Does light have an infinite lifetime?
bigthink.com
bigthink.com
If they have infinite lifetimes then does each one carry a memory of it's creation event? When I burn a log in my fireplace and a cinder flares and pops creating a spark, does the photon exist after the spark energy flares out and the cinder is no longer illuminated enough to be detected by my eyes?
If photons are infinite then harvesting light would be the first step in deciphering the complete history of the universe. All that would be left for us to do would be to derive the algorithms to unravel and categorize each photon into discrete groups based on their historical particle paths.
If we wanted to harvest light to test whether photons have infinite lifetimes we would need to design a structure that forms a light trap using materials with different refractive indices so that photons entering are forced onto paths from which they perfectly reflect in a lossless manner.
If photons are infinite then mirrors may have a memory if we can trap and monitor the photons that pass through them and force them to unravel their travel paths. Why can't I step in front of the mirror and have it replay every event that the mirror has seen? It would be a better replacement for photo or video mementos of lost loved ones if we could simply take the mirrors from their homes and spin back to watch their happiest moments forever by reconstructing the photon impingement history of the glass and mirror substrate.
He's also careful enough to point out that electrons don't really have an identity that would allow you to meaningfully define "not the same". :)
Or maybe that single electron hadn't quite made it to my battery on my first attempt. That's one busy e.
MBA's took over and cut corners everywhere - sourcing production from subpar isotopes, skimping down how much charge you get in each one, shrinkflation schemes packing less in every bag of amps, particle dilution with off-brand fake leptons... QA was downsized 'till all you got was beta junk that decays in no time. Now they just rent seek that single universal virtual electron, unlocked by keys you're forced to tie to the cloud, and it can be glitchy and pop in and out of existence from time to time especially driving through tunnels. Sorry to hear about your car, try upgrading to the new positron model on the roadmap for next year, they launched the presale NFT last week.
Turns out that an electron funnel isn't a fancy new tool. Instead, I already have several of them in my shop but just didn't make the connection. It became clear though when he handed me the plastic funnel after rubbing it through his hair vigorously for a few seconds and I got shocked by the crackling electrons streaming from the funnel to my fingers.
If this power thing ever happens to my battery again I'm just gonna get the big funnel from the set, rub it through the remnants of my hair and pour some electrons at it till it charges enough to start the engine.
Thanks for this suggestion about a new way to use an old tool.
> an electron
THE electron? /s
A photon jumps into the glass fiber and travels until it encounters an opto-electric coupler where the photon craps out and is converted to an energized stream of electrons, or maybe it borrows the only real electron in the universe for an instant as it flips across the coupler to the next glass fiber where a new photon is born, only to flare out at the next junction.
Isn't it more accurate to say that photons move at the speed of causality, when the medium is a pure vacuum? Because in some other medium like glass, the speed of light is slower than the speed of causality.
So my follow-up question is: do slower photons (such as those propagating through a fiber-optic strand, or water) then experience the advancement of time?
When light enters a medium there are two mostly (but not entirely) equal ways to think about what happens, one is to view light as a purely electromagnetic wave that interacts with atoms and causes the atoms to oscillate. This oscillation produces its own electromagnetic wave that interferes with the original wave. The result of this interference will be an electromagnetic wave with the same frequency, same amplitude, and travelling in the same direction as the incoming light but shifted backwards and it's that shift backwards that gives the appearance of light slowing down.
That explanation is pretty good and accounts for almost everything except for the latency of light through a medium.
If that's what you want to model, then it's better to think of light as made up of photons instead of being a wave, and then when photons enter a material they no longer exist as independent particles but through a process of absorption and reemission by electrons in the material become particles called polaritons. Polaritons do have mass and hence travel slower than the speed of light.
Neither of these explanations are perfect, but the full explanation is ridiculously complicated and there's no suitable metaphor for it. If you are interested in knowing the edge latency of light through a medium, then the polariton explanation is appropriate. If you want to know the "bandwidth" explanation of light through a medium, then the wave explanation is appropriate.
