Talk:Physical constant

Edit by Azhyd

Ok since I received a question about the detail of my edit:

I agree that I should have splitted the updates... I'll know better next time. Here are my changes beside layout and grouping changes:

• add Plank temperature
• add conductance quantum and resistance quantun
• add Josephson constant and magnetic flux quantum
• add von Klitzing constant
• add equation for Bohr radius
• add equation for electron g factor and use new value
• rename magnetic moment of protons in H20 and use new value
• rename proton resonance frequency per field in H20 and use new value
• add equation for Rydberg constant
• add equation for Boltzmann constant and Faraday constant
• add equation for first radiation constant and second radiation constant
• add equation for Stefan-Boltzmann constant

Azhyd 22:29, Jul 10, 2004 (UTC)

Hi Azhyd, thanks for the information. What are the new names of magnetic moment of protons in H20 and proton resonance frequency per field in H20 ? Also, what is the source of the new values for those two and electron g factor ? Thanks for your help. Wile E. Heresiarch 01:43, 11 Jul 2004 (UTC)

All my values and constants come from the NIST site. The new names are respectively "proton magnetic moment to Bohr magneton ratio" (which I later removed since I think all those ratio would be clutter) and "proton gyromagnetic constant" divided by 2pi. Azhyd 04:49, Jul 11, 2004 (UTC)

Great. Thanks for the info, and thanks for all your work on the article. Regards, Wile E. Heresiarch 16:22, 11 Jul 2004 (UTC)

Comparing to CODATA values

Hello. I was comparing the table in the article to the 2002 CODATA values at NIST [1]. I can't identify a couple of the table items. (1) IS "magnetic moment of protons in H₂0" in the article the same thing as "shielded proton magn. moment to Bohr magneton ratio" in the NIST CODATA list? (2) Is "proton resonance frequency per field in H₂0" the same thing as "shielded proton gyromagn. ratio over 2 pi" in the NIST CODATA list? Thanks for any light you can shed on this. Happy editing, Wile E. Heresiarch 03:12, 10 May 2004 (UTC)

Stupid question

It is impossible to access the link to "Planck's constant" & "Dirac's constant"

unclear superscripts on planks units

the ^1/2 (square root) on plank mass, length, time are unclear

singular vs plural on the table

Usually article titles are singular, but since this page is a list, I moved it to the plural. (It was already listed in the plural in the list of physics topics, and the plural page redirected to the singular). Michael Hardy 16:10, 5 Jan 2004 (UTC)

The list is getting rather long. Would it benefit from being sorted alphabetically or does it work better sorted by category? --Xwu 19:58, 9 Mar 2004 (UTC)

Lets not have categories inside a table. Sort alphabetically.Jay 04:30, 10 Mar 2004 (UTC)

Personaly, i prefer it catogarised, at least it helps in finding out what a constant is used for, oh, and the fact that lists are one of my pet hates ;-) tooto 13:54, 2 Oct 2004 (UTC)

What is reference

What does the 4th column "Ref." in the table mean ? Jay 04:30, 10 Mar 2004 (UTC)

Please, I meet Jay in the 4th column question. gl:user:Agremon

It refers to the references section: a is for the first reference (and they could be more later.

But they all come from the same reference, which is the BEST one. I propose dropping the Reference column, because in all cases the column is constant. 64.165.202.231 04:20, 31 Jan 2005 (UTC) This will also make the formating better.

Amen. Gene Nygaard 05:19, 31 Jan 2005 (UTC)

The reference column is, as it stands, entirely useless, so i'm going to remove it. When it serves a purpose (and the article explains that purpose) then it can be reinserted Fresheneesz 01:34, 3 December 2005 (UTC)

Constants that really aren't...

Avogadro's number and acceleration due to gravity on earth aren't physical constants, are they? Avogadro's number is a conversion factor between atomic mass units and grams, and acceleration due to gravity on earth is only constant on earth.

