We exploit the combination of a virtual world containing physicallyinteracting 4D objects with a multimodal haptics-driven user-interface model; the goal is to facilitate the development of accurate cognitive models enabling the visualization of 4D space. Our primary test domain supports tactile interaction with physically colliding and deformable curves and surfaces embedded in 4D, an importan...

In gravitational theories with extra dimensions, it is argued that the existence of a positive vacuum energy generically implies catastrophic instability of our four-dimensional world. The most generic instability is a decompactification transition to growth of the extra dimensions, although other equally bad transitions may take place. This follows from simple considerations based on the form ...