Is photon only a mathematical convenience and not really an entity?
553980
I like your question and hope it is one that you yourself thought up rather than someone handing you and expecting some pat answer back. \n\nThe difficulty we have in answering it is the word "entity." In our ordinary world, a door is an entity so is a kitten. When a kitten jumps through a door, there is no chance that the kitten will go through the door and come out as a rain of kittens (diffracting) with a solid seeming kitten in the center and some ghostly kittens further out. And yet, photons do that.\n\nWe allow photons to travel at the speed of light in a vacuum. Nothing else is allowed to do that. Hard to talk of entity with that exception given to it. \n\nI am not sure, even though I teach about photons, that we can talk very concretely about them as entities. Mathematical conveniences? Convenient? Had to learn a whole new way of doing math but yes, I guess. Information carriers might be an interesting way of putting it, too, in a Feinnman sort of way.\n\nNow I will be thinking about this all day. Good question.
624084
tut_einstein has the right idea here. A photon is an element that has no rest mass, and rest mass is what we speak of when talking about mass. But while traveling around at the speed of light it contributes to objects as if it does have mass. This is the relativistic mass that people are talking off. A photon though by definition and experiment is a massless entity. That doesnt mean it can't contribute to momentum and other forces. \n\nE=mc^2 is an equation that comes out of study of Einstein's theory of special relativity. This is meant to determine the conversion of energy into mass and vice versa. \n\nTaken from wikipedia:\nConversely, a single photon travelling in empty space cannot be considered to have an effective mass, m, according to the above equation. The reason is that such a photon cannot be measured in any way to be at "rest" and the formula above applies only to single particles when they are at rest. Photons are generally considered to be "massless," (i.e., they have no rest mass or invariant mass) even though they have varying amounts of energy.\n\nPhoton's cannot have mass because they cannot be at rest. The equation E=MC^2 as I have stated only applys to objects at rest. The total energy of a moving body is different it is calculated using the formula:\nE=(mc^2)/sqrt(1-v^2/c^2). If you solve for relative mass you can get the equation that E=m(realtice)c^2 and this equation is good for all particles moving or non moving. \n\nSo to sum it all up. A photon has no rest mass although it certainly has a relativistic mass when it is zipping through space at the speed of light.\n\nI hope that made sense
554379
light.\n\nlet me refer you to e=mc2...light has mass energy and inertia.\na light is a wave and a particle.\nIt is in motion, and objects in motion have inertia and thusly power.\n\nThe true absence of light would exist in a vacuum. There is no pwer in a true vacuum. Even if the absence of light was "massive", that word you chose is a relative term, which is to say that massive CAN NOT imply mass, inertia, etc. The absence of light is NOT measurable because there is nothing there to exist.
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Photon is not a substance.  It is pure energy.\n\nLight travels in discrete quantities called photons.  It is only called a particle due to the wave-particle duality.  That is, all energy and matter come in discrete amount, and travel in a wave (wave movement is not noticeable in matter because the wavelengths are extremely long)
339011
Qunatum uncertainty says that you can never be certain that space is empty at Planck distances, therefore on those scales there is always some matter-energy in the form of virtual photon / antiphoton pairs that suddenly come into existence and then annilihate one another.  This suggests to me that empty space cannot exist on its own unless there is something in it.  Ultimately, we can spin whatever theories we want and debate forever which ones we prefer - but unless someone can design practical experimental methods, then the arm chair physics will not resolve very much.
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Not sure that i can agree with Messrs Santras. Photons that do not have a mass? \nhmmm.. no mass, no energy, no time, no light. Anyway.. The  idea about photons that i find interesting are that they only have mass while they are moving. The mass disappears as a result of trying to observe it.\nMaybe the giving up of mass and the subsequent conversion of this mass to energy gives us the equal and opposite force to power...............TIME.\nAs for the rest of this question? Well if light is not electromagnetic then what is it? Are photons spots of energy or waves? This has been an argument for a long time. Maybe they are both. Each having their own laws to drive them.\nIf we consider the double slit experiments with light, we come up with some interesting results. One of which talks about the possibility that photons can communicate with each other! That there is some clandestine signalling goes on between a source of a photon and a recipient of a photon. This would have to happen at a super-light speed and therefore involve time travel of the signals! Maybe? The crux could be following the simplest form of physical law "the path of least resistance" how does a photon (light) know which direction is a straight line?\nPhoton theory isnt easy to think about. there are many established experiments out there to prove many things about photons but to manipulate photons in order to make something invisible? We would have to understand the fundementals of time, as yet this has not been achieved. We can only hope to observe its effect rather than it's mechanics.
416146
yes in the quantum world. hey and if no one reads this answer have i really typed it??
852892
No. A photon is both massless and has no electric charge - any interaction with a magnetic field would be impossible.
