Why?
Where does the energy even come from?
A hole/portal doesn’t create or generate energy it just passes things through.
Just think of it as a hole across space because that is exactly what a portal is.
It’s already established in Portal that energy can be created by changing elevation with portals. If the other portal is on the back of the train, you’d just fall out because you’d be shooting backwards at a speed that cancels out the speed of the back portal. If that portal were just sitting stationary you’d have to fly out at the speed you went in. The puzzle comes from people trying to apply ordinary physics to something that deliberately breaks them.
No energy is every transferred as a result of a portal
You fly in the air if you drop in one because you are carrying momentum downwards that suddenly translates to upwards
You are sat in the floor, a portal flies towards you. You are sat at the floor at the end, you had no momentum going in and no momentum going out
Exactly how fast do you think the people exit that portal? Train speed, less than train speed? What slows them down after they exit? If you blocked the stationary portal would you get hit by the people? If so, what force would cause that?
The people may be stationary relative to the area outside the first portal, but they already have velocity relative to the world outside the exit even before they go through
If there were no people on the track and you blocked the stationary portal, would you feel wind on your face?
