If a single photon could be observed (detected in an appropriately instrumented
laboratory) as it is emitted from a change of energy level in an isolated hydrogen
atom, would it appear as a spherical modulation to the ambient electromagnetic
field or as a somewhat collimated beamed modulation or would it have some
different structure? :unsure:

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For those inclined to oppose human meddling with the structure of the universe or the composition and configuration of objects and groups of objects within the universe, consider:
Whether there is a limit to the magnitude of a modulation of chaos below which order remains invariant? Or, is order but a fiction invented by perspectives applied over finite, however large, time intervals?

Ha, good question. I say it would be cylindrical (like a segment of a collimated laser beam), with the ends sheared off flat (a precise Planck length)... I don't see how/why it would be spherical...?

Hi Gourdhead,
Bloody good question in the proper forum.

I would suspect that the great majority of us, notwithstanding our interest in astrophysics, don't even understand your question - and it is therefore very important that questions like yours should be given as a challenge to the more technically informed.

Congratulations! Hopefully we less-technically-informed may have a chance to learn - as long as the language is simply couched.

Since some new minds have been added to the forum over the last several months, could I have the question reviewed and some new opinions presented or directions to sources of information. I consider the nature of photons considered singularly and in concert essential in order to understand what telescopes are telling us and how to grasp the finest structure of the cosmos.

__________________
For those inclined to oppose human meddling with the structure of the universe or the composition and configuration of objects and groups of objects within the universe, consider:
Whether there is a limit to the magnitude of a modulation of chaos below which order remains invariant? Or, is order but a fiction invented by perspectives applied over finite, however large, time intervals?

If you read my Sine Wave post in Alternative Theories which, regrettably, is not acknowledged by regular UT Forum posters, I would say that all photons travel essentially in as straight a line as possible, but ignoring gravity, photons would travel with a spin as if on a double-helix part of a roller coaster.
Actually, virtual photons would have no true directional spin (rotation), so I'd imagine that is why photons are weightless (to a degree).

At v=c, doesn't matter elongate in the direction that it's travelling?
I am doubting then, that a photon would be spherical.
The extent to which it would be 'strectched' would be fascinating to observe.

Am I right in thinking this?

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Everyone rises to their own level of incompetance.

So a photon could be so stretched, it could be a "string" extending across the fabric of the cosmos!

Actually I believe mass is compressed in the direciton of travel and expands orthogonally to the direction of travel, but this does not apply to photons.

__________________
For those inclined to oppose human meddling with the structure of the universe or the composition and configuration of objects and groups of objects within the universe, consider:
Whether there is a limit to the magnitude of a modulation of chaos below which order remains invariant? Or, is order but a fiction invented by perspectives applied over finite, however large, time intervals?

Presumably because photons do not have mass? But if they have no mass, how can they have a shape as per your original question? If you could observe them, why would they have any particular shape if there is no mass to give them a shape?

Or does this not make any sense at Planck distances? Can anything be said to have a shape at this level?

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Spike
:)

If a photon were traveling along the x axis of a cartesian frame, (from a dim memory implanted in my mind during a college physics course) during a cycle at its frequency its electric and magnetic field vectors vary in magnitude in the yz planes from zero to maximum and back to zero during each half cycle and then reverse sign and repeat for the next half cycle. Has the model changed? At the time I was introduced to the model, although it crossed my mind, I did not critically question the implied contradiction that the higher energy photons, having the shorter wavelengths, have less time each cycle for the vectors "to grow" assuming they grow at the speed of light and would therefore embody less energy. Perhaps some of you have a better, more modern, model or a better understanding of the one I described.

In the initiating question I was trying to focus on whether the photon, a single photon as opposed to a packet of them, travels off in all directions from the isolated atom, and , if not, how is its direction of travel away from the atom determined?

__________________
For those inclined to oppose human meddling with the structure of the universe or the composition and configuration of objects and groups of objects within the universe, consider:
Whether there is a limit to the magnitude of a modulation of chaos below which order remains invariant? Or, is order but a fiction invented by perspectives applied over finite, however large, time intervals?

E = mc²
Photons must have shape, because they also have mass.
Am I missing something?

Ah, the 'mass' vs 'rest mass' question ... again!

This is one example of why it's important, when doing science (or discussing it) to be the world's most pain-in-the-neck nitpicker (a.k.a. pedant).

In working with Relativity, you can choose either approach - 'mass' is 'invariant' (e.g. 'the mass of the proton is ...') OR the 'mass' of an object depends on its speed (and so varies, depending on how fast you see that it's travelling), and the thing which doesn't change is the object's 'rest mass' (e.g. 'the rest mass of the proton is ...). You can do the math perfectly well either way, but you quickly get yourself tied in knots if you 'mix and match'. I understand that in most good courses on relativity, the 'mass is invariant' approach is used, because it leads to cleaner interpretations and is (generally) easier to work with.

Thus, 'the mass of the photon is zero'.

Of course, in common usage, as in English generally, 'mix and match' is the norm, and ambiguity rampant.In a word, no.

One thing to always remember about quantum theory (the most successful theory in science, BTW, by the number of decimal places its predictions match observation) is common sense is not included.

