First, in your hoolahoop example both sides of the hoop are moving with the same velocity (this is essentially option 3 I described). But the entire thought experiment is "what if the two sides didn't move with the same velocity"

If you've played the game, you know that you don't instantly teleport when you touch the portal, you can be half in the portal. This means that when something enters the portal, it is deposited on the surface of the other portal. So as your arm enters the portal, your hand needs to move out of the way to make space for your arm.

If your hand doesn't move out of the way to make room for your arm (it is still because it has the same momentum that it had when it entered) then your arm will materialize in the same space as your hand. Now scale that down to the atomic level, if the atoms of your fingertips don't move for the next atoms, everything will be deposited in a 1 atom thick film.

If your hand does move out of the way fast enough to make room for your arm, then it is moving at the same speed that the train was moving. Your momentum from that speed would fling you into the air.

In no scenario do you just pop out intact but motionless.

[–] Lizardking27@lemmy.world 1 points 1 year ago (1 children)

I just don't agree that's how it would work. You can't gain momentum simply by passing through a portal. The portal cannot create momentum. The object passing through has no kinetic energy going in, it can't have kinetic energy coming out. It would exit the portal at the velocity of the first portal, as the entry portal passes over the object, and then the object would drop to the ground.

[–] PeriodicallyPedantic@lemmy.ca 4 points 1 year ago

There is no way that it works without breaking even more laws of physics than the game. So you're right, you can't gain momentum. Nor can you be deposited intact on the other side of the portal.

But of the options, the one you described seems the least likely. I keep telling you exactly how it wouldn't work, and rather than addressing the concerns you just say "no".

We can agree that you can partially enter a portal, so you can put your hand in and only your hand comes through the other side. So now tell me: how does your hand move out of the way for your arm to come through, without moving? Because if it moves, then it has gained momentum, which you've explicitly said doesn't happen.