Wikipedia talk:WikiProject Physics/Archive 13

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This is the archive "Wikipedia talk:WikiProject Physics/Archive 13". It is for January 2007.

Of possible interest

Wikipedia:Articles for deletion/Electric universe (concept). Comment as you will. --ScienceApologist 13:51, 1 January 2007 (UTC)

another AfD

Wikipedia:Articles_for_deletion/Harold_Aspden. Comment please. --ScienceApologist 00:20, 2 January 2007 (UTC)


While on New Page Patrol, I ran across the following page, which you may be able to assist: Pasotron. TonyTheTiger 16:58, 3 January 2007 (UTC)

At least this topic appears to be real. I added a little bit with a few external hyperlinks, but it could be expanded much more. Anville 19:36, 4 January 2007 (UTC)

AfD of interest

Comment here: Wikipedia:Articles for deletion/Ralph Juergens. --ScienceApologist 19:03, 5 January 2007 (UTC)

Physics anniversaries wanted

Portal:Physics now has an anniversaries section; additions to this section would be welcome at Portal:Physics/Anniversaries. Mike Peel 20:28, 5 January 2007 (UTC)

Science Collaboration of the Month

Supernova is the new Science Collaboration of the Month. Good work! NCurse work 09:37, 4 January 2007 (UTC)

This post here illustrates two probelms:
  • People do not know about Wikipedia:WikiProject Astronomy and Wikipedia:WikiProject Astronomical objects. It would be nice to direct astronomy-related talk items to those projects.
  • The labels for "WikiProject Physics" are overly invasive, apparently applied to virtually any article remotely related to physics. Perhaps some of these labels can be removed from astronomy-related articles.
Dr. Submillimeter 21:14, 4 January 2007 (UTC)
I mostly agree with the former, but think that it's also useful to notify people here who have an interest in astrophysics. The latter I disagree with, as I count astrophysical subjects to fall under both this wikiproject and WikiProject Astronomy; I've just spelled out my thinking on the matter on User:Dr. Submillimeter's talk page. Mike Peel 23:59, 4 January 2007 (UTC)
Most of astronomy uses some form of physics; it would be technically valid to label almost all astronomy articles as within the scope of WikiProject Physics. This is not useful in terms of contacting people with expertise on the subject, who mostly check announcements at WikiProject Astronomy or WikiProject Astronomical objects, not here.
Anyhow, Mike Peel has proposed a compromise solution that may satisfy everyone: some of the crossover articles will be labeled as both "WikiProject Astronomy" and "WikiProject Physics" articles. This might be more functional than the status quo. Dr. Submillimeter 09:10, 5 January 2007 (UTC)
Look, the article was assessed by the wikiproject physics. But now, I've dropped a message at all of the three projects you've mentioned. NCurse work 06:48, 5 January 2007 (UTC)

I've created Template:WPAstronomy, which will hopefully replace Template:Physics on the astrophysics pages. This new template includes the tagged articles in both the Astronomy worklist and this project's one when a astrophysics tag is added to the template call. Mike Peel 22:51, 8 January 2007 (UTC)

Prod question

The article on Thanu Padmanabhan is currently prodded. Can someone please check whether he and his credentials are worth an article. Tintin (talk) 08:19, 8 January 2007 (UTC)

Mereda (talk · contribs) already removed the prod by Radkris (talk · contribs). His edit summary says "add review citation to one of the books + deprod (he's a notable author and scientist))". Just so you know. JRSpriggs 09:16, 8 January 2007 (UTC)
Thank you, and from the lack of comment here I suppose there are no objections against the article. Tintin (talk)
Well, I never heard of him. But that proves nothing one way or the other. JRSpriggs 08:29, 9 January 2007 (UTC)

The WIP project to rewrite the physics lead

It can be found here. The voting page is here. I haven't seen anything change there for weeks. What happens next?--Filll 21:35, 8 January 2007 (UTC)

It has been the busy festive period, so I have left it lie over christmas. I will have a form up on the situation at the weekend. SFC9394 21:45, 8 January 2007 (UTC)

Hello, I'm kinda new here and just noticed the physics WIP, so I added my two cents to the discussion. I realise it's probably a little too late for them to be useful, but I figure one more opinion can't hurt. Cheers! - AllGoodNamesTaken 15:00, 9 January 2007 (UTC)

How many laws does Wein have?

So far I've found four laws by Wien:

Is this true? How many laws does he have? Anyone know? Also, the top two need to go to lower case and someone who knows these topics well should add the Wien-Planck law to Wikipedia. --Sadi Carnot 02:25, 8 January 2007 (UTC)

Wien's displacement law describes the relation between blackbody temperature and the peak wavelength of the thermal emission. This article is OK. However, both Wien's Distribution Law and Wien's Radiation Law appear to describw the short-wavelength approximation of the blackbody function that is sometimes called "Wien's law". The two articles should probably be merged, although neither article contains much to merge and Wien's Radiation Law is written much more clearly than Wien's Distribution Law. Would people object if I did this? I have my copy of Rybicki and Lightman right at hand. Dr. Submillimeter 09:52, 8 January 2007 (UTC)
Whatever one you do a merge on, the main one, in Wikipedia, should describe the one that Planck is referring to in is 1900 paper. That’s the one I’ve been searching for. --Sadi Carnot 17:22, 8 January 2007 (UTC)
That link refers to a "Wien's displacement law" and a "Wien's energy distribution law". Which would you like? Would it be OK if I just use what is written in Rybicki and Lightman? Dr. Submillimeter 18:02, 8 January 2007 (UTC)
Whatever is in Rybicki and Lightman sounds like a plan, just be sure to source it so that we all have a good reference to consult. I'm guessing the main one should be the "energy distribution law"? Thanks: --Sadi Carnot 02:51, 9 January 2007 (UTC)

We should leave Wien's law as a redirect. It is difficult to say that Wien has a "main law", although people more frequently refer to the displacement law instead of the radiation/distribution/whatever law. I will go ahead with these edits. Dr. Submillimeter 10:12, 9 January 2007 (UTC)

I also checked the like to the Wien-Planck law. It looks like that is another name for the Planck law. A redirect would be appropriate for that. Dr. Submillimeter 10:31, 9 January 2007 (UTC)

Wien-Planck law is now a redirect to the Planck law article. I will try to find a suitable name (i.e. a good name that is given in a textbook) for Wien's Distribution Law and Wien's Radiation Law before merging the two. Dr. Submillimeter 09:46, 10 January 2007 (UTC)
The section of the Planck law article on "The use of Stirling's formula" seems exceedingly weird to me. The Stirling approximation (for n factorial) isn't even used in the derivation in the article. Is this section a historical relic from some earlier editing? And what the heck is all that stuff about a "monster"? I haven't read through it at all thoroughly but it seems like a total non sequitur. HEL 20:07, 10 January 2007 (UTC)
Aha, I see it is being discussed further down this page. Good. HEL 20:17, 10 January 2007 (UTC)

Notability (science) criteria

May be of interest to people watching WPP -- WP:SCI, the work of a couple of editors to clearly delineate what should and should not be covered by WP. Sdedeo (tips) 20:29, 4 January 2007 (UTC)

Don't forget WP:FRINGE, which covers some of the same territory but is a little broader in scope. Anville 14:05, 5 January 2007 (UTC)
Good stuff here. The regulars/old-timers should definitely take a look. linas 04:33, 13 January 2007 (UTC)

What is Parity really about?

