A photon's point of view and the future of the Universe

[starbrush]

Talk of the fate of Betelgeuse got me thinking (again) about how a photon 'sees' the Universe. With the time-dilation of lightspeed a photon should experience its emission, and reception somewhere, somewhen, as an indivisible 'event' without duration or distance. For our part, we tend to think of the photon as having a journey, from A to B.
if it's true that a photon cannot be emitted unless it is received - i.e. that its 'event' cannot be 'unfulfilled' - does that offer us any clues about what we perceive as the future of the Universe?
It has been proposed that the exponentially expanding Universe will eventually 'go dark' because light will never make it across the ballooning distances. But this would entail unfulfilled photon events. The known material in the Universe is ever thinning out with expansion, thus further reducng the opportunities for a photon's interaction with matter. But evry photon must have its fulfilment.
That's the corner I've painted myself into!
Consider the last photon in the Universe, being fulfilled by an encounter with the last atom in the Universe. Then what? Does the last atom just sleep the sleep of zero Kelvin, or eventually decay? If it decays then I'd expect new photons, themselves needng fulfilment in turn.
Might these quantum-worldly notions of 'fulfilment' extend to, e.g., sub-lightspeed neutrinos? These hardly interact ta all with known mattter, and the opportunities to do so will become ever rarer with cosmic expansion; the timescales are hard to imagine.
A supernova's photons - indeed all the photons whizzing around in the Universe since the Big Bang - seem to require fulfilment: from their viewpoint in an indivisible instant; and from ours in possibly vast spans of time.

[BDanielMayfield]

Since no one else has replied I'll see if I can help starbrush. The whole crux of your dilemma arises from the proposition that "a photon cannot be emitted unless it is received". If that is false then your problem is resolved.

IMHO the idea that 'every photon requires fulfillment' is nonsense. In an infinitely large universe a photon could indeed travel forever without ever hitting anything. But really I think the size of the universe is irrelevant in this matter. Cause (a photon's emission) is independent of effect (a photon's absorption, etc.).

[Chris Peterson]

Since no one else has replied I'll see if I can help starbrush. The whole crux of your dilemma arises from the proposition that "a photon cannot be emitted unless it is received". If that is false then your problem is resolved.

IMHO the idea that 'every photon requires fulfillment' is nonsense. In an infinitely large universe a photon could indeed travel forever without ever hitting anything. But really I think the size of the universe is irrelevant in this matter. Cause (a photon's emission) is independent of effect (a photon's absorption, etc.).

What QM teaches us is that certain properties of a photon are poorly defined or exist in multiple simultaneous states until the photon is observed. It does not suggest that the photon doesn't exist until it is observed.

[BDanielMayfield]

Since no one else has replied I'll see if I can help starbrush. The whole crux of your dilemma arises from the proposition that "a photon cannot be emitted unless it is received". If that is false then your problem is resolved.

IMHO the idea that 'every photon requires fulfillment' is nonsense. In an infinitely large universe a photon could indeed travel forever without ever hitting anything. But really I think the size of the universe is irrelevant in this matter. Cause (a photon's emission) is independent of effect (a photon's absorption, etc.).

What QM teaches us is that certain properties of a photon are poorly defined or exist in multiple simultaneous states until the photon is observed. It does not suggest that the photon doesn't exist until it is observed.

Nice explanation.

[neufer]

In an infinitely large universe a photon could indeed travel forever without ever hitting anything. But really I think the size of the universe is irrelevant in this matter. Cause (a photon's emission) is independent of effect (a photon's absorption, etc.).

What QM teaches us is that certain properties of a photon are poorly defined or exist in multiple simultaneous states until the photon is observed. It does not suggest that the photon doesn't exist until it is observed.

<<Roger Penrose proposes that a quantum state remains in superposition until the difference of space-time curvature attains a significant level. It is an alternative to the Copenhagen interpretation, which posits that superposition fails when an observation is made (but that it is non-objective in nature), and the many-worlds interpretation, which states that alternative outcomes of a superposition are equally "real", while their mutual decoherence precludes subsequent observable interactions.

