Frames of reference matter. Whether the train or the people moving happened it doesnt matter to the portal. There is net movement and the momentum is the mass of the person moving x the speed of the train.

Imagine the train was moving the speed of light. If the person exiting the other end of the portal wasnt coming out at the speed of light their body would come out like a soup. All the atoms in their body compressing to escape at some randomly low speed... actually it might make a tiny black hole on the other end as the atoms compress infinitely.

[–] Bizarroland@kbin.social -2 points 1 year ago (1 children)

A portal is as another commenter has framed it, essentially a hula hoop with a different space on the other side of it.

It doesn't matter how fast a hula hoop falls over your body. You are not going to be launched out of the other side of the hula hoop even if the hula hoop is moving at the speed of light.

If the hula hoop is moving at the speed of light you are more likely to be killed by the shockwave of all of the atoms in front of the hula hoop compressing to adapt to the sudden intrusion of a lightspeed object with Mass, in which case it is very likely that you would pop out of the other side as some sort of soup, but that would not be because of your interaction with the portal inside of the hula hoop, or the acceleration of the hula hoop itself but rather the acceleration of the things around the hula hoop as it moved through space.

[–] PatFussy@lemm.ee 4 points 1 year ago* (last edited 1 year ago) (1 children)

When im talking about speed of light i am assuming it will be in a perfect vacuum. If this was in ambient under normal conditions, a train going the speed of light would ionize all the air around it causing insane levels of heat.

So with the thought of it moving in a vacuum, if you look at the portal on a frame by frame basis every nano second you would see either

1 nano second in his entire body is within some imaginary dimension between the 2 spaces
The body gets infinitely squeezed in 1 space turning them into a mini black hole
They leave the portal at the same rate they came in

These are my 3 options, i dont see how it can be any other way.

[–] Bizarroland@kbin.social -1 points 1 year ago (2 children)

I think that the velocity of the tram has nothing to do with the velocity the people it is running over until it actually runs them over and transfers momentum to them.

The portal puts a gap in between the tram and the victims, so there is no physical contact to transfer momentum. Momentum is a physical property, it cannot be transmitted without contact.

Therefore, in a frictionless vacuum the people must keep their original velocity and momentum regardless of the speed of the portal or whatever is pushing it forward.

If it worked the other way, Chell could not have leapt off of a ceiling and been launched out of the other side in the game. If portals transmit momentum without touch, then Chell would have first impacted an unmoving object with the same force as hitting the floor.

You can't have it both left moving objects fly though unimpeded keeping their original momentum and also have unmoving objects suddenly gain momentum from a moving portal.

The portal does not affect momentum, it is a break in momentum. Momentum does not transfer across portals.

The momentum stays with the object that passes through the portal.

[–] Natanael@slrpnk.net 2 points 1 year ago* (last edited 1 year ago)

Quantum states can jump long distances without particle interaction, this includes energy transfer (you just need a measurable latent possibility for particle interaction!)

https://www.discovermagazine.com/the-sciences/first-demonstration-of-energy-teleportation

https://www.scientificamerican.com/article/nil-communication-how-to-send-a-message-without-sending-anything-at-all/

https://www.nature.com/articles/ncomms7811

The scifi answer that makes sense is that the space curvature around portal and shifting the object between two frames of reference (perhaps through frame dragging effects / gravity-wave like space warping) imparts momentum and it is conveyed from the portal as it is the thing which has to put in energy to correctly warp space for the object transfer.