I agree, the accelleration due to gravity is only an approximate constant, and avogrado's number is based purely on the definition of a kilogram and is slightly arbitrary anyway. They probably should still be included, but perhaps in a different section? Fresheneesz 01:34, 3 December 2005 (UTC)

Also, how can a *constant* require specific conditions?? Look at "Loschmidt constant", "molar volume of an ideal gas", and "Sackur-Tetrode constant". It seems to me they're not constants if they change depending on certain conditions... Fresheneesz 22:42, 3 December 2005 (UTC)

Table format

Can someone who knows about this stuff make the tables work better? With the math in column 2, my browser makes that far too wide, and the stuff in column 3 is a jumbled mess, split numbers and split units of measure, etc. Gene Nygaard 22:22, 1 Jan 2005 (UTC)

how does it work now? I wiki-ized all the tables. Maybe it works better..? Fresheneesz 22:40, 3 December 2005 (UTC)

Scientific American Article

The article here [http://www.sciam.com/article.cfm?chanID=sa006&articleID=0005BFE6-2965-128A-A96583414B7F0000&pageNumber=1&catID=2 Inconstant Constants in the June 2005 Scientific American has interesting information about the changing of physical constants.

Extensive edits by user:fresheneesz

- I've made some extensive edits to the tables on this site, so I thought i'd better explain them. First of all, I wiki-ized a couple tables so far. Wiki formated tables are easier to edit, and shorter - all around better - I don't expect anyone should have a problem with that.

- However, I also CUT lots of things I deemed inappropriate for this page. This inluded the properties of some particles like a muon, electron, etc. I firmly believe that properties of particles belong on an entirely different page. This page is about physical constants not particle properties. Particle properties are unique to the particle they describe, and are not universal constants.

- I also cut the inverse of the "fine-structure constant" - If you want the inverse, just do it on a calculator - this page is not meant to do simple math for people. Fresheneesz 03:06, 3 December 2005 (UTC)

By the way, if all the values are now taken from single reference, can you please put that reference front and center, and please state explicitly that all values in all tables are taken from that reference. Thanks. Wile E. Heresiarch 03:04, 4 December 2005 (UTC)

- I came here for the particle stuff... maybe there should be a disambiguation page for blundering (and unpedantic :p) first-year undergraduates like myself. It could be under 'physical constants' but have an introduction explaining how it's a disambiguation for people looking for things commonly, yet wrongly, considered physical constants. This is the sort of accessability physics needs to not completely alienate everyone ever. Telling people curtly that particle properties are not constant without doing something to help future makers of this mistake makes people feel stupid when in fact they're just ignorant or not pedantic enough. That's my two cents anyway, I didn't mean to go on a rant there. --130.88.182.233 04:19, 13 December 2005 (UTC)

Suggestion by Picomp314

It seems that the constant .08206 L*atm/(mol*Kelvin) also known as the gas constant needs to be added somewhere on this table. Picomp314 15:54, 12 April 2006 (UTC)Picomp314

Physical vs Universal

It was my understanding that a physical constant is a universal constant, but a universal constant is not nessisarily a physical constant. Kevin Breitenstein has redirected universal constant to physical constant, and I was wondering if they are in fact the same thing, as I don't really know for sure.

These are matters of definition. For example pi is a universal constant. But when the state legislature of Tennessee decreed that that pi shall be three that also would have made made one and the other counting numbers into transcendental numbers. (Pretty hard to build a civilization with computers on that basis.) Fortunately reason has prevailed on this count. --Ancheta Wis 10:06, 8 July 2006 (UTC)

Thus a physical constant is not the same as a universal constant. But this is a matter for definition, and the Wikipedia community will decide. For what it's worth, the Pioneer plaque used graphic depictions of some physical relationships in hopes that universal constants might be used for communication with other civilizations. In this sense, a 'universal constant' could be considered to be 'a constant which would be understood across the universe'.

Thats decently close to what I had thought, thanks for the clarification.

Removed paragraph

I removed the following paragraph because I think it is wrong:

Unless the system of natural units is used, the numerical values of dimensionful physical constants are artifacts of the unit system used, such as SI or cgs; that is, they are essentially conversion factors of human construct.

The point is that constant quantities do not depend on the units used. To give an example: the height of the Eiffel tower is a physical constant. The height of the tower, however, is always the same independent on the units in use. The sentence confuses the physical quantity Q with its numerical factor {Q} which depends on the units.

