From: bill.sloman@ieee.org   
      
   On 14/02/2026 1:31 pm, Thomas 'PointedEars' Lahn wrote:   
   > Bill Sloman wrote:   
   >> On 14/02/2026 3:20 am, Stefan Ram wrote:   
   >>> Bill Sloman  wrote or quoted:   
   >>>>                         Energy has mass   
   >>>   
   >>>     Counterexample: The photon. It has energy, but no mass.   
   >>   
   >> Depending on how you define mass.   
   >   
   > No.   
   >   
   >> Newton had one definition.   
   >>   
   >> Einstein had another.   
   >   
   > No, Einstein's idea of mass is exactly the same as Newton's.   
      
   Really?   
      
   >  Einstein just explains its origin whereas Newton simply postulates it.   
      
   That ignores what was actually going on.   
      
   >> Light pressure does imply that a photon has momentum.   
   >   
   > That does not mean that its mass is non-zero.  As I indicated, its momentum   
   > is given by p⃗ = ℏ k⃗ where ℏ = ℎ/(2π) is the reduced Planck   
   constant, and   
   > k⃗ is the wave vector.   
      
   Depending on how you understand mass - or mass-energy which is now what   
   it thought to be conserved.   
      
   > Photons are *relativistic* *quantum* objects; they are *incompatible* with   
   > Newtonian mechanics.   
      
   Newtonian mechanics is an obsolete point of view. Photons are a useful   
   concept - they don't work unless they have their quantum of mass-energy.   
      
   --   
   Bill Sloman, Sydhney   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)