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    Light - The Ultimate Measure That Isn’t
    By Sascha Vongehr | February 23rd 2011 11:43 PM | 58 comments | Print | E-mail | Track Comments
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    About Sascha

    Dr. Sascha Vongehr [风洒沙] studied phil/math/chem/phys in Germany, obtained a BSc in theoretical physics (electro-mag) & MSc (stringtheory)...

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    Quantum physics and Einstein’s relativity theory, in theory as well as experiment, are extremely concerned with light and its photons. Why should fundamental science be obsessed with something so feeble? Well, it could not be any other way! Science is about what we can (experimentally) observe. As physics advances, it must be expected to be more and more concerned about the most reliable way to measure. It must investigate observation as such.

    If you measure a length with a wooden ruler, also called straightedge, you know the ruler may bend in moist and warm weather. It shrinks in a dry spell. The ruler is therefore not a good fundamental measure. If the ruler were taken as the basic reference, physics would become very complicated. The problem with the wooden ruler is that it is an object with many internal properties like moisture, tension, shape, color, and so on. The object has many internal interactions inside itself; it has an identity that may change.

    If the ruler changes and we mistakenly promoted the changing property, say the length of “one standard wooden ruler”, to the golden standard reference everyone uses, we will be in trouble: If the ruler is shorter than before, everything else measured with the ruler will now be longer in terms of standard rulers. The universe expanded because the ruler got dry. This would not be wrong (!), but the laws explaining how the whole universe is bigger due to there being a dry spell around the wooden ruler are going to be complicated.


    The ruler tattoo, found on a web page for useful body modifications. Lets hope he is at least old enough for the arm not to grow significantly, or it won't be so useful.

    The measure of all measures in fundamental physics may not be allowed to have any internal properties that could possibly change and thereby change the measure. Hence, the ultimately best reference has no internal properties at all. Optimally, it does not exist as a system itself. Anything that exists harbors the danger of change within it. If something exists, it may or may not become different, but if it does not exist, it obviously cannot change. Bingo! That is why light has become the measure of all measures at the cutting edge of fundamental physics:

    The preoccupation of fundamental physics with light results directly from the fact that light does not exist ‘relative to itself’ as an independent entity. Relativity makes light’s non-existence obvious and this odd seeming fact only confirms what is known from entirely unrelated quantum mechanics: classical relativity and non-relativistic quantum physics both agree on that light does not exist (as a system in itself) for entirely different reasons!

    Relativity measures lengths in space-time utilizing the best standard possible on principle, namely light, which cannot change its length, because it actually has zero length itself (it would, if it could, measure no spatial distance between sender and receiver). Quantum physics takes the system with the smallest internal action as the fundamental interaction employed for observing, namely light, because light has no internal interaction; its action is completely exhausted by being interaction.

    Why light? Would light in any other, different universe also take on the role of the ultimate measure? Well, if you ask for light in terms of a glowing, colorful sensation, then no. ‘Blind’ bats may be able to see such ‘light’ via their ultrasound capabilities, too. However, that is not what we mean by ‘light’ of course. We basically mean by ‘light’ the fundamental interaction that can be found in a world.

    Your homework: Could such light be found in any consistent world? Would a virtual reality without action quanta be able to have systems find a consistent and closed theory for their existence? Would we, if we lived in an emergent space-time on top of an Einstein-ether that is not somehow quantized, be able to find out that our experienced space-time is not the fundamental one and that the experienced light is not the truly fundamental interaction? Does the quantum aspect of the light (EPR entanglement type non-locality) thus prove we are not so emergent? Does the fact that light interaction carries angular momentum turn all this upside down, i.e. do we have to accept the polarization of a photon as its internal property? Or in other words again:does the spin ‘charge’ disqualify the photon just like the electron is refused fundamental measure status because it carries its rest mass and electric charge?

    Comments

    blue-green
    Homework Questions: 1) Could such light be found in any consistent world? 2) Would a virtual reality without action quanta be able to have systems find a consistent and closed theory for their existence? 3) Would we, if we lived in an emergent space-time on top of an Einstein-ether that is not somehow quantized, be able to find out that our experienced space-time is not the fundamental one and that the experienced light is not the truly fundamental interaction? 4) Does the quantum aspect of the light (EPR entanglement type non-locality) thus prove we are not so emergent? 5) Does the fact that light interaction carries angular momentum turn all this upside down, i.e. do we have to accept the polarization of a photon as its internal property? 6): Or in other words again: does the spin ‘charge’ disqualify the photon just like the electron is refused fundamental measure status because it carries its rest mass and electric charge? Some answers: 1): no 2): no 3): no 4): yes 5): magnitude yes; direction no (it’s a male thing) 6): no Comment on 6: an electron has cloaking issues …. kind of like a woman … it’s charge and mass are well defined and quite acceptable as fundamental measures … only at a respectable distance …. Photons do not have these issues, so photons are male.
    blue- green | 02/24/11 | 20:56 PM
    vongehr
    Being so cock-sure so fast may also be a male thing. ;-)
    Anyways, I question the consistency of your answers. Especially, how can you answer 3) in such a way if you are already so sure about the importance of quantization in the other answers. Would not the lack of it tip them off?
    I doubt that 1, 2, and 3 can simultaneously be "no" without some caveats.
    Sascha Vongehr | 02/25/11 | 01:57 AM
    Sascha, what is your solution for an e- p+ pair destruction?

    If light is not fundamental then there will be nothing left after a collision.

    Or you have to assume that "information" is not lost, "work" is preserved - but only transformed into impuls or speed [of other baryonic matter].

    Hannes (not verified) | 02/25/11 | 14:35 PM
    vongehr
    The electron-positron pair reaction is certainly worrying, especially the time reverse of the destruction. Two photons, traveling in opposite directions have a non-zero rest-mass (the compound system exists also relative to itself). One relative to the other is even infinitely energetic, as it is infinitely blue shifted [plenty of energy for pair creation]. Yet, they still do not interact but just go through each other. If you want to excite the vacuum to create something with pure light, you have to be adding something more to the mix. Light does not scatter light before you do not have at least as much energy as necessary to make electron-positron pairs as intermediates (or weak interactions may be possible, too, well, at some point even black hole creation). But at some point, systems are going to come into existence via light interacting with light.
    I do not think that this questions the main point, namely that the light is nothing but the interaction. I.e., in order to create an e-p pair, there must be two emitters for the two photons. The e-p pair exists relative to itself just like the interaction between sender and receiver of course exists and has rest (COM) mass, just like the light, as an interaction, certainly exists relative to us. The receiver is in this case the just created pair, or if you like, the interaction of the opposite emitter. None of it changes the fact that the light relative to itself has no existence, neither the photon from one nor from the other emitter.
    Bill may now charge that if that e-p pair exists relative to itself, so do all the virtual ones along all possible paths of the light and thus light exists (relative to who?) or some such, but the whole point of "virtual" is of course that they are not real, that is why we call them virtual. Here we have another trigger of the epiphany of light being at the very edge of something and nothing.
    Sascha Vongehr | 02/25/11 | 22:46 PM
    Nice, Sascha.

