Research Does light itself truly have an infinite lifetime?

[C C]

https://bigthink.com/starts-with-a-bang/...-lifetime/

KEY POINTS: In the expanding Universe, for billions upon billions of years, the photon seems to be one of the very few particles that has an apparently infinite lifetime. Photons are the quanta that compose light, and in the absence of any other interactions that force them to change their properties, are eternally stable, with no hint that they would transmute into any other particle. But how well do we know this to be true, and what evidence can we point to in order to determine their stability? It's a fascinating question that pushes us right to the limits of what we can scientifically observe and measure.

EXCERPTS: . . . While these observations are good enough to falsify the tired light hypothesis — and, in fact, were good enough to falsify it immediately, as soon as it was proposed — that’s only one possible way that light could be unstable. Light could either die out or convert into some other particle, and there’s a set of interesting ways to think about these possibilities.

The first arises simply from the fact that we have a cosmological redshift. Each and every photon that’s produced, irrespective of how it’s produced, whether thermally or from a quantum transition or from any other interaction, will stream through the Universe until it collides and interacts with another quantum of energy. But if you were a photon emitted from a quantum transition, unless you can engage in the inverse quantum reaction in rather rapid fashion, you’re going to begin traveling through intergalactic space, with your wavelength stretching due to the Universe’s expansion as you do. If you’re not lucky enough to be absorbed by a quantum bound state with the right allowable transition frequency, you’ll simply redshift and redshift until you’re below the longest possible wavelength that will ever allow you to be absorbed by such a transition ever again.

However, there’s a second set of possibilities that exists for all photons: they can interact with an otherwise free quantum particle, producing one of any number of effects. [...] In other words, even very low-energy photons can be converted into other particles — non-photons — by colliding with another high-enough-energy particle.

There’s yet a third way to alter a photon beyond cosmic expansion or through converting into particles with a non-zero rest mass: by scattering off of a particle that results in the production of still additional photons...

[...] The fourth-and-final factor of two comes from the cosmological expansion, which stretches the wavelength to double its original wavelength, thereby halving the energy-per-photon. On long enough timescales, this will cause the energy density of the Universe in the form of photons to asymptotically drop toward zero, but it will never quite reach it...

[...] So will they ever die out? Not according to the currently understood laws of physics. In fact, the situation is even more dire than you probably realize. You can think of every photon that was or will be:

• created in the Big Bang,
  
• created from quantum transitions,
  
• created from radiative corrections,
  
• created through the emission of energy,
  
• or created via black hole decay,
  

and even if you wait for all of those photons to reach arbitrarily low energies due to the Universe’s expansion, the Universe still won’t be devoid of photons.

Why’s that? Because the Universe still has dark energy in it... (MORE - missing details)

[Magical Realist]

"Eidolons"

By Walt Whitman

"I met a seer,
Passing the hues and objects of the world,
The fields of art and learning, pleasure, sense,
To glean eidolons.

Put in thy chants said he,
No more the puzzling hour nor day, nor segments, parts, put in,
Put first before the rest as light for all and entrance-song of all,
That of eidolons.

Ever the dim beginning,
Ever the growth, the rounding of the circle,
Ever the summit and the merge at last, (to surely start again,)
Eidolons! eidolons!

Ever the mutable,
Ever materials, changing, crumbling, re-cohering,
Ever the ateliers, the factories divine,
Issuing eidolons.

Lo, I or you,
Or woman, man, or state, known or unknown,
We seeming solid wealth, strength, beauty build,
But really build eidolons.

The ostent evanescent,
The substance of an artist’s mood or savan’s studies long,
Or warrior’s, martyr’s, hero’s toils,
To fashion his eidolon.

Of every human life,
(The units gather’d, posted, not a thought, emotion, deed, left out,)
The whole or large or small summ’d, added up,
In its eidolon.

The old, old urge,
Based on the ancient pinnacles, lo, newer, higher pinnacles,
From science and the modern still impell’d,
The old, old urge, eidolons.

The present now and here,
America’s busy, teeming, intricate whirl,
Of aggregate and segregate for only thence releasing,
To-day’s eidolons.

These with the past,
Of vanish’d lands, of all the reigns of kings across the sea,
Old conquerors, old campaigns, old sailors’ voyages,
Joining eidolons.

Densities, growth, facades,
Strata of mountains, soils, rocks, giant trees,
Far-born, far-dying, living long, to leave,
Eidolons everlasting.

Exalte, rapt, ecstatic,
The visible but their womb of birth,
Of orbic tendencies to shape and shape and shape,
The mighty earth-eidolon.

All space, all time,
(The stars, the terrible perturbations of the suns,
Swelling, collapsing, ending, serving their longer, shorter use,)
Fill’d with eidolons only.

The noiseless myriads,
The infinite oceans where the rivers empty,
The separate countless free identities, like eyesight,
The true realities, eidolons.

Not this the world,
Nor these the universes, they the universes,
Purport and end, ever the permanent life of life,
Eidolons, eidolons.

Beyond thy lectures learn’d professor,
Beyond thy telescope or spectroscope observer keen, beyond all mathematics,
Beyond the doctor’s surgery, anatomy, beyond the chemist with his chemistry,
The entities of entities, eidolons.

Unfix’d yet fix’d,
Ever shall be, ever have been and are,
Sweeping the present to the infinite future,
Eidolons, eidolons, eidolons.

