Not the way I'm using the word. The drive is not currently merely like an airplane, where it is obviously possible to fly (at least as well as birds), we just didn't know how to bang the rocks together correctly to do it. The Alcubierre drives requires things that we have every reason to believe are impossible. In English the term "negative mass" may just seem like, oh, someday maybe we'll advance and have this; in math, it's even worse than you may think I'm going to say. It isn't that we don't know what "negative mass" is. It in fact already appears in some of our equations. The problem is that the product of negative mass times the amount of time it exists seems to be fairly sharply bounded at literally dozens of orders of magnitude too small to conceivably be of any use.

We have every reason to believe that stable negative mass is impossible. Not just "we don't know how to do it yet", but impossible. Impossible is like "perfect"; technically, it doesn't admit of "degrees" of impossible. So moving from "impossible" to "impossible" is not progress.

People like to cite a lot of cases of various supposed boundaries being broken over time as evidence that maybe this one will be broken too, but there's a qualitative difference between some "elderly distinguished scientist" opining something is impossible, and the mathematics of physics saying something is impossible. It is not a sophisticated, open-minded position about the technological possibilities of the future to say that someday, man will break the barriers of the laws of thermodynamics and someday produce the perpetual motion machine; it is ignorance and scientific illiteracy. FTL is not quite that certain yet, but at the moment, the smart money is on it being the exact same sort of thing, not humanity someday overcoming it. At the moment I'd say that if you properly understand the science of the matter and just how thoroughly reality seems to stymie us in our every attempt to worm around the speed of light restriction, you are completely unjustified in giving even a .1% chance of FTL being possible, let alone that humanity will ever achieve it. It looks to be a lot closer to perpetual motion than breaking the sound "barrier", which barely even deserves the same English word as the speed of light barrier given their massive qualitative differences.

Now, as I say, the long shots sometimes pay off, so I don't advocate that nobody thinks about this. Even the process of discovering why the <.1% is better thought of as a flat 0% can be valuable scientific progress, plus there is always the chance I'm wrong. However, at the moment, it looks like FTL is a problem that is far harder than just waving a couple of hoary old quotes about scientists at it is going to solve. You're not fighting "scientists", but the math.

Personally, I tend to think Hawking probably got it right with his chronology protection conjecture, and that even if you do manage to build something that goes faster than light or travels back in time, the entire system will literally explode. FTL may not be just impossible because we don't know how to build it, but because it really is fundamentally impossible; spacetime will literally explode in your face even if you do manage it.

https://en.wikipedia.org/wiki/Chronology_protection_conjectu...