well at the end of Portal 2 (SPOILER ALERT!!!) a portal was opened on the moon and alot of air got sucked out of the room.  How long would the portal have to be open to remove all the earths atmosphere? days? weeks?  or would it just balance itself out?,(reply>), @eyflfla even better the destruction of the surface the portal is on would destroy it as well,(reply>), millions of years. eventually the moon will equalize in pressure with about 20% of the atmosphere lost, let's just say, and at that point it's just the moon slowly losing the oxygen due to low gravity.,(reply>), Andrew but we have this thing called gravity in reality,(reply>), Of cooursee it would balance itself out. With the universe, right?,(reply>), I wonder what kind of mass would be needed to plug the portal.  The portal originally talked about was in a lab.  If a government were to bomb the lab and surrounding area, would the rubble form a tight enough seal?