Wikipedia talk:WikiProject Physics/Archive February 2009

dark fluid

It needs some attention. Uncle G (talk) 01:51, 20 January 2009 (UTC)

• I added some references. It may be non-notable, but at least it's not flagrantly non-notable...At the very least, I found three Phys. Rev. articles on this topic by three different groups. Maybe there's a lot more, maybe not. But so far, I haven't seen anything that definitely establishes notability, so it may be a good candidate for deletion. --Steve (talk) 04:33, 20 January 2009 (UTC)

One problem that needs expert attention, that we haven't addressed yet, is that there are (or seem to be, after a cursory search) several different dark fluid hypotheses in physics, in addition to the one that the article currently discusses. (Apparently, several people separately groped for some new word other than "energy" or "matter", and all came up with "fluid".) Uncle G (talk) 00:41, 1 February 2009 (UTC)

Merge constant of motion and integral of motion

To the best of my knowledge these to are synonyms. (Or is one or the other used more broadly?) So, there is a clear case for a merger. The big question is which name should be the main article. Any thoughts? (TimothyRias (talk) 09:19, 30 January 2009 (UTC))

Talk:Constant of motion#Merge proposal. - Eldereft (cont.) 13:41, 30 January 2009 (UTC)

My impression was that (contrary to what the article says) "integral of motion" means any quantity which can be defined by integration and is independent of the path of the integration. For example, the section Kinetic energy#Derivation says "Since this is a total differential (that is, it only depends on the final state, not how the particle got there), we can integrate it and call the result kinetic energy". So kinetic energy is an integral of motion, but not usually a constant of motion. JRSpriggs (talk) 08:37, 31 January 2009 (UTC)

Well, that is not what mathworld says, nor is it the way that I have seen the term used. I think it is actually mostly question of which field you are working in. Physicists tend to call these constants of motion, will mathematicians talk about integrals of motion. (TimothyRias (talk) 06:43, 2 February 2009 (UTC))

Milestone Announcements

All WikiProjects are invited to have their "milestone-reached" announcements automatically placed onto Wikipedia's announcements page. Milestones could include the number of FAs, GAs or articles covered by the project. No work need be done by the project themselves; they just need to provide some details when they sign up. A bot will do all of the hard work. Click here for more information or to sign your project up.

I thought this WikiProject might be interested. Ping me with any specific queries or leave them on the page linked to above. Thanks! - Jarry1250 ^{(t, c)} 22:13, 1 February 2009 (UTC)

Black hole information paradox

Does anyone feel like dealing with Iron Condor, and with the article itself? I don't. Thread here: Talk:Black hole information paradox#Completely false premise. -- BenRG (talk) 20:05, 2 February 2009 (UTC)

Gravitational wave#Gravitational wave detectors

I just started trying to clean up this article, and another editor has twice re-inserted the paragraph:

Although most scientists would agree with Professor P. J. E. Peebles, who declared "Gravitational waves exist…," some scientists disagree. Professor Irwin I. Shapiro more cautiously wrote: "Should we now conclude that the existence of gravitational radiation has been established? Probably not."

Before I embarass myself, can someone take a look to see if this really belongs? Please keep in mind that our treatment needs to follow the preponderance of our most reliable sources, bound by WP:WEIGHT. Certainly the limitations of various detectors are appropriate (and I think made clear), but is this the correct section and the best way to treat the fact that there is still some reasonable doubt regarding whether the observations thus far made are best explained by gravitational waves? - Eldereft (cont.) 14:56, 4 February 2009 (UTC)

What do you all think about the title of Euclidean vector?

Don't you think that some other title might be better? -- Army1987 – Deeds, not words. 20:35, 1 January 2009 (UTC)

Yes. When I saw it, it wasn't clear to me what Euclidean was meant to specify. Better is Vector (physics) but I wouldn't be surprised if I liked something better that someone came up with. That's because abstract vector spaces are used in physics too, like the bras and kets in quantum mechanics. Although, I think the vast majority of people would think that Vector (physics) meant direction and magnitude rather than abstract vector. Maybe Vector (direction and magnitude). Good luck. --Bob K31416 (talk) 21:10, 1 January 2009 (UTC)

A (not-too-serious) problem with "direction and magnitude" is that, given a vector v of any normed vector space, no matter how abstract, one might refer to ||v|| as the "magnitude" of v, and to v/||v|| as its "direction". (Or mightn't he?) I like Vector (physics) because they are the ones a physicist is most likely to be referring to when using the term vector without adjectives (e.g., as for kets, I prefer to call them "state vectors" or even just "states"), but I'd be happy if someone was able to come up with a better title.

