Talk:Boltzmann constant/Archive 1

message: I have to say, CYD, I disagree with just about every change you made to my text in your latest edit. Apparently k is now "a fundmental quantity which relates temperature to energy". What were the other quantities you were thinking of? And is k really a quantity? What is it a quantity of? It seems to me that it's a proportionality constant -- you can't produce 3.6k of something, but you can use it to say 1K is equivalent (in some sense) to 1.38×10-23J. 
Why did you change the HTML specification of the value to <math>? The only visible difference is that it's not wikified anymore.
In my section on characteristic energy, I was attempting to hint at nomenclature used in solid state physics. I deliberately left out a specific example of what the characteristic energy is, because it shows up in both statistical mechanics and solid state/quantum. I wanted to give a sense that k is used in almost any field of physics involving temperature (which it is).
What's wrong with meV? 25.9 meV is so much nicer than 0.00259 eV.
Entropy is important, and I appreciate your new section on it. 
"Historically, the units of energy and temperature were defined before it was discovered that they were related." True. "As a result, the Boltzmann constant is expressed using the unit of temperature, and not the other way around." You've lost me. Which other way around? "Conceptually, however, the Boltzmann constant is the more fundamental quantity." Nope, still lost. More than what?
I think I can see what you're trying to get at with those last few paragraphs. My interpretation of the physical situation is that the relationship between energy and temperature is similar to the relationship between distance and time. In both cases, there are two sets of units originally defined in terms of physical quantities (e.g. orange-red radiation and triple points). Theoretically though, it would be much more sensible to define c=1, or c=α (the fine structure constant), in just the same way as it would be more sensible to set k = 1 and use Planck temperature. We can't necessarily argue that physically, k should be 1, but it should definitely be dimensionless.
-- Tim Starling 05:34 May 3, 2003 (UTC)
: I'm not particularly concerned about most of the changes, so I have tweaked them to suit your objections. --CYD
::Thanks. -- Tim
:As for the relationship between energy and temperature, the key idea is this: energy is a microscopic (mechanical) quantity, and temperature is a macroscopic (thermodynamic) one. The main reason Boltzmann's definition of the entropy is so important is that it shows us how this macroscopic property of a system emerges from the microscopic details of its constituents. If you know enough about the mechanical properties of atoms, Boltzmann's equation shows you how to define a quantity, the "temperature", of large assemblies of atoms. In this sense, Boltzmann's constant defines the temperature, and not the other way around. -- CYD
::The distinction between Boltzmann's constant defining temperature and temperature defining Boltzmann's constant seems rather arbitrary to me. Temperature is defined either macroscopically, by the properties of gases, or microscopically, with 1/(dS/dE) and Boltzmann's formalism. But in either case, k is merely a proportionality constant, and tells you about the units used to keep the books, not the physics involved. By itself, it tells you very little about the concept of temperature. It is Boltzmann's formalism (or the properties of gases), not k itself, that defines temperature.
::But I'm getting distracted by a discussion of physics, and forgetting our main goal. Would it be fair to say that if your final paragraph confused me, it's going to confuse the general public? If you can think of a more eloquent way to put your ideas, in such a way that seems intuitive and correct to me, I'll be happy. I know my current final paragraph says something completely different to what you were getting at, but I think some reference to Planck units is warranted. Tarquin tried to include something about them a while back, but I cut it out. -- Tim Starling 00:15 May 5, 2003 (UTC)
I am a physics student at a community college. the fellow who talked about botzmanns constant k, tim. did a very well job explaining the concept of k. thank you.  —Preceding unsigned comment added by 71.103.70.145 (talk) 04:21, 13 February 2008 (UTC)
thread_title:  Edits 

message: Quote:
:With 20:20 hindsight however, it is perhaps a pity that Boltzmann did not choose to introduce a rescaled entropy such that 
::{S^{\,'} = \ln \Omega} \; ; \; \; \; \Delta S^{\,'} = \int \frac{dQ}{kT}
:These are rather more natural forms; and this (dimensionless) rescaled entropy exactly corresponds to Shannon's subsequent information entropy, and could thereby have avoided much unnecessary subsequent confusion between the two.
I know some physics researchers have jumped the gap regarding this, and as a natural consequence, they will express temperature in the same unit as energy. I'll try to find a reference for that.
:What is \Omega and what is Q? The article makes no mention of what these represent. GoldenBoar 00:21, 8 January 2006 (UTC)
replies: text: -- For example, the Planck system, mentioned at the end of the article.  But I think you're right, it's not just in those units that people "drop the k". Jheald 10:25, 5 November 2005 (UTC)

text: -- the great Landau and Lifshitz adopt this convention, using an energy scale for T so k disappears (Statistical Physics, Part 1 (3e, 1980), Oxford: Pergamon Press). Jheald 21:52, 8 November 2005 (UTC)
replies: text:  although that is probably not a good idea to adopt these conventions in an article, with a reference to quote that might be worth mentioning, either in here or in the temperature article. ThorinMuglindir 22:31, 8 November 2005 (UTC)

