If photons have no mass, then how can they travel the speed of light?

[Phrak]

This is all theoretical physics.

I think what you're asking is "where do we discuss speculative physics on this message board?"

To which the answer is: ''on some other board".



PF is devoted to established, mainstream physics.

Well, that sucks. But then again, it means I can both giveth and receiveth all the standard answers about what doesn't really work. I've gotten a lot of standard miles closing one eye, squinting through the other, and relaying what I see.

 

[tiny-tim]

Hi Phrak!

I've gotten a lot of standard miles closing one eye, squinting through the other, and relaying what I see.

Technically, you can't squint with one eye shut …

squinting is when the two eyes point in different directions … see http://en.wikipedia.org/wiki/Strabismus"

 

[Phrak]

Hi Phrak!


Technically, you can't squint with one eye shut …

squinting is when the two eyes point in different directions … see http://en.wikipedia.org/wiki/Strabismus"

/ Squints with one eye at Tiny across the pond. /

 

[A. Neumaier]

Just out of curiosity, how do we know that a photon does not have any rest mass? Yes a rest mass is not necessary to study it's behavior, but does that mean that it does not have any rest mass?

Astronomical observations only pose an upper bound of currently 2 10^{-25} eV (approx. 3.6 10^{-61} kg) on the photon mass, but all known experimental data seem to be in agreement with the assumption that the mass of the photon is exactly zero, as in the standard model.

See the entry ''Is the photon necessarily massless?'' in Chapter B2 of my theoretical physics FAQ at http://arnold-neumaier.at/physfaq/physics-faq.html#photon