User talk:Headbomb/Archives/2008/November

Thank you!

• Thank you for the barnstar! Anomie⚔ 14:45, 2 November 2008 (UTC)

Thunderbird2's disruptive editing

• I've started compiling a RfCU and because I'm really busy with work at the moment I'm looking for some help with diffs to support the claims. I'll be adding some over the coming days. Fnagaton 05:31, 4 November 2008 (UTC)

User:Headbomb/Sandbox4

• Does the new banner on User:Headbomb/Sandbox4 render the boxes correctly?Headbomb {^ταλκ_{κοντριβς} – WP Physics} 18:07, 5 November 2008 (UTC)

• Yes that looks fine, thank you.—RJH (talk) 18:33, 5 November 2008 (UTC)

Physics Question

• Hi! I had a quick question. There is an article an anonymous user has requested be posted. However, I'm not sure if it is legitimate. Could you look at Wikipedia talk:Articles for creation/Submissions/Wigner - 3D? It lists a lot of references, but I doubt is credibility. Thanks in advance! TN‑X-Man 16:56, 7 November 2008 (UTC)

knock knock! apology

• Thread begun with asterisk, as requested.
• Sorry I specifically referred to you as "arrogant" recently. I was dealing with some relatively serious levels of burnout. I am now on what is either semi-retirement, retirement or an extended wikibreak. Dunno, but editing cut way, way down for an extended period of time.
• Sorry again, good luck Ling.Nut ^{(talk—WP:3IAR)} 03:57, 11 November 2008 (UTC)

• Bah it's alright, I reacted pretty strongly myself.Headbomb {^ταλκ_{κοντριβς} – WP Physics} 04:45, 11 November 2008 (UTC)

e-p scattering/annihilation

[MOVED THREAD FROM Wikipedia talk:WikiProject Physics. --Steve (talk) 03:49, 13 November 2008 (UTC)]

There's these two images on wiki. Now it seems to me that these just aren't right. I'm gonna ask the graphic labs to fix them, but I just want to make sure that I don't end up looking like idiot in doing so.

What I'd propose for the fix is this:

e+        e-

     γ

e-        e+

instead of

e+        e+

     γ

e-        e-

Is that all right? Headbomb {^ταλκ_{κοντριβς} – WP Physics}

Feynman Diagram of Electron-Positron Annihilation

For one thing, when people talk about "electron-positron annihilation", they're not talking about either of those diagrams, they're talking about this one on the right. Your diagrams (regardless of the labels) both describe scattering. --Steve (talk) 01:28, 12 November 2008 (UTC)

Thanks for pointing that out. I should've picked that up, but for some reason I didn't.

• Concerning the EP annihilation diagram, isn't the "middle part" sorta useless? Why not simply go for a single vertex diagram?
• I am correct in assuming the proposed correction for the scattering diagram is fine?

Headbomb {^ταλκ_{κοντριβς} – WP Physics} 01:44, 12 November 2008 (UTC)

I'm not sure about your proposed changes. Here's what I would do.

(1) Make it clear that time goes from left to right. This could be done by editing the diagram, inserting a little arrow and label, as in Image:Feynmann_Diagram_Gluon_Radiation.svg. It could also be done in the caption. Maybe you were assuming that time was going bottom to top? Both conventions are used (for example look at the figures in Feynman diagram), but I think whoever made this diagram wanted time to go from left to right.

(2) Sort out the directions of the arrows. A proper Feynman diagram should have arrows pointing opposite the physical motion of positrons, and the same as the physical motion of electrons. If you do it right, every vertex has one arrow in and one arrow out. Anyway, I think you would want to switch both of the top arrows in both of the diagrams.

To answer your other question, for the annihilation diagram, the middle part can't be thrown out. The rules of Feynman diagrams say that you're only allowed to use certain vertices in your diagrams (the list of allowed vertices is determined by the standard model Lagrangian). The vertex where two electrons and two photons come together at one vertex, isn't on the list of allowed vertices. --Steve (talk) 05:39, 12 November 2008 (UTC)

I mean the single vertex diagram
e⁻
+
e⁺
→
γ⁰
, not
e⁻
+
e⁺
→
γ⁰
+
γ⁰
. See [1] and [2] for what I mean.Headbomb {^ταλκ_{κοντριβς} – WP Physics} 19:38, 12 November 2008 (UTC)

Oh. An electron and positron have to annihilate into at least two photons, not just one. Otherwise it's impossible to satisfy energy-momentum conservation. To see this, put yourself in the reference frame where the total initial (electron+positron) momentum is zero...then the outgoing photon would be stuck with zero momentum but lots of energy. :-) --Steve (talk) 19:46, 12 November 2008 (UTC)

Also such designations as
γ⁰
should be avoided, because it is a gamma matrix. Use
γ
. Ruslik (talk) 20:12, 12 November 2008 (UTC)