    Another nice thing (if I may say so) about e-p pairs coming into existance, is that when they are born virtually they cannot have influence on themselves. If they would - it would violate the conservation of energy [which is a derivation of the energy equation from the first law of thermodynamics].

    The moment the electron and positron are separately existant particles [at a plancklenght distance] they should normally attract one another, either by charge difference or gravitational force. This is not the case, so there is no interaction between them, if the universe around them is not having influence. If there is f.i. an electromagnetic field outside, there would be an imbalance. In my opinion this would prevent the e-p pair coming into existance. There is a yes/no situation of virtual or real here.

    It shows that the laws of the underlying physics here determine the existence of a relationship between between sender and receiver. Between virtual particles coming into existance there is no actual relationship. Which would mean there is also no "light" between them.

    Hannes (not verified) | 03/01/11 | 14:30 PM
    Light does not scatter light before you do not have at least as much energy as necessary to make electron-positron pairs as intermediates.

    Is there a superfluous "not" in there? If not then I don't quite understand what "before you do not" means.  So I'll assume that you meant "before you have at least as much energy as necessary" - if I've not understood, my apologies.

    So, are you quite sure about that?  My QED is non-existent but after doing a lot of web-scraping, I understood that there was a non-zero scattering cross section for photons even below e-p creation. Something involving the sixth power of the energy if that helps. In fact I worked it out for a couple of typical CMB photons and it rather memorably came to a hundred googolths of an area the size of Wales. Or for the actual CMB photon density, one scattering a year in a "reasonable shape" that fits between us and Alpha Proxima.
    derek_potter (not verified) | 12/12/11 | 13:25 PM
    vongehr
    Sorry, the "not" there seems to be some sort of stylistic not (like "I ain't nothin' to do with it") that indeed should not be taken logically. You are also correct that together with quantum mechanics as far as we know it and no low probability cut off at all, there is always a probability for light to scatter light - I guess even just by exchange of a virtual black hole. ;-)
    Sascha Vongehr | 12/12/11 | 21:45 PM
    Thanks.

    I like the "low probability cut-off" idea. I don't suppose it actually means anything.  Does it?

    10 sec on Google suggested it's some sort of life-support system to retrieve Direct Reality from Many Worlds - so it becomes a "Worst of all Possible Worlds Interpretation".
    derek_potter (not verified) | 12/13/11 | 03:03 AM
    vongehr
    It means a lot actually, at least to me. Also others have suggested roughly similar, for example under the heading of "mangled worlds", which I however do not agree with at all. But the idea is there and not too new, but of course one should point out that it is certainly very hard (if not impossible) to have a framework where there is such a cut-off without it destroying the linearity of quantum mechanics that is already observed to very high accuracy. The cut-off would have to be indeed extremely low and somehow behaving well and not blowing up like the butterfly effect.
    Sascha Vongehr | 12/13/11 | 03:19 AM
    Just wondering if some of the non-vacuum mediums impact light like moisture or heat impacts the ruler... Doesn't speed of light actually change in some of those? If so - how's the light better than a wooden ruler then? And doesn't it mean, at least from a quantum perspective, that light exists as an inseparable part of a system formed by itself and its medium?

    Anonymous (not verified) | 02/25/11 | 14:37 PM
    vongehr
    In the quantum description, the refractive index of a medium "slows" the light (relative to light outside of the medium) via repeated absorptions and re-emissions with a slight delay. In between absorptions, the light outside and inside the medium goes at the same rate.
    In a more classical description, the light is absorbed by the whole medium much like the photon is absorbed by an atom. The light is in this sense no longer; there is excited medium instead. In both cases, the (for all we know) free light stays the best measure (the one with the least internal properties).
    If your are trying to make a more radical point ("how's the light better than a wooden ruler" = both cannot be perfect), please recall that the ruler is in a sense also fine, if you are willing to endure an unmanageable physics build on top of it.
    Sascha Vongehr | 02/25/11 | 22:16 PM
    (Ignoramus here.) You say In the quantum description the light is absorbed and re-emitted with a slight delay -- is this the same absorption and re-emission as the jump between energy levels? Would that not require a specific frequency?

    David George (not verified) | 03/06/11 | 19:00 PM
    vongehr
    The refractive index of a material is indeed dependent on the frequency. Your question considers the material as basically being a bunch of atoms, and every atom can only absorb a specific frequency. This neglects that the atoms are not isolated atoms but bound into the the background of other atoms. Secondly, the absorption you envision is the one where the light is not almost immediately re-emitted, i.e. when the material is not transparent. This second point is related to a further interesting aspect, namely the fundamental uncertainty of quantum mechanics. As the frequency is never sharp, the absorption is always one that goes with a certain probability. In a classical world, atoms could never absorb any light, because it would never be exactly the right frequency and thus absorption from one level to the other (if a classical atom still had levels) would violate energy conservation (atoms vibrate and even if you put a very sharp frequency into the material, the atoms move forth and back and see the light red and blue shifted!). That is why energy and time (= 1/frequency) are related by fundamental uncertainty. Without this fudge, nothing would be able to interact in nature.
    Sascha Vongehr | 03/06/11 | 23:55 PM
    Thank you very much, I have never seen the uncertainty explained in that way (I take it you are describing the Heisenberg uncertainty principle). Regarding the transparency of some matter, does transparency then depend on some degree of organization or structural pattern forming a "common background"? And (maybe a different question) how does the transfer of light through the glass compare to an acoustic transfer? (I promise not to carry on the questioning indefinitely!)

