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Do Photons Age?

  1. Nov 8, 2004 #1
    If not, then their incorporation within any Time-Dependant theory has to explain the Universe before any Photon pressure was exerted upon matter in the early Universe.

    Does a Photons Frequency of energy actually relay something about it Age?..in the context of its source?
  2. jcsd
  3. Nov 8, 2004 #2
    No photons do not age. They are all identical - one created now is identical to one created afterwards.

    Their only difference is energy and momentum (includes angular).

    Your comment about photon pressure etc. doesn't make sense. A theory does not have to explain how photon pressure was exerted - a photon is created in an electromagnetic field (well ok not created, the two go together), and that photon can exert pressure where it likes (not literally, but you know what I mean).
  4. Nov 8, 2004 #3
    I do understand the context of Time-Dependancy, but lets use another example to see if I can relay what I am thinking in better terms.

    E=Mc2 is the product of energy interactions, so when a photon hits an area around an Atom it interacts with the Electron, so we can say that the Photon does some work in lifting the Electron to a higher orbit. Then the Electron does the same to the photon, it does some work and send the Photon out from the area of an Atom.

    In the early Universe, Electrons have no Orbits in that atoms have not yet configured, so the interactions between photons and electrons becomes an energy exchange process, I believe that Electron and Photons are one and like?..so is it possible that in the Quantum realms of early epoch, particle creation is governed by fact that the density was such that the 'PRESSURE' of such an electron/photon density, triggers the moment of Space-Time?..What I am conveying is that the Electron and Photon seperate and become available for 'work', and it is this moment that is the 'creation' of all spacetimes?..and thus Photons that interact in a 3-D space, create Time?..Photons are the measure of observation, they relay all of our perceptions of anything relating to Time..is this just a coincedence?
  5. Nov 8, 2004 #4
    You are right -- electrons weren't configured in atoms, but that doesn't mean their interactions were any different (well ok they were, the quantum states were differentbut they still interacted the same way).

    No electrons and photons weren't the same - electrons interact via photons. In some as of yet untested theories, particles slowly assume the same identities at higher energies, but that's only theory.

    And there can be no pressure or density unless you have defined spacetime, so a photon cannot come before spacetime. Everything is a measure of observation. And it's not just relating to time, it is spacetime. This is just a coincidence -- there is nothing special about a photon apart from the fact that our eyes respond to them.
  6. Nov 16, 2004 #5
    Well, here is still another idea:
    If photons travel with the speed of light and if time stays still at the speed of light then photons cannot age..
    Right or wrong?
  7. Nov 16, 2004 #6

    Kane O'Donnell

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    'age' is sort of a meaningless concept for a photon. If you mean does time pass for a photon, the answer is that photons travel along paths of zero proper time in spacetime, so the answer is no. On the other hand, if you mean if we could somehow watch a photon travelling (from a frame that *wasn't* travelling at the speed of light) would time pass for *us* whilst we watch the photon, the answer is obviously yes. So we could arbitrarily assign an 'age' to the photon from our frame, say, it's time begins when it is emitted from the atom, and ends when it is absorbed by one. The problems are firstly that the age would be frame dependent (this is the whole idea behind proper time in the first place) and secondly we can't actually 'see' or observe a photon until it's been absorbed - it's path before measurement has no real meaning as far as we can make predictions about it. Therefore there is no process by which a photon could even be *given* an age, as far as I am aware. Meaningless concept.


    Kane O'Donnell
  8. Nov 16, 2004 #7


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    Yes, but... Astronomers routinely estimate the age of photons coming into their telescopes.

    A great deal of what we know about the universe is critically dependent upon the notion that a photon then is just like a photon now, as is the case for electrons and protons, quarks, and ..... A photon, when absorbed, is identical to that photon at birth. They do not change in and of themselves. (Strictly speaking, as photons do interact with gravitational fields they can change their frequency, and their polarization. But for the vast majority of circumstances, the gravitational perturbations are very negliable.)

    Reilly Atkinson
  9. Nov 16, 2004 #8
    Didn't Einstein postulate that we are traveling at c through time? Is it not true that to travel in any of the other three (spatial) dimensions we need to take away from speed c as nothing can go faster than c? And if photons travel at c, that means that they take away all of their "traveling through the temporal dimension" time in order to use it in their "traveling through the spatial dimensions" time? So then a photon does not experience the flow of time.

    *Does that mean it only moves in three dimensions?!!*

    Also, what are some materials that can slow photons down, how, and why can’t they be slowed down enough to be stopped? Why is c still considered constant if light can be slowed down?

