Wikipedia talk:WikiProject Physics/Archive October 2017

An offline App for Physics

Hello everyone,

The Kiwix people are working on an offline version of several Wikipedia subsets (based on this Foundation report). It basically would be like the Wikimed App (see here for the Android light version; iOS is in beta, DM me if interested), and the readership would likely be in the Global South (if Wikimed is any indication): people with little to no access to a decent internet connexion but who still would greatly benefit from our content.

What we do is take a snapshot at day D of all articles tagged by the project (minus Biographies) and package it into a compressed zim file that people can access anytime locally (ie once downloaded, no refresh needed). We also do a specific landing page that is more mobile-friendly, and that's when I need your quick input:

1. Would it be okay for you to have it as a subpage of the Wikiproject (e.g. WikiProject Physics/Offline)? Not that anyone should notice or care, but I'd rather notify & ask
2. Any breakdown of very top-level topics that you'd recommend? (see Wikipedia:WikiProject_Medicine/Open_Textbook_of_Medicine2 for what we're looking at in terms of simplicity) Usually people use the search function anyway, but a totally empty landing page isn't too useful either. Alternatively, if you guys use the Book: sorting, that can be helpful.

Thanks for your feedback! Stephane (Kiwix) (talk) 12:27, 10 October 2017 (UTC)

I'm not sure we have a breakdown of top-level topics already, but it ought to be straightforward enough to create one, for example by going down the list of courses in a typical undergraduate curriculum: classical mechanics, electromagnetism, thermodynamics/statistical physics, relativity, quantum mechanics, etc. XOR'easter (talk) 16:02, 10 October 2017 (UTC)

We have Outline of physics, which is nothing official, but might be a good start in organizing top level subjects. For grade school and high school simplicity, we have List of physics concepts in primary and secondary education curricula. —Mark viking (talk) 16:14, 10 October 2017 (UTC)

Awesome, we'll take it from there then. Thanks gentlemen. Stephane (Kiwix) (talk) 08:06, 12 October 2017 (UTC)

Discussion at Wikipedia:Articles for deletion/Camelback Potential

You are invited to join the discussion at Wikipedia:Articles for deletion/Camelback Potential. power~enwiki (π, ν) 15:55, 24 October 2017 (UTC)

Lorenz gauge condition, edit warring

User:Stephen_William_Wynn makes repeated edits to Lorenz_gauge_condition, changing signs relativistic notation and how signs interplay with raising and lowering indices. They also post about this on Physics StackExchange, e.g. at https://physics.stackexchange.com/q/360741. I am not familiar with Wikipedia's processes for such things and have little time to use the "conflict resolution" strategies that the help pages propose. I leave this comment here in case the more experiences Wikipedians of this project know what to do about this. contrary to the accepted versions in the literature, presumably because they misunderstand 2A01:5C0:16:791:6828:CFB7:14FE:936F (talk) 11:32, 3 October 2017 (UTC)

He made a similar change at Gauge fixing. JRSpriggs (talk) 17:30, 3 October 2017 (UTC)

I apologise if it's frowned upon to revert his changes before the "issue" is "resolved" but I can't bear to see the articles left in the wrong state. The mistake he's making is addressed in Four-gradient#Derivation. — dukwon (talk) (contribs) 17:36, 3 October 2017 (UTC)

I note that over on Physics StackExchange, he says, "The definition of the Lorenz gauge condition on Wikipedia has changed" and "They seem to have been influenced by my discussion" — when he's the one who changed it. Also, I added a couple textbook references (one for SI units, the other for Gaussian) which give the correct signs. XOR'easter (talk) 17:49, 3 October 2017 (UTC)

In four-gradient the Lorenz gauge condition is derived:

$\mathbf {\partial } \cdot \mathbf {A} =\partial ^{\mu }\eta _{\mu \nu }A^{\nu }=\partial _{\nu }A^{\nu }=\left({\frac {\partial _{t}}{c}},-{\vec {\nabla }}\right)\cdot \left({\frac {\phi }{c}},{\vec {a}}\right)={\frac {\partial _{t}}{c}}\left({\frac {\phi }{c}}\right)+{\vec {\nabla }}\cdot {\vec {a}}={\frac {\partial _{t}\phi }{c^{2}}}+{\vec {\nabla }}\cdot {\vec {a}}=0$

