[HN Gopher] Does light have an infinite lifetime?
___________________________________________________________________
Does light have an infinite lifetime?
Author : robertn702
Score : 88 points
Date : 2024-04-19 17:15 UTC (5 hours ago)
(HTM) web link (bigthink.com)
(TXT) w3m dump (bigthink.com)
| gwern wrote:
| Interesting. I had no idea that the universe would eventually be
| basically just photons. I wonder if that is why Stephen Baxter
| had his 'photino birds' as the final form of life in his
| Xeeleverse?
| mensetmanusman wrote:
| There is some debate whether this is knowable, some particles
| are not believed to decay into light at a rate faster than
| their spontaneous creation from light. (And humanity wont be
| around to check).
| barfbagginus wrote:
| The photino birds want the universe to be populated with white
| dwarfs, because they can feed off their gravity wells without
| the risk of deadly supernovas and black holes, which can kill
| them.
|
| 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:
|
| https://en.m.wikipedia.org/wiki/One-electron_universe
| codyd51 wrote:
| One potential hiccup with your one-photino-bird-universe
| theory (which is quite fun!): I believe I remember a scene in
| which the 'birth' of a photino bird was described. If I
| remember correctly, it was indeed described as a clone of its
| parent.
| kloop wrote:
| As long as we only see one birth, that's probably fine. It
| just implies a stable time loop.
| cwillu wrote:
| I believe proton decay is still considered hypothetical, and
| the electron is pretty confidently believed to be stable;
| https://profmattstrassler.com/articles-and-posts/particle-ph...
| is a good overview.
| ars wrote:
| If protons do decay, their decay product would include a
| positron that would in turn annihilate with the electron.
| Leaving a universe with just photons and neutrinos.
|
| 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.
| A_D_E_P_T wrote:
| > I believe proton decay is still considered hypothetical
|
| 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.
| jessriedel wrote:
| > 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.
| zem wrote:
| a truly beautiful exploration of that idea is landis's "the
| melancholy of infinite space":
| http://www.geoffreylandis.com/infinite.htp
| prettydeep wrote:
| Roger Penrose has a theory about a cyclical conformal universe,
| which requires that the universe eventually only contains
| photons. As photons travel at the speed of light, they do not
| experience the passage of time, so they also do not experience
| distance (space). So in the deep remote future, when only
| photons are left, the difference between the very large and
| miniscule disappears, and you get all photons in the universe
| existing at the same point at the same time, which causes a new
| big bang. At least, that is Penrose's theory. I believe they
| found some evidence in the CMB supporting it.
| AlexAndScripts wrote:
| https://en.m.wikipedia.org/wiki/Conformal_cyclic_cosmology
|
| It seems the paper made mistakes, using a non-standard model
| of the CMB that failed upon replication. It's an interesting
| theory thoughb.
| Kranar wrote:
| This is some absolutely crazy idea. I mean I'm in no position
| to analyze it critically but that is pretty mind blowing.
| colechristensen wrote:
| Huh? Light has zero lifetime, along with all massless particles.
| When you travel at _c_ your clock doesn't tick. From the
| viewpoint of a photon it is emitted and absorbed at the same
| instant. You cannot decay if you don't experience time. I'm not
| sure exactly how index of refraction works with this.
| Nevermark wrote:
| > You cannot decay if you don't experience time.
|
| 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.
| supportengineer wrote:
| Would that seem like a fold in spacetime to the photon?
| nick7376182 wrote:
| Probably more like a summer breeze
| Nevermark wrote:
| I can't top the sibling comment about a summer breeze! But
| it is an interesting question.
|
| 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.
| pixl97 wrote:
| >But if photons couldn't decay due to not experiencing time,
| they couldn't do anything else either.
|
| 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.
| nyrikki wrote:
| From a photons perspective, emition and absorption are
| simultaneous.
|
| 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.
| ryandamm wrote:
| Hoping a physicist can correct me here, but... I believe index
| of refraction is a function of the photon being absorbed and
| reemitted by the electrons in the dielectric material, so it's
| no longer correct to think of a photon moving at a fraction of
| the speed of light inside the material, it's more like a
| churning series of them being created (always moving at c) but
| constantly being absorbed and canceling each other out.
|
| 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.
| Modified3019 wrote:
| For those curious about what the above poster is talking
| about, here's a well done video explaining the topic of the
| apparent changes of light's "speed" through materials
|
| 3Blue1Brown - But why would light "slow down"? | Optics
| puzzles 3: https://m.youtube.com/watch?v=KTzGBJPuJwM
| amluto wrote:
| I think this is sort of besides the point. If you build a box,
| paint the walls black, and put a flashlight in the box, then
| the photons coming from the flashlight are shorter lived than
| if you shine the flashlight into the sky on a cloudless day or
| night. Not shorter lived from their own perspective -- shorter
| lived from an outside observer's perspective. Sure, one could
| quibble about the choice of observer, but you would he hard-
| pressed to put an observer in the box who thinks the photons
| last very long.