    David George (not verified) | 03/07/11 | 10:27 AM
    vongehr
    does transparency then depend on some degree of organization or structural pattern forming a "common background"
    Sure, carbon atoms can give you black coal or transparent (in the visible) diamonds.
    how does the transfer of light through the glass compare to an acoustic transfer
    Well, there are many similarities but also many differences. Not sure what you mean by "compare". I will better not point out too many similarities or Bill is going to destroy me.
    Sascha Vongehr | 03/07/11 | 20:28 PM
    I have never seen the uncertainty principle described that way either, primarily because it's incorrect. The reciprocal relationship between frequency spread and finite lifetime is not a magical property of quantum mechanics, it's a universal feature of anything that oscillates, whether that thing is classical or quantum.

    In the first place, trying to say what a classical atom does or does not do is a snipe hunt, because atoms are not classical, and you can always say that your classical atom is different from mine. Nevertheless, let's imagine it to be a number of charged particles going around in a little solar system while being subjected to an electromagnetic wave obeying Maxwell's Equations.

    In general the point is, a damped harmonic oscillator with natural frequency ω0 can be excited by a driving force with a different frequency ω. It will go ahead and oscillate with frequency ω even though ω ≠ ω0, with a gradually increasing amplitude. In other words, the incoming electromagnetic wave will gradually raise the electron from one orbit to the next, even though its frequency does not exactly match the beat frequency of the two orbits. Afterwards, the excited electron will gradually fall back to the lower orbit, emitting an electromagnetic wave packet having its own spread in frequency. The frequency spread of the packet is inversely proportional to the lifetime of the excited state (as determined by the oscillator's damping constant).

    None of this violates energy conservation because in our imaginary classical world, frequency and energy are not related. So for anyone trying to understand the difference between classical mechanics and quantum mechanics, it is not the magical "uncertainty principle" you need to focus on. The real difference is the connection between energy and frequency, E = hω, which holds in one framework but not the other.

    Bill K (not verified) | 03/07/11 | 13:15 PM
    vongehr
    "the uncertainty principle described that way either, primarily because it's incorrect"
    I give you the point on that my description carries a lot of caveats. You are pointing out that a classical description would still have the Fourier maths while I was saying that the atom is classical but still has energy levels. The big mistake here is not that I got the uncertainty wrong but that we both should better refrain from talking about "classical except for XYZ", which is always wrong.
    trying to say what a classical atom does or does not do is a snipe hunt, because atoms are not classical,
    Exactly! You are totally correct with pointing out the difference between Fourier and QM uncertainty. Not all uncertainty is quantum just like not all quantizations are quantum.
    My point was the following: If you consider two "perfect" atoms that can only emit/absorb at a certain, perfect frequency f (and that was somewhat inside the assumption of the question as far as I understood the question of the comment), then the chances that the second one absorbs what the first one emits are basically nil, because the universe expands and to get the second atom into exactly the right relative velocity to be able to see the photon with exactly zero red shift is pretty much impossible. Uncertainty (here about relative velocity (!) rather than energy) could be imagined to solve that.
    Again, you are right in that this try at being pedagogical backfires and I would never use it in an actual post - not without pointing out its drawbacks anyway. The world is not crazy-classical plus quantum, it is quantum. I should not have given in to the temptation to do the usual "in a perfect world (e.g. without friction or whatever) blah blah blah". Sorry and thanks for your reminder.
    Sascha Vongehr | 03/07/11 | 20:24 PM
    the atoms move forth and back and see the light red and blue shifted!

    Careful! Even a phase modulated sine wave contains the carrier frequency. It just has a bunch of sidebands as well.
    derek_potter (not verified) | 12/12/11 | 13:30 PM
    "Lets hope he is at least old enough for the arm not to grow significantly, or it won't be so useful."
    Also - ruler boy should think twice before moving to any part of the world that uses the metric system (ie most of it)

    DebF (not verified) | 02/26/11 | 23:39 PM
    * Light has no existence relative to itself *

    This seems to mean that this is so because light has no "internal movement". Because it is not a particle (it is immaterial, incorporeal), but rather pure/sheer energy (a unit of energy, a quantum of energy).

    It exists ("only") relative to others. It comes ("only") into existence thru "observation" by something else. Observation meaning not only perception by a conscious (human or animal) being, but interaction with a (some-) thing, a (an inanimate) particle (= something that has – as humans – internal movement). Light has "outer" movement. It proceeds/acts/exists in space.

    Internal movement means also unstable, perishable, unreliable [e.g. for measuring results ("judgments", evaluations) that are objective/factual, not subject to change). Light has an absolute existence (also relative to itself). It has existence by itself .. per se ("as such"), but not "to itself".

    Light exists because we can measure it. Owing to the (the influence of the) measurement (the "observation", the action of the interaction exchange particle) the wave function collapses (is reduced to a single local state). We cannot measure the whole wave, one has to "dephase" (to "decoherence") it.

    This doesn't sound very physical/mathematical, doesn't it? But maybe helps to understand (catch) a bit better a * non-existence relative to itself *.

    Axel (not verified) | 03/02/11 | 12:41 PM
    vongehr
    Because it is not a particle (it is immaterial, incorporeal), but rather pure/sheer energy
    It does not have any energy in its rest frame.
    Sascha Vongehr | 03/02/11 | 21:13 PM
    It does not have any energy in its rest frame

    OK .. I don't mind if it is not even (pure/sheer) energy ("in its rest frame") .. But light is something, isn't it? You may say: „Of course it's something (relative to us, to an "observer", a particle interacting with it). But it's nothing relative to itself " … But you are not saying that it is "absolutely" nothing, aren't you?

    Now the term rest frame: Rest frame is always the frame which I am in .. My frame of reference –– my "point of view" (my laboratory) –– from where I am observing ("measuring") something else.

    Now I can switch my "point of view". Instead of observing/measuring something, I can switch into the rest frame (frame of reference) of that something and observe "myself". Formerly I was at rest and that something moving. Now that something is at rest and I am moving.

    Maybe one should substitute the word moving with existence in order to (better) understand what *non existence relative to itself* means .. Formerly I was not moving relative to myself – I was in a rest frame – while observing something moving relative to me. Substitution: Formerly I was not existent relative to myself –– I was in a rest ("non existence") frame –– while observing something existing relative to me. After switching the "point of view" the same applies (the laws of physics are the same in all frames of reference).

    Of course both systems (frames) exist. So light exists. But what it is, is something one may have different points of view off (even though its physical fact/law is the same).