The last edit at Parity (physics) says "It is important that the determinant of the P matrix be -1, which does not happen for 180 degree rotation in 2-D. Here a parity transformation flips the sign of either one of x or y, not both.". This changes the article's position on Parity in 2-D. So my question is what is essential to the definition of Parity? Is the negative determinate a necessity or is it an accident due to our living in an odd-dimensional space? JRSpriggs 06:04, 12 January 2007 (UTC)

Parity is the transformation xi goes to -xi for each coordinate. So the sign of the determinant is negative in odd dimensions and positive in even dimensions. -Joshua Davis 06:27, 12 January 2007 (UTC)
If you are sure, then please revert the change in the article. JRSpriggs 08:57, 12 January 2007 (UTC)
Uhh, that sounds wrong. Parity is the operator that takes you between the (two) disconnected components of a (rotation) group. Since rotations always have determinant +1, the parity operator must have determinant -1. The original edit sounds like it was correct. linas 15:14, 12 January 2007 (UTC)
Linas, I stand corrected. On further thought, parity flips only an odd number of spatial directions and so has determinant -1. The equivalent group theoretic definition is rather nice. -Joshua Davis 17:12, 12 January 2007 (UTC)

Causal dynamic triangulation article in Scientific American

FYI, since the article falls under your project, the Feb 2007 issue of Scientific American on page 24 has a one page article discussing Causal dynamic triangulation. Since the CDT article is currently just a stub, I thought someone here might be interested in expanding it using some of the information from the magazine. The article contained some less formal but still useful information comparing CDT to string theory and loop quantum gravity, as well as where research efforts currently lie. Dugwiki 20:22, 12 January 2007 (UTC)

Plasma cosmology live!

Please take a look at plasma cosmology which has been newly revamped. Reference it, edit it, comment on it, etc. Thanks! --ScienceApologist 01:04, 13 January 2007 (UTC)

Wien lawlessness

While trying to sort through laws named after Wien in response to comments made by Sadi Carnot earlier on this talk page, I encountered a few problems related to naming. I would like some feedback on names before proceeding.

First, Wien has two laws that he is known for. The first, Wien's displacement law, has been given a name that is used everywhere. The function describes the peak wavelength or frequency at which light is emitted from a blackbody of a given temperature. That page and its name should be left alone.

Wien's other law (copied from one of the two Wikipedia pages on the subject, to be verified using Rybicki and Lightman) is

     (Equation X)

where is the energy density of a blackbody. This function is a good approximation for the short-wavelength end of the blackbody function. This function also does not have a good name. Among other things, I have seen it referred to as:

  • Wien's Law (Rybicki and Lightman as well as a couple of other textbooks)
  • Wien's tail of the blackbody function (or something similar from Chandrasekhar)
  • Wien's Distribution Law (Wikipedia and a few other odd references)
  • Wien's Radiation Law (Wikipedia mainly)

To add to the confusion, Wien's law redirects to Wien's displacement law, even though some textbooks use Wien's law to refer to Equation X up above.

So, my two questions are:

  • What do we call Equation X?
  • What do we do with Wien's law? Should it be a redirect, a disambiguation page, or an article page?

Please give me feedback on this. I have searched several statistical mechanics and radiative transfer books, and I have not found a good, consistently-used name for Equation X. Dr. Submillimeter 23:10, 12 January 2007 (UTC)

Isn't equation X the Wien approximation (aka Wien limit to the blackbody? As opposed to the Rayleigh-Jeans approximation or the Rayleigh-Jeans limit? --ScienceApologist 01:04, 13 January 2007 (UTC)
Google seems to confirm that Wien's approximation or Wien limit are both very good names for eqn X. I believe Wein's law should be a disambiguation page. linas 05:30, 13 January 2007 (UTC)
Agree: use Wien approximation as the name for the equation, with Wien's law as a disambig. --Sadi Carnot 14:54, 13 January 2007 (UTC)

I liked Wien approximation too, so I moved the page. I will add references and both the frequency-dependent and wavelength-dependent forms of the funcion to the page on Monday (when I am back at work with all my radiative transfer and statistical mechanics books). Dr. Submillimeter 21:41, 13 January 2007 (UTC)

Florentin Smarandache on afd

Hello. I have put Florentin Smarandache on articles for deletion. See: Wikipedia:Articles for deletion/Florentin Smarandache. Please vote. Wile E. Heresiarch 06:19, 14 January 2007 (UTC)

"Newton's laws of motion" are now semi-protected

For the moment at least, Newton's laws of motion has been granted semi-protection. This has quelled the flood of vandalism which was making it difficult to maintain the article. However, the lingering effects are still there. I invite you-all to look it over and try to perfect it now that it has become relatively safe to do so. JRSpriggs 11:38, 14 January 2007 (UTC)

A basic introduction to GTR which is anything but

Filll (talk · contribs) has added templates to Basic introduction to the mathematics of curved spacetime and Mathematics of general relativity which indicate that the former is a non-technical introduction to the latter. However, if you look at them, you will see that the former has a larger proportion of equations (and not simple ones), than the latter. JRSpriggs 12:59, 14 January 2007 (UTC)

Well then, this needs to be addressed I think.--Filll 13:38, 14 January 2007 (UTC)
I will point out that they are simple equations. And equations does not necessarily equate to more complicated. It is good I think to indicate what is the more introductory material and what is the more advanced material in a somewhat uniform manner. I do agree that the wording of the introductory tags might be a bit off in this case.--Filll 13:44, 14 January 2007 (UTC)

Misner space

Does anyone here know about Misner space? There seems to be some debate over its definition, kind of important as it was linked to in the did you know section of yesterdays main page. --Salix alba (talk) 09:59, 18 January 2007 (UTC)

Planck's law of black body radiation

I'm wondering if this article is getting a little weird. PAR 04:37, 10 January 2007 (UTC)

