Seth Lloyd has an interesting paper, "A Potentially Realizable Quantum Computer", available at ftp.santafe.edu (I don't know the exact path). It is based on a cellular automata material that receives pulsed/phased array strobing light. It uses reversible logic so it dissipates little energy. As I understand the proposal assumes future materials and manufacturing abilities, although Lloyd says that quantum dots may be the right direction. As gtoal mentions, the P vs. NP question is speculative. My intuition is that the many worlds hypothesis will not be a holy grail of computation (because similar theories about faster than light communcation ended up not being useable due to very low level conservation rules). Then again, we may be surprised. Paul E. Baclace peb@netcom.com