Why Photon Mass is Zero: Proving it with Relativity Theory

In summary: But even if we did know its speed was c, that would not definitively establish that the photon has zero mass.
  • #1
umair20
14
0
why rest mass of photon is zero? how to prove it by m=m'/√(1-v^2/c^2)?
 
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  • #2
You cannot prove something like this via analytical methods. Please read the FAQ subforum in the Relativity forum.

Zz.
 
  • #3
ZapperZ said:
You cannot prove something like this via analytical methods. Please read the FAQ subforum in the Relativity forum.

Zz.

REad about Photon!
 
  • #4
umair20 said:
why rest mass of photon is zero? how to prove it by m=m'/√(1-v^2/c^2)?

How would you prove the mass of the electron with that formula? You can't. Elementary particle masses are experimentally verified, not proved.
 
  • #5
moatasim23 said:
REad about Photon!

Which part of the photon did you want me to read?

Zz.
 
  • #6
umair20 said:
why rest mass of photon is zero? how to prove it by m=m'/√(1-v^2/c^2)?
In addition to the other answers, if photon's mass were different than zero, it should be infinite (according to the formula you have written) because v = c for a photon; its energy would be infinite too. Clearly that is a nonsense.
 
  • #7
lightarrow said:
In addition to the other answers, if photon's mass were different than zero, it should be infinite (according to the formula you have written) because v = c for a photon; its energy would be infinite too. Clearly that is a nonsense.

If the photon's mass is nonzero, then it doesn't have v=c.

The mass of the photon can only be established experimentally.

R.S. Lakes, "Experimental limits on the photon mass and cosmic magnetic vector potential", Physical Review Letters , 1998, 80, 1826-1829 http://silver.neep.wisc.edu/~lakes/mu.html

Luo et al., “New Experimental Limit on the Photon Rest Mass with a Rotating Torsion Balance”, Phys. Rev. Lett, 90, no. 8, 081801 (2003)

Zz, I'd suggest adding these two references to the FAQ entry.
 
  • #8
bcrowell said:
If the photon's mass is nonzero, then it doesn't have v=c.
The mass of the photon can only be established experimentally.
Of course. But the answer one can give, can also depend on the level of answer the OP was looking for: starting from the fact that a photon's speed is c, then a photon's mass different than zero generate an impossible situation.
 
  • #9
Just because you cannot divide by zero does not prove that photons must possesses a nonzero mass. Einstein's ideas concerning mass and speed are not just idle speculations, they have been verified through experiments. Keeping this in mind:

Since photons, by definition, travel at the speed of light, if they did possesses ANY mass their mass would have to be infinite. A particle the size of a photon with INFINITE mass would create a singularity that would consume everything it touched. Since this is clearly not the case, photons cannot have any mass.
 
  • #10
lightarrow said:
Of course. But the answer one can give, can also depend on the level of answer the OP was looking for: starting from the fact that a photon's speed is c, then a photon's mass different than zero generate an impossible situation.

The point is that we don't know that a photon's speed is c. We can only put a lower limit on its speed for a given energy.
 

Related to Why Photon Mass is Zero: Proving it with Relativity Theory

1. What is the concept of photon mass in relation to relativity theory?

The concept of photon mass refers to the idea that photons, which are particles of light, have a measurable mass. Relativity theory, on the other hand, states that mass and energy are equivalent and that the mass of an object increases as its speed approaches the speed of light. This creates a contradiction, as photons are always traveling at the speed of light and should therefore have an infinite mass according to relativity theory.

2. Why is it important to prove that photon mass is zero using relativity theory?

It is important to prove that photon mass is zero using relativity theory because it helps to further validate the theory and its predictions. Additionally, understanding the properties of photons is crucial for many fields of science, including quantum mechanics and astrophysics.

3. How does relativity theory explain the zero mass of photons?

Relativity theory explains the zero mass of photons by stating that they are massless particles that travel at the speed of light. The theory also explains that the energy of a photon is directly proportional to its frequency, and the frequency of a photon is inversely proportional to its wavelength. This means that as the frequency and energy of a photon increase, its wavelength decreases, allowing it to travel at the speed of light with zero mass.

4. Can the zero mass of photons be proven experimentally?

Yes, the zero mass of photons has been proven experimentally through various experiments, including the observation of the Compton effect and the photoelectric effect. These experiments have confirmed that photons do not have a measurable mass and support the predictions of relativity theory.

5. Are there any other theories or concepts that support the zero mass of photons?

Yes, there are other theories and concepts that support the zero mass of photons. For example, the theory of quantum electrodynamics also states that photons are massless particles. Additionally, the concept of gauge invariance, which is a fundamental principle in particle physics, predicts the zero mass of photons.

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