As for the current title, I think Euclidean vector space also applies to abstract spaces (I guess it applies to any finite-dimensional inner product space over R isomorphic to Rⁿ with the dot product). -- Army1987 – Deeds, not words. 21:52, 1 January 2009 (UTC)

Re "A (not-too-serious) problem with "direction and magnitude" is that, given a vector v of any normed vector space, no matter how abstract, one might refer to ||v|| as the "magnitude" of v, and to v/||v|| as its "direction"." - "One might" but does one? --Bob K31416 (talk) 01:08, 2 January 2009 (UTC)

From experience, I've seen many people and books that would refer to direction as v/||v||, especially in generalizations to higher dimensions. It was relatively common in my 3rd and 4th year of my bacchelor's degree and in my master's classes. About as common as writing a central force F = kr / ||r³|| instead of F = ku_r / r². I would not expect people to immediately recognize it as such however. Headbomb {^ταλκ_{κοντριβς} – WP Physics} 06:29, 6 January 2009 (UTC)

Army1987 (above) had a very good point: it is the [b]space[/b] not the vector that is Euclidean. Referring to the vectors themselves as Euclidean is only going to encourage confusion. After all: a 4-vector is a vector in a 4D Euclidean space too, but we just don't consider that Euclidean space interesting: it is the interval, not the Euclidean metric, that has physical significance.

Besides: shouldn't we be getting the reader ready for the revelation that what he calls 'vectors' in freshman physics classes si really a contravariant tensor of rank 1? 67.95.202.34 (talk) 04:41, 7 February 2009 (UTC)

Einstein, acceleration and g-forces

Could we have some knowledgeable input at Talk:G-force#Disputed tag please? --John (talk) 23:38, 19 January 2009 (UTC)

Does an accelerometer measure the vector sum of gravitational and accelerative forces? --John (talk) 07:51, 20 January 2009 (UTC)

As Wolfkeeper said, it measures the part of the acceleration which is not due to gravity, that is, the total acceleration minus the acceleration due to gravity. JRSpriggs (talk) 09:36, 21 January 2009 (UTC)

Doesn't that contradict general relativity? How does an accelerometer "know" what part of the force it measures comes from gravity and what part from acceleration? --John (talk) 14:14, 21 January 2009 (UTC)

No, it doesn't contradict GR. For example imagine the simplest case where an accelerometer in space next to the Earth. From the accelerometer's point of view, it isn't moving at all.- (User) Wolfkeeper (Talk) 14:57, 21 January 2009 (UTC)

But you shouldn't worry about GR for this, it's completely unnecessary; very much the same thing is predicted by Newtonian Mechanics at the speeds and masses we're talking about here; you can't feel acceleration due to gravity according to Newton's laws either.- (User) Wolfkeeper (Talk) 14:57, 21 January 2009 (UTC)

GR encourages one to use a free-falling reference frame...in such a reference frame, an accelerometer measures acceleration. Intro physics / Newtonian mechanics encourages one to use an "inertial reference frame"...in such a reference frame, an accelerometer measures acceleration minus gravity. There are a lot more readers who know intro physics than readers who know GR, so the article should stick with the Newtonian point of view. No one's taking an accelerometer into a black hole anyway. :-) --Steve (talk) 02:51, 22 January 2009 (UTC)

Ok, that just about makes sense to me (please be gentle as I am 20+ years down the line since my Physics courses). I come to this from a flying perspective, and I know that some planes are fitted with a 'g' readout. On the ground this definitely reads +1.0 g, and also when flying level. Pull back the stick in a turn and the number increases. If you push forward on the stick it decreases. Push too hard and it will go to 0.0 g, meaning you are in a ballistic parabola downwards. Push even further (not commonly done on purpose) and it will go to negative values. Is there any way this simple, real-world understanding can be a good addition to the article? I really want to avoid a detailed treatment of Mach, Einstein or Newton as I feel there are other articles on which this can more appropriately be done. --John (talk) 03:03, 22 January 2009 (UTC)

