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Don,

The Equivalance Princple implies more than your quibbling between the difference between an accerlating elevator and a gravitation field that is dropping at the inverse square law. The thought experiment was a *teaching tool*, not to be taken as something you can poke holes at! He, and I here, could have added that the gravitational field was locally shaped to be flat sloped, rather than dropping at the inverse square... as can be done with properly placed mass nearby. Refer to Dr. Robert L. Forward's work on shaping spacetime using local mass. Your silly quibble would be then obviated.

The Equivalance Principle also says something far more important. It states that rest mass, inertial mass, energy mass, all create and respond to gravity proportionally to their mass. That is to say, that one kilo of mass, as measured by its inertial properties, is going to create and react to a given gravitational field exactly the same. That inertial mass and graviational mass are the same.

If you will follow a lengthy thought experiment, I can show how these are related and possibly why. Again, this is a *teaching tool* not literally what may happen.

If we have a collection of objects with mass we can find a center of mass. We can also find a non accellerated inertial reference frame that is stationary with this center of mass. From Newton's laws we can say with certainty that that any interactions within that collection of objects may change the relative position and velocities, but the center of mass will remain stationary to our reference frame. If we then expand our collection of objects to more objects that may interact, we find a new center of mass and a new reference frame, etc... until we have included all of the mass of the universe. We then find that center of mass for the entire universe. BTW, this is *not* a universal absolute spatial reference. In fact this point may not even be found within the universe's space time!

To make the next step easier to visualize, since not all of us are gifted with the ablility to see five dimentional space, we imagine a one dimensional spacetime that is wrapped onto itself to form a perfect circle on a two dimensional plane. Take a pen and draw such a circle on a scrap of paper. Now draw a collection of point like objects of mass that are equidistant from one another on the circle. Take note that that the center of mass for this collection is at the center of the circle, not in the spacetime!

Now imaging that a subset, a group to one side of the circle, are brought close together. Now refigure where the center of mass would be....

Oops! The center of mass would have moved, in violation of Newton's laws. Newton's law restated becomes, "The center of mass of the universe is constant" So, this can't be what happens...

Instead, the spacetime deforms to keep the center of mass constant, it curves 'downward' toward the center of mass when mass is concentrated. This deformation of spacetime is gravity. Note that it is caused by the concentration of mass in direct proportion, exactly according to the Equivalence Principle.

Now, imagine if you can, this happening for a four dimensional spacetime (or ten if you like to include String Theory) wrapped around a "flat" or at least "flatter" dimension (perhaps the eleventh dimension in the full String Theory?). Add to this the Hubble Expansion of an expanding four dimensional universe with dimples where the superclusters, clusters, galaxies, stars, and planets are found, we find a useful model of our universe as we presently envision it.

Far from being "wrong", Einstein built on Newton to give us a framework to understand our universe.

--Candice H. Brown Elliott