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San José State University
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applet-magic.com Thayer Watkins Silicon Valley & Tornado Alley U.S.A. |
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| The Coupling Constants of Force Fields |
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The formulas for the forces due to various field involve constants whose magnitudes depend upon the system of dimensions being used. Because of this these constants, such as Planck's Constant h, cannot be fundamental. A fundamental constant must be dimensionless.
One of the most famous dimensionless constants is the fine structure constant. This is the ratio of the constant in
the formula for electrostatic force to hc where h is Planck's constant divided by 2π and
c is the speed of light in a vacuum.
Coulomb's Law of Electrostatics is that the force between two charges q1 and q2 separated by a distance r is given by
where (1/(4πε0)) is a constant equal to 9×109 kg*m3/s2. The quantity ε0 is known as the permittivity of free space.
The charge of any body is essentially equal to the net number of elementary charges it contains times the value of the elementary charge; qi=qeni. Thus the force formula could be represented as
Thus the force constant in units of kg*m3/s2 is
(1/(4πε))qe²=(8.98755×109)(1.60218x10-19)²
= 2.30709×10-28 kg*m3/s2.
The ratio of this constant to hc=3.1616×10-26 kg*m3/s2
is 7.297213×10-3 or approximately 1/137.04
The electrostatic case suggests that the structure constant for the general case would be kμ²/ (hc)
where k is the force constant and μ is the unit of charge. But the more general force formula would be
where f(z) is a function of the dimensionless ratio r/r0 and r0 is a length parameter for the force. The generic charges q and Q are multiples n and N of the unit of charge μ so the force formula is more properly
Now it can be said that the proper formula for the structure constant for a force is kμ²/ (hc).
Newton's Law of Gravitation is that the force between masses m1 and m2 separated by a distance r is given by
where G is a constant equal to 6.67259×10-11 m3/kg.
The mass of any body is essentially equal to the number of nucleons it contains times the mass of a nucleon; mi=mnni. Thus the force formula could be represented as
Thus the force constant in units of kg*m3/s2 is Gmn² = (6.67259×10-11)(1.6749×10-27)2 =1.871855×10-64 kg*m3/s2.
The ratio of this constant to the product of h-bar and the speed of light
in a vacuum,
hc=3.1616×10-26 kg*m3/s2,
is 3.76915×10-39. This is 5.166×10-37 times the structure constant
for the electrostatic force.
The force between two nucleons may be given by the formula
The justification for this formula is that the nuclear force is carried by particles subject to decay; i.e., the π mesons. The population of remaining particles is a negative exponential function of the time since emission which translates into a negative exponential function of distance. These remaining particles are spread over an area of 4πr². The intensity is thus proportional to e−λr/r². For more on this model see Nuclear Force.
A value of r0 may be found such that 1/r0 is equal to λ.
An estimate of H based upon the separation distance of the nucleons in a deuteron
being 3.2 fermi is 3.392372×10-26
kg*m3/s2. This makes H equal to 1.073105hc=(1/0.931875)hc;
i.e., the coupling constant for the nuclear force is 1.073105≅1.
This is 147.08 times the value for the electrostatic force.
This is a name given the phenomenon that Enrico Fermi proposed in 1933 for explaining the energy distribution of electrons ejected in the beta decay of nuclei. There is no proposed force formula for the weak nuclear force. The only way for estimating the coupling constant for the weak force is the suggestion that the lifetime of particles is inversely proportional to ths square of the coupling constant of the force associated with the nuclear decay.
Let αW and αS denote the coupling constants of the nuclear weak and and strong forces, respectively.
The ratio of the lifetimes of particles due to the weak force to those due to the so-called nuclear strong force is 9×10−14. This means that
Since αS≅1 this means
If the fine structure constant for the electrostatic force is denoted as α then the coupling constant for gravitation is 5.166×10-37α, that of the nuclear strong force is 147.08α and that of the weak force is 4.11×10-5α.
Planck's constant is a dimensioned quantity and so its magnitude can literally be any positive value. Nothing of physical significance can depend upon its magnitude. It is proportional to the fine structure constant α and the constant of proportionality depends upon the dimensions used.
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