Questions

[Little Bang]

The hydrogen atom can absorb a photon of a particular frequency and re-emit one of the same frequency, does the direction of the emitted photon have anything to do with the angle of incidence of the absorbed photon?

 

The helium atom has two electrons of equal ground state energy when it absorbs a photon does it emit one or two photons?

[CraigD]

The hydrogen atom can absorb a photon of a particular frequency and re-emit one of the same frequency, does the direction of the emitted photon have anything to do with the angle of incidence of the absorbed photon?

No.

 

A single atom, hydrogen or other, far from other atoms, can’t exhibit the quantum interference necessary to follow the laws of reflection, because there are electrons of other atoms for the photons wave package to interfere with.

 

Also, while a H atom may emit a photon of the same frequency it absorbs, it may also absorb several photons and emit a single one of higher frequency, or absorb one and emit several of lower. All quantum electrodynamics guarantees (and experiments verify) is that a H atom will absorb and emit only photons with frequencies corresponding to discrete changes of its electron from one level (orbital) to another. This is why hydrogen and other atoms have identifiable absorption and emission spectra, and why lasers can emit photons of higher frequency than those used to pump them.

The helium atom has two electrons of equal ground state energy when it absorbs a photon does it emit one or two photons?

The two electrons in an He atom independently follow the same absorption and emission laws as the single on in an H atom, so in cases where a single photon is absorbed, one of the electrons increases its orbital, then, if it immediately decreases to its previous orbital, emits one photon of the same frequency.

[Little Bang]

Thanks Craig. Can you suggest a text or site that I might educate myself?

[CraigD]

Thanks Craig. Can you suggest a text or site that I might educate myself?

QED: The Strange Theory of Light and Matter, a 1985 compilation by Feynman of 4 lectures he did in 1979, is often cited as an excellent, perhaps the best, text for the non-specialist.

 

If you find a legitimate online version of it, please let us know - I don't have it in paper or electronic form, and want to greatly!

[JMJones0424]

The wikipedia article you referenced said the lectures were originally given in 1979 in New Zealand, and the archived videos can be found at http://vega.org.uk/video/subseries/8

 

Looks like I have something to do this weekend, thanks! :)

 

Edit:

The book can be found at Scribd here:

http://www.scribd.com/doc/30975492/The-Strange-Theory-of-Light-and-Matter-by-Richard-Feynman

Edited November 18, 2010 by JMJones0424

[Ken]

No.

 

A single atom, hydrogen or other, far from other atoms, can’t exhibit the quantum interference necessary to follow the laws of reflection, because there are electrons of other atoms for the photons wave package to interfere with.

 

Also, while a H atom may emit a photon of the same frequency it absorbs, it may also absorb several photons and emit a single one of higher frequency, or absorb one and emit several of lower. All quantum electrodynamics guarantees (and experiments verify) is that a H atom will absorb and emit only photons with frequencies corresponding to discrete changes of its electron from one level (orbital) to another. This is why hydrogen and other atoms have identifiable absorption and emission spectra, and why lasers can emit photons of higher frequency than those used to pump them.

 

The two electrons in an He atom independently follow the same absorption and emission laws as the single on in an H atom, so in cases where a single photon is absorbed, one of the electrons increases its orbital, then, if it immediately decreases to its previous orbital, emits one photon of the same frequency.

 

 

Thanks for that clear explanation. I had naively suspected that Reflectivity could be scaled down to single atomic structure but never had the background (or the energy) to devote much thought to it.

 

My closest contact with photons was a function of graduate school replications of the Hect, Schlaer, & Pirenne analysis of Poisson distributions of photon levels necessary for determining absolute minimum threshold for human vision. I sort of :rolleyes: understood the statistics but the Physics of the experiment were beyond my comprehension.

 

BTW, their computation indicated that under ideal conditions about 7 to 11 photos received within a brief stimulation was an adequate stimulus. The fact that a dozen different teams of student replicators got matching data impressed the hell out of me.

 

Thanks, again.

[modest]

BTW, their computation indicated that under ideal conditions about 7 to 11 photos received within a brief stimulation was an adequate stimulus. The fact that a dozen different teams of student replicators got matching data impressed the hell out of me.

 

That's interesting

 

Here's an faq talking about it, http://www.phys.ncku.edu.tw/mirrors/physicsfaq/Quantum/see_a_photon.html

 

Cool stuff.

 

~modest

[Ken]

That's interesting

 

Here's an faq talking about it, http://www.phys.ncku.edu.tw/mirrors/physicsfaq/Quantum/see_a_photon.html

 

Cool stuff.

 

~modest

 

Great find.

 

One caveat... I'm not sure they emphasized enough that a transduction of photic energy into a neurochemical event can occur at single photon levels BUT no message is passed to the Central Nervous System until some multiple number of events occur within a brief duration.

