Talk:Vacuum/Archive 3

Issues of continuing interest
A number of issues of continuing interest can be found in the archive. If you would like to add to these discussions, please consult the archive first to find out what others have said, and then post your reply here. Some of these interesting topics are
 * Should we use SI units or Torrs?
 * What is the definition of vacuum? Is perfect vacuum possible?
 * The temperature of outer space should be clarified.

Interpretation of the Michelson-Morley null result is incorrect
In 1887, the Michelson-Morley experiment, using an interferometer to attempt to detect the change in the speed of light caused by the Earth moving with respect to the aether, was a famous null result, showing that there really was no static, pervasive medium throughout space and through which the Earth moved as though through a wind.

The null result of the Michelson-Morley experiment does not prove or disprove the existence of the luminiferous aether. It merely shows the results were invalid. The experiment cannot detect the aether wind because the interferometer itself undergoes Lorentzian contraction.

See: http://www.glafreniere.com/sa_Michelson.htm —Preceding unsigned comment added by 70.41.246.171 (talk) 02:49, 7 February 2009 (UTC)


 * STILL WRONG - Jun 23 2010 —Preceding unsigned comment added by 70.41.246.171 (talk) 10:18, 23 June 2010 (UTC)

Ideal vacuums inside molecules, ooer?
From the article: "An ideal vacuum cannot exist even inside of a molecule." - this statement and the accompanying elaboration seems vacuous (ha) as it doesn't even discuss the electron probability distribution |Ψ|2 of the molecule, which (nodes aside) is nonzero at any finite distance from the wavefunction centroid. I am not prepared to reword this however as I do not know the significance of nodes with respect to the real-life quantum vacuum, and question the meaningfulness of the whole paragraph in light of the zero-point energy. Expert attention potentially required. Eutactic (talk) 04:30, 7 September 2009 (UTC)

What is vacuum?
I don't really understand the explanation. Vacuum is a space (almost) void of matter. This is merely one of characteristics of vacuum.

But what is vacuum?

Could you write it so that laymen can understand it? Like explanation and definition? —Preceding unsigned comment added by 203.215.65.67 (talk) 14:40, 30 March 2010 (UTC)

Catholic Church & the Vacuum
The current edit reads: "Catholic Church regarded the idea of a vacuum as against nature or even heretical." There is a citation flag on this already. I have always been suspicious of this assertion which has been promoted by James Burke and others. I suspect the realty is much more benign and/or ambiguous than the lore. Does anyone have any solid source on this issue? —Preceding unsigned comment added by 67.242.118.143 (talk) 06:43, 7 August 2010 (UTC)

Effects on human and animals
The second and third lines in this section are misleading... "Blood and other body fluids do boil when their pressure drops below 6.3 kPa, (47 Torr) the vapour pressure of water at body temperature.[3] This condition is called ebullism."

That is a poor definition of ebullism. It is not the "boiling" of blood, but the formation of bubbles in the blood, which is not the same thing. The line about pressure is also misleading due to the fact that blood pressure does not drop below that point when the body is exposed to a vacuum as long as a person's heart continues beating. Scowie (talk) 23:30, 11 August 2010 (UTC)
 * Good points! Feel free to edit the article to clarify/etc. DMacks (talk) 00:10, 12 August 2010 (UTC)

Misuse of sources
This article has been edited by a user who is known to have misused sources to unduly promote certain views (see WP:Jagged 85 cleanup). Examination of the sources used by this editor often reveals that the sources have been selectively interpreted or blatantly misrepresented, going beyond any reasonable interpretation of the authors' intent.

Please help by viewing the entry for this article shown at the cleanup page, and check the edits to ensure that any claims are valid, and that any references do in fact verify what is claimed. Tobby72 (talk) 14:29, 18 September 2010 (UTC)

Merge proposal: from Free space
Since there has been a bit of warring over whether Free space is an inappropriate content fork that should redirect to vacuum, it seems best that the subtle distinctions be discussed within a single article, namely vacuum. At least we ought to get that discussion doing and see what the positions are on it. Agree? Dicklyon (talk) 17:26, 30 October 2010 (UTC)


 * Agree to merge. Imagine being a lay person discovering that we have separate articles for what you always have "known" to be one and the same. Subtle distinctions should not be discovered by reading and comparing two articles, but by reading a single section in the article. DVdm (talk) 18:05, 30 October 2010 (UTC)


 * The same argument could be used to merge QCD vacuum or vacuum state with vacuum, but I disagree with it. Each one should be mentioned and linked to in vacuum, but should be expanded upon in its own separate article.  Vacuum is meant to be read by laypeople, but the specific articles would be written to a more scientific audience. Pecos Joe (talk) 20:45, 30 October 2010 (UTC)


 * Can you then tell us what is the distinction that the free space article is supposed to make, relative to the vacuum article? I'm not seeing it.  Dicklyon (talk) 23:09, 1 November 2010 (UTC)


 * Keep separate In addition to the different audiences the articles are intended for (and thus, the level of detail possible within the article), the most reliable definitions of free space in that article appear to come from the US patent office,  and are something like "anything that is not a waveguide," or "any medium without obstructions," and appear to include, for example, water and the atmosphere.  Those definitions indicate that the topic of free space would not be adequately discussed within the context of vacuum.  Even if some other source was found to give a different definition of free space, the US patent office definitions could not be ignored, and thus free space should exist as a standalone article. Pecos Joe (talk) 20:45, 30 October 2010 (UTC)


 * Mostly that patent office ref is just a distraction, diluting the article's main topic by throwing in a different meaning of the same term. It should be kept out of the main stream, and just mentioned as an alternative meaning; if we merge to vacuum, it would be better to leave it out completely; it could be mentioned on free space (disambiguation). Dicklyon (talk) 01:02, 31 October 2010 (UTC)


 * I edited free space (disambiguation) to include the electrical engineering / patent office definition. --Steve (talk) 21:31, 8 January 2011 (UTC)


 * Simple redirect. There is no content to merge in free space: it is pure WP:OR and WP:SYNTH written to try push an extremely minority PoV. The U.S. PTO stuff is dicdef. Physchim62 (talk) 08:15, 31 October 2010 (UTC)
 * I've been trying to repair some of the worst of Dr. Brews's fantasy, and took out the stupid PTO stuff. It's looking more and more like an article on classical vacuum; a merge would be easy if there's not much new there.  Dicklyon (talk) 22:42, 31 October 2010 (UTC)


 * Comment. While I agree that vacuum, free space, absolute space and luminiferous aether mean essentially the same, these terms have some subtle historical and terminological differences. I suggest either merge them all (which would probably cause objections), or keep them all.Biophys (talk) 15:03, 31 October 2010 (UTC)
 * I don't think that's a valid reason to not attempt to do this merge first. If there are reasons to merge or not merge other stuff later, we can deal with that later.  Personally, I think that luminiferous aether is a very different concept, and I have no idea what absolute space is (but I'll look).  Dicklyon (talk) 22:42, 31 October 2010 (UTC)
 * According to Einstein, "To deny the ether is ultimately to assume that empty space has no physical qualities whatever. The fundamental facts of mechanics do not harmonize with this view. For the mechanical behaviour of a corporeal system hovering freely in empty space depends not only on relative positions (distances) and relative velocities, but also on its state of rotation, which physically may be taken as a characteristic not appertaining to the system in itself. In order to be able to look upon the rotation of the system, at least formally, as something real, Newton objectivises space. Since he classes his absolute space together with real things, for him rotation relative to an absolute space is also something real. Newton might no less well have called his absolute space “Ether”; what is essential is merely that besides observable objects, another thing, which is not perceptible, must be looked upon as real, to enable acceleration or rotation to be looked upon as something real". So, he is using some of these terms interchangeably. Nothing wrong with merging you suggested, providing that all important content was kept.Biophys (talk) 22:50, 1 November 2010 (UTC)
 * As I read this, Einstein is representing Newton as using these terms interchangeably, without in this passage fully declaring his own view, except to distance himself from one extreme. &mdash; MaxEnt 23:38, 3 May 2014 (UTC)


 * Agree, with free space redirecting to free space (disambiguation). Yes, this article already discusses the perfect vacuum limit. No need for a second article. --Steve (talk) 06:20, 8 November 2010 (UTC)


 * Agree to merge. Dicklyon makes the case convincingly. ScienceApologist (talk) 18:09, 8 November 2010 (UTC)

