On Thursday, November 1, 2018 at 10:21:57 PM UTC, Tom Roberts wrote:   
   > ...   
   > For test particles the GR prediction is unambiguous:   
   > regardless of the test particle's mass (including sign, if any) it   
   > "falls downward" toward a positive mass and "falls upward" away from a   
   > negative mass.   
   >   
   > 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?  As both positive and negative test masses are attracted   
   to the positive mass of the earth, then how can attraction to the earth   
   be used to distinguish between a positive and a negative test mass?   
      
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