On Saturday, January 12, 2019 at 7:09:29 PM UTC-6, Lawrence Crowell wrote: > > On Saturday, January 12, 2019 at 4:17:56 PM UTC-6, Brent wrote: >> >> >> >> On 1/12/2019 2:51 AM, Philip Thrift wrote: >> >> >> >> On Friday, January 11, 2019 at 7:19:06 PM UTC-6, Brent wrote: >>> >>> >>> >>> On 1/11/2019 1:57 PM, Philip Thrift wrote: >>> >>> >>> >>> On Friday, January 11, 2019 at 2:46:35 PM UTC-6, Brent wrote: >>>> >>>> >>>> >>>> On 1/11/2019 6:01 AM, John Clark wrote: >>>> >>>> On Thu, Jan 10, 2019 at 8:18 PM Brent Meeker <[email protected]> >>>> 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 Diagrams because they wanted to know >>>> what the Fine Structure Constant was, they already knew what that >>>> number was to many decimal places from exparament, they used 12,672 >>>> Feynman Diagrams because 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 >>>> >>>> >>> >>> >>> If Feynman Diagrams (tools) are sufficient (to match experimental data) >>> then Quantum Field Theory can be thrown in the wastebasket. >>> >>> >>> ?? Feynman Diagrams are just a mathematical trick for summing up terms >>> to approximate the propagator of QFT. >>> >>> Brent >>> >> >> >> You just make Feynman Diagrams the fundamental elements of the theory, >> and propagators derived from them. >> >> >> 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. >> >> >> Just like histories are made fundamental, and Hilbert Spaces are derived >> from them. >> >> >> Hilbert spaces are infinite dimensional vector spaces. So you have the >> same problem: How many histories? >> >> Brent >> > > The number of diagrams grows exponentially. As I recall the QED industry > is up to 12 orders of radiative corrections and renormalization orders. The > number of diagrams to evaluate and sum is in the millions if not billions. > This stuff is done on supercomputers these days. People do not really > evaluate Feynman diagrams, they write computer programs. > > LC >
Supercomputers are the future of theoretical physics it seems, like the one at LSU, SuperMike-II. http://www.hpc.lsu.edu/docs/guides.php?system=SuperMike2 *SuperMike-II is a 146 TFlops Peak Performance 440 compute node cluster running the Red Hat Enterprise Linux 6 operating system. Each node contains two 8-Core Sandy Bridge Xeon 64-bit processors operating at a core frequency of 2.6 GHz. Fifty of the compute nodes also have two NVIDIA M2090 GPUs that provide an additional 66 Tflops total Peak performance.* use in LQG: https://www.lsu.edu/mediacenter/news/2018/12/20physastro_singh_prl.php - pt -- 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.