That's exactly what he just said though, g-force/what an accelerometer measures is acceleration minus gravity. That's been in the article before, but Greg_L or somebody took it out, multiple times, including when I referenced it to an inertial navigation textbook.- (User) Wolfkeeper (Talk) 10:55, 22 January 2009 (UTC)

To John: What general relativity requires is that one be unable to distinguish between an acceleration due to gravity and a "fictitious" acceleration due to inertia in an accelerating reference frame. This is the equivalence principle. This is precisely why gravitational acceleration is non-measurable. An accelerometer is not affected by one's choice of a reference frame, so it cannot be affected by gravity either. The acceleration measured by an accelerometer sitting on the ground is just the result of the Earth pushing upwards on the accelerometer. That is, not the weight of the accelerometer, but the reaction to that weight. JRSpriggs (talk) 10:25, 22 January 2009 (UTC)

Yeah, and accelerometers can't measure any fictitious force(acceleration), including centrifugal force/acceleration or coriolis force/accelerations. They read zero on them, because fictitious forces are really momentum and not force/accelerations at all.- (User) Wolfkeeper (Talk) 22:36, 22 January 2009 (UTC)

Oh, my! Such confusion! If it is an accelerometer, then it should measure acceleration, period. Not force. And how on earth could it distinguish between acceleration due to gravity and acceleration due to some other force? Surely the only way it can do this is by calibration: you calibrate it to read 0 when at rest w.r.t the Earth. Or, as in the airplane example given above, calibrate it to read 1.0g when at rest w.r.t. the Earth. 67.95.202.34 (talk) 04:47, 7 February 2009 (UTC)

GHZ experiment

I just added a section to this article, based on the original paper by Greenberger, Horne, Shimony, and Zeilinger. This is my first attempt at an edit. I would welcome comments/corrections on the style, formatting, and, of course, content. 69.255.193.52 (talk) 00:44, 6 February 2009 (UTC)

Bhabha scattering - Feynman diagrams are wrong

I think that the arrows on the positrons on the first two Feynmann diagrams in the article on Bhabha scattering are the wrong way around. —Preceding unsigned comment added by 129.67.62.144 (talk) 15:40, 10 February 2009 (UTC)

I added a note that these aren't the usual Feynman-diagram arrows, but are instead particle-motion-indicating arrows. But someone who knows wiki-table-syntax should clean up the awkward manual line-breaking I put into this edit. :-) --Steve (talk) 19:42, 10 February 2009 (UTC)

I fixed it. For future reference, to get text to wrap in a table you needed to fix the width of the table. For example by adding style="width:220px" to the table header. (Or alternatively, you can fix the width of the individual cell that needs text to wrap.) (TimothyRias (talk) 13:04, 15 February 2009 (UTC))

{{val}}

{{val}} finally got fixed. It can now reliably display at least 12 significant digits, including zeros. Server problems prevent the template from reaching its full potential (14 significant digits guaranteed) but this will be fixed in the upcoming weeks apparently. A few examples of output:

• {{val|1.23456|e=-23}} → 1.23456×10⁻²³
  
• {{val|1.2345678|(23)|e=-23}} → 1.2345678(23)×10⁻²³
  
• {{val|4.340|+0.023|-0.045|e=-23|u=MeV/c2}} → 4.340+0.023
  −0.045×10⁻²³ MeV/c²
  
• {{val|4.340|0.023|u=m3}} → 4.340±0.023 m³
  

I thought I'd let you guys know, since ... well we use a lot of numbers. Headbomb {^ταλκ_{κοντριβς} – WP Physics} 11:48, 15 February 2009 (UTC)

Trying to make EPR paradox a little clearer

Hi all,

EPR paradox is very techical, so I've had a go at making the important part legible, although it clearly needs much more work. So I would be grateful if anyone could tell me whether my recent changes to the 'explanation of the paradox' section are an improvement, or whether they contain false statements. I've just tried to make things a little clearer, but I thought I'd better check it with some experienced people first. Mark J (talk) 20:19, 27 January 2009 (UTC)

Hi. This is ronjoseph.

It seems to me that in the "EPR Paradox" article, in the first sentence of the fifth paragraph (which begins with “The EPR paradox is a paradox”), there is a typo.

