It seems like whenever we talk about "released" energy the assumed form of that energy is electromagnetic radiation. Is it possible for "energy" that appears in any theory or process to exist in any form that is not:

  1. A photon, or
  2. A particle with non-zero mass, or
  3. Embodied in the relationship between massive particles with respect to some "fundamental force" (i.e., nuclear force binding, or space-time relative position or velocity)
  • $\begingroup$ Is potential energy allowed? $\endgroup$ – David White Jul 13 '17 at 18:35
  • $\begingroup$ You leave only gravitational interaction :-) $\endgroup$ – LLlAMnYP Jul 13 '17 at 18:37
  • $\begingroup$ @DavidWhite - Yes, I assume potential energy (including gravitational) would be encompassed in #3. $\endgroup$ – feetwet Jul 13 '17 at 18:46

Yes, dark energy is an example of energy that does not match any of the possibilities you mentioned. Actually we do not even know what it is.

The important thing to keep in mind is that energy (and its conservation law) is just an abstract idea that works as a bookkeeping device. There is no way to measure energy directly and what we do is just to observe processes and assign them a given amount of energy. By assuming that the total amount of energy is constant we can predict the possible processes in a system and whenever an unexpected process outcome (with respect to energy balance) we may suppose that the initial assumptions about processes/energies relation were wrong. That is so energy can show up in so many forms such as kinetic, gravitational, elastic, chemical, heat, electrical, radiation, rest mass, dark energy, etc.

  • $\begingroup$ It sounds like you're saying, "Yes, all known forms of energy are encompassed in the three categories you listed. We have observed some things that only make sense if there is a another form of energy we call "dark energy." But we don't have any direct knowledge of its embodiment. $\endgroup$ – feetwet Jul 13 '17 at 19:54
  • $\begingroup$ @feetwet That's correct. $\endgroup$ – Diracology Jul 16 '17 at 13:51

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