Physicist: Classically (according to Newton) kinetic energy is given by 
The difficulty comes from the fact that Newton’s laws paint an incomplete (and ultimately incorrect) picture.
Any object with mass travels slower than light and so may as well be stationary (#1).
Anything with zero mass always travels at the speed of light. But since the speed-of-light is always the speed-of-light to everyone (#2) there’s no way for these objects to ever be stationary (unlike massive stuff). Vive la différence des lois! It’s not important here, but things (like light) that travel at the speed of light never experience the passage of time. Isn’t that awesome?
The point is: light and ordinary matter are very different, and the laws that govern them are just as different.
Light and Matter: different
That being said, in 1905 Einstein managed to write a law that works whenever: 
For light m=0, so E=Pc (energy and momentum are proportional). Notice that you can never have zero momentum, since something with zero mass and zero energy isn’t something, it’s nothing. This is just another way of saying that light can never be stationary.
Also! Say you have an object with mass m, that isn’t moving (P=0). Then you get: E=mc2 (awesome)!
Unrelated tangent: It took a little while, but the laws governing the massive and the massless are even more inter-related than the ‘Stein originally thought. He figured out that the energy of a photon is related to it’s frequency (E=hf), but why are photons so special? Why do they get to have frequencies? They’re not special. Years later (1924) de Broglie drew the most natural line from Einstein’s various equations from light to matter. 
On the off chance that anyone out there got unduly excited about that last statement: the frequencies never go out of wack, you can’t tune them, more importantly they are utterly unimportant on the Human scale, or even the single-cell scale, and don’t ever buy a bracelet or anything else with “quantum” in the name.
No, no, no, no, no, no, no, no, no.
Hi,
An interesting article, indeed! What I’d like to ask in relation to photon mass, m=0, is how does this get explained in terms of the bending of light, through gravitational lensing? How can photons not have a mass as they have a dual nature–particle and wave? How can gravitational fields have any effect upon photons not having any mass? A useful link to look into where mass is defined according to its seven attributes mentioned therein: http://en.wikipedia.org/wiki/Mass.
Thank you.
Gravity doesn’t only affect particles with mass.
GR version (a): Matter/energy (same thing) changes the distance between events.* Since light always always always takes the shortest distance possible, gravity changes the trajectory light follows.
*Events are locations + times.
GR version (b): There’s no difference at all between accelerating upward and being stationary in a gravitational field pulling downward. Since acceleration will cause you to perceive light to bend, standing in a gravitational field will cause you to perceive light to bend. Therefore, gravity acts on massless as well as massive particles.
Hi,
I have some doubts regarding this topic so, please help ASAP.
(i)Here ‘m’ in energy expression is rest mass or is it gamma*m? And is this expression of total energy of the system i.e. including all types of Potential energies, nuclear energies, etc etc.
(ii)Let a body is in a free fall which was initially moving with velocity 0.4c so, how we will have to find the velocity at distance h below the starting point? And also tell what is the force due to gravity rest mass*g or gamma*rest mass*g and what is th corresponding acceleration of the body.
thanx
(i) rest mass. E here is more of a kinetic/rest-mass energy. All other forms of energy are tied up in the rest mass. But rather than figuring out how much energy is tied up in nuclear and chemical potentials, you can just weight the matter in question. For example Uranium literally weights more than an equivalent number of protons an neutrons, because of its binding energy which (M=E/C^2) actually does all the important stuff that matter does. Specifically, weighing more than nothing.
(ii) “gamma*rest mass*g”. The acceleration is a bit trickier. It kinda depends on who’s asking: the thing falling, or something standing on the planet that it’s falling toward.
But,shouldn’t the force of gravity be just rest mass*g(as that’s what the actual matter is) and to find acceleration we must equate it to gamma*rest mass*a. Please tell regarding both the frames- body itself and the planet. So, what about the energy conservation to find velocity at the bottom?? Would that also be different, please tell by that method also.
thanx a lot for such a spontaneous response!