This is combining co- and contravariant vectors with the Minkowski dot product signature (+---) which is wrong. They both have to be covariant or both contravariant. With signature  (++++) one has to be covariant and the other contravariant. So we have signature (+---): 

$\mathbf {\partial } \cdot \mathbf {A} =\partial ^{\mu }\eta _{\mu \nu }A^{\nu }=\partial _{\nu }A^{\nu }=\left({\frac {\partial _{t}}{c}},{\vec {\nabla }}\right)\cdot \left({\frac {\phi }{c}},{\vec {a}}\right)={\frac {\partial _{t}}{c}}\left({\frac {\phi }{c}}\right)-{\vec {\nabla }}\cdot {\vec {a}}={\frac {\partial _{t}\phi }{c^{2}}}-{\vec {\nabla }}\cdot {\vec {a}}=0$

Signature (++++):

$\mathbf {\partial } \cdot \mathbf {A} =\partial ^{\mu }\eta _{\mu \nu }A^{\nu }=\partial _{\nu }A^{\nu }=\left({\frac {\partial _{t}}{c}},-{\vec {\nabla }}\right)\cdot \left({\frac {\phi }{c}},{\vec {a}}\right)={\frac {\partial _{t}}{c}}\left({\frac {\phi }{c}}\right)-{\vec {\nabla }}\cdot {\vec {a}}={\frac {\partial _{t}\phi }{c^{2}}}-{\vec {\nabla }}\cdot {\vec {a}}=0$

— Preceding unsigned comment added by Stephen William Wynn (talk • contribs) 09:54, 5 October 2017 (UTC)

For the n^th time, $\partial ^{\mu }=\left({\frac {\partial _{t}}{c}},-{\vec {\nabla }}\right)$ not $\left({\frac {\partial _{t}}{c}},{\vec {\nabla }}\right)$. The contra- and co-variant forms of four-gradient has the opposite set of minus signs as a four-vector. It is explained at Four-gradient#Derivation and [1] and [2]. Please take the time to process and understand this instead of continuing to ignore it. — dukwon (talk) (contribs) 10:07, 5 October 2017 (UTC)

$\partial _{t}\phi +{\vec {\nabla }}\cdot {\vec {a}}$ is the divergence for the wrong group, the orthogonal group O(4). For the Lorentz group we need a minus $\partial _{t}\phi -{\vec {\nabla }}\cdot {\vec {a}}$. — Preceding unsigned comment added by Stephen William Wynn (talk • contribs) 12:50, 5 October 2017 (UTC)

If you trust the source you used at Talk:Lorenz gauge condition in order to define Lorentz invariance, note that the same course notes, two lectures later, give the correct sign. XOR'easter (talk) 15:23, 5 October 2017 (UTC)

These lecture notes are showing a plus, which is the wrong sign. Most, but not all the literature also has a plus. For Lorentz invariance there needs to be a minus. — Preceding unsigned comment added by Stephen William Wynn (talk • contribs) 16:41, 5 October 2017 (UTC)

All of the literature linked so far has a plus. Persistently repeating the same misconception doesn't make it any truer. The operator $\partial _{\mu }\equiv {\frac {\partial }{\partial x^{\mu }}}\equiv \left({\frac {1}{c}}{\frac {\partial }{\partial t}},{\frac {\partial }{\partial x}},{\frac {\partial }{\partial y}},{\frac {\partial }{\partial z}}\right)$ is covariant, not contravariant. It transforms like ${\frac {1}{x^{\mu }}}\equiv \left({\frac {1}{ct}},{\frac {1}{x}},{\frac {1}{y}},{\frac {1}{z}}\right)$ and $x_{\mu }\equiv \left(ct,-x,-y,-z\right)$. Therefore $\partial _{\mu }A^{\mu }={\frac {1}{c}}{\frac {\partial A^{0}}{\partial t}}+{\frac {\partial A^{1}}{\partial x}}+{\frac {\partial A^{2}}{\partial y}}+{\frac {\partial A^{3}}{\partial z}}$. — dukwon (talk) (contribs) 17:10, 5 October 2017 (UTC)

$\partial _{\mu }A^{\mu }={\frac {1}{c}}{\frac {\partial A^{0}}{\partial t}}+{\frac {\partial A^{1}}{\partial x}}+{\frac {\partial A^{2}}{\partial y}}+{\frac {\partial A^{3}}{\partial z}}$ is true for ordinary vector space group O(4) that is signature (++++). For the Lorenz group and Minkowski signature (+---), that is four-vectors we have

