Photon have mass?

Photon have mass?

    physics knowledge zone
  • Photon is an elementary and stable particle.
  • It have no mass at rest.
  • It have no charge.
  • In empty space, it travel at the speed of light(c)
It's energy and momentum is related by below equation:


Where-  E= energy of photon
              P= magnitude of the momentum
              C= speed of the light

The equation foe relativistic relation is given blow:

physics knowledge zone

A photon have dual nature: Wave and Particle. A photon is described by wave vector in quantum field theory.
The energy and momentum of a photon depends only on its frequency or inversely, its wavelength

          E=hv =hc/λ

So, Photon have no mass but it have momentum.

Photon have also a different quantity called spin angular momentum which not depends on frequency. The magnitude of the spin is root2h and the component measured along the direction of motion, it's helicity, must be +or-h. There are two possible helicity which called right handed and left handed.

Many people say that photon have mass. If a photon did have mass then it would not move at the speed of light in vacume. It would slower than c and depends on its frequency and also coulomb's law would be modified and the electromagnetic field would have an extra physical digree of freedom.

The Maxwell theory predicts that the energy of light wave depends on its intensity, not on its frequency. But after some time, many experiment show that energy of light wave depends only on its frequency, not on its intensity. After that time, investigation of blackbody, according to Einstein thge energy of any system that absorbs or emits electromagnetic radiation is an integer multiple of an energy quantum:


After that Einstein received the Nobel prize in physics in 1921.