I also removed/changed the following paragraph:

The fine-structure constant α is probably the most well-known dimensionless fundamental physical constant. The dimensionless ratios of masses (or other like-dimensioned properties) of fundamental particles are also fundamental physical constants, as are the measure of these properties in terms of natural units.

I do not think that dimensionless constants are more fundamental than other constants. This is a misunderstanding coming from the believe that quantities depend on systems of units. However, all quantities do not depend on the system of unit, independent wether they have dimensions or not. The ratio of the Eiffel tower to the empire state building is always the same and does not depend on units, as is the height of the Eiffel tower. --Kehrli 01:44, 12 August 2006 (UTC)

you are fully mistaken in thinking that dimensionless physical constants (like α) are not more fundamental than the dimensionful physical constants. the former are numbers that are properties of the universe (and the aliens on the planet Zog will come up with the same number) and the latter are human constructs. you should read and understand How Many Fundamental Constants Are There? from John Baez before injecting this truly mistaken POV into a science article. also you should buy or check out the John D. Barrow book The Constants of Nature to get a decent understanding about what the salient nature of these constants. also, take a look at the Natural units, Planck units, Dimensional analysis, and Nondimensionalization articles. you can learn something from them. r b-j 04:10, 1 September 2006 (UTC)

Rbj, I did read the pages of John Baez, Natural units, Planck units, Dimensional analysis and I did think a long time before I made my changes. I am aware Beaz is probably ten times more intelligent than I am, but here he is wrong.

besides Baez, you have some authorative insight into this that exceeds that of Michael Duff or John D. Barrow or Frank Wilczek or Gabriele Veneziano? somehow your understanding of this trumps theirs? Kehrli, you overestimate your understanding and consequently your "authority" to negate what these physicists have been saying for decades with your own flawed understanding (or shall i say "misconceptions"). that over-esteem of one's self knowledge/understanding is what is getting you into these POV wars. you don't really understand it, you change the world to make it agree with your understanding, and when it pushes back

Let us go through the details once again:

1) a constant physical quantity Q is the product of a numerical value n and a unit U: Q = n*U

unless if comes from a system of natural units, the unit U is a human construct and nature doesn't give a rat's ass about it.

2) it is true that the value n is an "artifact" of the choosen unit, but Q is not. You are mixing up Q and n. Q is the physical constant, not n.

if it's not a dimensionless quantity (perhaps a ratio of like dimensioned quantities like m_p/m_e or the mass of a particle divided by the Planck mass), it is of no consequence to nature. nature doesn't give a rat's ass what units humans decide to use.

3) in the case of α the quantity consists only of a numerical value n, no units: Q = n. Therefore the constant Q implies that n also is constant. This, however, is rather trivial and does not justify that α is considered more fundamental as let's say c. --Kehrli 06:13, 11 September 2006 (UTC)

this is evidence of your misconception, Kerhli. and it is a fundamental misconception. you take your ideas to the sci.physics.research USENET newsgroup and bounce it off of those guys and see how well it sticks. (but i have to warn you, Baez hangs out there a lot, but none of the other physicists would support you on this anyway.) r b-j 04:17, 12 September 2006 (UTC)

What the hell is happening? The values of dimensionful constants do depend on the choice of units. They are only a conversion factor between different units. We're used to measure the three space dimensions in metres and the time dimension in seconds, 299 752 458 m/s is just a conversion factor between them. Sailors are used to measure two space dimensions in nautical miles and the other space dimension in fathoms, and nobody would call the conversion factor 1 012.6859... nautical miles per fathom a fundamental constant. People using the same unit for all three space dimension don't need it, just like astronomers, who measure everything in (light-)years, don't need c. (I've never heard or read the phrase "one light year per year", which gives as few as 70 Google hits.) Boltzmann's constant is just the conversion factor betveen joules and kelvins. Avogadro's number just expresses how many times 1.2% of a certain piece of platinum and iridium in Sevres is heavier than an atom of carbon-12. One can get rid of all of these by choosing the right units (e.g. Planck units), but one can't get rid of the fine-structure constant or of the masses of particles expressed in Planck masses -- these are fundamental constants which are parameters of the Universe. --Army1987 09:00, 13 August 2006 (UTC)

Army, the speed of light c is a constant quantity. Einstein made his theory of relativity based on this assumption. If it would be possible to change c by simply choosing different units, his theory would collapse. You are mixing up the numerical value n and the quantity Q.

