On 1/11/2019 6:01 AM, John Clark wrote:
On Thu, Jan 10, 2019 at 8:18 PM Brent Meeker <meeke...@verizon.net
<mailto:meeke...@verizon.net>> wrote:
/> The fine structure constant is e^2/hbar*c. Those three values
are measured independent of any Feynman diagrams/
Absolutely correct. So if you use Feynman diagrams to predict what
some physical system is going to do, such as a physical system of 2
electrons being hit by a photon of light with a wavelength small
enough to contain enough energy to prevent the electrons repulsion,
then you'd better get a number very close to the Fine Structure
Constant. If you don't then Feynman Diagrams aren't any good.
They didn't use 12,672 Feynman Diagramsbecause they wanted to know
what the Fine Structure Constantwas, they already knew what that
number was to many decimal places from exparament, they used 12,672
Feynman Diagramsbecause they wanted to see if Feynman Diagrams worked.
And it turned out they worked spectacularly well in that situation,
and that gives scientists great confidence they can use Feynman
Diagrams in other situations to calculate what other physical systems
will do that involve the Electromagnetic Force.
There's always an interplay between theory and experiment. It's
completely analogous to Maxwell's discovery that light is EM waves.
There were already experimental values of the permittivity and
permeability of the vacuum and there were values for the speed of
light. Maxwell showed that his theory of EM predicted waves and using
the permittivity and permeability values the speed of the waves matched
that of light. Now the speed of light is a defined constant and so are
the permittivity and permeability of the vacuum. So the connecting of
the three values by a theory allows their values to be defined. In the
case of the anomalous magnetic moment of the electron, hbar and c are
already defined constants. So quantum field theory (for which Feynman
diagrams are just a calculational tool) linked them and e to g.
Brent
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