equal and opposite reaction is completely valid in a vaccum
Stormy?
The Planck length and units will be the base measurement of 4D universe. The Warping of the Planck unit is the basis of all deviation of space time. If there is an event horizon at the Planck length level it would open a new axis different than 4D.
Basic equal and opposite forces does not depend upon pushing on something - that is the resistance to the push.
Every action (force) has an equal and opposite reaction (medium is irrelevant) Media is the resistance to the force (or work/movement).