Portal [Interesting Physics]

[Reincarnate]

Originally Posted by qqwref

I imagine you would. If you just put something in one of these portals, it would oscillate back and forth, but eventually air friction should bring it to an effective stop.

It's a bit hard to imagine a gravitational field that completely switches directions on a line, but it's probably easier to imagine an electric field with the same behavior (at least thinking theoretically). A point charge in that field would show the same behavior.

Well the idea is that the momentum you have going through one portal is conserved, so you've basically got a velocity vector always pointing towards the ceiling and being pulled back down to earth, hence the oscillation (and, ideally, slowdown to a halt due to air friction).

However, it makes me wonder how forces work here since you're still feeling a downward force of gravity through the portal even though it's pointing up at the ceiling (meaning that the attraction between the earth and your body is somehow directly extending beyond the portal itself).

[qqwref]

Good point about gravity. It probably makes sense for gravity to extend beyond a portal; if we use the "2D rubber sheet" model the portal is a tiny cut in the sheet, and the area "behind" the portal is still affected properly, but if you think of gravity as relying on line-of-sight stuff, this breach in space would make the gravitational field beyond the portal really questionable. I wonder: if we put one portal on the ceiling, would someone be pulled towards the opposite portal? From the perspective of someone near the opposite portal, there is basically another earth beyond it, and it ought to provide its own gravitational attraction. The game seems to act like only matter and light can go through the portal (but not fields of fundamental forces), which is pretty odd from a physics standpoint.

I guess Portal physics is like a very tall cup with a hole at the bottom. If you look deep enough, you find that it doesn't hold water....

[LongGone]

Originally Posted by Reincarnate

However, it makes me wonder how forces work here since you're still feeling a downward force of gravity through the portal even though it's pointing up at the ceiling (meaning that the attraction between the earth and your body is somehow directly extending beyond the portal itself).

You probably just have a system where the object is divided into two by the portals (two lumps of group of atoms). Well, I think of portals as physical boundaries; forces/gravity does not extend past it, it just treats the portal as a solid barrier. Each half will independently experience gravity, however they are both linked by the portal so they exert a force of each half's own weight against each other. Equilibrium is reached when the plane of the portal cuts the centre of mass of the object; i.e. the total gravity force exerted by each half on each other is equal. If you displace the object slightly, the side with more mass will exert a slightly larger force (its weight) on the other side with less mass, thus oscillate

EDIT: On second thought, maybe forces do transmit through each other till a certain extent; since if you had a pole through a portal and you yank at it it pulls through (the atoms of the pole are all linked together by forces afterall). Maybe gravity does pull through to a certain extent? Or overlaps slightly on each other right on the portal

[Stewie7Griffin]

Two portal faces couldn't be pushed together with an object in between as the object would be pushing out of the other portal against itself, completely preventing you from pushing the portals together. Unless you can somehow defy the laws of physics by getting the object to ignore the it's own boundaries and go inside itself BEFORE you push the portals together, those portals are not going to go together.

[Izzy]

The portal has no physical properties. It is completely flat and can be described as only 2 dimensional. Having two portals push together would apply the same force the object in-between as if those portals weren't there. Except the left side is now pushing from the right and the right is pushing from the left.

[Stewie7Griffin]

0 [] 0

0=Portal
[]=Cube

When you push the portals together 0[]0 the cube will come out of the other side and push against itself, therefore, rendering it impossible to push the portals together any further than the width of the cube.
0][0