Since Photons are considered massless, than arent they dimensionless?
952119
The photon has zero mass (it does, however, have rest mass - as in M=E/C^2). \n\nLike all quanta, the photon exhibits wave and particle properties. \n\nIt is important to remember that mass and energy are equivalent. A photon is only referred to as a particle because of certain properties that light exhibits - the "particle" is actually no more than a quanta of pure light energy - and, as such, is indeed dimensionless in the conventional sense of density and volume.
108368
Momentum of the speed of light=zero\nMomentum is defined as mass times speed.\n\nthe light don't have a momentum beacuse don't have a mass.  light is just energy.
648240
E=mc^2\nlooking at this we can first thing about a photon which is said to have zero rest mass b/c it travels at the speed of light.  \nhowever, saying the faster you move the slower you get just isn't correct.  the faster you move the more massive you get.  this equation is really ment to show the link between mass and energy and how saying that mass is always conserved in reactions technically isn't correct.
619048
It's actually kind of unfortunate the the ultimate speed limit is generally referred to as "the speed of light", because the concepts are actually different.  Also, saying that "the mass increases" really only confuses the issue, and physicists don't really talk in terms of changing mass in relativistic systems.  The "mass increases" argument is actually just a kludge to keep the P=mv (momentum equals the product of mass and velocity) equation working at relativistic speeds, but it makes more sense just to use a relativistic momentum expression and not talk about changing masses.\n\nSpecial relativity, amply confirmed by experiment, shows that things we consider "obvious" about space and time, are not quite as simple as they appear.  Velocities don't strictly add  together, and faster objects become shorter, with clocks passing more slowly.  These results are, in fact, an inevitable outcome of Maxwell's equations, though it took a long time for them to be carried to their logical conclusion.\n\nSo, velocities aren't additive, and there is no global clock which passes equally for all observers.  Given these, it is possible to talk about the mathematics of relativity in flat space.  The math produces a sort of mapping, one which happens to reach asymptotes at the "speed of light".  This defines an ultimate speed limit, a speed beyond which it makes no sense to talk about things.  In a way, something moving at the speed of light is moving at infinite speed in a "mapped space" under the Lorentz equations which govern the way relativistic effects manifest themselves.\n\nSo, the mathematics of the Lorentz transforms lead to the existance of an ultimate speed limit, one for which there is no "faster than this", in the same way that there is no number "larger than infinity".  No matter how quickly you go, the speed of light is always the same relative speed to you, light always passes you at the same measured speed.\n\nLight moves at the ultimate speed limit because it is composed of massless particles, which are required to move exactly at the ultimate speed limit.\n\nSo, the speed limit is mathematical, externally imposed.  The speed of light is the same because photons are massless.  If photons were not massless, they would travel at less than "the speed of light", but there would still be an ultimate speed limit, one which photons could approach but never reach.\n\nThe speed of sound is related to the motion of atoms which carry a disturbance, and because the atoms have mass, they are not constrained to travel at the ultimate speed limit, and in fact are forbidden from doing so, so the speed of sound is below the speed of light.\n\nWhen light slows down, it's because it is being jostled, absorbed and re-emitted, generally impeded by obstacles.  In between such interruptions, it still moves at the ultimate speed limit, but the interruptions reduce the average speed.  To use an imperfect analogy, if you ran at full speed through an empty room, and measured your own ultimate speed, then filled the room with people, you would find that they would form obstacles that could slow you down, but would not speed you up.
936725
Photons are mass-less elementary particles.  There is a famous, and simple, experiment to prove this.  A small pinwheel in a vaccum sealed light blub which is balanced on a pin can be made to spin in proportion to the amount of light that falls on the vanes of the pinwheel.  The vanes are colored alternatively black and white.  The white vanes reflect photons and the black vanes absorb them, so the thing spins like crazy, proving that the photons have enough energy and speed (momentum) to impart motion on the pinwheel.\n\nPhotons are said to have no 'intrinsic mass' which means they don't have mass when 'at rest.'  Of course photons are never 'at rest' so there's something called 'relativistic mass' which accounts for mass-like properties of things traveling at high speed (like the speed of light, which photons travel at).
745459
light has no mass, therefore no weight.\n\nHowever, if all the energy of the light were somehow converted to mass, its mass would be m=E/c^2.
436716
First there was me, then I spake and there was the word, the word was light, and behold there was light.... Things got a lil complicated after that (won't bore you with the details), took me quite sometime to get it all right, in fact I'm still having trouble with those pesky humans, they were a mistake you know!... Well no one's infallible!\n\nWell to answer the other part of your question, there was only 'nothing' in the way that you understand it, there are dimensions upon dimensions, which make up the whole, the 'nothing' that is in one dimension is energy in another, time in another.  What you do is you focus your id onto the 'nothing' that is elsewhere and form the thought, the thought then becomes a word, and the word becomes every thing... Oops I think I might have just said too much.... Please don't tell anyone else.\n\nPS. All laws of nature that exist are only relevant in this universe/dimension, and only to those who are not aware of the other dimensions.