The typo is an extra parenthesis after the word “locality”, which confuses the meaning of the sentence.

I propose an edit that removes the erroneous parenthesis:

CHANGE:

(referred to as locality), realism

TO:

(referred to as locality, realism

Proof that a change is needed:

There are seven parentheses in that sentence. Parentheses must occur in pairs. There should be an even number of them. The extra parenthesis is a left parenthesis. The logic of the sentence dictates that the parenthesis I mentioned above is the superfluous one.

What do you think?

- ronjoseph —Preceding unsigned comment added by Ronjoseph (talk • contribs) 20:13, 16 February 2009 (UTC)

Trivial typo corrections do not require prior discussion. Just fix it already. –Henning Makholm (talk) 07:19, 17 February 2009 (UTC)

Atmospheric physics

In August of 2006 (thirty months ago), a comment within the talk page of atmospheric physics indicated that someone with a strong physics background should take a good look at the article and try to make it less slanted towards meteorology. As a meteorologist, I'm not sure I can do this myself. If someone from the physics project could look over the article and make specific suggestions as to how it could be improved, it would be greatly appreciated Thegreatdr (talk) 22:58, 18 February 2009 (UTC)

Particle overview

I've built this image to give an overview of the various families of particles etc... Any comments on accuracy and possible improvements? Headbomb {^ταλκ_{κοντριβς} – WP Physics} 06:33, 6 January 2009 (UTC)

Some remarks:

• You might want to include in someway that atoms are actually bound states of nuclei and leptons. The chart at the moment seems to suggest that atoms and molecules consist of only quarks.

• Yes I've been looking for a way to indicate that. Perhaps adding Baryons --> Nuclei and have nuclei and lepton point to atoms (then atoms to molecules)? However I'm wondering if some of the "exotic atoms" have been something other than bound states of baryons and leptons (such as bound states of lepton and antileptons?).Headbomb {^ταλκ_{κοντριβς} – WP Physics} 13:42, 6 January 2009 (UTC)

• Certainly, exotic atoms do not necessarily involve (hadronic) nuclei, but can also involve a lepton-antilepton pair (positronium) or can involve hadrons electrically bound to a nucleus. Some people even consider stuff like excitons involving quasiparticles as exotic atoms. Fortunately exotic atoms tend to play a very small role in nature and I think we can get away with atoms referring to just normal atoms in this chart. (TimothyRias (talk) 14:00, 6 January 2009 (UTC))
• (e.c.) Yes, see muonium, but I don't think the unqualified noun "atom", without adjectives, is usually understood to include those. -- Army1987 – Deeds, not words. 14:14, 6 January 2009 (UTC)

• I'm not sure about onia being referred as atoms... It's a shame no one bothers defining this terminology precisely. It wouldn't be a hard thing to do, and would go a long way into making things more accessible to the public.Headbomb {^ταλκ_{κοντριβς} – WP Physics} 17:01, 6 January 2009 (UTC)

• What exactly are you referring to with quark-lepton complementarity? And why is it the only thing marked with a question mark? (I would think that there are much bigger puzzles in particle physics. GUTs, ToEs and Quantum gravity would probably be bigger question marks in this diagram alone. (TimothyRias (talk) 08:29, 6 January 2009 (UTC))

• My impression is that ToE, GUT, Quantum Gravity are simply placeholders names for whatever theory will manage fit the "job description", while QL complementarity is more of an "open question" than a "placeholder name" for something. The question mark isn't to indicate unsolved puzzle, but rather to indicate whether the concept is something that will be found in nature. Now I my impressions may be wrong, and this usage of the question mark is possibly confusing or misleading.Headbomb {^ταλκ_{κοντριβς} – WP Physics} 13:42, 6 January 2009 (UTC)

• Anyway, quark-lepton complementarity is a very technical topic (and its article was awfully written last time I checked). I'm not sure it is very useful to include it in the diagram. -- Army1987 – Deeds, not words. 12:57, 8 January 2009 (UTC)

• One more question, what exactly is the purpose of this chart. (i.e. where do you want to use it?) (TimothyRias (talk) 14:00, 6 January 2009 (UTC))

• Well right now it's on Elementary particle but I can think of other places it might add something (such as composite particle, fundamental interaction, etc...Headbomb {^ταλκ_{κοντριβς} – WP Physics} 17:01, 6 January 2009 (UTC)

