Wikipedia talk:WikiProject Physics/Archive July 2012

Thermonuclear weapon

Hello,

I started a requested move of Teller–Ulam design to Thermonuclear weapon. Feedbacks are very welcome. -- Taku (talk) 23:57, 30 June 2012 (UTC)

These are not exactly the same topic because there are other possible designs for fusion weapons. For example, the fission trigger could be built in a sphere around the fusion core. Or Lithium deuteride could be replaced by other substances capable of fusion.

So I would suggest a more general article on thermonuclear weapons with a link to this particular design (which is the most commonly used). JRSpriggs (talk) 19:11, 1 July 2012 (UTC)

Don't we already have a general article at nuclear weapon design? That article already mentions fusion-boosted fission weapons (the spherical type), and links to Teller-Ulam design (from its "two-stage thermonuclear weapons" paragraph). In fact, the article looks well-written enough to be worth trying to polish to featured status IMO.

Regarding fuels other than lithium deuteride, that was only tried once to my knowledge (the Ivy Mike test). LiD turns out to be by far the most practical fuel for weapons. --Christopher Thomas (talk) 19:35, 1 July 2012 (UTC)

Escape velocity - scalar or vector ?

As part of a rewrite of sections of the escape velocity article, Zedshort (talk · contribs) wrote

"Escape velocity is a velocity in that it is the radial speed an object must have as it is directed radially away if it is to escape another mass's) gravitational pull. The escaping object may have an additional component of velocity normal to its radial velocity but in order to escape the planet's gravitational pull, it must have a speed in the radial direction at least as great in magnitude as the mass's "escape velocity"".

This idea that escape velocity depends on direction seemed to me such a fundamental error that I reverted their rewrite, explaining why on the talk page. In response, Zedshort says

"You are incorrect. Escape velocity is not just a speed but has a direction making it a vector quantity. The component of the speed in the radial direction must be equal to the escape velocity in magnitude."

To avoid a pointless back-and-forth argument, I would welcome other editors' input at Talk:Escape velocity#Reversion of rewrite. Gandalf61 (talk) 14:59, 2 July 2012 (UTC)

Proton spin crisis

This aritcle, Proton spin crisis, looks good to me but it is outside my scope of knowledge. I am hoping that someone who is well versed in this subject could have a look. I am seeing more self published articles on google scholar than anything else so I really don't know how mainstream this topic is. Thanks ---- Steve Quinn (talk) 19:18, 3 July 2012 (UTC)

The article seems plausible, and the editor that created it seems to be acting in good faith, but it might be a good idea to have someone very politely explain WP:COI to this person. They've spent quite a lot of time creating and revising Eliyahu Comay (edit | talk | history | protect | delete | links | watch | logs | views), and a paper from that person is cited as one of the references in the "latest findings about the spin crisis" subsection. Given that their username is Ofercomay (talk · contribs), it's raising flags for me.

That said, the user appears to know their field and be making what seem to be good contributions, so please do try to work constructively with them. WP:COI doesn't forbid writing about your own work (if that's what's happening here), it just says to be careful when doing it.

More thorough vetting would involve a particle physics type doing a literature search, to make sure that the references cited reflect the more prominent references in literature. I'm not in a position to do that. --Christopher Thomas (talk) 20:42, 3 July 2012 (UTC)

I am rather worried about the fact that the cited Comay paper is published in Progress in Physics. This tends to be a red flag for its contents not being widely endorsed.TR 21:41, 3 July 2012 (UTC)

As that and an arxiv preprint are the only references for the "latest findings" section, it's probably worth sticking a "needs improvement" template on that section and starting a talk page thread about it. A literature review would still be handy. --Christopher Thomas (talk) 22:27, 3 July 2012 (UTC)

Actually the other reference in that section is a PRL with over 50 citations. It is just the last bit that seems dubious.TR 06:36, 4 July 2012 (UTC)

Agreed. Xxanthippe (talk) 06:47, 4 July 2012 (UTC).

Would you mind updating the reference, then? The present citation gives no indication that the paper was actually published. --Christopher Thomas (talk) 06:52, 4 July 2012 (UTC)

huh? It says right there: " Interplay of Spin and Orbital Angular Momentum in the Proton. Physical Review Letters, 101, 102003 (2008)".TR 07:34, 4 July 2012 (UTC)

Apparently I'm more tired than I thought. I withdraw my comment. --Christopher Thomas (talk) 11:12, 4 July 2012 (UTC)

The Proton spin crisis is an important topic in physics with a substantial literature and deserves an article. The Comay paper does does not have enough cites in Google scholar to be considered a significant contribution to the subject (incidentally, it should be orbital, not spatial). Xxanthippe (talk) 23:02, 3 July 2012 (UTC).