>They cannot change between emission and absorption, no matter the distance.
From the point of view of a photon, neither time or space exist. They have no reference frame at all. However, from an outside frame of reference that is travelling less than the speed of light, photons do change for example they get red shifted as they move through stronger gravitational fields.
One electron theory. https://youtu.be/9dqtW9MslFk?si=qdWGUyJnDRCOns9F
Full text: https://www.physics.utoronto.ca/~jharlow/slowglass.htm
Part of the reason that I initially posted on this thread was to ponder the question about a world where mirrors have a memory function. A mirror with a memory would have perfect fidelity though the image would be a mirror image of reality, like looking into a replay from a mirror image universe. I wrote a poem on that subject a couple years ago and the whole question about photons and their potential infinite existence triggered the memory.
There is no universal time T in space time. Time is relative to the observer.
I suggest reading https://en.wikipedia.org/wiki/Minkowski_space for the mathematics.
If you're in a car on the highway, an observer standing still outside the car sees you moving at 50mph, but an observer inside the car with you, sees you not moving at all, but the world rushing past at 50mph. These are two different reference frames, and the second one is called a rest frame - any object can be considered to have a rest frame of reference where it isn't moving at all. Any object that is, which has mass.
Massless objects are always observed to be moving at the speed of light by any observer in any frame of reference. This is one of the most mind-bending parts of relativity, but it ultimately connects to the part of special relativity where speed affects time - the faster you go, the slower your clock runs compared to things moving slower than you, and the closer you get to the speed of light, the closer your clock gets to zero. Massless particles only travel at the speed of light, and thus have no clock, therefore they experience no time.
I hope I got that right, but even if I did, I still don't feel like I actually understand it at all!
A photon travels between an electron that emits it and an electron that absorbs it. These two electrons must agree on the photon transfer beforehand. This has some strange implications:
- When you see a star at night, it's because photons from the distant star hit your eyes.
- These photons started traveling billions of years ago, when neither you nor your eyes existed yet.
- Yet the electrons in your eyes and the electrons in the star (which may no longer even exist) must have agreed to transfer these photons.
- From the photon's perspective, it traveled instantaneously from the star to your eye; it traveled through billions of years of time!
This doesn’t mean there’s some cross time agreement between particles mediated by the photon because the reference frame of those particles are different than the photons and are necessarily slower than the speed of light.
Reality is stranger than fiction!!
After the xelee and humans leave, the universe becomes a cold place dominated by photino birds living in the cold pinpricks of white dwarfs. Eventually matter evaporates into photons, and the photino birds die.
However, it turns out photino birds can always just time travel to a time when the universe still had matter. So they're more or less indifferent to the eventual heat death .
See: https://xeelee.fandom.com/wiki/Photino_Birds
I hypothesize that there is may be only one photino bird. When it appears to die, it is just traveling to another time. When we see multiple photino birds, we're just looking at different segments of the same bird's world line. These are my own speculations, inspired by Wheeler's idea that the universe has only one electron, which travels back in time as a positron, and interacts with itself so many times that it creates the observable universe of matter:
Where is this described in the books? I don't remember the Photino Birds having this ability.
If neutrinos are their own antiparticle then they could react with each other and produce ??? Not sure, because you would have to find out of the lepton number is conserved.
Definitely.
> [link] is a good overview
That overview seems to overstate the likelihood of proton decay. In fact, it has it backwards. The default position is that protons are stable, per the standard model, not that they're susceptible to decay.
It's only the "default" in the sense that the simplest model explaining data gathered to date (the standard model) predicts no decay. However, most physicist do not believe the standard model is the last word (and surely it cannot be when you go to the Planck scale), and many models post-SM models predict proton decay. I would guess if you surveyed high energy physicists, you'd find the majority expect the proton does in fact decay, so it's the "default" in that sense.
