# Re: What is comparable and incomparable between casually disconnected universes?

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On 1/12/2019 2:51 AM, Philip Thrift wrote:
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On Friday, January 11, 2019 at 7:19:06 PM UTC-6, Brent wrote:

On 1/11/2019 1:57 PM, Philip Thrift wrote:
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On Friday, January 11, 2019 at 2:46:35 PM UTC-6, Brent wrote:

On 1/11/2019 6:01 AM, John Clark wrote:
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```        On Thu, Jan 10, 2019 at 8:18 PM Brent Meeker
<meek...@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.
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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

If Feynman Diagrams (tools) are sufficient (to match experimental
data) then Quantum Field Theory can be thrown in the wastebasket.
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?? Feynman Diagrams are just a mathematical trick for summing up
terms to approximate the propagator of QFT.

Brent

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You just make Feynman Diagrams the fundamental elements of the theory, and propagators derived from them.
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How many diagrams?  The propagator has a clear interpretation as connecting the field at x with the field at y.  Feynman showed that his diagrams provided a good mnemonic for the infinite number of terms that would sum to the propagator.  If you take the diagrams as fundamental you then need to specify how many.
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Just like histories are made fundamental, and Hilbert Spaces are derived from them.
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Hilbert spaces are infinite dimensional vector spaces.  So you have the same problem: How many histories?
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Brent

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https://arxiv.org/abs/1002.0589

Theories do not come from Mount Olympus.

- pt
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