    Rest frame is not something that is not moving at all (in an "absolute" sense). Non existing (relative to itself) light (photons) is (are) moving in space. At least because the universe (or should I say this universe) is – at present – expanding. So everything in it is in motion with it (even though it may have no internal movement). What about space itself? Is it also expanding? But then: Into what? But if space is simply existing ("there"), then it is the "absolute" frame (of reference). The real rest frame. At least for physicists. But how to measure something that is not moving? So we better use light (its speed) for practical (reliable, realistic, physical) purposes. Light in conjunction with space and time.

    Again: This doesn't sound very physical/mathematical, doesn't it? :-)

    Axel (not verified) | 03/03/11 | 11:17 AM
    vongehr
    But you are not saying that it is "absolutely" nothing, aren't you?
    I don't know how to write articles about absolutely nothing, not yet anyways, though some people are good at it, so it is not impossible. ;-)
    Formerly I was at rest ... now that something is at rest and I am moving.
    This is to be rejected as meaningless in a relativistic framework.
    understand what *non existence relative to itself* means
    Relativated existence is basic modal realism, i.e. the insight that the classical division into the categories of modality ("possible" versus "existence") are insufficient for modern physics, especially quantum physics, and taking the first step into improving terminology by declaring relative to what else something exists (e.g. "relative state description" in quantum physics). Similar happened with "past" and "future", which shows that relativating alone may not be enough. It does not have anything to do with movement.
    Sascha Vongehr | 03/03/11 | 19:45 PM
    It is not my intention to deviate too far from the actual purport of this blog which was .. well .. sort of a definition of light .. Or? And let me also say that I have not studied physics or "philosophy" (or something similar to both).

    When I wrote:

    Formerly I was at rest and that something moving. Now that something is at rest and I am moving,

    I wanted to enunciate that A the laws of physics are the same in all frames of reference and that B if two observers are moving relative to each other, each could say that he is moving and the other one at rest (or that he's at rest and the other one moving) ... Not going here into the subtleties of such an assertion.

    I am of the opinion the space exists in total ("per se"). Meaning that it was not created (did not come into existence) with the Big Bang ~ 13,7 billion years ago (and likewise not time). > In total < "by the way" also means, that I don't (can not) reject the existence of other (or parallel) universes. But they would "only" be a subset (part of the whole) of space.

    I also don't think that space is expanding. The masses in space are expanding – into space –, but not space itself. Space is simply "there". Endless (and also without beginning). Or, at least therefore – i.e. according to this definition/conception – without a discernible beginning and end. Which also would mean not moving = an absolute frame of reference. But not something relative to which we can determine (measure) speed. Here c is the ("current") best benchmark.

    When I say expanding I am not even sure whether this expansion is maybe not a contraction. Moving away (red shift) could also be moving (contracting) towards a point ..

    > Modal realism <

    Manner of expression? Meaning (content) of words, terms, concepts? Physics is less interpretable here, less relative than mental associations. Even though theoretical physics has a lot to do with imagination .. Well, based on concrete (precise) sense-perceptions (functions) .. Verified (or falsified) thru measurements ("observations"). And this mode (method) has led to great inventions ..

    By

    >> .. improving terminology by declaring relative to what else something exists <<

    you mean that "something always exists relative to something else"? I've found (via Google-search) this term (mode of expression) in conjunction with the Many-worlds interpretation of quantum mechanics .. That is ["more or less" :-)] what I meant by space in total (with maybe subsets of universes/worlds).

    >> .. Similar happened with "past" and "future", which shows that relativating alone may not be enough. It does not have anything to do with movement. <<

    Well, I guess past and future [and the infinitesimally present between :-)] have something to do with movement, change .. Internal and external movements .. With things moving in/with time and in space .. But relativating alone doesn’t seem to answer all questions .. But relativity is very true ..

    Axel (not verified) | 03/05/11 | 11:44 AM
    Aitch
    The preoccupation of fundamental physics with light results directly from the fact that light does not exist ‘relative to itself’ as an independent entity

    This is no more than a 'nonsense in logic'
    Nothing 'not exists relative to itself'
    Relativity absolutely means relative to 'other' not 'self'
    Light is no different to any other subject of relativity, in essence, relative to any observer/self.....it is simply 'other'
    For a self to suggest that anything 'is not' relative to itself is a nonsense, that even the self cannot achieve
    The self can never be both self and other, .....relatively

    Aitch
    Henry Cox | 03/07/11 | 14:05 PM
    vongehr
    I move with zero velocity relative to my own rest frame - there is no problem with that whatsoever. You make a problem where there is none at all. "relative" is used a certain way in relativity and in the QM relative state description and I use it in no other, frivolous ways.
    Sascha Vongehr | 03/07/11 | 19:54 PM
    do i exist then????

    Anonymous (not verified) | 04/02/11 | 10:49 AM
    sure. whatever you choose for your rest frame, most of your particles will be moving.

    Anonymous (not verified) | 06/13/11 | 17:26 PM
    Since in the standard model, all quantum fields are massless, would you therefore argue that fundamentally, not only light does not exist, but electrons also don't?

    MartinB (not verified) | 11/28/11 | 14:36 PM
    vongehr
    The standard model is a mathematical description that we know to be somehow reflecting symmetries of nature, otherwise it would not be so successful, but we also know that it cannot be the final answer. So, "electron" for me is that thingy that I can trap, with charge and rest mass. So is a photon, but there is nothing in the rest frame of the photon. Equally, a black hole is one of those black holes out there. In the GR description, there are black hole solutions that describe BH well (as far as we know and outside of the event horizon). Inside of GR, BH must have a singularity and we know that singularities and QM do not go well together, but all of that would not mean that I claim there are no BH.
    "that fundamentally, not only light does not exist, but electrons also don't?"
    Of course, this depends on how far "fundamentally" is supposed to go down. If it goes all the way down, the problem is how we use the word "exist". It is a big problem, and if one tried to actually write in a terminology that made sense, namely radical differentiation of actualization versus absolute existence versus relative existence for observers, I am sure nobody would read more than about the first paragraph. I do not know the best way - certainly my terminology here in this post is nowhere close to consistent.
    Sascha Vongehr | 11/28/11 | 22:36 PM
    " If it goes all the way down, the problem is how we use the word "exist"."
    To be honest, I think that this is the major problem of your post: You seem to start with a definition of exist that requires being able to get to the rest frame of something and then you draw some very strange conclusions. To me this suggests that the initial definition is flawed.
    Or, to put it bluntly: You surely would not mind if I do nothing to your eyes - so since light does not exist, you would not mind me pointing a laser at you...