Well there's a lot of notations that looks likes a lot of other notation in physics, so that's rather moot to argue that we shouldn't write the charge on photons when its clear we're talking about particle processes. I mean, we wouldn't argue against writing He⁺ because it "might be" confused with the interaction of Hydrogen and an antielectron :P. As for the single photon vertice, I'm not quite sure what you're getting at. If you're arguing that the single photon diagram is wrong, then wouldn't the diagram posted by Sbyrnes up there be twice as wrong, since there would be two reference frames where a photon is stuck with zero momentum but non-zero energy. Headbomb {^ταλκ_{κοντριβς} – WP Physics} 02:49, 13 November 2008 (UTC)

And yes I'm making no distinction between real and virtual process, 'cause I'm crazy like that. If you're talking about pair annihilation in real processes then we're on the same page. Headbomb {^ταλκ_{κοντριβς} – WP Physics} 03:01, 13 November 2008 (UTC)

I think we're talking past each other, and also getting off topic. I'm taking the liberty to move this thread to THIS PAGE. --Steve (talk) 03:49, 13 November 2008 (UTC)

Thread is now moved

When an electron and positron turn into two (real) photons, there's no violation of energy-momentum in any frame. For example, in the center-of-momentum frame, the e and p have equal and opposite momenta, then the two outgoing photons have equal and opposite momenta. There's no frame of reference in which either of the photons has zero momentum, nor does there need to be. Conservation of momentum means that the sum of the momenta has to be conserved. With two photons, it works out consistently in every frame.

It's also OK for an e and p to turn into a single virtual photon. In the center of momentum frame, the virtual photon would have zero momentum and a lot of energy. And that's fine; real photons need to have their momentum times c equals their energy, but virtual ones do not have this requirement. There's nothing wrong with a momentumless virtual photon. But if it's a virtual photon, it can't exit the Feynman diagram. So it turns into (for example) another e and p. That's what happens in one of the scattering diagrams you show. You agree with all that? --Steve (talk) 03:56, 13 November 2008 (UTC)

Yup. Like I said, I didn't distinguish between real and virtual processes.Headbomb {^ταλκ_{κοντριβς} – WP Physics} 04:08, 13 November 2008 (UTC)

OK, as best as I can tell, we're in agreement about everything. --Steve (talk) 04:14, 13 November 2008 (UTC)

Same here. I'll contact the graphic labs to make the appropriate changes. Headbomb {^ταλκ_{κοντριβς} – WP Physics} 04:16, 13 November 2008 (UTC)

Telescope

I seen the history and you seemed to have an interest in the telescope article. There are currently some editors trying to revert a strong consensus made months earlier. You might want to check it out. InternetHero (talk) 04:36, 13 November 2008 (UTC)

(Noice day to) Start Again

It's the knoife wot dun it!

For your contributions on Magnetospheric eternally collapsing object, I award you the Billy Idol / Noice Day to Start Again award. Cheers! --Goodmorningworld (talk) 02:20, 14 November 2008 (UTC)

Thunderbird2 is forum shopping again

Thunderbird2 is forum shopping again. I don't have time to add it to the RfC right now but I might do later on. Work to do... :) Fnagaton 17:58, 20 November 2008 (UTC)

Troll feeding.

I saw that IP pushing for electrons as made-up fairytales on the electron page. May I suggest that we collectively ignore him/her?Headbomb {^ταλκ_{κοντριβς} – WP Physics} 13:36, 22 November 2008 (UTC)

Unfortunately the troll is persistent. I just took to archiving it's nonsense under Talk:Electron/Arguments. RJH (talk) 16:48, 23 November 2008 (UTC)

Regarding your comment at Thunderbird2's RfC

This comment should be moved to the RfC's talk page (see the section below it, entitled "Discussion", for a justification). Rather than act unilaterally, I thought it'd be more polite to ask if you wanted to move it yourself. SHEFFIELDSTEEL^TALK 20:24, 26 November 2008 (UTC)

Move it as you see fit.Headbomb {^ταλκ_{κοντριβς} – WP Physics} 23:37, 26 November 2008 (UTC)

Unicite

Hi, I applaud your efforts with Unicite - you seem to be doing most of the coding there. Just to let you know that I've been slowly converting the {cite whatever} templates so they all use the same template ({citation/core}) to generate their output. I've got {cite journal} doing this, and {cite book} is just about to follow. You may find that the path of least resistance is to modify other {cite whatever} templates to use this common core; the process is simple enough. Just thought I'd offer you that suggestion so we don't end up duplicating each other's work! All the best, Martin (Smith609 – Talk) 19:25, 29 November 2008 (UTC)

Yeah I know. I kinda abandoned unicite for that reason. The problem I have with working on the "citation core" is that there's no defined "goal", which is what I was trying to get with {{unicite}}, so it's hard to know what to modify and what to modify it too. There's also the additional problem that the page is locked from editing, and not being an admin, I can't edit it. I'd use my sandbox, but the multilayeredness of the citation core makes trying to do something about it complete hell.Headbomb {^ταλκ_{κοντριβς} – WP Physics} 19:35, 29 November 2008 (UTC)