41

**Physics, Astronomy & Cosmology / Re: mass of a photon**

« **on:**07/09/2012 10:46:57 »

A slight clarification about the difference betweenMassandRest Mass:

- The photon, traveling at the speed of light
doeshave mass,and is deflected by a gravitational well like the Sun

photons do not have any "mass'

mass

A measure of the total amount of material in a body, defined either by the inertial properties of the body or by its gravitational influence on other bodies.

a Photon does not affect other particles gravitationally, cause it has zero mass....

No, photons do not have mass, but they do have momentum. The proper, general equation to use is E2 = m2c4 + p2c2 So in the case of a photon, m=0 so E = pc or p = E/c. On the other hand, for a particle with mass m at rest (i.e., p = 0), you get back the famous E = mc2.

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/960731.html

http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html

http://www.weburbia.com/physics/photon_mass.html

http://home.fnal.gov/~pompos/light/light_page31.html

The photon is massless,[Note 2] has no electric charge,[12] and is stable

http://en.wikipedia.org/wiki/Photon

I am not sure about your assertion that a photon cannot have a gravitational influence. General Relativity is much more complicated that just saying that mass is required for gravity. Photon have energy - energy and energy flux are parts of the calculations to determine curvature. Now I cannot believe we could possibly measure that gravitational influence at present - but I am not sure that it is zero.

However - one fly in ointment, a photon is a exemplary quantum mechanical object, our theory of gravity is GR which is not quantum.

I got the definition of mass from this link.

http://imagine.gsfc.nasa.gov/docs/dict_jp.html#mass ( the goddard space centers site )

mass

A measure of the total amount of material in a body, defined either by the inertial properties of the body or by its gravitational influence on other bodies.