It sounds to me like we have pretty good consensus. Anyone who sees material in Free space that could be merged here should go ahead and do it, and anyone who wants to make it a redirect or a disambig should do that, and I bet it will all converge with little pain. I'm going to stay out of it for now. Dicklyon (talk) 05:02, 9 November 2010 (UTC)


 * Keep separate ... subtle historical and terminological differences. Also, see  Manual of Style (summary style) ... particularly, Levels of desired details [eg., Summary style is based on the premise that information about a topic should not all be contained in a single article since different readers have different needs].--J. D. Redding 02:49, 28 November 2010 (UTC)


 * Which article are you saying should be summary style? And what are the subtle differences that we missed?  Dicklyon (talk) 03:59, 28 November 2010 (UTC)


 * Merge. Keeping it separate gives it an air of importance which is probably over the top. And it will not take much space (pun intended) in the Vac article. History2007 (talk) 12:12, 31 December 2010 (UTC)

Done, there's a clear consensus. I just redirected Free space to Free space (disambiguation). --Steve (talk) 21:27, 8 January 2011 (UTC)

"In classical electromagnetism" section
The "In classical electromagnetism" section...I don't understand why it belongs in this article. Basically it is saying, "In classical electromagnetism, in vacuum, the speed of light is c, the superposition principle is true, etc." All of this are important aspects of the theory of classical electromagnetism, but why are they important facts about the vacuum?

If this section should be here, why not have another section "In Newtonian mechanics" that says "In vacuum, assuming no gravity, things travel in a straight line at a constant velocity, etc." And a section "In Newtonian gravitation" that says "If you put two objects in a vacuum, they will orbit each other following Kepler's Laws, etc.". And a section "In statistical mechanics" that says "In vacuum, the photon density of states is proportional to volume, etc." And so on and so on. In other words, in every physics topic, people will say every 20 minutes, "Assume it's a vacuum...". But they're not saying anything special about the vacuum, they're just explaining a physics topic! :-) --Steve (talk) 05:33, 9 January 2011 (UTC)


 * It's not like I'm defending more than 1% of the crap that Brews had added at free space, but this little bit seemed relevant, given the cited source with section on "the classical vacuum as reference medium." Plus you already had these EM properties in an unsourced section; why isn't a sourced one better?  Dicklyon (talk) 05:37, 9 January 2011 (UTC)


 * I don't think the sourced or unsourced section should be there! The vacuum is a "reference medium" in classical electromagnetism just as it is a "reference medium" in calculating the orbits of flying objects. It just means "simple case that you should start with". Anyway, while it's there I had a go to make it more relevant. :-) --Steve (talk) 18:22, 9 January 2011 (UTC)


 * I reverted it back to what the cited source is about. The history of the ether concept is already discussed elsewhere.  I don't see what's bugging you about it.  I left a note on your talk page before I noticed your comment here, so you can ignore that one.  Dicklyon (talk) 19:03, 9 January 2011 (UTC)

Free space merge
Hi all, now that Free space redirects to a disambig, are any volunteers interested in helping WP:FIXDABLINKS? This tool makes the job easier, and actually enjoyable, in a puzzle-solving sort of way. (If you get into it, you may want to go to Dab solver and adjust the Preferences for even easier use.) Thanks, -- Ja Ga  talk 17:41, 9 January 2011 (UTC)

Vacuum in classical electromagnetism
Brews Ohare: We've been over this many times. Here's why I undid your rewrite of the intro, with its implication that there is something called a "classical vacuum" which is important in the SI definition of a meter. Let's walk through. --Steve (talk) 04:19, 20 December 2011 (UTC)
 * Metrological physicists are interested in making accurate distance measurements in this universe
 * This universe--the one we live in--is a quantum universe. It does not obey the laws of classical physics.
 * There is no physicists doing experiments where they attempt to suck the quantum fluctuations out of a box (suck out the dark energy, suck out the virtual photons, etc.) and measure how far light travels through that box in 1 / 299792458 seconds. They are not doing this experiment because it's completely ridiculous and impossible.
 * It is equally ridiculous to think that they ought to be trying to suck virtual photons out of a box.
 * The physicists who work at NIST, BIPM, and such, have never said that sucking virtual photons out of a box is an important and under-explored research agenda which is essential to ensuring the integrity of distance measurements.
 * BIPM says "light travels at 299792458 m/s through a vacuum". But everyone knows, extremely intense light travels through a real-world vacuum at a slightly different rate than low-intensity light, due to quantum fluctuations. There are two ways to reconcile this contradiction:
 * BIPM expects experimenters to suck the virtual photons and dark energy out of their experimental apparatuses
 * BIPM means the low-intensity limit, and didn't bother to say that explicitly because the difference is too small to measure with today's technology
 * Since the first is completely bizarre and ridiculous, the second is the most likely.
 * Therefore, the theory of classical electromagnetism has nothing in particular to do with how the meter is defined. The universe we live in--the universe that obeys the Standard Model of Particle Physics--is a perfectly adequate environment to define and measure a meter.
 * There is no such thing as a "classical vacuum". There is only "a perfect vacuum as understood in classical physics". This is because the word "thing" is conventionally understood to mean "something that could, at least hypothetically, exist in the universe".
 * Likewise, a statement like "the classical vacuum has the property of superposition principle" is better rephrased "in classical electromagnetism, the superposition principle is valid for waves in a vacuum", and so forth.