$\partial _{\mu }A^{\mu }={\frac {1}{c}}{\frac {\partial A^{0}}{\partial t}}-{\frac {\partial A^{1}}{\partial x}}-{\frac {\partial A^{2}}{\partial y}}-{\frac {\partial A^{3}}{\partial z}}$ — Preceding unsigned comment added by Stephen William Wynn (talk • contribs) 10:24, 6 October 2017 (UTC)

You talk about groups but ignore how things actually transform under these groups, choosing to instead focus on the minus signs. There's no way you aren't trolling at this point. — dukwon (talk) (contribs) 10:51, 6 October 2017 (UTC)

All of the literature does not have a plus, for example

https://books.google.co.uk/books?id=sZ1-G4hQgIIC&pg=PA6&lpg=PA6&dq=%22lorentz+divergence%22&source=bl&ots=an9RN8T5t3&sig=TGpqKb5gYOT4PmcPgveZgHKEUlc&hl=en&sa=X&ved=0ahUKEwj4hImczuXUAhUOYlAKHfBuCQ8Q6AEINzAE#v=onepage&q=%22lorentz%20divergence%22&f=false — Preceding unsigned comment added by Stephen William Wynn (talk • contribs) 11:57, 6 October 2017 (UTC)

$\partial _{\mu }A^{\mu }={\frac {1}{c}}{\frac {\partial A_{0}}{\partial t}}-{\frac {\partial A_{1}}{\partial x}}-{\frac {\partial A_{2}}{\partial y}}-{\frac {\partial A_{3}}{\partial z}}$ because you are taking the dot product of a covariant operator with a contravariant vector. Stephen William Wynn —Preceding undated comment added 17:39, 7 October 2017 (UTC)

So I have finally realised what the problem is. The Wikipedia article has a contravariant four-potential which produces a plus. I have a covariant four-potential with lower indices which produces a minus. I suggest they switch, starting with:

$\partial ^{\mu }A_{\mu }=0$

— Preceding unsigned comment added by (talk • contribs)

May I suggest you leave this to people that actually understand what they are doing? You have been wasting our time with your senseless ramblings long enough. And for the love of God please learn to sign your comments.TR 10:30, 8 October 2017 (UTC)

The people "that actually understand what they are doing" could not answer my question why I obtain $\nabla \cdot {\vec {A}}-{\frac {1}{c}}{\frac {\partial \phi }{\partial t}}=0$ for the Lorenz gauge condition and Wikipedia has $\nabla \cdot {\vec {A}}+{\frac {1}{c}}{\frac {\partial \phi }{\partial t}}=0$.   Its because I put ${\vec {A}}=(A_{1},A_{2},A_{3})$ and they put  ${\vec {A}}=(A^{1},A^{2},A^{3})$ and $(A_{1},A_{2},A_{3})=-(A^{1},A^{2},A^{3})$. Stephen William Wynn

Consideration of the defining equations of the electric and magnetic potentials,

$\mathbf {B} =\nabla \times \mathbf {A} \,,\quad \mathbf {E} =-\nabla \phi -{\frac {\partial \mathbf {A} }{\partial t}}\,,$

leads to the conclusion that the electric potential is not the time component of the magnetic potential. Rather it is its negative. That consideration also leads to the inference that the potential is a covariant four-vector. Otherwise the curl would make no sense.

So the generally invariant form of the Lorenz gauge must be

$0=g^{\alpha \beta }A_{\alpha ;\beta }=g^{\alpha \beta }A_{\alpha ,\beta }-g^{\alpha \beta }\Gamma _{\alpha ,\beta }^{\gamma }A_{\gamma }$.

If we restrict ourselves to SR, i.e. we ignore gravity and choose an inertial frame of reference (non-rotating free-falling Cartesian coordinates), then we get

$0=\eta ^{\alpha \beta }A_{\alpha ,\beta }={\frac {-1}{c^{2}}}{\frac {\partial (-\phi )}{\partial t}}+\nabla \cdot \mathbf {A} ={\frac {\partial \phi }{c^{2}\partial t}}+\nabla \cdot \mathbf {A}$.

