There may be MANY ways of going faster-than-light. We just haven't discovered one yet. Or, as the late Arthur C. Clarke once said. . .
When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
This is also known as Clarke's First Law. . .
Alcubierre’s theory only opened the door. There are people who have expanded on that beginning, and brought the energy requirements WAY down. We’ll have FTL ships someday.