    MartinB (not verified) | 11/29/11 | 01:37 AM
    vongehr
    The previous posts (this is the third part after all) have pointed out and this post repeats yet again that "exist" is here aimed at the parts independent of relativistic contributions for example. Not sure what the strange conclusions are. If I see you zipping by in a spaceship, all flat but double as heavy, I know that I should not signal you to get in shape and on a diet. With light, all of it is relativistic contribution. And what would one even expect to be there for itself without having any time to be?

    Just not caring and re-confusing general "existence" (of an interaction between Laser and eyes, of the concept of unicorns) and the "existence" of systems relative to themselves (I exist for me) is not a valid criticism. I would rather welcome suggestions about how to write such articles consistently without terminology and definitions that nobody who has a life ever reads. See, the point here is not academic sophistry about actualization versus counterfactual potentiality versus ontological commitment to theoretical entities, but to understand why something like "light" is important in GR and QM.

    What I mean by "if it goes all the way down ..." involves further complications on the here already understood use of "exist" (like that no system can fully observe itself and so on).
    Sascha Vongehr | 11/29/11 | 04:59 AM
    "Just not caring and re-confusing general "existence" (of an interaction between Laser and eyes, of the concept of unicorns) and the "existence" of systems relative to themselves (I exist for me) is not a valid criticism"

    So you write an article called "Non-existence" of light and then criticise me for taking issue with the claim that light does not exist? That's at least funny :-)

    In principle, I like the main idea and focus of the article. However, I still think that the existence of other massless particles with different properties makes the concpet somewhat problematic, though. Light is not "only interaction" because it transports momentum, angular momentum and energy from A to B, and other massless particles transport different quatities of these things.

    MartinB (not verified) | 11/29/11 | 05:32 AM
    vongehr
    So you write an article called "Non-existence" of light and then criticise me for taking issue with the claim that light does not exist? That's at least funny :-)
    There is no claim that light as an interaction does not exist!
    the existence of other massless particles with different properties makes the concpet somewhat problematic, though.
    Those massless particles are never free and "exist" only theory internal. I have never believed massless neutrinos or a naive Higgs mechanism giving mass either. No rest mass, no internal properties.
    Light is not "only interaction" because it transports momentum, angular momentum and energy from A to B
    "only interaction" means "nothing in itself above and beyond the interaction". "only" is not to insult "interaction". This interaction is mighty impressive and fundamentally not "transporting" anything. It does not take a quantum of energy and angular momentum on board and starts walking off. If that were the case, given the subtle relative velocities and so on between all emitters and receivers, nothing could ever be absorbed without violating conservation laws. The conservation laws are not violated if you take receiver and emitter both into account. That would never work if interaction is fundamentally little things transporting stuff. Interaction is a consistent entanglement between systems.
    Sascha Vongehr | 11/29/11 | 06:44 AM
    "Those massless particles are never free and "exist" only theory internal"
    So you also claim there are no gravitons?

    "If that were the case, given the subtle relative velocities and so on between all emitters and receivers, nothing could ever be absorbed without violating conservation laws."
    So why do I have conservation laws when I look at reactions only involving massive particles (like W-Bosons)?

    "This interaction is mighty impressive and fundamentally not "transporting" anything. "

    So in your picture, what a photon "does" is that it connects to spacetime-points lying on a light cone? This reminds me of the few things I know about Penroses Twistors - doesn't he also have lightcone as fundamental objects?

    MartinB (not verified) | 11/29/11 | 06:51 AM
    vongehr
    So you also claim there are no gravitons?
    Gravitons are a very heavy issue. Nobody knows whether gravity is quantized and whether its quantization, if such is necessary, leads to gravitons. All the gravitons, like the closed strings in string theory, need descriptions that are obviously faulty in some respect. Moreover, the masslessness here, I do not even know whether we can discuss it once we curl spacetime into gravity waves. Where is the mass? Where is the energy in a gravitational wave. These are extremely difficult issues that only ever make good sense in semi-classical descriptions. I do not dare claiming much about gravitons at all.
    So why do I have conservation laws when I look at reactions only involving massive particles (like W-Bosons)?
    ??? I hope my language did not somehow imply that interactions need massless fields? Consistency and entanglement that ensures such is primary. Interpretation in terms of particles (quantized interactions with the supposed field) is something that should not be taken too literally. I mean, since you ask me things like "So you also claim ...", let me counter, do you also claim there are 'really' an infinite amount of virtual particle loops going on in every little interaction?

    So in your picture, what a photon "does" is that it connects to spacetime-points lying on a light cone?
    In one useful description, say if we assume spacetime points first, one could possibly say so. I rather like to think of spacetime emerging this way in the first place.
    This reminds me of the few things I know about Penroses Twistors - doesn't he also have lightcone as fundamental objects?
    In my opinion, and names like Penrose or say Rovelli back me up, the light cone description is much more important than the misleading hyperplane foliations that "philosophers of science" like to fill academic papers with. Past light cones already separate the world into observers' records (determined causal pasts). If people had taken this message seriously right away, as they should have on grounds of in my opinion tautologically true philosophy (see e.g. my newest post), there would have never been an EPR paradox and all that nonsense. Everett relativity is already there in Einstein's theory - if you are not a blockuniverse block head that is ;-). People do still not appreciate this and it is still apparently impossible to publish on it if you are not already famous. "Philosophers of science" have as usually no clue.
    Sascha Vongehr | 11/29/11 | 07:51 AM
    "Nobody knows whether gravity is quantized and whether its quantization, if such is necessary, leads to gravitons"
    Of course - but your argument seems to imply that gravitons cannot exist - which would make me *very* suspicious.

    ??? I hope my language did not somehow imply that interactions need massless fields?
    Well, I (mis-?)understood your sentence "nothing could ever be absorbed without violating conservation laws."" in that way that only massless fields (photons) could ensure conservation laws.

    Just to make it clear: I like the concept of photons being a kind of "spacetime-instantaneous (i.e. ds=0)" connection between two spacetime points which seems to lie behind your argument. I am not so sure about your conclusions. (And considering that virtual photons are not exactly confined to the light cone, I see some problems there also).

    "Interpretation in terms of particles (quantized interactions with the supposed field) is something that should not be taken too literally."
    But doesn't your whole argument rely on the particle-interpretation of the photon, considering that the photon quantum field is not constrained to the light cone?

