From: intuitionist1@gmail.com   
      
   On Thursday, November 1, 2018 at 11:30:04 AM UTC+3, Jos Bergervoet wrote:   
   > On 10/31/2018 7:05 AM, Sabbir Rahman wrote:   
   > > On Friday, August 17, 2018 at 10:07:39 AM UTC+3, Phillip Helbig (undress   
   to reply) wrote:   
   > >> In article <2c0366cf-d2b2-4d5e-ad1b-47cd027030e5@googlegroups.com>,   
   > >>  writes:   
   > >>   
   > >>>> If you had two negative masses they would attract. Because with the   
   > >>>> negative mass acceleration is towards a positive mass this experiment   
   > >>>> may not be able to determine if antimatter is really negative mass.   
   > >>   
   > >> If I recall correctly, not long ago Steve Carlip pointed out here that   
   > >> positive mass attracts everything, including negative mass, and negative   
   > >> mass repels everything.   
   > >   
   > > I am a little bit late to join this thread (sorry), but I wanted to make a   
   > > few important points.   
   > >   
   > > In general people have to be more specific when they refer to "negative   
   > > mass". There are three mass types that enter into Newton's law of   
   > > gravitation for example - inertial, active and passive mass. If the signs   
   of   
   > > these three masses are I, A and P respectively, then the particle type can   
   > > be specified by (I,A,P) - so there are 8 types, (+++), (++-), (+-+), (+--),   
   > > (-++), (-+-), (--+) and (---). Obviously (+++) corresponds to ordinary   
   > > matter and the remaining 7 have at least one kind of negative mass, so you   
   > > need to be specific which type you mean. If you mean by negative mass type   
   > > (---), which is the one allowed by the WEP, then this will indeed fall   
   > > `downwards'. This type is also repels itself.   
   > >   
   > > Newton's law depends only on the product IP, so there are actually only 4   
   > > types of particle in terms of mutual interactions.   
   >   
   > Why is that? In Newtons laws there is the force depending on:   
   > 1 Mass creating the gravitational field (your active mass, presumably).   
   > 2 The mass acting as test particle feeling the force (passive mass).   
   > 3 Inertial mass determining which acceleration results from the force.   
   >   
   > So the acceleration that occurs depends on three kinds of mass. Or do   
   > you work with other subdivisions?   
   >   
   > --   
   > Jos   
      
   Well, if you consider two particles with signs of masses given by (I1,A1,P1)   
   and (I2,A2,P2) respectively, then according to Newton's law of gravitation,   
   the force on particle 1 due to particle 2 satisfies,   
      
   	F12 = I1 m1 a12 = G P1 m1 A2 m2 / r12^2   
      
   So the direction of the acceleration depends upon the product I1.P1.A2. This   
   means that if we change the sign of both I1 and P1 for particle 1, then the   
   direction of the acceleration on it will not change. This is why, for   
   example, a particle of type (-+-) interacts gravitationally just like   
   ordinary matter, even though it has negative inertial and passive mass.   
      
   Because of this invariance with respect to I and P both changing signs   
   simultaneously, if we are concerned only about the nature of the   
   gravitational interactions, we only need to consider 4 classes of particle   
   instead of the original 8. I hope that this is clear now.   
      
   By the way, I noticed a typo in my class definitions:-  Class C particles   
   are those of type (++-) and (-++), while Class D particles are those of   
   type (+--) and (--+). Apologies for any confusion caused.   
      
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