# EquivalencePrinciple

### From WikiWorld

The cornerstone of general relativity is the equivalence principle, by assuming gravitational acceleration was the same as inertial acceleration Einstein was able to expand the theory of Special Relativity to include gravitational systems.

Spacetime geodesics curve in toward masses exhibiting the equivalence principle.

In a sense, at least in part, inertia is the effort it takes for objects to escape their own gravity well according to General Relativity.

GR does not explain why but it can be understood from the quantum perspective if you consider that all energy in the quantum propagates only at the speed of light and matter is composed of such energy. The sum of all the light speed velocity vectors is zero in the rest frame of the object. The amount of energy you must apply to change the average to a different frame depends on the total energy or mass of the object.

It is easy to see how inertial mass is exhibited in this process. Understanding the gravitational effect is a bit more difficult.

In GR mass bends space such that energy flowing through/near the mass takes longer to travel than energy going past it at a distance. This time hysteresis exhibits the gravitational effect, or curving of spacetime.

The curvature of space mathematically has the exact same effect as acceleration making gravity equivalent to acceleration.

In the quantum light speed does not change but light travels further instead accounting for the additional delay by travelling in other dimensions orthogonal to our own. These so called "curled up" dimensions are not really curly at all. they are straight as arrows in other local directions.

The tricky part is understanding how this internal effect in a mass exhibits gravity external to the mass. To understand this, first consider, as Wheeler put it, that the vacuum energy is only marginally less energetic than matter, and that it constantly interacts with matter such that the vacuum is shaped by the interaction with matter.

As Wheeler said, space tells matter how to move, matter tells space how to bend.

If we accept that only spacetime exists which is animated by energy then, in the information model, gravity becomes equivalent to local spacetime entropy do to the time delay mass exhibits.

The equivalence between gravitational and inertial mass is that they are both a function of the total internal energy of the mass and both due the the bending of space due to the mass. Understanding how this happens requires examining the nature of the vacuum which resists changes in velocity and mass which resists changes in time together.