Aug 15, 2024 07:39 PM
https://bigthink.com/starts-with-a-bang/...e-forever/
EXCERPT: . . . Even at its very end, no matter how far into the future we go, the Universe will always continue to produce radiation, ensuring that it will never reach absolute zero, that it will always contain photons, and that even at the lowest energies it will ever reach, there ought to be nothing else for the photon to decay or transition into. Although the energy density of the Universe will continue to drop as the Universe expands, and the energy inherent to any individual photon will continue to drop as time ticks onward and onward into the future, there will never be anything “more fundamental” that they transition into.
There are exotic scenarios we can cook up that will change the story, of course. Perhaps it’s possible that photons really do have a non-zero rest mass, causing them to slow down to slower than the speed of light when enough time passes. Perhaps photons really are inherently unstable, and there’s something else that’s truly massless, like a combination of gravitons, that they can decay into. And perhaps there’s some sort of phase transition that will occur, far into the future, where the photon will reveal its true instability and will decay into a yet-unknown quantum state.
But if all we have is the photon as we understand it in the Standard Model, then the photon is truly stable. A Universe filled with dark energy ensures, even as the photons that exist today redshift to arbitrarily low energies, that new ones will always get created, leading to a Universe with a finite and positive photon number and photon energy density at all times. We can only be certain of the rules to the extent that we’ve measured them, but unless there’s a big piece of the puzzle missing that we simply haven’t uncovered yet, we can count on the fact that photons might fade away, but they’ll never truly die... (MORE - missing details)
EXCERPT: . . . Even at its very end, no matter how far into the future we go, the Universe will always continue to produce radiation, ensuring that it will never reach absolute zero, that it will always contain photons, and that even at the lowest energies it will ever reach, there ought to be nothing else for the photon to decay or transition into. Although the energy density of the Universe will continue to drop as the Universe expands, and the energy inherent to any individual photon will continue to drop as time ticks onward and onward into the future, there will never be anything “more fundamental” that they transition into.
There are exotic scenarios we can cook up that will change the story, of course. Perhaps it’s possible that photons really do have a non-zero rest mass, causing them to slow down to slower than the speed of light when enough time passes. Perhaps photons really are inherently unstable, and there’s something else that’s truly massless, like a combination of gravitons, that they can decay into. And perhaps there’s some sort of phase transition that will occur, far into the future, where the photon will reveal its true instability and will decay into a yet-unknown quantum state.
But if all we have is the photon as we understand it in the Standard Model, then the photon is truly stable. A Universe filled with dark energy ensures, even as the photons that exist today redshift to arbitrarily low energies, that new ones will always get created, leading to a Universe with a finite and positive photon number and photon energy density at all times. We can only be certain of the rules to the extent that we’ve measured them, but unless there’s a big piece of the puzzle missing that we simply haven’t uncovered yet, we can count on the fact that photons might fade away, but they’ll never truly die... (MORE - missing details)