as it eludes me, but it involved a material that blocked gravity waves. Anyway, Einstein theorized the existence of gravity waves, & recently they were actually detected! Now, they plan to send probes out to detect more of them:
http://newatlas.com/esa-space-gravity-waves/46195/?utm_source=Gizmag+Subscribers&utm_campaign=453c9017a4-UA-2235360-4&utm_medium=email&utm_term=0_65b67362bd-453c9017a4-76704577
