Photon have its rest mass zero, Why ?

Answer 1

if you look at the variation of mass in the special thoery of relativity, as the speed of a body increases its mass tends to increase. At the speed of light the mass is infinity!!!
A photon travels at the speed of light, right
no body can have infinite mass hence a photon is forced to be massless!!!

Answer 2

If the rest mass of the photon was non-zero, the theory of quantum electrodynamics would be "in trouble" primarily through loss of gauge invariance, which would make it non-renormalizable; also, charge-conservation would no longer be absolutely guaranteed, as it is if photons have vanishing rest-mass. However, whatever theory says, it is still necessary to check theory against experiment.

It is almost certainly impossible to do any experiment which would establish that the photon rest mass is exactly zero. The best we can hope to do is place limits on it. A non-zero rest mass would lead to a change in the inverse square Coulomb law of electrostatic forces. There would be a small damping factor making it weaker over very large distances.

The behavior of static magnetic fields is likewise modified. A limit on the photon mass can be obtained through satellite measurements of planetary magnetic fields. The Charge Composition Explorer spacecraft was used to derive a limit of 6x10-16 eV with high certainty. This was slightly improved in 1998 by Roderic Lakes in a laborartory experiment which looked for anomalous forces on a Cavendish balance. The new limit is 7x10-17 eV. Studies of galactic magnetic fields suggest a much better limit of less than 3x10-27 eV but there is some doubt about the validity of this method.

Answer 3

Because a photon is energy, not matter.

By the way, saying a photon must have no mass because having mass would invalidate a theory is bad logic. Theories have to be based on physical reality, not the other way around. If it turns out that we missed some physical aspect that invalidates a theory, then the theory is tossed aside for a better one.

Answer 4

The light is one instant matter, the another instant a wave.
So is it energy or matter ? Both !!
But if we were blind, its energy..(So Universally, photon is Energy...)

In my own knowledge, EVERYTHING IS WAVE !!
(The universal "dance" of Nataraja is a representation of this fact, who say dance say sound, who say sound say wave)

I don't think the mass of Photon is zero..
But my question is how to calculate the mass when we know that photon is always in motion..(If only we can stop the photon...)

Answer 5

Quantum of light is a privileged particle.
Only the speed of a light quantum has
a maximal, constant, absolute quantity of c=1.
No other particle can travel with the speed c = 1.
If quantum of light flies always rectilinearly c=1, it is a mad one.
Is he really mad?
* * *
The Soviet/Russian academic S. Vavilov suggested an
interesting idea. In his book 'Isaac Newton' he wrote.
The force, according to the Newton,s Second Law,
is equal to : F= ma.
This force is possible to consider as absolute independent
quantity - impulse. When in case with light quanta
the impulse is equal to: mc.
He continued.
Let us now imagine that light quanta falls on a black body,
and it absolutely absorbs this light quanta
( it means light quanta stops).
Then, according to the Lebedev,s law, light quanta
renders pressure on the black body: E/c.
Therefore it is possible to write: mc=E/c.
It means that the stopping light quanta
has rest mass ( potential energy/mass):
M=E/c^2. (E=Mc^2).
=========================
The potential energy/mass of light quanta
can transform in its kinetic energy.
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http://www.socratus.com

Answer 6

Because there is no referent system in which the photon would rest (not move).

Answer 7

Since it is not a matter, its rest mass zero. It is energy in motion and its energy is full of kinetic energy and has no internal energy.

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