There's also the EmDrive (https://en.wikipedia.org/wiki/RF_resonant_cavity_thruster https://en.wikipedia.org/wiki/RF_resonant_cavity_thruster), which is controv

There's also the EmDrive (https://en.wikipedia.org/wiki/RF_resonant_cavity_thruster https://en.wikipedia.org/wiki/RF_resonant_cavity_thruster), which is controversial because it seems to violate all known physical laws. But there are prototypes that seem to work and have been replicated a handful of times by responsible and credible research teams. In each case, there are possible sources of error, but the fact that it appears to be replicated and we can't (yet) rule out the idea that it does work is very exciting. It should be aggressively pursued, because if it does work it's a very big deal. Instead of looking at things like this with jaded skepticism, we should look at them with excitement and pursue them aggressively! The moment we get overconfident in our own knowledge is the moment we cease to discover new things.