Talk:Hydrogen line

I've read through the source quoted for the currently stated value of the hyperfine transition of hydrogen, and while it is mentioned, the IEEE source actually recommends a different value which is the average of the two results obtained (aka 1 420 405 751.768(2) Hz).

I've also found another article from Nature Communications that states the other value as the 'literature value' here. Can I go change the current value (1 420 405 751.7667(9) Hz) to the value recommended by the IEEE publication (1 420 405 751.768(2) Hz)?

I'm new here, so sorry if this is a silly question or anything. Also, I can't find the Wikipedia policies for writing measured values (or, at least, it's not immediately obvious) - can somebody show me where it is?

MeasureWell (talk) 07:40, 21 June 2021 (UTC)

Edit 1: formatting.
Edit 2: more formatting.
Edit 3: even more formatting.

This article first gives a frequency for this Hydrogen line of 1420 (and some change) MHz which is 1.420 (ditto) GHz. But then it says,

This frequency falls below the microwave region of the electromagnetic spectrum, which begins at 3.0 GHz (10 cm wavelength)...

Is that correct? Yes, it falls below 3.0 GHz, which (according to other WP articles) is the top end of the microwave range--the cut-off between microwave and infrared (by some definitions, anyway). But then those articles give the other end of the microwave range (the border with radio waves, if microwaves are not considered radio waves) as 300 MHz. This puts the Hydrogen line within the microwave range. Or am I misunderstanding something? Uporządnicki (talk) 15:33, 20 April 2023 (UTC)

The wording up to 15 December 2021 was "This wavelength falls within the microwave region of the electromagnetic spectrum, and it is observed frequently in radio astronomy because those radio waves can penetrate the large clouds of interstellar cosmic dust that are opaque to visible light." This was changed to the current wording by an edit from some user showing only as an iP address on 15 December 2021.

This is yet another example of either clumsy editing or deliberate vandalism from somebody without an account. It plagues Wikipedia.

You might like to change the wording back to what it was before December 2021. TowardsTheLight (talk) 18:08, 20 April 2023 (UTC)

I should add that, yes, different sources define microwaves slightly differently, so there is ambiguity over whether 21cm, 1420 MHz, is in the microwave region or not. Perhaps describing the radiation as short-wavelength radio waves would avoid these issues. TowardsTheLight (talk) 21:19, 20 April 2023 (UTC)

@TowardsTheLight Sorry, this thing called "life" got in the way. Actually, looking things up (full disclosure: I'm doing all this "looking up" right here in Wikipedia), I see two things. First, the Hydrogen line is within both of the two definitions of Microwaves given in that article. I don't know about any other definitions. Second, the term "short wave" is even more informal, and subject to more definitions, than Microwave. I don't want to get too much into what might be described as OR (especially when the OR isn't, because it's right here). But I note that the line is in the UHF radio band. Perhaps I'll edit things to say that, and leave it there. Uporządnicki (talk) 16:59, 4 May 2023 (UTC)

And now, I see that the Hydrogen line falls within the ITU definition of UHF, but not the IEEE definition. Uporządnicki (talk) 14:45, 5 May 2023 (UTC)

Yes, according to the microwave article, 1.42 GHz lies inside the "300 MHz and 300 GHz" frequency range. The statement in the header contradicts the cited statement in the "In radio astronomy" section. The term "falls below" is vague and ambiguous wording in that context, so the statement needs to be clarified. Praemonitus (talk) 18:20, 5 May 2023 (UTC)

I was WP:BOLD and made an update to the statement. Praemonitus (talk) 13:48, 15 May 2023 (UTC)

Good. TowardsTheLight (talk) 16:14, 15 May 2023 (UTC)

If an "In popular culture" section were added it could reference the Star Trek TNG episode "Galaxy's Child" which refers to this phenomena

The article says:

When the spins are parallel, the magnetic dipole moments are antiparallel (because the electron and proton have opposite charge), thus one would expect this configuration to actually have lower energy just as two magnets will align so that the north pole of one is closest to the south pole of the other. This logic fails here because the wave functions of the electron and the proton overlap; that is, the electron is not spatially displaced from the proton, but encompasses it.

In my opinion it should be the opposite:

When the spins are parallel, the magnetic dipole moments are antiparallel because the electron and proton have opposite charges. This configuration has higher energy, much like two magnets forced into an opposing alignment. Just as macroscopic magnets tend to align their magnetic moments to reach a stable, lower-energy state, the electron's magnetic moment tends to align with that of the proton. Due to the opposite charges of the two particles, this stable configuration (aligned moments) corresponds to the antiparallel spins. ~2026-96646-1 (talk) 17:16, 12 February 2026 (UTC)