Confusion regarding light velocity and photon mass?

Question

According to theory of relativity a body moving with speed of light has infinite mass.

Again light is composed of particles called photons which has minute but definite mass.

How do one account for this contradiction?

Answer 1

Photons are quantum (energy packet) of electromagnetic radiation; the elementary particle of photon radiation therapy. X rays and gamma rays are photon radiation.

They are simply energy, they have no mass, no charge etc.

E=mc^2 is where the theory of infinite mass is shown as the speed of light is reached.

Answer 2

If a tardyon (a particle always moving at speeds less than the speed of light and having finite proper mass, aka rest mass) were to move at the speed of light then it's inertial mass would be infinite. However a photon is not a tardyon, it's a luxon meaning that it always moves a the speed of light. That implies that it's "proper mass" is zero.

I noticed someone claiming that the mass of a photon is hf/c^2 is not inertial mass but another way of expressing energy. That is a common misconception and based on a misunderstanding of the difference between mass and energy. Energy is a quantity having units kg*m/s^2 and is a conserved quantity whereas mass is the quantity which describes a bodies inertia, i.e. it's resistance to motion. Claiming that m = E/c^2 is just another way expressing energy is like saying that E = hf is another way of expressing the frequency of a photon. Pay no attention to that misconception.

Answer 3

The statement the a body moving at the speed of light has infinite mass only applies to objects with a nonzero rest mass.

Photons have a rest of zero. This means that if you could somehow stop a photon and measure its mass, you would find that it is zero. However photons are particles of light and always travel at the speed of light so the idea of a photon rest mass is kind of meaningless.They do however have a relativistic mass of E/c^2, where E is the energy of the photon.

Answer 4

this may be a truism. Photons shuttle on the value of sunshine because of the fact they are easy! How ought to they shuttle on the different velocity? i do no longer remember any slacker photons traveling slower. additionally, if something has NO MASS, this is no longer, and this is no longer GOING everywhere. How ought to a tension be exerted on something without mass? remember E=mc²? Mass and ability are one and the comparable, so even ability has mass, regardless of if this is totally, very small. attempt looking up Tachyons. they are meant to flow swifter than photons, that should be exciting.

Answer 5

One of the parameters for the existence of a photon is it's velocity.
Mass has nothing to do with it.
If you eliminate it's velocity the photon goes out of existence.

Answer 6

Well one can account for this contradiction because current nature of light is very confusing u can make out whether light is a particle or wave therefor even quantum nature of light which is based on its particle nature doesn't hold good when its wave nature is considered.Well once i posted a similar question regarding quantum nature of light and few conventional people called me an idiot,but for that i cannot stop thinking unconventionally.I would like to contact u because u too think unconventionally like me and i am sure we could help each other.
mail me at:[e-mail]

Answer 7

By accepting that photons do --not-- have any rest mass (since they're never at rest) and that all of their 'relativistic' mass is given by m = E/c² where E is the energy of the photon.

Doug

Answer 8

Photons have no mass. They have a mass-equivalent of energy which is h*f/c^2 but that is not an inertial mass, just another way of expressing the energy.

Answer 9

Since when do photons have mass?