For example, millions of words have been written about the 'wave-particle dual nature' of photons (and other tiny things); much of this misses the point - 'the photon' is a construct in quantum theory! IOW, you can only 'understand' its nature by working with that theory. Now for most of us this is quite unsatisfactory, so clever people who do (more or less) understand the theory* write books trying to explain it all, in everyday English, to the rest of us*. Often this works well enough; many times though it leads clever people (who haven't 'done the math') to draw skewif conclusions.

So, one cannot 'observe a single photon as it is emitted from a change of energy level in an isolated H atom'. However, one can make a detailed description of a (thought) experiment, and describe what the results would be.

Would you like to have a go GOURDHEAD? I'll start with one: I 'measure' the wavelength of a high energy photon emitted from the electronic transition {detailed spec goes here; in layman's terms, an H-like jump, in a highly ionised Fe atom} by calculating it (using the Planck equation) from its observed energy, which I determine by using {insert detailed description of X-ray detector here}.

*For the record, I Nereid do NOT 'understand' quantum theory.

Isn't the concept of a photon being a particle, just that, a concept? We don't know what light is; we only describe it using terms and concepts we can understand, like thinking of light as a little package of energy (the photon). Yet when that's not convenient, we say it's a wave.

IMO, if we're not even sure if light is a particle or a wave or even if it's either at all, it will be hard to tell what shape it is.

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Nothing in life is good nor bad; thinking makes it so.

Why change the thought experiment to introduce an H-like jump in a highly ionized iron atom? Isn't a simple isolated hydrogen atom complex enough? After we digest such a thought experiment, we can start adding complexites. A more likely scenario might be electron/positron anihilation in a hypothesized chunk of true physical vacuum with each particle prior to the annihilation being free of significant kinetic energy. Later we could add sufficient kinetic energy to the particles prior to annihilation to cause the resulting photon to have sufficient energy to decay into a proton/anti-proton pair and discuss whether the laws of physics would allow this. If it is not allowed, how is it prohibited? Would the electron and positron, due to their kinetic energy caused by their velocities relative to each other, cause them to change into a protron and an anti-proton within a few planck times of the annihilation event?

After this we could introduce the complexities arising from having our initial particles travel through a "sea" of virtual particles (indeed how could it ever be avoided if such is the nature of the virtual vacuum) with a large range of kinetic energies as a test probe to determine what could be learned about the density and frequencies of occurences of virtual particles...at least at the limits.

And emboldened by our success so far, we can design the experiment to investigate non-locality and "knowability" of each particle with respect to the other. See this,
this,and this. Having thus established a baseline dataset we would then be ready to investigate the Lens-Thirring effects of super massive black holes by having the initiating event take place at various longitudes, latitudes, and altitudes with respect to the event horizon of the SMBH.

Alas! each aspect of this is beyond my capabilities.....even as a thought experiment.

__________________
For those inclined to oppose human meddling with the structure of the universe or the composition and configuration of objects and groups of objects within the universe, consider:
Whether there is a limit to the magnitude of a modulation of chaos below which order remains invariant? Or, is order but a fiction invented by perspectives applied over finite, however large, time intervals?

first of all, due to the dual nature of the photon, relativistic effects can be forgotten.
secondly, it should be remembered that a photon is the smallest amount of energy that can be present.let it carry energy=E
So we cannot observe it with any energy<E.
if we observe it with energy=E, we will get (due to the dual nature) an interference pattern.
if we use energy>E, the uncertainty principle would come into play& we will only get a probabilitic distrubution pattern of the photon.

i hope i'm talking sense.

This brings the question whether there is a photon of least energy and an associated question of whether there is a photon of such low energy that its wavelength subtends the entire universe. Here we assume there was a big bang and the resulting universe is of finite size and time duration although each of these is much larger than the observable universe and the time for which observations are germain, respectively. Also, where in the domain of photon energies would the various neutrinos fall? ...Well up from the low end I would imagine.

__________________
For those inclined to oppose human meddling with the structure of the universe or the composition and configuration of objects and groups of objects within the universe, consider:
Whether there is a limit to the magnitude of a modulation of chaos below which order remains invariant? Or, is order but a fiction invented by perspectives applied over finite, however large, time intervals?

As aelous said, we do not fully understand what a ohton actually is. And we cannot measure a single photon. We cannot measure anything. We can only measure its effects. With a photon we can only detect its prescence by detecting its energy when it collides with a sensor. For example you cannot see a laser in a vacuum, because none of the phtons are hitting your eye.

As such we cannot detect the shape of a photon because to detect it we need to absorb its energy (which will not proveide a shape anyway). We could try and shine a laser beam on it, but the interaction would be on the wave of the photon, not the particle.

A phton would not have a defined shape because it has a width/radius of 0. So it is of all shapes, and of none.

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When an atom changes energy states, something happens and propagates through spacetime. This something is of non-zero value in each dimension of space and duration of time. How can it avoid having a shape, fleeting though it may be.

__________________
For those inclined to oppose human meddling with the structure of the universe or the composition and configuration of objects and groups of objects within the universe, consider:
Whether there is a limit to the magnitude of a modulation of chaos below which order remains invariant? Or, is order but a fiction invented by perspectives applied over finite, however large, time intervals?