'Kay, Let's define why a photon is said to be massless.

1. It has no frame where it is at rest.

2. It has no acceleration

3. Therefore no inertia.

Inertia is a property of invariant mass.

But let us assume a inertia.

"This depends on what you mean by "inertial mass".

In Newtonian mechanics it is clear: inertial mass is the m in F=ma, and p=mv. But those equations do not hold in relativity. Moreover, for a photon, a) there is no way to apply any force to use the first equation, and b) there is no generalization of the second equation that applies to photons.

In relativity, "inertial mass" has essentially no utility because the defining equations don't hold, and what little utility it might have cannot be applied to photons.

Another quibble: we say "a photon has zero mass", omitting your "rest", because a) a photon has no rest frame, and b) the word "mass" now means the invariant mass of an object.

(Saying "has no mass" sort of implies that "mass" does not apply, so it's better

to say "has zero mass" or "has a mass of zero".)"

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Maybe you are assuming an aeteher Jartza?

So, anyone up to proving that a photon has a mass?

Experimentally I mean

Didn't think so either.

It also seems that Bose Einstein particles (condensates) built on the idea of massless photons, even though Einstein later made it valid for some massive particles too?

"Bose was interested deriving Planck's radiation formula, which Planck obtained largely by guessing. Using the particle picture of Einstein, Bose was able to derive the radiation formula by systematically developing a statistics of massless particles without the constraint of particle number conservation. He was quite successful, but was not able to publish his work, because no journals in Europe would accept his paper.

"This "Bose-Einstein statistics" described the behavior of a "Bose gas" composed of uniform particles of integer spin (i.e. bosons). When cooled to extremely low temperatures, Bose-Einstein statistics predicts that the particles in a Bose gas will collapse into their lowest accessible quantum state, creating a new form of matter, which is called a superfluid. This is a specific form of condensation which has special properties. "

In 1924, Bose wrote to Einstein (in Germany) explaining his work and enclosed his manuscript written in English. Einstein was so happy with Bose's work that he translated the manuscript into German and arranged its publication in Zeitschrift f. Physik (the most prestigious physics journal at that time). Furthermore, in 1926, Einstein completed the Bose-Einstein statistics by extending Bose's work to the case of massive particles with particle-number conservation."

(And the condensates exist.)

Let us go back to the photon statistics formula derived by Bose. There is a factor "2" sitting on the numerator of this formula. The usual explanation is that it is because photons are massless particles. Then why not 1 or 3 ? Bose argued that the photon can have two degenerate states. This eventually led to the concept of photon spin parallel or anti-parallel to the momentum.

The question of why the photon spin should be only along the direction of momentum has a stormy history. Eugene Wigner (1939) showed that the internal space-time symmetry of massless particles is isomorphic to the symmetry of two-dimensional Euclidean space consisting of one rotation and two translational degrees of freedom. It is not difficult to associate the rotational degree with the photon spin either parallel or anti-parallel to the momentum, but what physics is associated with the translational degrees of freedom.

These translational degrees were later identified as gauge transformations. This does not solve the whole problem because there is one gauge degree of freedom while there are two translational degrees of freedom. How do they collapse into the one gauge degree of freedom? This problem was not completely solved until 1990."

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It may be that you consider momentum the exact equivalent to mass?

But it's not, not if we're taking invariant mass. There's too many real life observations of the difference between light and a piece of matter for me to agree on a perfect equivalence.

And even if we agreed on a perfect equivalence you would still need to show what was 'acting' on the photon to make it 'weak'. Normally when we act upon something that is thought to bring energy (mass) to the object, but in this case I get the impression that you mean the opposite?

The negative pressure (expansion)? Nope, not at a black hole.

zero point energies from quantum fluctuations?

They can be both 'positive' and 'negative' it seems?

also they are what we call 'virtual' whatever that may mean in form of Planck time?

You got me stymied here?

[4 posts combined. Relating to original quotes would be useful in future. Thanks, Mod][ Bose and Einstein. And so it all begun:) ]