    But anyway, that’s going off track. Since a photon does not experience time, it does not age. However, we CAN say for how long it has existed (the example with astronomers estimating the “ages” of photons given by reilly).

    I think that there is a clear distinction between physical age and the time for which something has existed. This stems mainly from the difference in reference frames. For example, if you could go in a rocket ship at something like 99.9999% c, and die in the process (el oh el), your death certificate would not take into account the fact that you had barely aged for the time you had traveled at nearly c, even if it equaled out to hundreds of “Earth years”. This is because only the time for which you have existed, in the Earth reference frame, is acknowledged.

    Photons do not age, but we find it convenient to say for how long they existed. Something does not have to age in order to exist in a temporal dimension.

    - Alisa
  10. Nov 17, 2004 #9

    Kane O'Donnell

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    Yeah, sorry about that confusion. Obviously you can detect a photon, record the time and then guess how long roughly it's been travelling for. What I was implying was firstly that 'age' is not something you can intrinsically associate with a photon (it looks the same at all points in time whilst it exists), and secondly that you can't actually watch a photon age - if you see it, it's already gone :smile: This is a fairly trivial statement, but I was trying to stop the thread shooting off into la-la land.


    Kane O'Donnell
  11. Nov 17, 2004 #10
    There was a moment of Creation, the 'Big-[or small]-Bang', this for simplicity is a (Birth-Date)?

    We can state that the Universe in its present format did not exist, up to a certain moment. Why does Photons seem to be exempt from a Time dependant theory??

    The creation of Space-Time must correspond to the creation of the 'FIRST' photon, they are one and the same!

    If one asks some simple questions to the role of Photon Energies:In the begining there was Darkness, out of the Darkness came a single Photon. Out of the single photon came Spacetime, out of Spacetime came forward Observers, out of Observers came the question..Why? o:)
  12. Nov 17, 2004 #11
    Hi all,

    It is really cool how many interesting reactions came up last night!

    I still have a couple of comments and more questions:

    To Wave´s Hand:
    As far as I read, the EM force (photons) and the weak force were not separated from the very beginning (Big Bang, lets say t=0). That happened at 10-11 s when temperatures cooled down to 1015 K.

    Thus, we might not even be able to speak of "photons" before that time. At least photons were similar to Ws and Zs.

    Hi Alisa, I like your posting:

    Is this proven? Does anybody know about it?

    Or is this too much "la-la-land", Kane? :smile:
    (Thank you for your many replies!)
    I mean a little philosophy is not bad. Isn´t this is how all physics started out in old Greece? And Einstein was inspired by Mach´s philosophies when formulating the SRT.

    But if time does not change for a proton, does that imply it cannot physically interact? Because for a physical reaction a change in time is necessary. Or must one assume that the photon is slowed down during the absorption process, thus it experiences time and can interact? (But then it "ages"...)

    Hi Reilly,

    Do you only refer to the deflection of light by gravitational force:

    Or is there more to know about it? What happens to the polarization and why?

    And is this a physical reaction of the photon in which the photon does "experience" something has changed over time?

    Hm. I am sorry that there are more questions than before.

    Last edited: Nov 17, 2004
  13. Nov 17, 2004 #12
    For my comment on Einstein's postulate, I'm pretty sure you can say it's been proven as we do do observe that those traveling faster (such as astronauts) age slower (they take a greater sum away from their speed c through time).

    I think that it is wrong to say that photons have "age", because of totally different reference frames: In their reference frame, time is not ticking due to their speed. However, in our reference frame time surely IS ticking, rendering comparison useless.

    We can merely say how long a proton has been "flying around" for according to our particular reference frame. NOTE! This is the time it has been "flying around" for, NOT ITS AGE! As I mentioned earlier, something does not have to age to exist. For example, those objects near a black hole event horizon will barely be aging at all. However, were we to say for HOW LONG THEY'VE EXISTED, we would totally disregard this! We would only pay attention to HOW LONG they've sat by the black hole! This can be thousands of years. But we all know that the objects actually wouldn't AGE all that much.

    Same thing for photons, except they do not age at all.

    - Alisa
    Last edited: Nov 17, 2004
  14. Nov 17, 2004 #13


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    All materials slow light down; even plain ol' water does it quite well. They slow down light by absorbing and then re-emitting photons, over and over again, delaying it slightly each time.

    The constant c specifically refers to the speed of light in a vacuum, and that speed never changes. The speed of light is different, slower than c, in other media.
    Different observers will measure different times, so you can only specify the 'age' of a photon if you also specify the frame of reference in which that measurement was made.