Could you be more specific? What do you see as the problem at Planck's law of black body radiation? JRSpriggs 09:00, 10 January 2007 (UTC)
I do not know what PAR was talking about, but the The use of Stirling's formula in the theory of black body radiation section seems rather lengthy for something that is really of minor relevance to the topic. Radiative Processes in Astrophysics by Rybicki and Lightman, for example, never discusses such an approximation. Maybe the section should be a separate article? Dr. Submillimeter 09:44, 10 January 2007 (UTC)
Glancing through that section, it looks to me like original research. Could someone confirm that it isn't, and if possible add more appropriate references to it? Mike Peel 10:07, 10 January 2007 (UTC)
While the content of that bit is mostly correct, it is written about in a surprisingly non-NPOV and weirdly OR fashion! Any decent statistical mechanics book will show how the Stirling Approximation can be used to obtain the formula for blackbody radiation (usually from special considerations of LTE). It is in some ways more general and cleaner to use the Einstein relations between As and Bs to do derive the formula (I think this is how Rybicki and Lightman do it). However, what is weird is that the author seems to be criticizing the use of the Stirling approximation. In particular the author seems skeptical that:
log (n!) = n log (n) - n. For large n, log(n) >> 1 so log (n!) = n log (n)
and as typical in physics the correction term 1 is ignored. To argue it is incorrect they use small n! I think whoever wrote the prose in this section was very misguided in their attempts to critique this approximation. --ScienceApologist 14:19, 10 January 2007 (UTC)
Just for reference, Rybicki and Lightman derive the Planck spectrum using the assumption that the photons are in a Boltzmann distribution. Dr. Submillimeter 16:24, 10 January 2007 (UTC)

Two more observations:

At the very least, the Stirling's formula section is esoteric and should be removed or placed in its own article. Dr. Submillimeter 13:39, 10 January 2007 (UTC)

I have asked C. Trifle to discuss the article here. Dr. Submillimeter 13:55, 10 January 2007 (UTC)
Thank you for the invitation Dr. Submillimeter . I am very glad to see that the Stirling Approximation section has finally caught attention though I am inclined to think that it was partly due to the Monster. Good job, Monster.
Thank you for the observation that most of the text is correct, ScienceApologist .
Now may I answer the criticisms:
I disagree that the problem is of minor importance, ScienceApologist . As I have written, the approximation is highly nonlinear for small n . It could correspond to the uncertainty principle and some other things, which is what I have written. But there is one more thing. For big n one could let it be, in a way, but not quite, because it is about the logic of the derivation. The problem is that it might not be an approximation at all. To me the equation n!= nn and what follows could represent a transition from one "arrangement" , "state" or "phase" , as you wish, to another. (Example: surface to volume.)
"Much of it is written in non-NPOV and weirdly OR fashion" ScienceApologist . The only thing that indeed may begin to seem as OR is the Monster. It is weird because it is his job. But there are some monsters on Wikipedia. Remember Cookie Monster. Why Planck cannot have a Monster, I don't know. The rest is basically Planck and others, according to the references, as I see it, and these people really did write it. If the authentic texts are now seen as weird while at the age of 100 years they should be about reaching maturity, I can not help.
"The article is getting weird" PAR has been familiar with my remarks on the talk page since the day I introduced the Stirling approximation at the beginning of October 2006 and I have been asking for comments. No one answered.
It is not the article that is getting weird. I am afraid that now seems OR Mike Peel is just referring to the authentic text. What could seem weird is that the way in which Planck's law was originally derived has not appeared in both popular textbooks and articles for over a 100 years. Some of those writers might not have been informed (a long list of about a 100 books I looked up for it - found nothing). This makes writing this article difficult , JRSpriggs . You can only refer to the historic papers and nothing else (I mean, no textbook probably, I have not found any). That's why I had to refer to the course I taught! But what is so bad in the fact that Planck used combinatorics?
I must apologize for too much text and for the monster. What can be done about it:
I agree that the article is getting lengthy. The best choice seems to me:
Include short information about the use of combinatorics and the other important points of the original derivation into the History section, which is where this bit should indeed be,
cut down on the Stirling bit, leaving the information that this could mean a transition. Planck's paper is 106 years old. Even if my comment on the "transition" were classified as OR, which I did not quite expect, it's no use banning it. It was included into my consultation hours, which is the reference I can provide and I hope it can be certified on request. (The info about the basic points of the course I taught is still displayed on the website, so that is the reference, if nothing else will be found.) The oral form of publication is also a kind of publication. As the thing is not new any more, let it stay, I suppose. I can try to take the Monster to a new article on the use of Stirling etc or just let it go, ScienceApologist . Some monsters do not like being completely thrown out, and they might be getting malicious. Not this one I hope. Thank you for your remarks.
If no one else will do anything with the History section sooner, which I suppose is not urgent, I will try to make the necessary corrections tomorrow afternoon, because now it is getting late. --C. Trifle 21:44, 10 January 2007 (UTC)
I'm afraid you've missed the point regarding the large number approximation. A Planck distribution does not (cannot!) exist for small n. Having three (or six or even 1000) photons in a box will not yield a blackbody curve no matter how hard you try to get the energy to thermalize. The only way to get a Planck distribution is to have a large nubmer of photons so that a continuum level can be reached. It is only then that the smooth blackbody curve will show up. I suggest scrapping the entire section and rewriting it from standard statistical mechanics sources. Pathria may be a good one to begin from. --ScienceApologist 21:51, 10 January 2007 (UTC)
You are both right and wrong. You are right when you are saying that even a 1000 photons (or any other elements) will not give a distribution which exists for a large number of elements. But I have not said it will and I have not said the problem is there. The example of 100 "photons" (it would be better to say "energy elements") in 10 resonators is not mine. It was given by Planck 106 years ago. And he got the black body spectrum. The problem is in the model of the interaction(s). It is not me who invented models in chemistry, physics, and so on. These models were built using a small number of elements, then repeated for large populations and the idea was then statistically tested. Look at the idea of the atom of hydrogen (not mine either). A proton and an electron - two elements - and hundreds of research papers on the model and its statistics. How about genes, DNA? The problem concerns what is probably repeated. About scraping the whole section, don't blame me for what people wrote 100 years ago. I understand that we would have either to use a time machine and persuade Planck not to write what he wrote or (now) try to understand him. He did it and it worked. Let's try to understand why.--C. Trifle 23:53, 10 January 2007 (UTC)
I agree with ScienceApologist on scrapping and rewriting the section using a standard textbook. If most textbooks do not present C. Trifle's type of derivation for the Planck law, then it is not notable. It should not be given undue weight in the article (i.e. approximately half of the article), although it may be worth mentioning briefly, or it may be worth mentioning in a separate article. Also note that Wikipedia is not a soapbox. This is not the place to preach about a lost technique for deriving a physical relation. Finally, please note that personal references generally cannot be used as references on Wikipedia unless they have passed through a rigorous peer-review process.
On another note, I have been looking over Wikipedia:Template messages/Cleanup to see if any of these messages may be approrpiate for the Stirling's formula section. I think Template:Story might be appropriate. The section does lack formality (for example, "...the writers, who all were excellent physicists, preferred... " and "...though perhaps not memory in the meaning used in psychology." and the link to monster). Dr. Submillimeter 00:37, 11 January 2007 (UTC)
Hi folks, maybe I can make a couple of comments? When physics subjects like blackbody radiation, quantum mechanics, etc. are taught, the presentation does not necessarily follow the detailed historical development of the topic. When I taught blackbody radiation and Planck's law last week I used the derivation developed by Debye in 1910 (which is what's done in the Wikipedia article too). Sometimes the original derivation of a result is correct but ugly, and clearer and more elegant derivations come along later. I think that our articles on physics topics should follow the most clear approach possible. However, there is also a place to report on physics history; I think a study of Planck's original derivation would fall into the history realm. Perhaps this calls for the creation of a new article on the historical development of the theory of blackbody radiation, written from a science historian's point of view? At the same time, I have to comment that it is not our place on Wikipedia to "Let's try to understand why", because this would be original research. Our Wikipedia discussion of the history of Planck's derivation must come from external, reliable, verifiable sources. Finally I have to say that I don't understand at all what the concern is with Stirling's approximation; you lost me in that last paragraph... HEL 00:39, 11 January 2007 (UTC)
After edit conflict: I agree with Dr. Submillimeter 100%. HEL 00:44, 11 January 2007 (UTC)
In connection to this discussion, the section on "History" of Stirling's approximation should be looked at. There are some OR-sounding comments on "the link between the "first order" Stirling's approximation and modern physical theories". HEL 00:57, 11 January 2007 (UTC)

