  It has recently been claimed that relativity's most famous equation, E =
mc^2, has a cosmological basis, representing the gravitational binding energy
for a particle to escape from the origin to a gravitational horizon of the
universe. In this paper, I examine these claims in detail, concluding that they
result from a misinterpretation of motion of particles in the cosmological
space-time, and an incorrect application of 4-vectors. Finally, I demonstrate
that the origin of E = mc^2 comes from its usual relativistic interpretation,
namely that it is the energy of a particle as seen in its own rest-frame.
