I don't think they would be involved with aliens, any alien race able to travel across space would reject humans because we are so stupid. I do, however, believe the government (both US and Australian) is hiding something. They spend so much on wars that seem completely pointless... what are they up to I wonder...
I dunno, I mean I can see having secret alliances with alien races I suppose.
But putting a barrier around the earth, discovering Earth 2.0, that kind of stuff...I dunno about that. Just because the whole WORLD would have to be in on it. China has a pretty active space program, just as an example, they even have a freakin post office in space (I'm not kidding [link] )
So keeping that a secret means hushing up and working with...everybody else. Not just the ones with the tech to get up there, the ones with the tech to SEE up there- which is pretty much everybody.
And I have a really, really hard time believing that all the governments would agree to go along on this little ploy when they can't get along with anything else.