Penrose's idea is a type of objective collapse theory. For these theories, the wavefunction is a physical wave, which experiences wave function collapse as a physical process, with observers not having any special role. Penrose theorises that the wave function cannot be sustained in superposition beyond a certain energy difference between the quantum states. He gives an approximate value for this difference: a Planck mass worth of matter, which he calls the "'one-graviton' level". He then hypothesizes that this energy difference causes the wave function to collapse to a single state, with a probability based on its amplitude in the original wave function, a procedure derived from standard quantum mechanics. Penrose's "'one-graviton' level" criterion forms the basis of his prediction, providing an objective criterion for wave function collapse.

Accepting that wavefunctions are physically real, Penrose believes that matter can exist in more than one place at one time. In his opinion, a macroscopic system, like a human being, cannot exist in more than one place for a measurable time, as the corresponding energy difference is very large. A microscopic system, like an electron, can exist in more than one location significantly longer (thousands of years), until its space-time curvature separation reaches collapse threshold.

Wavefunctions collapse when inextricably entangled with the environment

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In Einstein's theory, any object that has mass causes a warp in the structure of space and time around it. This warping produces the effect we experience as gravity. Penrose points out that tiny objects, such as dust specks, atoms and electrons, produce space-time warps as well. Ignoring these warps is where most physicists go awry. If a dust speck is in two locations at the same time, each one should create its own distortions in space-time, yielding two superposed gravitational fields. According to Penrose's theory, it takes energy to sustain these dual fields. The stability of a system depends on the amount of energy involved: the higher the energy required to sustain a system, the less stable it is. Over time, an unstable system tends to settle back to its simplest, lowest-energy state: in this case, one object in one location producing one gravitational field. If Penrose is right, gravity yanks objects back into a single location, without any need to invoke observers or parallel universes.

Penrose speculates that the transition between macroscopic and quantum states begins at the scale of dust particles (the mass of which is close to a Planck mass). He has proposed an experiment to test this theory, called FELIX (free-orbit experiment with laser interferometry X-rays), in which an X-ray laser in space is directed toward a tiny mirror, and fissioned by a beam splitter from tens of thousands of miles away, with which the photons are directed toward other mirrors and reflected back. One photon will strike the tiny mirror moving en route to another mirror and move the tiny mirror back as it returns, and according to conventional quantum theories, the tiny mirror can exist in superposition for a significant period of time. This would prevent any photons from reaching the detector. If Penrose's hypothesis is correct, the mirror's superposition will collapse to one location in about a second, allowing half the photons to reach the detector. However, because this experiment would be difficult to arrange, a table-top version that uses optical cavities to trap the photons long enough for achieving the desired delay has been proposed instead.>>

[THX1138]

Wow, just wow.

[starbrush]

These are great. Thanks, all. I do still wonder if, for a photon travelling at 'c', an enormous journey (as we describe it) in the future Universe would nevertheless seem (to the photon) to be an instant. Anyway, I can't ask any photon for its opinion and, as you'll no doubt have guessed, I'm not that mathematically fluent.
Since I wrote, there was a fine programme on (UK) BBC4 last week about Einstein's Quantum Riddle - entanglement. I think it was on PBS America first. Anyone enjoy it?

[Chris Peterson]

These are great. Thanks, all. I do still wonder if, for a photon travelling at 'c', an enormous journey (as we describe it) in the future Universe would nevertheless seem (to the photon) to be an instant. Anyway, I can't ask any photon for its opinion and, as you'll no doubt have guessed, I'm not that mathematically fluent.
Since I wrote, there was a fine programme on (UK) BBC4 last week about Einstein's Quantum Riddle - entanglement. I think it was on PBS America first. Anyone enjoy it?

Consider this: as a photon travels through an expanding universe, its wavelength changes. Locally, at least, it loses energy. (Where this energy goes leads to some very complex, and not well resolved physics. It may be conserved gravitationally, or it may not be conserved at all. An interesting problem.) This increasing wavelength is local to the frame of the photon- it does not depend upon the observer when the photon is finally absorbed at some point. If the properties of the photon are changing over time, it's hard to imagine how the photon itself can't be "aware" of the passage of time as it travels.

[neufer]

These are great. Thanks, all. I do still wonder if, for a photon travelling at 'c', an enormous journey (as we describe it) in the future Universe would nevertheless seem (to the photon) to be an instant. Anyway, I can't ask any photon for its opinion and, as you'll no doubt have guessed, I'm not that mathematically fluent.

A photon is a rather ephemeral entity.