 * I have a hard time following the technical details of this argument. What's clear is that Dr. Brews got himself topic-banned for a  year, and than blocked for another year, for continuing to push his idiosyncratic point of view on the whole speed of light issue.  And when he came back he said he wasn't going to re-engage in that.  And here he is.  Probably not a good idea.  He should go get his ideas refereed and published, and then maybe we can refer to them here.   Dicklyon (talk) 06:38, 20 December 2011 (UTC)
 * To DickLyon: I do object to your intervening in this conversation simply to say that you don't understand the matter, but do want nonetheless to chastise myself in advance, to put words in my mouth that I have never said, and to declare my opinions not yet expressed as idiosyncratic. Those very inauspicious actions have the seeming objective to avoid substance and merely raise the temperature rather than the clarity of the discussion here. Brews ohare (talk) 13:58, 20 December 2011 (UTC)
 * Objection noted. I'm not going to spend any time on the substance of your arguments, because I know from past experience where that leads.  I'll let Steve do that if he wants, as he seems to have a good handle on it, but I know you'll keep the argument alive long after he has said all that there is to say.  As usual, you are arguing your own logic, rather than showing sources that do it your way, and with nobody supporting you; that's why I call it idiosyncratic.  As for putting words in your mouth, I apologize; I see that I probably misinterpreted where you said "I have no intention of engaging in any discussion on this topic" here.  Dicklyon (talk) 01:05, 21 December 2011 (UTC)
 * Yes, it is not a "probable" misinterpretation, but an actual one. And you are criticizing my future behavior, as you imagine it to become, not anything that has occurred since my return here. How about a little breathing room, eh? Brews ohare (talk) 17:01, 21 December 2011 (UTC)
 * To Steve Byrnes: I doubt that we have much to disagree about, but your edit has gone a bit overboard. Let's take a look at the first few points you raise. You say:
 * "There are two ways to reconcile this contradiction:
 * BIPM expects experimenters to suck the virtual photons and dark energy out of their experimental apparatuses
 * BIPM means the low-intensity limit, and didn't bother to say that explicitly because the difference is too small to measure with today's technology
 * Since the first is completely bizarre and ridiculous, the second is the most likely."
 * There is no disagreement that the first alternative is silly; The second alternative is a suggestion about how to establish the connections necessary to refer experiments to 'vacuum'. I suppose 'low-intensity limit' could be elaborated to include things like the limit of zero partial pressure, zero field strengths, zero vacuum fluctuations, and so forth. I certainly would understand BIPM's unwillingness to enter into any elaboration, and in fact they have left the matter as one of implementing "standard good practice", or something like that wording.
 * These choices do not fully complete the discussion however. There are two aspects: one is this experimental issue of how measurements are to be referred to 'vacuum'. And the other is "what are the electromagnetic properties of the reference state of 'vacuum' that is referred to?" This last is answered by the section Vacuum. It is also fully described by NIST and the BIPM at these links: the defined values c, c0, μ0 and the subsidiary derived properties with exact values ε0 and Z0.
 * One might ask how BIPM and NIST arrived at the derived values of ε0 and Z0? If one accepts the classical Maxwell equations, and the constitutive relations for a 'vacuum' medium: D=&epsilon;0E, B=&mu;0H, then they lead to exactly the formulas used by BIPM to deduce ε0 and Z0 from the defined values c, c0, μ0. Do you doubt that that is how these formulas were arrived at?
 * This connection to classical electromagnetism is one basis for some authors to call this reference vacuum "classical vacuum". A related reason is that various field-theoretical vacuums are known to exhibit vacuum fluctuations both experimentally (via the Lamb shift and spontaneous emission, for example) and theoretically (via their calculated relative permeabilities and relative permittivities which are not identically 1). The adjective classical appended to vacuum is meant only to distinguish the reference 'vacuum' with relative permeability and permittivity identically 1 from these 'quantum vacuums' like QCD vacuum.
 * I don't see anything controversial in this, and I wonder if you, Steve, have really any objections to these remarks? Brews ohare (talk) 12:24, 20 December 2011 (UTC)
 * A number of pertinent sources are found in the section Vacuum. Brews ohare (talk) 13:58, 20 December 2011 (UTC)
 * After you say how to make a vacuum ("take a box, suck out the air, shield the magnetic fields, etc."), that completes the discussion. You can't also say "what are the electromagnetic properties of the vacuum". That would be dictating the laws of the universe. The electromagnetic properties are whatever they are! Of course, BIPM has a pretty darn good idea of what they are (i.e., the standard model of particle physics), but it's not up to them to decide!!
 * How did BIPM and NIST arrive at the formula for ε0 and Z0? Certainly, being competent physicists, they used the standard model of particle physics (the most accurate known theory of electromagnetism in our universe). Presumably, they noticed that in the case of interest, Maxwell's equations provide a good-enough approximation to the standard model, so they use and discuss Maxwell's equations as a convenient approximation and shorthand.
 * There is no need to come up with a term to describe "the reference 'vacuum' with relative permeability and permittivity identically 1", because we should not be talking about this thing in the first place. People discussing "vacuum" are always talking about just one thing -- a box in this universe with no air etc. When discussing this thing, people might use approximate theories to describe it approximately, or they might use more exact theories to describe it more exactly. But they're still talking about the same box. --Steve (talk) 21:40, 20 December 2011 (UTC)
 * Steve: Apparently you have a very particular usage for the term 'vacuum' that relates it to a realizable 'vacuum' or to one that is an idealization of a realizable vacuum. Because the electromagnetic medium with properties c, c0, μ0 and the subsidiary derived properties with exact values ε0 and Z0 does not allow vacuum fluctuations you do not accept the terminology 'classical vacuum' to be applied to it. Is that what you are saying?
 * Some published sources don't find these restrictions upon the usage of 'classical vacuum' to be a necessity. Brews ohare (talk) 16:13, 21 December 2011 (UTC)
 * Here are two examples from the above Google book search:
 * §4.1 "The classical vacuum of electromagnetics"
 * §4.1 The classical vacuum as reference medium
 * That is not to say that 'classical vacuum' is everybody's choice of terms, but this usage does occur in reputable sources. Brews ohare (talk) 17:17, 21 December 2011 (UTC)
 * Steve, it seems to me that you view 'vacuum' as a real physical entity, which is fine but not necessarily the only way this term can be used. At the same time, the BIPM web listings of c, c0, μ0 and the subsidiary derived properties with exact values ε0 and Z0 are exact values, not measurements with measurement errors. So with the notion of a real 'vacuum', these exact properties make no sense.
 * A reasonable interpretation of the hypothetical electromagnetic medium with c, c0, μ0 and the subsidiary derived properties with exact values ε0 and Z0 is to see it as a reference medium, as described by the above two sources. The idea is simply that the measurement of the electromagnetic properties of any real 'vacuum' can be expressed in terms of the relative dielectric permittivity and relative magnetic permeability of that medium, which are ratios referred to ε0 and μ0. Likewise the theoretical calculations of the relative dielectric permittivity and relative magnetic permeability of the vacuum of quantum electrodynamics, and of the QCD vacuum are expressed in terms of the ratios to ε0 and μ0. See this note for sources.
 * I expect you are quite comfortable with this standard practice, and your reservations are simply that the wording 'classical vacuum' to you suggests that this reference medium really exists, when in fact it cannot exist even in principle. This unrealizability does not prevent its usefulness as a reference medium, however, whatever name you wish to attach to it. I'd say your limitations upon the usage of 'classical vacuum' is one view, but not universally shared. Brews ohare (talk) 20:02, 21 December 2011 (UTC)
 * I have adapted the introduction to better address your concerns. Brews ohare (talk) 20:51, 22 December 2011 (UTC)


 * Brews, let's work out a new intro here, and then add it to the article. Besides the objections above, we need to get the style more sensible.  You've rewritten it to be about the term, rather that about the topic itself (but you didn't italicize the term, so it's not even consistent).  And your single quotes around terms are not OK.  Fundamentally, though, we need to make sure that the lead is a summary, with sensible weight, or what's in the article; and only parts that are well sourced.  The part "In electromagnetism" on the classical vacuum is still a bit of a mess, as the footnotes that one expects to lead to sources about the terminology lead instead in some cases to more interpretive stuff and refs to the tangents (e.g. refs 38 and 39 after the introduction of the term classical vacuum).  Fix that up better and it will be easier to summarize in the lead.  Dicklyon (talk) 21:25, 22 December 2011 (UTC)
 * Brews, my main objection is to your assertion that the "classical vacuum" is essential to the SI definition of the meter (or anything else in SI). On the contrary, precision metrological physicists do not use the theory of classical electromagnetism for any purpose (except for shorthand simplifications) because precision metrological physicists only use the most precise theories.
 * You read far too much into the "exactness" of c0. Your failure to understand what the "exactness" of c0 does and does not mean caused endless arguments (and banning) previously. I will spell it out in great detail. Of course, the same applies to Z0, ε0, etc.
 * The statement "c0 expressed in meters per second is an exact value with no measurement uncertainty in SI", is true. You draw the implication "So with the notion of a real 'vacuum', these exact properties make no sense." On the contrary, the exactness of c0 means nothing whatsoever except that it means that the meter is defined in terms of the speed of light. That's just simple logic, not so complicated.
 * Now, BIPM presumably wants the meter to be defined well, so that it is a fixed unit of length. Therefore we can infer that the scientists at BIPM believe that intensity- and frequency-variations of the speed of light in "real" vacuums (vacuums obeying the laws of physics of our universe, i.e. with vacuum fluctuations) are either exactly zero, or negligibly small.
 * There is no logical contradiction in saying "The speed of light in vacuum, expressed in meters per second, is exactly fixed" and also saying "The speed of light in vacuum is not exactly fixed". If both are true, that just means the meter is not defined exactly. Two labs can measure different lengths, and each can say "this is the length of the meter", and both are equally correct. It means that BIPM did not define the meter as well as they could have or should have. It means that the meter is not (quite) "a unit of length" but instead "a range of units of length". But again, it is not a logical contradiction. (It becomes like the kilogram, which everyone already agrees is not a unit of mass, but a range of units of mass....unfortunate but not unthinkable.)
 * On another note: You found lots of sources that use the term "classical vacuum". These authors use the words as a synonym/shorthand of "vacuum, and by the way I'm the classical electromagnetism approximation right now". I have no problem with that usage. I don't object to describing the properties that were attributed to the vacuum before the discovery of quantum mechanics. I do object to saying that the properties are relevant for something besides a simplifying approximation to our real universe.
 * On another note, if "classical vacuum" is a "reference medium", then we should understand it's properties very well to able to "refer" to them. So, please answer this question: "If I put an electron in a classical vacuum, does it still have the same charge? If not, what is its charge?" Remember, the "bare charge" of an electron (without vacuum fluctuations) is infinite . --Steve (talk) 17:53, 23 December 2011 (UTC)
 * Steve Byrnes: A number of your statements above are simply incorrect. I will attempt to sort things out below, quoting first your paragraphs, and then my response to them.

