this post was submitted on 18 Aug 2023
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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.
I say its B, because if we jump in a portal we fly out of the other one. Now the difference is here the portal is moving and not the person, but in physics we are only interested in the motion of two bodys relative to each other. If you are standing on the train you would see the portal as stationary and the people coming towards it. Because the object/person enters the portal with speed it also comes out with the same speed.
The portal is a connection of two spaces, but the spaces themselves are not moving. It's hard to say though because some sort of force would have to push you into place, but momentum is conserved so... Who knows.
If you jump into a portal, YOU have momentum, these people are stationary and therefore have no momentum, the answer is A.
There is no momentum without saying relative to what. A train is moving relative to the people not on the train. The earth is moving relative to the sun. But if you are on earth the sun is moving and you are stationary and your viewpoint is not wrong! The reason is, that there is no underlying space we are moving relative to. Maybe this helps: Imagine a train in a train. Driving with the same speed but in the opposite direction. Now from the outside the inner train is not moving at all, but the outer train is. From the inside the inner train is moving and the world around them is. If there is now a portal inside the outer train and the inside train is passing through. What happens. Nothing because the inside train is not moving or it shoots out because it is moving?
But the object doesn't enter at speed here it's stationary. If a hoop is thrown at an object and passes around the object the object is still stationary. The speed of the portal relative to the object does not impart movement on the object.
The quicker the portal moves the quicker the object appears on the other side but for the object to shoot out it means energy is being transfered from the car to the object.
If you're right then what happens If the two portals are moving at equal and opposite speeds?