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Procyan
2009-Mar-31, 04:29 AM
This has dogged me for years, I hope I'm missing something that I can understand:

an electron jumps from one orbital to a higher energy orbital when it absorbs a photon of the right wavelength. BUT it does not physically travel the intervening distance. :hand:

I understand that the orbital is really a probability "cloud", the electron is not a tiny black ball, that it can't be pinned down due to Heisenberg etc. But is it true that it disappears from one shell and instantly appears in another? :doh:

If so, I just want to float one idea, or question...

Whatever an electron may or may not be, it is a bit of matter. Soooo, isn't quantum leaping a "mundane" example of FTL travel? Or some weird wormhole magic? Happens everyday everywhere all the time. Not ATM. I'm not an ATM sort of bloke.

Nor am I trying to understand QM on an intuitive level. But this phenomenon is so often cited, so iron-clad, so we should be able to single it out for what it is. Which is what? FTL...I'm asking.

Jeff Root
2009-Mar-31, 01:01 PM
I think that the jump from one level to another is being considered too
literally. There is nothing to detect or measure during the jump, so it
has no meaning to say that the electron is in transit between levels.
Nothing FTL is involved, just a fundamental inability to see things that
are fundamentally unseeable. :)

-- Jeff, in Minneapolis

Cougar
2009-Mar-31, 02:15 PM
an electron jumps from one orbital to a higher energy orbital when it absorbs a photon of the right wavelength. BUT it does not physically travel the intervening distance. :hand:

I understand that the orbital is really a probability "cloud", the electron is not a tiny black ball, that it can't be pinned down due to Heisenberg etc. But is it true that it disappears from one shell and instantly appears in another? :doh:

I think part of the key is, as you say, the electron jumps when the atom "absorbs a photon of the right wavelength." There are only certain wavelengths that it will take. If the photon energy level is somewhere in between, the atom can't absorb it, and there is no jump. It's the whole idea of quanta and quantization - it only happens at discrete wavelengths. Discrete, as in not continuous. The atom can take in one level of energy or another, but not in between, and hence the electron is either at one level or another, but not in between. Whether this occurs instantaneously or at the speed of light, I don't know, but I do know that it would take an extremely short amount of time for light to travel the extremely short distance we're talking about.

Plus, remember, electrons are not just particles but also waves. They are in one quantum state, and with the absorption of a certain quantum of energy, the electron is suddenly in a different quantum state. I'm not sure that a "leap" through a certain distance is really the analogy to be using in the circumstance....

Procyan
2009-Mar-31, 10:26 PM
Thanks Jeff/Cougar. If I understand you perhaps I should think of two different electrons. A low energy electron "cancels out" simultaneously as a higher energy one materializes. Still weird but not FTL

Do you think humans will ever come to reconcile with QM in the sense that we understand a cup of tea or baking a cake, you know, gut level? Or will it remain the bearnaise sauce of physics, you never know for sure how it will come out, so you have to hope for the best :lol:

publius
2009-Apr-01, 12:46 AM
I think in QED that process can be modelled a bit more completely than in terms of a "jump" that we learn of in more elementary QM. Maxwell still holds (in the quantum form) and such a jump with an emission or absorption of a photon involves a change in the charge distribution which agrees with Maxwellian radiation processes.

While very fast, you still have a rearrangement of the charge distribution that occurs in finite time. That rearrangement will be a matter of probabilities and not deterministic certainty of course, but it's still there.

-Richard

Jeff Root
2009-Apr-01, 01:04 AM
Do you know whether, in QED, emission and absorption of photons are
considered to take some amount of time, or are considered instantaneous?

-- Jeff, in Minneapolis

publius
2009-Apr-01, 04:00 AM
As I understand it, it is not instantaneous. The before and after states are best thought of as an equilibrium with a very "fuzzy" transition period. Before you have an electron in higher energy level, and afterwards you have a lower energy electron and a photon. But there is brief period in between where things are fuzzy and you can't say what you have. But that period is finite.

As can be seen in Maxwell, you can't have an instantaneous rearrangement of charge. There would be infinite radiation reaction. While QED is far more complex than Maxwell, it still "respects" these principles.

I forget how it goes exactly, but you can see how some transitions are forbidden by these Maxwellian radiation principles. For example, consider a change from one spherical orbital to another. There could be no radiation dipole moment during such a transition (in terms of the change in charge distribution) and so it doesn't happen. Allowed transitions do have a dipole moment during the fuzzy period. :)

-Richard

astromark
2009-Apr-01, 05:17 AM
Understanding that these things are not particles of anything. What an electron actually is... um... its a ..., well err.. sort of, a energy particle wave form....
I have seen demonstrated the structure of iron. Right down at the atomic scale the distance from the nuclei to the orbiting electron. If the nuclei was scaled up to be as a football. The electron would be marble sized and 230 feet away. Now if at the atomic scale these thing move about very quickly. Changing that electron nuclei distance in the speed of An electron might be as the speed of light... Mathematical scaling tells me this is the rule in this universe. Nothing is instant.. It just looks that way.
This might help... Light as a photon at c if it could be made to orbit Earth it would be 7 revolutions in 1 second. Way down at the sub atomic scale that would be some Very, very small part of time to go about a nuclei. Any change in circumference at that scale would be hideously small...

Jeff Root
2009-Apr-01, 09:42 AM
As I understand it...
Your understanding must not be very good, because it agrees
completey with my intuitive understanding. Whenever you know
something, it always contradicts my intuitive understanding.



... it is not instantaneous. The before and after states are best
thought of as an equilibrium with a very "fuzzy" transition period.
Before you have an electron in higher energy level, and afterwards
you have a lower energy electron and a photon. But there is brief
period in between where things are fuzzy and you can't say what
you have. But that period is finite.
That's exactly what I was hoping, because it makes "sense" to me.

So the next question is: How does the transition period relate to
the period of the emitted or absorbed light? Is it the same?
Completely unrelated? Or what?

-- Jeff, in Minneapolis

papageno
2009-Apr-01, 09:54 AM
an electron jumps from one orbital to a higher energy orbital when it absorbs a photon of the right wavelength. BUT it does not physically travel the intervening distance. :hand:

This is because the jump is in energy, not in position.
If you look at the wavefunctions corresponding to different energy states, you can see that they actually overlap. Witout this overlap, the electron would not be able to change from one state to another.

Using an orbit analogy, an electron changing energy level is like a rocket that has fired its engines for a brief moment. The position has not changed significantly, but the kinetic energy has, and the consequence is that the rocket is now following a different orbit than before. That is, the rocket has changed state without jumping from one position to another in space.