Continuity mistake: When Ally gets on the plane to go see Jack she is wearing sneakers (you can see them when she lays on the couch in the plane) then in the next scene when she's on stage singing with Jack she's wearing shoes with a high heel. (00:34:45 - 00:42:10)
Continuity mistake: When Jackson asks Ally to go onstage and play, her hair is brushed with a bang falling on her forehead. Shot changes to Jack watching her with a live video playing of her behind, and now her hair is messed up. Angle back on Ally and it's neat as before.
Answer: It is highly improbable they could do this, but being a movie, reality is suspended.
raywest