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Thread: Heavy light, is there such a thing?

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    Heavy light, is there such a thing?

    Do all forms of light weigh the same? If we wanted to make "heavy light" what would/could we change?
    I know that I know nothing, so I question everything. - Socrates/Descartes

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    Well my first thought is in basic layman terms - "weight" as the general accepted definition is the measurement of mass in relation to a gravity field from another mass, for example I "weigh" here on the surface of Earth (1G) around 170lbs, where as on the surface of the moon this would be much less, in the vacuum of space nothing at all, even though my "rest mass" remains constant.

    Since light is considered mass less I can't see how its "weight" (in this context) can be measured to be greater than zero?

    Someone with more knowledge on the subject may educate me different, which I greatly welcome!

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    Light is massless and weightless.

    Are you possibly having fun with us?

    Light/heavy?

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    Quote Originally Posted by DaveC426913 View Post
    ... Are you possibly having fun with us?

    Light/heavy?
    Right! He might be looking for an Oxymoron.

    The question in the OP "what would/could we change?" seems odd. We can't change anything about light.
    Forming opinions as we speak

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    Quote Originally Posted by DaveC426913 View Post
    Light is massless and weightless.

    Are you possibly having fun with us?

    Light/heavy?
    LOL, it's kind of a childish question but I was serious about an answer.

    Quote Originally Posted by antoniseb View Post
    Right! He might be looking for an Oxymoron.

    The question in the OP "what would/could we change?" seems odd. We can't change anything about light.
    What about frequency, color, mass???. Are all photons created equal? No matter the source.
    I know that I know nothing, so I question everything. - Socrates/Descartes

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    Quote Originally Posted by DaCaptain View Post
    What about frequency, color, mass???.
    The higher the frequency, the greater its energy. Since e=mc2, thus m = e/c2, then in this sense they have mass, but not rest mass. Momentum is a better way to think of the mass effect, at least for me.

    Photons each are both particles and waves of electric and magnetic energy. They don't have color since color is just our brains responding to stimuli from the retina. The different frequencies of photons trigger different color cones that signal the brain, which then decides what color to assign that combination of signals.

    Are all photons created equal? No matter the source.
    There are about 1089 number of photons in the observable universe at a huge range of frequencies. However, their em nature and their speed are the same.
    We know time flies, we just can't see its wings.

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    Quote Originally Posted by George View Post
    The higher the frequency, the greater its energy. Since e=mc2, thus m = e/c2, then in this sense they have mass, but not rest mass. Momentum is a better way to think of the mass effect, at least for me.
    The m in E=mc2 is explicitly rest mass because the equivalence is only true when the momentum is zero. The equation is actually E2 = (mc2)2 + pc2.

    Photons don't have rest mass and relativistic mass is a horrible concept. It is more correct to say that gravity depends on the stress-energy-momentum tensor and thus higher energy photons contribute more to a gravitational field.

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    Quote Originally Posted by Shaula View Post
    The m in E=mc2 is explicitly rest mass because the equivalence is only true when the momentum is zero. The equation is actually E2 = (mc2)2 + pc2.

    Photons don't have rest mass and relativistic mass is a horrible concept. It is more correct to say that gravity depends on the stress-energy-momentum tensor and thus higher energy photons contribute more to a gravitational field.
    Yes, that's important and even the momentum isn't p=mv but p = h/wavelength (h is Planck's constant). It's not all that easy, however, to say which description is less "horrible". Tensor Aversion Syndrome may be more real than not, at least for folks like me.

    It is a little tricky to answer this kind of OP question because it's easy to either oversimplify or overcomplicate the answer, especially if we don't know what level of answer is desired. The Bohr atom, for example, is a great start for atoms even if it's more complicated than this simple model. Since photons behave as if they are particles of mass, such as a laser-power shining upon a sail in space, it helps me, at least, to associate the only thing I understand them to have (ie energy) with mass-like behavior and e=mc2 helps me even if it's an imagined handle to try and hold.

    For comparison, would it not also be fair to consider neutrinos, though they don't have zero rest mass, to be more correctly described by saying that "gravity depends on the stress-energy-momentum tensor"? [I honestly don't know.]
    We know time flies, we just can't see its wings.

