Since Photons are considered massless, than arent they dimensionless?

Question

Isnt a mass equal to the density of an entity times its volume?

Answer 1

The photon has zero mass (it does, however, have rest mass - as in M=E/C^2).

Like all quanta, the photon exhibits wave and particle properties.

It is important to remember that mass and energy are equivalent. A photon is only referred to as a particle because of certain properties that light exhibits - the "particle" is actually no more than a quanta of pure light energy - and, as such, is indeed dimensionless in the conventional sense of density and volume.

Answer 2

Well it starts getting weird when you talk about single particles like a single photon. They don't have dimensions like a classical sphere, they have a probability wavelength that is determined by the Debroglie formula:

Wavelength = Plank's Constant / Momentum

And this formula may vary because momentum can not be precisely measured due to the uncertainty principle.

Basically it makes no sense to talk about a definate location or dimension of a particle beyond a certain point.

Even for particles with mass we can only say we believe the probability of the particle is here is X%. But we can never say to 100% confidence where a particle is because physics just doesn't allow this.

Answer 3

Space is massless, and yet it has a very large volume. Photons are different, but it's the same concept. But youre right, M = DV, but energy particles are different

Answer 4

and so light, which has zero rest mass and zero density can therefore have any volume? Quaint, but you cannot suppose an equation for the density of matter can be applied to energy. There are equations that relate to energy density.

Answer 5

Someone who knows more than me once said that anything that exhibits the property of inertia is a mass. He said that during a discussion of light. He also said that he didn't understand anything beyond that idea. Light is weird. It is energy, AND it is mass. I don't understand beyond that either. I have guessed that if we moved at the speed of light we would become light. In that sense, if light were slowed down it might become a form of matter we could understand.