Talk:Free space (electromagnetism)

Disambiguation page

The introduction to this article uses the same references as the first paragraph of the article on WP. However, it is constructed around these references differently. John R. Brews 04:16, 25 November 2010 (UTC)

Might I suggest a disambiguation page, since free space also is used in computer disk management and hydraulic engineering? Howard C. Berkowitz 04:22, 25 November 2010 (UTC)

Does Citizendium have a For..see.. template? I've just added a line myself. John R. Brews 15:22, 25 November 2010 (UTC)

Actually, I intended to do that, but could not find an article describing free space on a computer. John R. Brews 15:25, 25 November 2010 (UTC)

I set up Free space (disambiguation). "electromagnetism" is a placeholder for whatever disambiguating term you want to use for your article. If you like, I'll move the article to the new name and do the necessary housekeeping -- there are tricky parts.

When creating an article, and you think there should be disambiguation, just go ahead and set up a page, such as I did, for the missing articles -- you don't even need to create a preliminary definition, since a redlink will still show up in text search. Howard C. Berkowitz 17:19, 25 November 2010 (UTC)

John, is this what you want? {{dambigbox|Free space (xxxx)|Free space}} , where xxxx could be "physics" or "electromagnetism" or whatever, and this article could be moved to the new title as Howard has offered to do for you. The template produces this:

This article is about Free space (electromagnetism). For other uses of the term Free space, please see Free space (disambiguation).

Milton Beychok 17:35, 25 November 2010 (UTC)

(unindent)Milton: I'd elect Free space (electromagnetism) as the new title. Can you implement this for me? John R. Brews 17:41, 25 November 2010 (UTC)

Yes, I will. Since it will take some time, please stop any main article edits and talk page posts for the next 30 minutes. Milton Beychok 18:05, 25 November 2010 (UTC)

Done. Milton Beychok 18:28, 25 November 2010 (UTC)

The F, N, and A terms need to be defined

John, the first two equations in the "Classical case" section assume that the reader knows what F, N and A are ... and that may not be a correct assumption. I think the article would benefit from having those terms defined. Milton Beychok 06:44, 25 November 2010 (UTC)

Good idea, I've done that. John R. Brews 15:22, 25 November 2010 (UTC)

Quantum case

This section needs some attention to make it more understandable. That may involve either (i) writing another article that goes into the details of response functions and how they are computed for vacuum, or (ii) adding more detail here, but not so extensive as that. Can anyone help out here? John R. Brews 15:30, 25 November 2010 (UTC)

For what its worth, my inclination would be option (ii) and a {{See also|Response functions}} or a {{Main|Response functions}} template just under the section header. Although the links would be red, that's okay. Hopefully, red links may motivate others to write the those articles.. Milton Beychok 20:19, 25 November 2010 (UTC)

"Instead the particle has a zero-point energy..." — Really? For a harmonic oscillator, the zero-point energy is proportional to the frequency. For a free particle (zero potential), the frequency is zero, and therefore... Boris Tsirelson 15:45, 30 November 2010 (UTC)

Boris: I've no particular attachment to how this point is expressed. If you have a more careful wording with an appropriate source, please feel free to change things. John R. Brews 19:29, 30 November 2010 (UTC)

OK, then I propose to replace the text

The Heisenberg uncertainty principle for a particle in one dimension does not allow a state of rest in which the particle is simultaneously at a fixed location, say the origin of coordinates, and has also zero momentum. Instead the particle has a zero-point energy and a range of momentum and spread in location attributable to quantum fluctuations.

An uncertainty principle applies to all quantum mechanical operators that do not commute.

with the text

The Heisenberg uncertainty principle for a particle does not allow a state in which the particle is simultaneously at a definite location and has also a definite momentum. Instead the particle has a range of momentum and spread in location attributable to quantum fluctuations.

An uncertainty principle applies to most of quantum mechanical operators that do not commute (specifically, to every pair of operators whose commutator is a non-zero scalar operator).

See for instance WP.

Boris Tsirelson 19:55, 30 November 2010 (UTC)

Boris: I added a published source to my text; I suggest you do the same. John R. Brews 20:33, 30 November 2010 (UTC)

Really, our rules do not demand it (in contrast to Wikipedia), unless the matter is controversial. It should be written in quite many textbooks on quantum theory; the problem is that I has no one at home. But this should be good:

Peter W. Milonni, The quantum vacuum, Academic Press, 1994, 522 pp.

Boris Tsirelson 21:10, 30 November 2010 (UTC)

In fact, the essence of my proposal is not to add new claim(s) to the text, but to remove a wrong and rather irrelevant claim about zero-point energy. Thus, why should I add a source? Boris Tsirelson 21:19, 30 November 2010 (UTC)

Hi Boris: Perhaps we should engage in more discussion about what should be said here? For example, this text connects vacuum fluctuations and zero point energy to the noncommutability of operators. I think that is all I'm trying to suggest. What would you like to see here? John R. Brews 21:49, 30 November 2010 (UTC)

Edit conflict; here is my text written a minute before:

Well, really, (1) I am not a physics editor, and therefore I am not responsible for the physics content; and (2) all this is only a small remark to the article. Sorry for bothering you with trifles; I leave the point to physics editors, if they want to bother.

