This thought experiment involves a friction-free snooker table, in a vacuum. The cue-ball is alone on the table, placed centrally on the balk cushion.

At t=0 the cue strikes it, sending it straight up the table at constant velocity, v, with constant momentum, p.

At t=1 it crosses the green spot.
At t=2 it crosses the blue spot.
At t=3 it arrives at the pink spot; at which point, time is reversed.

It crosses the blue and green spots at t=2 and t=1, respectively.

What happens to v and p, both are vectors, so at t=2 and t=1, in reversed time, the ball is travelling towards the balk cushion, but the vectors point away from it?

There never was nothing.