In the mass’ own frame it thinks it’s gravity is dependent only on its rest mass. However, once it gets moving that’s no longer the case.
Energy conservation is maintained, and is probably the best way to calculate how much speed increases.
However, I’ve never done the calculation myself, and I’d feel nervous directing someone else.
do you can calculate virtual photon mass in C.M frame?we have the c.m energy of e-e+ collision in e-e+—>phton-photon process
There are many pot holes which occur in todays science, and you have just stepped into just one of them.
Here is another which may explain why we are oten confused.
It seems strange that Universities and schools are still teaching our new physics students who are travelling at incredible velocities on a moving planet, the wonders of a stationary 3 dimensional quantum atomic model.
A question for The Physicist:
Frank Close, in “The New Cosmic Onion” says (Table 4.3 Yukawa and the Pion):
“A photon has no mass, so it is possible for the photon to carry no energy at all. In this case it could voyage for infinite time and transmit the electromagnetic force over infinite distance.”
How is it possible to reconcile the contradiction that a photon “has energy” but can “carry no energy at all”?
The amount of energy that a photon carries is proportional to the frequency of that photon. The photon’s frequency can be arbitrarily small. However, the smaller the frequency, the more uncertain the photon’s position. At zero frequency, the photon has no definable position, and even worse, no definable emission time.
In general, nothing has a definite frequency. It’s better to think of every photon as having a “frequency envelope”; a set of frequencies simultaneously. This is actually a requirement of the uncertainty principle. While one of those frequencies can be zero, there are a lot of problems with there being only one frequency (especially if it’s zero).
I’m told a photon contains no mass. However all photons examined, I think, are said to contain no mass because the scale is not large enough. Most photons seem to be lab created or created on Earth for the purpose of X-rays.
If one examined a photon on a much larger scale…say…the Sun’s corona or the photons released in a nuclear explosion….then could a photon demonstrate that is has mass? And with the new scientific information about the expansion of the universe being at a faster rate than once thought couldn’t the photon now be seen differently?
Especially if factoring in a value for the speed of light, C, which may be subject to change due to the faster accelerating universe?
Thanks for any information or thoughts.
The weight of anything has two contributions, a) the rest mass and b) the contribution from binding energy. So if we weigh a hydrogen molecule we get the weights of the particles and a weight contribution from the stored electromagnetic and nuclear energies. Similarly as light passes by a planet, the planet is effectively “weighing” the light. The photon rest mass is zero and so the weight contribution is from effective mass. (Gravitational mass and inertial mass being equivalent). It carries momentum is the same “effective” way, so although it has no rest mass, it has both weight and momentum. When an excited atom emits a photon, the atom recoils. Photons also scatter free electrons which means they exchange momentum with them.
Is Keith Allpress a mathematician or a physicist?
Thanks
Don’t know.
So….If the photon has “effective mass” then it should be considered to hold
mass in the broad sense of the word mass. My point in this endeavor is to get
the world to stop saying photons are “massless.” You may have proven my point,
effective mass as you say……….conjures up a sense of mass…therefore the photon isn’t
mass-less. Am I right here? Thanks for any support on this…the photon certainly behaves as a mass-holding object. Thanks again.
Wait!
Photons definitely don’t behave like “mass-holding objects”, although it’s hard to tell the difference between massive and massless things outside of the language of relativity. Specifically, there’s a universal law called the “Energy-Momentum relation“: E2=m2c4+p2c2, where m is the “rest mass”. For light we find that E=pc, always. That is, we find that m=0 in every experiment concerned with light, regardless of source.
More than that (again, this is relativity), objects with mass can have a variety of velocities, including zero, and light never travels any slower than exactly 299,792,458 meters per second (light speed!).
The physicist “light never travels slower than…..” Do you mean faster?
Or if you did mean slower, should you add ‘in a vacuum’?
Nope!
