Comment on Which is it Lemmy?
meekah@discuss.tchncs.de 5 days agoI don’t think this can work. Think through it in several steps rather than just one. Once the cube just started entering the portal, a part of it will already be on the other side, as close to the 2nd portal as possible. When the portal continues moving, more of the cube needs to be on the other side, so it “pushes” the first part of the cube further away. The cube imparts momentum onto itself.
Another way to look at it is using reference frames. It really doesn’t make a difference whether the cube is moving towards the portal or the portal towards the cube. It only matters what the difference of velocity is. The difference of velocity must be maintained on the other side of the portal, and since the 2nd portal is stationary, the cube must move.
portifornia@piefed.social 5 days ago
Hmm, maybe? But two things to (re) consider:
Saying “
the cube imparts momentum onto itself” sounds like it would violate the law of conservation of energy. The ‘energy can’t be created or destroyed’ theory, so where did it actually come from? Did the cube suck force going at one vector (the portal) and convert it into the opposite vector? That feels like it violates inertia. And since momentum is mass*velocity, that means the mass of the portal would play into the math changing the cube’s own momentum. And I’d honestly assume the portal’s mass is zero, which still maintains it wouldn’t impart any energy onto the cube, right?Secondly, regarding inertia from another standpoint, I have a thought experiment: let’s say the portal is coming at the cube blazingly fast, then immediately stops halfway through enveloping the cube, so it’s just chilling 50/50 on each side. By your statement of “
it pushes the first part of the cube...” That would mean one half would have momentum at the same time the other half, not yet through the horizon, would still have none. Maybe so much so that (1) the cube would be pulled the rest of the way through even through the portal had stopped because half the atoms of the cube suddenly had momentum for some reason, or (2) the cube would rip in half (brittle cube I guess, but let’s ignore the material considerations for simpliciry) because half the cube now suddenly has momentum while the other half still has none.So I think I understand your perspective, but I can’t yet get around what seems to be a few lingering problems. All the same, I’m enjoying the discussion, thanks net-neighbor!
imadethis@fedinsfw.app 4 days ago
Conservation of energy is already broken by portals. Consider the portals in a frictionless tube (it could be frictioned, but that would be less fun) that use the earth’s gravity to accelerate the cube to the speed of light. If we are take the cube’s effect on the earth as non-negligible, then the earth has also accelerated a significant bit in the ‘upwards’ direction that the tube has. Simply run to the other side of the earth, put the ‘exit’ portal aiming towards the same direction as the ‘upwards’ of the tube, in this case directly at the earth, and now you have accelerated the earth twice as much in that ‘upwards’ direction with no apparent gain or loss of energy (and also have obliterated the earth, but let’s not talk about a cube’s mass hitting the earth at c.
As for the portal suddenly stopping while moving blazingly fast, sure, it’s a good quandary. It seems insane to think of the cube suddenly gaining momentum, but it’s also insane to think that a particle (in this case the portion of the cube’s atoms that are through the portal already) that is moving at speed somehow has no momentum.