1. Brews, my main objection is to your assertion that the "classical vacuum" is essential to the SI definition of the meter (or anything else in SI). On the contrary, precision metrological physicists do not use the theory of classical electromagnetism for any purpose (except for shorthand simplifications) because precision metrological physicists only use the most precise theories. --Steve (talk) 17:53, 23 December 2011 (UTC)


 * There is no mention of the essential nature of classical electromagnetism here, only that the defined values of the electromagnetic properties of 'vacuum' are related to the derived values by the relations of classical electromagnetism in a region with no electric charges or currents, in particular, by the formula c02 = (&epsilon;0&mu;0)&minus;1. One may view this as a coincidence or as a convenient choice, but it is not necessary to view it as an endorsement of all of classical electromagnetism, lock, stock and barrel.


 * There also is no mention on the NIST or BIPM pages that define 'vacuum" to the topics of measurement "precision" or "precise theories", which are, of course, irrelevant to definitions, which are not subject to either theory or measurement.


 * As you are aware, the definition of the metre refers to the defined speed of light that can be found on the NIST website, for example, as linked here: speed of light in vacuum, c,c0 with the exact value 299 792 458 m s-1. The term classical vacuum refers to a hypothetical medium with exact properties &mu;0 and  speed of light in vacuum, c,c0 and defined properties with exact values &epsilon;0 and the characteristic impedance of 'vacuum' Z0. Brews ohare (talk) 14:16, 29 December 2011 (UTC)

2. The statement "c0 expressed in meters per second is an exact value with no measurement uncertainty in SI", is true. You draw the implication "So with the notion of a real 'vacuum', these exact properties make no sense." On the contrary, the exactness of c0 means nothing whatsoever except that it means that the meter is defined in terms of the speed of light. That's just simple logic, not so complicated. --Steve (talk) 17:53, 23 December 2011 (UTC)


 * I am glad we agree that it is true that c0 is a defined exact value. Apparently there is some confusion about how I understand exact defined properties for a real medium. It may be that the confusion relates to measured versus defined properties. I'll explain this point further.
 * The speed of light c0 is just one of several electromagnetic properties of the 'vacuum' referred to in the definition of 'vacuum', as listed above. Of course, the prescription of exact values for a medium exceeds the capacity of any measurement on any real medium. Measurement always is subject to uncertainty. Thus, no real medium can be known with certainty to be a realization in the laboratory of the defined 'vacuum'.
 * In fact, all theories of real vacuums show that they cannot have these defined properties, because these theories identify vacuum fluctuations and virtual particles as properties that underlie the experimentally observed phenomena of spontaneous emission and the Lamb shift (among others). These underlying features are known theoretically to result in different electromagnetic properties than the defined 'vacuum'. Although the measurement of these electromagnetic properties has not been done directly, the above experimental phenomena related to them have been known since the forties. Consequently, it is clear that whatever the ultimate theory of the vacuum may turn out to be, it will not be the defined 'vacuum', and no real vacuum will be an example of the defined 'vacuum'.
 * Despite the impossibility of producing a laboratory version of the defined 'vacuum', it remains useful as a reference medium to which any medium, including real vacuum can be compared through its electromagnetic properties, its relative permittivity &epsilon;&thinsp;&frasl;&thinsp;&epsilon;0 and it relative permeablity &mu;&thinsp;&frasl;&thinsp;&mu;0. Here, of course, &epsilon;0 is the electric constant also known as the permittivity of vacuum and &mu;0 is the magnetic constant also know as the permeability of vacuum.
 * I think you actually do agree with these observations, although that isn't clear from these recent remarks of yours. Perhaps you could make your position more clear on these basic points. The real disagreement between us is next. Brews ohare (talk) 14:16, 29 December 2011 (UTC)

3. Now, BIPM presumably wants the meter to be defined well, so that it is a fixed unit of length. Therefore we can infer that the scientists at BIPM believe that intensity- and frequency-variations of the speed of light in "real" vacuums (vacuums obeying the laws of physics of our universe, i.e. with vacuum fluctuations) are either exactly zero, or negligibly small. --Steve (talk) 17:53, 23 December 2011 (UTC)
 * I find this remark confused. First, there is no need or value in speculating what BIPM scientists believe. That is simply a way to make BIPM a spokesman for views entertained by yourself, and there is no evidence of what BIPM believes, nor what thier notions are of a "well" defined metre or a "fixed" unit of length. So lets stick to what can be established. Brews ohare (talk) 14:16, 29 December 2011 (UTC)

4. There is no logical contradiction in saying "The speed of light in vacuum, expressed in meters per second, is exactly fixed" and also saying "The speed of light in vacuum is not exactly fixed". If both are true, that just means the meter is not defined exactly. Two labs can measure different lengths, and each can say "this is the length of the meter", and both are equally correct. It means that BIPM did not define the meter as well as they could have or should have. It means that the meter is not (quite) "a unit of length" but instead "a range of units of length". But again, it is not a logical contradiction. (It becomes like the kilogram, which everyone already agrees is not a unit of mass, but a range of units of mass....unfortunate but not unthinkable.) --Steve (talk) 17:53, 23 December 2011 (UTC)
 * I completely understand the point that no realization of the metre is exact, because of course the laboratory metre is fashioned in some real medium with some only approximately known refractive index, and because the transit time of light across the metre is not exactly measurable, and because the standard second is subject to uncertainty. If an interferometer is used, additional sources of uncertainty are introduced, such as uncertainty in the frequency of the source and number of wavelengths counted.
 * I cannot see that these practical matters allow you to say: " There is no logical contradiction in saying 'The speed of light in vacuum, expressed in meters per second, is exactly fixed' and also saying 'The speed of light in vacuum is not exactly fixed'. This belief that a statement and its negation are both valid is logical nonsense. So I suspect this is a rhetorical device of some kind, but I don't get it. You continue: 'If both are true, that just means the meter is not defined exactly. Two labs can measure different lengths, and each can say "this is the length of the meter", and both are equally correct.' In fact, neither lab would make such a statement. What lab 1 would say is "this is the length of this realization of the metre, and it is accurate to ±&Delta;1" and lab 2 would say "this is the length of this realization of the metre, and it is accurate to ±&Delta;2". I see no problem here. The question you believe I pose about logical consistency never arises in my mind, and it is impossible to phrase things as a seeming 'logical' contradiction between statements from different labs about different realizations of the metre. Brews ohare (talk) 14:16, 29 December 2011 (UTC)

5. On another note: You found lots of sources that use the term "classical vacuum". These authors use the words as a synonym/shorthand of "vacuum, and by the way I'm the classical electromagnetism approximation right now". I have no problem with that usage. I don't object to describing the properties that were attributed to the vacuum before the discovery of quantum mechanics. I do object to saying that the properties are relevant for something besides a simplifying approximation to our real universe. --Steve (talk) 17:53, 23 December 2011 (UTC)
 * There is a confusion here about a reference state, the 'vacuum' with defined exact properties, and a model of real vacuum that predates field-theoretic vacuums. There is no claim that the reference state is some primitive model of vacuum, nor is it some approximation to vacuum. It is a reference, a base line or origin, from which the departures of any medium can be found including real vacuum. Departures don't have to be from some realizable 'vacuum'; all that is necessary is that the departures have to be calculable and measurable. Brews ohare (talk) 14:16, 29 December 2011 (UTC)

6. On another note, if "classical vacuum" is a "reference medium", then we should understand it's properties very well to able to "refer" to them. So, please answer this question: "If I put an electron in a classical vacuum, does it still have the same charge? If not, what is its charge?" Remember, the "bare charge" of an electron (without vacuum fluctuations) is infinite .--Steve (talk) 17:53, 23 December 2011 (UTC)
 * You raise a very good point, but your question does not address that point. There is no need to determine a complete theory of electromagnetism associated with charges and currents in the defined 'vacuum'. The presence of charges and currents, or virtual particles and fluctuations, indicates the presence of a medium. What we need is to be able to calculate and to measure this medium's permittivity and permeability, and to divide those quantities by &epsilon;0 and &mu;0 to obtain the relative permittivity and relative permeability values relative to defined 'vacuum'. Brews ohare (talk) 14:16, 29 December 2011 (UTC)
 * This calculation would be done with whatever theory is appropriate (perhaps QCD) and measured by whatever experimental means is current. Brews ohare (talk) 14:42, 29 December 2011 (UTC)


