Alcubierre drive
There was a time where relativists realized that instead of solving the Einstein equations subject to initial conditions coupled to some matter stress energy terms, they could instead fully specify what spacetime looks like, ram it through the Einstein equations and get a stress energy tensor on the right hand side.The Einstein equations became a recipe generator: if you want this spacetime, then you need this matter/energy.Unfortunately, all the interesting spacetimes (such as the Alcubierre drive) require exotic matter, matter unlike anything we have ever seen. Other spacetimes people were interested in generating were stable wormholes. If we could ever produce such matter then we could start some spacetime engineerinng. Meanwhile, we are left with these oddities.I heard that Alcubierre somewhat regrets having his name on this spacetime as he gets contacted by all kinds of Star Trek fans and other people who believe they can produce the drive. He has done all kinds of other quality research in General Relativity, but this is what he will be famous for.