The energy that is present even in otherwise empty space. This energy has been measured to exist (in the "Casimir Effect"). Whereas matter causes the expansion of the Universe to slow down, vacuum energy actually causes the expansion to speed up.
A particle which cannot be directly detected, but is assumed to exist due to its indirect effects on real particles. Virtual particles can form in pairs from the vacuum of space.
The SXS project is a collaborative research effort involving multiple institutions. Our goal is the simulation of black holes and other extreme spacetimes to gain a better understanding of Relativity, and the physics of exotic objects in the distant cosmos.
The SXS project is supported by Canada Research Chairs, CFI, CIfAR, Compute Canada, Max Planck Society, NASA, NSERC, the NSF, Ontario MEDI, the Sherman Fairchild Foundation, and XSEDE.