Imagine a thrust engine which requires no propellant and seemingly violates the conservation of momentum law. Wired.co.uk reports research groups in three different countries, including a group associated with NASA, have apparently demonstrated that microwaves can be used to create thrust without the use of reaction mass or propellant.
No one is exactly sure how a microwave drive could possibly work, but they find it does so. Remembering the cold fusion boomlet, which went nowhere, suggests caution with regard to these results. If something appears too good to be true, it normally is not true.
Popular Science has an article about the same research.