 * I say: There is no logical contradiction in saying "The speed of light in vacuum, expressed in meters per second, is exactly fixed" and also saying "The speed of light in vacuum is not exactly fixed". You say: "No, it's a logical contradiction, one statement is the negation of the other." OK, I'll break it down for you in a simpler situation with the same logical structure. Do you agree or disagree: "The mass of the IPK, expressed in kilograms, is exactly fixed." (i.e., exactly 1 kilogram.) Do you agree or disagree: "The mass of the IPK is not exactly fixed." (i.e., it regularly gains and loses a few atoms.) If you can agree with both, then you are capable of understanding the logic involved here.
 * You say: "c0 [expressed in meters per second] is an exact value, not a measurement with measurement errors. So with the notion of a real 'vacuum', these exact properties make no sense." By the same token, here is a statement: "The mass of the IPK, expressed in kilograms, is an exact value, not a measurement with measurement errors. So the notion that the IPK is a real physical object in France makes no sense. The IPK has to be a hypothetical object." You disagree, I presume, with the latter. Can't you see the same logical error in the former? --Steve (talk) 19:55, 31 December 2011 (UTC)
 * Hi Steve: So you avoid logical nonsense by using two meanings for 'fixed', so "A is fixed1" does not contradict "A is not fixed2". Very clever, but maybe not the best way to be clear.
 * In the present instance c0, often referred to as the speed of light in the SI units, is a specific exact number, and this number is fixed by definition. However, the physical phenomena of the speed of light, for example as the limit upon the maximum speed of transfer of information, may or may not be fixed (that is an empirical matter that cannot be settled by definition, but requires experimental observation).
 * So where does that all take us? Let's see: the simplest way is to notice that BIPM and the standards orgs have posted the defined values c, c0, μ0 and the subsidiary related properties with the exact values ε0 and Z0. What do these values mean? Why are they posted?
 * I'd say they set up units. So for example, in a realizable medium of which partial vacuum is an example, the speed of light in that medium can be measured and the value expressed as a fraction of c0, within some measurement error, its relative permittivity can be expressed as &epsilon;&thinsp;&frasl;&thinsp;&epsilon;0, and its relative permeability can be expressed as &mu;&thinsp;&frasl;&thinsp;&mu;0, again within some measurement error. So the phenomena are not "fixed", but the base to which comparison is made is fixed. The BIPM posted properties are arbitrary and exact, but some base line has to be set, and that is what BIPM has done. There is no physics here at all, there is no necessary connection of these properties to any realizable physical medium. The arbitrary nature of the units, set by metrology, is why exact values can be defined and no measurement is necessary.
 * How's that sound? Do we agree on this? Brews ohare (talk) 23:25, 31 December 2011 (UTC)

New intro
DickLyon has suggested that "Brews, let's work out a new intro here, and then add it to the article." Here are the items that I think have to appear in the intro:

(i) The everyday idea of vacuum as a region devoid of particles.

(ii) The fact that a perfect vacuum is not obtainable. That view is based upon several facts; among them is the impossibility of getting all the particles out of a vacuum including black-body photons, but more than that, there is the impossibility of eliminating virtual particles.

(iii) The role played by the medium with electromagnetic properties &epsilon;0, &mu;0 with a defined speed of light c02=1&thinsp;&frasl;&thinsp;(&epsilon;0&mu;0) These properties are defined to infinite accuracy on the NIST website, and are measurement-independent exactly known constants. It may be noted that these parameters were once known as the permittivity of vacuum and permeability of vacuum. That isn't just a curiosity.

(iv) The part played by the defined speed of light in real vacuum. The speed of light in 'vacuum' is not the speed of light in any realizable vacuum. The reason for this fact is vacuum fluctuations, an experimentally observed and theoretically predicted phenomena. The speed c0 is related via Maxwell's equations to the properties &epsilon;0 and &mu;0, and these last properties do not allow for vacuum fluctuations. A number of sources agree that there is no medium that exhibits vacuum fluctuations where the speed of light is c0, simply because the permittivity and permeability of real vacuums are not &epsilon;0 and &mu;0, even in principle.

There is strong resistance among a number of authors here on WP to open description of items (iii) and (iv). That resistance leads to very extreme views that are not supported by sources, but are forced upon WP anyway. One has to walk around the subject on tip-toes.

Before an adequate introduction can be constructed in the WP environment, some agreement on the role of these factors has to be reached. They should not be settled by fiat rather than fact. Brews ohare (talk) 22:54, 22 December 2011 (UTC)


 * I also suggested that we get it right in the body of the article before summarizing in the lead. It's not clear to me that your items i-iv are a great way to summarize the concept of vacuum.  Even the notion of "everyday" seems designed to deflect attention away from the usual and toward the super-picky viewpoint.  Dicklyon (talk) 23:01, 22 December 2011 (UTC)
 * I'd suggest we deal with these four points here, on the Talk page, and then the ramifications will fall into place. Brews ohare (talk) 23:05, 22 December 2011 (UTC)
 * IMO, the first two sentences of the present intro cover the everyday meaning of vacuum adequately. Brews ohare (talk) 23:07, 22 December 2011 (UTC)
 * My thoughts are that iii and iv have no place in the lead as being of little interest to most readers and not necessary for either defining or understanding the vacuum. For most readers a vacuum is simply a physical state: an absence of matter. People may be have come across the concept in the context of a vacuum flask, a thermometer, a vacuum tube, or outer space. A more educated reader might know of or be interested the different qualities of vacuum and that there is no such thing as a perfect vacuum. None of this depends on, or even relates to, electromagnetism or the speed of light. If there is any need to relate it to other physics topics it's to quantum mechanics, as the reason for the non-existence of a perfect vacuum.-- JohnBlackburne wordsdeeds 07:18, 23 December 2011 (UTC)
 * Hi John: I'd agree that it should be noted that vacuum as the absence of everything is not just difficult but impossible to achieve, even in principle because of virtual particles. It should be added to this that for the same reason, vacuum is not a blank, inert medium, but exhibits electric and magnetic polarizability affecting its behavior, as evidenced in experimental observations like spontaneous emission, the Lamb shift, the Casimir effect and so forth. These things are not just curiosities, they are the subject of general discussions. They link to aspects of nature of interest to many readers. It is normal for the introduction of a topic to mention briefly its profound connections, and not only the banal. Brews ohare (talk) 13:57, 23 December 2011 (UTC)
 * Here is a discussion of vacuum that could serve as a model. Brews ohare (talk) 14:03, 23 December 2011 (UTC)
 * Some books say the quantum fluctuations are a property of a perfect vacuum, not something that makes perfect vacuum impossible.  That could be discussed, but not in the lead.  They also say perfect vacuum is impossible for other reasons, like that the positions of particles always have uncertainty; so what?  Dicklyon (talk) 18:23, 23 December 2011 (UTC)
 * Dick: You say: "So what?" I believe that the discussion is really about various descriptions of 'vacuum', how they differ, and what is a realizable vacuum, and what is not. That could help the reader understand some of the complexities of this matter, and some of the shortcomings of seeing vacuum as simply the absence of everything, and why vacuum is a very important topic in physics today. Instead of going into all this, of course, you could invoke Wikipedia is not a dictionary, eh? That way the whole subject disappears. Brews ohare (talk) 01:14, 24 December 2011 (UTC)
 * If "it should be noted that vacuum as the absence of everything is not just difficult but impossible to achieve, even in principle because of virtual particles," then find us some evidence in sources that it should be noted. Find some evidence that it matters to someone other than you.  If it's of minor importance, it might still go in the article, but not in the lead.  The "so what" is a request follow up with what's important about what you say; in my experience, you typically push minor technicalities way out of proportion to their importance.  Your points are often "idiosyncratic" in the sense that they are points that reliable sources never, or almost never, make.  Dicklyon (talk) 06:03, 24 December 2011 (UTC)
 * Hi Dick: Sorry you are losing your cool. You are aware already of this source for example, mentioned earlier. It discusses 'vacuum' in many ways. Of course there are many more such published discussions, and I know you can Google them if you want to become educated on this subject and make a contribution here. On WP there also are the articles on QCD vacuum and Vacuum state. This parent topic Vaccum has some discussion of these topics, along with the Vacuum The question at hand here is not whether these things are worth discussing, but how these subtopics should be addressed in the introduction to alert readers about this content and how to put it into perspective. Those subjects are more pertinent than your unsupportable appraisal of my overall contributions to WP in uncomplimentary terms. Brews ohare (talk) 17:02, 24 December 2011 (UTC)