Light speed is always the same, even in materials. Rather than just slowing light down, a material absorbs and re-emits light over and over, which leads to a lower average speed. But in between those absorptions, the light is screaming along at the usual speed.
“For light we find that E=pc…”
Wait…isn’t momentum = mass*velocity? So for light, E=(mc)c=mc^2? If something has no mass, how can it have momentum?
That’s the incomplete picture that Newton’s laws paint; momentum is p=mv for objects with mass, but for massless objects (like light) that equation is invalid. All you can say is that E=pc.
It really doesn’t make sense to say photon HAS momentum but no mass . And you’re trying to explain some bizarre ideas in a paper (by Mr Stien’s) to the others. That paper is written in some sort of fabulous notation and
Yes I accept most of it and I agree that no one has yet disproved it, but having momentum and no mass , that’s the funny part.
Why you’re not just answering the question ?
( Instead of referring to this E^2=m^2*c^4+p^2*c^2 equation)
It really makes no sense at all.
Just one thing, I was in doubt when I said “no one has yet disproved it”. I think Planck has done it, NOT for the hole paper, but in some few parts.
The fact that photons carry momentum isn’t a debate, it’s a well established thing. The momentum of light gives rise to, among other things, photon pressure, which has very broad repercussions.
Pingback: Astronomers should be sued for false advertizing. - Page 97 - Christian Forums
Pingback: Astronomers should be sued for false advertizing. (2) - Page 2 - Christian Forums
If energy equals mass (E=M) than light photons should have mass, by simple reasoning.
The problem might lie in the definition as to what is energy? According to physicist Richard Feynman years back, he stated that no one has yet to define what energy really is. I would appreciate any comments or feed back. Thank you.
Pingback: Why Do People Post Stuff Like This? - Page 4
Has the notion that photons are massless been verified experimentally?
Isn’t there a point where light and matter meet? I mean like in the universe.
I’m thinking of a black hole.
So……I may be able to PROVE my photons CAN have mass argument
if we take all this in the perspective of space. Within a black hole, certainly
not the world in which we live presently, but in a black hole, the speed of
light photon may convert to mass! Finally, a breakthrough!
There are different theories and if you calculate with the mechanic of Newton you never get the results for the light as they are in experiments. You need the mechanic of Einstein to do that.
But if you still use only Newton mechanic, you need mass for the light … but it does not fit with everything.
If you use the mechanic of Einstein, if the photon has a mass and velocity of light, it has energy more than any number you can write. Nothing can stop it. Or may be just an other photon…
So for theory of Einstein we need massless photons; Actually we need the theory of Einstein to describe the photons right.
Hey Physicist . Awesome! Thank you for giving so much insight in this blog. Really cheers me up. Thanks!
When you revisit an ond blog that nobody has touched for a long time, it is called “Grave digging”. I don’t know what you call a long running blog though…but hey. I’m back! The question about photon mass – and all questions like this – are great questions. You are right to ask for credentials up front – I have an ancient science degree in chemistry 🙂 but be aware, Einstein was an office clerk in the patent office when he published his first monumental paper). So never let anyone try to bamboozle you with math or technical answers that you can’t follow easily or check up for yourself by corroborating the details. Patient dissection of an argument or explanation is gold, ad hominem attacks are about the only thing that should be disallowed. Learning is sacrosanct and learning spaces should be sacred. Small blogs like this one are great as places to learn, especially a the large science forums can be unpleasant places populated by arrogant know-it-alls practicing fascistic censorship policies.
One of the problems is that a question like this photon question draws you into a web of complicated ideas that are also needed to understand the initial question. But ah well, that’s nature for you.
It is not at all clear how a particle like a photon can have no “rest mass” and yet “carry momentum”. PhDs in science struggle with these same questions. The top people will say that nobody understands quantum mechanics at its core, but the job we lay people have is to understand enough to get a philosophical handle on it.
We have to do two things to begin to understand this. Firstly a) clarify exactly what behaviour or properties we are talking about – ie make the definitions very clear, and
b) Try to construct a physical picture of the situation.
