George Levy wrote:

Negative matter/energy however are different. If negative matter/energy could exist they would give space a negative curvature.

The issue of negative curvature is somewhat separate from negative mass, though--if the density of matter/energy in our universe was below the critical density Omega, the universe would have negative curvature, no need for negative mass (see http://tinyurl.com/9ox67 ). It might be true that adding a certain density of negative mass/energy would have the same effect on spacetime curvature as subtracting the same amount from the density of positive mass/energy though, I'm not sure.

Negative matter/energy may be identical to dark energy.

I think dark energy has negative pressure (tension, basically), but not negative energy--see section 6 of the article at http://tinyurl.com/8kepb , the one titled "Negative Pressure". But the "Casimir effect" that pulls two parallel plates together (see http://tinyurl.com/anoky ) might qualify as negative energy--at least, the energy density between the plates is lower than the energy of the ground state of the quantum vacuum, but whether this would actually have the same effect as "negative energy" in GR is probably something physicists can't be sure of without a theory of quantum gravity.

Here's an article on negative mass/energy, and its relevance to keeping wormholes open in GR:

http://www.physics.hku.hk/~tboyce/sf/topics/wormhole/wormhole.html

Jesse


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