    Thanks for the comments on Twistors - as I said, I know next to nothing about them.

    MartinB (not verified) | 11/29/11 | 08:21 AM
    vongehr
    your argument seems to imply that gravitons cannot exist - which would make me *very* suspicious.
    No Gravitons makes you more suspicious than no photons? ;-) That cannot be it. I think you mean because I doubted massless neutrinos, this perhaps implying that in my opinion nothing but light is massless. In terms of the articles, GR waves are "light". "Light" is here the ultimate thing that seems to always go with lightspeed and all that. If we had no electromagnetism, GR waves would eventually fill that role.
    And considering that virtual photons are not exactly confined to the light cone, I see some problems there also
    You come from the particle physics angle, and this means we like to use "exist" and "real" differently. For all I care, virtual particles do not "exist" outside of the mathematics where we add up infinities of them in order to predict probabilities in some effective theory. Fundamental particles do not "exist" anyway as anything else but quantized interactions, not even the massive ones. Objects that can be described as consisting of such interacting particles, they have some identity over time and "exist". I can measure them and they remain even though my observation changes them.
    But doesn't your whole argument rely on the particle-interpretation of the photon
    I think the relativistic argument is sufficient to show that light itself (over and above being an interaction) cannot be said to fully "exist". It does not even have time. If I claimed unicorns exist, and then if you want me to show you one, I go like "well they only exist for zero time ...
    Sascha Vongehr | 11/29/11 | 09:23 AM
    "In terms of the articles, GR waves are "light"."
    O.k. so there are two different things that are only defined by their interaction, but have no "existence" in themselves - why not.

    "I think the relativistic argument is sufficient to show that light itself (over and above being an interaction) cannot be said to fully "exist"."
    But my point here is that light is never fully and completely restricted to the lightcone, if you look closely enough (i.e. on a quantum scale) whereas your argument seems to be that light, to be light, must be on the lightcone always.

    MartinB (not verified) | 11/29/11 | 09:38 AM
    vongehr
    O.k. so there are two different things that are only defined by their interaction, but have no "existence" in themselves - why not.
    You have a talent for turning things upside down so they sound silly. There are different kinds of interactions, that is all.
    But my point here is that light is never fully and completely restricted to the lightcone,
    This is because you argue that anything inside RQFT, e. g. virtual particles, "exists". Where has there ever been a measurement that caught light away from the light cone so far that you would not be able to turn the result around into location uncertainty of the measure tape or emission timing? On principle, you cannot, this is what the consistency of QM assures. After all, the lightcone is precisely where the light is detected! There is no lightcone before the light and then the light walks along that cone.
    Sascha Vongehr | 11/29/11 | 22:19 PM
    "You have a talent for turning things upside down so they sound silly."
    Sorry for sounding ironic - my "why not" was absolutely serious, I just did not get this point before.

    "This is because you argue that anything inside RQFT, e. g. virtual particles, "exists"."
    No, I do not argue with virtual particles, but with quantum fields.

    "here has there ever been a measurement that caught light away from the light cone"
    Let's look at some process that invloves a photon exchange (now I do use virtual particles, just for ease of speech, of course you can in principle use this argument completely non-pertubatively). Correct probability amplitudes are only calculated when you allow the virtual photon to leave the light-cone.
    I do understand that you argue that this is not a "real" photon and therefore not "real" light, but my problem with this point of view is that a "real" photon is just a limiting case whereas in your way of thinking it seems to be something completely different. I don't see how you culd make your argument rigorous within any kind of QFT.

    And you cannot easily transfer uncertainties to other particles/observables - photon exchange should also work for two "classical" charges (so you only treat the photon with QFT, but not the charge - that's entirely possible in QFT).

    MartinB (not verified) | 11/30/11 | 01:51 AM
    vongehr
    I do understand that you argue that this is not a "real" photon and therefore not "real" light, but my problem with this point of view is that a "real" photon is just a limiting case whereas in your way of thinking it seems to be something completely different.
    Different people use terms differently. I do not use "real" much, because everybody understands something else. I have no problem with the "real" photon being in some description well described as a limit. In my "way of thinking", a photon is not "something completely different". It is what you define it to be, and then we can discuss on those terms. I do not think I could argue your "real photon" to fit to your "non-existent" without violating the definitions you set down.
    There is no measurement that finds light away from the light-cone while not allowing an interpretation in terms of uncertainty of clocks and rulers.
    I don't see how you culd make your argument rigorous within any kind of QFT.
    I do not want to rely on what is possibly wrong. That something like light is the fundamental measure holds in any physics. QFT is great, but we know it cannot be the final answer, singularities and infinities and no gravity and all.

    Do you have some ontological commitment to those infinities of virtual particles in higher order loops that we need in our mathematical description?
    Sascha Vongehr | 11/30/11 | 02:31 AM
    "Do you have some ontological commitment to those infinities of virtual particles in higher order loops that we need in our mathematical description?"
    Nope, I put my money on current QFT being an effective theory where the infinities will at one point be removed by some better theory (Quantum Gravity or whatever).

    "That something like light is the fundamental measure holds in any physics. QFT is great, but we know it cannot be the final answer, singularities and infinities and no gravity and all."
    So you say that your idea of how light behaves is in a sense more fundamental than QFT? I don't agree but I think this point of view cannot be disproved, so that's fine with me then. We can simply agree to disagree (I still do not get your sentecne concerning conservation laws. though.)

    However, I'll tell you why this argument makes me so suspicious: It seems as if you say that it is a logical necessity for a consistent universe that there is something behaving the way light does. (And this seems to imply even that relativity is in some way a logical necessity.)
    And this kind of thing always makes me wary - reminds me of Kant proving (very convincingly) that Absolute space and absolue time are necessary to our thinking. Physics cannot be derived from logical necessities without experimental input - at least it never worked that way in the past.

