Roger Shawyer has developed an engine with no moving parts that he believes can replace rockets and make trains, planes and automobiles obsolete. ... The device that has sparked their interest is an engine that generates thrust purely from electromagnetic radiation — microwaves to be precise — by exploiting the strange properties of relativity. It has no moving parts, and releases no exhaust or noxious emissions. Potentially, it could pack the punch of a rocket in a box the size of a suitcase. It could one day replace the engines on almost any spacecraft. More advanced versions might allow cars to lift from the ground and hover.

The forces inside the latest accelerator cavities are so large that they stretch the chambers like plasticine. To counteract this, engineers use piezoelectric actuators to squeeze the cavities back into shape. "I doubt they've ever thought of turning the force to other uses," he says.