John M wrote:
Jesse and George: the cobbler apprentice speaketh: you, mathematically high-minded savants look for a primitive realization of 'negative mass' etc, while you find it natural to use negative numbers. If I was 185lb last week and now 180 lb, then I have 5 lb in negative. Of course I cannot physically identify the 'missing mass', but mathematically it exists and I can calculate with it, speak about it, think about it: it 'exists'.
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. Likewise, in general relativity only negative mass/energy would be able to hold open a wormhole, there'd be no way to arrange positive mass/energy to do that.