Memes

I think it's A because I assume a portal stitches two points in space to each other.

So if I have a surface A and B with a portal ']' in the middle A0 A1 ] A2 A3. B0 B1 [ B2 B3

A portal creates a new surface

A0 A1 ][ B2 B3

And if you move the portal the new surface changes.

A0 A1 A2 ][ B3

Speed is distance over time. When a portal moves the object that passed through the portal stays stationary. Let's say I am standing on B2. When the portal advances I find myself standing on A2 , have i moved? No the environment has changed but i am still in the same relative position with respect to the portal surface. No distance travelled so no speed.

A, the people are traveling towards the portal, not the other way around.

If they were falling/running at the portal it would be different.

Here the portal is moving forward towards them, they have no momentum.tk travel through the portal.

The only way it could be B in this universe is if the train also decelerates equivalent to how the people accelerate. If the people accelerate and the train maintains velocity you've created energy in a closed system.