• I think Higgs boson should be added to this diagram. Particles predicted by MSSM may be also included. Ruslik (talk) 09:04, 8 January 2009 (UTC)

How/where would you include the higgs in this scheme?Headbomb {^ταλκ_{κοντριβς} – WP Physics} 05:57, 21 February 2009 (UTC)

• I think it might have a place in the article on Matter, where I have argued (with mixed success) that since matter "takes up space", it should be defined as anything composed of elementary fermions, and is thus subject to the Pauli exclusion principle, and the Spin statistics theorem. I have believed that the fact that super-fluid ⁴He has this space-filling property, even though composed of atoms that are bosons (and all in the same quantum state), is because ultimately it is made up of elementary fermions. However I do not have a source for this claim, nor am I even certain it is correct. I'd be delighted if someone here could clarify the point. Wwheaton (talk) 16:09, 31 January 2009 (UTC)

• That's not right. Bosonic matter also occupies space. Think of an empty box. Now keep the box's walls at a constant temperature. the box fills up with electromagnetic radiation (a bosonic fluid). That radiation will apply pressure on the walls, will have a temperature, will occupy a volume, will obey an equation of state, etc. If you now compress the box, the temperature and pressure of the radiation will increase according to the radiation's equation of state and the first law of thermodynamic (you are doing work on the system). How is that any different then fermionic matter? Dauto (talk) 18:17, 31 January 2009 (UTC)

• Thanks. But that's just the Uncertainty principle, which applies to all particles, even massless ones. Yet the colloquial meanings of "takes up space" and "occupies space" are not quite the same. And bosonic matter does not exclude other matter from its space. I think that is what was meant when the authors of my high school physics text wrote that "matter has mass and takes up space", even though they likely did not really have the exclusion principle in mind. (I was troubled by that statement at the time, knowing that atoms are nearly "empty".) But without the exclusion principle, I suppose the Earth would be smaller than an atom—and thus a black hole. Cheers, Wwheaton (talk) 19:43, 31 January 2009 (UTC)
• Fermionic matter doesn't exclude other matter from its space either. It only requires other identical particles to have different quantum numbers. I don't think that some high school book says should necessarily be taken very seriously.

• And yet there is a need for a definition of the term Matter, and unless we simply wish it to be synonymous with Energy, some criterion is needed. One that is consistent with, or at least related to, historical notions seems desirable. Wwheaton (talk) 20:43, 31 January 2009 (UTC)

And there is one: matter's what made of elementary fermions. Basically the left half of the diagram. Headbomb {^ταλκ_{κοντριβς} – WP Physics} 06:16, 1 February 2009 (UTC)

• Yes, that's one way to see it. But it is not the only one. And since there is no scientic definition of matter, the debate continues. I personally have no problem with refering to electromagnetic radiation as a kind of bosonic matter. Dauto (talk) 13:59, 1 February 2009 (UTC)

Science FAC symposium

I'm letting you guys know about it because a lot of what is said there is also relevant for you guys. Plus your feedback would definitely be both relevant and appreciated. Headbomb {^ταλκ_{κοντριβς} – WP Physics} 04:11, 20 February 2009 (UTC)

Wikipedia invents new SI unit

Yeah, we can't watch all disambigs, but over three years staying power is remarkable:

• http://en.wikipedia.org/w/index.php?title=Danton&diff=prev&oldid=28270039

--Pjacobi (talk) 12:18, 20 February 2009 (UTC)

The length of time for vandalism to get fixed has a very long tail. See [1]...This study found that (for example) 0.06% of vandalisms were still there after 10,000 page-views. One article (Message) was blanked by somebody, and then it was viewed 250,000 times before being restored 35 hours later. :-) (This was early 2006, before ClueBot.) --Steve (talk) 00:36, 22 February 2009 (UTC)

Moon shadow image in muons to be speedy deleted.... help!

