Light absorption and linewidth (split from A rational explanation for the dual slit experiment)

[bangstrom]

11 hours ago, swansont said:

Regardless of whether this can be demonstrated, “I don’t see” is not an argument that carries much weight. It’s argument from personal incredulity 

My "I don't see how" was a reply to a suggestion from  "studiot." I see no need for rigor.

[exchemist]

17 hours ago, swansont said:

It’s both. A floor wax and a dessert topping.

You have a process of entangling particles or creating particles that are entangled, and you have the state of entanglement 

Regardless of whether this can be demonstrated, “I don’t see” is not an argument that carries much weight. It’s argument from personal incredulity 

That's something I didn't know. I had not been aware of any process that starts with two unentangled QM entities and then entangles them. Have you an example?  

[studiot]

57 minutes ago, exchemist said:

That's something I didn't know. I had not been aware of any process that starts with two unentangled QM entities and then entangles them. Have you an example?  

The two electrons in a ground state hydrogen molecule are entangled (by spin).

The two electrons in two separate hydrogen atoms are not.

The process of bonding is also a process of entanglement.

 

But entanglement is really off topic for a discussion of linewidths related to quanta.

 

However this brings me back neatly to the question bangstrom keeps avoiding.

If an electron in a ground state hydrogen molecule absorbs em radiation, thereby being promoted to an excited state.

Which happens first ?

The absorbtion or the promotion ?

Or is bangstom promoting the idea that a system can exist in two different states simultaneously ?

Edited November 12, 2021 by studiot

[exchemist]

23 hours ago, studiot said:

The two electrons in a ground state hydrogen molecule are entangled (by spin).

The two electrons in two separate hydrogen atoms are not.

The process of bonding is also a process of entanglement.

 

But entanglement is really off topic for a discussion of linewidths related to quanta.

 

However this brings me back neatly to the question bangstrom keeps avoiding.

If an electron in a ground state hydrogen molecule absorbs em radiation, thereby being promoted to an excited state.

Which happens first ?

The absorbtion or the promotion ?

Or is bangstom promoting the idea that a system can exist in two different states simultaneously ?

Re entanglement, yes, I suppose bond formation could be an example of a process by which two unentangled entities become entangled. Good one.

Re absorption, I think referring to the link I posted on transition dipole moments may help. My understanding is that during the process, (speaking in crude, semiclassical terms) the electron's state becomes coupled to the electric vector and oscillates between the ground and excited states.  The energy of the photon will oscillate between the photon and the electron, too. Whether this process finishes in the excited state with absorption of the photon, or in the ground state with continuation of the photon seems to be a matter of the transition probability. (If I'm remembering Peter Atkins' lectures correctly, 45 years on, which I may not be.)

As I understand it (from those lectures), absorption is the limiting case of the process that that causes dispersion (in the sense of change of refractive index with frequency) at frequency ranges not too far from an absorption band. This is often described by a coupling of the electric vector of the light to the electrons in the medium, which " borrow" energy from it and give it back, altering the phase velocity of the light in the process. The dispersion of glass, for example is due to an absorption in the UV being not too far away from the frequencies of visible light. Glass with higher refractive index has a UV absorption closer to the visible than lower refractive index varieties. The light needs to be in a frequency range close enough to the absorption transition to to begin to mix the excited state into the electrons' state, temporarily, as the light passes. 

 

Edited November 13, 2021 by exchemist

[studiot]

I have a great deal of respect for Proff Atkins and several of his books.

Funny, when I was first at university most of the important names of british chemistry books were light blue, eg Moelwyn-Hughes.

 

One thing that I recall is the difference between classical and quantum systems.

You cannot divorce a quantum system from its environment, there are no 'free body diagrams' in QM.

[exchemist]

2 hours ago, studiot said:

I have a great deal of respect for Proff Atkins and several of his books.

Funny, when I was first at university most of the important names of british chemistry books were light blue, eg Moelwyn-Hughes.

 

One thing that I recall is the difference between classical and quantum systems.

You cannot divorce a quantum system from its environment, there are no 'free body diagrams' in QM.