Q = n * U

c = 300'000 * km/s

c = 300'000'000 * m/s

The numerical value n changed, the unit changed, c is constant. Do you really think changing the speed of light is as simple as choosing another unit? All you change is the numerical factor, which is very trivial since it is only an artefact of the unit. The product of the numerical factor and the unit is what matters, and that is constant for dimensionless quantities as well as for quantities with dimensions. --Kehrli 09:33, 11 September 2006 (UTC)

This is because you are used to consider time and space as different entities, and need a conversion factor between units of time and units of space. People considering work and heat as different entities need a 'constant' called 'mechanical equivalent of heat' or something like that, equal to 4186.8 J/kcal. Yes, you can change the number and the unit with their product staying constant, e.g 778.17 ft lbf/BTU. But once you realize that work and heat are the same quantity (namely, energy), you can use the same unit for both work and heat, and you no longer need any conversion factor. Likewise, if you measure space and time with the same units, you don't need any factor of conversion such as 'speed of light'.

For example, imagine we didn't define the unit force as simplily the force which would give an unit acceleration to an unit mass. In Newton's second law we'd see a 'constant' such as 23.8 pond seconds per pound knot. --Army1987 12:32, 11 September 2006 (UTC)

I completely agree with what you say, but what is the point? Even if you get rid of units that does not make constant quantities depending on units. If you know it uses 1 cal to heat 1 cm^2 of water for one K, you can get rid of cal and switch to J, but it will still need the same amount of energy to do the process. The (constant) amount of energy needed does not depend on the units you use. And: I cannot change the length of the Eiffel tower by merely using different units. This is very trivial. And when I decide to measure the Eiffel tower with a time quantity it still does not change its height. (The only reason why the height of the Eiffel tower is not a fundamental constant is that the aliens on planet Zog do not know the Eiffel tower or have their own version which most probably does not have the same height. It is not because "height" it is a dimensioned quantity.) --Kehrli 18:25, 11 September 2006 (UTC)

They have defined the metre to be the space travelled by light in 1/299792458 s. If they had defined it to be 1/299792459 s, the light would travel at 299792459 m/s, the Eiffel tower (and anything else in the universe) would be longer by about 3 part per billion. You could not change the value of the fine-structure constant by changing units, instead.

The kilogram is defined as the mass of a piece of metal in Sévres. If I somehow managed to steal that artifact, use half of it to make a checkers piece set, and put the other half back where it was, my mass would immediately change from 86 kg to 172 kg. Newton's constant would change from 6.67×10⁻¹¹ N m²/kg² to 3.34×10⁻¹¹ N m²/kg², Planck's constant would change from 6.626×10⁻³⁴ J s to 3.313×10⁻³⁴ J s, and the elementary charge (given the way the ampere is defined) would change from 1.602×10⁻¹⁹ C to 1.133×10⁻¹⁹ C. But the fine-structure constant would stay 1/137.036, the mass ratios between elementary particles would stay the same, and any experiment would have the same outcome as before, except that any quantity involving mass (or electric charge, given the way ampere is defined) would change its numerical value.

no reading of any present instrument would change if you were to somehow fudge the International Prototype Kilogram. but when the various national prototypes get recalibrated, there would be a big problem (and if this radical discrepency between the Paris prototype and the national prototypes were simply accepted and the national prototypes changed to match it and, given enough time, weighing instruments including bathroom scales were recalibrated or redesigned to the new prototypes, then, if you bought a new scale, your new scale would say your weight is 172 kg.

