Quantum particles expand space?

[Spinnor]

If we put a quantum particle in it's ground state in a cylinder with a movable piston there is an outward force on the piston? If we now put a quantum particle in the universe is there an outward force on space time however small?

Thanks for any help!

 

[Khashishi]

Space isn't a thing that you can exert a force on. But pressure does affect the curvature of space.