Atkins wasn't yet a prof when I was there. He was a fellow at one of the colleges, Lincoln, I think, where he had a bit of a reputation as a tartar to his undergraduates. But he was a charismatic lecturer, amazingly, on quantum chemistry, the most abstract and mathematical supplementary option available on the course. My maths and QM tutor told me Atkins would get really worked up and nervous before he went on to give a lecture, just like any actor before curtain up. He had a certain bone-dry wit, which he somehow managed to introduce somewhere in every lecture. 

But we digress.............

 

[John Cuthber]

3 hours ago, studiot said:

I have a great deal of respect for Proff Atkins and several of his books.

Funny, when I was first at university most of the important names of british chemistry books were light blue, eg Moelwyn-Hughes.

 

One thing that I recall is the difference between classical and quantum systems.

You cannot divorce a quantum system from its environment, there are no 'free body diagrams' in QM.

Here is a page from Peter Atkins' book "Physical Chemistry" which refers to a particle in a box.
The purpose of the box is to exclude the environment. It's as close to a free body diagram as anything else.
He was a good lecturer, but his habit of producing new editions of the book was annoyingly good at dropping their re-sale value. That's why I still have mine from '84.
When I was there, Oxon had the largest chemistry department in the Western world.

[studiot]

32 minutes ago, John Cuthber said:

Here is a page from Peter Atkins' book "Physical Chemistry" which refers to a particle in a box.
The purpose of the box is to exclude the environment. It's as close to a free body diagram as anything else.
He was a good lecturer, but his habit of producing new editions of the book was annoyingly good at dropping their re-sale value. That's why I still have mine from '84.
When I was there, Oxon had the largest chemistry department in the Western world.

 

Seems to me that the 'environment' is shown at the sides (ends) of the waveforms using the standard ground symbols.

The particle in a box is certainly not isolated since it is in a box.

QM does offer an analysis of a body under no constraints ie a freely moving particle.

But then a free body diagram with no replacement forces is a bit trivial.

[swansont]

The purpose of the box is to provide the boundaries of confinement, so that have nodes for the wave function and you get quantized energy levels.

You get isolation from the environment by not including any interactions, because it’s a physics problem and there’s no mention of any other interactions. It’s not like it’s an actual experiment. It’s a generic particle in a box; we aren’t told if it’s subject to the EM or the strong interactions, (or gravity, for that matter) because it’s irrelevant to the problem what the confinement is due to. The potential term in Schrödinger’s equation doesn’t specify the source of the potential. 

 

[exchemist]

44 minutes ago, swansont said:

The purpose of the box is to provide the boundaries of confinement, so that have nodes for the wave function and you get quantized energy levels.

You get isolation from the environment by not including any interactions, because it’s a physics problem and there’s no mention of any other interactions. It’s not like it’s an actual experiment. It’s a generic particle in a box; we aren’t told if it’s subject to the EM or the strong interactions, (or gravity, for that matter) because it’s irrelevant to the problem what the confinement is due to. The potential term in Schrödinger’s equation doesn’t specify the source of the potential. 

 

Yes. My understanding is that you need the QM analogue of periodic motion to get quantisation. So the notional "particle" is reflected repeatedly from the ends of the box, or in rotating systems, e.g molecules, it revolves repeatedly, in both cases as a result of some form of constraint on the motion. With no constraint you get a continuum without quantisation, e.g as in ionisation limits in spectra.   

[swansont]

47 minutes ago, exchemist said:

Yes. My understanding is that you need the QM analogue of periodic motion to get quantisation.

Not periodic motion, as such, since motion is not directly implied. (it’s inferred by imposing classical notions on QM, and that usually ends up causing problems) QM avoids saying anything about trajectories in situations like the particle in a box. It’s one of the things that distinguishes it from classical, and also why free body diagrams are not part of QM. 

 

 

[John Cuthber]

4 hours ago, studiot said:

Seems to me that the 'environment' is shown at the sides (ends) of the waveforms using the standard ground symbols.

The  standard way of depicting mirrors in a ray diagram is a line with shading on the "back" of it.

https://en.wikipedia.org/wiki/Geometrical_optics#/media/File:Reflection_angles.svg

Interestingly, the  PIAB model works for a particle in the universe.