File:Moons shodow in muons.gif

I'd provide a fair use rational, but I just don't know where to go! Help! Headbomb {^ταλκ_{κοντριβς} – WP Physics} 20:11, 25 February 2009 (UTC)

If it is a work of the United States Government, then it is not copyright-able. There is a special template to use in that case. JRSpriggs (talk) 22:48, 25 February 2009 (UTC)

Perhaps but I really don't know what to do or where to go. The commons is incredibly confusing and user-unfriendly (meaning that it doesn't do a whole lot to orient users, not that the users from the commons are unfriendly).Headbomb {^ταλκ_{κοντριβς} – WP Physics} 06:00, 26 February 2009 (UTC)

Bahjat Muhyedeen and cranck science

The article is written as if photons don'exist, that E = mc^2 is false, that it is instead E = mcb, GR and SR false, QM false, and a whole lot of crank stuff. Also the article is AfD'd.Headbomb {^ταλκ_{κοντριβς} – WP Physics} 05:58, 26 February 2009 (UTC)

Inertia tensor of triangle

Inertia tensor of triangle has been proposed for deletion via WP:PROD 76.66.193.90 (talk) 07:16, 26 February 2009 (UTC)

Brainstorming for checklist for new members

I would like to start a check list for new WikiProject Physics members to help introduce them to the arcane ways of wikipedia. Such a list would have to be relatively short to be effective, but will also need to link to articles where they can get clear information on a focused topic about using wikipedia. (An example of this would be a glossary of wikipedia's alphabet soup will be useful.)

I imagine the checklist should include a list of useful pages to watch. For that the main WikiProject Physics page seems appropriate along with the activity page (which I didn't even know you could watch until recently). What other pages should be on this list?

I imagine we should also include instructions for dealing with vandalism and on rating articles. Having them add their name to the list of participants should be on the check list as well. Anything else?

Summary of questions:

• What pages are important for a newbie to watch?
• What pages are important for advanced editors to watch?
• What should be included in a checklist?

• Watch these pages

• Project Page
• Activity Page

• dealing with vandals

• Revert x vandalisms?

• signing up on participants list

TStein (talk) 15:00, 26 February 2009 (UTC)

Great initiative. Then we can incorporate this into {{WP Physics Welcome}} (or otherwise modify it).Headbomb {^ταλκ_{κοντριβς} – WP Physics} 16:08, 26 February 2009 (UTC)

Dispute/OR/COI at Yang-Mills theory

I would try to summarize the issues here, but I'm afraid I can't do so without slanting the debate one way or the other. So instead, I'm asking for people more knowledgeable than I to take a look at the page. I am willing to moderate this if needed. Headbomb {^ταλκ_{κοντριβς} – WP Physics} 17:27, 26 February 2009 (UTC)

Reviving the Fluid Dynamics Taskforce

Some of you may have noticed the sudden increase in the number of articles in the scope of the project. Crowsnest expressed interest in reviving this project, so I tagged a bunch of stuff related to Fluid dynamics (and I took the opportunity to tag stuff for the Relativity and Acoustics taskforces as well, even if they are not very active). I've overhauled the looks and archived old discussion, installed articles alerts (same for other taskforces), and some other tweaks. If you are interested, please join it. And if you aren't, but know people who would be interested (IRL or on wiki) please let them know.Headbomb {^ταλκ_{κοντριβς} – WP Physics} 00:35, 28 February 2009 (UTC)

Coordinators' working group

Hi! I'd like to draw your attention to the new WikiProject coordinators' working group, an effort to bring both official and unofficial WikiProject coordinators together so that the projects can more easily develop consensus and collaborate. This group has been created after discussion regarding possible changes to the A-Class review system, and that may be one of the first things discussed by interested coordinators.

All designated project coordinators are invited to join this working group. If your project hasn't formally designated any editors as coordinators, but you are someone who regularly deals with coordination tasks in the project, please feel free to join as well. — Delievered by §hepBot (Disable) on behalf of the WikiProject coordinators' working group at 06:17, 28 February 2009 (UTC)

Proposed project of interest - organismal biomechanics

Hi all, I'm trying to start a Wikiproject to cover Organismal Biomechanics, and I was wondering if anyone else would be interested? Articles such as animal locomotion. gait, muscle, and similar would be our targets. See my userpage for a list of what I'm planning to work on, including some truly awful articles in desperate need of attention. See proposal page at Wikipedia:WikiProject_Council/Proposals#Wikiproject_Organismal_Biomechanics. I'll keep anyone who signs up updated via their userpages until I get a project page made. Help of all kinds is appreciated, from brain dumps to wikifying, grammar and dealing with references. Mokele (talk) 22:38, 28 February 2009 (UTC)