I agree that the history section should be cleaned up. But note that we don't need to replace it with another derivation because it's already there, see here. This derivation is actually more rigorous than what you typically find in textbooks. E.g. F. Reif simply imposes periodic bopundary conditions. That simplifies the math but it is physically completely nonsensical. But of course, in the thermodynamical limit the boundary conditions don't matter... Count Iblis 01:17, 11 January 2007 (UTC)

I have added a warning on the language of The use of Stirling's formula in the theory of black body radiation to the section. The tone is simply too informal. I also added an off-topic warning to Lewis photon model and the logical variable, which does not discuss Planck's law directly but instead discusses the history of the concept of the photon. While Planck's law does depend on the concept of using photons, the extended discussion on the photon itself belongs in another article. If I look at the section more, I may add more clean-up warnings. Dr. Submillimeter 08:44, 11 January 2007 (UTC)
Thanks folks for your kind-hearted comments.

Now to the point:

Language: Dr. Submillimeter wants formal language while HEL desires the most clear approach possible. To agree with both is difficult because it requires a short text with highly specialized vocabulary. Wikipedia is "everybody's encyclopedia", so different audiences want to participate and benefit. This includes a number of users of English as a foreign language. You guys will only be talking to a few. It would be better to use a multilevel approach.
Content: Count Iblis says we don't need to replace it with another derivation because it's already there, Dr. Submillimeter This is not the place to preach about a lost technique for deriving a physical relation. Even so, different people read Wikipedia. Someone might ask a few questions like for example:
Why do these guys use Planck's law if they hate his derivation?
'Cos it's right? HEL 01:27, 12 January 2007 (UTC)
Then one might look at the values of Planck's constant h and Boltzmann constant k according to 2002 CODATA, compare with what is written in Planck's paper and use a calculator. Such a user would see that the error of the value of h calculated by Planck is greater than 69 thousand times the standard deviation of the 2002 measurements, while for the Boltzmann constant it is more than 14 thousand times behind the standard deviation. In many measurement techniques just three standard deviations are enough to reject the hypothesis, according to the standard curve. (Or at least begin to have some doubts.) So one could ask:
Why do these guys use a law that seems so faulty that one could hardly find one chance in the whole Universe for Planck's 1901 values to be the same as now . Maybe h and k are not constants at all?
'Cos Planck's error bars were a heck of a lot bigger in 1901 than they are 101 years later? HEL 01:27, 12 January 2007 (UTC)
Then someone who knows that Planck's law is used to measure temperature of stars could look at the derivation. It begins by closing the radiation in a rectangular box where vectors vanish at the walls. One could ask:
How are these guys going to close a star in the rectangular box so that the whole radiation was enclosed in it and how they are going to measure that radiation if it is completely inside?
'Cos you don't need to close a star in a box; a star is a pretty good blackbody all on its own? HEL 01:27, 12 January 2007 (UTC)
One could also ask why neither Planck nor Einstein used the notion of the speed of photon in their, respectively, 1901 and 1905 articles, and they did not use the word photon.
'Cos the word hadn't been coined yet? Duh. HEL 01:27, 12 January 2007 (UTC)
And one could have some more questions like that and then you can tell that person: Come on man, these questions don't qualify here! You have read the authentic Planck and authentic Einstein. This is what we call Original Research. There is no place for that on Wikipedia. Why can't one read the authentic published paper, ask questions and compare? It is natural to ask some questions when you read. I really would like to know how HEL imagines the creation of a new article on the historical development of the theory of blackbody radiation, on Wikipedia, written from a science historian's point of view, without asking questions about the meaning of the original text? And if those questions are qualified as OR then what to do?
How about finding some WP:RS publications by actual science historians? Sorry, but the inanity of this argument is starting to annoy me. HEL 01:27, 12 January 2007 (UTC)

Several important but difficult postulates have been put forward, two warning banners have been put up and there is a threat of a few more. All that about one monster, one Lewis and one Max Planck. OK, it may stay like that for next 106 years. As I have written on the talk page, my text is available under the GNU license to anybody willing to use it. I am cooperative in peace and quite, with people who are willing to cooperate. Good health and happiness, and patience to everybody.--C. Trifle 18:15, 11 January 2007 (UTC)