[exchemist]

2 hours ago, swansont said:

Not periodic motion, as such, since motion is not directly implied. (it’s inferred by imposing classical notions on QM, and that usually ends up causing problems) QM avoids saying anything about trajectories in situations like the particle in a box. It’s one of the things that distinguishes it from classical, and also why free body diagrams are not part of QM. 

 

 

Yup, that's what I meant by the QM analogue of motion: perhaps I should have spelled out that I meant the QM representation of what would in classical physics involve motion. I realise of course there are no trajectories in QM, even though there are still properties associated with motion (e.g. momentum).  

Edited November 13, 2021 by exchemist

[studiot]

I suggest another way of looking at it is to say that classical mechanics (of the sort we have been talking about) is about localisation, quantum mechanics is about delocalisation.

 

19 hours ago, John Cuthber said:

When I was there, Oxon had the largest chemistry department in the Western world.

I was at Loughborough in 1968, 69 and 70.

The Chemistry department was dwarfed by the Chemical Engineering department.

The Physics department was even smaller than the Chemistry.

But that is all a long story.

[bangstrom]

On 11/12/2021 at 4:56 AM, studiot said:

However this brings me back neatly to the question bangstrom keeps avoiding.

If an electron in a ground state hydrogen molecule absorbs em radiation, thereby being promoted to an excited state.

Which happens first ?

The question you asked me on Nov 9 was, “Re phrasing for absorbtion,

Are you telling me you that the electron can 'jump' before absorbtion takes place ?

Surely the fundamental question is

Which must happen first, absorption, or the electron transition ? “

 

The question strikes me as asking, Which came first, the shell or the nut? For one thing, you can’t tell precisely when the transition took place because of the impossibility of observing the event and the terms absorption and transition are essentially synonymous.

My answer was that I can’t possibly see how anyone can time the events.

I could have guessed and said absorption comes first. I suspect that is the answer you were looking for but that is not an answer I can support since I see the timing as unknowable. I have no idea where you are going with your “spectral lines” example so I expect you to explain whatever you are trying to explain.

The problem can be viewed theoretically as a problem of math and this has been done by Carver Mead. Carver Mead is a former colleague of Richard Feynman and well known for his innovative work with transistors and IC’s so I suspect he knows what he is talking about.

Mead's calculations are time-symmetric with waves going simultaneously forward and backward in time so the concepts of first and last are meaningless. The calculations can be found in the book “Collective Electrodynamics” by Carver Mead in Part 5 “Electromagnetic Interaction of Atoms.”

The time of duration in his equations is represented by the letter alpha. I don’t understand Mead’s calculations well enough to give a reliable explanation but it is obvious from his descriptions that he has moved on from photon theory.

 

On 11/12/2021 at 4:56 AM, studiot said:

The absorbtion or the promotion ?

Or is bangstom promoting the idea that a system can exist in two different states simultaneously ?

This is not quite what I am saying. I am saying that two separate particles with different quantum states can share a common existence as if they were side-by-side even though they may be light centuries apart. More specifically, an electron in one part of the universe can share energy with an electron in a another part of the universe by means of entanglement so long as they reside on the same light cone.

On 11/13/2021 at 4:23 AM, exchemist said:

Re entanglement, yes, I suppose bond formation could be an example of a process by which two unentangled entities become entangled. Good one.

Re absorption, I think referring to the link I posted on transition dipole moments may help. My understanding is that during the process, (speaking in crude, semiclassical terms) the electron's state becomes coupled to the electric vector and oscillates between the ground and excited states.  The energy of the photon will oscillate between the photon and the electron, too. Whether this process finishes in the excited state with absorption of the photon, or in the ground state with continuation of the photon seems to be a matter of the transition probability. 

Why can’t an electron in an excited state couple with an electron in a ground state and the energy be free to oscillate directly between the two? When the oscillation stops, the greater energy level will be randomly found either one or the other of the two electrons. If the energy lands in the formerly ground state electron...we have a transition.

With entangled electrons, there is no need for the transition to be local. The entangled electrons could be in atoms galaxies apart. From the perspective paired atoms, an electron in one atom drops to a lower orbital as an electron in the other atom simultaneously rises to a higher orbital. Energy is conserved and there is no separation of energy from matter. The “movement” of energy from one point to another in this view is cinematic like the lights on a moving sign board rather than moving through space. There is no need for the energy in one entangled electron to physically move through space to its partner electron in a ground state. The only motion takes place within the atoms themselves as an energized electron drops to a lower orbital in one atom as its ground state partner rises to a higher orbital in another atom.

