Here is something that I thought was interesting. For an electromagnetic
field, the energy density is equal to the sum of the electric and
magnetic field energy densities, given by:
U = 1/[2*(permittivity of free space)*E^2] +
1/[2*(permeability of free space)*B^2]
Which can be simplified to,
U = {sqrt[(permittivity of free space)/(permeability of free
space)]}*{E*B}
Where U - is the total energy density
E - is the electric field
B - is the magnetic field
But, this equation has an interesting part to it, namely the,
sqrt[(permittivity of free space)/(permeability of free space)]
If you take the inverse of this so that you end up with,
sqrt[(permeability of free space)/(permittivity of free space)]
This will give you an exact value of (376.7303 ohms). What "ohms",
that's right the units are equivalent to electrical resistance, plus, it
is a constant.
This value is equal to the resistivity of a material capable of
completely absorbing all electromagnetic signals striking it.
I'm not sure if there is a direct relationship between this value and
virtual photons/particles of the vacuum, but I do find it quite
interesting.
Terry