# "The Portal problem" (Classical Mechanics solution)

AlbertCG93
Hello,

Lately I've seen many different explanations to the following problem based on "Portal" and "Portal 2" videogames (which I personally played and enjoyed).
Since the explanations didn't convince me, I drafted my own.
Hope you find it intersting and we can discuss it :)

Problem:

http://41.media.tumblr.com/tumblr_mbbrvkhFEz1ro2gsmo1_400.jpg [Broken]

Proposed solution:
A

Proposed explanation:

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DavidSnider
Gold Member
Wouldn't portals make free energy possible?

Simon Bridge
Homework Helper
Lately I've seen many different explanations to the following problem based on "Portal" and "Portal 2" videogames ...
... where? What were they?
Since the explanations didn't convince me, I drafted my own.
... why didn't you find them convincing and how does your explanation address the issue?

You'll get a bigger audience by providing this sort of information.

I'd go for B on the grounds that you go through a portal exactly as you go through a hole in a thin partition ... only the exit result is displaced and rotated to the position and orientation of the exit portal.

AlbertCG93
Wouldn't portals make free energy possible?

I don't think so, as I said, they're active dispositives; so, in fact, they would require energy to opperate, as far as I'm concerned.

... where? What were they?
... why didn't you find them convincing and how does your explanation address the issue?

You'll get a bigger audience by providing this sort of information.

I'd go for B on the grounds that you go through a portal exactly as you go through a hole in a thin partition ... only the exit result is displaced and rotated to the position and orientation of the exit portal.

In 9GAG; sources:

http://9gag.com/gag/am9YBY4/the-sol...t-into-this-title-quick-something-witty-beans

And there are many more.
All those explanations don't seem to work with the physics rather than try to distort them to prove their points.

I'm trying to give a sensible explanation to the phenomenon using a transformate approach to the conservation of linear momentum.

And for your solution, think that the block itself has no linear momentum associated; hence, as I pointed out in the PDF, I think it should be A.

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DavidSnider
Gold Member
I don't think so, as I said, they're active dispositives; so, in fact, they would require energy to opperate, as far as I'm concerned.
So if I put a portal at the bottom of a pool and one on the ceiling and put a waterwheel inbetween what happens?

AlbertCG93
So if I put a portal at the bottom of a pool and one on the ceiling and put a waterwheel inbetween what happens?

As you would expect, you'll generate power from the waterwheel. However, the portal itself would have given that potential energy to the water on the first place.

DavidSnider
Gold Member
As you would expect, you'll generate power from the waterwheel. However, the portal itself would have given that potential energy to the water on the first place.

But the water goes through the ceiling and back into the pool and back through the ceiling.... how could it have the potential energy for infinite trips?

AlbertCG93
But the water goes through the ceiling and back into the pool and back through the ceiling.... how could it have the potential energy for infinite trips?

It's not that the water has energy for many trips; but just that every time it passes through the portal, the portal itself does the required amount of work to put the water to a non-equilibrium state.

Staff Emeritus
The game rule is "Portals do not move along the portal direction." (I thought it was that they do not move at all, a rule broken in the neutrotoxin room in Portal 2, but I was corrected by Gabe Newell himself) You can test this yourself in Chamber 10 in Portal 1.

So this goes back to the question "What do the laws of physics say if we break the laws of physics?" only here it's not real physics but game physics.

And the Cake is a lie.

AlbertCG93
The game rule is "Portals do not move along the portal direction." (I thought it was that they do not move at all, a rule broken in the neutrotoxin room in Portal 2, but I was corrected by Gabe Newell himself) You can test this yourself in Chamber 10 in Portal 1.

So this goes back to the question "What do the laws of physics say if we break the laws of physics?" only here it's not real physics but game physics.

And the Cake is a lie.

Yet I think we can derive an insteresting discussion from my assertion, if you're willing to give it a look :)

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Simon Bridge
Homework Helper
I don't think so, as I said, they're active dispositives; so, in fact, they would require energy to opperate, as far as I'm concerned.
... where from?

Presumably there is something catching the difference in momentum too ... basically, the part of the portal operation that makes it obey conservation of energy and momentum is hidden from the player.
You can test the pmm in-game by setting entry portal in the ground and firing an exit to the ceiling directly above, then dropping a cube through.
The cube will wizz by for a bit but is quickly ejected ... but the portals are not diminished in any way. They would need to be drawing energy from someplace.
Possibly, since only some surfaces support portals, the surface itself contains conduits for the portals to get their energy, with a large power source hidden someplace else.

Try attaching the coordinate system to the orange portal, see if the result is consistent.

Yet I think we can derive an insteresting discussion from my assertion, if you're willing to give it a look :)
What would make the discussion "interesting" in the scientific sense is if there is some way to test the ideas experimentally, within the game.
As it is, the long-fall boots are tricky enough... gravity does not appear to work the way we are used to.