Re: Are dimensions any use in an MKSA-only context?

robert bristow-johnson wrote:
One problem is that it is hard to measure G, which is used when defining
the other: time, length, mass, charge and temperature. As on (hopefully
reliable)
http://en.wikipedia.org/wiki/Planck_units

the article got crapped up a lot since 2007. ...
...the Planck Unit expressions are still correct, ...

I just looked at the expressions and the measurement accuracy of the constants.

one reason is that i got
banned from Wikipedia for daring to take on the nasty partisans at the
Intelligent Design article.

The Wikipedia is only good for facts that everyone agrees on. Even if facts are clear, if they are difficult to understand, they can get messed up. Some Nobel laureate mentioned he edited something and was curios to see if someone else would take it away - perhaps that is a mind one needs to have to get the prize: charge ahead and don't worry about set-backs, even if they are wrongful.

anyway, about G, you're correct, and the result would be that even
though they define the meter in such a way to fix c, and they *can*
define the kg in such a way to fix hbar, what is left is the
definition of second and G. there is no way that they will redefine
the second from counting a fixed number of cycles of radiation of
Cs-133 to another definition that fixes G, but if they did, that would
be equivalent to defining the meter, kg, and second to be fixed
multiples of their respective Planck units.

One will have to think carefully what happens in a lab when measuring the units from the definitions. The definition of the second is dictated by the fact that there are cesium clocks readily available, and length can be accurately measured using lasers.

now, just as we expect that G is truly constant, but we just don't
know precisely what that constant is (in terms of our meters,
kilograms, and seconds), for the same reason i believe that the meter,
kg, and second (or any unit of length, mass, and time) are fixed
dimensionless multiples of their respective Planck units, but we just
do not know precisely what those multiples are.

If G can be measured down accurately some time in the future, perhaps there is time for a change. But it might be better to use e, and drop G.

Hans

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Relevant Pages

  • Re: Are dimensions any use in an MKSA-only context?
    ... time, length, mass, charge and temperature. ... though they define the meter in such a way to fix c, ... multiples of their respective Planck units. ...
    (sci.physics.research)
  • Re: Are dimensions any use in an MKSA-only context?
    ... Planck Units and Natural Units articles, ... though they define the meter in such a way to fix c, ... units would mess up experimental physicists a lot. ... informing us on updated values for G (as measurements get ...
    (sci.physics.research)