From: richalivingston@gmail.com   
      
   On Saturday, September 23, 2023 at 4:08:40=E2=80=AFPM UTC-5, Stefan Ram wrote:   
   > I prefer to learn from books. But videos have two advantages: One   
   > can watch/listen to them while doing household chores, and one also   
   > learns the correct English pronunciation of the technical terms.   
   > So I listened to some videos of QFT lectures by Prof. Susskind.   
   >   
   > However, after about three videos so far, I am rather disappointed.   
   > I have the impression that Susskind deliberately wants to   
   > counteract all too flowery gobbledygook with a "don't talk, but   
   > calculate" approach. I have always found such an approach absurd   
   > in physics, but especially devastating in teaching. ...   
      
   Stefan,   
      
   I share your frustration and opinions.  I've been trying to "understand"   
   QFT for almost 50 years now and still have some issues.  Almost   
   everyone treats it as a math problem and it gets very abstract.  After   
   transforming to momentum space and doing a Wick rotation I'm not   
   sure what we are  calculating anymore.  I have some more fundamental   
   questions that may or may not be valid (I'm undecided on these):   
      
   -Transforming the path integrals to momentum space fundamentally   
   changes the integration.  I'd have no issue with this in Newtonian   
   space-time, but the Fourier transform in Minkowski space-time does   
   not cover the same space-time volume as the spatial integration.  My   
   real concern here is that the high momentum parts of the integration   
   is covering the same physical paths over and over again, and I   
   wonder if weighting the momentum integration proportionalto the   
   volume of space it represents might reduce the infinities calculated   
   and give a more reasonable result?   
      
   -I'm not sure how much this would affect the calculation of   
   macroscopic problems, as the wave function outside the light cone   
   is clearly attenuated, but for very small distances and very high   
   energies there is a bit of "fuzzyness" to the light cone, and I wonder   
   if that is part of the source of the infinities calculated particularly at   
   higher energies and short distances.   
      
   -The Lagrangian used universally has F_{\mu\nu}F^{\mu\nu}, which   
   includes an electromagnetic field energy, which integrated over all   
   space gives an infinite result.  This has been an embarrassment for   
   over 100 years now.  I wonder (and this is by far an unconventional   
   opinion) if the concept of EM field energy is a mistake.  It has been   
   known since at least the 1920's that if you do EM via potentials that   
   the energy of interaction  has to be on the charges, not in the fields.   
   Wheeler and Feynman advocated for this briefly in the 1940's but   
   gave it up in light of the Lamb shift results.  I wonder if maybe they   
   were too quick to give up on it?   
      
   Part of the problem is that QFT is necessarily a very advanced mathematical   
   theory, and the people who can do the math easily are mathematicians.   
   But I'm a Physicist and I want to understand what the math is modeling,   
   and I'm often suspicious that mathematical transformations are  changing   
   what is being modeled.   
      
   If you are inclined, I'd be interested in discussing issues and ideas, and   
   I'll try not to bother you too much with my heretical thoughts.  We might   
   be able to help each other.   
      
   Rich L.   
      
   --- SoupGate-Win32 v1.05   
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