    MartinB (not verified) | 11/30/11 | 02:45 AM
    vongehr
    I put my money on current QFT being an effective theory where the infinities will at one point be removed
    What if this removed the very first loop, the virtual particle?
    So you say that your idea of how light behaves is in a sense more fundamental than QFT?
    What do you mean by my "idea of how light behaves"?!?

    logical necessity for a consistent universe that there is something behaving the way light does.
    Forget the universe. The physicists in any universe will do anything to get rid of internal properties of measures. Whether they end up with something like our light is a different question, but they sure try to do so. If I wanted to annoy you, I would now claim constructionism, but lets not blow up bridges. ;-)
    Kant proving (very convincingly) that Absolute space and absolue time are necessary to our thinking. Physics cannot be derived from logical necessities without experimental input - at least it never worked that way in the past.
    Yes, because we are too silly, look at us humans, look at the news. However, if there is a final description eventually, it should be easy to turn it around and show that it follows from pure logic. The closer we come, and QM seems pretty close because it already includes other possibilities (what is self-consistently possible at all), the more we can hope that this kind of thinking gives us important hints. I do believe we can make some progress especially in QM this way.
    Sascha Vongehr | 11/30/11 | 03:04 AM
    "What if this removed the very first loop, the virtual particle?"
    Probably I don't understand what you mea - why should this happen? Especially considering how good results from these calculations are?

    "What do you mean by my "idea of how light behaves"?!?"
    Perhaps I misunderstand everything you are saying - to me it seems as if you are saying that light is in a sense defined by connecting spacetime-events on lightcones. I think that this is not how we would see things within a QFT, but I freely admit that QFT may not be the final word and so you may be right.

    "if there is a final description eventually, it should be easy to turn it around and show that it follows from pure logic."
    I totally disagree on that - but that's more a matter of taste than physics. I doubt that our world (or a multiverse) can follow from any kind of logical necessity alone.

    MartinB (not verified) | 11/30/11 | 04:18 AM
    vongehr
    "What if this removed the very first loop, the virtual particle?" ... why should this happen? Especially considering how good results from these calculations are?
    Well they are even better including the infinity. Why would you expect the infinity to go away considering how good the results are?
    you are saying that light is in a sense defined by connecting spacetime-events on lightcones. I think that this is not how we would see things within a QFT, but I freely admit that QFT may not be the final word and so you may be right.
    I do not see why one description must be totally wrong for another one to be also an applicable description. Look at AdS/CFT duality or thermalization on the event horizon versus falling into a singularity. These are dual descriptions. As long as they are predicting what is measured, ... . Again, I am not "saying that light is in a sense defined...", I am saying that you can define it different ways. At least for this article, I prefer to be close to the measurements that can be observed (partially because of the audience - "normal" people do not trust our virtual tricks, not at all.)
    I doubt that our world (or a multiverse) can follow from any kind of logical necessity alone.
    What else but logic could possibly constrain everything that is self-consistently possible? QM seems to be about precisely that. QM many world models follows from pure logic. The multiverse perhaps not.
    Sascha Vongehr | 11/30/11 | 05:12 AM
    "Well they are even better including the infinity. "
    Not really - if you regularise one way or the other does not really matter, does it?

    O.k., I can live with that duality idea. I still don't see that it actually gets us somewhere (and I'm not sure that this duality idea is fully consistent with what we know), but o.k., time will tell.

    "QM many world models follows from pure logic."
    Do you seriously believe that? (Yes, I saw that other post...) Then why did none of all those pure logic thinkers find this out before experimental results came in, if you just need pure logic to deduce QM many worlds?
    Back in Kants time, absolute time and space seemed to follow from pure logic.
    Somehow, pure logic always seems to prove that the current ideas in science are logically necessary - until new ideas come up. Or as feynman said
    I believe that sounds like wagging the dog by the tail. ... I do not think that you can get the whole thing from arguments about consistencies.

    MartinB (not verified) | 11/30/11 | 05:38 AM
    vongehr
    O.k., I can live with that duality idea. I still don't see that it actually gets us somewhere
    Well, as you know, different problems solve easier in different descriptions. Moreover, some duals may be worse for usual problems but more promising for the next step into the direction of, say, unification. For example, lightcones versus manifolds.
    "QM many world models follows from pure logic."
    Do you seriously believe that? (Yes, I saw that other post...)
    Not sure which post. I have never posted about the main reason: There is no consistent terminology where one could make the distinction between absolutely actualized and relatively actualized. "Many worlds models" are not ontology, they are plainly intuitive pictures of the only sensible modal terminology that distinguishes between actualized and counterfactual in a way that makes a verifiable (significant) distinction.
    Then why did none of all those pure logic thinkers find this out before experimental results came in, if you just need pure logic to deduce QM many worlds?
    Classical many worlds have been around for at least 2000 years, I think much longer even, without any hint of experimental verification of QM world entanglement. Entanglement has not yet been supported by pure logic (that is what I would like to do). About "all those pure logic thinkers": This seems focused on big names in history? Those that made sense I think agree, though the terminologies are always different and there are thus different readings. But making sense is not what makes fame.
    Sascha Vongehr | 11/30/11 | 06:17 AM
    "Not sure which post."
    I mean that about many worlds being obvious and necessary. Where you said that without many worlds, the color of the shirt I wear today is a direct result from the fundamental laws of nature. (Again something I disagree with...)

    "Entanglement has not yet been supported by pure logic (that is what I would like to do)."
    Good luck with that (I mean it - although I doubt it's possible, it would be cool if it were.)

    "Those that made sense I think agree"
    Don't know what you mean here - my point was simply that many thinkers in the past had ideas what was "absolutely logically necessary" only to have these shattered by physics (absolute space and time as most prominent example). So if all these people thought they could prove things logically (but didn't), I'm very suspicious that *just now* things are different and our logical proofs are any better.

    But this is something where we can simply agree to disagree since neither can prove he is right.

    MartinB (not verified) | 11/30/11 | 06:39 AM
    vongehr
    without many worlds, the color of the shirt I wear today is a direct result from the fundamental laws of nature. (Again something I disagree with...)
    I wonder how you disagree. Maybe you can comment over there?
    many thinkers in the past had ideas what was "absolutely logically necessary" only to have these shattered by physics (absolute space and time as most prominent example).
    You take a guy (Kant) who bend logic to fit his ethics, as the example.
    So if all these people thought they could prove things logically (but didn't)
    Perhaps the biggest failures are the most famous? I don't know how many examples you have (all these people). People who were rational all the way and became well known and turned out totally wrong.
    Sascha Vongehr | 11/30/11 | 07:42 AM
    "I wonder how you disagree. Maybe you can comment over there?"
    Sorry, but this would probably need lots of writing. But basically, I doubt that these are questions that we are able to answer at all.