Can we get some help at Time?

I have recently come upon the article Time and found that the lede definition (the very first sentence) was written strictly from the POV of experimental physicists, essentially saying that time is a measurement. The lede said nothing about how time is normally experienced by humans (and other beings) as, for lack of better words, our sequential progress in our existence. This is what is in the primary definitions of all three major English dictionaries. It's highly POV to require the lede definition of time to be defined only in terms of measurement. As if time has no meaning outside of measurement. Especially when it ignores the dictionary definition and especially when there exists a Time in physics article.

Primary definitions from 3 English language dictionaries:

thefreedictionary.com (obviously drawn from AH)

a. A nonspatial continuum in which events occur in apparently irreversible succession from the past through the present to the future.

b. An interval separating two points on this continuum; a duration: a long time since the last war; passed the time reading.

c. A number, as of years, days, or minutes, representing such an interval: ran the course in a time just under four minutes.

d. A similar number representing a specific point on this continuum, reckoned in hours and minutes: checked her watch and recorded the time, 6:17 a.m.

e. A system by which such intervals are measured or such numbers are reckoned: solar time.

Merriam-Webster Dictionary

a : the measured or measurable period during which an action, process, or condition exists or continues : duration

b : a nonspatial continuum that is measured in terms of events which succeed one another from past through present to future

American Heritage Dictionary

a. A nonspatial continuum in which events occur in apparently irreversible succession from the past through the present to the future.

b. An interval separating two points on this continuum; a duration:a long time since the last war; passed the time reading.

c. A number, as of years, days, or minutes, representing such an interval:ran the course in a time just under four minutes.

d. A similar number representing a specific point on this continuum, reckoned in hours and minutes:checked her watch and recorded the time, 6:17 AM.

e. A system by which such intervals are measured or such numbers are reckoned:solar time.

Oxford English Dictionary (1971 Compact Edition)

1. A limited stretch or space of continued existence, as the interval between two successive events or acts, or the period through which an action, condition, or state continues.

Can we get some help there at Time? 71.169.176.253 (talk) 14:45, 4 July 2012 (UTC)

Before anyone makes any drastic changes, I suggest digging through the archives at Talk:Time, as I remember a long-running debate about the topic from a few years back. If memory serves, most of the article was written from a philosophical rather than measurement perspective back then, though it's possible that I'm misremembering. Either way, most of the discussion should be happening on that page (and if possible contain a summary of the old threads about the debate for context). --Christopher Thomas (talk) 22:03, 4 July 2012 (UTC)

As of now, the lead begins with “It is difficult to substantiate that time is actually a sensation or experience.” I don't think that's the right way to start an article. (Before we reinvent the wheel, I'd suggest taking a look at articles about time on other encyclopaedias such as Britannica: what are they about?) A. di M. (talk) 08:59, 7 July 2012 (UTC)

Davisson-Germer experiment

Can somebody check if the image at Davisson-Germer experiment is ok?? I believe I have addressed the main points(see talk page for details). Please check if there is any correction/addition that needs to be done. Thanks. Roshan220195 (talk) 17:12, 4 July 2012 (UTC)

One more thing, "I would like to comment that the essential conclusion of this article is actually wrong according to Davissons and Germers original articles. Since Davisson and Germer worked with low energy elektron diffraction, LEED, it is not possible to use the Bragg equation in the way given in the article. This is due to the wavelength dependent refraction index of the nickel crystal." was a comment added in the talk page. Is this right?? — Preceding unsigned comment added by Roshan220195 (talk • contribs) 19:45, 4 July 2012 (UTC)

I don't have the expertise to tell, but it sounds like it could be a legitimate concern. If someone with a library near them digs up the original article about it, that should provide an easy way to check the wiki article's formulae. --Christopher Thomas (talk) 05:25, 5 July 2012 (UTC)

Unify articles on Ultraviolet divergence and UV completion

More than a year ago, a user suggested mergin Ultraviolet divergence and UV completion into an article titled Ultraviolet limit. Given that it's a very old proposal that's still standing, I hope that we can come to a solution on this soon, either to merge or to close the merge proposal, so I'd like to see your input on the suggestion, which can be found on this talk page. Thanks. Trinitresque (talk) 17:27, 8 July 2012 (UTC)