Vacuum is defined as the ground state (lowest energy state) in the context of quantum field theory. So, given some system with specified boundary conditions, like a box where you specify the boundary conditions of the fields on the boundary, you can solve for the states that have a well defined energy. If the interactions between the fields (also the self interaction) is weak in some sense, you can define a particle content of these states. Intuitively, this is obvious, you'll have a zero particle state with the lowest energy, and then there will be many one particle states such that that particle's wavefunction is a solution of the Schrodinger equation satisfying the boundary conditions and then you'll have two particle states etc. etc. The lowest energy state is how the vacuum is defined in general. The difference with classical physics is that the vacuum has non-trivial properties. Count Iblis (talk) 12:55, 24 December 2011 (UTC)


 * The current intro is OK except I'd rather have the intro say "Vacuum is space that is mostly or completely empty of matter" to capture the term as it's used in practice. Also, "An approximation to such vacuum" is awkward wording, I'd rather see something like "Vacuums in practice are...". I think that Brews's original points (iii) and (iv) should not be discussed at all because Brews's understanding of them is incorrect, and that the SI meter can be (and is) defined perfectly well in vacuums containing quantum fluctuations, just as the SI second is. By the same token, I think that the primary description in the literature I've seen, and the one we should exclusively use in this article, is "a perfect vacuum has quantum fluctuations" rather than "a perfect vacuum cannot exist because of quantum fluctuations", although it's true that you can find the latter sometimes if you look long and hard. --Steve (talk) 18:19, 26 December 2011 (UTC)


 * Steve: Your remark that "Brews's original points (iii) and (iv) should not be discussed at all because Brews's understanding of them is incorrect" is rather harsh. For example, point (iii) is the following:
 * (iii) The role played by the medium with electromagnetic properties &epsilon;0, &mu;0 with a defined speed of light c02=1&thinsp;&frasl;&thinsp;(&epsilon;0&mu;0) These properties are defined to infinite accuracy on the NIST website, and are measurement-independent exactly known constants. It may be noted that these parameters were once known as the permittivity of vacuum and permeability of vacuum. That isn't just a curiosity.
 * Now, there is nothing here attributable to me or my understanding. What is said is simply to point at the NIST website for the values of ε0, μ0 and c0 posted there, and to point out the ancient names of these properties, which are readily found to be exactly what is stated with a simple Google search.


 * Item (iv) says:
 * (iv) The part played by the defined speed of light in real vacuum. The speed of light in 'vacuum' is not the speed of light in any realizable vacuum. The reason for this fact is vacuum fluctuations, an experimentally observed and theoretically predicted phenomena. The speed c0 is related via Maxwell's equations to the properties &epsilon;0 and &mu;0, and these last properties do not allow for vacuum fluctuations. A number of sources agree that there is no medium that exhibits vacuum fluctuations where the speed of light is c0, simply because the permittivity and permeability of real vacuums are not &epsilon;0 and &mu;0, even in principle.
 * I am sure that you agree that the speed of light in a medium is c=c0/n, with n the refractive index of the medium. And I am sure you also have read the references that say n ≠ 1 in any of the field-theoretic vacuums. Inasmuch as experimentally documented behavior such as spontaneous emission and the Lamb shift are known to occur in field-theoretic vacuums where n ≠ 1, it is clear that any real vacuum, whatever the details, has n ≠ 1, so there is nothing controversial in point (iv), the speed of light in any realizable vacuum is not c0 but c0/n with n ≠ 1, and there is no failure of understanding on my part. Brews ohare (talk) 01:34, 27 December 2011 (UTC)
 * Yes, but this depends on boundary conditions and background fields. By normalizing things properly, the speed of light is still c. The bottom line is that the real vacuum, which includes vacuum fluctuations, will look more and more like the hypothetical classical vacuum at large enough scales. Now, you can rescale things on paper by rescaling variables in the equations properly. This freedom to rescale things appears explicitly in the form of the dimensional constants c and hbar when using SI units. A simple analogy. The operational definition of temperature involves a gas thermometer and the equations of an ideal gas. But in reality, there is no such thing as an ideal gas. But a real gas will look more and more like an ideal gas in the limit that it becomes more and more dilute. Count Iblis (talk) 15:11, 27 December 2011 (UTC)
 * Count: I have opened a new thread on this topic below. Thanks for your interest. Brews ohare (talk) 15:39, 27 December 2011 (UTC)
 * The gist is that although the speed of light in a real vacuum may approximate the value c0 in certain regimes where short distances or times are unimportant, or regimes where fields are low enough that nonlinearity in the fields is insignificant, that correspondence with c0 is restricted. Accordingly the 'vacuum' that NIST has referred to with defined properties c, c0, μ0 and the subsidiary derived properties with exact values ε0 and Z0 that are independent of frequency, wavelength, and field strengths in all regimes and combinations, properties that exhibit perfect isotropy, no polarization dependence, and no regard for the shape of any bounding surface, remains an idealized unobtainable 'vacuum' medium not found in nature. Brews ohare (talk) 17:20, 28 December 2011 (UTC)

Boundary conditions and the speed of light
Count Iblis has said above:
 * "Yes, but this depends on boundary conditions and background fields. By normalizing things properly, the speed of light is still c. The bottom line is that the real vacuum, which includes vacuum fluctuations, will look more and more like the hypothetical classical vacuum at large enough scales. Now, you can rescale things on paper by rescaling variables in the equations properly. This freedom to rescale things appears explicitely in the form of the dimensional constants c and hbar when using SI units. A simple analogy. The operational definition of temperature involves a gas thermometer and the equations of an ideal gas. But in reality, there is no such thing as an ideal gas. But a real gas will look more and more like an ideal gas in the limit that it becomes more and more dilute." Count Iblis (talk) 15:11, 27 December 2011 (UTC)

I have seen discussion of the Casimir effect that of course requires boundary conditions. There are, however, other phenomena like spontaneous emission, or the Lamb shift that demonstrate the presence of virtual particles and vacuum fluctuations. According to these sources media exhibiting these effects possess n ≠ 1. Is it your view that these situations and these references also are subject to boundary conditions effects that can be "scaled away"? Can you provide some indication of how one can scale away relative permittivities and permeabilities that have (i) frequency dependence, (ii) wavelength dependence (iii) anisotropy, (iv) nonlinear field dependencies, (v) polarization dependence all of which violate a refractive index that is identically unity? Can you provide some sources where I can read how this is accomplished?

My prejudice is that the boundary condition argument is very limited in scope. Brews ohare (talk) 15:34, 27 December 2011 (UTC)

It seems likely to me that if a scaling of such complexity as to renormalize away all these dependencies (frequency, wavelength, nonlinearity...) can be devised, it could be used to make the speed of light in any medium, say a ferroelectric for example, c = c0. It is hard to see what meaning can be attached to the "speed of light" under such circumstances. The concept of refractive index seems to be scaled away. Brews ohare (talk) 15:50, 27 December 2011 (UTC)

On re-reading your comments, Count, I wonder if what you are suggesting is that the effects upon n introduced by vacuum fluctuations are on such a small spatial scale that they can be simply "averaged away" using some coarsening process? Then the speed of light, being affected only at short wavelengths, would return to c0 in the averaged medium.