After that, then we cn be sure that any remaining confusion is the same confusion that the scientists have, without all the additional confusions not the least of which are the gross media simplifications we must suffer. Every time I see yet another solar system picture of electrons orbiting an atom I will throw a brick through my television. YABAM! Yet another broken atom model.
a) is easy enough, we can extrapolate from large objects.
A rock has weight, that is a force of gravity. Gravitational mass, that is the property relating to that force. Force experienced in a lift – that is inertial force, so inertial mass is the related property. Good, so now we have two kinds of mass. Weightless is the lack of gravitational force as the amusement park ride briefly free falls. Caution – weightlessness is not the abscence of gravity – The ISS astronauts are weightless but they are in low earth orbit – plenty of gravity present! Einstein very kindly established some equivalences for us, between gravitational and inertial mass for example, and between energy and mass. He also kicked off quantum theory by a charming little paper demonstrating the quantisation of light. The photoelectric effect.
And that is when the trouble really started. Hmm. B).
Suppose you have a source of UV light and metal surface that can absorb light and emit electron current.
Below a certain frequency there is no absorption. At and above that frequency the metal absorbs light and emits electrons. For a given frequency, the number of electrons is directly proportional to the light intensity. The photon energy is converting into electron motion, but also the photon momentum pc is producing electron momentum mv.
Words like “produce” and “carry” are picturesque. We could say “coupled” but that is also picturesque.The notion of a photon as a particle is picturesque. The notion of a particle as a particle is picturesque. Even the notion of a property is picturesque.
(The best writer about quantum mechanics has to be Charles Dodgson, better known as Lewis Carrol. Schrodinger’s cat is a Cheshire Cat, slowly fading away until only the grin remains. What fabulous fun it must be to be a physicist, playing strange games of chess with queens who pass judgment before the trial begins. What use is a memory that doesn’t work backwards?)
What of this photon, this carrier of quanta of energy and momentum? This particle that has no rest mass. It has no rest mass becuase it has no rest. It cannot move slower than the fastest possible speed that can be moved by anything. (Which makes you think what “thing” means). As the record holder it lays claim to the title, and that speed was thereafter is named after record holder, the speed of light. If Neutrinos were discovered first we might be calling it the speed of neutrino, but such is history.
And of course by gaining particles we didn’t lose electromagnetism. Michael Faraday gave us Electric motors and A/C power generation and we don’t need particle theory for that…The radiation theory of light says that an electric field induces a magnetic field which induces and electric field which….well that is a runaway process as far as free radiation goes so we can see that it would be very handy to tie that down to a physical parameter or the whole universe would be over in no time.
So there we have it, a particle that can only move as fast as possible, and no slower. Or to put it another way, it cannot exist at any slower speed, or to put it even stronger, it can only be defined at the speed of light.
But at the speed of light it is not a real world in the real sense of the world.
Nothing that has a real mass can move that fast, because the mass it carries gets more massive as it approches higher speeds.
At the speed of light, none of the physical properties like time and space make much sense either. Time shrinks down to zero and so does space so everything is already everywhere.
Einstein can give us some clues about how we can make phyical pictures. He conceived of gravity as a curvature in spacetime. So we can think of massless photons carrying momentum as a process of tracking the movement of curvature. (Just as an aside, when you get into general relativity effects it is also true that an electromagnetic field can produce a gravitational field but it is very very weak, so at this stage don’t rush out and file a patent. )
Engineers use mathematical objects called tensors to manage multi-dimensional calculations for things like buildings, or fluid flow. Its the same in spacetime theory,
in general it is an energy-momentum tensor quantity that gives the physical picture, which means you have not just curvature but other kinds of distortion mixed in – the whole subject is quantum gravity.
So in short the photon has no mass. It is like the cheshire cat playing soccer. You have the kick without the ball. And the explanation also appears to involve the astroturf, and how big the field is in relation to the ball, and when the game took place, and whether the other teams goalpost is part of the game or not….
