Energy as force applied over distance is the capacity to do work. The law of conservation of energy states that the energy of a closed system should be constant, so if our universe is a closed system it should conserve energy overall.
Yet physics also tells us that our universe is expanding. This means that the wavelength of every photon in it is now a bit longer than it was a moment ago, so it now has a bit less energy than it did before. The cosmic background radiation that was once white hot is now freezing cold because expanding space took its energy and didn’t give it back. That the universe is expanding suggests that it is not closed and that all light loses energy as the universe expands suggests that energy isn’t universally conserved.
The coldness of cosmic background radiation challenges the naïve view that we are in a closed system. A system that constantly expands can’t be closed nor can it have a constant energy because to expand requires energy. The expansion of space is the exception that breaks the rule that energy is universally conserved. Energy is conserved locally, as solar panels, dams and windmills convert radiant, wind and gravitational energy into electricity, but it isn’t universal. Just as the number of bank notes in a country might stay the same while inflation still decreases their value, so the expansion of space devalues energy globally.
Yet the number of free photons is always conserved. When a solar sail turns radiant energy into kinetic energy, the photons go into the matter and so are conserved. When a rocket crashes on Jupiter with more energy than it took to leave the earth, energy isn’t conserved but photons are because the rocket acquires photons from the mass of Jupiter via its gravity. Energy is conserved when photons are conserved, and when energy isn’t conserved, photons are still conserved.
When our universe began, inflation made a finite number of photons that since then have remained constant and the expansion of space didn’t change this. Our universe is made of photons in various forms, whether in light, matter or gravity exchanges, and they are always conserved. In current physics, energy is an abstract that is conserved but in quantum realism actual photons are conserved.
In quantum realism, every physical event is a processing reboot where the processing before and after is the same. Current physics conserves matter, charge, energy, momentum, isospin, quark flavor and color but each “law” is partial, as matter isn’t conserved in nuclear reactions and quark flavor isn’t conserved in weak interactions. Quantum realism suggests that the conservation energy is an aspect of a more fundamental universal conservation, namely the conservation of photons. Physical events come and go but photons are always conserved.