## Description

The rest energy of an object is based on its mass, otherwise known as mass-energy equivalence – the famous Einstein **E=m****c ^{2}** equation. In energy wave theory, mass is the sum of a particle’s standing waves of longitudinal wave energy. A standing wave structure changes based on amplitude and frequency, thus mass may change. At rest, meaning the particle has no velocity (v=0), there is no change in amplitude or frequency. A particle resonates with the frequency of the universal waves traveling the aether.

Mass is apparent in the Longitudinal Energy Equation, as it is energy divided by the square of the wave speed (c^{2}). Therefore, the mass-energy equivalence equation is a **simple derivation of the Longitudinal Wave Equation**.

## Derivation

The derivation begins with the Energy Wave Equation. The energy for a particle is based on its number of wave centers (K). Energy and mass equations are simply a difference between the speed of light squared. This derivation includes descriptions that are addressed in the Particles section, such as the volume and radius assumptions, and definitions of wave centers and shells. It is highly suggested that the reader visit the Particles section first to understand this derivation. Further details are in the *Key Physics Equations and Experiments* paper.

## Proof

Particle energies were calculated in Particles, including the electron which found to have 10 wave centers (K). The calculation of electron mass is below. It matches in both numerical value and units. Units are kg.

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