Hmmm…no one has taken on the task of my” breakthrough”: That is, no one has
grappled with the idea of mass bearing photons that can be proven in space.
My idea was that in a black hole, light is swallowed anyway. Light does not
exist in its own right in a black hole hence the name black hole. This is the same light
that has sped across space at light speed, entrapped into a black hole. Hmm…..does
“matter” come into play here? Something overrules the light and halts its existence.
Also,….I’m wondering (off the immediate topic of mass-bearing photons) if there is photon to photon interaction. Do photons, sharing for an instance, the same confined
space, interact with one another? Do they exert force on one another if trapped for a tiny instant in the same space before they exit the space in one avenue of egress?
As we are aware of the momentum of photons, can we assume there is force of some kind, when photons are crowded together just before they escape their chamber? I’m thinking of a small part of a medical diagnostic X-ray machine. Just before the photons go on to create the X-ray image they are confined very briefly by the machine. So is there photon to photon interaction by some force (coulombic or otherwise) or are they truly indifferent to one another while existing in a small confined space?
There is an extremely small “coupling” between photons, but it involves intermediate particles that are more likely to exist in higher energy environments. In a nutshell, if a pair of photons have more energy than a pair of electrons and anti-protons, then they will sometimes “hit” each other, and create this pair of particles.
However! Photons with that much energy are very rare. The amount of energy in this kind of photon completely dwarfs the amount of energy in, say, the photons we get from the Sun.
Thank you for considering my query re: interactive or colliding photons.
So..I’m not completely wrong: In the scenario I presented, the photons are
coexisting in the small and final area of a (medical) diagnostic X-ray machine.
The final product, the shorter waved X-rays (the longer waved -rays have been
eliminated in the X-ray machine as they’re useless), coexist in the small and final
compartment of the X-ray machine in the microseconds before they leave to go on
to create an X-ray image. So my thought that they were interacting or colliding with one another in the compartment represented an area of too low an energy? I think that’s what you’re saying. I often wondered how the basis of my idea of interactive photons played out on an area of high energy-the Sun or it’s corona. I had already surmised that the Sun’s high energy generating ability created photons too numerous to count. In the scenario of the Sun or it’s corona….the photons are no longer indifferent to one another – that’s what you’re saying. My allegory of photon life in the last part of the X-ray machine did not represent extremely high energy such as energy in our Sun. The end result of my idea of less energy delivered, less than what was “dialed in” by the X-ray technician then won’t be entirely true. As the creation of X-rays (photons) takes place in the vacuum tube of an X-ray machine, the amount of photons generated should be 100% predictable given the X-ray machine’s settings: milliamperes, kiloVolts used in generating medically useful X-rays (photons).
As we know there is heat produced in X-ray tubes (there’s one energy loss) and the amount of longer waved photons filtered out by the filter in the X-ray machine representing a very minor loss, then my theory of less energy delivered than what was intended (dialed in by the -ray tech) is only partially true. It seems there is only a slight amount of energy loss, not enough to force the X-ray tech to readjust the amount of energy dialed in? Or, an adjustment of slightly MORE milliamperes and kiloVolts could potentially be “dialed up” if X-ray machines had minutial settings.
X-ray settings of milliamperes and kiloVolts are expressed in whole numbers, not fractions of whole numbers. Again this entire idea relates to bremsstrahlung created photons only, the majority of the X-ray beam, not characteristic radiation which accounts for some photon creation. I have often wondered when looking at the accepted model of bremsstrahlung created photons, if anything else is spewed out of the photon creation moment along with the photon, but much less popular? Perhaps
something near the X-ray wavelength in the E-M spectrum? If so…no one else have ever addressed it.
Perhaps the “stuff” that may be generated, or born, along with a photon in bremsstrahlung radiation is just debris of some sort?
Even in the Sun the photons are completely indifferent to each other. The Sun isn’t nearly hot enough. Same thing for X-ray machines; the photons involved fall way short of the energy necessary to generate new particles, so they also ignore each other.
