Question

does light have mass? If not, then how come its speed is only constant in a vacuum?

Answer 1

light as I know it does not have mass. the speed of light is always constant though a medium, not just a vacuum. the speed of light is constant through water, air, glass or what not, it's a different constant though different mediums. it's the medium that determines what the speed of light is thought it. the speed of light is the greatest in a vacuum.

Answer 2

ur statements are incomplete

Answer 3

light definately has a mass. negligible in most circumstances. But from a fire, the ashes/heat/light/sound and smoke make up the same total mass as the material being burned.

Answer 4

instead of light we can use the word photons , packets of energy
, the photons do not have any mass
just check out this link it may be helpful -
http://www.desy.de/user/projects/Physics/ParticleAndNuclear/photon_mass.html

Answer 5

From my vague understanding a photon in the Large Hadron Collider actually weighs around 400kgs by the time it reaches 99.97% of the speed of light. So, I'd say yes it has mass, But I'm not expert.

Answer 6

Light, as electromagentic waves, are made up of photons.These photons make up wavepackets which in turn produce a photon pressure and give give result to momentum of the photons. Unlike normal matter, the momentum of light is not due to the mass ie it isnt p=mv but rather p=hf/c, so even though there photons do not have mass, they can exhibit characteristic like those of massive objects.

As for whether the speed of light, c, is constant through all mediums. the reason why light does not propogate at c through other materials is due to the fact you have a denser material. In dense material light is slowed down versus in not so dense material light travels closer to the speed of light.

Answer 7

in large hardon collider , that mass is the relativistic mass , and by convention relativistic mass is not the mass of particle in contemporary physics