Notice that the minus signs cancel leaving a plus sign. Also the units are consistent. JRSpriggs (talk) 18:39, 8 October 2017 (UTC)

$\mathbf {B} =\nabla \times \mathbf {A} \,,\quad \mathbf {E} =-\nabla \phi -{\frac {\partial \mathbf {A} }{\partial t}}\,,$

I prefer:

$\mathbf {B} =-\nabla \times \mathbf {A} \,,\quad \mathbf {E} =-\nabla \phi +{\frac {\partial \mathbf {A} }{\partial t}}\,,$

I explain E at:  Why is ${\vec {E}}$ defined as $-\nabla \phi -\partial {\vec {A}}/\partial t$?:

https://physics.stackexchange.com/questions/342533/why-is-vece-defined-as-nabla-phi-partial-veca-partial-

This is why I am interested in the Lorenz gauge condition. The misleading definition on Wikipedia has been causing problems. —Preceding undated comment added 10:44, 9 October 2017 (UTC)

Under gauge-fixing it says:

"==Lorenz gauge==

The Lorenz gauge is given, in SI units, by:

$\nabla \cdot {\mathbf {A} }+{\frac {1}{c^{2}}}{\frac {\partial \varphi }{\partial t}}=0$

and in Gaussian units by:

$\nabla \cdot {\mathbf {A} }+{\frac {1}{c}}{\frac {\partial \varphi }{\partial t}}=0.$

This may be rewritten as:

$\partial ^{\mu }A_{\mu }=0.$"

This is wrong. Should be:

$\nabla \cdot {\mathbf {A} }-{\frac {1}{c^{2}}}{\frac {\partial \varphi }{\partial t}}=0$

and in Gaussian units by:

$\nabla \cdot {\mathbf {A} }-{\frac {1}{c}}{\frac {\partial \varphi }{\partial t}}=0.$

Because: $\partial ^{\mu }=({\frac {1}{c}}{\frac {\partial }{\partial t}},-{\frac {\partial }{\partial x}},-{\frac {\partial }{\partial y}},-{\frac {\partial }{\partial z}})$ 

Stephen William Wynn

To Stephen William Wynn: The formula $\mathbf {B} =\nabla \times \mathbf {A}$ is generally accepted (as I just verified with Google). Changing the sign of A would be very disruptive because it would invalidate essentially all use of the magnetic potential in the literature. Certainly, an encyclopedia like Wikipedia should not do such a thing. Changing conventions just to try to win an argument is totally unacceptable. JRSpriggs (talk) 19:50, 9 October 2017 (UTC)

To quote:

Because: $\partial ^{\mu }=({\frac {1}{c}}{\frac {\partial }{\partial t}},-{\frac {\partial }{\partial x}},-{\frac {\partial }{\partial y}},-{\frac {\partial }{\partial z}})$

Wow finally you got that part right, after being told countless times. So it follows simply that $\partial _{\mu }A^{\mu }\equiv \partial ^{\mu }A_{\mu }={\frac {1}{c}}{\frac {\partial A^{0}}{\partial t}}+{\frac {\partial A^{1}}{\partial x}}+{\frac {\partial A^{2}}{\partial y}}+{\frac {\partial A^{3}}{\partial z}}$ and we can finally put the matter to rest. — dukwon (talk) (contribs) 22:25, 9 October 2017 (UTC)

Piling on: I am 100% confident that the formula $\mathbf {B} =-\nabla \times \mathbf {A}$ is in contradiction with every one of the dozens of electromagnetism textbooks that I have read, and 95% confident that it is in contradiction with every single mainstream electromagnetism textbook ever written. All physicists use the definition $\mathbf {B} =+\nabla \times \mathbf {A}$. Stephen, if you "prefer" the minus sign, well you can use whatever definition you like in the privacy of your own home, but when you edit Wikipedia you need to stick to the definitions and terminologies that everyone else uses. I can think of dozens of things in mainstream physics that are not defined in the way that I would "prefer"—for example I would "prefer" if everyone used Lorentz-Heaviside electromagnetism units instead of SI, I would "prefer" if electrical charge was defined such that the electron is positive, etc. etc. But I edit wikipedia in a way that's compatible with mainstream physics, not my preferences. :-D --Steve (talk) 01:04, 10 October 2017 (UTC)

Case closed. Drink deep, or taste not the Pierian Spring. Xxanthippe (talk) 02:24, 10 October 2017 (UTC).