Regarding language: It is easy to write clearly in a formal tone. In fact, it may be easier to write clearly in a formal tone, as fewer colloquialisms and inappropriate analogies (which may confuse the reader) will be present, and fewer unnecessary phrases (which detract from the message being presented in the text) will be present . Note that I did not call for adding jargon to the text. The language can be formalized without adding jargon. Dr. Submillimeter 19:02, 11 January 2007 (UTC)
I agree that the language must be both clear and formal. The range of vocabulary should be suitable for general audience. But we must give correct information. I wouldn't have even started the Stirling approximation section if the approximation had been mentioned in either of the Overview, Derivation or History Sections. We can reduce that section indeed having corrected the misleading content of the first sections. As they are misleading, I've decided to label them with warnings. I will write below what in my opinion should be improved. --C. Trifle 00:15, 12 January 2007 (UTC)
I have provided references for the Overview and Derivation and have hence removed the "unreferenced" tags on those two sections. HEL 01:23, 12 January 2007 (UTC)
The part I find most misleading in the Overview is this:
"He found that the above function, Planck's function, fit the data for all wavelengths remarkably well. In constructing a derivation of this law, he considered the possible ways of distributing electromagnetic energy over the different modes of charged oscillators in matter. "
The above implies that it was electromagnetic energy that was somehow a priori quantized. If the charged oscillators had some modes, one immediately associates them with quantum oscillators. Compare with the History section:
"An article by Helge Kragh[1] gives a lucid account of what actually happened. Contrary to popular opinion, Planck did not quantize light. This is evident from his original 1901 paper [2] and the references therein to his earlier work.
Helghe Kragh is right. Planck wrote about "vibrational energy" in par. 1. He assumed that "If amplitude and phase both remained absolutely constant, which means completely homogeneous vibrations, no entropy could exist and the vibrational energy would have to be completely free to be converted into work."
Then he introduced entropy according to Boltzmann:
"We now set the entropy SN of the system proportional to the logarithm of its probability W, within an arbitrary additive constant, so that the N resonators together have the energy EN:
(#3) SN = k log W + constant
In my opinion this actually serves as a definition of the probability W, since in the basic assumptions of electromagnetic theory there is no definite evidence for such a probability. The suitability of this expression is evident from the outset, in view of its simplicity and close connection with a theorem from kinetic gas theory. " (here the reference to Boltzmann 1877).
The problem in Planck's derivation is that the comment does not make it absolutely clear what powers the radiating system: kinetic vibrations or the "radiation field" . If the field, then where does it come from? If the collisions of molecules (resonators), then why is the energy so high? If Planck had written that collisions of molecules trigger somehow the internal energy stored in the molecules, and accumulated through collisions, it would be a certain model. Another problem in Planck's article is that his reference to Boltzmann is not quite clear. It is not mentioned what did actually these people do: Debye, Bose , de Broglie, Einstein in the area of black body.
The above problems are not discussed in the article. Instead, the Derivation section is written in such a way that it is misleading because it is not referenced. Planck did not derive his law in this way. It is not clear who actually derived the law as shown, so it might be OR. (As I hear the referenceas are now provided, this is OK.)
The problem is where OR begins and where this kind of writing can be called simply commenting on the published source. And why these comments have to be sometimes weird is that some comments in the original work were not quite clear. Planck did not assume he would write for an encyclopaedia. This is not everything that is necessary. Maybe really better divide into several articles, I don't know.--C. Trifle 02:19, 12 January 2007 (UTC)

Based on a couple of references (e.g. Statistical Physics by T. Guenault), I have come to the conclusion that the entire discussion on Stirling's approximation is about the Boltzmann distribution, not Planck's law itself (which can be derived from the Boltzmann distribution). In that case, the extended discussion on Stirling's approximation really belongs elsewhere, possibly in the Boltzmann distribution article. What do other people think of this? (I also reformatted C. Trifle's comments; the staggered indentation made it difficult to read his text.) Dr. Submillimeter 11:56, 12 January 2007 (UTC)

I have now placed a warning that the Stirling's formula section is off-topic (because it deals with the Boltzmann distribution and not Planck's law directly). Unless I receive strong objections, I will remove the section on 20 Jan 2007 and place it on the article's talk page. Dr. Submillimeter 23:18, 13 January 2007 (UTC)

Remember the monster was created as part of the materials for discussion in English as a foreign language. I have now added a reference to the "educated rebel" (Berger) , where the origin of the monster can be traced. The idea is currently being evaluated in our Computer Graphics Department. If it proves to be useful to help simulate a natural phenomenon of some kind, it may be addressed to a particular Wikipedia page after January 20. If not, I agree that its best place will be indeed on the talk page. --C. Trifle 12:31, 15 January 2007 (UTC)
After the discussion in the Computer Graphics Dept I come with the following:
Planck's entropy can indeed be treated as a double spiral, one growing one way and the other opposite,
To be treated as part of an algorithm, n+p must be specified because one does not add elephants to monkeys. This has been done. n+p has been defined as a number of operations with the outcome "tails" or "heads".
I also have to communicate the result of U/V in the Derivation section, which is 7.56579* 10-16 J* m-3 K-4 * T4. This is supposed to be the total energy of the electromagnetic standing wave (of all frequencies?) in a cube with the walls made of a conducting material (vectors of electric and magnetic field vanish as described). How can one explain:
How to measure the blackbody radiation from the outside?
What does the calculated value really mean?
There have been many comments on the Stirling section and the old Planck, but the "standard" modern Derivation contains some unexplored points too.--C. Trifle 21:05, 17 January 2007 (UTC)
The Derivation section requires L grow to infintity for the cube made with walls made of a conducting material. The frequency of the fields that have to vanish is not specified, so the cube must be made of infinitely long thick metal walls. Will radiation pressure support the walls and protect them from falling down towards the centre of the cube? How about the finished Universe? Can heat radiation be produced there? This seems to be the real Leviathan ship on the sees outside the infinity. And the discharge of static on the edges?
Why not assume that it is a logical standing wave of probability and purely logical walls?--C. Trifle 21:21, 17 January 2007 (UTC)
I did not understand the paragraph about the double spiral and the elephants and the monkeys. That paragraph should not be included. I also do not understand why C. Trifle needs "to communicate the result of U/V". I do not see why a statement needs to be made about observing the blackbody radiation inside the theoretical box used for the calculation. Many of the rest of the comments seem to be nit-picking comments about the theoretical derivation that, if addressed, would detract from the subject rather than enhance the subject. Dr. Submillimeter 10:36, 18 January 2007 (UTC)
Excise this prose with impunity. A mention of Stirling's approximation on the derivation of the Boltzmann distribution indeed makes the most sense. --ScienceApologist 14:37, 18 January 2007 (UTC)
Derivation - U/V If you use a black body of V = 1 m3 at a temperature of 1500K, you obtain 7.56579* 10-16 * 1 * 15004 = 0.0038 J as the total energy of the electromagnetic standing wave in the cube. According to the comment, this is integrated for all frequencies from zero to infinity and no other energy is mentioned. It is possible for a human to use a 60W lamp of a similar temperature and a calculator. Within one hour the lamp, this poor imition of the black body will radiate 56 million times the energy calculated in the derivation. It is natural for the reader to ask about the meaning of the value calculated according to the derivation."
Derivation - opaque cube The necessary condition for the present derivation is the cube having opaque, fully isolating walls, if you assume the electromagnetic nature of light. If you are outside, how do you measure what is inside? If you are inside, you are affecting the standing wave.
Derivation - infinite L The infinitely great real cube with metal walls filled with real wave inside will have to solve the problem of whether to break down due to gravity or stand supported by the wave pressure on its own, if you don't help.
Different animals According to some dictionaries, nit-pickers are those who quarrel with trivialities of expression and meaning, but who usually end up without making concrete or justified suggestions for improvement. The concrete suggestion is to define a logical operation whose result would give objects belonging to different categories rather than simply add two different categories.
One does not usually add two chairs to five tables to get seven (what - tablechairs?), five monkeys to two elephants (seven monkelephants), two resonators to five energy elements (seven what?). Instead, and that was what I suppose Planck meant, one can add operations providing space for a component that belongs to either category, as decided by the outcome. --C. Trifle 00:02, 19 January 2007 (UTC)
The comment on the derivation of U/V would require original research, which is not permitted. (In this particular case, the statements about the light bulb make me wonder if C. Trifle misunderstands how a light bulb works.) The comments on the oqaque cube and infinite cube size are irrelevant, since the derivation is based on a theoretical construct, not a practical lab experiment. The comment on the animals is incoherent. I see no reason to discuss this topic any further. Dr. Submillimeter 10:24, 19 January 2007 (UTC)


