Alan Baker wrote:
Because the push is caused by the impact of countless air molecules
with the surface of wing. If those collisions fall to zero (i.e. in a
perfect vacuum) then there is zero push.

But there is no set of circumstances that can make the number of
collisions be negative.

Pedantically speaking, outgassing would occur for a while that would create
a force on your wing surface when it is exposed to a vacuum. Pedantically
speaking, I don't see why those couldn't be called negative collisions.

(Last worked on a fancy high-vaccum system back in college, wherein my lab
mate and I attempted to replicate the Lamb-Retherford experiment.)