Re: Fields and Forces

[Samuel Held <Held@RHIP.PHYS.UTK.EDU>]

James,
        I had particle theory over a year ago but if I remember
correctly, the coupling constants that are to be compared are unitless.
They are the ones that occur at the vertices of Feynman Diagrams for the
different forces.  I mistakenly wrote G in last time I think.  But an
example of this is for E&M, we do use 1/4 pi epsilon_{o}, but the fine
structure constant, alpha.  There are alphas for the three "strongest"
forces (sorry don't know how else to categorize them), but not for
gravity because there is no quantum scale for it yet.  Anyone know
anybody who knows about this?
        My best guess is that they compare the forces between two
nucleons or something that size and make ratios of all the forces given
those units.  So the original discussion about this failing over cosmic
distance probably has some truth.  Especially for the strong force which
has asymptotic freedom.


Sam Held

-----Original Message-----
From: James McLean [mailto:jmclean@CHEM.UCSD.EDU]
Sent: Saturday, May 22, 1999 7:47 PM
To: PHYS-L@LISTS.NAU.EDU
Subject: Re: Fields and Forces


> In truth, the constants in the equations for gravity and for electrical
> force are of vastly different magnitude.  Many people therefor say
> that the electrical "force" is stronger than the gravity "force", but
> this statement is wrong.

Speak of this...
I've never really understood how the constants are compared, considering
that their units are very different.  How do you convert from Coulombs
to kilograms?  In first year physics (where this topic often comes up),
we tell students that you *can't* make such a conversion.  I would hope
that the students would get very suspicious.

--
--James McLean
jmclean@chem.ucsd.edu
post doc, UC San Diego, Chemistry
moving to SUNY Geneseo Physics this fall