text: Boltzmann's constant k is the bridge between the macroscopic and microscopic physics. Macroscopically, the amount of matter is measured in joule per kelvin, according to the ideal gas law: volume×pressure/temperature. Microscopically, matter consists of molecules. k tells how many J/K make a molecule. You may say that k is the size of one molecule. The kelvin temperature scale is somewhat arbitrary, being based on the triple point temperature of water, which is not of fundamental physical significance.  Measuring gas in molecules give the temperature unit joule per molecule. k joule per molecule = 1 kelvin. Bo Jacoby 22:24, 29 January 2006 (UTC)
thread_title:  Boltzmann's constant and Entropy 

message: Is there any reason to mention the value of 1/k in K/eV instead of simply listing k in eV/K. I would change it, but I suppose there is a good reason to give the value of 1/k instead of k Glaurung 15:09, 18 January 2006 (UTC)
replies: text: I agree.  I think it should be changed.  It is just as easy to divide by k as it is to multiply by 1/k.  In addition, it is clearly more consitent to use dimensions of energy per absolute temperature regardless of the units of measure (joules/kelvin versus electron-volts/kelvin).  -- Metacomet 00:34, 20 January 2006 (UTC)

text: I went ahead and made the change, along with a few other things.  -- Metacomet 00:49, 20 January 2006 (UTC)
thread_title:  eV/K value 

message: A long section of this article is called 'Physical significance'. However it has always seemed to me that this constant has none - it is simply (like Avogadro's number) a dimensionless conversion factor. The paragraph that starts 'In hindsight however, it is perhaps a pity ...' doesn't really make sense, because there is exactly the same justification for measuring entropy in macroscopic units as there is for measuring temperature in such (i.e. K, rather than J or ev). Should this be rewritten? The way, the truth, and the light 23:14, 1 May 2007 (UTC)
thread_title:  Physical meaning 

message: The article lists boltzman's constant as 1.380 6504(24)×10−23.  That is very precise.  How is it measured?  (Also, what is the source for this that is claiming such accuracy?) RJFJR 15:05, 16 November 2007 (UTC)
thread_title:  Precision 

message: :
Values of k   	Units	Comments
1.380 6504(24)	J/K  	SI units, 2002 CODATA value
8.617 343(15) 	eV/K 	1 electronvolt = 1.602 176 53(14) J
6.336 281(73) 	Ryd/K	1 Rydberg = 13.6 eV
1.3807        	erg/K	
:The digits in parentheses are the standard measurement uncertainty in the last two digits of the measured value. k can also be expressed with the unit mol (such as 1.99 calories/(mole * kelvin)); for historical reasons it is then called the gas constant.
:Since k is a constant of proportionality of temperature and energy, the numerical value of k depends on the choice of units for energy and temperature. The very small numerical value of the Boltzmann constant in SI units reflects how the energy associated with thermal motion of particles at room temperature is exceedingly small compared to the kinetic energy of macroscopic objects, measured in Joule. On the other hand, the Plank units of temperature and energy are defined in such a way that k=1. If we choose to measure temperature in units of energy then of Boltzmann's constant would not be needed at all.
(*Kalinin, M; Kononogov, S, "Boltzmann's Constant, the Energy Meaning of Temperature, and Thermodynamic Irreversibility", Measurement Techniques, pp632-636, vol 48, no 7, July 2005).
--V. (talk) 01:24, 13 May 2008 (UTC)
replies: text: Room temperature has nothing to do with it. SpinningSpark 18:52, 14 May 2008 (UTC)
replies: text:  k is a conversion factor. If we would just pick our units in a sensible way it would not be needed. So why does everybody use it? Why did we pick out unit of temperature to be the Kelvin or the Celsius and our unit of energy to be Joule? It is because those units are natural to use in the environment that we actually experience. As I said before my thermometer reads Celsius. Tomorrows temperature forecast tells me about 25 Celsius, not 4*10^-21 Joules. The kinetic energy of a baseball is about 100 Joules. We picked out units for practical considerations at roughly room temperature. That means k has to be really small. That is why we bother with a conversion factor rather than to report the weather in Joules. But please rephrase if you like.  --V. (talk) 22:47, 14 May 2008 (UTC)

text: Lack of further comment was not a sign of agreement, it was a sign of exhaustion after the debate with Lucretius.  Neither the Joule nor the Kelvin have anything to do with room temperature or the properties of anything at room temperature.  The Kelvin on the other hand has a lot to do with the properties of water, as stated.  k is small because it is small relative to a Kelvin.  It is still small relative to 1 deg K difference at 50oK as much as it is at 300oK. SpinningSpark 19:11, 4 June 2008 (UTC)

text: Sorry for appearing unco-operative.  I had a bad experience earlier in this debate (along with many others I suspect) of suggesting a draft only to have it re-injected with an agenda and then claiming I was in support.  I will work on it tomorrow. SpinningSpark 22:39, 5 June 2008 (UTC)
thread_title:  The numerical value of k