How will the Debt of Gravitational Energy manifest itself at the end of the Universe when it is time to repay?

IF (a mighty big if) the rate of expansion continues to increase, we will reach a point where even atoms will not be able to remain together (because space expands everywhere, including inside atoms). The binding energy will be carried away as a photon (or some boson, maybe) while mass will slowly disappear as hadrons will be split into quarks and the quarks themselves into... (we do not know what, yet).

There will come a point, in a few gazillion years, where expansion will be so fast that each individual photon of energy remaining will be alone in its own "light cone", unable to perceive anything from even the nearest photon. At that point, there will be no gravitational gradient anywhere within any of the "Observable universes" (each one containing one single photon). As expansion continues, the wavelength of each lone photon continues to increase (expansion of space takes place everywhere, including "inside" the photon) so that its energy content decreases.

Will the energy content of the photon be asymptotic to zero? If so, its effect (if it has any) on the Higgs field will also be asymptotic to zero, thereby bringing the gravitational energy content (the negative value in the equation) also asymptotically close to zero.

This is the best guess (until the next guess) as to what happens to the "debt".

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I wonder if there is a debt. We do WORK to increase gravitational potential energy, or give up kinetic energy to increase the potential energy. Is that a debt situation? I really don't know, but don't think so. No, I'm not an expert like Sagan, Clarke and Hawking, but sometimes we find ourselves practicing outside our area of competence. Would you want a physician to maintain your airliner, or an aircraft mechanic to do brain surgery? No... but we have theologians who tell us about science and scientists who tell us about theology, which may be similar.

Gravity is not a force, so the only energy is frictional when infalling bodies are braked to a common momentum.

That is also why Dark Energy is no sort of energy...

Do not let loose talk distract you.

What debt? Gravity didn't sign any contract and has absolutely no intention of paying anything back. Gravity knows its rights.

In Hill.