Photon Mass?

(Originally published in my Junkier Science blog.)

Does a photon have any mass? Science  says no … yet sunlight is able to propel objects that have solar sails (large surfaces like above) Here is one attempt at an answer from Physlink.com explanation:

“Indeed, photons have no mass. However, they DO have energy and momentum. It turns out that energy and momentum are the requirements that make a solar sail work, not mass.”

However, momentum is defined as “mass times acceleration” and, if photons have no mass, how can they have any momentum?  Also energy is scientifically synonymous with power … whose units are “Newtons times mass” … again this mass thingie.

So, it seems that they have some mass, however tiny, as a requisite for a photon’s ability to push a solar sail (a large thin metallic surface orthogonal to the sun’s rays.)

But things get much more complicated:

There are more issues with photons … one being that they are slightly repelled when they pass by an object of massive gravity.  But, if photons have any mass, wouldn’t they be bent toward the massive object instead of away from it? (I know, I know, Einstein attributes this to a “warp in the space-time continuum” … perhaps his way of resolving this paradox?)

However, black holes have such enormous gravity that light can’t escape them. Does this not suggest that photons have mass?

Signed,

Perplexed

Afterward: Scientists agree that electrons can be comprised of a neutrino and a photon … neither of which has mass  … yet electrons have a very small mass. From whence?

Another afterward:  Curious thought … we see from the above that, if photons have any mass, it is extremely small. And if a photons mass derives from its energy … then perhaps it  mass (from e = mc^2) might be equivalent to e/c^2. That would be very very very very small!

More afterwards: For reference, the energy in a radio-wave photon (1 hertz) is 4.135667697 × 10 −15 eV .

STAND UP FOR PHOTONS!