In conclusion, the only meaningful answer to the question "what if light travelled at 50 mph?" is "I would be 13,9 micrometres tall, Earth would be 476 millimetres in radius, but we would notice nothing strange". --Army1987 20:18, 11 September 2006 (UTC)

i dunno if you got your calculation correct, Army. 13.9e-6 m × (299792458/(50*0.44704)) is 186 meters. i don't think you're that tall. nonetheless, you would still measure your height to be the same length as you did before because your meter stick also shrinks by the same about (from the POV of some "god-like" observer who is somehow not affected by the hypothesized reduction of c from 299792458 m/s to 22.352 m/s or 50 mph). r b-j 04:17, 12 September 2006 (UTC)

i reverted Kehrli's content edits (only discovered them yesterday) but i thought the new subsection headers he/she put in were a good idea (except it's called the "Anthropic principle" not "Anthroposiphic" which is not a word but is very close to Anthroposophic in spelling, which is completely non sequitur to the subject here). r b-j 04:10, 1 September 2006 (UTC)

Rbj, please revert your changes (not my spelling errors, of course). In my opinion they are wrong. Please read the IUPAC green book to get a better idea about quantities. Thanks. --Kehrli 09:33, 11 September 2006 (UTC)

Kerhli, you got conceptual issues to straighten out before making these substantive changes. take this up with the experts (like sci.physics.research). also i suggest that you submit your content editing a bit more to the folks at Wikipedia:WikiProject_Physics or write and publish your own book. besides not entirely knowing or understanding the facts, i am a little concerned for your fact-checking effort as reflected by the use of "Anthroposiphic" which is not really a mispelling of "Anthropic" but more like a misspelling of something completely non sequitur. Kehrli, edits like yours are one reason Wikipedia is getting such a bad rap. the real experts come here and look at an article and blanch. r b-j 04:17, 12 September 2006 (UTC)

What is wrong, exactly? They state that the numerical value of dimensionful constant depends on the choice of units. This is true. The numerical value of c is 299792458 in SI and 29979245800 in cgs. The numerical value of k_C is 1 in esu and 8,987,551,787.3681764 in SI. Army1987 20:30, 11 September 2006 (UTC)

So you agree with "the value of a physical constant does not depend on the unit"? --Kehrli 08:42, 12 September 2006 (UTC)

one last remark. there is a semantic issue about the use of the word "fundamental" to differentiate between physical constants that have dimension and those which do not (which are more fundamental in defining the nature of the universe). but sites like NIST as well as other places that list dimensionful physical constants call them "fundamental". but this is semantic. physicists everywhere (except for Kerhli) recognize that it's only the dimensionless physical constants that are parameters of meaning that define the nature of the universe. dimensionful physical constants are not on that list. and there's a reason for it. anyway, if this topic changes to that of renaming Fundamental physical constants to Dimensionless physical constants, that is a different issue and is only semantic. r b-j 04:28, 12 September 2006 (UTC)

is α an artifact too ?

Some people seem to think that α is a more fundamental constant than, let's say, c. The reason being that α has always the same numerical value independent on the units used. Is this really true? α is defined as:

$\alpha ={\frac {e^{2}}{\hbar c\ 4\pi \epsilon _{0}}}={\frac {1}{137.03599911(46)}}$

I agree that if you use a "reasonable" system of units, the units of α cancel and the numerical factor is always the same. However, if you use a "unreasonable" system of units where you use, for example, SI units for the quantities in the denominator and atomic units of charge for the nominator, the units do no longer cancel and the numerical factor changes too. Not that I want to promote the use of such "unreasonable" systems of units. My point is just that the "lack of units" of α is also somewhat arbitrary and can be removed by choosing an "inconvenient" system of units. Or, in other words, dimensionless is not quite equivalent to unitless. --Kehrli 09:53, 11 September 2006 (UTC)

the above has little meaning without a clearer definition of a "reasonable" system of units and "unreasonable" system of units. i have no idea what is meant by the difference. r b-j 05:30, 12 September 2006 (UTC)

with a "unreasonable" system of units I mean a system where different units are used for quantities that may have the same dimension. See the example of Army who understood what I meant: you can use cal for thermodynamic energies and J for mechanical energies, as it was common to do for a long time. Now we use J for both and thereby get a "reasonable system". --Kehrli 08:36, 12 September 2006 (UTC)

