Certainly the Alcubiere warp drive requires exotic matter which may not exist. There's now a scheme that doesn't require negative energy. https://newatlas.com

Certainly the Alcubiere warp drive requires exotic matter which may not exist. There's now a scheme that doesn't require negative energy. https://newatlas.com/physics/ftl-warp-drive-no-negative-energy/ https://newatlas.com/physics/ftl-warp-drive-no-negative-ener... It may be almost impossible to build due to the energy required, but it isn't prohibited by the physics we currently know.