The prophet and the bard,
Shall yet maintain themselves, in higher stages yet,
Shall mediate to the Modern, to Democracy, interpret yet to them,
God and eidolons.

And thee my soul,
Joys, ceaseless exercises, exaltations,
Thy yearning amply fed at last, prepared to meet,
Thy mates, eidolons.

Thy body permanent,
The body lurking there within thy body,
The only purport of the form thou art, the real I myself,
An image, an eidolon.

Thy very songs not in thy songs,
No special strains to sing, none for itself,
But from the whole resulting, rising at last and floating,
A round full-orb’d eidolon."

[Zinjanthropos]

Have no time right now to look this up…..Never heard this asked so I might as well ask it….could light be causing the expansion of the universe? At the same time could light be making space out of nothing? I would think a good chunk of the first photons could still be out there, way out there, the leading edge of an expanding universe.

[C C]

Have no time right now to look this up…..Never heard this asked so I might as well ask it….could light be causing the expansion of the universe? At the same time could light be making space out of nothing? I would think a good chunk of the first photons could still be out there, way out there, the leading edge of an expanding universe.

As far as "just-so" theories go (due to nothing better to plug into a slot), the inflaton field (of cosmological inflation) drove the initial, rapid expansion. And it was "coasting" slower until six billion years ago when the effects of supposed dark energy became stronger or overtook the gradual weakening and began accelerating it again.

https://www.astronomy.com/science/the-be...he-cosmos/

Inflation puts the “bang” in the Big Bang, courtesy of a strange substance: a field called the inflaton, which acts as a source of antigravity, and propels the universe’s exponential, accelerated expansion — albeit only briefly.

Locally, the universe is expanding slower than the speed of light, but incrementally acquires the appearance of expanding faster than light the farther the distance from us. (If one were actually at one of those distant points, it would instead be similar to local.)

https://www.space.com/33306-how-does-the...light.html

The notion of the absolute speed limit comes from special relativity, but who ever said that special relativity should apply to things on the other side of the universe? That's the domain of a more general theory. A theory like…general relativity.

It's true that in special relativity, nothing can move faster than light. But special relativity is a local law of physics. Or in other words, it's a law of local physics. That means that you will never, ever watch a rocket ship blast by your face faster than the speed of light. Local motion, local laws.

But a galaxy on the far side of the universe? That's the domain of general relativity, and general relativity says: who cares! That galaxy can have any speed it wants, as long as it stays way far away, and not up next to your face.

It goes deeper than this. Concepts like a well-defined "velocity" make sense only in local regions of space. You can only measure something's velocity and actually call it a "velocity" when it's nearby and when the rules of special relativity apply. Stuff super-duper far away, like the galaxies we're talking about it? If it's not close, it doesn't count as a “velocity” in the way that special relativity cares about.

[confused2]

Have no time right now to look this up…..Never heard this asked so I might as well ask it….could light be causing the expansion of the universe? At the same time could light be making space out of nothing? I would think a good chunk of the first photons could still be out there, way out there, the leading edge of an expanding universe.

As far as "just-so" theories go (due to nothing better to plug into a slot), the inflaton field (of cosmological inflation) drove the initial, rapid expansion. And it was "coasting" slower until six billion years ago when the effects of supposed dark energy became stronger or overtook the gradual weakening and began accelerating it again.

https://www.astronomy.com/science/the-be...he-cosmos/

Inflation puts the “bang” in the Big Bang, courtesy of a strange substance: a field called the inflaton, which acts as a source of antigravity, and propels the universe’s exponential, accelerated expansion — albeit only briefly.

Locally, the universe is expanding slower than the speed of light, but incrementally acquires the appearance of expanding faster than light the farther the distance from us. (If one were actually at one of those distant points, it would instead be similar to local.)

https://www.space.com/33306-how-does-the...light.html

The notion of the absolute speed limit comes from special relativity, but who ever said that special relativity should apply to things on the other side of the universe? That's the domain of a more general theory. A theory like…general relativity.

It's true that in special relativity, nothing can move faster than light. But special relativity is a local law of physics. Or in other words, it's a law of local physics. That means that you will never, ever watch a rocket ship blast by your face faster than the speed of light. Local motion, local laws.

But a galaxy on the far side of the universe? That's the domain of general relativity, and general relativity says: who cares! That galaxy can have any speed it wants, as long as it stays way far away, and not up next to your face.

It goes deeper than this. Concepts like a well-defined "velocity" make sense only in local regions of space. You can only measure something's velocity and actually call it a "velocity" when it's nearby and when the rules of special relativity apply. Stuff super-duper far away, like the galaxies we're talking about it? If it's not close, it doesn't count as a “velocity” in the way that special relativity cares about.

If it's not close, it doesn't count as a “velocity” in the way that special relativity cares about.

Humff.
I have no idea why space is expanding (at an increasing rate) but an interest in understanding the consequences. This is the best I can do..
If we go with "events are where they are when they happen" then events get shifted by the expansion of spacetime 'then'. More recent events can be shifted further away by the increased rate of expansion of space than older events.

There's a particle horizon ( https://en.wikipedia.org/wiki/Particle_horizon ) which is the maximum distance light from an event could reach us at the speed of light.

There seems to be a much more subtle horizon with something in common with looking out of a black hole .. I need more time on this.