Re: Is this why we have Gravity?

I think that #1 was stated in the form of the infamous elevator thought experiment, where it was stated that someone in an elevator could not tell the difference if (1) it was on/near a planet (or mass) or (2) it was being towed / pushed at the same G rate. Well, if you hold to that, there are SIMPLE experiments inside the elevator that will tell (and i am NOT talking of measuring wall stresses).

The elevator picture is an explanation, not a theory. Gravity is local, which means that it obeys a differential equation, as opposed to (say) an integral equation, which (often). The physical extent of the elevator is assumed to be infinitesimal, so things depending on tides (i.e. on gradients of the gravitational field) are out of court.

Cheers

Phil Hobbs

Probably not.

mike

John

So, the experimental results show that gravity propagates at c (+-3dB). I like it.

Bob

An elevator allows at least one person to be (comfortably) inside, so that person could use the Mossbauer effect to determine a gravity gradient..

That's the point--tides are out of court because they only affect extended objects, whereas the elevator picture is intended to be infinitesimal in size compared to the length scale on which the gravitational field varies.

There's no elevator in Einstein's field equations, any more than there's a test mass in Newton's law of gravitation, or a microscopic void in Maxwell's equations. They're all fully local, because they involve only differentials of quantities evaluated at the exact same point.

Cheers

Phil Hobbs

I guess Einstein moved slowly, in later life ;-)

So, no elevator..gotta talk to that cable man again!

Later the elevator got upgraded to a constant acceleration rocket.