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    Quote Originally Posted by George View Post
    For comparison, would it not also be fair to consider neutrinos, though they don't have zero rest mass, to be more correctly described by saying that "gravity depends on the stress-energy-momentum tensor"? [I honestly don't know.]
    Any time the momentum component of the energy is of similar or greater magnitude to the rest mass you should really be using GR terms.

    I'd actually have no issue with relativistic mass if it were caveated correctly. If up front there was a disclaimer saying "This is not mass. This is something we do to try to avoid actually using General Relativity when we are in a situation where we really should. Don't treat it like mass outside the very narrow range of applications, don't try to reason with it as if it were mass. And whatever you do don't confuse it with rest mass. If you want to do anything other than some relatively low energy kinematic approximations step away from the Relativistic Mass and pick up the textbook."

    Edit to add: Why this is relevant to the OP is that it touches on what is meant by heavy light. If you mean has a larger rest mass - no, it cannot. If you want to use the concept of relativistic mass then it can but you have to be very careful what you take away from this.
    Last edited by Shaula; 2018-Jun-13 at 04:38 PM.

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    Quote Originally Posted by Shaula View Post
    Why this is relevant to the OP is that it touches on what is meant by heavy light. If you mean has a larger rest mass - no, it cannot. If you want to use the concept of relativistic mass then it can but you have to be very careful what you take away from this.
    Hmm, I guess initially I was thinking rest mass. It seems odd that all photons are identical no matter the source. The photons I see coming from the tiny led on my computer is the same as a photon coming from the sun.
    I know that I know nothing, so I question everything. - Socrates/Descartes

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    Quote Originally Posted by DaCaptain View Post
    Hmm, I guess initially I was thinking rest mass. It seems odd that all photons are identical no matter the source. The photons I see coming from the tiny led on my computer is the same as a photon coming from the sun.
    They are the same species of objects might be one way to see it, and no two are exactly the same if you include their direction. Otherwise, their difference in wavelength gives each character, else we wouldn't have a colorful universe.
    We know time flies, we just can't see its wings.

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    Quote Originally Posted by Shaula View Post
    Any time the momentum component of the energy is of similar or greater magnitude to the rest mass you should really be using GR terms.
    That makes sense. Yet I thought GR and particle physics (ie quantum mechanics) were like oil and water. Is this unification something fairly new or is it just highly limited in QM? It seems ironic that the relativity in e=mc^2 can be problematic, but GR is not.

    I'd actually have no issue with relativistic mass if it were caveated correctly. If up front there was a disclaimer saying "This is not mass. This is something we do to try to avoid actually using General Relativity when we are in a situation where we really should. Don't treat it like mass outside the very narrow range of applications, don't try to reason with it as if it were mass. And whatever you do don't confuse it with rest mass. If you want to do anything other than some relatively low energy kinematic approximations step away from the Relativistic Mass and pick up the textbook."
    Do you recommend a general velocity range that should place emphasis on the GR approach? Radioactive decay, for instance, I would assume would be fine with the relativistic mass approach. But the 7% conversion of mass to energy in the Sun's core requires very high velocities, but don't they simply use e=mc^2 for this as well? Is there an example of the GR approach for something like this that will help my eyes get its daily doze of glazing?
    We know time flies, we just can't see its wings.

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    Quote Originally Posted by DaCaptain View Post
    Hmm, I guess initially I was thinking rest mass. It seems odd that all photons are identical no matter the source. The photons I see coming from the tiny led on my computer is the same as a photon coming from the sun.
    That's true of fundamental particles in general, though. The electrons carrying current in a wire are indistinguishable from the electrons emitted by beta decay from Carbon-14. The high energy protons we observe as cosmic rays are fundamentally the same as the protons that are the nuclei of ordinary hydrogen (and that are part of the nuclei of all other atoms). That's actually one of the phenomenal successes of the Standard Model: that we can explain all the amazingly different things we see in the universe with only 17 distinct types of thing.
    Conserve energy. Commute with the Hamiltonian.

