From: helbig@asclothestro.multivax.de   
      
   In article , Steven Carlip   
    writes:   
      
   > According to the equivalence   
   > principle, the trajectory of an object in a gravitational field   
   > is independent of its mass.  In a vacuum, a hammer falls with the   
   > same acceleration as a feather; a negative mass hammer would do   
   > the same.  It's simply not true that a negative mass particle   
   > would be repelled by a black hole, in either general relativity   
   > or Newtonian gravity.   
   >   
   > It *is* true that a particle, of positive or negative mass, would   
   > be repelled by a negative mass black hole.  But that's irrelevant   
   > to Hawking radiation, and it's probably irrelevant to everything,   
   > since there's no reason to believe that negative mass black holes   
   > can exist.   
      
   Two questions:   
      
   First, if negative-mass black holes don't exist, can one by the same   
   argument rule out negative-mass hammers?   
      
   Second, isn't there a contradiction in your second statement?  If it is   
   not true that a negative-mass particle would be repelled by a   
   (positive-mass) black hole, why should a negative-mass black hole repel   
   a positive-mass (or negative-mass) particle?  Aren't the two cases   
   equivalent, due to symmetry?  Imagine if the particle is itself a black   
   hole.  Presumably, the "first" black hole notices only the gravitational   
   field of the particle (second black hole); it can't know that it is also   
   a black hole.   
      
   I'm sure that there is an easy answer; perhaps we are talking past each   
   other.   
      
   [[Mod. note -- The simplest way to think of it is that   
   (a) a positive-mass black hole attracts everything, and   
   (b) a negative-mass black hole (usually called a "white hole")   
       repels everything.   
   As the author notes, the behavior of a binary system consisting   
   of one positive-mass and one negative-mass black/white hole is not   
   immediately obvious.   
      
   But as Steven Carlip notes, there's no reason to believe that   
   white holes actually exist in the universe.   
   -- jt]]   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)