George Levy wrote:

Jesse wrote

Well, you're free to define "negative mass" however you like, of course--but this is not how physicists would use the term. When you plug negative values of mass or energy into various physics equations it leads to weird consequences that we don't see in everyday life, such as the fact that negative-mass objects would be gravitationally repelled by positive-mass objects, rather than attracted to them.

Jesse you are too quick. If you actually plug the right signs in Newton's equations: F=ma and F=Gmm'/r2 you'll discover that positive mass attracts everything including negative mass, and that negative mass repels everything including negative mass.

You're right, I got it backwards, I was just going from memory there. The negative-mass object will be attracted to the positive-mass one, while the positive-mass object will be repelled by the negative-mass one. So if you have two masses of equal and opposite magnitude, they'll accelerate continuously in the direction of the positive-mass object, with the distance between them never changing (at least according to Newtonian mechanics, it might not work quite the same way in GR).


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