It is unacceptable using upper indices for the four-potential because this makes it contravariant. So we have:

$\partial _{\mu }A^{\mu }\equiv \partial ^{\mu }A_{\mu }={\frac {1}{c}}{\frac {\partial A_{0}}{\partial t}}-{\frac {\partial A_{1}}{\partial x}}-{\frac {\partial A_{2}}{\partial y}}-{\frac {\partial A_{3}}{\partial z}}$

But this is incompatible with:

$\mathbf {B} =\nabla \times \mathbf {A} \,,\quad \mathbf {E} =-\nabla \phi -{\frac {\partial \mathbf {A} }{\partial t}}\,,$

As I point out in the case of E at:

https://physics.stackexchange.com/questions/342533/why-is-vece-defined-as-nabla-phi-partial-veca-partial-t

So we have to change the definition of E to $\mathbf {E} =-\nabla \phi +{\frac {\partial {\vec {A}}}{\partial t}}$ It turns out we also have to redefine $\mathbf {B} =-\nabla \times {\vec {A}}$

Stephen William Wynn —Preceding undated comment added 10:08, 10 October 2017 (UTC)

This is a case of shit in means shit out. Also is signing your comments really that hard.TR 11:02, 10 October 2017 (UTC)

I suggest that this thread be collapsed and any extension of it be considered trolling. Xxanthippe (talk) 23:07, 10 October 2017 (UTC).

So we are now agreed that the Lorenz gauge condition is:

$\nabla \cdot {\mathbf {A} }-{\frac {1}{c}}{\frac {\partial \varphi }{\partial t}}=0$

where we are using lower indices:

$A_{\mu }=(\varphi ,\,\mathbf {A} )$ is the electromagnetic four-potential  Stephen William Wynn (talk) 12:21, 11 October 2017 (UTC)

No. Obviously.TR 13:19, 11 October 2017 (UTC)

This is getting tiresome. Wikipedia is not the place to argue that every textbook on a topic is wrong. XOR'easter (talk) 18:25, 11 October 2017 (UTC)

I am saying $\partial ^{\mu }A_{\mu }=0.$ implies 

$\nabla \cdot {\mathbf {A} }-{\frac {1}{c}}{\frac {\partial \varphi }{\partial t}}=0$

not

$\nabla \cdot {\mathbf {A} }+{\frac {1}{c}}{\frac {\partial \varphi }{\partial t}}=0$

in most but not all of the literature. Wikipedia should be an authority, not making elementary schoolboy mistakes.

I am not able to sign this comment because Wikipedia wants me to type in a character which is not on my keyboard and I cannot find it to do a copy. Stephen William Wynn (talk) 10:26, 12 October 2017 (UTC)

You don't have to repeat yourself; it's all here on this page. Earlier you had the correct definition of $A^{\mu }$ but the wrong definition of $\partial ^{\mu }$. Now you've accepted the correct definition of $\partial ^{\mu }$ but changed your definition of $A^{\mu }$ to preserve the same (incorrect) conclusion. The four-vector $\left(\varphi ,\mathbf {A} \right)$ transforms contravariantly, despite your opinion that it's "totally unacceptable". — dukwon (talk) (contribs) 11:04, 12 October 2017 (UTC)

@Stephen William Wynn: here you go, for signing copy this: ~~~~ .  Purgy (talk) 11:26, 12 October 2017 (UTC)

Under four-potential it says "the electromagnetic four-potential is Lorentz covariant". It is a four-vector which can be covariant or contravariant. It is covariant in the first instance. Using a contravariant four-potential in the definition of the Lorenz gauge condition on Wikipedia is confusing. People are looking on Wikipedia and saying I am wrong, not noticing that Wikipedia is using a contravariant four-potential. This has bought discussions to a standstill. Stephen William Wynn (talk) 17:41, 12 October 2017 (UTC)

Lorentz covariance and the covariance and contravariance of vectors are separate matters. In Lorentz covariance it states (correctly) that "[b]oth covariant and contravariant four-vectors can be Lorentz covariant quantities". I don't see a problem here. — dukwon (talk) (contribs) 18:03, 12 October 2017 (UTC)

While it is true that EM 4-potential is most naturally expressed as a covariant vector, or more precisely a u(1) valued 1-form, the relation with the electric (scalar) potential, and the magnetic (vector) potential is more naturally given with it contravariant form:

$A^{\alpha }=(\phi ,{\vec {A}})$

The fact that ${\vec {A}}$ is a contravariant vector field should have tipped you off. More importantly this relation can be found in any textbook (on EM).TR 19:27, 12 October 2017 (UTC)

The Lorenz gauge condition $\partial ^{\mu }A_{\mu }=0$ contains a minus when expanded:   $\partial ^{\mu }A_{\mu }=({\frac {1}{c}}{\frac {\partial }{\partial t}},-{\frac {\partial }{\partial x}},-{\frac {\partial }{\partial y}},-{\frac {\partial }{\partial z}}).(\varphi ,A_{1},A_{2},A_{3})={\frac {1}{c}}{\frac {\partial \varphi }{\partial t}}-\nabla \cdot {\vec {A}}$

where ${\vec {A}}=(A_{1},A_{2},A_{3})$. But for example under gauge-fixing Lorenz gauge there is instead a plus. I need the minus to stay as a minus and not be continually flipping into a plus. Stephen William Wynn (talk) 16:37, 13 October 2017 (UTC)

My colleagues have been very patient in trying to educate you on problems with your edits and how to properly edit Wikipedia. Let me be more direct. The fundamental goal of Wikipedia is to build an encyclopedia based on summarizing established, reliable sources. I have seen no evidence of your edits being based on reliable sources; they instead seem based your own personal view of how physics should be. Such personal point-of-view (POV) edits, what we term original research, have no place on Wikipedia. You are welcome to rewrite the theory of relativity off-site; but none of that has any place on Wikipedia. Please stop making POV edits and start basing edits on reliable sources. --Mark viking (talk) 18:44, 13 October 2017 (UTC)

I feel like I'm banging my head against a brick wall: ${\vec {A}}=(A^{1},A^{2},A^{3})$. You're not going to win this argument by insisting on a completely non-standard notation. I honestly can't believe you haven't taken this on board, yet. The frustrating thing is that you had this part right while you were trying to argue the wrong definition of four-gradient. — dukwon (talk) (contribs) 00:27, 14 October 2017 (UTC)

You say I should have used upper indices. So repeating the argument using upper indices.    The Lorenz gauge condition $\partial _{\mu }A^{\mu }=0$ contains a minus when expanded:   $\partial _{\mu }A^{\mu }=({\frac {1}{c}}{\frac {\partial }{\partial t}},{\frac {\partial }{\partial x}},{\frac {\partial }{\partial y}},{\frac {\partial }{\partial z}}).(\varphi ,-A^{1},-A^{2},-A^{3})={\frac {1}{c}}{\frac {\partial \varphi }{\partial t}}-\nabla \cdot {\vec {A}}$ where ${\vec {A}}=(A^{1},A^{2},A^{3})$. Stephen William Wynn (talk) 10:06, 16 October 2017 (UTC)

But $A^{\mu }=(\varphi ,A^{1},A^{2},A^{3})$. Please stop this, it's just tedious. — dukwon (talk) (contribs) 10:14, 16 October 2017 (UTC)

A is the "magnetic vector potential". Looking in Wikipedia under magnetic potential we find: "The magnetic vector potential A is a vector field". Then look under vector field we  find they are using lower indices e.g.  

$\operatorname {div} \mathbf {F} =\nabla \cdot \mathbf {F} ={\frac {\partial F_{1}}{\partial x}}+{\frac {\partial F_{2}}{\partial y}}+{\frac {\partial F_{3}}{\partial z}}$

Whether you use upper or lower indices for A seems to be a question of the level of depth reached. Beginners start using lower indices for A because that implies covariant vectors, when you are more advanced you use upper indices because that is a convention. Stephen William Wynn (talk) 13:37, 22 October 2017 (UTC)

In the article vector, the formula you cite is preceded by "The divergence of a vector field on Euclidean space is a function (or scalar field). In three-dimensions, the divergence is defined by" (emphasis added). In a Euclidean space (unlike Minkowski space) when using Cartesian coordinates, we are not picky about distinguishing between covariant and contravariant because the metric is $g_{\alpha \beta }=\delta _{\alpha }^{\beta }=g^{\alpha \beta }$. For more general coordinates, superscripts should be used to indicate contravariance of the vector field whose divergence is being calculated. Worse, it needs to be a density or else it is necessary to add a term using a Christoffel symbol to make the divergence an invariant. JRSpriggs (talk) 01:43, 23 October 2017 (UTC)

