The National Inst. of Standards and Technology NIST has a(adsbygoogle = window.adsbygoogle || []).push({});

fundamental physical constants website

http://physics.nist.gov/cuu/Constants/

and until sometime this year what they posted were the

1998 CODATA recommended values

(same as those in Physics Today August 2000, or the CRC Handbook of Chemistry and Physics, or a bunch of other places)

CODATA is an international committee whose job is to establish the world's best current values for the constants, and estimate the uncertainties.

Now CODATA has come out with the official 2002 recommended values and the NIST site has changed over. I just noticed this, dont know when it happened.

Planck units are gradually creeping into CODATA

1998 was the first year they had them, and they just listed 3:

planck mass

planck length

planck time

in the 1998 listing the uncertainty given was 7.5E-4 (same for all three)

Now the uncertainty has been reduced to 7.5E-5 (order of magnitude improvement) and a new one has been added: planck temperature.

Here are the 2002 CODATA rec. values (numbers in parenthesis show the std. deviation in last two digits)

planck mass 2.17645(16) E-8 kilogram

planck length 1.61624(12) E-35 meter

planck time 5.39121(40) E-44 second

planck temperature 1.41679(11) E32 Kelvin

A good thing to know in connection with natural units is that the planck mass is 13E18 times the proton mass. Thirteen quintillion.

Frank Wilczek had a series of articles about this number in Physics Today a year or two ago---"Scaling Mount Planck". Its a basic number, basic to how the universe is.

The proton mass is 1/(13E18) natural mass units.

Wilczek was trying to explain how it happens that number is as small as it is.

sorry if this strikes anyone as foolish but these are the units built into nature so I want to know what is an ordinary temperature----like outdoors on today 28 December----in those terms. And what is the average mass of an air molecule in these terms.

Well temperature here is 2E-30

An air molecule has an average of 29 nucleons

each contributing 1/(13E18) of the planck mass,

so an average molecule of air is 29/(13E18) natural mass units.

OK I confess, I'm crazy about planck units. Can PF stand another off-beat enthusiast? Probably wont even notice. So I want to calculate the speed of sound in planck units. That is, as a fraction of the speed of light since the planck speed unit is c.

[tex]\sqrt{\frac{7}{5}*\frac{T}{29/N}}[/tex]

[tex]\sqrt{\frac{7}{5}*\frac{NT}{29}}[/tex]

Plug in 2E-30 for T, the temperature. Boltzmann k = 1, so kT is 2E-30 natural units of energy. Numerator is an energy, denominator is mass, so the fraction is the square of a velocity and sqrt gives speed.

Plug in 13E18 for N, a multipurpose number in natural units contexts.

you should get about a millionth----more exactly 1.1E-6---because that's the speed of sound in air at today's temperature of 2E-30 natural.

the 7/5 is the ratio of specific heats for a biatomic gas---good chance anyone reading this knows that already and is familiar with the formula, though maybe not in a planck units context

Well I checked when the new values for the fundamental constants became available and it turns out it was just this month.

The 2002 CODATA values were issued December 2003 and they incorporate the experimental data available as of 31 December 2002

http://physics.nist.gov/cuu/Constants/bibliography.html

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# New more precise natural units at nist.gov

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