It is my understanding that this is currently the best model for EM transmission and there are detailed explanations for how it works. The most elaborate model is John Cramer’s Transactional Interpretation TIQM. This is Carver Mead’s working model.

A non-local exchange of energy among charged particles not new idea. It can be found in the old Wheeler-Feynman Absorber Theory and in an article published in the Zeitschrift fur Physics by Hugo Tetrode in 1922.

“Suppose two atoms in different states of excitation are located near each other, normally it is to be expected that they would have little influence on each other; however, under special conditions with respect to positions and velocities, possibly also in the vicinity of a third atom, it might be that strong interactions occur. Such a situation could well lead to an energy transfer between atoms such that their excited states are exchanged.” Hugo Tetrode- Translation by A. F. Kracklauer.

Tetrode explained elsewhere in the article that the two atoms “under special conditions” can be solar systems apart so distance is no consideration. Tetrode also describes their common connection as a Schroedinger wave.

His “special conditions” appear to be what we now call ‘entanglement.’

[studiot]

10 hours ago, bangstrom said:

On 11/12/2021 at 10:56 AM, studiot said:

However this brings me back neatly to the question bangstrom keeps avoiding.

If an electron in a ground state hydrogen molecule absorbs em radiation, thereby being promoted to an excited state.

Which happens first ?

The question you asked me on Nov 9 was, “Re phrasing for absorbtion,

Are you telling me you that the electron can 'jump' before absorbtion takes place ?

Surely the fundamental question is

Which must happen first, absorption, or the electron transition ? “

 

The question strikes me as asking, Which came first, the shell or the nut? For one thing, you can’t tell precisely when the transition took place because of the impossibility of observing the event and the terms absorption and transition are essentially synonymous.

My answer was that I can’t possibly see how anyone can time the events.

I could have guessed and said absorption comes first. I suspect that is the answer you were looking for but that is not an answer I can support since I see the timing as unknowable. I have no idea where you are going with your “spectral lines” example so I expect you to explain whatever you are trying to explain.

The problem can be viewed theoretically as a problem of math and this has been done by Carver Mead. Carver Mead is a former colleague of Richard Feynman and well known for his innovative work with transistors and IC’s so I suspect he knows what he is talking about.

Mead's calculations are time-symmetric with waves going simultaneously forward and backward in time so the concepts of first and last are meaningless. The calculations can be found in the book “Collective Electrodynamics” by Carver Mead in Part 5 “Electromagnetic Interaction of Atoms.”

The time of duration in his equations is represented by the letter alpha. I don’t understand Mead’s calculations well enough to give a reliable explanation but it is obvious from his descriptions that he has moved on from photon theory.

 

On 11/12/2021 at 10:56 AM, studiot said:

The absorbtion or the promotion ?

Or is bangstom promoting the idea that a system can exist in two different states simultaneously ?

This is not quite what I am saying. I am saying that two separate particles with different quantum states can share a common existence as if they were side-by-side even though they may be light centuries apart. More specifically, an electron in one part of the universe can share energy with an electron in a another part of the universe by means of entanglement so long as they reside on the same light cone.

But, with all that waffle, you still have not addressed my question.

You have just tried to sweep it under the carpet.

I would hazard a guess that everyone else reading this thread can see that I have tried to ask the same question in different ways in order to try to make it as clear as  I possibly can. Rephrasing sometimes helps.

However you persistently address different questions, from the one I asked you.

10 hours ago, bangstrom said:

This is not quite what I am saying.

Of course not, you are answering a differnt question that you posed to yourself.

Easy sidestep.

10 hours ago, bangstrom said:

My answer was that I can’t possibly see how anyone can time the events.

 

Whether we are able to measure something or not has no bearing on that something itself.

It would still be the same, even if we did not exist at all to attempt a measurement.

So as not to appear grumpy and churlish I will offer a line of analytical thinking in more detail.

A great many of our achievements in Science and Engineering are founded on the technique considering a very small piece of something and then considering what happens to our theory when we shrink that piece to zero.

