======What Doesn't Exist======
//Dry Molecular Nanotechnology:// Modern 'wet' nanotechnology uses DNA, self-assembling protein molecules, and gengineered viruses. Nanoscale systems are products of top-down assembly using atomic force microscopes. 'Dry' nanorobots working at the molecular level are still confined to the lab.

//Force Fields:// No fields exist that can stop solid objects or directed energy beams.

//FTL, Time Travel, and Gravity Control:// No faster-than-light (FTL) travel or communications system, or time-travel technology, has been developed, nor have any machines been built to neutralize or create gravity. Some researchers hope that the study of primordial black holes may lead to breakthroughs.

//Reactionless Drives:// None have been invented.

//Room-Temperature Superconductors:// These have been achieved (such as metallic hydrogen wires) but are too fragile, costly, or unstable for widespread use. Robust superconductors that require limited cooling do exist.