I don't think it's the case that many post-SM models predict proton decay. A few do, but even those are now tightly constrained by observations that place the proton's half life at more than 10^34 years. A lot of models that previously predicted proton decay have been empirically falsified on such grounds, and those that remain are looking pretty shaky. So I don't know. If you run that survey, I believe that the average physicist would come out against proton decay. It would be an interesting survey, in any case!!
It seems the paper made mistakes, using a non-standard model of the CMB that failed upon replication. It's an interesting theory thoughb.
None of this stuff is “real”, but boy does the bookkeeping seem to work out...
Interesting take! But if photons couldn't decay due to not experiencing time, they couldn't do anything else either.
The reality is that a photons creation and destruction are not prohibited, but simply "experienced" as two events at different locations at the same time, with the photon being the "thing" that connects those events.
Given that interpretation, it might be reasonable to assume that all photons have beginnings and ends, regardless of the duration we perceive between them, or they wouldn't exist.
Time being no barrier at all for photons.
Not only does the photon not experience any delay between its two end points, but it experiences its path between them as a simple shortest-distance straight line segment, even if the same path looks like a curve through gravitationally warped space-time to us.
The photon does experience a form of distance, i.e. the number of wave lengths between its ends. But just the number of cycles, not the actual wave lengths which we would see varying as we experienced dark energy and space stretching the photon's wavelength from our viewpoint.
So a photon "experiences" two spacially separated ends, and a number of wave cycles between them, and that's it? Perhaps.
I mean we are jumping way out of the classical behavior that objects like you and I exist in. To the photon itself is a timeless object. It 'moves' in a null geodesic where t=0. Attempting to apply any classical behavior that occurs in time-like objects just isn't going to work when applying them to massless light-like objects.
While from our perspective it is a form of causal connection, that is mearly due to the frame of reference.
While we can infer the connection between each, it is possibly better to consider the speed of light as the speed of causality.
But as there are no privileged reference frames under GR the choice is yours.
But from the photons perspective, it doesn't experience time at all so it can't be a barrier.
But don't confuse the map for the territory. GR is a model, not the system itself.
The fact that almost every test we can figure out has only confirmed it doesn't change that.
Under the 'all models are wrong but some are useful' idea, in GR photons not experiencing time is important to that model.
I also seem to recall that the speed of light below c is actually the group velocity, and each individual photon still would move at c. I'm also not entirely sure if photons can be said to exist except at creation and absorption; isn't a photon a phenomenon best described by particle interactions, and moving through free space it's more correctly described as a field? Genuine question, though I somehow doubt I'd understand any good elaboration.
IANAPhysicist, though. I just play with light recreationally.
3Blue1Brown - But why would light "slow down"? | Optics puzzles 3: https://m.youtube.com/watch?v=KTzGBJPuJwM
lets take two magical particles that have clocks on it. One is a photon and the other is a neutrino. I send these off towards you in a perfect vacuum. When you receive these particles the clock on the photon will be 0. It will be be the exact same photon that left my emitter, it will not have changed in any way as it did not interact with anything along the way. And as long as you are not moving relative to me, you'll perceive the photon as the same color/wavelength I emitted it at.
Meanwhile that neutrino will arrive billions of a second later (well depending on our distance) and will have oscallated at least trillions of times if not far more. The clock on the neutrino will have ticked the difference between the photon arrival to the neutrino arrival.
Don't apply classical behavior to light-like objects. They play be different sets of rules.
[0] General relativity has no preferred “at rest” frame, but the generally accepted FLRW model of the universe does. You can be at rest with respect to the universe, or you can be moving. If you are moving, distant objects in front of you will appear blue-shifted on average as compared to distant objects behind you.
From the point of view of the photon, time doesn't even exist. So it is pointless to ask the question from the point of view of the photon.
The Lorentz transformations are defined only between reference systems where the relative speed between them is less than the speed of light.
It is not possible to attach a reference system to a photon or to any other particle that moves with the speed of light, because there are no conversion rules between the coordinates in such a system and those in a normal reference system.
Therefore it is not correct to say that the lifetime of a photon in a reference system attached to it is zero or infinite or it has any other value.