| pixl97 wrote:
| Why is the speed of causality beside the point?
|
| 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.
| amluto wrote:
| This is all true, but the article isn't about how long a
| photon thinks it lives or how much it experiences the
| passage of tone. It's about whether the photon keeps going
| forever from the perspective of someone approximately at
| rest [0] in the universe (like astronomers on Earth!).
|
| [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.
| amelius wrote:
| But if your clock doesn't tick, then infinite lifetime means
| the same as zero lifetime.
|
| 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.
| adrian_b wrote:
| From the point of view of any observer, a photon has a definite
| lifetime, between the moments of its emission and its
| absorption.
|
| 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.
| akira2501 wrote:
| If it's travelling at c then isn't the length contraction
| infinite? Or is that dependent on Lorentz transformations as
| well?
| adrian_b wrote:
| Length contraction and time dilation are words that
| describe changes that are the consequence of a Lorentz
| transformation.
|
| 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.
| animatethrow wrote:
| Consider a simpler example from basic math. Is 1/x infinite
| when x==0? The answer is that 1/x is _undefined_ when x==0.
| In calculus one can take limits as x "approaches" 0 but
| x==0 is still undefined. Likewise, the Lorentz length
| contraction is _undefined_ when traveling at c.
| TheOtherHobbes wrote:
| I wish people would stop repeating this.
|
| 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."
| bequanna wrote:
| Right, but doesn't light travel at less than c in some
| situations (passing through glass, etc)? Would we say they
| experience "time" in those cases?
| samus wrote:
| In these situation photons are either bouncing off matter or
| are getting absorbed and emitted by matter. In the former
| case they don't travel a straight path, in the latter case
| there is a short time lag between absorption and emission.
| kmm wrote:
| > You cannot decay if you don't experience time
|
| 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]
|
| 1: https://arxiv.org/abs/hep-th/9508018
| barfbagginus wrote:
| I feel like this article could be condensed into a simple answer.
| I got tto annoyed looking for it to find more than the answer,
| "yes, if the standard model holds"
|
| 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.
| cwoolfe wrote:
| "God is light." (1John 1:5)
| pc86 wrote:
| Do you have something constructive to add related to the
| content of the article or are we just quoting random bible
| verses on HN for no reason?
| ClarityJones wrote:
| It wasn't exactly random. The topic of the article is that
| light is eternal, and the commenter shared a quote from over
| a thousand years ago stating the same thing. So, the idea of
| light having an infinite lifetime is apparently not new...
| even if the mechanics of light are better understood these
| days.
| xyzelement wrote:
| This is in line for me with the moment of "creation." For
| most of the history of science as a thing, the scientific
| view held that the universe was infinitely old cosmos
| without a beginning or end. The greek model. It was only in
| 1900s that big bang was theorized (by a catholic priest)
| that science now views that there was a moment before which
| the universe didn't exist and after which it did.
|
| 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.
| cwoolfe wrote:
| "The light shines in the darkness, and the darkness can never
| extinguish it.
|
| 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)
| xyzelement wrote:
| Genesis 1:3 has: "And G-d said, Let there be light, and there
| was light[0]." This says on the literal level that light is a
| created thing distinct from G-d, and thus finite (though
| created very close to the creation of the universe itself, on
| day 1).
|
| 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] "vayo'mer elohiym y@hiyvor vay@hiyvor"
| akomtu wrote:
| Isn't it a meaningless question? Photons aren't things, but
| loosely localized areas of motion energy that's temporarily
| assumed the shape of a photon. Upon collision with other similar
| waves, it may change shape and become another partickey like an
| electron. But the light itself is a motion itself, which is a
| pure abstraction. At the end of the universe, photons probably
| will keep spreading over larger and larger areas, slowly turning
| into a uniform sea of that pure motion.
| doodlebugging wrote:
| Where do the photons that hit my retina go when I finish with
| them?
|
| 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.
| adonovan wrote:
| Feynmann is very clear that the photons bouncing off a mirror
| are not the same ones that hit it. They are absorbed by
| electric oscillators (free electrons in the material) and
| destroyed; then new ones are created and emitted.