801467
No, not really.\n\nEven high school labs now do light experiments that show photons are quanta.  One simple experiment, is with the photometer that emits electrons when struck by light.  The electrons are like billiard balls and the photons are the cue balls striking them to send them on their merry way.\n\nIf light were simply a ray (a force field), the amount of electrons emitted would be proportional to the strength of the light beam.  But they aren't and the number of electrons actually follow a step-function where at a given threshold of light, the electrons suddenly burst forth after none up until that threshold.\n\nThe photon concept, as bundles of energy, is the result of what I would call good physics.  Good physics is physics that starts with the physical phenomenon and then derives equations to explain it.  Bad physics, like string theory, starts with the math and then tries to explain a physical phenomenon, like strings.\n\nAs to your last assertion, think about it...would even physicists, who are renowned for their weird jargon, call something a "matter," which is a synonym for "mass" if it were not a mass?  No, dark matter is a mass...more correctly a mass-energy (due to E = mc^2).  DM accounts for about 96% of all the mass-energy in our known universe.  \n\nUntil just recently, DM has not been observed, which is why they called it dark.  But a recent observation of two galaxies colliding has seen the effects of the dark masses surrounding those two galaxies also colliding.  So, there is now observable evidence that the dark matter exists...the theory has been validated. [See source.]
122784
yes... its a photon (a particle that makes up lights according to quantum physics)
697713
I think instead of "weight" you mean "mass".  "Weight" refers only to the measurment of matter in a gravatational field.  But that's another issue.\n\nThe answer is "no" light (or photons) have no mass.  Or as close to none that it isn't worth mentioning. \n\nRemember, light is the fastest thing we know of.  The closer any bit of matter gets to moving at the speed of light, the more massive (if it helps, think "heavier") it becomes.  Eventually it becomes so massive that the engergy it would take to actually get it to move AT the speed of light is infinate.  So any object with mass cannot move at the speed of light.  Since light DOES move at the speed of light (duh) it can't have mass.\n\nBUT...light does have energy.  And Einstein says energy = mass.  And that's true.  If you took a great big sheet of aluminum foil a mile across and stuck in into space, all the photons (bits of light) coming from the sun would whack into the foil.  Eventually all that whacking would start to make the foil move. Just like the wind blows a sail.  In fact, this sort of aluminum foil gizmo is called a "solar sail".  So light DOES have a sort of mass when it is moving.\n\nBut for the most part when you're talking about an object having mass, you're talking about it's mass when it is sitting still.  This is called it's "rest mass".  And sitting still (if it could sit still) light has zero mass.
9267
photons don't have mass, they're packets of energy.
66479
No Way Man!  Photon-photon scattering?  Highly dubious.  Photons don't have charge. They don't self-interact, that's why the electro-weak theory works so well... right?\n\nResponse to Dr. Bob's response:\n\nI agree that this process occurs (although a photon that decays into a e+e- pair has to be close to another mass so momentum can be transfered; isolated photons cant decay into e+e-).  But in such a case, would you really say that "one light ray has bounced off another?" I'd say that it was "bouncing" off the electron/positron pairs.  Just semantics I suppose.
388909
Photons are EM waves. They have the same speed.
59698
It is not possible to experimentally measure something to have a value of exactly zero. The current limit on the mass of the photon is < 10^25 times lighter than the proton.\n\nThe idea of a particle's mass changing with velocity has not been used by serious physicists for several decades. We now rewrite the momentum equation as\nmomentum = gamma*mass*velocity , where the factor gamma describes the effect previously known as "relativistic mass".\n\nThe energy of a particle is \nenergy = gamma * mass * c^2 (try setting gamma=1 for a stationary particle) \nso we can write momentum = energy * velocity / c^2\nor momentum = energy/c  for particles moving at the speed of light.\nSo, even though a photon has zero (or very small) mass, it still has momentum, which it can transfer to an electron.
1017395
A photon is a quantum of the vibrational energy of the space grid (as in the image above). At any one point on the wave, photons are produced out of the zero-point and then oppositely, photon holes are produced. Hence, it must be the case that these oscillations up and down come in discrete steps--or quanta.\n\n \n\nWhen a particle from the quantum vacuum acquires energy from a charged particle of matter, it may expand from the addition of this excitation energy to become an ordinary photon. Energy, therefore, expands the size of a virtual photon in ground state.\n\n \n\nA virtual photon, thus, is a "collapsed" short-range quantum that becomes an ordinary photon when given energy from an excited charged particle. Hence, the primary reason that we do not observe the photons that exist in the quantum vacuum, is because the quanta of space-time that compose the vacuum have a very minute amount of energy within them and are, therefore, too small to be observed directly. However, such vacuum quanta may become observable and measurable as ordinary photons after emission.\n\n \n\nWhen actualization takes place, we may measure photons and photonic energy hitting a measuring device.  But, while in-flight, we may not speak about photons at all, because technically speaking they are not photons.  So, when Planck's equation says that energy comes in lumps E = hf, this only refers to a state of an EM wave after an actualization or measurement has happened.  Prior to this we have only Kant's noumenal "wave" condition.  \n\nphotons must have higher frequencies, by exactly one hertz, than the expected difference of the energy levels of the electrons from which they received energy. Additionally, photon wavelengths must include a very long 3 x 10^8 meters to be added to all emitted wave fronts
154756
It essentially means that mass and energy are really the same thing. The true energy of an object is its mass times the speed of light squared.\n\nYes it's still considered valid...and always will be.\n\nYou can read more about it here:\n\nhttp://en.wikipedia.org/wiki/E%3Dmc%C2%B2
1089315
I'd say option B. Each photon contains one fragment of the image. But actually, there are no such things as photon particles. The "waves" that "photon particles" create are actually part of the photon themselves.