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    Quote Originally Posted by George View Post
    That makes sense. Yet I thought GR and particle physics (ie quantum mechanics) were like oil and water. Is this unification something fairly new or is it just highly limited in QM? It seems ironic that the relativity in e=mc^2 can be problematic, but GR is not.
    It is just limited. But hardly new - the first results relating to relativistic wave equations were from the 30s, I believe.

    Quote Originally Posted by George View Post
    Do you recommend a general velocity range that should place emphasis on the GR approach? Radioactive decay, for instance, I would assume would be fine with the relativistic mass approach. But the 7% conversion of mass to energy in the Sun's core requires very high velocities, but don't they simply use e=mc^2 for this as well? Is there an example of the GR approach for something like this that will help my eyes get its daily doze of glazing?
    In fusion and fission calculations using E=mc^2 as it is commonly used is fine because what you are interested in is the change in the rest mass between the parent system and the daughter products to understand the amount of energy released. If you wanted to dive into the kinematics of the reaction you may need to consider relativistic effects. I can't give you a fixed velocity range for when it becomes important - you need to look at the system and what you want to understand about it. For example we got along just fine with classical optics for a long time and still use it despite the main component of the theory travelling at c. But you can't understand, for example, why gold is so unreactive and that particular colour without considering relativistic effects.

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    Quote Originally Posted by Shaula View Post
    In fusion and fission calculations using E=mc^2 as it is commonly used is fine because what you are interested in is the change in the rest mass between the parent system and the daughter products to understand the amount of energy released. If you wanted to dive into the kinematics of the reaction you may need to consider relativistic effects. I can't give you a fixed velocity range for when it becomes important - you need to look at the system and what you want to understand about it. For example we got along just fine with classical optics for a long time and still use it despite the main component of the theory travelling at c. But you can't understand, for example, why gold is so unreactive and that particular colour without considering relativistic effects.
    Thanks, that's helpful and interesting.
    We know time flies, we just can't see its wings.

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    Quote Originally Posted by publiusr View Post
    But excitons are not photons, they are pseudoparticles like phonons, magnons, spinons and so on. They are very interesting, but not photons.

    Quote Originally Posted by publiusr View Post
    So you have a coupled photon/electron system. Saying that makes the photon have mass is kind of like saying I made a proton weigh 238x the mass of a proton - but to do it I had to bind it into a uranium atom!

    These are very interesting bits of physics - but the photon remains massless.

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    And then there are "dark photons" ... theoretical entities produced by theories of particle physics (more?) which go (way!) beyond the Standard Model ...

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    What's more, bear in mind that all we can really say about the photon is that the simplest model for it is to make it massless. We have no idea that the photons we already have are actually massless, we only know if they have mass, it is below our ability to detect. Indeed, it might be natural to expect the mass not to be zero, because a tiny thing is often easier to achieve than a zero thing. If so, the answer to "what would we need to do to light" would be "nothing." However, it can be assumed that what is meant is not, what could we do to light to give it mass, but rather, to give it a measurable amount of mass. To light, probably nothing, but what we might be able to do is something to our measuring techniques-- we might find a way to detect the mass of light, as was done with neutrinos.

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    Quote Originally Posted by Ken G View Post
    What's more, bear in mind that all we can really say about the photon is that the simplest model for it is to make it massless. We have no idea that the photons we already have are actually massless, we only know if they have mass, it is below our ability to detect. Indeed, it might be natural to expect the mass not to be zero, because a tiny thing is often easier to achieve than a zero thing. If so, the answer to "what would we need to do to light" would be "nothing." However, it can be assumed that what is meant is not, what could we do to light to give it mass, but rather, to give it a measurable amount of mass. To light, probably nothing, but what we might be able to do is something to our measuring techniques-- we might find a way to detect the mass of light, as was done with neutrinos.
    If the photon has mass then QED become non-renormalisable because the gauge invariance associated with the U(1) photon field is broken. The effects of this show up in the covariant derivative - a massive photon means that the Ward-Takahashi identities cannot be used as the U(1) field is no longer symmetric under relevant global transformations. This in turn means that the ultraviolet divergence reappears with a vengeance.