You say: "superscripts should be used to indicate contravariance of the vector field whose divergence is being calculated". I don't understand why mathematically. This seems to be just a convention. It is a convention to define the Lorenz gauge condition:

$\partial _{\mu }A^{\mu }=0$

But mathematically in my opinion:

$\partial ^{\mu }A_{\mu }=0$

is better. Stephen William Wynn (talk) 12:05, 23 October 2017 (UTC)

a) Your (or my) opinion is irrelevant here.

b) obviously, per definition

$\partial _{\mu }A^{\mu }=\partial ^{\mu }A_{\mu }$

The thing that you seem to be confused about is that the vector potential is a contravariant 3-vector. Hence when defining the 4-potential in terms of the vector potential it needs to written as a contravariant 4-vector, (which can be transformed into a covariant 4-vector by contracting with the metric as you wish).TR 12:52, 23 October 2017 (UTC)

You say "the vector potential is a contravariant 3-vector". What does "is" mean? That is I cannot see any reason why it should be contravariant rather than covariant. It seems that someone decided it should be contravariant and we are stuck with it. Stephen William Wynn (talk) 16:16, 23 October 2017 (UTC)

So you don't understand what contravariant means? That is fine, but maybe you should stop waisting our time. The three potential has to be a contravariant vector because the curl is a differential operators that maps contravariant vector fields into contravariant vector fields. The vector formulation of Maxwell's equations uses exclusively contravariant vectors. If you doubt these statements here is a bit of homework, recall the expressions for the gradient, curl, and divergence in cylindrical coordinates.TR 19:28, 23 October 2017 (UTC)

On electromagnetic tensor they start with A being covariant, contrary to what you say it has to be contravariant. They start with

$F_{\mu \nu }=\partial _{\mu }A_{\nu }-\partial _{\nu }A_{\mu }.$

It seems to me that is okay. They can switch to the four potential being contravariant later simply by changing the sign of the space components. Not a big deal. Stephen William Wynn (talk) 09:57, 28 October 2017 (UTC)

Please help review Draft:Tesla shield

This AFC submission needs to be evaluated by a topic specialist. I'm aware that there is a lot of poor quality information related to Tesla available, I'm not able to properly review this draft. Roger (Dodger67) (talk) 17:22, 25 October 2017 (UTC)

The primary source for whatever "scalar waves" are in this context is a "physics" paper written by electronics engineers[3], which is always a bad sign. I stopped reading here:

"The scalar wave goes in all direction into the surrounding. But these waves do not exist in the ordinary world. They are transmitted through hyperspace or false vacuum and go around regular space."

Smells like crackpottery to me. — dukwon (talk) (contribs) 18:15, 25 October 2017 (UTC)

Oh, very much so. It's essentially impressive gibberish written to sound real. Primefac (talk) 18:18, 25 October 2017 (UTC)

A clarification - it's Tesla's real ideas but expanded with enough real-world jargon (which as-used is gibberish) to make them seem legitimate. Primefac (talk) 18:28, 25 October 2017 (UTC)

Perhaps it aims for legitimacy, but the target it hits is closer to "manual for a forgettably generic video game". I mean... "The Tesla shield places a thin 3-dimensional hemispherical shell of energy over a large defended area, with the hemispherical shell being impenetrable. Any object penetrating the shell, which consists of globes or hemispheres layered within each other, receives both an Electro Gravitational Pulse (EGP) and Electromagnetic Pulse (EMP)arising inside it, from within its local space-time. The EMP will dud all electronics and explode all high explosive materials." XOR'easter (talk) 20:23, 25 October 2017 (UTC)

In addition to the crackpottery, we know by direct experimentation that it doesn't work. We already tried an EM shield as the Christofilos effect. Maury Markowitz (talk) 19:02, 31 October 2017 (UTC)

Valid criticism

See Wikipedia’s Science Articles Are Elitist for a valid criticism of Wiki science. Far too often the articles are written for other science specialists with little thought to the general reader who might want to learn a bit, but is driven away by sci nerds talking/showing off to other sci nerds. Thoughts? Vsmith (talk) 18:24, 13 October 2017 (UTC)

Yes wikipedia science articles have room for improvement in their clarity & pedagogy. I have never ever seen a wiki science article that didn't have room for improvement in that respect. It's not that way on purpose; rather it is hard and time-consuming to write articles that are correct, comprehensive, and maximally clear & pedagogical. Even people who try to write clearly and for a wide audience sometimes fail, but more often people are just trying to make an article incrementally less bad and less incomplete and incrementally more helpful to incrementally more people, within the constraints of a highly limited amount of time and effort. I find the Vice article a bit annoying for suggesting that people are maybe sometimes deliberately writing incomprehensibly (something I've never seen in 10 years†), and for using the click-baity term "elitist" in this context. But the writer does more-or-less acknowledge at the end that he can blame himself as much as anyone else.

