But the pedestrians have no momentum, only the portal has momentum.
Replace the portal with a normal open doorway, or that gameshow "hole in the wall", when someone passes through the hole, they aren't launched out of the other side, they're still just standing there as the door passes around them.
They have momentum though. They're on the earth (presumably), which is yeeting through space at a rapid pace. Portals must respect relative speed, otherwise everything would fly out due to their speed.
But the pedestrians have no momentum, only the portal has momentum.
Replace the portal with a normal open doorway, or that gameshow "hole in the wall", when someone passes through the hole, they aren't launched out of the other side, they're still just standing there as the door passes around them.
They have momentum though. They're on the earth (presumably), which is yeeting through space at a rapid pace. Portals must respect relative speed, otherwise everything would fly out due to their speed.