    - Warren
  15. Nov 17, 2004 #14


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    Sorry, but this is all pretty much garbage. The term 'spacetime' has a well-defined meaning in physics, and you seem to be using it to mean all sorts of others things. Please refrain from posting unsupported pseudo-philosophical meanderings on our forum, as per the site posting guidelines.

    - Warren
  16. Nov 18, 2004 #15
    One is simply asking a question. Do you agree that photons cannot exist out of Spacetime?..if your knowledge of Spacetime is so, then I ask you again, if one retrace's all of the Photons that have been given out by our Galaxy, there will exist a moment wherby the Luminosity of our Galaxy wane's, the Photon emission cease. The frame of reference of our Galaxy no longer exists if one rewinds the Einstein field equations directly from our Galactic Luminocity function, all the Galactic Photons 'disappear'.

    Now give me your personal guidance for the all the Photons for where our Galaxy used to be?
  17. Nov 18, 2004 #16
    Hi Alisa,
    Oh definitely yes!
    But my question meant the postulate on travelling through time at the speed of c. And thus implying that all speeds through space and time add up to c (but not beyond). Is this a proven theory? I haven´t heard of it before. Is it correct that time passes 10% slower at 10% of the speed of light?
    - Carsten
  18. Nov 18, 2004 #17

    Kane O'Donnell

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    Not really. If you (as an observer) were to observe the *rate* at which time was passing in a frame moving at 0.1c, you would measure it to be slower, but it isn't by 10%, it's more like 0.5%. The relationship is non-linear. However, for the people (or objects, or whatever) at rest in the moving frame, time would appear to be moving at the usual rate.

    And by the way, yes, some of the things said on this thread have been too much in la-la land. I doubt Science started with the ancient Greek philosophers - they refused to do experiments (considering it an insult to logic) and hence made many, many grievous errors about the nature of the world. Their mathematics was much more successful, because Maths *is* something that can be studied without reference to the universe.

    I suspect Science has been around as long as animals could learn from experience. There probably is a place for philosophy in science - but it isn't to try and make predictions about the physical characteristics of the universe. We have Physics for that, and it works better.


    Kane O'Donnell
  19. Nov 18, 2004 #18

    Asked in this context?.the reply of post #10

    Do Photons 'actually' travel back in Time?..or is this a consequence of the Feynman Path integral formulation?

    Lets make a clear example of a thought experiment(if clear can be correct).

    A two-body system is observed to have a Photon oscillating from A to B.

    A detector is placed to monitor the frequency of the photon. Setup is placed on board a craft, craft moves away at linearly, constant speed.

    Now onboard the craft the detector relays its data to an exact point on Earth wherby the experiment is observed. The craft is NOT going backwards in Time, but for the fact that the Earth is gauged as the Present Time, for instance at the timescale of 24hrs on Earth, the Craft has traveled a certain 'distance' away from Earth , the Observers do not say that the craft is at a location of 24hrs, or Yesterday?

    Now the data being recieved shows that the frequency of the photon diminishes for distance, it becomes Red-shifted as a consequence of its distance, this is correlated to the fact that Earthbound experiments detect the shift as Hubble facts. Now lets say what is happening to the Photon on board..is it travelling backwards in Time, or is it Ageless?..is its frequency onboard the craft actually going through change?..or is the 'data-signal' that is relayed back to the Earth, the cause of change?
    Last edited: Nov 18, 2004
  20. Nov 18, 2004 #19

    Kane O'Donnell

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    There are too many holes in the thought experiment. Firstly, you can't have a photon oscillating - photons don't have classical trajectories, as has already been stated in this thread. Secondly, to measure a photon's frequency, you destroy the photon. Third, you have to specify how the data signal is encoded, otherwise we couldn't tell you whether relativity will have a relevant effect on the data stream. Fourth, *every* photon emitted from the moving object will be Doppler shifted, not just the one you're talking about, which as I have already said, was destroyed when you first measured it's frequency. The thought experiment you have proposed doesn't make any sense.

    Next, you make it sound like you think time is some fixed thing that is the same for all observers. It isn't, and it can't be. If a clock moved at the speed of light (thought experiment only) relative to some observer, the observer would never see the clock tick. Ever. Similarly, we can never, ever see time pass for a photon. To do this, we'd have to be in it's frame, which is relativistically impossible, since *every* inertial observer must measure light to travel at c in a vacuum.

    On the other hand, we definately can see time dilation for moving objects with v < c. So, for example, if you had a ball on a spring oscillating, and some device measuring it's oscillation frequency, moving in a spaceship at a constant speed relative to you, then you would see a reduced frequency. However, this has nothing to do with how the information is transmitted, it is a property of the Lorentz transformation between the frames.