If that is the argument, it has no effect upon the statement that the reference 'vacuum' of NIST and BIPM is not realizable because its refractive index is identically 1 at all wavelengths, and that the speed of light in this 'vacuum' that is c0 at all wavelengths is not realizable in any real vacuum. Do you agree? Brews ohare (talk) 16:14, 27 December 2011 (UTC)


 * Yes, the effect on n exists on a very small scale; if we chose to only look at long wavelengths, you don't see the quantum effects anymore, because necessarily, you have to impose the boundary conditions farther away..
 * Both boundary conditions and the presence of charges or fields can cause non-trivial effects, making the vacuum behave as if it were a medium. In the latter case, you could argue thaty this isn't a vacuum anyway, as we put charges of fields in a vacuum. However, you can still consider a nucleus in a vacuum and then the vacuum around that charge will show effects similar to that of a polarizable medium. These sorts of effects cause the Lamb shift. The effects of only boundary conditions in an otherwise completely empty vacuum (like the vacuum between two metal plates) are much weaker, see e.g. the Scharnhorst effect.
 * In quantum electrodynamics, if you average away everything, except for the leading effects of vacuum polarization, you get an effective theory of electromagentism described by Euler-Heisenberg Lagrangian. The index of refraction of light travelling through a homogeneous magnetic field in a magnetic field is given here. So, here you see that the index of refraction is different from 1, but then you do have a magnetic field. Without any fields or particles, vacuum polarization effects can only be due to boundary conditions. Count Iblis (talk) 00:12, 29 December 2011 (UTC)
 * Count: These are interesting links. I was unaware of this material. According to the last link, a magnetic field introduces a permittivity and permeability tensor in a vacuum. These tensors tend to unity as the field strengths drop to zero. These results apply under the circumstances of spatially slowly varying fields, and the case of rapidly varying fields is not discussed.
 * It would appear to me that your conclusion that electromagnetic properties of vacuum arise only due to boundary effects may be true only under restricted circumstances. Would you care to comment upon these references? Brews ohare (talk) 18:33, 4 January 2012 (UTC)

Meanings of vacuum
DickLyon has removed the reference to "everyday usage" espousing this view:
 * "everyday usage" would be applicable to a usage issue of a term; this sentence is about vacuum itself, not the term"

That stance is incorrect, because 'vacuum' does not simply refer to a single concept, as the rest of the article Vacuum makes clear. The various ideas all referred to at least on occasion as simply 'vacuum' include:
 * 1) the absence of everything
 * 2) some approximation to the absence of everything, which includes such different things as field-theoretic vacuum and partial vacuum
 * 3) the medium where the speed of light is c0

The introduction could be altered so that a more general meaning of 'vacuum' was presented, but at the moment the introduction is focused upon what is more carefully described as partial vacuum, that is upon one meaning of many.

So this change should be reverted. Brews ohare (talk) 15:17, 26 December 2011 (UTC)
 * I agree with User:Dicklyon, "everyday usage" is redundant. Every article should be accessible so start with the everyday definition of the word, if there is one. And there clearly is an everyday definition here, it's the one most people understand, and the one described by the first half of the article.-- JohnBlackburne wordsdeeds 15:42, 26 December 2011 (UTC)
 * Dicklyon's elimination of "everyday usage" is not simply the removal of redundancy. What Dick did was to change the lead sentence to read:
 * "Vacuum is space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure1"
 * The footnote is to a work on vacuum physics, that is, to a work about methods to achieve good partial vacuum.
 * Thus, far from being redundant, the now deleted words "everyday usage" clarify that the term 'vacuum' is not restricted to this meaning, and has other usages. Without these words, the lead statement is an assertion that 'vacuum' is partial vacuum. That assertion is misleading. Brews ohare (talk) 16:13, 26 December 2011 (UTC)
 * I have made a very minor change, breaking the lead sentence into two parts, that removes this difficulty. Brews ohare (talk) 16:20, 26 December 2011 (UTC)

Blackburne's deletion
In this edit JohnBlackburne removed reference in the leading paragraphs to the modern (since quantum electrodynamics ) conception of the vacuum and links to the WP articles vacuum fluctuations and virtual particles that amplify these brief remarks. The rationale for these deletions are provided only in the one-line edit summary repeated below:
 * Reverted 4 edits by Brews ohare (talk): Per WP:LEAD (too long), WP:QUOTE (not pertinent and relevance not explained) and what does 'phyisical attributes' mean?

The dry observation from G.E. Brown:
 * "In eighteenth-century physics the three-body problem was insoluble. With the birth of relativity around 1910 and quantum electrodynamics in 1930, the two- and one-body problems became insoluble. And within modern quantum field theory, the problem of zero bodies (vacuum) is insoluble. So if we are after exact solutions, no bodies at all is already too many!"

may not appeal to every taste, of course, and although my personal feeling is that it adds some flavor to the topic, I can understand relegating it to a footnote, though I see no reason to delete it altogether.

The restoration of a single sentence to mention the modern conception of vacuum and link to other WP articles is not an undue strain upon brevity.

The attribution "physical attributes" is too vague according to Blackburne, so I have added the example properties of permittivity and permeability with their WP links to provide more clarity.

Perhaps editor Blackburne might entertain a more detailed attention in his reversions, and execute them more surgically? Brews ohare (talk) 17:19, 31 December 2011 (UTC)


 * This is an encyclopaedia, so 'flavor' has no place here. Here is the policy:
 * Where a quotation presents rhetorical language in place of more neutral, dispassionate tone preferred for encyclopedias, it can be a backdoor method of inserting a non-neutral treatment of a controversial subject into Wikipedia's narrative on the subject, and should be avoided.
 * Overuse happens when:
 * a quotation is used without pertinence
 * This means that a quotation is visually on the page, but its relevance is not explained anywhere (my emphasis).
 * Adding the quote with only the explanation for it "a dry quote" fails to explain it and it is clearly non-neutral and rhetorical. WP:LEAD is very clear that the lead should be at most four paragraphs, not six. And we already had a discussion on whether permittivity, permeability should be mentioned in the lead; you should not be adding them now against that consensus.-- JohnBlackburne wordsdeeds 17:41, 31 December 2011 (UTC)
 * Adding the quote with only the explanation for it "a dry quote" fails to explain it and it is clearly non-neutral and rhetorical. WP:LEAD is very clear that the lead should be at most four paragraphs, not six. And we already had a discussion on whether permittivity, permeability should be mentioned in the lead; you should not be adding them now against that consensus.-- JohnBlackburne wordsdeeds 17:41, 31 December 2011 (UTC)


 * Originally I referred to "physical attributes" without elaboration, and you called me on that as "too vague". Now you say examples to add precision contradict an earlier discussion. Sounds like a Catch 22, eh? Brews ohare (talk) 18:01, 31 December 2011 (UTC)
 * I think you misunderstand the purpose of the quote, which is not intended by either Mattuck or Brown as non-neutral or rhetorical. It is a metaphysical wringing of the hands, a "well, what can I say?" that brings a smile to physicists, who wish to simplify explanation only to find the simplest things become more complicated. Brews ohare (talk) 18:01, 31 December 2011 (UTC)
 * One version of your addition doesn't belong because it's too vague, the other as it's against consensus. Simply resolved by removing it. Articles are supposed to be factual, not funny. Adding non-pertinent quotes to make readers smile is never appropriate, no matter how much you like them. And the changes still leave the lead far too long.-- JohnBlackburne wordsdeeds 18:32, 31 December 2011 (UTC)


 * John: Perhaps you can explain why the introduction is better served by removing a pertinent remark concerning the modern physical conception of the field-theoretic vacuum, while you are happy to retain the present prolonged description of the restricted meaning of 'vacuum' as partial vacuum, an exposition that greatly extends the length of the introduction for a purpose much better served in a separate subsection?
 * The pertinent addition I recommend is the sentence:
 * The notion of a perfect vacuum has become more complex with time, and today involves the ideas of virtual particles and vacuum fluctuations, which provide vacuum with physical attributes.1


 * 1For example, QCD vacuum is paramagnetic, while QED vacuum is diamagnetic. See


 * Your reluctance in making this change appears to have no basis in WP policy. Brews ohare (talk) 19:29, 31 December 2011 (UTC)

Did you not see the links to the relevant policies I provided above and in my first edit summary, as well as the link to the previous discussion? I can't think of anything to add to what I've written already, so does anyone else have a view?-- JohnBlackburne wordsdeeds 19:34, 31 December 2011 (UTC)

RfC Should the introduction to Vacuum be amended to include some mention of field-theoretic vacuum?
Should the introduction to the article Vacuum be amended to include the following reference to field-theoretic vacuum:
 * The notion of a perfect vacuum has become more complex with time, and today involves the ideas of virtual particles and vacuum fluctuations, which provide vacuum with physical attributes.1
 * 1For example, QCD vacuum is paramagnetic, while QED vacuum is diamagnetic. See Brews ohare (talk) 21:00, 31 December 2011 (UTC)

At present the emphasis of the introduction is upon partial vacuum, a good deal of which discussion could be moved to a subsection on partial vacuum. On the other hand, the modern view of vacuum, which underlies the experimental phenomena of spontaneous emission. the Lamb shift and Casimir effect. while mentioned later in the article, is skipped over in the introduction as a parenthetic comment squeezed into a paragraph about partial vacuum. Brews ohare (talk) 21:00, 31 December 2011 (UTC)