A neutrino from the Big Bang, however, is now less than 14 years old [= 13.8 x 10⁹/sqrt(2 x 5.6 x 10^-19)].

<<Lorentz violating frameworks such as the Standard-Model Extension including Lorentz-violating neutrino oscillations allow for indirect determinations of deviations between light speed and neutrino speed by measuring their energy and the decay rates of other particles over large distances. By this method, such as by Stecker et al.:

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[Ann]

A photon is a rather ephemeral entity.

A neutrino from the Big Bang, however, is now less than 14 years old [= 13.8 x 10⁹/sqrt(2 x 5.6 x 10^-19)].

<<Lorentz violating frameworks such as the Standard-Model Extension including Lorentz-violating neutrino oscillations allow for indirect determinations of deviations between light speed and neutrino speed by measuring their energy and the decay rates of other particles over large distances. By this method, such as by Stecker et al.:

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What you said about the age of a neutrino is amazing and totally incomprehensible to me. Don't bother explaining, though, because math idiots are math idiots because they can't wrap their heads around equations.

But hey, you said,

A photon is a rather ephemeral entity.

So you're saying that when we see the Andromeda Galaxy in the sky, we're not seeing photons that are more than 2 million years old? And when the Planck telescope observed the cosmic microwave background, it did not detect photons that were more than 13 billion years old?

Ann

[Chris Peterson]

A photon is a rather ephemeral entity.

A neutrino from the Big Bang, however, is now less than 14 years old [= 13.8 x 10⁹/sqrt(2 x 5.6 x 10^-19)].

<<Lorentz violating frameworks such as the Standard-Model Extension including Lorentz-violating neutrino oscillations allow for indirect determinations of deviations between light speed and neutrino speed by measuring their energy and the decay rates of other particles over large distances. By this method, such as by Stecker et al.:

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What you said about the age of a neutrino is amazing and totally incomprehensible to me. Don't bother explaining, though, because math idiots are math idiots because they can't wrap their heads around equations.

But hey, you said,

A photon is a rather ephemeral entity.

So you're saying that when we see the Andromeda Galaxy in the sky, we're not seeing photons that are more than 2 million years old? And when the Planck telescope observed the cosmic microwave background, it did not detect photons that were more than 13 billion years old?

It's rather unclear on what it means to refer to the age of a photon. It is better to say that you're seeing a photon that was emitted some period of time ago. Those aren't necessarily equivalent.

(As a secondary issue, a photon traveling in a medium undergoes scattering, which in this case means the photon is absorbed and another one emitted. Even the interstellar medium isn't a perfect vacuum, and certainly the last of a photon's travel, through the atmosphere, and then through the structure of your eye, means that the actual photon that hits your retina will not be the same one that was emitted by the distant object.)

[Ann]

It's rather unclear on what it means to refer to the age of a photon. It is better to say that you're seeing a photon that was emitted some period of time ago. Those aren't necessarily equivalent.

(As a secondary issue, a photon traveling in a medium undergoes scattering, which in this case means the photon is absorbed and another one emitted. Even the interstellar medium isn't a perfect vacuum, and certainly the last of a photon's travel, through the atmosphere, and then through the structure of your eye, means that the actual photon that hits your retina will not be the same one that was emitted by the distant object.)

Thanks, Chris, that makes the "age of a photon issue" a lot clearer.

Ann

[neufer]

A photon is a rather ephemeral entity.

So you're saying that when we see the Andromeda Galaxy in the sky, we're not seeing photons that are more than 2 million years old? And when the Planck telescope observed the cosmic microwave background, it did not detect photons that were more than 13 billion years old?

ephemera (n.) late 14c., originally a medical term, from Medieval Latin ephemera (febris) "(fever) lasting a day," from fem. of ephemerus, from Greek ephemeros "daily, for the day," also "lasting or living only one day, short-lived," from epi "on" (see epi-) + hemerai, dative of hemera "day." Sense extended 17c. to short-lived insects (Modern Latin ephemera musca) and flowers; general sense of "thing of transitory existence" is first attested 1751. Compare Greek ephemeroi "men," literally "creatures of a day."

Perhaps I should have said that a photon is a rather unsubstantial (mass less) entity about whose sentient qualities I wouldn't spend a minute of my time contemplating. (Einstein might contemplate catching up to a photon but would never try to imagine being one.)

Now, a neutrino OTOH is something that I can relate to.