Engineer has developed an emdrive

The thruster works by exploiting the properties of relativity and the ability of electromagnetic radiation to exert force on surfaces.

For years [Shawyer] has explored ways to confine microwaves inside waveguides, hollow tubes that trap radiation and direct it along their length. Take a standard copper waveguide and close off both ends. Now create microwaves using a magnetron, a device found in every microwave oven. If you inject these microwaves into the cavity, the microwaves will bounce from one end of the cavity to the other. According to the principles outlined by [physicist James Clerk Maxwell], this will produce a tiny force on the end walls. Now carefully match the size of the cavity to the wavelength of the microwaves and you create a chamber in which the microwaves resonate, allowing it to store large amounts of energy.