"The Portal problem" (Classical Mechanics solution)

  • Thread starter AlbertCG93
  • Start date
  • #1
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:
https://drive.google.com/file/d/0BxtmJRf-jSFtTVlIVDM4S1B5c28/view?usp=sharing
 
Last edited by a moderator:

Answers and Replies

  • #2
DavidSnider
Gold Member
502
143
Wouldn't portals make free energy possible?
 
  • #3
Simon Bridge
Science Advisor
Homework Helper
17,874
1,655
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.
 
  • #4
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/aNnAEoK/portal-problem-the-answer-is-b

http://9gag.com/gag/adj90GB/moving-portal-problem

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

http://9gag.com/gag/am9YXAX/the-real-answer-and-trust-me-i-really-am-an-engineer

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.
 
Last edited by a moderator:
  • #5
DavidSnider
Gold Member
502
143
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?
 
  • #6
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.
 
  • #7
DavidSnider
Gold Member
502
143
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?
 
  • #8
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.
 
  • #9
Vanadium 50
Staff Emeritus
Science Advisor
Education Advisor
27,661
11,880
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.
 
  • #10
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 :)
 
Last edited by a moderator:
  • #11
Simon Bridge
Science Advisor
Homework Helper
17,874
1,655
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.

Is it not possible to summarize your "assertion" so we don't have to follow links?
There are several flaws in reasoning - the most important I think being that you assert that the object emerges through the blue portal at the same rate that it enters the orange one but has "zero valued linear momentum" once it has completely emerged.
How does something emerge at speed but afterward have zero velocity?

Apparently the situation given in the problem statement is one that does not appear in the game (check?) ... if a portal were projected on a surface that moved in the direction of the portal, then the portal would, presumably, fail (This is what seems to happen in P1.10). The question posed in the problem statement does not arise. However, moving portals have been observed in portal 2, is that correct? Therefore an experiment to see if the portal motion (that would be relative motion between the endpoints) affects the velocity of the object passing through.
 
Last edited:

Related Threads on "The Portal problem" (Classical Mechanics solution)

Replies
13
Views
2K
  • Last Post
Replies
2
Views
659
  • Last Post
Replies
7
Views
11K
  • Last Post
Replies
10
Views
2K
Replies
11
Views
4K
Replies
3
Views
4K
D
  • Last Post
Replies
1
Views
1K
D
Replies
14
Views
10K
Replies
8
Views
2K
J
Top