    Another issue is that charge conservation is linked, via Noether's theorem, to the gauge invariance of the EM field. Again, a massive photon breaks that and leads to potential charge non-conservation we don't see.

    So there are good theoretical reasons to say that the photons is likely massless. And there are good indirect ways to study photon mass. It is always important to check things like this experimentally, but in this case it more natural (given the levels to which the two things above have been probed) to conclude that the photon is massless and fundamentally different to the neutrino.

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    Quote Originally Posted by Shaula View Post
    If the photon has mass then QED become non-renormalisable because the gauge invariance associated with the U(1) photon field is broken.
    Yet this is not necessarily any great problem, if we adopt the expectation that all theories will prove incomplete, and all symmetries are made to be broken.
    This in turn means that the ultraviolet divergence reappears with a vengeance.
    And will need solving in some other way, which is normal.
    Another issue is that charge conservation is linked, via Noether's theorem, to the gauge invariance of the EM field. Again, a massive photon breaks that and leads to potential charge non-conservation we don't see.
    Correction, we don't see it at the level to which we can currently look. Don't make the mistake of the ancient Greeks-- that if the Earth moved, there would be stellar parallax that they didn't see.

    So there are good theoretical reasons to say that the photons is likely massless.
    A thousand times no. There is never, ever, a theoretical reason to make any statements about reality. All statements about reality come from observations, the role of theory is strictly to make sense of existing observations, and to guide new ones. Yes, theories can tell us what to look for, and possibly find, like the Higgs boson and the neutrino and the positron. But theories can also have us look for things that don't exist, like the luminiferous aether and the speeding up of light entering glass (which Newton's theory said to look for). We always have to look.

    And there are good indirect ways to study photon mass. It is always important to check things like this experimentally, but in this case it more natural (given the levels to which the two things above have been probed) to conclude that the photon is massless and fundamentally different to the neutrino.
    Physicists should never conclude things like "photons are massless." That's just not the correct way to do science! The correct conclusion is "our best current model of a photon is that it is massless." That could change tomorrow, and if it does, it will make our heads spin how fast the former language gets dropped like a hot potato. Such is the surprising progress of science.

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    Quote Originally Posted by Ken G View Post
    Yet this is not necessarily any great problem, if we adopt the expectation that all theories will prove incomplete, and all symmetries are made to be broken.
    Thank you for Kensplaining this to me.

    Quote Originally Posted by Ken G View Post
    A thousand times no. There is never, ever, a theoretical reason to make any statements about reality.
    I made no such statement. I said that there are good theoretical reasons to say that the photon is likely massless. Photons are intrinsically linked to the theories used to interpret observations we make. In these theories the concept of a photon becomes very difficult to reconcile with observations if we give it mass. In the case of a massive photon it is likely that a new theory is needed which will redefine (or may not include) a photon. You know my stance on reality and physics by now, Ken. Physics should avoid such a nebulous concept as 'reality'.

    Quote Originally Posted by Ken G View Post
    Physicists should never conclude things like "photons are massless." That's just not the correct way to do science! The correct conclusion is "our best current model of a photon is that it is massless." That could change tomorrow, and if it does, it will make our heads spin how fast the former language gets dropped like a hot potato. Such is the surprising progress of science.
    We'll have to disagree. I would argue that characterising and testing the characteristics of entities we define within scientific models is exactly the right thing to do as a scientist. We define what a photon is via our theories. so it is fine to say that it is massless if there are compelling reasons to within the current theory.

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    Quote Originally Posted by Ken G View Post
    There is never, ever, a theoretical reason to make any statements about reality.
    Surely science never makes statements about "reality" (whatever that is). I interpreted it to mean that there are good theoretical reasons that the thing we label a "photon" is massless. This is a statement about the model, not reality.

    Quote Originally Posted by Shaula View Post
    Thank you for Kensplaining this to me.