 

I don't recall the PsychoPhysical methods used by H,S,&P. The FAQ author suggests a method called The Method of Limits where the stimulus is systematically lowered then raised to find the point of threshold perception. There are some procedural issues with that approach since you quickly develop an expectation that the next stimulus will be brighter or dimmer then the previous one. In our replications we used a method called the Method of Constant Stimuli which is really a procedure of presenting random intensities for hundreds of trials and then doing a frequency analysis on the data.

 

Being a subject in such an experiment (and we took turns) involved seating in an absolutely light-proof chamber, with bite-board with your dental impression locking your head into position, and continuing for around 3 hours to get enough data.. :blink:

 

Wikipedia has a good write-up on PsychoPhysical Methods.

[Rade]

OK, I have a few philosophic questions about this for anyone.

 

Could we say that the ability of the rods to "see" a single photon (but pass no message), would be an example of "sensation" of a primary energy stimulus of a single quantum of energy (that is, photon as particle as thought by Einstein) ?

 

Then, "perception" would be when some number of single photons (pi) as a set {p1,p2,p3...pn) forms an informational "message" that is passed on ? That is, the human does not perceive single photos, it only perceives a set of photons {p1,p2,p3...pn), and this is what is open to explanation--the set ?

 

Thus we can say the eye "sees" in two fundamental ways (1) via sensation, (2) via perception. So, it cannot be true that "seeing is believing", because any single photon we "see" via pure sensation can never enter any belief system via perception?

 

Sorry to be so abstract.

[Ken]

OK, I have a few philosophic questions about this for anyone.

 

Could we say that the ability of the rods to "see" a single photon (but pass no message), would be an example of "sensation" of a primary energy stimulus of a single quantum of energy (that is, photon as particle as thought by Einstein) ?

 

Then, "perception" would be when some number of single photons (pi) as a set {p1,p2,p3...pn) forms an informational "message" that is passed on ? That is, the human does not perceive single photos, it only perceives a set of photons {p1,p2,p3...pn), and this is what is open to explanation--the set ?

 

Thus we can say the eye "sees" in two fundamental ways (1) via sensation, (2) via perception. So, it cannot be true that "seeing is believing", because any single photon we "see" via pure sensation can never enter any belief system via perception?

 

Sorry to be so abstract.

 

An interesting question. I think the main issue is how one defines Sensation.

 

I've discussed it previously as though it was a two step process - Sensation producing Perception, but it's really best thought of as a three step process. 1) External stimulus in the form of some energy change (photic, thermal, etc.) in the external environment. 2) Transduction - a process where the energy change is detected and produces some modification in the receptor system and communicates that modification over distance to an effector system. And 3) an integrative system (which has components at the general receptor point as well as specific components "higher" up the Nervous System.

 

At the receptor, in rods for instance, a single photon of light that is absorbed by a molecule of Rhodopsin initiates a cis-trans change in the configuration of the molecule. That's all the Organic Chemistry I know B) but one result, as I understand it, is that a small change occurs in the cross-membrane potential. If a sufficient number of these potential changes occur within some short (millisecond) time interval they will summate and the Rod will pass a local current to the next layer of relevant retinal cells - the bipolars. If enough bipolar cells are stimulated with specific time and and area of retina a slow signal is passed to the Ganglion cells. Once a threshold voltage is reached in a ganglion cell a true nerve impulse is propagated up the optic nerve.

 

All of that is from a very specialized field of retinal electroneurophysiology and I am not up-to-date on the latest views, so the summation points I described might be pushed up or down a layer, but the conceptual understanding is pretty solid and has been since I was a Graduate Student.

 

Analysis can occur (low-level) at the layer of rods, bipolars, ganglion cells, mid-level at visual centers in Thalamus and projections to other visual centers and to the higher centers of the Visual Cortex in the Occipital Lobe of the brain.

 

Back to your initial question. I don't think it helps to describe a photon that is not absorbed by a molecule of Rhodopsin as having been "seen". For that particular photon the Rod is transparent. No absorption, no transfer of energy, no cis-trans transformation, no output from the Rod and by my definition no Sensation.

 

Your other comment about "Seeing is Believing" is the stuff that optical illusions are made of... They are errors of the selection of relevant stimuli from a huge panoply of competing or simultaneous stimuli and an interpretation of the those stimuli based on both neural circuits and past experience.

 

Hopefully this will give you another way to "see" what's going on. :D

[Rade]

Back to your initial question. I don't think it helps to describe a photon that is not absorbed by a molecule of Rhodopsin as having been "seen". For that particular photon the Rod is transparent. No absorption, no transfer of energy, no cis-trans transformation, no output from the Rod and by my definition no Sensation.

Thanks for the excellent reply. So, the tree when it falls really does make a sound if no one hears it. The situation is nothing more than energy not "absorbed" as sensation--if that would be the best term.

[Ken]

Thanks for the excellent reply. So, the tree when it falls really does make a sound if no one hears it. The situation is nothing more than energy not "absorbed" as sensation--if that would be the best term.

 

 

That's my story and I'm sticking to it.