photons and mass?

[jajrussel]

I have been reading about virtual particles, and my mind drifted to photons which are said to be massless yet still seem to exhibit properties of mass, so the question is would it be entirely wrong to apply the view of virtual particles to massless particles in the sense that what we have is in effect virtual mass? It only exist so long as the condition exist?

 

I don't know if condition is the right word, and I am just learning about virtual particles, so it might need some adjustment in the comparison.

Edited March 22, 2015 by jajrussel

[ajb]

Virtual particles are not constrained to obey the classical equations of motion, in particular the mass-shell condition

 

[math]E^{2}-p^{2} = m^{2}[/math] (setting c=1)

 

In this sense virtual photons may be massive.

 

A virtual particle will 'live longer' the closer it is to the the mass-shell condition. In fact, we can only really ever detect virtual particles, as all particles we observe need to interact with others for us to measure them. Say for example the photons that enter your eye. However, these virtual photons are so close to the mass-shell condition that we can happily say that are real photons.

 

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p.s. This is a good question.

Edited March 22, 2015 by ajb

[swansont]

I have been reading about virtual particles, and my mind drifted to photons which are said to be massless yet still seem to exhibit properties of mass

 

As mass is itself a property, perhaps this is a function of needing an adjustment in how you perceive the situation. Momentum and energy, for example, are not properties of mass. They are properties of particles, which usually also have mass.

[Sensei]

Confusion arise because some people use "mass" while they mean "invariant mass",

and other people use "mass" while they mean "relativistic mass" (total energy divided by c²: m=E/c²).

When two such incompatible persons meet they need to figure out in what sense they use "mass" in the first place.

 

Suppose so we have hermetic box with mirror walls and inside of it (not visible from outside) light source.

It's starting emitting light. IMHO box doesn't get lighter just because photons are emitted. They're all there, just bouncing from mirror walls..

 

If it would become lighter (less mass) we could detect when light source is turned on or turned off, on weighing scale.

Edited March 22, 2015 by Sensei

[J.C.MacSwell]

Confusion arise because some people use "mass" while they mean "invariant mass",

and other people use "mass" while they mean "relativistic mass" (total energy divided by c²: m=E/c²).

When two such incompatible persons meet they need to figure out in what sense they use "mass" in the first place.

 

Suppose so we have hermetic box with mirror walls and inside of it (not visible from outside) light source.

It's starting emitting light. IMHO box doesn't get lighter just because photons are emitted. They're all there, just bouncing from mirror walls..

 

If it would become lighter (less mass) we could detect when light source is turned on or turned off, on weighing scale.

Your humble opinion would be correct. While the photons emitted are themselves massless, they contribute to the mass (invariant mass) of the box/system