Zordim, can it be claimed, with any degree of certainty, that any object is at rest?
The elementary energy is the photon.
The energy of a photon is at the same time its total energy, its electromagnetic energy, and its kinetic energy. There do not exist non-moving photons. Photons move with velocity which is determined with epsilon and mu properties of space.
Photon's mass is non-inertial. It is the measure of coupling (interaction, convolution) of photon's energy, and epsilon and mu properties of the space.
Elementary particle which has inertial mass is the two-photons-whirl.
In absolute sense, we cannot say that the two-photons-whirl is at rest. It is the whirl.
But, theoretically, the
two-photons-whirl as a whole could, at least at the moment immediately after formation, be at absolute rest, meaning, that the kinetic energy of the
whirl as a whole is 0.
Two-photons-whirls cannot be formed by just any photons. A rather strict conditions must be fulfilled for that. One of these conditions is the minimal energy which photons have to have. If they have a bit higher energy than that minimal necessary energy, and if they manage to form the whirl, that whirl as a whole would have kinetic energy >0.
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By the way, there are a few more places where I have presented the FEMME:
http://www.science20.com/forums/theories_everything [nofollow]http://cosmoquest.org/forum/showthread.php?140393-Fundamental-Electro-Magneto-Mechanics-of-Existence-(FEMME [nofollow])