|
| 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". :)
| dylan604 wrote:
| Electrons? We were just told that there is only one single
| electron in yesterday's posts. It's almost like they don't
| know what an electron _is_
| doodlebugging wrote:
| I believe they're right about there being only one single
| electron. I tried to start my Pathfinder yesterday and it
| was dead as a doornail. None of the dash lights lit and
| there was not even a click from the starter. Someone else
| must've been using that electron though since I tried again
| a few minutes later and it cranked right up. I had my turn
| with it so I'm not mad at all.
| westmeal wrote:
| Um maybe check your battery terminals for corrosion :)
| doodlebugging wrote:
| I covered all those bases. I'm not 100% sure what
| happened but when I initially tried to start the vehicle
| I had it connected to a solar battery maintainer in full
| sunlight. It should've had bazillions of photons
| sacrificing part of themselves to be stored electrons but
| instead I got nothing. After disconnecting that from the
| battery and testing all the fuses I made another attempt
| to start it up and it worked fine. It's possible that the
| voltage output of the panel swamped the voltage expected
| by the ECU and it refused to energize to save the system
| from electrical damage by overvoltage.
|
| Or maybe that single electron hadn't quite made it to my
| battery on my first attempt. That's one busy e.
| westmeal wrote:
| I find pouring electrons into a funnel usually helps by
| avoiding an electron spill all over your battery. Glad it
| works tho!
| mmmBacon wrote:
| It's a true statement that _they_ don't know what the
| electron is. In the standard model the electron is a point
| particle with no volume.
| AgentME wrote:
| Electrons aren't unique in not having identities. Photons of
| the same wavelength are similarly fungible if I remember
| right, though it's a little more defensible to call the
| reflected light not the same photons since the original
| photons are transformed to something we don't call photons
| before photons are produced again.
| doodlebugging wrote:
| But at a reflection event you aren't producing a new
| photon, you are only reflecting a portion of the original
| determined by the refractive indices of the reflection
| interface. At that interface, part of the original photon
| is reflected and the rest is transmitted across the
| interface as a new photon and both have a modified
| bandwidth relative to the parent photon. So the one you see
| reflected is the same photon after modification by the
| medium it traversed and the transmitted components escape
| your view unless you are monitoring the other side of the
| medium.
| wizzwizz4 wrote:
| That would imply a frequency shift, which clearly doesn't
| happen (mirrors don't redshift the light that hits them).
| ASalazarMX wrote:
| I balked at that too, because infinite mirrors and mirror
| houses also don't show any wavelenght shift no matter how
| many reflections they do. They do change perceived
| amplitude, as no mirror is perfectly reflective.
| mmmBacon wrote:
| A photon is indivisible that's the quantum nature of
| light. You aren't reflecting a part of it. To do so is a
| classical wave interpretation of light. The photon after
| reflection is not the same photon.
| doodlebugging wrote:
| I wonder about the all the photons lost in fiber optic
| installations. What happens to them in their short lives?
| There must be a creation and an extinction event.
|
| 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.
| lolc wrote:
| My understanding is that photons don't have a life the way
| we do. They move at the speed of light and thus time does
| not advance for them. They cannot change between emission
| and absorption, no matter the distance. Always bends my
| mind to think about it.
| rvbissell wrote:
| > They move at the speed of light and thus time does not
| advance for them.
|
| 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?
| Kranar wrote:
| There is no such thing as slow photons, photons always
| travel at the speed of light.
|
| 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.
| Kranar wrote:
| Almost everything you said is correct. Photons do not
| have a reference frame, so time does not advance because
| for a photon there is no time coordinate system in the
| first place. It's not simply that photons don't
| experience time, it's that time and space don't exist for
| photons.
|
| >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.
| nullserver wrote:
| It could be the same electron after all. Although probably
| not.
|
| One electron theory.
| https://youtu.be/9dqtW9MslFk?si=qdWGUyJnDRCOns9F
| DennisP wrote:
| If you haven't yet, you should definitely read the famous
| little scifi story _Light of Other Days_.
|
| Full text:
| https://www.physics.utoronto.ca/~jharlow/slowglass.htm
| holoduke wrote:
| Since there is no time from the perspective of a photon, there is
| only one photon everywhere at anytime. Our perception of multiple
| photons is incorrect. Its just multiple timelines with the same
| photon.
| urbandw311er wrote:
| Anybody care to attempt a TL;DR of this?
| henry2023 wrote:
| From the perspective of a photon, there is no such thing as time.
| It's emitted, and might exist for hundreds of trillions of years,
| but for the photon, there's zero time elapsed between when it's
| emitted and when it's absorbed again. It doesn't experience
| distance either.
___________________________________________________________________
(page generated 2024-04-19 23:01 UTC)