Just for the record, I formulate my opinion. The Hamiltonian of a free particle is proportional to the square of its momentum. The momentum operator is well-known to have a continuous spectrum filling the whole line. Thus, its square has a continuous spectrum filling [0,infinity). Thus I wonder, what is meant by zero-point energy in this case. Uncertainty relations do ensure fluctuations, but not any energy gap.

Boris Tsirelson 21:53, 30 November 2010 (UTC)

Answer to the message before the edit conflict: surely there are relations between vacuum fluctuations, zero point energy and the noncommutability of operators! I only want formulations to be accurate. Boris Tsirelson 21:56, 30 November 2010 (UTC)

Boris: The concept of an energy gap has not arisen here. The point of the uncertainty principle is simply that spatial localization is in a trade-off with momentum localization. This trade off arises because p and x do not commute.

Perhaps you could say specifically in so many words what you find misleading about the presentation so it can be fixed? John R. Brews 22:03, 30 November 2010 (UTC)

Quite simple: not to say that a free particle has zero-point energy (or to explain what exactly is meant by that). Boris Tsirelson 22:08, 30 November 2010 (UTC)

Boris: This book describes the zero-point energy of a particle as an automatic consequence of solving Schrödinger's equation for a confined particle. Is this point unclear from the presentation in the article? John R. Brews 22:19, 30 November 2010 (UTC)

I have inserted the modifier "confined" in the text. How's that? John R. Brews 22:23, 30 November 2010 (UTC)

Just a few suggestions

John, Citizendium has existing articles for Speed of light, Electric constant and Magnetic constant , all of which you have defined by in-text hyper-links to NIST. I suggest that those in-text hyper-links be replaced by simply wiki linking those phrases to our existing articles rather than sending the readers off to the NIST website,

There is also an existing article on Vacuum permittivity and the Magnetism article discusses magnetic permeability. I suggest using those two wiki links which would mean that reference (6) would not be needed (it could be placed in the Bibliography subpage when you populate that subpage).

I haven't gone through the entire article as yet ... but perhaps there are even other hyper-linked phrases or phrase references that could also be replaced by wiki links to other existing Citizendium articles.

Please consider these suggestions. And now I'm off to a Thanksgiving dinner for a few hours. Milton Beychok 00:07, 26 November 2010 (UTC)

I'll look at this more, but a few instant reactions:

The NIST website is a global source for these numbers; if you go to BIPM for example, they redirect you here. The site also is a useful source for commentary and for other data as well. So it seems to me to be an excellent resource as well as providing clear authority for the values, and the fact that they are exact values. I do think linking the CZ articles is important, though.

I don't think a general article on magnetism is pertinent. The article on Vacuum permittivity covers some of the same ground, and Free space might benefit from some rearrangement to take that into account. I'll look at that more carefully in a few days.

Thanks for your help and for these suggestions. John R. Brews 16:24, 26 November 2010 (UTC)

Fair enough. Milton Beychok 17:59, 26 November 2010 (UTC)

Milton: There is a can of worms here that I hesitate to involve myself in. On WP they led to a huge brouhaha that sputters on and off to this day. The underlying issue is that the SI units replace the unit of length by the transit time of light, so how long is it? is answered in seconds of transit for light. That makes c a defined quantity (c = c₀ regardless of the numerical value for c₀) because the metre is how far light travels in 1/c₀ seconds.

I'm not familiar with the treatment of this topic on CZ. Perhaps you can guide me through it. I modified Magnetic constant in this respect. John R. Brews 13:55, 29 November 2010 (UTC)

Please take a look at my comments on Talk:Speed_of_light and Talk:Gaussian units. John R. Brews 14:29, 29 November 2010 (UTC)

Take a look at International System of Units. The definition of the metre in that article mentions that it is based on the transit time of light. Milton Beychok 17:35, 29 November 2010 (UTC)

Indent for 'quantum case'

John, you have reverted my edit to the 'quantum case' section, indenting part of it. I have not seen this style of indenting before. Would you please explain why you think it should be indented?

By the way, let me welcome you to the Citizendium! Johan A. Förberg 21:51, 30 November 2010 (UTC)

Johan: Thanks for aligning the equations. The indent (in my mind) formats an aside so the reader can easily identify it and skip it to proceed with the main argument, paying no attention to it unless they are so inclined. The indented material (IMO) is pertinent only to someone who wants to delve into how the fields become quantized and so exhibit fluctuations. It isn't of interest to every reader. John R. Brews 22:12, 30 November 2010 (UTC)

I see. In my eyes, it rather attracts attention than diverts it though. This is not strictly important to me, but I think there should be a better way.

Maybe if someone else would offer their opinion? Johan A. Förberg 22:28, 30 November 2010 (UTC)