I’m shocked that the photons created on the Sun or it’s corona are not interacting with one another as the Sun isn’t “hot enough!” Wow.
So,…where IS the appropriate source for this generator of photons if not the Sun?
Are you suggesting a nuclear reaction? Gamma rays would enter into the equation, so to speak, at that point. Or are you referring to a photon generator? Like a man made photon generator? Thanks! This is very exciting!
Regarding my other idea, (putting aside interacting photons for a moment), isn’t it possible that something else can be simultaneously created when a photon is born as a result of bremsstrahlung, such as the way the majority of photons are created in X-rays? Maybe, considering your last comment about the medical diagnostic X-ray machine being too weak a source, in higher energy instances? I was thinking that something very minute could spew out (as a result of bremsstrahlung) as well as the photon that we all expect to see. Perhaps something in the same slot of the E-M spectrum as the X-ray? In nature there is always some sort of “debris” spewn out from anything that is newly created, though I realize with photons we’re talking about pure energy (quantum energy) and not mass. The idea that the pristine photon emerges from a bremsstrahlung encounter is an the accepted model of photon creation, at least of the ways (characteristic energy being another), is just too “clean” a reaction or a product. Isn’t there a possibility of some debris or sub quantum debris?
Bremsstrahlung just generates photons. It’s fairly “dirty” in that the batch of photons so created have fairly high entropy, but nothing else is generated.
There are situations where you can generate particles using only very high powered lasers, but it’s not easy.
What a wonderful reply! Thank you! So I wasn’t entirely crazy in my hunch that something else can be created from these reactions, apparently though, not via bremsstrahlung. “Generate particles using only very high powered lasers,” a quite similar concept! Since I think of lasers as photon cousins….so…”debris” or other particles are possible with high powered lasers? Would love to hear about the “debris” field. Again…guess I wasn’t entirely crazy in my thinking,…just went down the bremsstrahlung avenue. Interesting that via bremsstrahlung both short AND long wavelength photons are created….so in a sense the photons aren’t all created equal. The long wavelength photons don’t get much press but are created by the same process. And, X-ray machines filter out the long wavelength photons as they are considered useless in creating the latent image needed.
Thanks!
When you make analogies between photons in a box and gases, you have to be a bit careful that you don’t take the picture too literally.
Photons are force carriers, not mass carriers, they carry the electromagnetic force. I like to think of them as “excitations”. Unlike fermions, photons can share the same state (they can be at the same place at the same time) as other photons so when you cross two beams of light they don’t scatter. But if you look closely at a random arrival pattern of photons, there tends to be more coincidences or bunching behaviours than classical statistics would predict. Its not that they are attracted to eachother, but this sociability is just a correlation effect. If you split the beam you get these numerical correlations too, and they vary with the beam intensity. No classical particle model explains that.
The change in thinking needed is that you have to view the photon number as a dynamical variable. So the idea of how many photons there are in a given spacetime volume is a statistic. Its not a lot of little points or ripples moving about in well defined trajectories. The whole idea of a trajectory of a particle went out the window anyway when the uncertainty fairy flew in. If you want a knowable photon number in a spacetime volume then you need something like a laser, but then you get quantum wierdness in spades.
Now we can talk about the collision between a photon and an electron say, by making a little story, but it is just that – a partial story, even if it seems more real. We have to remember that we can only connect this story to the bigger story if we follow the rules. We have to stitch together statistical narratives according to the rules, we can’t just extrapolate to a classical gas model.
Hmm…. ability to generate “particles” via bremsstrahlung at very high energies.
Do you mean in addition to photons being generated simultaneously in the same
moment? This directly addresses my question of whether or not something “else”
is created simultaneously with the photon that is a “given.” That is we are all aware that a photon is created, that’s why the reaction was set up to create photons.
So other “debris” that can be created simultaneously with the photon – is that what you meant by “particles?”
