From: relativity@paulba.no   
      
   Den 06.01.2026 23:27, skrev Thomas 'PointedEars' Lahn:   
   > Paul.B.Andersen wrote:   
   >   
   >> The mass of an objects is invariant,   
   >   
   > It is _Lorentz_-invariant, NOT invariant /per se/.   
   >   
   >> and so is the energy content of the object.   
   >   
   > No.   
   >   
   >> The E in the equation E = mc² is invariant,   
   >   
   > This pop-cultural equation is *wrong*, as I have pointed out /ad nauseam/.>   
   >> which means that it is independent of the speed of the object.   
   >   
   > /Ex falso quodlibet./   
   >   
   >> It makes no sense to call E = mc² "the *rest* energy of   
   >> _an object_ whose mass is m."   
   >   
   > It *does*.  That is what it *is*.  "Rest energy" is the agreed   
   > physical/scientific term for that form of energy.   
      
   You are right, E₀ = mc² is called the "Rest energy" of   
   a body with mass m.   
   It is also called "the invariant energy" of a body with mass m.   
      
   Because the energy E₀ = mc² is invariant, the same in all   
   frames of reference, independent of the speed of the object.   
      
   That's why find the name "rest energy" rather misleading.   
      
      
   Above I was quoted to have said:   
   "The E in the equation E = mc² is invariant, which means   
     that it is independent of the speed of the object."   
      
   Your response was:   
   "This pop-cultural equation is *wrong*, as I have pointed out   
     /ad nauseam/.   
      
   Can you explain your response?   
      
   -----------------------------------   
   To give the context of discussion below:   
      
   One possible fission process is:   
      
   1n + U-235 → Ba-141 + Kr-92 + 3n   
      
   The atomic weight of these are:   
      
   Left side:   
   1n      1.008664  u   
   U-235 235.0439299 u   
   -------------------   
          236.0525939 u  = 3.919748214E-25 kg   
      
   Right side:   
   Ba-141   140.914412 u   
   Kr-92     91.926156 u   
   3n         3.025992 u   
   ---------------------   
             235.866560 u = 3.916659047E-25 kg   
      
   Lost mass: m = 0.1860339 u = 3.089167695E-28 kg   
      
   E = mc² ≈ 2.776404839E-11 J ≈ 174 MeV   
      
      
   >> Energy before fission:   
   >> Energy content of mass m₁: E = m₁c² = 3.522894007E-8 J   
   >>   
   >> Energy after fission:   
   >> Energy content of mass m₂: E  = m₁c²= 3.520117602E-8 J   
   >>   
   >> The difference is ΔE = m₁c² - m₁c² = Δm⋅c² = 2.776404839E-11 J   
   >>   
   >> The binding energy holding the nucleons together is   
   >> part of the energy content of the mass of the U-235 nucleus.   
   >> When the nucleus is split, the binding energy in the Ba-141   
   >> and Kr-92 nuclei will be ΔE less. The sum of the kinetic energy   
   >> of the two nuclei and 3 neutrons will be ΔE = 2.776404839E-11 J   
   >   
   > You keep missing the point.   
      
   Which point am I missing?   
      
   >> I say that the mass Δm lost from the U-235 nucleus is converted   
   >> to kinetic energy  of the two nuclei and 3 neutrons.   
   >   
   > Which is simply the wrong idea.   
   >   
   > What actually happens here is that rest energy is (partially) converted to   
   > other forms of energy.  This is equivalent to a reduction in mass;   
      
   How is this different from what I said?   
      
   The "rest energy" of the U-238 nucleus is   
   E = m₁c² = 3.522894007E-8 J   
      
   The part of this energy ΔE = 3.089167695E-28 J   
   is converted to kinetic energy.   
      
   This is equivalent to a reduction in mass Δm = 3.089167695E-28 kg   
      
   The energy equivalent of the reduction of the mass   
   is Δm⋅c² = 2.776404839E-11 J   
   This energy is converted to kinetic energy.   
      
      
   --   
   Paul   
      
   https://paulba.no/   
      
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