We don’t know that Dark Matter exists other than we know there is (a lot of) mass missing which is needed to reconcile our observations (or we need to modify ou

We don’t know that Dark Matter exists other than we know there is (a lot of) mass missing which is needed to reconcile our observations (or we need to modify our theories around gravity which is where things like MOND come into play). Dark Matter is just a placeholder term for that missing mass with a lot of candidates ranging from normal (baryonic) matter to more and more exotic things. Negative mass does not contradict existing theories such as the standard model in fact it’s somewhat built into them. But overall yes we haven’t found any evidence of it actually existing we know that anti matter (probably one of the best candidates for it) has positive inertial mass from experimentation we didn’t experimentally proven that it’s gravitational mass is also positive but it most likely is as if it isn’t it would be probably the most interesting discovery since it would violate the equivalence principle. In general you’ll find people getting excited about any possibility for an FTL means of transport since otherwise we are unlikely to ever be able to explore the universe with anything other than telescopes. I fore one hope that we do find a way around the pesky speed limit because if not it seems that it’s quite a bit of waste of space otherwise.