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With the introduction of the co-op levels I thought it would open up the possibility to send one of my portals through my partner's already established portals. This would allow me to create a portal in a place that might not be accessible otherwise.

I think the game is capable of supporting this behavior but when I tried it (and I have tried many times during the co-op game) all it ever did was ruin one of my partner's portals.

Are there special test chambers where this is allowed? I have not finished all of them yet.

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You can shoot through the portal sorta. You just need to be standing in the portal sticking out far enough so you can shoot an exit portal and step back through before it lands. – Jeff Mercado Feb 8 '12 at 6:44
Narbacular Drop supported this even with 1 Player, but it caused the gameplay to get a lot easier, and I imagine would make puzzles harder to make. I think it may have been a deliberate decision to not support this. – Chris Burt-Brown Feb 8 '12 at 9:35
@JeffMercado No, that's Portal 1. In Portal 2, the portals basically don't have a travel time, so this isn't really possible. Unless you use that glitch with gravity adjustment, but in normal gameplay, not so much. – a cat Feb 8 '12 at 16:22
@lunboks: Oh so that doesn't work on Portal 2? I have to admit, I haven't tried doing it in P2 and assumed it was the same. – Jeff Mercado Feb 8 '12 at 16:49
fwiw, you can do this with the knock-off portal gun in Darksiders. :) – Kip Feb 15 '12 at 13:48
up vote 18 down vote accepted

No. There is never any case in Portal 2 where you can send a portal through another portal. As you noticed, shooting a portal at an existing portal replaces the existing portal. The behavior you are describing would be inconsistent with that, so it cannot happen.

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what about Linked portal doors? – Chris Bye Feb 8 '12 at 13:53
@Slothsberry in game, those do not act like portals from the player's point of view, so they are not relevant to the question. – murgatroid99 Feb 8 '12 at 14:54
Narbacular Drop (an earlier portal-based game from the pre-Valve team) actually features this mechanic as a feature. – Xkeeper Feb 8 '12 at 16:45 – badp Feb 14 '12 at 8:06
@badp I don't think that was the kind of thing they were asking for. – murgatroid99 Feb 14 '12 at 15:07

Nope, the game does not allow this, you will at most just end up placing another portal in the same spot.

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As a minor point, I doubt this is part of the physics engine. That would deal with how objects move and react to each other in terms of mass, inertia, gravity, impulse, etc. This is almost certainly just a specific design decision, with the game engine checking if your target is a valid, portal-able (new word!) area or not. – Alex Feb 8 '12 at 13:19

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