From: intuitionist1@gmail.com   
      
   On Saturday, November 3, 2018 at 8:46:03 PM UTC+3, Tom Roberts wrote:   
   > On 11/2/18 1:24 AM, ben6993@hotmail.com wrote:   
   > > On Thursday, November 1, 2018 at 10:21:57 PM UTC, Tom Roberts wrote:   
   > >> While there is currently no experimental evidence of antimatter's   
   > >> behavior in gravity, the mass of every known antiparticle is   
   > >> unequivocally positive.   
   > >   
   > > I am not clear how it is shown that antimatter unequivocally has   
   > > positive mass?   
   >   
   > We know about antiparticles only from interactions among subatomic   
   > particles at high energies (i.e. energies high enough to produce new   
   > particles, roughly greater than ~ 250 MeV; in some cases enormously   
   > greater). In literally zillions of experiments, the mass of each   
   > anti-particle is measured to be equal to the mass of the corresponding   
   > particle.   
   >   
   > There are many dozens of such particle/antiparticle pairs for which   
   > accurate masses are known. Negative masses are completely excluded; for   
   > e-/e+ and mu-/mu+, negative mass is excluded by more than 10 million   
   > sigma (!).   
      
   It is not negative mass that is excluded. It is negative energy. They   
   are not the same thing and do not necessarily have the same   
   sign. Antimatter can have negative mass but positive energy.   
      
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