LOL What the hell did Rush find out? What's with all the cloak and dagger? Lets hear it.
In a previous episode, Rush attempted to open the stargate, straight to Earth. He succeeded. However, the extra power supply need to hold the gate open, didn't hold. Rush seems to want the others to go back to Earth, though it does seem that he would rather remain on the ship.
If Rush knew how to get back to Earth, I'm pretty sure he would send the rest of the crew back to Earth, while he stayed on the ship keeping his imaginary friends for company.
I don't think Rush knows how to get back to Earth.