I hate to shoot down the shielding theory, but the force woule be like a gas around BB's, acting uniformly. It can't come from outside without being here too because we've not just had seconds, minutes, or hours to reach equilibrium with it, but billions of years. If it came from elsewhere we'd have noticed that distant objects act differently elsewhere, and we haven't.
I think I must not have explained it clearly enough. I'm talking about the vacuum energy that pervades the entire universe. It's not from outside, it's from inside, everywhere.