†Oh wait, I saw it happen once, arguably. It was a medical article. Some anonymous person (my hero) replaced the word "prophylactic" with "preventative" everywhere in the article. Then someone else (the villain of my story) undid the change. I think the villain's motivation was probably not to deliberately confuse lay-people, but I don't know what it was instead. --Steve (talk) 18:52, 13 October 2017 (UTC)

That many technical articles are hard to understand for non-specialists is a valid criticism and a well-known problem. Blaming that problem on 'elitist nerds afraid of criticism' is assuming bad faith on the part of editors here. I have never seen (correct) prose in physics articles redacted because it is too clear or too easy to understand. Indeed, WP:TECHNICAL is a guideline that explicitly encourages writing as simply as possible. Writing such clear prose is hard, however, and WP is a work in progress. Regarding the jarring transition from accessible lede to difficult main content, well, that is the compromise (WP:EXPLAINLEAD) we have come up with for covering both the accessible and the technically difficult aspects of a subject. I personally love to see physics explained clearly and try to encourage such when I can. --Mark viking (talk) 19:12, 13 October 2017 (UTC)

Yep. It's far easier to add a technical, jargon-rich sentence than it is to organize a structured exposition. Technical prose that is rather disjointed at the paragraph-to-paragraph level is what naturally happens when knowledgeable people come by to add little bits in their free time. The writer of the Motherboard piece says, "Writers don't just dip in, produce some Wikipedia copy, and bounce." But I think a lot of them do. Perhaps they return a week or a month later and produce more copy, but the contribution made at each encounter is fairly small. And then: "In a way you can imagine impenetrable writing as a defensive strategy wielded to scare off editor-meddlers." No, that's what we use acronyms for. Are your edits in compliance with WP:NOR, WP:BLP and WP:PROF#C2? XOR'easter (talk) 19:40, 13 October 2017 (UTC)

We are also not writing a WP:TEXTBOOK for the masses, or a quick 'what is it 2 two sentences?' compendium. We're writing trying to write a comprehensive encyclopedia. Try as you might, the CKM matrix is an inherently technical subject, as is TWDP fading. Headbomb {t · c · p · b} 14:51, 23 October 2017 (UTC)

I agree very much with the original article. Many articles on physics in the wiki are written in ways that other parts of the project would reject. For instance, the literature-related parts of the project reject writing that is "in universe", yet the average article in physics is written with copious jargon used only in the related sub-field. When this is pointed out, the response is almost always to claim that it's not possible to do otherwise.

Look at the post (currently) directly above this one. Here we have the claim that the CKM matrix is "inherently technical" and thus, what, it has to suck? Really? Hmmm. Well to start with, the article's lede mentions unitary matrix for some reason, which doesn't explain anything, yet introduces jargon. Then it starts its attempt at an explanation by linking to an article on the Cabibbo angle, but that's just a redir back into this article. Thanks. And who thought "on the effectively rotated nonstrange and strange vector and axial weak currents" was the way to describe it? How about "In modern terms, the Cabibbo angle describes the probability that one flavor of quark (d or s) will change into another flavor (u) under the action of the weak force."? And why doesn't this article mention the actual observations that led to anyone looking for this in the first place? This is just a bad article, and there is no reason for that.

This is hardly limited to the wiki, however, as science writing in general is a topic few of the practitioners bother with. When there is a need to interact with the layman, they generally turn to their university's press department, and hilarity ensues. Maury Markowitz (talk) 16:13, 31 October 2017 (UTC)

And further, the TWDP fading is an even better example of something that is very easy to explain to the average reader, but was instead a terrible mash of jargon lacking anything like a basic explanation. @Headbomb:, you seem to be picking examples of precisely the problem the OP is illustrating. Maury Markowitz (talk) 19:10, 31 October 2017 (UTC)