    Finally, I would like to say that I suspect the point Feynmann was making was that with photons *it does not matter* what a photon 'does' in time - there is *no* frame in the universe from which we can observe a photon 'moving in time' - the instant we know a particular photon exists (say, when it strikes a detector), it's gone. It's the ultimate shock therapy.

    The problem with this discussion is that quantum electrodynamics deals with photons on a different footing from the 'wave packets' of classical electromagnetism, and usually when you're discussing relativity on it's own you talk about 'waves' and 'particles' having classical properties. The unification of SR, EM and QM brings new insight into the problem, but it goes way beyond the scope of the colloquial physics here.


    Kane O'Donnell
  21. Nov 18, 2004 #20
    CarstenDierks, please refer to Brian Greene's book "The Elegant Universe", which is where I first heard about this theory. I don't wish to misguide, as I've read it quite a while ago, so I suggest you read it yourself. It's not very long. = )

    - Alisa
  22. Nov 19, 2004 #21
    I agree with your observation that my 'thought' experiment has been ill defined, and there are a number of reasons that will not be conveyed here, so lets just retract the original question without the ill definitions.

    The early Universe as seen from our location(hubble deep field), shows that there are 'more' rather than 'less' Galaxies appearing based on what we expect from the Big-Bang model. The Universe as we see it , should be focused along a lightcone evolution form our 'present' to our 'Past' early beginning. This should correspond to an area that has 'LESS' volume than today, the Universe started from a SINGLE finite Volume.

    So it has been estimated that the size and volume was less than the average scale of the present time Proton?...the question now is:In the deep field images from Hubble, there are numerous 'new' Galaxies, every Galaxy has luminosity, therefore it is correct to state that every Galaxy has Stars, Stars that are throwing out visable Photons, this is what hubble see's. Thus it has been estimated that for our Local Star, all photons emminating have been locked within the Star core for a great length of Time, before emerging as a visible, and detected energy as Starlight.

    If one adds the Time of Photons take to well up to the surface of average Stars like our Sun, then the 'New' Galaxies in the Hubble deep field, cannot be emerging at the same rate of that estimated by todays theorized timescales? we see their photons, these to would have been Time-stamped within Stellar Core's?

    Either Photons 'age' or the predicted frequency of hv Varies in Time?..every single photon that reaches us today has been absorbed and emmitted by a vast amount of 'intervening' atoms in-between the source 'early-Universe' and present Universe.

    As chroot statesAll materials slow light down; even plain ol' water does it quite well. They slow down light by absorbing and then re-emitting photons, over and over again, delaying it slightly each time.

    The Early Universe was compact, smaller due to Expansion principles than that of Today?..something that is Expanding at all moments, means that at one preceeding moment its size will evidently be 'LESS' than at any given later moment?...so the Time for photons during a 'low-vacuum' epoch(due to the compactness and density of all Atoms that happen to be around) the total speed of Photons must have been far 'slower', again as chroot states:ALL MATERIALS SLOW DOWN LIGHT.

    The constancy of speed and the frequency of Photons must be 'ill' defined?
  23. Nov 20, 2004 #22

    Kane O'Donnell

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    No - the photons we see on Earth from the Sun have not been 'locked in' the Sun at all, although it is correct to say that 'light' as a bulk-photon phenomena travels slowly in the sun due to the high refractive index. I think your idea of what a photon is might be physically incorrect. The only thing I can really say about it at a very rudimentary level is that photons have no labels, you can't tell them apart or 'track' a photon. Photons *always* travel at the speed of light - chroot is talking about the effect of absorption/reemission of photons on the macroscopic average of gazillons of photons.

    The other thing is, photon numbers are not conserved - a photon destroyed by absorption is not the same one that is reemitted. It's just a photon - they're *all* the same. In fact, one of the reasons QFT is appealing is that it explains *why* all photons are the same.

    The photons we see from the Sun are *very* unlikely to be created in the Sun's core. This is because the Sun's core is so dense that a photon would be almost invariably absorbed before it got very far at all, and once it's absorbed, it no longer exists. Also, as far as we know, photons don't 'exist' before they are emitted. I'm afraid Feynmann was very disappointed in himself being unable to explain this exact concept to his father, and if he couldn't, I sure as hell can't. All I can say is that what you are saying doesn't make any sense to me.


  24. Nov 20, 2004 #23
    Photons are just manifestations of energy and momentum. Energy that any charged particle has can be transferred to energy that a photon has, and similarly for momentum.

    This is why photons do not exist before they are created. They don't "come out"of electrons. They weren't inside to begin with. They are made at the point where they exist.
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