledo, Ohio
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I think the best description of an electron was that it was a probability function until it is looked at.
That means a single hydrogen atom with a single electron can have that electron positioned anywhere in the universe. there is an extremely high probability that it is in a described shell area around the proton but there exists also a very tiny probability that the electron is on the other side of the universe.
This probability 'collapses' when the electron is observed and its position definitely established...but the act of observing also disturbs other characteristics of the electron and so, at observation, it is not possible to define all the characteristics of that electron.
This leads to some really counter-intuitive predictions.
For example, if you place a barrier across an atom dividing it in half, the electron may be found on either side of the barrier (since there is an equal probability on which side it is on).
What gets weird is the electron can be found on one side and then the other while the barrier remains intact, thus the concept of 'tunneling' arises.
Quantum theory says there is a probability function which describes the likelihood of finding the electron in a certain locale. This likelihood is irrespective of the electrons ability to transverse the physical universe to get there.
Pesse (Hogan's Hero's had nothing on the old electron.) Mist
Edited by Pess (07/15/08 10:41 AM)
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