Nothing 

“Tell me, somebody, is there somewhere in space where nothing exists, and if there is, how the hell do I get there?” someone said.
“If you go to a place where nothing exists, and, you know, occupy that space, then that place wont exist anymore.” began one.
“And since he is occupying the space that used to be occupied by the space that was unoccupied, would there be an unoccupied space in the space where he used to be?” continued another, obviously on a roll.
“Only if there is no-one there” hinted a third, darkly, a chill piercing their very souls, for some reason.
“But if there is no one there, where is everybody?”
There it was, out in the open.
“Where is everybody?” cried another.
“Where the hell is everybody?” was repeated by all lips, accelerated somehow, gaining momentum as the fear threatened to shriek apart every central nervous system not grounded in the twilight zone.
“We’re all right here!” they realized simultaneously, bursting out laughing and marveling at how close they came this time.
And they didn’t even know how wrong they were.