This lifetime is just undefined, while the lifetimes in any other reference systems are well defined.
The photon does not decay in the absence of interactions with other particles because that would violate several conservation laws. However, when the photons have energies that are high enough, the interaction between themselves can generate other particles, in particle-antiparticle pairs, in order to satisfy all conservation laws.
Like I have said, the formulae of a Lorentz transformation are defined only when the relative velocity between the two systems is less than the speed of light.
Attempting to pass to a limit when the relative speed approaches the speed of light does not produce any useful result, because at the limit you no longer obtain a reference system, so you no longer get a transformation between reference systems.
Without a reference system, there is no meaning for the concepts of distance and time.
Any reference system for the 4-dimensional space-time must be attached to normal matter made of leptons and quarks, it cannot be attached to photons. In any reference system for the 4-dimensional space-time, the photons are particles that move with equal speeds in space and in time, while the normal matter moves faster in time than in space. The notion of proper time (i.e. the time measured for an object that moves only in time, without moving in space) is not defined for photons, because they always also move in space, not only in time.
This should be obvious from the rule introduced by Einstein that the speed of light is the same in all possible reference systems, from which the Lorentz transformations can be deduced. If a reference system were attached to a photon, in that reference system the speed of light could not have the same value as in the normal reference systems, so within Einstein's theory such a reference system cannot exist.
If light is emitted and absorbed at the same instant, how does it know when/where in spacetime it's been emitted and absorbed?
You cannot apply SR to light in this naive way. SR works just fine for anything with mass, but without a theory of quantum gravity no one has the first clue how massless particles operate in spacetime, or what they do or don't "experience."
That's a common misconception, there's no a priori reason a particle without a restframe can't decay. For all known particles with a finite lifetime we give this lifetime as measured in its restframe (i.e. with the particle standing still), but in principle it is an observer-dependent quantity, faster moving particles will take longer to decay. If we, for example, assume the lifetime of a massless particle is proportional to its energy, we retain the same expected Lorentz covariance.
Of course, if you actually go through the math, the known massless particles in our universe, photons and gluons, turn out to be stable.[1]
The passage discusses whether photons, the quantum particles of light, have a finite or infinite lifetime. It explains that while photons can be created and destroyed through various interactions, they cannot truly be "killed off" entirely. Even as the universe expands and photons redshift to lower and lower energies, new photons will continue to be produced, ensuring that photons will always exist in some form. The passage also dismisses the "tired light" hypothesis as a way for photons to lose energy, as it is not supported by observational evidence. Overall, the passage concludes that based on our current understanding of physics, photons appear to have an infinite lifetime and will continue to exist in the universe indefinitely.
So at the risk of venting unconstructively, I wish I had a way of screening physics writing that is not a physics paper. Articles like this are frustrating because they only have one or two interesting tidbits for me, but they hide them in a whole lot of highschool level hand waving.
Honestly HN would be perfect if it only allowed physics papers - no pop-physics - and if it banned any blogs or news sites with paywalls or newsletter nagware (looking at you, medium, new york times).
Alas. I'm wishing for something I will have to build if I really want it.
The fact that someone reading Genesis would have had a more accurate conception of the origin of the universe, prior to big bang becoming popularized very recently in the grand scheme of things is noteworthy.
God sent a man, John the Baptist, to tell about the light so that everyone might believe because of his testimony. John himself was not the light; he was simply a witness to tell about the light. The one who is the true light, who gives light to everyone, was coming into the world.
He came into the very world he created, but the world didn’t recognize him. He came to his own people, and even they rejected him. But to all who believed him and accepted him, he gave the right to become children of God."(John 1:5-12)
To be clear, light is a very common metaphor for G-dliness in Judaism and the quote from John resonates as a perfectly fine metaphor, rather than a literal assertion of equivalence.
[0] "וַיֹּ֥אמֶר אֱלֹהִ֖ים יְהִי־א֑וֹר וַֽיְהִי־אֽוֹר"