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    Quote Originally Posted by Shaula View Post
    I said that there are good theoretical reasons to say that the photon is likely massless.
    And I said no such statement is possible within the scientific method. If there is one thing history has shown us, over and over, it's that. There's no such thing as a good theoretical reason to assert the nature of reality, such is never science. The structure of science is to let the nature of things be revealed by observations, and theory is simply how we understand and predict what we see. If we have a theory that says the photon is massless, it's a good theory, it might last a few thousand years, or just a few hundred. Galileo had lots of good theoretical reasons to think velocities simply added, and Newton had lots of good theoretical reasons to think time was absolute. It took 300 years to know they, and their theoretical reasons, were quite wrong. That's just how it goes in science, it doesn't make their theories bad and we still use them-- it just makes them not right.

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    Quote Originally Posted by Strange View Post
    Surely science never makes statements about "reality" (whatever that is).
    The statement "the photon is likely massless" is certainly a statement about reality. It is certainly not a statement about a given model of photons, because then the correct statement looks much simpler and contains no "likely" in it anywhere: "we choose to model the photon as a massless particle because it suits us to do so for a variety of reasons." See the difference? How would you put a "likely" in there anywhere and still have it make sense? We could always choose to avoid such statements about reality entirely, and banish the first language in favor of the second-- I'd be fine with that, it's true to science. But we do like to use language about reality, which is why we must temper it with avoidance of mistaking good theories for statements about what is "likely" the truth.
    I interpreted it to mean that there are good theoretical reasons that the thing we label a "photon" is massless.
    Then why is the word "likely" in there? Are you saying it is likely that the model we use for the photon is indeed the model we use for the photon? Such language makes no sense, of course it is the model we use for the photon, what's "likely" about it? If the statement is simply "our model of a photon is a massless particle," that statement does not require any claims about symmetries or gauge invariance, it is simply a fact about a model. The issue here is not "what is our model of a photon," we all know that-- it is whether or not we should say that our model is "likely the truth." We know the model works, but that does not make it likely the truth, as has been true so many times in the past.

    Let me be more specific. Ptolemy could have, and likely did, say words to the effect that "for lots of theoretical reasons, it is likely true that the Earth is the stationary center of the universe." See how that language is different from what would have been fine: "for lots of theoretical reasons, I am choosing to model the Earth as the center of the universe." That language produces no problems at all, no trial of Galileo, no flat earthers, no young Earth creationists. Galileo could have said "to a high degree of accuracy within the domain it has been tested, the velocity of an object simply adds to that of its observer." Newton could have said "in my model, it works well to treat time as absolute." All that would have been fine, but very different language from "the photon is likely massless," or "velocities likely add," or "time is likely absolute." If we are just explaining an attribute of our model, what is the word "likely" doing in there? We already know the model, there's no "likely" anywhere in the correct statement.
    Last edited by Ken G; 2018-Jul-01 at 01:01 AM.

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    Quote Originally Posted by Ken G View Post
    The statement "the photon is likely massless" is certainly a statement about reality.
    No it is not. It have told you before I have no time for the concept of reality in physics. I have no interest, at all, in going down yet another rabbit hole on this. Every statement I make about an entity in a theory is about an entity in a theory. Not about some poorly defined, subjective concept such as a 'real thing'

    Quote Originally Posted by Ken G View Post
    It is certainly not a statement about a given model of photons, because then the correct statement looks much simpler and contains no "likely" in it anywhere
    The word likely is there because there may be a small amount of theoretical wiggle room within the standard model relating to the electroweak unification theory (specifically in how the 'generator' function splits the U(1) group into U(1)y and U(1)em). I personally don't think there is much scope for this, but I left the word likely in there to indicate that others may disagree. Most other cases where the photon has mass break the standard model, ergo photons are likely massless.

    Anyway, there are two parts to this. The bit we are never going to get around is that you and I come from very different schools of philosophy with regards to physics and I have no interest, at all, in having that debate again. The other is a quibble over the exact words I used. Now I know you need to 'win' this so I'll leave it with this: Thank you for highlighting the possible communication issue and I hope this debate about one word in my post has cleared up what I meant for anyone else who read it in the same way.

