[MonroeDNA]

OK, here's a question I've been asking various people for over 15 years:

Einstien stated that there is no way to measurably differentiate between gravity and accelleration.

Newton invented calculus to prove that any gravitational mass can be treated as if all the gravity was coming from a single point, at the center of mass. A point source.

Let's suppose that you were in an elevator, under either accelleration or gravity, and you hung two static pendulums from the ceiling, from strings.

My question: Under gravity, wouldn't the pendulum strings angle toward each other, exactly towards Newton's common point? But under accelleration, wouldn't the strings would be perfectly parallel?

[RightWhale]

Good question. Don't know right off. We'll get back to you.

[RightWhale]

Technical staff has examined the situation and wants to know the size of the elevator. Is it small -- 20 passengers or so, or is it large -- the size of the moon? Makes a difference. If it's small, it will be impossible to measure a difference. If it is large, the gravity field will have measurable curvature and the acceleration will be of course uniformly flat. So it depends on whether you want to treat the gravity field as a uniformly flat, infinitesimally small segment of the spherical gravity field.

[PatrickHenry]

My question: Under gravity, wouldn't the pendulum strings angle toward each other, exactly towards Newton's common point? But under accelleration, wouldn't the strings would be perfectly parallel?

They would gravitate toward each other under either circumstance (whether the elevator they were in was sitting on the ground or being lifted.) A passenger in the elevator wouldn't know which was the true situation.