I have read that the issue with a 1g rocket is that no fuel in existence is powerful enough to provide a constant acceleration of 9.8 meters per second for years on end, and it would take hundreds of tons of fuel just to reach our nearest star.
I have also read that metallic hydrogen would be the most powerful and efficient rocket fuel we've ever seen.
Would metallic hydrogen be powerful and efficient enough to make a 1g rocket feasible?
Achieving an acceleration of 1g is not difficult - a Formula 1 car can easily achieve accelerations in excess of 1g. Maintaining that acceleration for years rather than seconds is going to be a problem for any fuel, no matter how efficient it is. Even if we assume a super-fuel that is a hundred times more efficient than any conventional propellant, a back-of-the-envelope calculation says that maintaining an acceleration of 1g for years at a time will require millions of tons of propellant, not hundreds.
Of course, there are also theoretical exotic fuels such as antimatter (as discussed in the comments below). But if you plan to launch yourself to the stars on top of many tons of antimatter, I will wave you off from a very great distance.
