On Thursday, January 10, 2019 at 8:27:20 PM UTC-6, Bruce wrote:
> On Fri, Jan 11, 2019 at 12:18 PM Brent Meeker <meek...@verizon.net 
> <javascript:>> 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

As the Robert Geroch, James Hartle paper points out

*    the issue of whether the existence of an algorithm to implement a 
theory should be adopted*
*    as a criterion for acceptable physical theories.* 

if you want measurable constants to be computable, adopt a theory that does 

- pt

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