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    Quote Originally Posted by Shaula View Post
    Every statement I make about an entity in a theory is about an entity in a theory.
    Nothing I'm saying hinges on the reality concept, we both agree that physics is about making models and testing them. The problem is that you are using the theoretical structure (symmetries, ultraviolet divergences, etc.) of a current model (wherein the photon is taken to be massless in the model) to make the claim "the photon is likely massless." There is no way you can claim that is a statement about our current model of a photon, because the current model is obviously massless, that's the model. So you must be trying to anticipate the future of all the models of photons that will come down the line for the next ten thousand years. You are clearly stating a personal belief that in ten thousand years, our model of a photon will still be massless! That's all I mean by "in reality." If you are not claiming that you believe all future models will "likely" be massless, then what could your statement possibly mean?

    I'm saying we never take the theoretical structure of current models and use them to try to anticipate the structure of future models on the grounds that we like the current structure. That's all a "theoretical reason" could ever be, and we learned that mistake with Ptolemy's theoretical reasons to think the Earth was the stationary center of the universe, with Galileo's theoretical reasons for thinking velocities add, and with Newton's theoretical reasons for thinking time was absolute.

    The word likely is there because there may be a small amount of theoretical wiggle room within the standard model relating to the electroweak unification theory (specifically in how the 'generator' function splits the U(1) group into U(1)y and U(1)em).
    Ah, so you are saying that all future models of a photon will "likely" include the attribute of masslessness on the grounds that the current theory could accomodate that within its "wiggle room"? But that's just more reasoning from theoretical prejudice! The only kind of wiggle room that matters in science is the considerable wiggle room left by all the observations that have not yet been done. Observations have not yet been done that could find a tiny mass of the photon, that's all the wiggle room we need-- we have no reason to care at all about wiggle room in theories, did Ptolemy's model have wiggle room for the Earth to move a little bit? Did Newton's theory have wiggle room for time to be personal to every observer? We never ask "how violently would we have to change our model," we ask "what observation would be needed to force us to violently change our model."
    We have needed violent changes many many times, that's what makes science so much fun.

    Anyway, there are two parts to this. The bit we are never going to get around is that you and I come from very different schools of philosophy with regards to physics and I have no interest, at all, in having that debate again.
    But I can present an ironclad logical argument that is based on only two things: the definition of the scientific method, and the history of its application. Can you find any logical basis for claiming "the photon is likely massless"? I'm sure you cannot, it is a personal belief of yours, purely and simply. So you are applying a philosophy, but I am using scientific reasoning, not philosophy. I'm certain I cannot change your mind, I'm presenting a logical argument to expose that you are just voicing a belief, and it is not a scientific position. That's what I will always do on here.
    Last edited by Ken G; 2018-Jul-01 at 02:03 PM.

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    Ken, when I come into Q&A I want to hear answers based on our best current understanding of physics. I do not want to read any sidetracked arguments about "the nature of reality".

    Shaula's response is well within our current understanding and models of physics and I took it as such, nothing more. Of course models and theories change with time. Right now, we have every reason to believe and experiments/models to support the photon is massless. I do not need you to interject "well, that doesn't mean the photon is actually massless", because like you said, if the day comes we do detect a tiny presence of mass then our models and theories will change accordingly. But not today.

    Thus I ask you keep those kind of discussions separate out of Q&A so it doesn't unnecessarily confuse the OP or others reading it who are just looking for mainstream answers.

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    Quote Originally Posted by Exposed View Post
    Ken, when I come into Q&A I want to hear answers based on our best current understanding of physics. I do not want to read any sidetracked arguments about "the nature of reality".
    No part of my answer rests on the concept of "the nature of reality," it is purely a logical conclusion based on:
    1) the definition of the scientific method, and
    2) the documented history of the progress of science.
    Similarly, those two pillars could be applied to a statement made at any time between 100 and 1500 AD that went "how could we put the Earth in motion," and I would have equal criticism of any answer like "the Earth likely cannot be made to move because our best model does not have enough wiggle room for that."

