George Levy wrote:

Negative matter/energy however are different. If negative matter/energycould 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