Made some comments for help about the energy article on the main page that might better have gone here. Feel free to move them if they offend. SBHarris 12:38, 19 January 2007 (UTC)

"Energy It's a mess, trying to do too many things. One of the problems is the blasted Wikiproject science template. You wouldn't try to do this with momentum or mass or electricity. Needs major disambiguation, and roles in society even for the definable joule kind of science energy, need subarticles and drastic cutting. Finally, much inanity needs removal. Help." (Moved from main page; it's more appropriate here. Mike Peel 18:18, 19 January 2007 (UTC))
Thanks. SBHarris 18:31, 19 January 2007 (UTC)


Is a picture really necessary? Or could it be written as (uudds)? Thanks, CarpD 17:44, 20 January 2007 (UTC)

Bohr model intro image debate help needed

Please comment here: Talk:Bohr model#Intro image debate to help reach consensus as to what “Bohr’s atom model” actually looked like. Thanks: --Sadi Carnot 07:31, 23 January 2007 (UTC)

At the scale of those images, the nucleus would be a point. JRSpriggs 10:24, 24 January 2007 (UTC)

Carl Sagan FAR

Carl Sagan has been nominated for a featured article review. Articles are typically reviewed for two weeks. Please leave your comments and help us to return the article to featured quality. If concerns are not addressed during the review period, articles are moved onto the Featured Article Removal Candidates list for a further period, where editors may declare "Keep" or "Remove" the article from featured status. The instructions for the review process are here. Reviewers' concerns are here. SandyGeorgia (Talk) 20:23, 23 January 2007 (UTC)

Assessing article status

I just rearranged and added to the Angular velocity article. It is presently classified as start-class, but perhaps it warrants an upgrade. I am not very practiced in asessing article status, nor do I know the procedure for asking someone else to take a look. Can someone give me some pointers? Thanks - PAR 03:21, 22 January 2007 (UTC)

Edit the template at the top of the talk page, and change "start" to "B" (or "A" if you think its that, etc.).linas 01:40, 25 January 2007 (UTC)

Request for comment: Afshar experiment

See Talk:Afshar experiment#Neutrality Discussion. Article is primarily edited by the professor who ran the eponymous experiment, and there is a lot of dispute going on regarding accusations of WP:OWN, contentious editing, etc. A lot of self-proclaimed scientists are throwing a LOT of words around on the talk page and it's getting increasingly hard to follow.-Dmz5*Edits**Talk* 03:16, 24 January 2007 (UTC)

FWIW, I have found Prof. Afshar to be a reasonable and well-tempered personality. Unfortunately, his ideas attract negaitve attention. I've attempted to mediate in the past, with little success. Danko should be barred from the talk page; he is incompetent on this subject matter (his knowledge is at the level of freshman physics). I have found Micheal C. Price, an editor I otherwise respect, to have crossed the line, repeatedly, in being uncivil, and in repeatedly adding his own original research in attempting to debunk (incorrectly) the Afshar experiment. I'm sorry to say, he should also probably be banned from that article, at least temporarily. Although it is difficult to wade through the arguments, for the most part I think Afshar has acted with nobility, and is not the party at fault here. (Full disclosure: yes, I've got a doctorate in quantum, yes, my initial reaction, like the rest of the world, was to disparage the topic. I've since warmed enough to it to realie that it should not dismissed out-of-hand; the arguments are subtle, and my impression is that the WP nay-sayers don't have the background to appreciate the subtlties.) linas 02:03, 25 January 2007 (UTC)
As a completely uninvolved party, and with admittedly only half a semester of graduate-level quantum mechanics under my belt, I would be willing to mediate this dispute. I have come across the Afshar experiment only once before, in reference to Freeman Dyson's suggestion that the uncertainty principle would not hold for suitably large scales. I've read through the article and the related pages and have to say that a lot of the arguments seem to not be over the physics (except where some obvious errors are made by User:Danko) or the point-in-fact science of the work but rather the philosophical interpretations or original research connections. As with all quantum articles, normal "philosophy warnings" associated with quantum mechanics should be followed. I'll e-mail Ashfar and cross-post this suggestion at the article in question. --ScienceApologist 03:14, 25 January 2007 (UTC)
Dear ScienseApologist, please show a clear statement that is wrong. Since we defend opposing viewpoints with Linas, Afshar, etc, it is perfectly understandable that they think I am incompetent. Alas, there is growing number of physicists supporting my thesis, and before you characterize my work I recommend you to read my PhilSci paper. Danko Georgiev MD 06:01, 25 January 2007 (UTC)

Dear ScienseApologist, You are welcome to attempt to mediate. At this point, common sense, and patience, not high learning, are needed. I don't know what to do with Danko. A good while ago, we exchanged a half dozen private emails; Danko had recently purchased a book on complex analysis, and was having trouble with basic complex numbers. Given that this is college freshman math, or maybe even high-school math, I urged him on in his studies (enthusiasm is a good thing), but advised him to stop pestering Afshar. As you see above, the advice was not heeded, which is why I recommend a ban. Most of the other participants seem knowledgable, but seem to want to insert amateurish debunking arguments. I view these debunking attempts to be "original research" in the full sense, but have been unable to persuade the debunkers from adding this type of material. linas 04:49, 26 January 2007 (UTC)

AfD List of physics formulae

FYI. Wikipedia:Articles for deletion/List of physics formulae linas 05:34, 26 January 2007 (UTC)

Event Horizon caused by increasing escape velocity?

