Levitating Using Gravity

(using Dad's email address with his permission)Could a heavier than air item be suspended (levitated, floated, ant-gravitated) in air either by a counterweight from space, or from a point on the opposite side of the Earth? I imagine a ship, like a bobber, could "float" in air if it were attached to an object of equal mass from a point 180 degrees away on the other side of the Earth. Could the gravity acting on both masses achieve equilibrium?
- Juliet Wheeler (age 13)
Wapakoneta, Ohio, United States

That's a very nice idea, just the sort of thing a future physicist is likely to think about. As it happens, it won't work. There's a theorem due to Earnshaw that says that any gravitational arrangement, no matter how clever, is unstable. Your arrangement can have zero net force on the object, but there will always be some direction where a tiny wobble would accelerate away, like a pencil tipping over if it wobbles just a little from straight up.

Mike W.

(published on 03/13/2019)