870020
While photons don't have any force-mitigated interactions, there can be interference.  Matter (fermions) has the Pauli Exclusion Priniciple preventing, say, two electrons from being in the same spin-state in the same sub-orbital...there's a destructive interference term in the probability wave equation that comes from their half-spin states.  \n\nSimilarly, there's an inverse sort of "Pauli Inclusion Principle" for bosons (which have integral spin states and includes photons) to constructively interfere in the wave equation such that there's an increased probability for them to be in the same place at the same time.  \n\nOne might be able to, as you say, 'channel' this and force them to work together by creating an energetic population inversion of electrons ready to emit, then sending through a photon of the proper wavelength to produce a cascade of stimulated emission...Oh wait, that's a laser.
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>we know that physically one photon can not pass through the two slits at a time\n\nThat's kind of the whole point of considering the single photon case of the double slit experiment: it give results that don't match classical predictions, and so it becomes a good argument for quantum mechanics.  \n\nIf light were a classical particle, then yes, it can't go through both slits, and you'd end up with two overlapping Gaussian bands of light, and not an interference pattern if you summed up the results of many single photon experiments \n\nIf light were a classical wave, you'd get an interference pattern, but you'd expect the energy from it to be spread out all over the detector or photographic plate, just very faint.  \n\nWhat actually happens when this experiment is done is that the energy gets delivered to the detector all in one place, as if light is a classical particle.  But, the locations where the energy gets delivered, if the experiment is done one photon at a time and the results are stacked up, conforms to the interference pattern you'd expect from a classical wave.\n\nSo, we have something that matches neither a classical particle nor a classical wave in  behaviour.  \n\nBut, in quantum mechanics we have a description of something that does fit this behaviour.  That is, we have a wave which, when measured, has to provide energy in quantized steps.  To get from the wavelike portion to the particlelike portion, we have to recognize that there isn't a completely deterministic answer but rather a statistical one.  So, while this model descibes what a real photon does in the double slit experiment, it can't predict the exact behaviour of a specific given photon.  As best we can tell so far, this isn't just a shortcoming of the theory, it's actually how physical reality operates.\n\n\nEdit:  Ramblingman, it can be done with either an electron beam or a photon beam.  Both will show the same sort of effect, but traveling electrons will have a much shorter wavelength than light.  Quantum mechanics works for both things that were classically considered as waves, like photons, and things that were classically considered as particles, like electrons.
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indeed light is as said before photons although according to quantum physics everything in the universe is made from molecules, molecules are made from protons neutrons and electrons and those are made from quanta's.But quanta's are in fact (in a way at least)compressed energy. So you can't really say that they are made from something different technically speaking at least
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It depends on what you mean by size.  Photons are odd.  They have no measurable mass, yet do have energy, momemtum, and of course wavelength and frequency.  Photon interaction occurs in the very small scale, so you have to look to quantum physics as well.\n\nThere is no standard "size" of a photon, in terms that use our standard frames of reference.  You can try to approximate the location of a photon with Schrodinger's wave equation.  That gives a probability distribution.  Related to that is Heisenberg's uncertainty principle, which states that you can only know the combination of momentum or position of small "particles" to a maximum certainty.  If you know more about the momentum, you will know less about the position, and vice-versa.  There is a fundamental "quantum" effect going on here, in that space is not exactly continuous in this small scale (or for that matter, engergy, mass etc).\n\nIf you loosen the definition of "size" to mean something more like "heft", then you can think of high-energy photons (like gamma or cosmic rays) as being "bigger".  They have more momentum and energy, although the wavelength is shorter.\n\nIn summary I think that photons operate on such a quantum scale that I think "size" doesn't exactly correspond to our common notion of size.
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CIH is spot on, but you should also realise from what he said that electromagnetic waves or particles are ways of describing and calculating what a photon will do, they are not the actual photon itself (whatever that is). \n\nSometimes it easy to think that the description of an object IS the object, especially if it fits it well. If it was possible to write an equation or model which fully described a motor vehicle, you still wouldn't be able to drive it to the shops, but you would be able to accurately descibe how it drove there.\n\nIsn't physics wonderful! Philosopy and science all neatly wrapped up in one unifying theory of lots of theories!
36613
it doesnt satisfy the qualities of being a matter, like having mass and volume, but it does have particles called photons, light behaves like a particle at times and sometimes as a wave
643023
excellet question. This got much deeper meaning then most people understand.\n\nIts energy, you see photons.  You touch and feel photon/photon exchanges.\n\nSince E=MCC, All matter are energy also, Photons.\n\nPhotons are travel at excatly the speed of light, and that makes them see the universe as a zero volume dot.\nIt takes no time at all to a photon to go from one end to the other end of the universe.\n\nThe next great question will be, where did all this energy came from.
801276
Light is a particle. Wave is its function.
300067
A photon, which is a quanta of evergy below which you cannot go-this is the smallest, and only, particle which carries radiant energy.  The photon is the energetic equivalent of the quark in matter.