Interested to know if anyone is going to explore the “debris” field with me; the “debris” field consists of potential stuff (whatever that may be) that is
simultaneously created when the photon is created via bremsstrahlung?
Obviously I’m making a big assumption that the photon isn’t the only
thing to come out of the bremsstrahlung creation story. I just don’t know
what the “debris” would be called….if there is debris, or other stuff, created
at the same time as a photon’s birth.
No takers for the “debris field?”
Speaking to the idea of the photon, then isn’t a photon really just an ion when one
dissects the nature of the photon? The word photon seems to be a contracted word: contracted from photoelectric ion. As it’s massless (except for what I’ve learned in the “rest mass” number which is just assigned for math equation reasons) it appears to take on the behavior of an ion. So….who made a distinction between the word “ion” and the word “photon?” The two exhibit such similar qualities.
Referencing the 2/24/13 comment by “the physicist:”
“…situations where you can generate particles using only very
high powered laser…”
What are the names of these “particles?”
The vast majority of them are electrons and positrons, since they’re the least massive kind of particle.
Heh:)
Love it.
Not that I found a definite definition, but the vitality of ideas here makes me smile. To me the momentum is something ‘mass less’, when it comes to a photon, although coupled to the idea of energy having a equivalence to mass.
Maybe one question would be to ask how I should relate a ‘photon’ to a particle size:) that is assuming the equivalence we expect it to share with mass mass=energy. Rest mass is presumed to reserve a ‘place’, although I freely admit that you can question that one sometimes, as in condensates with helium4 for example.
Another question might be why the momentum isn’t infinite? If the momentum is limited, to what do we define that, its energy solely? What about ‘size’? Do scaling up a photon give it a size 🙂
Nah. it’s like symmetries somehow to me. ‘Mass’ becoming a emergence, but I’m not sure relative what, energy constricted? To what? What does observer dependencies say about relativistic definitions of a position in space and time? Have we examples of particles of mass created through light surviving? Why don’t they?
A ‘light box’ is a quite nice idea, but if I define a rest mass as something ‘intrinsically invariant’, no matter what frame of reference I place it in would heating that rest mass also increase its ‘rest mass’? Or is that a relativistic expression, relative particles increased kinetic energy?
To me a ‘photon’ must be mass less, if relativity is correct.
“Zero” mass like Zero is an imagination and makes no sense . Photon being the atom of radiation ,something Non Zero, must have definite mass and energy and other mechanical properties.The question is trivial but has been complicated by the incorrect 2nd Postulate of STR which is not only redundant but even contradictory to 1st Postulate. The” c” appearing in STR is the mathematical limit of the speed and like any mathematical limit can never be achieved by any physical object.( Consider S=1+1/2+1/4+1/8+ =2, representing growth of some property of an object .then can the property “S” ever achieve a value=2, never) .Seeking the answer to the question ” What can move with the highest speed and what will be that speed”,the author had long back discovered that the said speed is that of a wave similar to the Electromagnetic wave in Vacuum and the value of the same is the ratio of the two Force Constants of Electrodynamics. But there is no way to imagine that this wave is Light or Photon. Similarly identifying E= hf as the energy of a Photon is highly erroneous as it ruins the identity of the Photon as elementary particle and so is the case with p=hf/c .In fact if these are regarded as the Energy and Momentum of any particle ,then the author has discovered that in certain cases the principle of conservation of Energy and Momentum both are not satisfied. Similarly if “c”is regarded to be the speed of Photons then again the author has found that as per STR the trajectory of Photons can not bend due to gravitational Field of any massive body which is certainly incorrect. Therefore we have to :
1- Abandon the the 2nd Postulate of STR
2-Determine the actual Mass and Ultimate Energy of Photons like any other Particle 3- Find out the dynamical Laws of imparting momentum to Photon
and then the present confusion of particles having Zero Mass have non Zero Energy and non Zero Momentum prevailing since year 1905 can banish