    "I don't know how many examples you have"
    Here are a few (I assume there are many more, but my philosphy studies are waaay back ans I don't have the time right now to look them up ...):
    Leibniz: Our world must be the best possible one.
    Descartes: I think, therefore I am, therefore God exists.
    Kant: Space and Time are necessary to our thinking (and there was not much of ethics in the pure reason, that came later)
    Wittgenstein, who believed to have solved all philosophical problems once and for all.
    Feynman also quotes some philospher (unnamed, unfortunately) who claimed that science would necessarily end if the same conditions would not yield the same results always

    MartinB (not verified) | 11/30/11 | 08:04 AM
    vongehr
    probably need lots of writing. But basically, I doubt that these are questions that we are able to answer at all.
    Sounds good (much better than confusing initial conditions with fundamental laws or some such). Make it a blog article. We can rip each other apart - always makes for more readers, ha ha. ;-)
    Leibniz: Our world must be the best possible one ... therefore God exists ... Kant ...
    I think you just made my point by taking the most obviously crazy examples that went famous because people are generally nuts ...
    Lets forget crazy. Arguments about how we measure at all made Einstein come up with relativity theory. He would have never bothered with the math if he did not know already for "philosophical" reasons. QM is closing in on what is possible as phenomena at all. I have reason to expect that if it is at that point, it will be naturally already argued in terms of the conscious observers' consistency ("pure logic"). This POV served me well, I never had trouble with EPR or aging twins. Again: this isn't a clever guy's logic on top of ill-put "questions". It is about consistent terminologies in which questions must be put to be able to have an answer (perhaps close to what you mean up there). Many worlds do not "exist"; relative actualization is the only sensible terminology.
    Sascha Vongehr | 11/30/11 | 09:00 AM
    "Arguments about how we measure at all made Einstein come up with relativity theory."
    Well, weren't there things like Maxwell's equations being inconsistent involved, too?

    Or to put it more bluntly: Even if you can successfully prove logically that there mmust be sucha thing as "light" (i.e. something that defines lightcones), that does not necessarily mean that this thing is actually very relevant to your world - our world could, for example be dominated by other interactions (with massive particles, for example) and the lightcone-particle could be irrelevant (just imagine the electric charge being incredibly weak and the weak force being incredibly strong and the gauge boson masses being much smaller, to cook up something).

    "I think you just made my point by taking the most obviously crazy examples that went famous because people are generally nuts ..."
    Sure - and one day's rationalist is next day's nuts guy; so I would be wary to claim that after all those failures I've logically proven some physics to be necessary...

    MartinB (not verified) | 11/30/11 | 09:15 AM
    vongehr
    that does not necessarily mean that this thing is actually very relevant to your world - our world could, for example be dominated by other interactions
    You keep missing the vital point all the time (epistemology and positivistic terminology is fundamental, ontology is for kids reading PM magazine). It is not about assumed worlds but what physics does. A measure with rest mass is never as fundamental as one without such even being applicable (rather than simply happening to be zero), simply because what isn't there cannot change (say over time or among multiverses). Without EM, although GR waves are very feeble, eventually they would become the most fundamental measure! We are just very lucky to have EM.
    Sure - and one day's rationalist is next day's nuts guy; so I would be wary to claim that after all those failures
    I get your point, but you need to argue it much better than pointing at the most common interpretations of famous examples who would never have gotten famous if they had stayed rational. Philosophy/science does not float in a social vacuum.
    Sascha Vongehr | 11/30/11 | 21:52 PM
    O.k., about Kant let's not discuss further - I totally and emphatically disagree. In hindsight, many of the things he said may seem trivial, but the same could be said about Galilei or Newton (or even Einstein if you are correct that relativity is self-evident by logic). And I think most people (physicists included) still don't grasp the full impact of the antinomies.

    "Without EM, although GR waves are very feeble, eventually they would become the most fundamental measure!"
    I do understand that you say that physicist will always choose that "thing" as a measure that has the simplest properties - in our case light - and that with light properties are so simple because it can be argued to "not exist" in your sense of the word - right so far?

    I still don't like the way you seem to disregard the fundamentals of QFT .
    Furthermore, I also don't see why such a "fundamental measure" should need to exist at all, whereas you seem to think that it is a logical necessity.

    MartinB (not verified) | 12/01/11 | 01:50 AM
    vongehr
    if you are correct that relativity is self-evident by logic
    Everett relativity yes. But special relativity, perhaps no. If we lived in a non SO(D,1) ether, fundamental relativity would perhaps be a necessarily valid description of the totality of the ether setup (some bulk around the ether must allow a relativistic description). But I never claimed such dogmatically.
    I still don't like the way you seem to disregard the fundamentals of QFT .
    ??? You mean my care with what looks like over-interpretation of a still imperfect mathematical description? What does "disregard" mean here? And what are the fundamentals if not empirical verification?
    Furthermore, I also don't see why such a "fundamental measure" should need to exist at all, whereas you seem to think that it is a logical necessity.
    Maybe there is logical necessity, I do not know. Physics tries to "create" it anyway. Can "in-itself non-existing", purely relational measures always be constructed? If there is a SO(D,1)-ether sitting inside another ether sitting inside a fundamentally relational universe (i.e. another ether description does not apply), would those living inside the ether in the other ether always find out, assuming no limit on time/intelligence/... and the stratified ether-in ether setup not being dual to simpler descriptions (say a holographic solipsism)?
    Sascha Vongehr | 12/01/11 | 02:57 AM
    This was very interesting, and I thought it over last night. There actually are interactions with photons that do not consume it and its information. It is bent by gravity - is this not an interaction? Its path is also bent by materials, like passing through water, ie refraction. It is reflected - a mirror will bounce it at a predictable angle. Is this not an interaction? And does this not then mean that it does actually exist, in a qm sense if not a reletavisitc one?

    Greg (not verified) | 07/10/12 | 09:33 AM
    A photon emitted from sun must have existed for at least 9 minutes as per our earth-time before it reaches earth although it did not have any time to exist in its own reference frame. Similarly light from a star situated a million light-years away from earth must have to exist for a million years according to our earth-time before it can reach the earth although it will not have any time to exist in its own reference frame. Similarly it can be said that something can exist for an eternity according to our earth-time although it will not have any time to exist in its own reference frame. So instead of concluding that light does not exist because it does not have any time to exist will it not be better if we change our notion about existence, that existence always means existing in space and time? Otherwise we will have to conclude that our entire earth-life is an illusion.

    Udaybhanu Chitrakar (not verified) | 08/10/12 | 03:11 AM