No. You mean 2.843×10⁻³⁵ au²/C²? That's still the same real number, since the quantity au²/C² is a pure number and equals 2.367×10^-38. Multiplied by 2.843×10⁻³⁵ you get 0.0073, i.e. 1/137. --Army1987 12:54, 11 September 2006 (UTC)

yes, exactly:

2.843×10⁻³⁵ au²/C². and

1/137

are the same constant quantity exatly as

300'000 km/s and

300'000'000 m/s

are the same. For α it is exactly the same story as for c. You can express the speed of light c in different units but you can always transform back to SI system and you will always get the 300'000 km/s. The only difference is that km/s is not a pure number but 10^-3 m/s. The numerical value n is not constant, it is the product of the numerical value and the unit which is constant. Therefore there is no big difference between dimensionless units and units with dimensions. --Kehrli 17:04, 11 September 2006 (UTC)

Kerhli, this quote of yours immediately above is the smoking gun. i think it is pretty definitive of your misconception of the subject. just as there is a big conceptual difference between dimensionless quantities and dimensionful quantities (which you don't appear to understand), the same is true of dimensionful units and dimensionless units (that latter is about units applied to dimensionless quantities, osensibly to make the measurement more anthropocentric). degrees of angle is a unit on a dimensionless quantity. measuring angles in radians is both dimensionless and unitless. r b-j 05:30, 12 September 2006 (UTC)

Rbj, I know that there is a difference between dimensonfull and dimensionless quantities. All I am saying is that the difference is not large enough to justify calling all dimensionfull quantites "not funtamental". That's all. And NIST seems to agree with me since they list all those quantities like c, G ... as fundamental quantities. The notion that only dimensionless quantities are fundamental is only backed by a non-reviewed web articel of Baez. Therefore I think it is POV. --Kehrli 08:58, 12 September 2006 (UTC)

Yeah, formula would get much simpler, if besides c and $\hbar$ we also set α and 2π to 1. Setting -1 to 1 would in addition eliminate all those pesky sign errors. --Pjacobi 08:40, 12 September 2006 (UTC)

Important friendly notice

I feel obligated to stop by and inform those involved in this discussion about the history of this discussion. I hope no one (especially Kehrli) feels that I am trying to discredit or bias anyone against Kehrli. There is currently an arbitation case to be found at Wikipedia:Requests_for_arbitration/Kehrli that is relevant to this discussion. There are also volumes of similar discussions to this one at Talk:Mass-to-charge_ratio regarding the officially dimensionless measurement m/z. This area is not my area and I do not have a lot to contibute here but I would suggest that anyone involved in this discussion inform themselves before engaging too deeply in it. My advice is to look up whatever the dispute is about in a modern college level textbook and be done with it. If the vast majority of scientists in the field are somehow mistaken let the mistake be corrected in the scientific literature before it is corrected here. Engage in discussions about truth at your own risk. Just a friendly note. --Nick Y. 20:58, 11 September 2006 (UTC)

i didn't want to jump into either the MS thing or the arbitration thing, but i may have to now, at least the latter. these kind-of non-experts correction of the well established state of accepted science (or history or whatever subject) is what gives Wikipedia a bad rep. r b-j 04:32, 12 September 2006 (UTC)

Rjb, did you ever consider that you could be the one that is too self-assured? Did you ever consider that you could be wrong? Did you ever consider that you could be the kind of persons that harms the quality of Wikipedia? Please calm down and get engaged in a real discussion. --Kehrli 09:14, 12 September 2006 (UTC)

Let's come to the point

There has been a lot of distractive discussion going on. Many things have been stated by Army that I perfectly agree with, but which are not to the point. What is the point? Here it is:

The values of dimensionful constants do depend on the choice of units. (from Army)

I think this sencence is wrong. It is only the numerical value n that depends on the units, but this is very trivial since Q = n*U. Can we agree on the following sentence:

The value of a dimensionful physical quantity (and hence also a constant physical quantiy) does not depend on the units used.

Army, what do you think? --Kehrli 09:11, 12 September 2006 (UTC)