In the section event horizon of the article Black hole it says "At the event horizon, the escape velocity is more than the speed of light. This is why anything inside the event horizon, including a photon, is prevented from escaping across the event horizon by the extremely strong gravitational field." But it's the curvature of space-time not the escape velocity which causes the point of no return so this is simply false imo. Furthermore the escape velocity at the event horizon is equal too, not more than, the speed of light. I tried to edit it, but someone instantly reversed it, so perhaps someone more qualified could have a look at it? Berrick (talk) 21:25, 8 January 2007 (UTC)

The problem may lie in the other part of your edit where you say "It is a common misconception that nothing can escape a black hole because of the non-relativistic argument that the escape velocity near a black hole is higher than the speed of light. This is not true since it would enable accelerated objects to escape a black hole which is not the case.". Objects traveling at the speed of light cannot accelerate in their direction of motion (outward in this case). They can only accelerate sideways. Thus you are wrong. JRSpriggs 08:40, 9 January 2007 (UTC)
I was not talking about accelerating objects that move at the speed of light, but merely about accelerating objects out of inner region of the event horizon. As described in the section event horizon, a black hole is just a non-relativistic phenomenon as described by John Michell. Like it is said in the section Inside the event horizon: "In Michell's theory, the escape velocity equals the speed of light, but it would still, for example, be theoretically possible to hoist an object out of a black hole using a rope. General relativity eliminates such loopholes...". This is what I meant by an accelerated object. I didn't expect my edit to last because I'm fairly new here, but i thought at least someone would see the obvious error in the original writing and would replace or modify my edit in stead of simply reversing it. Berrick (talk) 11:06, 10 January 2007 (UTC)
Michell's theory is based on pre-relativistic physics, so he does not give the speed of light the same significance that we do. Presumably, he believed that light from the star inside would be slowed down by gravity and fall back onto the star. That is not how we think of it today.
Suppose you start from just inside the event horizon in a rocket ship and try to escape. As you turn on your engine (aiming outward), you also send a flash of light outward. Since light in a vacuum is always faster than any material object, you clearly can never overtake or pass the flash of light, regardless of how much you accelerate. Since the flash of light cannot cross the horizon going outward, then neither can you.
However, there is one sentence in the section "Inside the horizon" which I think may be wrong. It is "A consequence of this is that a pilot in a powerful rocket ship that had just crossed the event horizon who tried to accelerate away from the singularity would reach it sooner in his frame, since geodesics (unaccelerated paths) are paths that maximize proper time.". That argument assumes that the central singularity is a single event. But I think that that is not so. JRSpriggs 11:56, 10 January 2007 (UTC)
I do understand why nothing can escape from inside the event horizon since I took a course in General Relativity. This has nothing to do with escape velocity in contrast to what the section event horizon suggests. Hence that section is incorrect. If one were to look only at the escape velocity and not at the curvature of space-time, light would be able to escape from a black hole, even if the escape velocity was greater then the speed of light, because non-relativistically light isn't influenced by gravity. Light is only bend by gravity indirectly through the curvature of space-time.
The section "Inside the horizon", however, is correct. Since any acceleration will cause an object to diverge from its geodesic, the proper time before arriving at the singularity will decrease. But this doesn't have anything to do with my point. Berrick 12:26, 10 January 2007 (UTC)
I don't want to nitpick but it isn't really the curvature of spacetime, either. At the horizon of a very large black hole, the various curvature invariants can be arbitrarily small. The horizon is really more of a global property(turning over of light cone) than anything to do with curvature, which is a local property. -Joshua Davis 18:37, 10 January 2007 (UTC)

The point I have been trying (apparently unsuccessfully) to make is that Berrick is misinterpreting the meaning of escape velocity. It is defined by "... the escape velocity is the minimum speed an object without propulsion needs to have to move away indefinitely from the source of the field, as opposed to falling back or staying in an orbit within a bounded distance from the source. The object is assumed to be influenced by no forces except the gravitational field; ...". This is exactly what we are talking about. Berrick seems to be reading into this a non-relativistic concept which is not there. He said "... because non-relativistically light isn't influenced by gravity. Light is only bend by gravity indirectly through the curvature of space-time.". But we are talking relativistically. And the gravitational force-field (Christoffel symbol) is caused by curvature, not the other way around. And it does affect light as well as matter. JRSpriggs 08:07, 11 January 2007 (UTC)

Berrick makes another mistake. The location of an event horizon depends on the acceleration of the observer. Or, equivalently, as Joshua Davis points out, its a global property, not a local property.
JRSpriggs, please be careful, as the "you can't outrun a photon" argument is fallacious. For example, suppose you are orbiting a very large (rotating) black hole. You fire your rockets, and boost your orbit upwards until you escape from the influence of the black hole. However, I believe that all the photons you emit early-on will fall into the black hole (or remain orbiting forever, failing to escape), as these will be inside the event horizon for an unaccelerated observer. Basically, the location of the event horizon for an observer attempting to hover above a black hole (without angular momentum) is much "farther away" (larger "radius") than for one who is orbiting. You can "get closer" by orbiting, and you fall in if you slow/stop orbiting, and no amount of acceleration will get you out once you've slowed your orbit too much. For thosee poor photons who failed to strap on a rocket engine when they made their jump, it is the end. linas 15:40, 12 January 2007 (UTC)
To Joshua: I thought that if there was no curvature at all we would live in a Minkowskian space and light cones would not turn over at all. Regardless, you must agree that the fact that escape velocity exceeds the speed of light is not the reason that nothing can escape a black hole.
To JRSpriggs: My remark that escape velocity is something non-relativistic was perhaps incorrect, although, I haven't seen it used in any relativistic writing. But to show that the argument about escape velocity in the section is incorrect, consider the following:
First of all, the escape velocity only concerns unaccelerated objects. But what if an object (moving slowely) would be pulled out by a (non-gravitational) force greater than the gravitational force of the black hole? It would escape, which is not possible.
Secondly, if an object's speed is smaller than the escape velocity it only means it cannot escape to infinity. This doesn't mean it can't move a finite distance outward. But inside the event horizon there is no outward movement possible at all.
To Linas: The location of the event horizon is the same for any observer. Off course, a coordinate transformation could change it but if you were to draw a circle around the black hole indicating the event horizon, anyone crossing that circle regardless of acceleration would end up at the singularity. But this is totally besides the point of my original post. Could we please stay on-topic?
I invite anyone to correctly modify the section event horizon, for, somehow, this error is really bugging me. Berrick 16:03, 12 January 2007 (UTC)
Hrmm? Sorry to go off-topic. The "circle" you draw is known as the "Schwarzchild radius" (SR) for a non-rotating black hole, and it is not the same thing as the event horizon. The event horizon for an infalling observer is clearly very different than that for an observer trying to hover above the SR. An infalling observer who has crossed the SR can certainly "see" stuff going on "inside" the SR; what they can't do is tell anyone what they saw. This is particularly dramatic for a supermassive black hole, where the tidal forces at the SR are miniscule. For an infalling observer, life continues on pretty normally as they cross the SR, at least for a little while. (Disclaimer: Its been a few decades since I've studied GR, but I'm pretty sure I'm not that confused). linas 23:32, 12 January 2007 (UTC)
You seem to be talking about the apparent horizon while I am talking about the absolute horizon. The latter is in general what one means when talking about the event horizon. Berrick 01:02, 13 January 2007 (UTC)
These articles are wrong, or at least incomplete. They should mention, among other things, the existence of several horizons, encompassing a zone around a rotating black hole that is a kind of absolute horizon, for observers that wish to hover, but can never-the-less be escaped from, if the observer is in orbit. This is a part of the Kerr solution, and is closely related to frame dragging. The Kerr solution article seems to list all the jargon/keywords, but fails to give a plain language explanation of the basic concepts. Oh well. linas 05:00, 13 January 2007 (UTC)
On page 836 of "Gravitation (book)" by Misner, Thorne, and Wheeler, exercise 31.4 "How long to live?" on Kruskal-Szekeres coordinates for the Schwarzschild solution contains a hint which indicates that free falling bodies inside a black hole may have different amounts of time until they hit the central singularity. This time depends not only on where the body is but also on its velocity. So a single course-correction (brief burst of rocket fire) may be necessary to maximize one's survival time. Thereafter, one should not accelerate. The optimal orbit is one which one would be in if he began at the Schwarzschild radius at rest and fell freely. Those who fell across the horizon would have to fire their engines to get into such an orbit. The singularity is one-dimensional, not merely a zero-dimensional event. Where (or should I say when?) one arrives at the singularity determines the maximum time you have to survive.
To Linas: If a rocket emits a spherical burst of light, how could it ever accelerate out of the interior of that sphere without violating the topology of space-time? JRSpriggs 06:59, 16 January 2007 (UTC)
Sorry for belated answer, I've been busy. The Kerr solution is different than the Schwarzschild solution. The Schwarzschild solution has one unambiguous horizon; the Kerr solution has several. See WP articles on ergosphere, Cauchy horizon, Reissner-Nordström solution, photon sphere and Killing horizon. More than one can shake a stick at. linas 01:07, 25 January 2007 (UTC)