So consider an electron gaining energy by absorbtion, with a start time and a finish time separated by a very small time interval.
(Note I have not specified absorbtion of any type of EM radiation, just energy from whatever source.
Such non EM sources undoubtedly exist and are studied in basic physics.)

Now QM tells us that the electron cannot make the transition to the higher state until the entire quantity of energy is available, whenever that occurs.
Perhaps it cannot even start that transition until that point in time is reached.

So we now consider a transition of the electron with its own, yet to be defined, start and end points, which correspond to different states of the electron (by definition)

Put these together in a critical path analysis and then see what happens as you shrink either or both to zero.

'Instantaneous' would require both these very short time intervals to be exactly zero.

Which would imply that the electron is in two different states at once.

 

Still the same question, just with more detail.

Schrodinger asked it way back about his cat.

 

 

[bangstrom]

9 hours ago, studiot said:

But, with all that waffle, you still have not addressed my question.

You have just tried to sweep it under the carpet.

I would hazard a guess that everyone else reading this thread can see that I have tried to ask the same question in different ways in order to try to make it as clear as  I possibly can. Rephrasing sometimes helps.

However you persistently address different questions, from the one I asked you.

Of course not, you are answering a differnt question that you posed to yourself.

Easy sidestep.

 

Whether we are able to measure something or not has no bearing on that something itself.

It would still be the same, even if we did not exist at all to attempt a measurement.

So as not to appear grumpy and churlish I will offer a line of analytical thinking in more detail.

A great many of our achievements in Science and Engineering are founded on the technique considering a very small piece of something and then considering what happens to our theory when we shrink that piece to zero.

So consider an electron gaining energy by absorbtion, with a start time and a finish time separated by a very small time interval.
(Note I have not specified absorbtion of any type of EM radiation, just energy from whatever source.
Such non EM sources undoubtedly exist and are studied in basic physics.)

Now QM tells us that the electron cannot make the transition to the higher state until the entire quantity of energy is available, whenever that occurs.
Perhaps it cannot even start that transition until that point in time is reached.

So we now consider a transition of the electron with its own, yet to be defined, start and end points, which correspond to different states of the electron (by definition)

Put these together in a critical path analysis and then see what happens as you shrink either or both to zero.

'Instantaneous' would require both these very short time intervals to be exactly zero.

Which would imply that the electron is in two different states at once.

 

Still the same question, just with more detail.

Schrodinger asked it way back about his cat.

 

 

Thank for your lengthy response. I think I see the problem now and it applies broadly to this entire discussion- others included. As for your specific question, I have been answering it repeatedly but my answer was not what you expected so you didn't recognize it as an answer. You have just rephrased your question in words we both can understand, "Schrodinger  asked it way back about his cat." That's the question exactly.

My answer has been that an excited electron in one atom at the signal drops to a lower orbital as an electron in an atom at the receiver end rises to a higher orbital. It is a non-local exchange of energy among entangled particles. There is no time for an atom to absorb a quantum of energy from the outside because the absorption is entirely internal.  

It is unsettling to think that an atom at the receiver end has just as much influence over an emission of EM energy as an atom at the signal end but that has been an important part of modern theories of light since Wheeler and Feynman described light as a two-way wave-like connection between signal and receiver with waves going both forward and backward in time.

[studiot]

11 minutes ago, bangstrom said:

My answer has been that an excited electron in one atom at the signal drops to a lower orbital as an electron in an atom at the receiver end rises to a higher orbital. It is a non-local exchange of energy among entangled particles. There is no time for an atom to absorb a quantum of energy from the outside because the absorption is entirely internal.  

 

That is not, and never has been, the situation I described.

As it is clear you are not going to even attempt to follow my question, let alone begin to answer it, we are done here with your fairy tales.

[swansont]

24 minutes ago, bangstrom said:

My answer has been that an excited electron in one atom at the signal drops to a lower orbital as an electron in an atom at the receiver end rises to a higher orbital. It is a non-local exchange of energy among entangled particles. There is no time for an atom to absorb a quantum of energy from the outside because the absorption is entirely internal.  

Since the particles need not be entangled for an excitation, I concur that this is indeed a fairy tale.