Wikipedia:Reference desk/Archives/Science/2024 June 25

= June 25 =

I'm looking for examples of "irregular" light, i.e. light carryiing "irregular" quantities of physical properties.
Such as light carrying an infinite wavelength, i.e. zero-frequency, i.e. zero-momentum, i.e zero-energy, and the like. For the time being, I'd like to ignore the property of velocity.

Is there any evidence of such irregular properties of any light? If no evidence, then what about any theory mentioning this kind of irregular properties of light, as a hypothetically possible option? Maybe when light unsuccessfully tries to escape a black hole? HOTmag (talk) 00:32, 25 June 2024 (UTC)
 * Weird stuff with light: Caustic (optics); Photon sphere; Atmospheric ghost lights, Fata Morgana (mirage); Electromagnetically induced transparency which also covers stopped light; Orbital angular momentum of light. Also Unruh effect where light appears if acceleration is great enough. Graeme Bartlett (talk) 09:34, 25 June 2024 (UTC)
 * Thank you. Do your examples include information about light carrying an infinite wavelength, i.e. a zero-amplitude, i.e. a zero-frequency? Please see my thread below. HOTmag (talk) 10:38, 25 June 2024 (UTC)
 * If zero-energy photons (or any zero-energy particles) exist, there is no way to detect them. If you think of particles as being an excited state of a quantum field, zero-energy particles are obviously not excited, so they are in fact not real particles. --Lambiam 10:28, 25 June 2024 (UTC)
 * Technically speaking, you are right. But please see my thread below. HOTmag (talk) 10:38, 25 June 2024 (UTC)

infinite wavelength, zero-amplitude, zero-frequency, and the like.
Our article Renormalization points out:

Every process involving charged particles emits infinitely many coherent photons of infinite wavelength, and the amplitude for emitting any finite number of photons is zero.

Do those hypothetical photons of infinite wavelength, i.e. of zero-amplitude, i.e. of zero-frequency, have a name? Is there any article where I can read about them? HOTmag (talk) 10:35, 25 June 2024 (UTC)
 * static electricity or magnets have an electromagnetic field with 0 frequency. Probably not the answer to your question though. Graeme Bartlett (talk) 10:57, 25 June 2024 (UTC)
 * The adjective evanescent describes an oscillating electric or magnetic field that propagates as an electromagnetic wave but has its energy spatially bound in the vicinity of its source. Philvoids (talk) 11:55, 26 June 2024 (UTC)

Salts at the borderline of Pourbaix diagram


For example, at the Pourbaix diagram beside, there is a borderline between Fe(3+) and FeO4(2-). Can a solution at that border be considered a solution of [Fe(3+)]2[FeO4(2-)]3, and if yes, can this salt be isolated?

More generally, if a cation and an anion touch in a Pourbaix diagram, do they form a salt? Nucleus hydro elemon (talk) 11:17, 25 June 2024 (UTC)
 * In this case it could not be the compound you suggest, as ferric oxide in itself is not alkaline enough to make the ferrate. So there would have to be some extra alkali around. On the line it could be either of the species from 0% to 100% and not necessarily in a 3:2 ratio to balance the charge. The charge is balanced by something like Na+ ions. In general it may be balanced by ions derived from water OH− or H+. Graeme Bartlett (talk) 11:56, 25 June 2024 (UTC)

I'm looking for an accepted or common term, for a free photon that hasn't been absorbed by matter yet.
Admittedly, I know I could simply say "photon" without adjectives, because if it had already been absorbed then it would no longer be a photon, but I still wonder if there's any direct adjective expressing more precisely the very fact - that this photon is still free - in the above sense. I think the term "free" photon is not sufficient. Maybe "unabsorbed" photon? HOTmag (talk) 16:05, 25 June 2024 (UTC)


 * Yes, I know that, but how does it answer my question? Have I ever claimed bosons and fermions belong to the same category? I asked about photons only, rather than about their whole category. HOTmag (talk) 19:43, 25 June 2024 (UTC)
 * You can say "propagating photon". Ruslik_ Zero 20:17, 25 June 2024 (UTC)


 * You could say "existing photon" (versus a no-longer-existing photon or a not-yet-emitted photon), but really, as you admit yourself, there's no need for such an adjective, so no such adjective is in common use. PiusImpavidus (talk) 07:59, 26 June 2024 (UTC)