To Linas: If you were replying to my point, I do not get it. You did not address how the rocket ship could get outside of the sphere of light it emitted earlier. In a rotating black hole, one might be able to pass through the hole in the ring-shaped singularity, but that would at best get you into another universe, not our universe. And you would still be within the expanding sphere of light. JRSpriggs 08:07, 25 January 2007 (UTC)

Yes, I surely mis-stated something. Its been several decades since I studied GR; it was not a topic I'd ever mastered; and I was trying to reconstruct some dimly remembered argument about frame dragging, which I got wrong. The only real point I wanted to make was to urge caution in the definition and construction of "the" horizon, as there are several different things that deserve to be called horizons; thinking only of the Schwarzschild model is an over-simplification.linas 05:05, 26 January 2007 (UTC)
OK. Then I think we may be in agreement now. The horizon depends on the world-line of the observer who either can or cannot see things depending on whether they are on his side of the horizon or not. The horizon does NOT depend the state of motion of the poor sap who is trying to cross from the wrong side to the right side. Is that not so? JRSpriggs 10:31, 26 January 2007 (UTC)
That is not so. Err .. "The horizon depends on the world-line of the observer", but the world line of the observer depends on the observer's acceleratation, ergo, "the horizon" does depend on the "state of motion". And we've also established that there are multiple varieties of horizons, such as the ergosphere and the photon sphere, not just one. I also get the impression that this is an argument for the sake of arguing. Are we trying to fix some article, or are we having a pissing match? linas 00:53, 27 January 2007 (UTC)
Continued in a new section below #Defining event horizon. JRSpriggs 04:21, 27 January 2007 (UTC)

Defining event horizon

Continued from above #Event Horizon caused by increasing escape velocity?. Copied over two remarks:

OK. Then I think we may be in agreement now. The horizon depends on the world-line of the observer who either can or cannot see things depending on whether they are on his side of the horizon or not. The horizon does NOT depend the state of motion of the poor sap who is trying to cross from the wrong side to the right side. Is that not so? JRSpriggs 10:31, 26 January 2007 (UTC)

That is not so. Err .. "The horizon depends on the world-line of the observer", but the world line of the observer depends on the observer's acceleration, ergo, "the horizon" does depend on the "state of motion". And we've also established that there are multiple varieties of horizons, such as the ergosphere and the photon sphere, not just one. I also get the impression that this is an argument for the sake of arguing. Are we trying to fix some article, or are we having a pissing match? linas 00:53, 27 January 2007 (UTC)
I am just trying to get us onto the same wave-length. By the observer whose world-line determines the horizon, I mean someone who is usually taken to be very far away from the black hole. By the poor sap trying to cross the horizon, I mean the guy who foolishly fell into the black hole and is now trying to get back out, a different person. The state of motion of the observer far away is relevant -- if he accelerates continuously, he can create a horizon across the whole universe cutting it in half. But the sap who fell in cannot by any means accelerate enough to cross the horizon once he is on the other side from the observer.
Although ergosphere is an important concept -- the outer boundary of the region where one cannot stay at one place by any application of force, I would not call it an event horizon. The photon sphere, if I understand it correctly, is the outer boundary of the region where one cannot be in a stable "circular" orbit around the black hole. That is also different from the event horizon -- the outer boundary of the region where one cannot escape along any path whatever. Am I right? JRSpriggs 04:43, 27 January 2007 (UTC)
Correction. I just checked Gravitation (book) pages 879, 880, 894. The static limit is the outer boundary of where one cannot stay still. The ergosphere is the region between the static limit and the event horizon (which is inside it). The static limit and the horizon touch at the north and south poles of a rotating black hole. For a non-rotating black hole, they are of course the same surface.
Also, on second thought I see that where the stable circular orbits for a rotating black hole can exist depends on the direction of orbiting compared to the direction that the black hole is rotating. So the "photon sphere" (which I did NOT find in MTW) cannot just be a surface, it has to be a more complicated structure. JRSpriggs 05:26, 27 January 2007 (UTC)


The frame-dragging article has recently been subject to some highly POV editing between two competing points of view, with accusations of censorship and other name-calling in the other article text. See, for example, recent edits by User:, and various other Italian IP addresses beginning with 87, some of the most recent of which accuse other editors of censorship, with accusations that they are mentally ill (see this edit and this edit). It has also grown a rather large bibliography, yet currently lacks any specific supporting citations or attributions for any of the controversial opinions in the article.

Since most of the content of this article seems to be the disputed content, I have now removed all the disputed content, reducing the article to a very brief but uncontentious stub. This article now needs to be rebuilt, with serious attention to WP:NPOV and WP:CITE, to bring it up to date with current scientific knowledge, explicitly mentioning which areas are the subject of current scientific controversy. -- The Anome 12:27, 29 January 2007 (UTC)

Since the above, I've done quite a lot of tidying, and tried to turn the bibliography into a proper list of references. I'd still appreciate any comments from other editors on the current version of the article. -- The Anome 13:49, 29 January 2007 (UTC)

Faster than light paradoxes

I've noticed that many articles here on wiki (e.g. the special relativity article) don't explain what's so problematic about faster than light signals correctly. Of course, it is trivial to note that in some frames the "cause" will happen later than the "effect". However, this in itself is not a problem, as is explained in this article on pages 10 to 13. It is the causal paradox you could get which is the problem.

The Scharnhorst effect cannot be used to create a causal paradox, so it is not a problem. The wiki article on this topic fails to mention this and the impression is left that the faster than c propagation of light in the Casimir vacuum could cause problems... Count Iblis 14:02, 29 January 2007 (UTC)