Why do we get answers that the photon is masslless,when it was tested that it does have mass?

Question

Arent all masses at rest ,that is at zero velocity ,all have zero momentum?So light wouldnot be an exception?

Answer 1

To answer your question in a short little line:


Photons have no mass.

Photons only contain energy, and this term is dubed as 'Relative Mass', which just means that it has another form of mass - energy - as described by E=mc^2 where E=m :)

Answer 2

The m in E = mc^2 is inertial mass, not perfect mass. the relationship E_0 = m_0c^2 is the relationship between a photon's perfect mass and it is perfect power. the full power of a particle is the sum of the debris perfect power and kinetic power. that is the reason physicists say that the flexibility of a photon is all kinetic power. The inertial power of a photon is defined because the m in p = mv. If the photon is a tardyon (i.e. it strikes at speeds less than the speed of light) then it would nicely be shown that m = m_0/sqrt(a million - v^2/c^2). For a luxon (i.e. a particle that strikes on the speed of light) it would nicely be shown that m_0 = 0. when you consider that for a photon v = c and E = pc. It follows that p = mc => m = % = (E/c)/c = E/c^2. that is why E = mc^2 for a photon.

Answer 3

I never saw an experiment that shows photons have mass. Where did you see it? It has been shown that gravity 'bends' light, but actually the gravity is bending space/time light is traveling through. Also, I've never heard of light being at 'rest'. There is a force associated with light - you would think it has mass. I understand if you were in space, not affected by gravity from any source, and you turned on a flashlight - you would start to move opposite the direction of the beam. Kinda like a 'light powered engine'. It seems you would need some sort of mass to do that.

Answer 4

"One feature of this new law is quite easy to understand is this: In Einstein relativity theory, anything which has energy has mass -- mass in the sense that it is attracted gravitationaly. Even light, which has energy, has a "mass". When a light beam, which has energy in it, comes past the sun there is attraction on it by the sun." [See source.]

E = mc^2, which means anything possessing energy has an equivalent mass even though its rest mass m0 may be zero. This equivalent mass is often called the "gravitational mass" because it is affected by gravity. The bend of light as the ray passesses near a massive planet for example. Light quanta are packets of energy; so they exhibit gravitational mass no matter what velocity they are traveling at.

Answer 5

All things have mass, but since it's so small (compared to everyday things that we can see and touch), that some people might consider that it has no mass. Since it's such a small small, really small thing that some people would say - 'it weighs nothing at all.' But since it's less than 3x10 to the negative whatever, it has mass even when it's at rest or whatever. Light, everything has mass. Light, I believe has millions and millions of particles, that is if you get more in depth into physics, you learn that light starts to behave like, well, who better to explain all this is -- Feynman's Lectures. Check it out.

Answer 6

http://en.wikipedia.org/wiki/Photon
In modern physics, the photon is the elementary particle responsible for electromagnetic phenomena. It mediates electromagnetic interactions and makes up all forms of light. The photon has zero invariant mass and travels at the constant speed c, the speed of light in empty space. However, in the presence of matter, a photon can be slowed or even absorbed, transferring energy and momentum proportional to its frequency. Like all quanta, the photon has both wave and particle properties; it exhibits wave–particle duality.

The modern concept of the photon was developed gradually (1905–17) by Albert Einstein[2][3][4][5] to explain experimental observations that did not fit the classical wave model of light. In particular, the photon model accounted for the frequency dependence of light's energy, and explained the ability of matter and radiation to be in thermal equilibrium. Other physicists sought to explain these anomalous observations by semiclassical models, in which light is still described by Maxwell's equations but the material objects that emit and absorb light are quantized. Although these semiclassical models contributed to the development of quantum mechanics, further experiments proved Einstein's hypothesis that light itself is quantized; the quanta of light are photons.

The photon concept has led to momentous advances in experimental and theoretical physics, such as lasers, Bose–Einstein condensation, quantum field theory, and the probabilistic interpretation of quantum mechanics. According to the Standard Model of particle physics, photons are responsible for producing all electric and magnetic fields, and are themselves the product of requiring that physical laws have a certain symmetry at every point in spacetime. The intrinsic properties of photons — such as charge, mass and spin — are determined by the properties of this gauge symmetry. Photons have many applications in technology such as photochemistry, high-resolution microscopy, and measurements of molecular distances. Recently, photons have been studied as elements of quantum computers and for sophisticated applications in optical communication such as quantum cryptography.

The photon is massless,[10] has no electric charge[11] and does not decay spontaneously in empty space. A photon has two possible polarization states and is described by three continuous parameters: the components of its wave vector, which determine its wavelength and its direction of propagation. Photons are emitted in many natural processes, e.g., when a charge is accelerated, when an atom or a nucleus jumps from a higher to lower energy level, or when a particle and its antiparticle are annihilated. Photons are absorbed in the time-reversed processes which correspond to those mentioned above: for example, in the production of particle–antiparticle pairs or in atomic or nuclear transitions to a higher energy level.

Since the photon is massless, the photon moves at (the speed of light in empty space) and its energy and momentum are related by , where is the magnitude of the momentum. For comparison, the corresponding equation for particles with an invariant mass would be , as shown in special relativity.

The energy and momentum of a photon depend only on its frequency or, equivalently, its wavelength

Answer 7

Because even an empty can will still rattle. Remember that when you have nothing you still have something...and that is nothing.

Answer 8

I think you are thinking of Wave–particle duality.