    I can repeat the logic. The question was, "if we wanted to make heavy light, what would we change?" Now, if that question is interpreted as "within our best current model of a photon, how would we give it mass," the question is nonsensical, since the current best model of a photon is that it is massless. Similarly, the current best model of the electron is that it is a point particle with zero permanent dipole moment, so if someone asked, "within our best current model, how would we give the electron a nonzero dipole moment", the answer is again, that question makes no sense.

    Nevertheless, scientists interested in progress, and not simply the dogma of the current models, are actively pursuing attempts to detect a nonzero dipole moment of an electron, and a nonzero mass of the photon, just as Galileo looked to see if the Earth was already in motion. So the way that we would find ourselves dealing with "heavy light," meaning light that has mass, would always require replacing QED with a newer theory. So that's what I said. Then I was told this approach would "likely" not work, and I responded that answers based on pure theoretical prejudice, meaning based on the fact that we like the features of our current models, are unscientific-- just as unscientific as Ptolemy concluding the Earth was "likely" the stationary center of the universe, or Galileo concluding that the velocity of an object "likely" adds directly to the velocity of an observer, or Newton concluding that time was "likely" absolute. So I repeat: the easiest path to light with mass is more precise observations of the light we already have.
    Shaula's response is well within our current understanding and models of physics and I took it as such, nothing more.
    And that is the claim that is clearly wrong, because the statement "the photon is likely massless" goes way beyond our current understanding, it asserts beyond what we know. I had no issue with Shaula pointing out the attractive elements of our current theories that would have to be thrown out if light was found to have mass, that's a very valuable and important thing. It would be exactly the same as Ptolemy pointing out that if the Earth moved, it means the stars have to be incredibly far away, or Galileo pointing out that if velocities don't simply add, then there has to be some universal velocity scale, all of which would seem like very unpalatable elements of alternative theories. We should always be aware of what we like about our theories, and what observations would be required to get us to let go of those attractive elements.

    No, that wasn't the problem at all. The problem was with the ideological prejudices that must go before a statement like "the photon is likely massless." Obviously this is not a statement about QED, any more than "the electron is likely a point particle" would be-- the word "likely" has no place in either statements if they are taken as simple repetitions of the attributes of the QED model.
    I do not need you to interject "well, that doesn't mean the photon is actually massless", because like you said, if the day comes we do detect a tiny presence of mass then our models and theories will change accordingly.
    But would you say "the photon is likely massless," or wouldn't you? That's the issue here. You see, if you would not say that, then you are actually agreeing with me even as you protest that I took issue with that statement. And if you would say that, then you are clearly not being honest with yourself when you now claim you don't need me to remind you that it doesn't mean the photon is actually massless.
    Thus I ask you keep those kind of discussions separate out of Q&A so it doesn't unnecessarily confuse the OP or others reading it who are just looking for mainstream answers.
    All I can tell you is that the OP question is quite obviously asking something other than "does the photon have mass in the QED model." That's an easy one: our best model gives it zero mass, and to use new models that give it mass would involve painful compromises to various unifying symmetries and other elements we like in our current theory. Done, one sentence, not a very interesting thread except the relevant points about the structure of QED.

    But the question is actually how would we give it mass. There is a very clear answer to that question: do more precise observations. That's why scientists are always actually doing that. If we did detect a mass for the photon, then we would need to discover a whole new theory, and with the new theory, we might find ways to create other kinds of photons as well, perhaps those with more mass than the ones we normally encounter. When we discovered the Earth was moving, we eventually found ways to visit its neighboring planets. No one would have ever dreamed that was "likely" given the theoretical prejudices of the Ptolemaic model, which is the reason it is so important to always remember the way science actually works-- even those who claim they need no such reminding, but do.

    Of course people come to Q&A for mainstream answers. That's why I provide them-- I just remind you how science works, in the mainstream.
    Last edited by Ken G; 2018-Jul-01 at 06:18 PM.

  30. #30
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    Quote Originally Posted by Exposed View Post
    Ken, when I come into Q&A I want to hear answers based on our best current understanding of physics. I do not want to read any sidetracked arguments about "the nature of reality".

    [...]

    Thus I ask you keep those kind of discussions separate out of Q&A so it doesn't unnecessarily confuse the OP or others reading it who are just looking for mainstream answers.
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