Comments

 * Comment: It may be that these last mentioned remarks should be combined in some way with this suggested addition in a separate paragraph. Brews ohare (talk) 21:00, 31 December 2011 (UTC)


 * For example, the last few sentences of the existing paragraph about the quality of partial vacuum could be excerpted and combined as a paragraph:
 * Even if every single atom and particle could be removed from a volume, it would still not be "empty" due to vacuum fluctuations, virtual particles and dark energy, and other phenomena of quantum physics. In modern particle physics, a field theoretical vacuum is considered as the ground state of the fields. The quantum aspects provide the vacuum with physical attributes.1
 * 1For example, QCD vacuum is paramagnetic, while QED vacuum is diamagnetic. See Brews ohare (talk) 21:28, 31 December 2011 (UTC)


 * Comment:
 * As already noted 'physical attributes' is too vague. My thoughts on first reading it were it either referred to something physical such as a force or mass of Newtonian physics, or is meaningless as everything a physics article concerns is physical, much as the content of a maths article is mathematical. Readers should not have to read a footnote to understand what is meant by the text, especially not in the lead. But the footnote text is even less clear, just a series of links (one of them a redlink), unexplained terms and abbreviations.
 * More generally the point it is trying to make seems very obscure: the lead already mentions the consequences of QM for vacuums, which is only a small part of the article. To add more and effectively expand it to a paragraph, one of four in the lead (so something else would have to be removed) would accord it undue emphasis and weight. And as written it (including the footnote) is too technical for an otherwise much more accessible lead.-- JohnBlackburne wordsdeeds 05:30, 1 January 2012 (UTC)
 * Reply: The description "physical attributes" indeed is vague. It could be replaced by "electromagnetic properties", for example. The footnote is not necessary to understanding the sentence, but is an elaboration for those with a deeper interest in exploring what has been said, providing a source for more details. Brews ohare (talk) 15:47, 3 January 2012 (UTC)
 * It is odd that QCD vacuum has a separate article, while the more often used QED vacuum does not. The link could be changed, but there is no single WP article that properly addresses the aspects of QED vacuum that are touched upon in Virtual particles, Vacuum state, Vacuum polarization, Vacuum fluctuations. Brews ohare (talk) 16:32, 3 January 2012 (UTC)
 * I've started an article titled QED vacuum. Brews ohare (talk) 18:41, 8 January 2012 (UTC)


 * Comment:
 * The lead should not explain the topic. It should be a summary of the article, preferably in the same order as the article sections. That would be "Etymology, Uses, Vacuum-driven machines, Outer space, etc" Starting with "Uses" before explaining what a vacuum is isn't good. I've moved the sections around a bit hoping the new order is better. The Historical interpretation section is a bit bulky but your addition should really go there first I think. When that is done the lead may summarize it if that is still required. 84.106.26.81 (talk) 13:21, 1 January 2012 (UTC)
 * Reply: As I understand your comment, you dislike the introduction in its entirety. I imagine that my one-sentence addition that is the subject of this RfC is in keeping with your goal of an introduction that mentions what is contained in the rest of the article. So perhaps you could address this particular issue? Brews ohare (talk) 15:47, 3 January 2012 (UTC)


 * Comment: I am not enough of a physicist to criticise the material or concepts, but there is no question in my mind about the current lede being wrongly conceived. It is far too long; about all that you could justify putting there (in suitable terminology and sense) is to mention vacuum as an idea of emptiness or absence of matter, plus that in recent times the physical, technological and philosophical aspects and implications have grown dramatically. Adequately and clearly stated, and well written at that, all that should fit into 50-100 words. If you need more than that (you are currently well over 300 words!) then omit aspects, no matter how important. Mentioning all the ramifications is what we have TOCs and section headers etc for. All the other stuff in the current lede looks good to me, but should be distributed judiciously within the other sections. What to do with the rest of the structure is open to a lot more discussion, but IMO a lot of what currently is included should be in tributary articles with no more than brief intros in the root article. The rest of the comments that I have read here seem to me to be well taken, so I offer no detailed criticism, but the subject is nowadays so large and so technical that one unconditionally does need a very carefully structured treatment with careful choice of sections and subsections. The current title, "Vacuum", irrespective of the final form, should be the "root", because it is the title that most users would look for first, and accordingly its structure should dictate the whole treatment. It also would be a very large article if it were a single item; I would recommend that "Vacuum" should contain (sayyy...) the introductory section, (as opposed to the lede) covering the lay aspects and perhaps the history of the concepts. The rest of the concepts, including field-, experimental-, technological-, theoretical, observational, and other aspects could be included as essentially stub sections in the root article, about equivalent to ledes for the respective topics in tributary articles. The full discussions could then be in their own articles, linked both ways to the root structure in the "Vacuum" article. Any section in this subject that needs more than say, 500 words should be exported to its own article. Note that the core article would be crucially important for conveying perspective and those aspects that the non-technical readers would like to know about; such persons typically would shudder at the very term "field-theoretic vacuum". My 2c! JonRichfield (talk) 11:36, 4 January 2012 (UTC)
 * Reply: Jon, your points are well taken, and separate articles should be supplied for, say, Vacuum (introductory), Vacuum (partial), Vacuum (field-theoretic), Vacuum (SI units). In fact, there were a number of these separate articles a year or so ago, but they were consolidated by reducing each to a paragraph in this root article. At the moment, any attempt to break the article up again will meet rigid opposition. Such is WP: sometimes improving, sometimes not so much. Brews ohare (talk) 15:43, 4 January 2012 (UTC)
 * Well Brews, I may be comparatively a WP newbie, but I have already seen enough not to be a bit surprised at that sad history. ;-) Still, sooner you you than me to steer the vessel through those rapids! As I hinted of course, the option remains of keeping the structure as one article, consisting of an equivalent structure of sections. I dislike the idea though; the result, however well-written and conceived, will be preeeety big if it is to be reasonably comprehensive!  You have my genuine sympathy and my best wishes for good luck.  I might come back some time for a read of a most interesting topic, but WP has a habit of swallowing one's time, so all I'll seriously undertake at this moment is to cross my fingers in your behalf.  :-)  Cheers,  JonRichfield (talk) 18:53, 4 January 2012 (UTC)


 * Comment: Saying something has "physical attributes" is saying nothing at all. What would it mean to not have physical attributes? (Even if there's an answer to this question, it's not obvious.) (Replacing "physical attributes" with "electromagnetic properties" does not help this problem.) "The notion of a perfect vacuum has become more complex with time..." introduces unnecessary complexity. It's like saying "there are vacuum fluctuations, but we didn't know 100 years ago that there were vacuum fluctuations". It's simpler and better to just say "there are vacuum fluctuations". Anyway, I suggest: "Even if every single atom and particle could be removed from a volume, it would still not be "empty" due to vacuum fluctuations, virtual particles and dark energy, and other phenomena of quantum physics (see vacuum state)." (I added the last three words.) I don't see any need for the other two sentences. Also, the footnote is a bit strange...better to say that the "standard model vacuum" (i.e., the vacuum in our universe) is paramagnetic (or diamagnetic as the case may be). --Steve (talk) 03:40, 5 January 2012 (UTC)
 * Reply: Saying the modern vacuum has "electromagnetic properties" specifies a vacuum quite different from the vacuum that prevailed following dropping of the ether concept, a vacuum which had no properties, being a featureless nothingness. The footnote simply indicates in a bit more detail what some of these electromagnetic properties are, in case the reader has no idea what that means. If you read the general references listed at the end of Vacuum you will see how published authors have dealt with shifting from featureless nothingness to modern vacuum. It is not a transition unworthy of comment. Brews ohare (talk) 06:00, 5 January 2012 (UTC)
 * And how! But I urge Steve to reflect that this is not the point to begin discussing meaningful terminology. There will be plenty of time for that (and plenty of volume, if my experience is ought to go by!) when the RFC has been settled. JonRichfield (talk) 15:15, 5 January 2012 (UTC)


 * No Too technical for the introduction, but should be included in the article. Remember the target audience for Wikipedia is the general reader. Nobody Ent 04:12, 7 January 2012 (UTC)
 * Reply: The "general reader" is a nonspecialist, not an ignoramus. Brews ohare (talk) 17:03, 9 January 2012 (UTC)