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Squark comments on Open thread, July 21-27, 2014 - Less Wrong
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Comments (160)
I think the answer B makes more sense. There's no reason this portal configuration should conserve momentum since it breaks space translation symmetry. On the other hand, if you're looking at the object from the exit portal then you expect its trajectory to be smooth. More formally, the portal can be implemented by making space into an appropriate Riemannian manifold (with singularity at portal edges) and mechanics with the usual Lagrangian leads to B.
I'm confused. Both trajectories are smooth.
Well, yes, but I think the question is concerned with the peculiar implementation of portals in the game, which apparently conserves momentum.
If you're looking from the exit portal you see the object coming towards you. Therefore, when it crosses the portal you expect it to keep moving with the same velocity rather than suddenly stopping (I assume that the portal is a smooth geometric surgery of space and nothing singular is happening at the boundary except at the edge).
I have no idea about the game (never played it). I'm just saying what seems more natural from the POV of physics.