On Fri, Jan 11, 2019 at 12:18 PM Brent Meeker <[email protected]> wrote:
> On 1/10/2019 4:21 PM, John Clark wrote: > > *So even Feynman knew that there was no theoretical value for the FSC, >> alpha.* >> > > No, he knew very well there was a theory that could come up with a value > because his own Feynman Diagrams could do it. But what he didn't know and > what nobody knows is why his theory came up with that particular pure > number when he never specifically stuck that number into the rules on how > the diagrams should operate. > > > The fine structure constant is e^2/hbar*c. Those three values are > measured independent of any Feynman diagrams of quantum field theory. The > calculation using Feynman diagrams is of the anamolous magnetic moment. A > correction to the value of g that depend on relativistic effects (hence the > occurence of c in the denominator). The anamolous magnetic moment can be > measure experimentally and using Feynman's diagrams and the measured values > of e, hbar, and c a value can be calculated that includes the relativistic > effects of quantum field theory. That's why the agreement with measurement > is significant. > Right. The relation between fundamental physical constants, alpha = e^2/hbar*c, is the closest one gets to a "theoretical" value for the FSC. But that defines it in terms of other measured quantities. (Except that these days, c is a defined number, not a measured physical parameter.) The CODATA group use these theoretical relationships between constants, together with the best available measurements, to make simultaneous fits to all the constants and the data.That is where independent, "best values" for these parameters come from. It is using these in the Feynman diagram calculation of corrections to g-2 that gives the remarkable agreement between theory and experiment. The point, though, is that the value of the FSC used in calculating g-2 must be obtained independently of the g-2 measurement or else it is not a test of QED.. Conversely, of course, the g-2 measurement can be use to estimate the FSC independently of other measurements. Bruce > Brent > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
