# Could it ever be possible to generate small gravitational waves? [duplicate]

Would it ever be possible to make a device that could generate small,short gravitational waves? If so, it would then be possible to use artificial gravitation for space travel. Assuming that gravitational waves would be longitudinal -1st half of wave, slightly compressed space-time, to 2nd half, slightly rarified space-time. Were it possible, then with say 3 such devices focus these waves so that the rarified portions (sic) converge. Were that possible, you would then create a "pseudo-gravity" source. A vehicle could then "lift itself up by its own bootstraps." But could such a thing as a "gravitational wave generator" ever be built?

## marked as duplicate by Danu, user36790, ACuriousMind♦, John Rennie, Kyle KanosFeb 15 '16 at 12:46

• It's fairly simple to build a gravitational wave generator: spin something around. Ceiling fans generate gravitational waves, for example. But you couldn't propel a spacecraft with such a gravity motor as you describe, since the "slightly rarified spacetime" still contains an attractive gravitational field, not a repulsive one. – Asher Jul 7 '15 at 15:05
• To add to Asher, the problem is not that one can't build gravitational wave generators, the problem is that one can't build efficient ones for technological purposes because the coupling of mass to space is so small. If one could, the resulting device would still not have any advantage over a photon drive because weak gravitational waves are, except for symmetry properties, not much different from electromagnetic wave for your purposes. And, no, gravitational waves are not longitudinal waves, but second degree tensor waves. – CuriousOne Jul 7 '15 at 19:23
• simply spinning something around is not enough to generate gravitational waves if the rotating object has axial symmetry along the spinning axis. Gravitational waves are created by the time derivatives of the quadrupolar mass moments, which are zero for an isolated object spinning inertially – diffeomorphism Nov 11 '15 at 13:08