3 ms·
Real physicists can correct me, but here's my understanding of it: if only the electromagnetic force is involved, the numbers provided by QED are amazingly accu
by not2b 5y ago
Real physicists can correct me, but here's my understanding of it: if only the electromagnetic force is involved, the numbers provided by QED are amazingly accurate (for example, calculating the magnetic moment of an electron). But when the strong force is involved, as for the radius of the proton, the calculations are much more difficult: you can't calculate what the radius should be.
- davrosthedalek 5y agoThat's correct. It's very hard to calculate the proton radius ab initio, even with LatticeQCD approaches.
- dataflow 5y agoWhat does "very hard" mean here? e.g., the math is advanced? The calculations are onerous? You need too many potentially risky assumptions? etc.
- Koshkin 5y agoGood question. According to Wikipedia, Numerical lattice QCD calculations using Monte Carlo methods can be extremely computationally intensive.
- davrosthedalek 5y agoYeah, for form factors at small Q^2, you need large lattices and the convergence isn't very good --> very computational intensive.
- evanb 5y agoI am a LQCD practitioner. “Very hard” means that even with a nontrivial fraction of all the available leadership-class supercomputing in the world we don’t have enough computer power.
- monocasa 5y agoPart of this is also that a proton isn't a elementary particle. And in fact it's not only the three quarks typically ascribed; that's just only a little over 1% of it's mass. The rest is a maelstrom of virtual particles. Defining the radius anything more than extremely statistically runs up against the uncertainty principle of all these constituent particles.